A Review of Passive RFID Tag Antenna-Based Sensors and Systems for Structural Health Monitoring Applications
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paper_title: Rail corrosion forensics using 3D imaging and finite element analysis

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Rail infrastructure renewal maintenance is capital intensive. As a contributor to rail deterioration, corrosion damage needs to be accurately analysed for renewal maintenance planning. The main contribution of this study is to introduce an information-dense forensic analysis method for characterizing rail corrosion damage in situ based on 3D imaging. Two state-of-the-art technologies, an arm laser scanner and handheld laser scanner, are employed for onsite digitization of the rail surface. Acquired 3D image data is analysed to characterize pitting corrosion in terms of volume, surface area coverage and average pit depth. Cyclic loading of the sampled rail is simulated using finite element analysis of the 3D image to establish risk potential for crack initiation. A case project was used to validate the feasibility of the developed approach. The results of this study demonstrate the usefulness of applying forensic methodology to renewal maintenance planning.
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paper_title: Non-Destructive Testing with Micro- and MM-Waves — Where We are — Where We Go

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Test methods based on microwaves are well suited to characterize mainly electrically non-conducting materials and to detect and image defects in non-destructive and in many cases in contactless way. While in the past the often complicated and expensive microwave equipment prevented the widespread application of microwave methods this situation is now changing due to the increasing availability of low-cost high integrated microwave components. Microwave testing has found an important application in the field of security, e. g. to detect and image dangerous objects hidden under clothes. The principles of this technique can be applied in the domain of joining (e. g. welding of plastics or gluing plastic to plastic) for contactless detection of defects under cover layers.
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paper_title: Antenna Sensors in Passive Wireless Sensing Systems

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Antenna sensors have received considerable interests in recent years due to their passive wireless operation, simple configuration, compact size, multiplexing capability, and multimodality sensitivity. Based on the principle of antenna backscattering, an antenna sensor can be wirelessly interrogated at middle range distances without an onboard battery. Since the antenna serves the dual function of sensing and communicating, an antenna sensor can be implemented with minimum number of components. As narrowband resonators, antenna sensors can be easily multiplexed based on the principle of frequency division multiplexing. In addition, different types of antenna sensors that are sensitive to a variety of physical measurands have been demonstrated. Due to these unique features, antenna sensor technology could play a vital role in our drive toward ubiquitous sensing. This chapter provides a comprehensive review of this exciting technology with detailed descriptions on the operational principle and wireless interrogation of batteryless antenna sensors. Four application examples of using antenna sensors for moisture, dynamic strain, temperature, and crack sensing are discussed. Future research directions and open problems are suggested.
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paper_title: Flexible Wireless Antenna Sensor: A Review

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This review paper summarizes a new flexible sensor concept based on the microstrip patch antenna technology. The principle of the patch antenna as a sensing element and the wireless interrogation of the antenna sensors are presented first, followed by the description of the antenna design and fabrication using flexible film components. The applications of the flexible antenna sensor for wireless strain sensing and crack detection are presented. The design and testing of inserting a flexible layer to improve the reliability of the flexible antenna sensor is also discussed. Because the flexible antenna sensors can be wirelessly interrogated with ultra-low power consumption and can be frequency division multiplexed, the complexity of implementing a large sensor array is greatly reduced.
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paper_title: Microwave and millimetre wave sensors for crack detection

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Non-destructive detection and evaluation of stress-induced fatigue cracks in metals is an important practical issue in several critical environments including surface transportation (steel bridges, railroad tracks, railroad car wheels, etc.), aerospace transportation (aircraft fuselage, landing gears, etc.) and power plants (steam generator tubings, etc.). Although there are several standard non-destructive evaluation techniques, near-field microwave and millimetre wave techniques have shown tremendous potential for significantly adding to the available non-destructive 'toolbox' for this purpose. This paper serves as a review of recent advances made in this area and the capabilities of these techniques for detecting cracks and evaluating their various dimensional properties including determining a crack tip location accurately. These techniques include using open-ended rectangular probes (in two distinct modes) and open-ended coaxial probes.
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paper_title: Wireless Power Transmission: R&D Activities Within Europe

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Wireless power transmission (WPT) is an emerging technology that is gaining increased visibility in recent years. Efficient WPT circuits, systems and strategies can address a large group of applications spanning from batteryless systems, battery-free sensors, passive RF identification, near-field communications, and many others. WPT is a fundamental enabling technology of the Internet of Things concept, as well as machine-to-machine communications, since it minimizes the use of batteries and eliminates wired power connections. WPT technology brings together RF and dc circuit and system designers with different backgrounds on circuit design, novel materials and applications, and regulatory issues, forming a cross disciplinary team in order to achieve an efficient transmission of power over the air interface. This paper aims to present WPT technology in an integrated way, addressing state-of-the-art and challenges, and to discuss future R&D perspectives summarizing recent activities in Europe.
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paper_title: Utilising microstrip patch antenna strain sensors for structural health monitoring

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In this article, the feasibility of using a circular microstrip patch antenna to measure strain and the effects of different materials on sensitivity of the patch antenna are investigated. Also, the effect of strain direction on the frequency shift is studied. The theoretical model shows a linear relationship between strain and the shift in the resonant frequency of the antenna in any material. Both finite element analysis (FEA) and experimental tests have been undertaken to corroborate the relationship between strain and frequency shift. In addition, a new antenna sensor based on a meandered microstrip patch antennas has been designed and tested to overcome the shortcomings of the circular patch. The meandered circular microstrip patch antenna exhibited a threefold increase in sensitivity and a fivefold reduction in its physical size, when compared to the simple circular patch. The ultimate intention of this work is to configure antennas for the detection of relatively small damage zones in structures and to do so wirelessly.
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paper_title: A Novel Enhanced-Performance Flexible RFID-Enabled Embroidered Wireless Integrated Module for Sensing Applications

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A novel wireless embroidered integrated platform for radio frequency identification (RFID)-enabled strain sensing that takes advantage of the nonlinear behavior of the RFID chip impedance as a function of the incident power is introduced. Due to the nonlinearity of the chip impedance as a function of the power, a large variation of chip impedance value and thus a large difference of radar cross section values for appropriately chosen power levels are achieved. Taking advantage of this idea, the sensing parameter is detected by interrogation of the sensor tag using two distinct transmitting power levels and calculating the difference of backscattered response. As a proof of concept, we applied the proposed method for the detection of an embroidered RFID-enabled strain sensor that is fabricated using electrotextiles in order to observe the variations of the magnitude and the corresponding strain levels. The proposed model for the chip impedance helps in predicting the RFID chip impedance variation for different strain conditions, an extremely important issue for RF/RFID modules and packages operating over a wide power dynamic range as well as enabling the accurate estimation of the maximum range of the RFID-enabled sensing modules for the maximum allowable power levels.
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paper_title: Passive Wireless Frequency Doubling Antenna Sensor for Strain and Crack Sensing

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This paper presents the design, simulation, and validation experiments of a passive (battery-free) wireless frequency doubling antenna sensor for strain and crack sensing. Since the length of a patch antenna governs the antenna’s resonance frequency, a patch antenna bonded to a structural surface can be used to measure mechanical strain or crack propagation by interrogating resonance frequency shift due to antenna length change. In comparison with previous approaches such as radio frequency identification, the frequency doubling scheme is proposed as a new signal modulation approach for the antenna sensor. The proposed approach can easily distinguish backscattered passive sensor signal (at the doubled frequency $2{f}$ ::: ) from environmental electromagnetic reflections (at original reader interrogation frequency $f$ ::: ). To accurately estimate the performance of the frequency doubling antenna sensor, a multi-physics coupled simulation framework is proposed to aid the sensor design while considering both the mechanical and electromagnetic behaviors. Two commercial software packages, COMSOL and Advanced Design System (ADS), are combined to leverage the features from each other. The simulated performance of the frequency doubling antenna sensor is further validated by experiments. The results show that the sensor is capable of detecting small strain changes and the growth of a small crack.
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paper_title: A Passive Radio-Frequency Identification (RFID) Gas Sensor With Self-Correction Against Fluctuations of Ambient Temperature.

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Uncontrolled fluctuations of ambient temperature in the field typically greatly reduce accuracy of gas sensors. In this study, we developed an approach for the self-correction against fluctuations of ambient temperature of individual gas and vapor sensors. The main innovation of our work is in the temperature correction which is accomplished without the need for a separate uncoated reference sensor or a separate temperature sensor. Our sensors are resonant inductor-capacitor-resistor (LCR) transducers coated with sensing materials and operated as multivariable passive (battery-free) radio-frequency identification (RFID) sensors. Using our developed approach, we performed quantitation of an exemplary vapor over the temperature range from 25 to 40 °C. This technical solution will be attractive in numerous applications where temperature stabilization of a gas sensor or addition of auxiliary temperature or uncoated reference sensors is prohibitive.
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paper_title: Passive RFID Strain-Sensor Based on Meander-Line Antennas

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The processing of backscattered signals coming from RFID tags is potentially useful to detect the physical state of the tagged object. It is here shown how to design a completely passive UHF RFID sensor for strain monitoring starting from a flexible meander-line dipole whose shape factor and feed section are engineered to achieve the desired sensing resolution and dynamic range. This class of devices is low-cost, promises sub-millimeter resolution and may found interesting applications in the Structural Health Monitoring of damaged structures and vehicles as well as during extreme and adverse events.
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paper_title: An Antenna Sensor for Crack Detection and Monitoring

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A major goal of structural health monitoring (SHM) is crack detection and monitoring. Because cracks are localized defects, quantifying the sizes and locations of the cracks would require placing many sensors over a large area. We present a crack sensor that is suitable for densely distributed sensor network because they can be remotely interrogated and do not need any wiring for data transmission or power supply. A rectangular patch antenna, consisting of a metallic patch on one side of a dielectric substrate and a ground plane on the other side of the substrate, is studied in this paper for crack detection and monitoring. The presence of a crack in the ground plane of the antenna changes its conductivity, which in turn reduces the resonant frequency of the antenna sensor. Experimental results demonstrated that the antenna sensor can monitor crack growth with sub-millimeter spatial resolution. Detailed experimental set-up and measurement results are presented.
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paper_title: Humidity Sensing by Polymer-Loaded UHF RFID Antennas

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Passive ultra high-frequency radio frequency identification tags, besides item labeling, are also able to exploit capability to sense the physical state of the tagged object as well as of the surrounding environment. Here, a new family of polymer-doped tags are proposed and fully characterized for the detection of ambient humidity. A sensitive chemical species based on PEDOT:PSS is used to load a shaped slot, carved into a folded-like patch tag. The communication and sensing capabilities of the resulting radio-sensor are investigated by means of simulation and measurements that show how to control and balance above opposite requirements by a proper deposition of the sensitive material. The device could have interesting applications in the assessment of the air quality within living and controlled rooms, in the monitoring of the conservation state of foods, in the preservation of walls, and even in the medical field, e.g., to monitor the healing of wounds.
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paper_title: Identification and characterisation of steel corrosion using passive high frequency RFID sensors

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Abstract High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.
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paper_title: Wireless Crack Monitoring by Stationary Phase Measurements from Coupled RFID Tags

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Abstract—The possibility to wirelessly monitor the state and ::: the evolution of cracks is of increasing interest in emerging ::: Structural Health Monitoring Systems. A simple and effective measurement method considers the placement of two passive RFID antennas on top of the crack, so that the crack’s evolution will produce a change of the inter-antenna coupling and in turn of the phase of the backscattered field. An ad-hoc design technique, ::: based onto the coupled-mode physics, permits to maximize the sensor’s sensitivity avoiding, or at least mitigating, the read range reduction during the evolution of the displacement that is instead typical of amplitude-oriented RFID displacement sensors. The proposed idea is demonstrated by numerical and experimental ::: examples showing the possibility of sub-millimeter resolution with low-cost devices.
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paper_title: Monitoring fatigue crack growth and opening using antenna sensors

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Fatigue cracking is one of the most common failure modes of various load-bearing structures. Even though sensors of many different types have been developed for crack detection, very few can monitor crack growth with a high sensitivity. This paper presents an antenna sensor that is capable of monitoring the growth of fatigue cracks with a sub-millimeter resolution. According to microstrip patch antenna theory, the resonant frequencies of a dual-frequency patch antenna are inversely proportional to the electrical lengths of the corresponding antenna radiation modes. The presence of a crack in the ground plane or the elongation of the antenna patch due to crack opening increases the electric length, thereby causing a shift in its corresponding resonant frequency. As a result, crack propagation and opening can be monitored from the resonant frequency shifts of the patch antenna. The patch antenna's capability of monitoring crack growth was validated using fatigue testing of a compact tension specimen. The specimen preparation, sensor fabrication, and experimental procedure are presented. The experimental results demonstrated that the corresponding resonant frequency of the antenna sensor shifted linearly with crack growth. On average, 1 mm crack growth caused the antenna frequency to shift by 22.1 MHz. The orientation of the crack and the effect of crack closure on the resonant frequencies of the antenna sensor are also discussed.
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paper_title: Development of a Low Cost Printable Chipless RFID Humidity Sensor

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A novel low-cost chipless radio frequency identification tag sensor is presented. The tag sensor provides identification data as well as monitors relative humidity (RH) of tagged objects. The tag sensor is made of passive microwave circuit that uses humidity sensitive polymer material for RH sensing. The aim of this paper is to investigate RF sensing properties of moisture absorbing polymer polyvinyl alcohol at microwave frequency. In addition, frequency shifting technique is used to encode data bits for high data capacity. The overall size of the proposed tag sensor is 15 mm × 6.8 mm and has 6 bit data capacity for ID generation and single bit for humidity sensing. Results presented here show ~ 607 MHz frequency deviation for 50% RH increase. The tag sensor has potential to be printed on flexible laminates such as plastic and paper for ultra-low cost item level tagging and ubiquitous sensing.
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paper_title: Passive wireless displacement sensor based on RFID technology

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Abstract This research demonstrates feasibility of using off-the-shelf radio frequency identification (RFID) tags to build a low cost passive wireless displacement sensor, suitable for applications such as crack detection in buildings and bridges. The sensor was constructed by splitting a RFID tag into two component parts consisting of the tag antenna and the chip-loop, which can be displaced by a distance represented by ‘ d ’. The displacement d could represent the width of a structural crack that may be found in a building or bridge. A loop antenna attached to a RFID reader can be placed at some distance ‘ D’ in proximity to the sensor to measure the effect of the displacement ( d ) on the power transmitted by the RFID chip back to the reader. By incrementally increasing the power transmitted by the RFID reader to the sensor ( P t ) when interrogating the RFID chip, calibration curves of the displacement d versus transmitted power P t for different values of D were obtained. The use of the calibration curves along with known values of the transmitted power P t allows for the determination of the displacement ‘ d ’.
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paper_title: Design, Calibration and Experimentation of an Epidermal RFID Sensor for Remote Temperature Monitoring

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An epidermal radiofrequency identification technology (RFID) sensor consists of a flexible antenna provided with a radiofrequency identification and sensing microchip directly stuck over the human skin by means of a sub-millimeter bio-compatible membrane. A compact-size epidermal RFID thermometer is here proposed and extensively experimented concerning its electromagnetic and thermal performance in case of battery-less and battery-assisted configurations. The antenna element embeds a mechanism for a post-manufacturing frequency retuning in order to adapt its response to the specific placement over the body. When attached over the skin, the sensor is readable from up to 0.7 m in battery-less mode and 2.3 m in battery-assisted mode. A calibration procedure improved the accuracy of the IC sensor down to 0.18 °C. The time constant evaluated by the first-order response of the IC to impulse heating (photo-flash) resulted in 4.3 s. The epidermal wireless thermometer was experimented in both supervised applications (manual reading) and in un-supervised architectures where users were continuously monitored by a fixed remote antenna or during the crossing of a surveillance gate. In all the considered cases, the reliability of the interrogation link was experimentally quantified and resulted robust for health monitoring applications in clinical and domestic settings and even for the automatic detection of anomalous temperature peaks of people walking within airports and at country border crossing.
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paper_title: Epidermal Passive RFID Strain Sensor for Assisted Technologies

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An epidermal passive wireless strain sensor using radio frequency identification (RFID) tags is presented. The tag is intended to detect eyebrow or neck skin stretch where paraplegic patients have the capability to tweak facial muscles. The tag is designed on a barium-titanate-loaded polydimethylsiloxane (PDMS) substrate and is assessed to demonstrate the strain gauge sensitivity and repeatability as a function of skin stretch.
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paper_title: UHF RFID Tag Antenna-Based Sensing for Corrosion Detection & Characterization Using Principal Component Analysis

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The authors identified errors in [1, eq. (1)] , which states \begin{align*} P_{R\leftarrow T}[\Psi (\theta,\phi)]=\frac {1}{4\pi }& \left({\frac {\lambda _{0}}{4\pi d}}\right)^{2} \\ & \times \,P_{in}G_{R}^{2}(\theta,\phi)\eta ^{2}_{p}RCS[\Psi (\theta,\phi)].\end{align*} Knowing that the dimensions of $P_{R\leftarrow T}$ function, $\lambda _{0}$ , $ P_{\mathrm {in}}, ~d$ , and RCS function are watt, meter, watt, meter, and square meter, respectively, also $\eta _{p}$ and $G_{R}$ functions do not have any dimension—it is seen that both sides of [1, eq. (1)] are not in the same dimension. Looking at another reference, [2, eq. (3)] , it is seen that the mathematical power of $d$ is equal to 2 \begin{align*} P_{R\leftarrow T}[\Psi (\theta,\phi)]=\frac {1}{4\pi }& \left({\frac {\lambda _{0}}{4\pi d^{2}}}\right)^{2} \\[-1pt]&\times \,P_{in}G_{R}^{2}(\theta,\phi)\eta ^{2}_{p}RCS[\Psi (\theta,\phi)]\end{align*} and the mathematical power of $d$ is not 1 as given in [1, eq. (1)] . However, the rest of the paper and analysis given in [1] are still correct.
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paper_title: Wireless surface acoustic wave radio frequency identification (SAW-RFID) sensor system for temperature and strain measurements

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The testing, validation, and monitoring of aerostructural design and health conditions require a non-intrusive and in-situ means to provide real time strain/stress and vibration data of turbine engine structures. However, taking such a measurement is difficult due to the extremely harsh environment in turbine engines. The SAW-RFID sensor provides a promising tool to operate in such a harsh environment, because it takes advantage of being passive, wireless and tolerant for high temperatures. These characteristics give it the ability to measure the strain/stress and temperature on engine blades in real time. In this paper, we present our work on the design, fabrication and testing of SAW-RFID devices as wireless temperature and strain sensors. The SAW-RFID sensors were first designed based upon the Finite Element Modeling (FEM). The aero structural designs sensors are then fabricated with micro-fabrication techniques. The antennas of the SAW sensor and RFID reader were also developed. The fabricated sensors were tested. Finally, we demonstrate the capability of our SAW sensor for the temperature and strain measurements, which show the consistence with the simulation values.
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paper_title: Rapid structural condition assessment using radio frequency identification (RFID) based wireless strain sensor

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Abstract This paper presents a wireless structural condition scanning system that utilizes the building information modeling (BIM) and radio frequency identification (RFID) based wireless strain sensor technologies to enable non-contact scanning of structural deformation. In buildings, structural members are often hidden behind drywalls, and thus buckling or yielding in steel members are difficult to detect, often requiring removal of coverings and thus time consuming and costly. Fast and accurate assessment of structural conditions is important to the occupant safety and uninterrupted use after extreme load events such as strong earthquakes. BIM can integrate all types of structural and condition assessment information collected in the life cycle of civil structures and also provides the visual data displaying mechanism that makes the structural health monitoring information easily understandable and actionable. Breakage-triggered (BT) strain sensor that uses RFID tag for non-contact scanning of structural deformation condition has been developed to detect the surpass of pre-set strain threshold corresponding to structural damage conditions such as yielding or buckling. This system can rapidly identify the spot where the pre-set strain threshold has been surpassed and the corresponding structural element in the BIM model would be highlighted to provide alert signal to engineers and decision makers.
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paper_title: RFID Passive Gas Sensor Integrating Carbon Nanotubes

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Carbon nanotube (CNT) composites are sensitive to the presence of gases due to their high surface-to-volume ratio and hollow structure that are well suited for gas molecule absorption and storage. Such sensing capability is here integrated with UHF RF identification (RFID) technology to achieve passive and low-cost sensors, remotely readable. CNT film (buckypaper) is used as a localized variable resistive load integrated into a tag antenna, which becomes able to transduce the presence of hazardous gas in the environment, ammonia in this case, into a change of its electromagnetic features. The dynamic range and the hysteresis of the radio sensor are investigated by simulations, equivalent circuits, and articulated experimentations within a true RFID link, providing the proof of concept and some guidelines for tag design.
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paper_title: Passive Wireless Temperature Sensor Based on Time-Coded UWB Chipless RFID Tags

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In this paper, an RF identification sensor system is developed. It comprises passive sensors and an ultra-wideband (UWB) reader. The sensors are based on time-coded chipless tags. They consist of an UWB antenna connected to a delay line that is, in turn, loaded with a resistive temperature sensor. This sensor modulates the amplitude of the backscattered signals as a function of the temperature. The sensor tags are identified by changing the length of the delay line. In this paper, the operation principle and design of time-coded tags is presented and the integration of sensors in these tags is addressed. In addition, two measurement techniques are compared to implement the UWB reader. The first one is based on frequency sweeping and uses a vector network analyzer. The second one is based on a low-cost UWB radar. A full characterization of the sensor system is provided.
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paper_title: The internet of things: a survey

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In recent year, the Internet of Things (IoT) has drawn significant research attention. IoT is considered as a part of the Internet of the future and will comprise billions of intelligent communicating `things'. The future of the Internet will consist of heterogeneously connected devices that will further extend the borders of the world with physical entities and virtual components. The Internet of Things (IoT) will empower the connected things with new capabilities. In this survey, the definitions, architecture, fundamental technologies, and applications of IoT are systematically reviewed. Firstly, various definitions of IoT are introduced; secondly, emerging techniques for the implementation of IoT are discussed; thirdly, some open issues related to the IoT applications are explored; finally, the major challenges which need addressing by the research community and corresponding potential solutions are investigated.
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paper_title: Inkjet-Printed Humidity Sensor for Passive UHF RFID Systems

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This paper presents a novel inkjet-printed humidity sensor tag for passive radio-frequency identification (RFID) systems operating at ultrahigh frequencies (UHFs). During recent years, various humidity sensors have been developed by researchers around the world for HF and UHF RFID systems. However, to our best knowledge, the humidity sensor presented in this paper is one of the first passive UHF RFID humidity sensor tags fabricated using inkjet technology. This paper describes the structure and operation principle of the sensor tag as well as discusses the method of performing humidity measurements in practice. Furthermore, measurement results are presented, which include air humidity-sensitivity characterization and tag identification performance measurements.
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paper_title: Printed Humidity Sensor With Memory Functionality for Passive RFID Tags

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This paper presents a printed UHF radio frequency identification (RFID) sensor solution that indicates whether a passive RFID tag has been exposed to a certain degree of humidity. The printed sensor operates as a write-once read-many-times resistive memory as it permanently changes its resistance from about 2 ${\rm k}\Omega$ to less than 50 $\Omega$ after exposure to humidity or water. The change of the sensor resistance is used to modulate the properties of a UHF RFID tag antenna by changing antenna input impedance and also introducing or removing ohmic losses in the antenna structure. The final result is reflected in the change of the minimum transmit power required to power-up the RFID tag. Both the sensor and the tag antenna are printed horizontally on a paper substrate. Different geometric combinations of sensor and antenna structures are investigated. Typical applications include noninvasive methods for detecting wetness or humidity levels in hidden locations, such as within construction structures. The sensor setup can also serve to provide information as to whether a package sent over a supply chain has exceeded a certain level of humidity during its route.
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paper_title: Smart Sensing Materials for Low-Cost Chipless RFID Sensor

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Smart materials for chipless RFID sensors have not been developed for the broadband/high speed wireless data communication yet. Their applications are confined to some dc and very high frequency physical sensors. In this paper, various smart materials for RF sensing applications and their characteristics in the influence of various physical parameters have been analyzed. The working principle of chipless RFID sensors along with their various design and experimental results as well as their potential application is also presented. This paper provides a pathway to low cost, passive, fully printable sensor nodes for realtime condition monitoring.
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paper_title: Towards chipless RFID-based sensing for pervasive surface crack detection

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We present Surface Crack Antenna Reflectometric Sensing or SCARS: a chipless RFID sensor that enables pervasive, wireless surface crack detection in structural materials. We outline the sensor design and demonstrate how crack length and orientation can be related to the backscatter signal signature of the SCARS sensor. In doing so, design techniques that improve sensor sensitivity and signal fidelity are presented. Proof of concept is then demonstrated via numerical simulation and the implementation of a laboratory prototype. Finally, an envisioned pervasive health monitoring and data extraction strategy using these sensors is also discussed.
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paper_title: Stretchable RFID for Wireless Strain Sensing With Silver Nano Ink

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Flexible and stretchable inductor-capacitor (LC) resonator-based chipless radio frequency identification (RFID) tags have been fabricated by the direct stamping with silver nano ink. The tags are optimized based on the sympathetic oscillation of LC circuit at specifically designed resonant frequencies ranged from 1.12 to 1.7 GHz by adjusting dimensions of the inductor and capacitor in a tag. Pressure applied to the layer of silver nano ink during the stamping procedure helps densification of silver nanoparticles inside trenches of the stamp before heat-annealing of them. Transfer stamping process is simulated to demonstrate stress distribution across the layer of silver nanoparticles. Compaction of silver nanoparticles, in turn, positively affects mechanical strength of the final silver electrode and enables RFID strain sensors on polydimethylsiloxane to be stretchable up to 7%. By the stretchable RFID strain sensors, wireless strain sensing is demonstrated with a gauge factor of 0.51. Multiple encoded identifications with combination of double tags and stretching behavior of fabricated tags are also demonstrated. This stretchable RFID sensor is promising for biomedical applications such as real-time monitoring of motion detection.
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paper_title: RFID tags for wireless electrochemical detection of volatile chemicals

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Abstract This work outlines a new approach for the construction of a wireless and battery-free broad response vapour sensor. Carbon black/organic polymer composites are known to swell reversibly upon exposure to volatile chemicals. We integrated these types of composites into the electronic elements of a conventional passive RFID tag circuitry to produce resistance changes that result in a change in the RFID tag's output signal frequency and amplitude. To identify vapours, arrays of RFID tags with such vapour-sensing elements were constructed, with each tag containing carbon black as the conducting element and a polymer as the sensing element. The different gas–solid partition coefficients for the polymers in the sensor array produce a unique pattern of signal changes that can be used to classify vapours. This sensor array was able to identify and quantify several vapours of interest (water, ammonia, ethanol and toluene).
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paper_title: SAW-RFID enabled temperature sensor

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Abstract Wireless sensors based on surface acoustic wave (SAW) technology has its own advantages over its counterparts. In this paper, a novel SAW radio frequency identification (RFID) enabled temperature sensor is proposed for industrial applications, in which short measurement range but high accuracy is usually required. The encoding scheme for the sensor using pulse positions combined with phase information is adopted, and then the relationship between the length of a time slot and the decoding errors is deduced to ensure the sensor can be accurately identified, even though ambient temperature fluctuates. In order to solve the phase ambiguity problem involved in temperature measurements more efficiently and reduce the cost of obtaining the unwrapping temperature characteristic curves in the calibration process, an analytical procedure for calculating the variation of phase delay differences with respect to temperature has been proposed. A self-developed burst transceiver supporting online data analysis is also presented. The experimental results demonstrate the effectiveness and practicality of the proposed SAW-RFID enabled temperature sensing scheme, and the prototype sensor within a temperature-controlled oven 2 m away from the center of the transceiver antenna in a horizontal orientation achieves an accuracy of ±0.3 °C in the temperature range 0–40 °C.
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paper_title: Sub-Millimeter Displacement Sensing by Passive UHF RFID Antennas

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A slotted patch is transformed into a wireless passive UHF-RFID sensor of uni-dimensional displacements by introducing a mechanic-electromagnetic modulation capable to convert sub-millimeter deformations into changes of the antenna's response, remotely detectable. A design methodology allows to obtain the desired sensitivity and dynamic range in a fully controllable way. The sensor and the methodology are discussed through the help of preliminary laboratory experimentations on a concrete brick, showing the possibility to achieve resolutions better than 0.1 mm with low cost readers.
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paper_title: Detecting crack orientation using patch antenna sensors

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Crack orientation is a very important parameter for structural integrity analysis. Even though many sensors have been developed to detect crack presence and length, very few sensors can detect crack orientation. Recently, we have demonstrated a patch antenna sensor that can detect crack propagation with sub-millimeter resolution. In this paper, the capability of the antenna sensors for crack orientation detection is studied. An antenna sensor with a rectangular antenna patch radiates at two fundamental modes. The effect of a ground-plane crack on these two resonant frequencies depends on its orientation. Hence, the crack orientations can be monitored by analyzing the crack-induced shifts of both antenna resonant frequencies. The principle of operation will be discussed first, followed by detailed descriptions on the numerical simulation, sensor fabrication, experimental procedure, results and analysis. Simulation as well as experimental results confirmed that the antenna sensor is capable of providing quantified information about the crack orientation.
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paper_title: Development of Wireless and Passive Corrosion Sensors for Material Degradation Monitoring in Coastal Zones and Immersed Environment

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Wireless and fully energetically passive corrosion sensors inspired from the chipless Radio-Frequency IDentification (RFID) technology are presented for the monitoring of degradation of infrastructures located in coastal zones and underwater environments. The device consists of a reader and a remote passive sensor. This study presents two radio-frequency (RF) corrosion-sensitive resonators that can be integrated in such a device. The first is sensitive to a loss of metal due to its degradation, and the second is sensitive to the corrosion potential of metals, with respect to a reference electrode. The RF characterization of these two resonators demonstrates unambiguously the sensitivity of the method to corrosion of metal, passivation of steel as well as degradation of organic coatings. Then, their integration in a demonstrator including antennas is considered. The main parameters that influence the RF wave propagation and thus the reading distance are discussed. Following the presented results, the proposed method is considered as a reliable and versatile tool which should be able to be deployed in immersed, tidal, and splash zones, for example, for offshore facilities monitoring.
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paper_title: Embedded wireless strain sensors based on printed RFID tag

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Purpose – The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency identification (RFID) technology and it can be embedded into a variety of structures.Design/methodology/approach – Silver ink conductors and RFID tags were printed by the screen printing method on stretchable polyvinyl chloride and fabric substrates. The development of the strain‐sensitive RFID tag was based on the behavior of the selected antenna and substrate materials. Performance of the tags and the effect of mechanical strain on tag functioning were examined.Findings – The results showed that large displacements can be successfully measured wirelessly using a stretchable RFID tag as a strain‐sensitive structure. The behavior of the tag can be modified by selection of the material.Research limitations/implications – New tag designs, which are more sensitive to small levels of strain and which have a linear response will be the subje...
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paper_title: Passive wireless antenna sensor for strain and crack sensing—electromagnetic modeling, simulation, and testing

paper_content:

This research investigates a passive wireless antenna sensor designed for strain and crack sensing. When the antenna experiences deformation, the antenna shape changes, causing a shift in the electromagnetic resonance frequency of the antenna. A radio frequency identification (RFID) chip is adopted for antenna signal modulation, so that a wireless reader can easily distinguish the backscattered sensor signal from unwanted environmental reflections. The RFID chip captures its operating power from an interrogation electromagnetic wave emitted by the reader, which allows the antenna sensor to be passive (battery-free). This paper first reports the latest simulation results on radiation patterns, surface current density, and electromagnetic field distribution. The simulation results are followed with experimental results on the strain and crack sensing performance of the antenna sensor. Tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20???, and can perform well at large strains higher than 10?000???. With a high-gain reader antenna, the wireless interrogation distance can be increased up to 2.1?m. Furthermore, an array of antenna sensors is capable of measuring the strain distribution in close proximity. During emulated crack and fatigue crack tests, the antenna sensor is able to detect the growth of a small crack.
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paper_title: Sensitivity Modeling of an RFID-Based Strain-Sensing Antenna With Dielectric Constant Change

paper_content:

An radiofrequency identification (RFID)-based folded patch antenna has been developed as a novel passive wire- less sensor to measure surface strain and crack, for the structural health monitoring of metallic structures. Up to 2.5 m of read range is achieved by a proof-of-concept prototype patch antenna sensor with a strain sensitivity around �760 Hz/μe ,w hich is equivalent to a normalized strain sensitivity of �0.74 ppm/μe. In this paper, we propose to consider the change of the substrate dielectric constant due to strain when modeling the antenna sensor. An enhanced strain sensitivity model is introduced for more accurately estimating the strain sensing performance of the hereby introduced smart skin antenna sensor. Laboratory experiments are carried out to quantify the dielectric constant change under strain. The measurement results are incorporated into a mechanics-electromagnetics coupled simulation model. Accuracy of the multi-physics coupled simulation is improved by integrating dielectric constant change in the model.
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paper_title: High-density chipless RFID tag for temperature sensing

paper_content:

A 30 bit high-density circular chipless RF identification tag based on C-shaped open end polarisation independent slots is presented. The encoding capacity of this design is enhanced in a compact size. Patch diameter of the tag is 24 mm. Circularly polarised incident plane waves are used for excitation. Data capacity of 30 bits is achieved in the frequency band of 3.1–11.7 GHz. Spectral signature-based radar cross-section results are also measured for flexible and temperature sensor integrated design. The prototype is inkjet printed on Kapton® HN heat resistant conformal sheet.
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paper_title: Pseudo-orthogonal frequency coded wireless SAW RFID temperature sensor tags

paper_content:

SAW sensors are ideal for various wireless, passive multi-sensor applications because they are small, rugged, radiation hard, and offer a wide range of material choices for operation over broad temperature ranges. The readable distance of a tag in a multi-sensor environment is dependent on the insertion loss of the device and the processing gain of the system. Single-frequency code division multiple access (CDMA) tags that are used in high-volume commercial applications must have universal coding schemes and large numbers of codes. The use of a large number of bits at the common center frequency to achieve sufficient code diversity in CDMA tags necessitates reflector banks with >30 dB loss. Orthogonal frequency coding is a spread-spectrum approach that employs frequency and time diversity to achieve enhanced tag properties. The use of orthogonal frequency coded (OFC) SAW tags reduces adjacent reflector interactions for low insertion loss, increased range, complex coding, and system processing gain. This work describes a SAW tag-sensor platform that reduces device loss by implementing long reflector banks with optimized spectral coding. This new pseudo-OFC (POFC) coding is defined and contrasted with the previously defined OFC coding scheme. Auto- and cross-correlation properties of the chips and their relation to reflectivity per strip and reflector length are discussed. Results at 250 MHz of 8-chip OFC and POFC SAW tags will be compared. The key parameters of insertion loss, cross-correlation, and autocorrelation of the two types of frequency-coded tags will be analyzed, contrasted, and discussed. It is shown that coded reflector banks can be achieved with near-zero loss and still maintain good coding properties. Experimental results and results predicted by the coupling of modes model are presented for varying reflector designs and codes. A prototype 915-MHz POFC sensor tag is used as a wireless temperature sensor and the results are shown.
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paper_title: Internet of Things: A Survey on Enabling Technologies, Protocols, and Applications

paper_content:

This paper provides an overview of the Internet of Things (IoT) with emphasis on enabling technologies, protocols, and application issues. The IoT is enabled by the latest developments in RFID, smart sensors, communication technologies, and Internet protocols. The basic premise is to have smart sensors collaborate directly without human involvement to deliver a new class of applications. The current revolution in Internet, mobile, and machine-to-machine (M2M) technologies can be seen as the first phase of the IoT. In the coming years, the IoT is expected to bridge diverse technologies to enable new applications by connecting physical objects together in support of intelligent decision making. This paper starts by providing a horizontal overview of the IoT. Then, we give an overview of some technical details that pertain to the IoT enabling technologies, protocols, and applications. Compared to other survey papers in the field, our objective is to provide a more thorough summary of the most relevant protocols and application issues to enable researchers and application developers to get up to speed quickly on how the different protocols fit together to deliver desired functionalities without having to go through RFCs and the standards specifications. We also provide an overview of some of the key IoT challenges presented in the recent literature and provide a summary of related research work. Moreover, we explore the relation between the IoT and other emerging technologies including big data analytics and cloud and fog computing. We also present the need for better horizontal integration among IoT services. Finally, we present detailed service use-cases to illustrate how the different protocols presented in the paper fit together to deliver desired IoT services.
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paper_title: Modeling and Applications of a Chemical-Loaded UHF RFID Sensing Antenna With Tuning Capability

paper_content:

A key-issue of the wireless gas sensing by radio frequency identification is the capability to control the sensor's response while minimizing the amount of chemical interactive materials (CIM) required to dope the tag antenna. An open-circuit shielded slot-line layout is proposed as a general purpose tunable radio frequency identification (RFID) radiator, suitable to host small amounts of CIM. It operates both as a very efficient passive sensor and as a tool to estimate the electromagnetic equivalent parameters of the CIM during the gas exposure. A hybrid distributed-lumped model permits to separate the CIM's contribution from the antenna's response and, in addition, it provides a simple tool to shape the calibration curve relating RFID power signals to the physical changes of the environment. The tag layout and the method are applied to the UHF characterization of the conductive polymer Pedot:PSS and to the optimization of high-performance humidity sensor capable of a three-times higher sensitivity than those achieved by the current state of the art RFID devices.
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paper_title: RFID Tag Antenna-Based Sensing for Pervasive Surface Crack Detection

paper_content:

We introduce the concept of using an RFID tag's antenna to sense surface cracks. Our contribution is two fold. First, we present the design of an inductively coupled loop antenna that can be used as a crack detector. Second, we propose the development of a 2-D grid of tags to improve spatial coverage and discuss how it can be used to monitor typical crack patterns in civil infrastructure. We demonstrate that the technique works reliably over a read distance of 1 m and in different types of environments. Potential engineering extensions and future research directions are also discussed.
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paper_title: Low frequency (LF) RFID sensors and selective transient feature extraction for corrosion characterisation

paper_content:

Abstract In this paper, Low Frequency (LF) RFID sensing system is used to characterise marine atmospheric corrosion on steel samples. Considering the conductivity and permeability variation in the corrosion layer, optimisation of sensing sensitivity and communication distance of commercial RFID tags placed on both coated and uncoated samples (exposure duration between 1 and 12 months) for impedance matching and appropriate operation frequencies are analysed. To balance the communication distance between RFID reader and tag and to match the impedance variation of RFID tags on metallic samples, a concept of wireless power transfer (WPT) through strongly coupled magnetic resonance (SCMR) method at RFID is applied. Static and transient features are extracted and selected to characterise corrosion. To enhance the sensing sensitivity to corrosion characterisation, further experimental studies have been carried out using ferrite sheets. The proposed LF RFID sensing system has been validated using commercial RFID tags with different feature extractions and selection of features for corrosion characterisation.
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paper_title: LC Passive Wireless Sensors Toward a Wireless Sensing Platform: Status, Prospects, and Challenges

paper_content:

Inductor–capacitor ( $LC$ ) passive wireless sensors use a transformer with loose coupling between an external readout coil and an inductor that receives power through this inductive coupling. Changes in the sensor are wirelessly and remotely detected by the readout coil, which makes them highly useful in applications that require the sensor to be powered remotely and to occupy a small volume, such as harsh and sealed environments, where physical access to the sensor is difficult. Although the sensor to accomplish this function dates from the 1960’s, its rapid extension over the past decades has benefited from microelectromechanical systems. This paper provides an overview of the status and challenges in the $LC$ passive wireless sensor toward a wireless sensing platform. The basic sensing principles are first categorized into detecting changes of the sensor in response to the capacitance, resistance, inductance, or coupling distance due to the parameter of interest through monitoring the impedance magnitude and phase spectrum. The present state of the art in sensor applications for pressure, strain, temperature, humidity, biochemical, gas, and so on is then reviewed and compared. For emerging applications from many Internet of Things scenarios, geometrical constraints, such as small and non-invasive coils, reduce the magnetic coupling between the sensor and the readout coil, resulting in a limited interrogation distance. Furthermore, an increasing number of applications also require the simultaneous measurement of multiple parameters. Recent efforts to increase the interrogation distance and to extend the measurement of single parameter to multiple parameters are finally outlined. [2016-0093]
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paper_title: Space Time Coding for Backscatter RFID

paper_content:

In this work, the use of Space-Time Codes in passive Radio Frequency IDentification (RFID) systems is explored; this is feasible whenever a tag possesses multiple antennas. Information is encoded across the multiple tag antennas and received by an RFID reader, also typically equipped with multiple antennas. The nature of passive RFID induces a unique fading channel known as the dyadic backscatter channel, which differs statistically compared to the canonical Rayleigh fading channel. We introduce a modified dyadic channel for RFID backscatter that adequately captures the space-time coding paradigm. We then propose known orthogonal space-time codes and derive an upper bound on the the pairwise error probability (PEP), leading to estimates of the (asymptotic) diversity order. Interestingly, the diversity order is shown to depend only on the number of tag antennas but not the number of receive antennas; the resultant performance trade-offs is discussed. Lastly, simulation of the symbol error rates for different channel configurations are conducted to validate the analysis.
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paper_title: Rail corrosion forensics using 3D imaging and finite element analysis

paper_content:

Rail infrastructure renewal maintenance is capital intensive. As a contributor to rail deterioration, corrosion damage needs to be accurately analysed for renewal maintenance planning. The main contribution of this study is to introduce an information-dense forensic analysis method for characterizing rail corrosion damage in situ based on 3D imaging. Two state-of-the-art technologies, an arm laser scanner and handheld laser scanner, are employed for onsite digitization of the rail surface. Acquired 3D image data is analysed to characterize pitting corrosion in terms of volume, surface area coverage and average pit depth. Cyclic loading of the sampled rail is simulated using finite element analysis of the 3D image to establish risk potential for crack initiation. A case project was used to validate the feasibility of the developed approach. The results of this study demonstrate the usefulness of applying forensic methodology to renewal maintenance planning.
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paper_title: Increased Range Bistatic Scatter Radio

paper_content:

Scatter radio achieves communication by reflection and requires low-cost and low-power RF front-ends. However, its use in wireless sensor networks (WSNs) is limited, since commercial scatter radio (e.g. RFID) offers short ranges of a few tens of meters. This work redesigns scatter radio systems and maximizes range through non-classic bistatic architectures: the carrier emitter is detached from the reader. It is shown that conventional radio receivers may show a potential 3dB performance loss, since they do not exploit the correct signal model for scatter radio links. Receivers for on-off-keying (OOK) and frequency-shift keying (FSK) that overcome the frequency offset between the carrier emitter and the reader are presented. Additionally, non-coherent designs are also offered. This work emphasizes that sensor tag design should accompany receiver design. Impact of important parameters such as the antenna structural mode are presented through bit error rate (BER) results. Experimental measurements corroborate the long-range ability of bistatic radio; ranges of up to 130 meters with 20 milliwatts of carrier power are experimentally demonstrated, with commodity software radio and no directional antennas. Therefore, bistatic scatter radio may be viewed as a key enabling technology for large-scale, low-cost and low-power WSNs.
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paper_title: RFID: From Supply Chains to Sensor Nets

paper_content:

The next generation internet will be the internet of things (and not just of computing devices like PCs, PDAs); this is presumed to be enabled by integrating simple computing plus communications capabilities into common objects of everyday use. Radio-frequency identification (RFID) is a compelling technology for creation of such pervasive sensor networks due to its potential for ubiquitous, low-cost/low-maintenance use. However, the current drivers for RFID deployment emphasize supply chain management using passive tags, implying that RFID sensor nets require advances beyond the components and system designs aimed at supply chain applications. This work provides a glimpse of how this may be achieved.
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paper_title: Antenna Sensors in Passive Wireless Sensing Systems

paper_content:

Antenna sensors have received considerable interests in recent years due to their passive wireless operation, simple configuration, compact size, multiplexing capability, and multimodality sensitivity. Based on the principle of antenna backscattering, an antenna sensor can be wirelessly interrogated at middle range distances without an onboard battery. Since the antenna serves the dual function of sensing and communicating, an antenna sensor can be implemented with minimum number of components. As narrowband resonators, antenna sensors can be easily multiplexed based on the principle of frequency division multiplexing. In addition, different types of antenna sensors that are sensitive to a variety of physical measurands have been demonstrated. Due to these unique features, antenna sensor technology could play a vital role in our drive toward ubiquitous sensing. This chapter provides a comprehensive review of this exciting technology with detailed descriptions on the operational principle and wireless interrogation of batteryless antenna sensors. Four application examples of using antenna sensors for moisture, dynamic strain, temperature, and crack sensing are discussed. Future research directions and open problems are suggested.
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paper_title: Phase based spatial identification of UHF RFID tags

paper_content:

In this paper, we give an overview of spatial identification (determining position and velocity) of modulated backscatter UHF RFID tags using RF phase information. We describe three main techniques based on PDOA (Phase Difference of Arrival): TD (Time Domain), FD (Frequency Domain), and SD (Spatial Domain). The techniques are illustrated with modeling and simulation example in free space and in presence of multipath using a multi-ray channel model for amplitude and phase of the received tag signal in deterministic environment. We also present and discuss the experiments performed in a real RFID warehouse portal environment.
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paper_title: Novel RSSI evaluation models for accurate indoor localization with sensor networks

paper_content:

In a Wireless Sensor Network (WSN), it is often necessary to know the accurate location of one or more nodes. Various localization methods have been proposed, namely: TDOA, TOA, AOA, GPS and RSSI. All methods except RSSI require added hardware which increases the cost of the WSN. Moreover, the RSSI value of received radio signals is easily available on most sensor nodes. We propose a set of three techniques (mean+filter, mode, mode+filter) for evaluating RSSI for accurate indoor localization. The techniques are developed with the help of rigorous experimental data collected with TelosB nodes. Localization performance with all the models is compared with an existing technique, the mean technique. We assert that the mode-filter technique achieves a 64.86% less error over the mean technique in distance estimation between the transmitter and the receiver, and it has a 21.33% lower error in location estimation.
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paper_title: Space Time Coding for Backscatter RFID

paper_content:

In this work, the use of Space-Time Codes in passive Radio Frequency IDentification (RFID) systems is explored; this is feasible whenever a tag possesses multiple antennas. Information is encoded across the multiple tag antennas and received by an RFID reader, also typically equipped with multiple antennas. The nature of passive RFID induces a unique fading channel known as the dyadic backscatter channel, which differs statistically compared to the canonical Rayleigh fading channel. We introduce a modified dyadic channel for RFID backscatter that adequately captures the space-time coding paradigm. We then propose known orthogonal space-time codes and derive an upper bound on the the pairwise error probability (PEP), leading to estimates of the (asymptotic) diversity order. Interestingly, the diversity order is shown to depend only on the number of tag antennas but not the number of receive antennas; the resultant performance trade-offs is discussed. Lastly, simulation of the symbol error rates for different channel configurations are conducted to validate the analysis.
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paper_title: Optimal Training Sequence for MIMO Wireless Systems in Colored Environments

paper_content:

In this paper, we design the training signal for a multi-input multi-output (MIMO) communication system in a colored medium. We assume that the known channel covariance matrix (CM) is a Kronecker product of a transmit channel CM and a receive channel CM. Similarly, the CM of the additive Gaussian noise is modeled by a Kronecker product of a temporal CM and a spatial CM. We maximize the differential entropy gained by receiver for a limited energy budget for training at the transmitter. Using, singular value decomposition of the involved CMs, we turn this problem into a convex optimization problem. We prove that the left and right singular vectors of the optimal training matrix are eigenvectors of the channel transmit CM and the noise temporal CM. In general case, this problem can be solved numerically using efficient methods. The impact of the optimal training is more significant in environments with larger eigenvalue spread. The expression of the optimal solution is interesting for some specific cases. For uncorrelated receive channel, the optimal training looks like water filling, i.e., more training power must be invested on the directions which have more impact. For high signal-to-noise ratios (SNRs), any orthogonal training is optimal; this means that if large amount of energy is available, it must be invested uniformly in all directions. In low SNR scenarios where low amount of energy is available for channel training, all the energy must be allocated to the best mode of channel (which has the highest ratio of the received channel variance to the received noise power).
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paper_title: Modulation and sensitivity limits for backscatter receivers

paper_content:

This paper discusses how a low-powered RFID tag or sensor mote's backscatter modulation scheme - limited in ways that conventional digital wireless systems are not - may be adapted to the peculiar non-white noise properties of a backscatter receiver's radio frequency electronic chain to maximize detection. The analysis and results in this paper enable longer-range operation of today's passive, or semi-passive RFID tags as well as future backscatter sensor links that operate in higher frequency bands.
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paper_title: Revisiting RFID Link Budgets for Technology Scaling: Range Maximization of RFID Tags

paper_content:

Passive RF identification (RFID) tags are traditionally assumed to be downlink limited since typical tag sensitivity is considerably poorer than reader sensitivity, due to stringent power limitations. On the other hand, semipassive tags are generally uplink limited because of improvement in tag sensitivity for battery-assisted tags. In this paper, it is demonstrated that judicious choice and use of integrated circuit impedance for backscatter modulation will be needed to simultaneously maximize tag uplink and downlink ranges as passive tag designs improve. Optimal backscatter modulation indices for amplitude shift keying are derived for range maximization of next-generation low-power RFID tags.
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paper_title: Performance Analysis of Passive UHF RFID Systems Under Cascaded Fading Channels and Interference Effects

paper_content:

In this paper, the performance of monostatic and bistatic passive ultra high frequency radio frequency identification (UHF RFID) systems under the effects of cascaded fading channels and interference is studied. The performance metric used is tag detection probability defined as the probability that the instantaneous received power is higher than the reader's sensitivity. A closed-form expression of the detection probability is derived using cascaded forward and backscatter fading channels and the reader antennas orientation relative to the tag. Furthermore, the performance of passive UHF RFID systems under reader-to-tag interference caused by both the desired RFID signal and multiple RFID interferers is analyzed, and the effect of constructive and destructive interferences is examined. In addition, the maximum reading range in ideal, multipath fading, and interfering environments is presented. To the best of our knowledge, this is the first work that provides a 3-D performance analysis of the passive UHF RFID systems under cascaded fading channels. The obtained results are very useful for the design and optimization of passive UHF RFID systems from an RF physical channel point of view.
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paper_title: Complete Link Budgets for Backscatter-Radio and RFID Systems

paper_content:

Backscatter radio - wireless communication by modulating signals scattered from a transponder (RF tag) - is fundamentally different from conventional radio because it involves two distinct links: the power-up link for powering passive RF tags, and the backscatter link for describing backscatter communication. Because of severe power constraints on the RF tag, a thorough knowledge of the backscatter channel is necessary to maximize backscatter-radio and radio-frequency identification (RFID) system performance. This article presents four link budgets that account for the major propagation mechanisms of the backscatter channel, along with a detailed discussion of each. Use of the link budgets is demonstrated by a practical UHF RFID portal example. The benefits of future 5.8 GHz multi-antenna backscatter-radio systems are shown. An intuitive analogy for understanding the antenna polarization of RF tag systems is presented.
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paper_title: Received signal strength indication signature for passive UHF tags

paper_content:

Received signal strength indication (RSSI) has commonly been used for estimating the distance between a radio frequency identification (RFID) tag and its reader. However a plot of RSSI vs. frequency reveals a signature specific to the physical surrounding environment. In an attempt to understand how the environment impacts the RSSI signature, an experiment was performed in a “real world” environment where the test setup was shifted incrementally though an open room to see how the RSSI signature changes. In another experiment, the RSSI signature was measured in an anechoic chamber with and without absorbers on the floor so the effect of the ground plane reflection on the RSSI signature could be isolated and examined. The RSSI signature was found to be too complex to pinpoint a single feature as being caused by the ground plane reflection; however it can be concluded that not only is the RSSI signature repeatable within an unchanged physical environment (and therefore not merely random noise), small changes in the environment result in small changes in the RSSI signature. These experiments demonstrate a potential improvement in fingerprinting and distance estimation, if frequency hopping is used to measure RSSI, by averaging RSSI over a frequency range.
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paper_title: Gains For RF Tags Using Multiple Antennas

paper_content:

Backscatter radio systems, including high frequency radio frequency identification (RFID), operate in the dyadic backscatter channel - a two-way pinhole channel that has deeper small-scale fades than that of a conventional one-way channel. This paper shows that pinhole diversity is available in a rich scattering environment caused by modulating backscatter with multiple RF tag antennas - no diversity combining at the reader, channel knowledge, or signaling scheme change is required. Pinhole diversity, along with increased RF tag scattering aperture, can cause up to a 10 dB reduction in the power required to maintain a constant bit-error-rate for an RF tag with two antennas. Through examples, it is shown that this gain results in increased backscatter radio system communication reliability and up to a 78% increase in RF tag operating range.
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paper_title: Effect of air gap on cylindrical dielectric resonator antenna operating in TM01 mode

paper_content:

The results of a numerical study pertaining to the effect of an air gap on the input impedance and resonance frequency of a cylindrical dielectric resonator (CDR) antenna operating in the TM 01 mode as a function of dielectric constant are presented. The CDR resides on a conducting ground plane and is excited by a coaxial probe through the bottom of the ground plane. Some of the numerical results are validated experimentally
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paper_title: Impedance, bandwidth, and Q of antennas

paper_content:

To address the need for fundamental universally valid definitions of exact bandwidth and quality factor (Q) of tuned antennas, as well as the need for efficient accurate approximate formulas for computing this bandwidth and Q, exact and approximate expressions are found for the bandwidth and Q of a general single-feed (one-port) lossy or lossless linear antenna tuned to resonance or antiresonance. The approximate expression derived for the exact bandwidth of a tuned antenna differs from previous approximate expressions in that it is inversely proportional to the magnitude |Z'/sub 0/(/spl omega//sub 0/)| of the frequency derivative of the input impedance and, for not too large a bandwidth, it is nearly equal to the exact bandwidth of the tuned antenna at every frequency /spl omega//sub 0/, that is, throughout antiresonant as well as resonant frequency bands. It is also shown that an appropriately defined exact Q of a tuned lossy or lossless antenna is approximately proportional to |Z'/sub 0/(/spl omega//sub 0/)| and thus this Q is approximately inversely proportional to the bandwidth (for not too large a bandwidth) of a simply tuned antenna at all frequencies. The exact Q of a tuned antenna is defined in terms of average internal energies that emerge naturally from Maxwell's equations applied to the tuned antenna. These internal energies, which are similar but not identical to previously defined quality-factor energies, and the associated Q are proven to increase without bound as the size of an antenna is decreased. Numerical solutions to thin straight-wire and wire-loop lossy and lossless antennas, as well as to a Yagi antenna and a straight-wire antenna embedded in a lossy dispersive dielectric, confirm the accuracy of the approximate expressions and the inverse relationship between the defined bandwidth and the defined Q over frequency ranges that cover several resonant and antiresonant frequency bands.
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paper_title: Wireless Passive RFID Crack Width Sensor for Structural Health Monitoring

paper_content:

All mechanical structures are subjected to deformation and cracks, due to fatigue, stress, and/or environmental factors. It is, therefore, of uttermost importance to monitor the mechanical condition of critical structures, in order to prevent catastrophic failures, but also to minimize maintenance costs, i.e., avoid unnecessary inspections. A number of technologies and systems can be used for this purpose: among them, the ones proposing the use of wireless passive crackmeters have a strong impact potential, in terms of simplicity of installation and measurement and low cost. This paper, hence, shows a crack width wireless radio-frequency identification sensor, developed for applications on various materials (such as concrete and metal) and able to detect submillimeter deformations occurring on the object, on which it is placed. A design method based on high-sensitivity phase detection is shown.
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paper_title: Modulation and sensitivity limits for backscatter receivers

paper_content:

This paper discusses how a low-powered RFID tag or sensor mote's backscatter modulation scheme - limited in ways that conventional digital wireless systems are not - may be adapted to the peculiar non-white noise properties of a backscatter receiver's radio frequency electronic chain to maximize detection. The analysis and results in this paper enable longer-range operation of today's passive, or semi-passive RFID tags as well as future backscatter sensor links that operate in higher frequency bands.
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paper_title: The Radiation $Q$ -Factor of a Horizontal $\lambda/2$ Dipole Above Ground Plane

paper_content:

Closed-form equations are given for radiation quality factor of a thin-wire $\lambda/2$ dipole above an infinite electric ground plane. Particular results of interest include a simple formula for a small separation between the dipole and the ground and for one dipole in free space.
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paper_title: Pseudorandom Noise based Channel Coding Scheme for Tag to Reader Communication in UHF-RFID Systems

paper_content:

This paper presents the capabilities of using Pseudorandom noise (PN) codes as a channel-coding scheme for the tag to reader communication. A comparative of the standardized coding scheme and the PN is presented. To take advantage of the PN code's orthogonality an example is shown using gold sequences of length 31 coding 16 symbols, which encodes the information that is backscattered by the tag. At the reader the corresponding correlation receiver is implemented to detect any of the 16 possible symbols. The decision is made using a maximum-likelihood method. This coding scheme will be compared to the EPCglobal GEN 2 standardized Miller codes in order to establish its advantages and disadvantages.
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paper_title: Waveguide Probe Loaded With Split-Ring Resonators for Crack Detection in Metallic Surfaces

paper_content:

We present a near-field waveguide probe with an embedded array of split-ring resonators (SRRs) that operate at 16.65 GHz. When the probe scans a metal surface, the magnetic flux generated from the currents on the metallic surface strongly affects the equivalent lumped parameters of the SRRs. This, in turn, affects the reflection coefficient of the feeding port leading to high sensitivity in detecting anomalies such as cracks in the surface. Experimental results indicated the feasibility of detecting cracks, as small as 25 μm in width, in metallic surfaces. Additionally, the probe achieves good resolution in detecting closely spaced cracks.
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paper_title: Constrained-Design of Passive UHF RFID Sensor Antennas

paper_content:

Passive UHF RFID tags may be used, beside labeling, to remotely observe the physical/chemical change of the tagged object, through modulation of their impedance and gain, thus acting as sensor antennas. The design of this new class of devices can be mastered by fully understanding the relationship between communication and sensing with the purpose to balance the maximization of the dynamic range of the response with the stability of the read distance. A new kind of communication/sensing nomogram permits to display both behaviors in a unitary way and to predict their physical limits, as well as to formalize a multi-parameter general-purpose optimization methodology. The procedure is demonstrated by application to the design of a strain-gauge tag and of a level-detector wireless sensor.
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paper_title: Advances in antenna designs for UHF RFID tags mountable on conductive items

paper_content:

The design of antennas for metal-mountable radio-frequency identification tags is driven by a unique set of challenges: cheap, small, low-profile, and conformal structures need to provide reliable operation when tags are mounted on conductive platforms of various shapes and sizes. During the past decade, a tremendous amount of research has been dedicated to meeting these stringent requirements. Currently, the tag-reading ranges of several meters are achieved with flexible-label types of tags. Moreover, a whole spectrum of tag-size performance ratios has been demonstrated through a variety of innovative antenna-design approaches. This article reviews and summarizes the progress made in antennas for metal-mountable tags, and presents future prospects.
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paper_title: Microstrip Antenna Design Handbook

paper_content:

Initiated as an update of Bahl and Bhartia's 1980 work, Microstrip Antennas, this resource for designers took on a new form completely to accommodate the field's many new developments. It emphasizes design approaches that have lasting value among the full-wave techniques; these approaches for various antenna types center around cavity model analysis, chosen as a good compromise between accuracy and complexity. The book is organized in 12 chapters providing introductory material and covering analysis techniques; prominent antenna types such as rectangular patches, circular patches, triangular patches, dipoles, and slots; circularly polarized antennas; loaded and active (integrated) antennas; broadbanding techniques; and array antennas.Book News, Inc.Â®, Portland, OR
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paper_title: Multi-Loaded Modulated Scatterer Technique for Sensing Applications

paper_content:

Modulated scatterer technique (MST) probes have been commonly used for near-field mapping application in antenna measurements as well as in imaging applications. Although they can be used as a general sensor, they present limitations in the amount of information that can be obtained. The paper proposes a new configuration for MST probes that can be used for sensing applications, which consists in using a set of impedances (at least three different impedances) instead of the conventional two impedance loads. Additional sensitive loads, such as thermistors, can be added to the multi-load MST sensor, in order to remotely sense their variation and perform further sensing of parameters which could not always be sensed by conventional MST. The paper presents the formulation and approaches that can be used to exploit the sensing capabilities of such multi-loaded MST sensor, as well as experimental validations through the measurement of the temperature in the neighborhood of the sensor.
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paper_title: Physical Bounds and Optimal Currents on Antennas

paper_content:

Physical bounds on the directivity Q-factor quotient and optimal current distributions are determined for antennas of arbitrary shape and size using an optimization formulation. A variational approach offers closed form solutions for small antennas expressed in the polarizability of the antenna structure. Finite sized antennas are solved using Lagrangian parameters in a method of moments formulation. It is also shown that the considered stored electric energy can be negative for electrically large objects. This effect is mitigated by a Helmholtz decomposition of the current density. Moreover, it is shown that the optimal charge density for a small antenna can be generated by several current densities. Numerical examples for small and large antennas are used to illustrate the results. (Less)
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paper_title: A Novel Metal-Mountable Electrically Small Antenna for RFID Tag Applications With Practical Guidelines for the Antenna Design

paper_content:

A novel dual-layer electrically small radio-frequency-identification (RFID) tag antenna is proposed for metallic object applications. With a proximity-coupled feed method, two rotationally symmetric loaded via-patches are fed through an embedded dual-element planar inverted-F antenna (PIFA) array. With this configuration, the antenna volume is reduced to 0.08 λ×0.04 λ×0.007 λ while the measured antenna gain is 0.08 dBi at the frequency of 923 MHz. Studies demonstrate that the proposed antenna is a good candidate for ultra-high-frequency RFID tags to be mounted on metallic surfaces, especially in size-constrained scenarios. Meanwhile, a figure of merit, namely, NBG, is presented, with which a comparison among electrically small tag antennas is carried out. Finally, several guidelines are given out to facilitate the miniaturization of RFID tag antennas for metallic object applications.
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paper_title: Complete Link Budgets for Backscatter-Radio and RFID Systems

paper_content:

Backscatter radio - wireless communication by modulating signals scattered from a transponder (RF tag) - is fundamentally different from conventional radio because it involves two distinct links: the power-up link for powering passive RF tags, and the backscatter link for describing backscatter communication. Because of severe power constraints on the RF tag, a thorough knowledge of the backscatter channel is necessary to maximize backscatter-radio and radio-frequency identification (RFID) system performance. This article presents four link budgets that account for the major propagation mechanisms of the backscatter channel, along with a detailed discussion of each. Use of the link budgets is demonstrated by a practical UHF RFID portal example. The benefits of future 5.8 GHz multi-antenna backscatter-radio systems are shown. An intuitive analogy for understanding the antenna polarization of RF tag systems is presented.
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paper_title: Antenna Theory: Analysis and Design

paper_content:

The most-up-to-date resource available on antenna theory and design. Expanded coverage of design procedures and equations makes meeting ABET design requirements easy and prepares readers for authentic situations in industry. New coverage of microstrip antennas exposes readers to information vital to a wide variety of practical applications.Computer programs at end of each chapter and the accompanying disk assist in problem solving, design projects and data plotting.-- Includes updated material on moment methods, radar cross section, mutual impedances, aperture and horn antennas, and antenna measurements.-- Outstanding 3-dimensional illustrations help readers visualize the entire antenna radiation pattern.
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paper_title: High-impedance electromagnetic surfaces with a forbidden frequency band

paper_content:

A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.
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paper_title: Near-field probes using double and single negative media

paper_content:

Evanescent probe imaging is a powerful characterization technique with subwavelength resolution. In this paper, we present a theoretical and numerical study of the effect of using double negative (DNG) and single negative (SNG) metamaterials in evanescent probe imaging. A sensitivity definition is introduced for evanescent probes and it is shown using quantitative measures that the sensitivity can be increased using DNG material for a target in vacuum and for a buried target. A minimum DNG thickness is required to achieve an improvement in the sensitivity. For a buried target, there is a fundamental limitation on the maximum achievable sensitivity, in addition to a limitation due to the loss of DNG materials. SNG metamaterials have similar improvements over the sensitivity as the DNG materials but there are additional limitations due to the different transmission characteristics of SNG media. To validate the theoretical findings, numerical simulations are presented.
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paper_title: Utilising microstrip patch antenna strain sensors for structural health monitoring

paper_content:

In this article, the feasibility of using a circular microstrip patch antenna to measure strain and the effects of different materials on sensitivity of the patch antenna are investigated. Also, the effect of strain direction on the frequency shift is studied. The theoretical model shows a linear relationship between strain and the shift in the resonant frequency of the antenna in any material. Both finite element analysis (FEA) and experimental tests have been undertaken to corroborate the relationship between strain and frequency shift. In addition, a new antenna sensor based on a meandered microstrip patch antennas has been designed and tested to overcome the shortcomings of the circular patch. The meandered circular microstrip patch antenna exhibited a threefold increase in sensitivity and a fivefold reduction in its physical size, when compared to the simple circular patch. The ultimate intention of this work is to configure antennas for the detection of relatively small damage zones in structures and to do so wirelessly.
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paper_title: Passive Wireless Frequency Doubling Antenna Sensor for Strain and Crack Sensing

paper_content:

This paper presents the design, simulation, and validation experiments of a passive (battery-free) wireless frequency doubling antenna sensor for strain and crack sensing. Since the length of a patch antenna governs the antenna’s resonance frequency, a patch antenna bonded to a structural surface can be used to measure mechanical strain or crack propagation by interrogating resonance frequency shift due to antenna length change. In comparison with previous approaches such as radio frequency identification, the frequency doubling scheme is proposed as a new signal modulation approach for the antenna sensor. The proposed approach can easily distinguish backscattered passive sensor signal (at the doubled frequency $2{f}$ ::: ) from environmental electromagnetic reflections (at original reader interrogation frequency $f$ ::: ). To accurately estimate the performance of the frequency doubling antenna sensor, a multi-physics coupled simulation framework is proposed to aid the sensor design while considering both the mechanical and electromagnetic behaviors. Two commercial software packages, COMSOL and Advanced Design System (ADS), are combined to leverage the features from each other. The simulated performance of the frequency doubling antenna sensor is further validated by experiments. The results show that the sensor is capable of detecting small strain changes and the growth of a small crack.
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paper_title: Passive RFID Strain-Sensor Based on Meander-Line Antennas

paper_content:

The processing of backscattered signals coming from RFID tags is potentially useful to detect the physical state of the tagged object. It is here shown how to design a completely passive UHF RFID sensor for strain monitoring starting from a flexible meander-line dipole whose shape factor and feed section are engineered to achieve the desired sensing resolution and dynamic range. This class of devices is low-cost, promises sub-millimeter resolution and may found interesting applications in the Structural Health Monitoring of damaged structures and vehicles as well as during extreme and adverse events.
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paper_title: Implementation of a Dual-Interrogation-Mode Embroidered RFID-Enabled Strain Sensor

paper_content:

This letter studies a dual-interrogation-mode (hybrid chip-enabled/chipless) technique to detect an embroidered radio frequency identification (RFID)-enabled sensor. We have created a hybrid RFID strain sensor utilizing both chipped and chipless approaches. A comparison between the read-range extraction technique, which relies upon the detection of the threshold power that is required to activate an RFID IC, and a radar-cross-section (RCS)-based technique that does not require any protocol is presented. An embroidered RFID sensor with an electrical length that is directly linked to the applied strain is realized and interrogated using both techniques. The sensitivities for the chipless radar technique and for the chip-enabled read range extraction technique are 0.66% and 0.43% frequency shift, respectively, for 1% strain variation. Simulations and measurements validate the dual interrogation mode and provide the proof of concept that a chip-enabled RFID sensor tag can be detected accurately utilizing backscattering RCS measurements.
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paper_title: Epidermal Passive RFID Strain Sensor for Assisted Technologies

paper_content:

An epidermal passive wireless strain sensor using radio frequency identification (RFID) tags is presented. The tag is intended to detect eyebrow or neck skin stretch where paraplegic patients have the capability to tweak facial muscles. The tag is designed on a barium-titanate-loaded polydimethylsiloxane (PDMS) substrate and is assessed to demonstrate the strain gauge sensitivity and repeatability as a function of skin stretch.
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paper_title: Stretchable RFID for Wireless Strain Sensing With Silver Nano Ink

paper_content:

Flexible and stretchable inductor-capacitor (LC) resonator-based chipless radio frequency identification (RFID) tags have been fabricated by the direct stamping with silver nano ink. The tags are optimized based on the sympathetic oscillation of LC circuit at specifically designed resonant frequencies ranged from 1.12 to 1.7 GHz by adjusting dimensions of the inductor and capacitor in a tag. Pressure applied to the layer of silver nano ink during the stamping procedure helps densification of silver nanoparticles inside trenches of the stamp before heat-annealing of them. Transfer stamping process is simulated to demonstrate stress distribution across the layer of silver nanoparticles. Compaction of silver nanoparticles, in turn, positively affects mechanical strength of the final silver electrode and enables RFID strain sensors on polydimethylsiloxane to be stretchable up to 7%. By the stretchable RFID strain sensors, wireless strain sensing is demonstrated with a gauge factor of 0.51. Multiple encoded identifications with combination of double tags and stretching behavior of fabricated tags are also demonstrated. This stretchable RFID sensor is promising for biomedical applications such as real-time monitoring of motion detection.
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paper_title: Graphene-based transparent strain sensor

paper_content:

Transparent strain sensors based on graphene were fabricated in a form of rosette on a flexible plastic or stretchable rubber substrate by using reactive ion etching and stamping techniques. Their piezoresistive properties were investigated under a tensile strain up to 7.1%. We demonstrated this sensor on a transparent glove and measured magnitudes and directions of the principal strains on the glove induced by the motion of fingers.
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paper_title: Embedded wireless strain sensors based on printed RFID tag

paper_content:

Purpose – The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency identification (RFID) technology and it can be embedded into a variety of structures.Design/methodology/approach – Silver ink conductors and RFID tags were printed by the screen printing method on stretchable polyvinyl chloride and fabric substrates. The development of the strain‐sensitive RFID tag was based on the behavior of the selected antenna and substrate materials. Performance of the tags and the effect of mechanical strain on tag functioning were examined.Findings – The results showed that large displacements can be successfully measured wirelessly using a stretchable RFID tag as a strain‐sensitive structure. The behavior of the tag can be modified by selection of the material.Research limitations/implications – New tag designs, which are more sensitive to small levels of strain and which have a linear response will be the subje...
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paper_title: Passive wireless antenna sensor for strain and crack sensing—electromagnetic modeling, simulation, and testing

paper_content:

This research investigates a passive wireless antenna sensor designed for strain and crack sensing. When the antenna experiences deformation, the antenna shape changes, causing a shift in the electromagnetic resonance frequency of the antenna. A radio frequency identification (RFID) chip is adopted for antenna signal modulation, so that a wireless reader can easily distinguish the backscattered sensor signal from unwanted environmental reflections. The RFID chip captures its operating power from an interrogation electromagnetic wave emitted by the reader, which allows the antenna sensor to be passive (battery-free). This paper first reports the latest simulation results on radiation patterns, surface current density, and electromagnetic field distribution. The simulation results are followed with experimental results on the strain and crack sensing performance of the antenna sensor. Tensile tests show that the wireless antenna sensor can detect small strain changes lower than 20???, and can perform well at large strains higher than 10?000???. With a high-gain reader antenna, the wireless interrogation distance can be increased up to 2.1?m. Furthermore, an array of antenna sensors is capable of measuring the strain distribution in close proximity. During emulated crack and fatigue crack tests, the antenna sensor is able to detect the growth of a small crack.
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paper_title: Sensitivity Modeling of an RFID-Based Strain-Sensing Antenna With Dielectric Constant Change

paper_content:

An radiofrequency identification (RFID)-based folded patch antenna has been developed as a novel passive wire- less sensor to measure surface strain and crack, for the structural health monitoring of metallic structures. Up to 2.5 m of read range is achieved by a proof-of-concept prototype patch antenna sensor with a strain sensitivity around �760 Hz/μe ,w hich is equivalent to a normalized strain sensitivity of �0.74 ppm/μe. In this paper, we propose to consider the change of the substrate dielectric constant due to strain when modeling the antenna sensor. An enhanced strain sensitivity model is introduced for more accurately estimating the strain sensing performance of the hereby introduced smart skin antenna sensor. Laboratory experiments are carried out to quantify the dielectric constant change under strain. The measurement results are incorporated into a mechanics-electromagnetics coupled simulation model. Accuracy of the multi-physics coupled simulation is improved by integrating dielectric constant change in the model.
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paper_title: Detection and evaluation of the depth of surface cracks in conductive materials by using a loop antenna

paper_content:

A new method is developed for detection and evaluation of the depth of surface cracks in conductive materials. The main components of the measurement equipment are a conductive wire and a loop antenna, both of which are located as close as possible to the surface of the investigated material, while the antenna loop is perpendicular to the surface and parallel to the wire. Supplying of electrical potential with microwave frequency f and amplitude |s| to the wire results in spreading of induced current close beneath the surface of the material. The induced current redistributes in the vicinity of surface cracks, and some of the current paths flow along the crack walls. This leads to generation of a time-variable magnetic field mostly within the volume of the crack, which is detected by the loop antenna. A theoretical analysis is presented of the contributions of the different types of generated magnetic fields to the potential drop with amplitude |Us| measured by the antenna. The distribution of the ratio R(dB)=|U|/|Us| is measured for specimens of paramagnetic and ferromagnetic steel which contain three artificial cracks with depths of 0.5 mm, 1 mm, and 2 mm, and frequency f=300 MHz of the supplied electrical potential. It turns out that artificial cracks with a depth of d ≥0.5 mm, located at distances from x=3 mm to x=15 mm from the wire, can be detected. The largest sensitivity of crack detection is achieved for x∼4 mm when the long axis of a crack is perpendicular to the wire. The crack response of the measured ratio R is proportional to the crack depth when the loop of the antenna is located above or slightly outside an artificial crack, and at least 4 mm from the wire. This relation could be used for evaluation of the depth of real surface cracks. The notable decrement of the crack response outside the crack can indicate the location of the crack tips on the surface of the specimen. It is shown that a loop antenna with a diameter of 7 mm provides the largest crack response, as well as that the developed method can be applied to both paramagnetic and ferromagnetic materials. An example of the detection of a real crack by an antenna is reported for the first time.
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paper_title: Wireless Passive RFID Crack Width Sensor for Structural Health Monitoring

paper_content:

All mechanical structures are subjected to deformation and cracks, due to fatigue, stress, and/or environmental factors. It is, therefore, of uttermost importance to monitor the mechanical condition of critical structures, in order to prevent catastrophic failures, but also to minimize maintenance costs, i.e., avoid unnecessary inspections. A number of technologies and systems can be used for this purpose: among them, the ones proposing the use of wireless passive crackmeters have a strong impact potential, in terms of simplicity of installation and measurement and low cost. This paper, hence, shows a crack width wireless radio-frequency identification sensor, developed for applications on various materials (such as concrete and metal) and able to detect submillimeter deformations occurring on the object, on which it is placed. A design method based on high-sensitivity phase detection is shown.
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paper_title: Wireless Crack Monitoring by Stationary Phase Measurements from Coupled RFID Tags

paper_content:

Abstract—The possibility to wirelessly monitor the state and ::: the evolution of cracks is of increasing interest in emerging ::: Structural Health Monitoring Systems. A simple and effective measurement method considers the placement of two passive RFID antennas on top of the crack, so that the crack’s evolution will produce a change of the inter-antenna coupling and in turn of the phase of the backscattered field. An ad-hoc design technique, ::: based onto the coupled-mode physics, permits to maximize the sensor’s sensitivity avoiding, or at least mitigating, the read range reduction during the evolution of the displacement that is instead typical of amplitude-oriented RFID displacement sensors. The proposed idea is demonstrated by numerical and experimental ::: examples showing the possibility of sub-millimeter resolution with low-cost devices.
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paper_title: Towards chipless RFID-based sensing for pervasive surface crack detection

paper_content:

We present Surface Crack Antenna Reflectometric Sensing or SCARS: a chipless RFID sensor that enables pervasive, wireless surface crack detection in structural materials. We outline the sensor design and demonstrate how crack length and orientation can be related to the backscatter signal signature of the SCARS sensor. In doing so, design techniques that improve sensor sensitivity and signal fidelity are presented. Proof of concept is then demonstrated via numerical simulation and the implementation of a laboratory prototype. Finally, an envisioned pervasive health monitoring and data extraction strategy using these sensors is also discussed.
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paper_title: Detecting crack orientation using patch antenna sensors

paper_content:

Crack orientation is a very important parameter for structural integrity analysis. Even though many sensors have been developed to detect crack presence and length, very few sensors can detect crack orientation. Recently, we have demonstrated a patch antenna sensor that can detect crack propagation with sub-millimeter resolution. In this paper, the capability of the antenna sensors for crack orientation detection is studied. An antenna sensor with a rectangular antenna patch radiates at two fundamental modes. The effect of a ground-plane crack on these two resonant frequencies depends on its orientation. Hence, the crack orientations can be monitored by analyzing the crack-induced shifts of both antenna resonant frequencies. The principle of operation will be discussed first, followed by detailed descriptions on the numerical simulation, sensor fabrication, experimental procedure, results and analysis. Simulation as well as experimental results confirmed that the antenna sensor is capable of providing quantified information about the crack orientation.
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paper_title: RFID Tag Antenna-Based Sensing for Pervasive Surface Crack Detection

paper_content:

We introduce the concept of using an RFID tag's antenna to sense surface cracks. Our contribution is two fold. First, we present the design of an inductively coupled loop antenna that can be used as a crack detector. Second, we propose the development of a 2-D grid of tags to improve spatial coverage and discuss how it can be used to monitor typical crack patterns in civil infrastructure. We demonstrate that the technique works reliably over a read distance of 1 m and in different types of environments. Potential engineering extensions and future research directions are also discussed.
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paper_title: Antenna Q and Stored Energy Expressed in the Fields, Currents, and Input Impedance

paper_content:

Although the stored energy of an antenna is instrumental in the evaluation of antenna Q and the associated physical bounds, it is difficult to strictly define stored energy. Classically, the stored energy is either determined from the input impedance of the antenna or the electromagnetic fields around the antenna. The new energy expressions proposed by Vandenbosch express the stored energy in the current densities in the antenna structure. These expressions are equal to the stored energy defined from the difference between the energy density and the far field energy for many but not all cases. Here, the different approaches to determine the stored energy are compared for dipole, loop, inverted L-antennas, and bow-tie antennas. We use Brune synthesized circuit models to determine the stored energy from the input impedance. We also compare the results with differentiation of the input impedance and the obtained bandwidth. The results indicate that the stored energy in the fields, currents, and circuit models agree well for small antennas. For higher frequencies, the stored energy expressed in the currents agrees with the stored energy determined from Brune synthesized circuit models whereas the stored energy approximated by differentiation of input impedance gives a lower value for some cases. The corresponding results for the bandwidth suggest that the inverse proportionality between the fractional bandwidth and Q-factor depends on the threshold level of the reflection coefficient.
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paper_title: Identification and characterisation of steel corrosion using passive high frequency RFID sensors

paper_content:

Abstract High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.
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paper_title: UHF RFID Tag Antenna-Based Sensing for Corrosion Detection & Characterization Using Principal Component Analysis

paper_content:

The authors identified errors in [1, eq. (1)] , which states \begin{align*} P_{R\leftarrow T}[\Psi (\theta,\phi)]=\frac {1}{4\pi }& \left({\frac {\lambda _{0}}{4\pi d}}\right)^{2} \\ & \times \,P_{in}G_{R}^{2}(\theta,\phi)\eta ^{2}_{p}RCS[\Psi (\theta,\phi)].\end{align*} Knowing that the dimensions of $P_{R\leftarrow T}$ function, $\lambda _{0}$ , $ P_{\mathrm {in}}, ~d$ , and RCS function are watt, meter, watt, meter, and square meter, respectively, also $\eta _{p}$ and $G_{R}$ functions do not have any dimension—it is seen that both sides of [1, eq. (1)] are not in the same dimension. Looking at another reference, [2, eq. (3)] , it is seen that the mathematical power of $d$ is equal to 2 \begin{align*} P_{R\leftarrow T}[\Psi (\theta,\phi)]=\frac {1}{4\pi }& \left({\frac {\lambda _{0}}{4\pi d^{2}}}\right)^{2} \\[-1pt]&\times \,P_{in}G_{R}^{2}(\theta,\phi)\eta ^{2}_{p}RCS[\Psi (\theta,\phi)]\end{align*} and the mathematical power of $d$ is not 1 as given in [1, eq. (1)] . However, the rest of the paper and analysis given in [1] are still correct.
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paper_title: Constrained-Design of Passive UHF RFID Sensor Antennas

paper_content:

Passive UHF RFID tags may be used, beside labeling, to remotely observe the physical/chemical change of the tagged object, through modulation of their impedance and gain, thus acting as sensor antennas. The design of this new class of devices can be mastered by fully understanding the relationship between communication and sensing with the purpose to balance the maximization of the dynamic range of the response with the stability of the read distance. A new kind of communication/sensing nomogram permits to display both behaviors in a unitary way and to predict their physical limits, as well as to formalize a multi-parameter general-purpose optimization methodology. The procedure is demonstrated by application to the design of a strain-gauge tag and of a level-detector wireless sensor.
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paper_title: Stress corrosion cracking detection using non-contact ultrasonic techniques

paper_content:

In this work a method is presented for detecting and locating stress corrosion cracking (SCC) in stainless steel pipe samples. The method combines laser generation and either laser or electromagnetic acoustic transducer (EMAT) detection, scanning the generation point across the sample surface. Using laser-generated ultrasonic waves that interact with the cracks, and performing time–frequency analysis techniques to examine changes in the generated wavemodes, surface plots that clearly resolve the spatial extent and geometric alignment of the cracks are created and presented here. The method is demonstrated using components removed from service after exhibiting SCC.
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paper_title: Electromagnetic nondestructive testing of rust region in steel

paper_content:

The inspection of rust region in steel is important in the petrochemical plant, etc. The B--H curve and the conductivity of rust region in steel are different from those of the normal steel. Then, the detection of rust region in steel is possible by detecting the difference of those electromagnetic properties using an inspection method. In this paper, those electromagnetic properties of the rust region in steel are measured utilizing three-dimensional (3-D) axis-symmetric finite-element method (FEM) and experiment. The electromagnetic inspection technique of the rust region is examined using 3-D edge-based hexahedral nonlinear FEM. The possibility of detecting the rust region using the proposed inspection system is illustrated. In addition, the experimental verification is also carried out.
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paper_title: Development of Wireless and Passive Corrosion Sensors for Material Degradation Monitoring in Coastal Zones and Immersed Environment

paper_content:

Wireless and fully energetically passive corrosion sensors inspired from the chipless Radio-Frequency IDentification (RFID) technology are presented for the monitoring of degradation of infrastructures located in coastal zones and underwater environments. The device consists of a reader and a remote passive sensor. This study presents two radio-frequency (RF) corrosion-sensitive resonators that can be integrated in such a device. The first is sensitive to a loss of metal due to its degradation, and the second is sensitive to the corrosion potential of metals, with respect to a reference electrode. The RF characterization of these two resonators demonstrates unambiguously the sensitivity of the method to corrosion of metal, passivation of steel as well as degradation of organic coatings. Then, their integration in a demonstrator including antennas is considered. The main parameters that influence the RF wave propagation and thus the reading distance are discussed. Following the presented results, the proposed method is considered as a reliable and versatile tool which should be able to be deployed in immersed, tidal, and splash zones, for example, for offshore facilities monitoring.
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paper_title: Multivariable passive RFID vapor sensors: roll-to-roll fabrication on a flexible substrate

paper_content:

We demonstrate roll-to-roll (R2R) fabrication of highly selective, battery-free radio frequency identification (RFID) sensors on a flexible polyethylene terephthalate (PET) polymeric substrate. Selectivity of our developed RFID sensors is provided by measurements of their resonance impedance spectra, followed by the multivariate analysis of spectral features, and correlation of these spectral features to the concentrations of vapors of interest. The multivariate analysis of spectral features also provides the ability for the rejection of ambient interferences. As a demonstration of our R2R fabrication process, we employed polyetherurethane (PEUT) as a “classic” sensing material, extruded this sensing material as 25, 75, and 125-μm thick films, and thermally laminated the films onto RFID inlays, rapidly producing approximately 5000 vapor sensors. We further tested these RFID vapor sensors for their response selectivity toward several model vapors such as toluene, acetone, and ethanol as well as water vapor as an abundant interferent. Our RFID sensing concept features 16-bit resolution provided by the sensor reader, granting a highly desired independence from costly proprietary RFID memory chips with a low-resolution analog input. Future steps are being planned for field-testing of these sensors in numerous conditions.
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paper_title: Recent Progress in Materials and Devices toward Printable and Flexible Sensors.

paper_content:

Printable electronics present a new era of wearable electronic technologies. Detailed technologies consisting of novel ink semiconductor materials, flexible substrates, and unique processing methods can be integrated to create flexible sensors. To detect various stimuli of the human body, as well as specific environments, unique electronic devices formed by “ink-based semiconductors” onto flexible and/or stretchable substrates have become a major research trend in recent years. Materials such as inorganic, organic, and hybrid semiconductors with various structures (i.e., 1D, 2D and 3D) with printing capabilities have been considered for bio and medical applications. In this review, we report recent progress in materials and devices for future wearable sensor technologies.
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paper_title: Printable electronics: flexibility for the future

paper_content:

Printed electronics is an emerging technology with huge potential. Market studies predict a multi-billion dollar market size within less than 5 years. Due to its compatibility with flexible substrates and low-cost fabrication, printed electronics is able to bring electronic functionality to markets unfit for rigid and expensive silicon electronics. Key to its success are innovative printing technologies and high-quality material systems, engineered for specific device applications. Printed electronics is a complex multidisciplinary research area, with still a number of fundamental problems to be solved before the technology can grow to its full potential. Evonik Industries is involved in the development of printed electronics through its unique science-to-business concept. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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paper_title: Conductive Nanomaterials for Printed Electronics

paper_content:

This is a review on recent developments in the field of conductive nanomaterials and their application in printed electronics, with particular emphasis on inkjet printing of ink formulations based on metal nanoparticles, carbon nanotubes, and graphene sheets. The review describes the basic properties of conductive nanomaterials suitable for printed electronics (metal nanoparticles, carbon nanotubes, and graphene), their stabilization in dispersions, formulations of conductive inks, and obtaining conductive patterns by using various sintering methods. Applications of conductive nanomaterials for electronic devices (transparent electrodes, metallization of solar cells, RFID antennas, TFTs, and light emitting devices) are also briefly reviewed.
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paper_title: Current Trends on Medical and Pharmaceutical Applications of Inkjet Printing Technology

paper_content:

Inkjet printing is an attractive material deposition and patterning technology that has received significant attention in the recent years. It has been exploited for novel applications including high throughput screening, pharmaceutical formulations, medical devices and implants. Moreover, inkjet printing has been implemented in cutting–edge 3D–printing healthcare areas such as tissue engineering and regenerative medicine. Recent inkjet advances enabled 3D printing of artificial cartilage and skin, or cell constructs for transplantation therapies. In the coming years inkjet printing is anticipated to revolutionize personalized medicine and push the innovation portfolio by offering new paths in patient - specific treatments.
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paper_title: Inkjet printing of conductive materials: a review

paper_content:

Purpose – The purpose of this paper is to present an exhaustive review of research studies and activities in the inkjet printing of conductive materials.Design/methodology/approach – This paper gives a detailed literature survey of research carried out in inkjet printing of conductive materials.Findings – This article explains the inkjet printing process and the various types of conductive inks. It then examines the various factors that affect the quality of inkjet printed interconnects such as printing parameters, materials and substrate treatments. Methods of characterising both the inkjet printing process and the electrical properties of printed conductive materials are also presented. Finally relevant applications of this technology are described.Originality/value – Inkjet printing is currently one of the cheapest direct write techniques for manufacturing. The use of this technique in electronic manufacturing, where interconnects and other conductive features are required is an area of increasing rele...
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paper_title: Flexible and printable sensors

paper_content:

Technical systems have become more and more complicated in recent decades and require more detailed control of their operation. This primarily relates to the safety, reliability, and efficiency of devices used in medicine, electronics, and other fields. Furthermore, with the development of the conception of the Internet of Things, a lot of attention has been paid to the interaction between humans and high-tech equipment and personal devices. Highly detailed information on the operation of a device or complex system can only be given by a large number of small sensors of different types. As we know, the most sophisticated sensory machine is a living organism. Formerly this thought led to the idea of creating a multisensory platform which would mimic the human skin capabilities. Electronic skin can simultaneously monitor many parameters such as temperature, strain, pressure, magnetic field, and intensity of light; it is also possible to emulate tactile and chemical perception. Nanotechnology serves as a tool for the creation of new sensor materials, and the development of printing technologies supports engineering low-cost, thin, lightweight, transparent, easily deformable, and biocompatible (even transient) electronic devices for monitoring external factors and processing information. In this review we discuss the state-of-the-art and prospects of new materials and technologies towards emerging flexible sensors.
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paper_title: Development of a Low Cost Printable Chipless RFID Humidity Sensor

paper_content:

A novel low-cost chipless radio frequency identification tag sensor is presented. The tag sensor provides identification data as well as monitors relative humidity (RH) of tagged objects. The tag sensor is made of passive microwave circuit that uses humidity sensitive polymer material for RH sensing. The aim of this paper is to investigate RF sensing properties of moisture absorbing polymer polyvinyl alcohol at microwave frequency. In addition, frequency shifting technique is used to encode data bits for high data capacity. The overall size of the proposed tag sensor is 15 mm × 6.8 mm and has 6 bit data capacity for ID generation and single bit for humidity sensing. Results presented here show ~ 607 MHz frequency deviation for 50% RH increase. The tag sensor has potential to be printed on flexible laminates such as plastic and paper for ultra-low cost item level tagging and ubiquitous sensing.
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paper_title: Graphene Nanoflakes Printed Flexible Meandered-Line Dipole Antenna on Paper Substrate for Low-Cost RFID and Sensing Applications

paper_content:

In this letter, a graphene nanoflakes printed antenna is presented. Graphene nanoflakes conductive ink has been screen-printed on paper substrate and compressed to achieve the conductivity of $\text{0.43} \times {\text{10}^{\text{5}}} \hbox{\,S/m}$ . Low-profile meandered-line dipole antenna has been fabricated as a proof of concept due to its electrically small size and simple structure. The maximum gain is measured to be ${-}\hbox{4 dBi}$ , the ${-} \hbox{10-dB}$ bandwidth ranges from 984 to 1052 MHz (6.67%), and the radiation pattern is verified as being typical radiation patterns of a dipole-type antenna. The radiation efficiency is 32%. The measurement results reveal that graphene nanoflakes printed antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns for mid- and short-range RFID, and sensing applications. Furthermore, screen-printing technique employed in this work is of extremely low cost and capable of producing antennas in mass production.
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paper_title: Conductive Inkjet-Printed Antennas on Flexible Low-Cost Paper-Based Substrates for RFID and WSN Applications

paper_content:

In this paper, a review of the authors' work on inkjet-printed flexible antennas, fabricated on paper substrates, is given. This is presented as a system-level solution for ultra-low-cost mass production of UHF radio-frequency identification (RFID) tags and wireless sensor nodes (WSN), in an approach that could be easily extended to other microwave and wireless applications. First, we discuss the benefits of using paper as a substrate for high-frequency applications, reporting its very good electrical/dielectric performance up to at least 1 GHz. The RF characteristics of the paper-based substrate are studied by using a microstrip-ring resonator, in order to characterize the dielectric properties (dielectric constant and loss tangent). We then give details about the inkjet-printing technology, including the characterization of the conductive ink, which consists of nano-silver particles. We highlight the importance of this technology as a fast and simple fabrication technique, especially on flexible organic (e.g., LCP) or paper-based substrates. A compact inkjet-printed UHF ldquopassive RFIDrdquo antenna, using the classic T-match approach and designed to match the IC's complex impedance, is presented as a demonstration prototype for this technology. In addition, we briefly touch upon the state-of-the-art area of fully-integrated wireless sensor modules on paper. We show the first-ever two-dimensional sensor integration with an RFID tag module on paper, as well as the possibility of a three-dimensional multilayer paper-based RF/microwave structure.
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paper_title: Flexible Tactile Sensors Using Screen-Printed P(VDF-TrFE) and MWCNT/PDMS Composites

paper_content:

This paper presents and compares two different types of screen-printed flexible and conformable pressure sensors arrays. In both variants, the flexible pressure sensors are in the form of segmental arrays of parallel plate structure—sandwiching the piezoelectric polymer polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] between two printed metal layers of silver (Ag) in one case and the piezoresistive [multiwall carbon nanotube (MWCNT) mixed with poly(dimethylsiloxane (PDMS)] layer in the other. Each sensor module consists of $4 \times 4$ sensors array with 1-mm $\times 1$ -mm sensitive area of each sensor. The screen-printed piezoelectric sensors array exploits the change in polarization level of P(VDF-TrFE) to detect dynamic tactile parameter such as contact force. Similarly, the piezoresistive sensors array exploits the change in resistance of the bulk printed layer of MWCNT/PDMS composite. The two variants are compared on the basis of fabrication by printing on plastic substrate, ease of processing and handling of the materials, compatibility of the dissimilar materials in multilayers structure, adhesion, and finally according to the response to the normal compressive forces. The foldable pressure sensors arrays are completely realized using screen-printing technology and are targeted toward realizing low-cost electronic skin.
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paper_title: Epidermal Passive RFID Strain Sensor for Assisted Technologies

paper_content:

An epidermal passive wireless strain sensor using radio frequency identification (RFID) tags is presented. The tag is intended to detect eyebrow or neck skin stretch where paraplegic patients have the capability to tweak facial muscles. The tag is designed on a barium-titanate-loaded polydimethylsiloxane (PDMS) substrate and is assessed to demonstrate the strain gauge sensitivity and repeatability as a function of skin stretch.
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paper_title: Progress Towards the First Wireless Sensor Networks Consisting of Inkjet-Printed, Paper-Based RFID-Enabled Sensor Tags

paper_content:

This paper discusses the evolution towards the first integrated radio-frequency identification (RFID)-enabled wireless sensor network infrastructure using ultra-high frequency/radio frequency (UHF/RF) RFID-enabled sensor nodes and inkjet-printed electronics technologies on flexible and paper substrates for the first time ever. The first sections highlight the unique capabilities of inkjet printed electronics as well as the benefits of using paper as the ultra-low-cost, conformal and environmentally friendly substrate for the mass-scale ubiquitous implementation of the first RFID-enabled wireless sensing applications. Various inkjet-printed antenna configurations are presented for enhanced-range compact RFID-enabled sensing platforms in “rugged” environments up to 7 GHz, followed by the discussion of their 2-D integration with integrated circuit (IC) and sensors on paper. This integration is extended to a power-scavenging “smart-shoe” batteryless integrated RFID module on paper that could be used for autonomous wearable sensing applications with enhanced range. The paper concludes discussing the details for establishing for the first time an asynchronous wireless link between the aforementioned RFID-tags and a widely used commercial wireless sensor network (WSN) mote using a simplified protocol; a paramount step that could potentially create ubiquitous ultra-low-cost sensor networks and large-scale RFID implementations eliminating the need of expensive RFID reader infrastructure and linking RFIDs to the mature level of WSNs.
---
paper_title: Surface analysis of polymeric substrates used for inkjet printing technology

paper_content:

Purpose – This paper aims to find an optimal surface treatment of commonly used polymeric substrates for achieve the high adhesion of printed structures. For this reason, the investigation of substrates surfaces from different perspectives is presented in this paper. Design/methodology/approach – The contact angle measurements as well as the roughness measurements were realised for the analysis of surface properties of investigated substrates. The impact of applied chemical agents for surface treatment onto the wettability is analysed for polyimide, polyethylene terephthalate and polyethylene naphthalene substrates. Findings – The results prove the correlation among wettability, surface energy and work of adhesion with respect to the theoretical background. The surface treatment of polymeric substrates by chemical agents, such as acetone, toluene, ethanol, isopropyl and fluor silane polymer, has a significant impact onto the wettability of substrates which affects the final deposition process of nanoinks....
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paper_title: Silver nanoparticles ink synthesis for conductive patterns fabrication using inkjet printing technology

paper_content:

In this paper we present silver nanoparticles ink synthesis targeting conductive patterns for micro fabricated devices by inkjet printing technology. The well dispersed nanoparticles ink was composed of silver colloid with an average particle diameter less than 10 nm. These nanoparticles were protected by a capping layer of poly(N-vinylpyrrolidone) (PVP) even at silver concentration of 20 wt%. Stable aqueous inks were formulated by using a combination of solvent and co-solvents and under vigorous stirring. Various factors affecting the adhesion between the ink and the substrate were investigated, such as solvent and co-solvent content. The ink containing 20 wt% silver has a viscosity of about 9.5 cP and a surface tension of 32 to 36 mN m−1 at room temperature, meeting inkjet printer requirements. The ink stored under ambient conditions was stable against aggregation for more than one month. Silver nanoparticles patterns have been successfully printed on various substrates.
---
paper_title: Fabrication and Characterization of Graphene Antenna for Low-Cost and Environmentally Friendly RFID Tags

paper_content:

We present the fabrication and testing of graphene-based dipole antennas on cardboard, which is a promising low-cost, recyclable, and flexible substrate for future wireless electronics. The letter presents the details of the manufacturing, as well as results from the measurements and simulations. The measured sheet resistance of graphene antenna is 1.9 $~\Omega /{\hbox{sq}}$ . Overall, a graphene-based planar dipole antenna with the length of 143 mm achieved the measured total efficiency of 40% and the realized gain of $ - \hbox{2.18 dBi}$ at 889 MHz. Moreover, a passive ultra-high-frequency radio-frequency tag based on a graphene dipole antenna on cardboard achieved the attainable read range of more than 5 m at 950 MHz.
---
paper_title: Technologies for Printing Sensors and Electronics Over Large Flexible Substrates: A Review

paper_content:

Printing sensors and electronics over flexible substrates are an area of significant interest due to low-cost fabrication and possibility of obtaining multifunctional electronics over large areas. Over the years, a number of printing technologies have been developed to pattern a wide range of electronic materials on diverse substrates. As further expansion of printed technologies is expected in future for sensors and electronics, it is opportune to review the common features, the complementarities, and the challenges associated with various printing technologies. This paper presents a comprehensive review of various printing technologies, commonly used substrates and electronic materials. Various solution/dry printing and contact/noncontact printing technologies have been assessed on the basis of technological, materials, and process-related developments in the field. Critical challenges in various printing techniques and potential research directions have been highlighted. Possibilities of merging various printing methodologies have been explored to extend the lab developed standalone systems to high-speed roll-to-roll production lines for system level integration.
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paper_title: Stretchable RFID for Wireless Strain Sensing With Silver Nano Ink

paper_content:

Flexible and stretchable inductor-capacitor (LC) resonator-based chipless radio frequency identification (RFID) tags have been fabricated by the direct stamping with silver nano ink. The tags are optimized based on the sympathetic oscillation of LC circuit at specifically designed resonant frequencies ranged from 1.12 to 1.7 GHz by adjusting dimensions of the inductor and capacitor in a tag. Pressure applied to the layer of silver nano ink during the stamping procedure helps densification of silver nanoparticles inside trenches of the stamp before heat-annealing of them. Transfer stamping process is simulated to demonstrate stress distribution across the layer of silver nanoparticles. Compaction of silver nanoparticles, in turn, positively affects mechanical strength of the final silver electrode and enables RFID strain sensors on polydimethylsiloxane to be stretchable up to 7%. By the stretchable RFID strain sensors, wireless strain sensing is demonstrated with a gauge factor of 0.51. Multiple encoded identifications with combination of double tags and stretching behavior of fabricated tags are also demonstrated. This stretchable RFID sensor is promising for biomedical applications such as real-time monitoring of motion detection.
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paper_title: A review of non-contact micro- and nano-printing technologies

paper_content:

Printing technologies have undergone signficant development because they are an enabler in science and engineering research; they also have significant practical applications in manufacturing. Micro- and nano-printing techniques have found a number of applications in electronics, biotechnology, and material synthesis/patterning. In this review, we look at the important printing methods, including high precision traditional printing methods as well as recently emerging techniques. We also discuss the materials that are printable by these technologies, the challenges for future development, and the applications of micro- and nano-printing.
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paper_title: Electrical and mechanical properties of RFID chip joints assembled on flexible substrates

paper_content:

Purpose – The purpose of this paper is to examine electrical and mechanical properties of radio frequency identification (RFID) chip joints assembled on a flexible substrate and made from isotropic conductive adhesives (ICAs) reinforced with graphene nanoplatelets (GPNs) or graphite nanofibers (GFNs). Design/methodology/approach – The ICAs reinforced with GPNs or GFNs were prepared and screen printed on a test pattern to investigate resistance and thickness of these adhesive layers. Differential Scanning Calorimetry (DSC) was performed to assess a curing behaviour of the prepared ICAs. Then, RFID chips were mounted with the prepared ICAs to the pattern of silver tracks prepared on foil. Shear test was carried out to evaluate mechanical durability of the created chip joints, and resistance measurements were carried out to evaluate electrical properties of the tested ICAs. Findings – The 0.5 per cent (by weight) addition of GFNs or GPNs to the ICA improved shear force values of the assembled RFID chip joint...
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paper_title: RFID System Based on Fully Printable Chipless Tag for Paper-/Plastic-ltem Tagging

paper_content:

An RFID system, utilizing a chipless RFID tag on a 90 μm thin Taconic TF290 laminate, is presented. The chipless tag consists of two cross-polarized ultra-wideband antennas and a multi-resonating circuit. The data encoding is performed in the multi-resonating circuit, which is composed of multiple stop-band spiral resonators. The chipless tag encodes data into the spectral signature in both the magnitude and phase of the spectrum. The design and operation of two prototype RFID readers is also presented. The RFID readers operate between 1.9 GHz to 2.5 GHz and 5 GHz to 10.7 GHz, and can successfully detect a chipless tag at close range. The tag design can be easily transferred to plastic and paper, making it suitable for mass deployment for low-cost items. It has the potential to replace trillions of barcodes printed each year. The RFID reader is suitable for mounting over conveyor-belt systems.
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paper_title: RFID Tag and RF Structures on a Paper Substrate Using Inkjet-Printing Technology

paper_content:

In this paper, inkjet-printed UHF and microwave circuits fabricated on paper substrates are investigated for the first time as an approach that aims for a system-level solution for fast and ultra-low-cost mass production. First, the RF characteristics of the paper substrate are studied by using the microstrip ring resonator in order to characterize the relative permittivity (epsivr) and loss tangent (tan delta) of the substrate at the UHF band for the first time reported. A UHF RFID tag module is then developed with the inkjet-printing technology, proving this approach could function as an enabling technology for much simpler and faster fabrication on/in paper. Simulation and well-agreed measurement results, which show very good agreement, verify a good performance of the tag module. In addition, the possibility of multilayer RF structures on a paper substrate is explored, and a multilayer patch resonator bandpass filter demonstrates the feasibility of ultra-low-cost 3-D paper-on-paper RF/wireless structures.
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paper_title: Graphene Oxide-Assisted Liquid Phase Exfoliation of Graphite into Graphene for Highly Conductive Film and Electromechanical Sensors.

paper_content:

Here, we report a new method to prepare graphene from graphite by the liquid phase exfoliation process with sonication using graphene oxide (GO) as a dispersant. It was found that GO nanosheets act a as surfactant to the mediated exfoliation of graphite into a GO-adsorbed graphene complex in the aqueous solution, from which graphene was separated by an additional process. The preparation of isolated graphene from a single to a few layers is routinely achieved with an exfoliation yield of up to higher than 40% from the initial graphite material. The prepared graphene sheets showed a high quality (C/O ∼ 21.5), low defect (ID/IG ∼ 0.12), and high conductivity (6.2 × 10(4) S/m). Moreover, the large lateral size ranging from 5 to 10 μm of graphene, which is believed to be due to the shielding effect of GO avoiding damage under ultrasonic jets and cavitation formed by the sonication process. The thin graphene film prepared by the spray-coating technique showed a sheet resistance of 668 Ω/sq with a transmittance of 80% at 550 nm after annealing at 350 °C for 3 h. The transparent electrode was even greater with the resistance only 66.02 Ω when graphene is deposited on an interdigitated electrode (1 mm gap). Finally, a flexible sensor based on a graphene spray-coating polydimethylsiloxane (PDMS) is demonstrated showing excellent performance working under human touch pressure (<10 kPa). The graphene prepared by this method has some distinct properties showing it as a promising material for applications in electronics including thin film coatings, transparent electrodes, wearable electronics, human monitoring sensors, and RFID tags.
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paper_title: A Novel Enhanced-Performance Flexible RFID-Enabled Embroidered Wireless Integrated Module for Sensing Applications

paper_content:

A novel wireless embroidered integrated platform for radio frequency identification (RFID)-enabled strain sensing that takes advantage of the nonlinear behavior of the RFID chip impedance as a function of the incident power is introduced. Due to the nonlinearity of the chip impedance as a function of the power, a large variation of chip impedance value and thus a large difference of radar cross section values for appropriately chosen power levels are achieved. Taking advantage of this idea, the sensing parameter is detected by interrogation of the sensor tag using two distinct transmitting power levels and calculating the difference of backscattered response. As a proof of concept, we applied the proposed method for the detection of an embroidered RFID-enabled strain sensor that is fabricated using electrotextiles in order to observe the variations of the magnitude and the corresponding strain levels. The proposed model for the chip impedance helps in predicting the RFID chip impedance variation for different strain conditions, an extremely important issue for RF/RFID modules and packages operating over a wide power dynamic range as well as enabling the accurate estimation of the maximum range of the RFID-enabled sensing modules for the maximum allowable power levels.
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paper_title: Precision and Accuracy in UHF-RFID Power Measurements for Passive Sensing

paper_content:

In spite of analog radio frequency identification (RFID) sensors are gaining increasing attention from academic and industrial domains, their true applicability in the real world is still in question, since it is not clear whether and in which conditions the variation of the measured signals related to the sensing activity may be distinguished from the measurement uncertainties. The RFID platform for analog sensing, namely, with no dedicated sensing electronics, is here characterized in term of precision and accuracy with reference to the arrangement and the reproducibility of the setup. Numerical analysis and laboratory experimentations demonstrated that the precision of power metrics measurement is twice the resolution of low-cost readers and that the uncertainty on the distance and the alignment may play a major role on the data accuracy. The environment-independent indicator, such as the analog identifier, revealed once again to be a very stable and robust metric. In overall, the obtained results suggest that analog RFID devices can be used as indicative sensing platform to identify a few levels of the phenomenon under observation. The sensing granularity can be improved using low-power ICs, while classification algorithms could be applied to increase the robustness of the detection.
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paper_title: Identification and characterisation of steel corrosion using passive high frequency RFID sensors

paper_content:

Abstract High frequency RFID sensors are attractive in diverse applications where sensor performance is required at a low cost and dimension restriction. An approach adapting commercial passive 13.56 MHz RFID tags has been developed for sensing corrosion stage. This investigation includes balance of sensing and positioning of RFID sensors for corrosion detection by analysing real and imaginary parts of the complex impedance. With passive HF RFID sensors, real part and imaginary part of complex impedance have been extracted from the reader coil with VNA (vector network analyser) and delivering a unique capability for corrosion sensing with different atmospheric exposure time steel samples (1 month, 6 months, 10 months and 12 months). With different positioning (5–25 mm), features extraction based on the complex impedance with PCA (principal component analysis) has been designed for position-independent corrosion evaluation.
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paper_title: Wireless Passive RFID Crack Width Sensor for Structural Health Monitoring

paper_content:

All mechanical structures are subjected to deformation and cracks, due to fatigue, stress, and/or environmental factors. It is, therefore, of uttermost importance to monitor the mechanical condition of critical structures, in order to prevent catastrophic failures, but also to minimize maintenance costs, i.e., avoid unnecessary inspections. A number of technologies and systems can be used for this purpose: among them, the ones proposing the use of wireless passive crackmeters have a strong impact potential, in terms of simplicity of installation and measurement and low cost. This paper, hence, shows a crack width wireless radio-frequency identification sensor, developed for applications on various materials (such as concrete and metal) and able to detect submillimeter deformations occurring on the object, on which it is placed. A design method based on high-sensitivity phase detection is shown.
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paper_title: Simple Test and Modeling of RFID Tag Backscatter

paper_content:

We consider here worst-case analysis of backscatter from passive radio frequency identification (RFID) tags. The basis is a figure of merit “B” to relate link power at reader ports to tag circuit parameters. A minimum bound for received monostatic backscatter can be determined by inspection from measured B. The bound is general for narrowband signals in any causal linear propagation. For an assembled tag, this minimum varies only with reader transmit power, tag antenna tuning, and chip power sensitivity of different commands. To validate this model, we propose a backscatter calibration device to enable measurements with estimated 0.5 dB uncertainty. We then demonstrate how the minimum bound can inform reader sensitivity specification to help ensure reliable inventory performance.
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paper_title: Internet of Things in Industries: A Survey

paper_content:

Internet of Things (IoT) has provided a promising opportunity to build powerful industrial systems and applications by leveraging the growing ubiquity of radio-frequency identification (RFID), and wireless, mobile, and sensor devices. A wide range of industrial IoT applications have been developed and deployed in recent years. In an effort to understand the development of IoT in industries, this paper reviews the current research of IoT, key enabling technologies, major IoT applications in industries, and identifies research trends and challenges. A main contribution of this review paper is that it summarizes the current state-of-the-art IoT in industries systematically.
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paper_title: Uncertainty and applicability of rfid power measurements for passive sensing

paper_content:

Although RFID sensors are gaining increasing attention from Academic and Industrial world, their true applicability is still in question. The aim of the work is to characterize the RFID sensing platform in term of repeatability and reproducibility, such to answer the question whether and in which condition it is possible to distinguish the variation of the measured signals due to the sensing activity from the measurement uncertainties. The analysis presents theoretical and experimental contributions.
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paper_title: Coherent detection and channel coding for bistatic scatter radio sensor networking

paper_content:

With low monetary cost and minimal energy consumption, communications by means of reflection and scatter radio have emerged as key enabler for low-cost, large-scale and dense ubiquitous wireless sensor network applications. This work maximizes scatter radio communication range by (a) proposing a novel coherent receiver of frequency-shift keying (FSK) modulation for the bistatic scatter radio channel (i.e., carrier emitter and receiver are dislocated) and (b) employing specific short block-length cyclic error-correcting codes. Despite the presence of three unknown channel links due to the bistatic setup and multiple unknown scatter radio-related parameters, the proposed receiver vastly improves BER performance compared to state-of-the-art bistatic scatter radio receivers. Experimental corroborating results are offered, with a commodity software-defined radio (SDR) reader, a custom scatter radio tag and omnidirectional antennas. Tag-to-reader ranges up to 150 meters are reported with as little as 20 milliWatt transmission power, offering range extension of approximately 10 additional meters compared to state-of-the-art bistatic receivers.
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paper_title: Constrained Pole-Zero Synthesis of Phase-Oriented RFID Sensor Antennas

paper_content:

Passive sensing by means of radiofrequency identification has been extensively explored for various applications, such as gas detection, temperature change, and deformation. The sensing indicator is generally based on the amplitude and phase of the backscattered field. However, a degradation of the communication performance must be usually accepted for achieving the sensing capability. This work introduces a design method suitable for phase-based RFID sensors that permits to shape the phase response while preserving the impedance matching between the antenna and the microchip. The RFID sensor is modeled as a two-ports scatterer comprising a lumped sensor at one of the ports and an RFID chip at the other port. A pole-zero representation of the electromagnetic interaction between the reader and the RFID sensor allows to introduce a constrained design of the antenna with a full control on the sensor dynamic range and on the communication performance. The proposed method is numerically and experimentally validated by means of a pair of strongly coupled dipoles connected to a voltage-controlled varactor emulating a dynamic sensor response.
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paper_title: Determination of measurement uncertainties applied to the RCS and the differential RCS of UHF passive RFID tags

paper_content:

Measurement methodology and theoretical equations to RCS and ΔRCS determination are recalled and the measurement uncertainties are evaluated in this paper. Even if measurement uncertainties are generally not required for RFID, it is important to understand and to be able to determine the measurement uncertainty. Currently, manufacturers and testing laboratories present some results of RFID measurements but never show the associated uncertainty. Yet, seeing the values of the uncertainties, it is clear that they are not negligible.
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paper_title: Hybrid analog-digital backscatter: A new approach for battery-free sensing

paper_content:

After comparing the properties of analog backscatter and digital backscatter, we propose that a combination of the two can provide a solution for high data rate battery free wireless sensing that is superior to either approach on its own. We present a hybrid analog-digital backscatter platform that uses digital backscatter for addressability and control but switches into analog backscatter mode for high data rate transmission of sensor data. Using hybrid backscatter, we report the first digitally addressable real-time battery free wireless microphone. We develop the hybrid backscatter platform by integrating an electret microphone and RF switch with a digital RFID platform (WISP). The hybrid WISP operates by default in digital mode, transmitting and receiving digital data using the EPC Gen 2 RFID protocol but switching into analog mode to backscatter audio sensor data when activated by Gen 2 READ command. The data is recovered using a USRP-based Software Defined RFID reader. We report an operating range of 7.4 meters for the analog backscatter microphone and 2.7 meters for hybrid microphone with 26.7 dBm output power USRP-based RFID reader.
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paper_title: Low frequency (LF) RFID sensors and selective transient feature extraction for corrosion characterisation

paper_content:

Abstract In this paper, Low Frequency (LF) RFID sensing system is used to characterise marine atmospheric corrosion on steel samples. Considering the conductivity and permeability variation in the corrosion layer, optimisation of sensing sensitivity and communication distance of commercial RFID tags placed on both coated and uncoated samples (exposure duration between 1 and 12 months) for impedance matching and appropriate operation frequencies are analysed. To balance the communication distance between RFID reader and tag and to match the impedance variation of RFID tags on metallic samples, a concept of wireless power transfer (WPT) through strongly coupled magnetic resonance (SCMR) method at RFID is applied. Static and transient features are extracted and selected to characterise corrosion. To enhance the sensing sensitivity to corrosion characterisation, further experimental studies have been carried out using ferrite sheets. The proposed LF RFID sensing system has been validated using commercial RFID tags with different feature extractions and selection of features for corrosion characterisation.
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paper_title: Self-sensing passive RFID: From theory to tag design and experimentation

paper_content:

A passive UHF RFID system may be used as a self-sensing devices able to sense the geometrical and physical variation of the tagged object without the use of any specific sensor. This possibility is constrained to the design of multi-chip tags and to the definition of proper measurements modalities. This theoretical idea is here fully demonstrated experimentally for what concerns the wireless monitoring of the change of materials inside a plastic container. The paper describes some measurement techniques and simple data inversion algorithms.
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paper_title: Broadband Equivalent Circuit Models for Antenna Impedances and Fields Using Characteristic Modes

paper_content:

An approach for modeling antenna impedances and radiation fields in terms of fundamental eigenmodes is presented. Our method utilizes the simple frequency behavior of the characteristic modes to develop fundamental building blocks that superimpose to create the total response. In this paper, we study the modes of a dipole, but the method may be applied to more complicated structures as the modes retain many of their characteristics. We show that the eigenmode-based approach results in a more accurate model for the same complexity compared to a typical series RLC resonator model. Higher order modes can be more accurately modeled with added circuit complexity, but we show that this may not always be necessary. Because this method is based on the physical behavior of the fundamental modes, it also accurately connects circuit models to radiation patterns and other field behavior. To demonstrate this, we show that far field patterns, gain, and beam width of a dipole can be accurately extrapolated over a decade of bandwidth using data at two frequency points.
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paper_title: Precision and Accuracy in UHF-RFID Power Measurements for Passive Sensing

paper_content:

In spite of analog radio frequency identification (RFID) sensors are gaining increasing attention from academic and industrial domains, their true applicability in the real world is still in question, since it is not clear whether and in which conditions the variation of the measured signals related to the sensing activity may be distinguished from the measurement uncertainties. The RFID platform for analog sensing, namely, with no dedicated sensing electronics, is here characterized in term of precision and accuracy with reference to the arrangement and the reproducibility of the setup. Numerical analysis and laboratory experimentations demonstrated that the precision of power metrics measurement is twice the resolution of low-cost readers and that the uncertainty on the distance and the alignment may play a major role on the data accuracy. The environment-independent indicator, such as the analog identifier, revealed once again to be a very stable and robust metric. In overall, the obtained results suggest that analog RFID devices can be used as indicative sensing platform to identify a few levels of the phenomenon under observation. The sensing granularity can be improved using low-power ICs, while classification algorithms could be applied to increase the robustness of the detection.
---
paper_title: A novel method for determination of dielectric properties of materials using a combined embedded modulated scattering and near-field microwave techniques-Part I: forward model

paper_content:

The use of combined embedded modulated scattering technique and near-field microwave nondestructive testing techniques is investigated as a novel method for evaluating the dielectric properties of a material. The forward formulation for determining the reflection coefficient at the aperture of a waveguide radiating into a dielectric half-space in which a PIN diode-loaded dipole (i.e., modulated scattering technique probe) is embedded is presented. This formulation is based upon calculating the near-field coupling between the waveguide and the dipole as a mutual impedance.
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paper_title: Buried crack reconstruction through far-field electromagnetic inverse scattering measurement

paper_content:

An alternative approach to common methods in NDT for detection and identification of buried rectangular cracks on PEC surface is introduced. Goals are reached by solving a far-field inverse scattering problem. This approach enables us to reconstruct dielectric filled cracks under one or more dielectric layers with no need to touch the surface by any probes, but rather by measurements in the far-field of an antenna array. Suggested solution is applied by both TEz and TMz polarizations to two-dimensional structures with various crack's depth-to-width ratios; approximations for long three-dimensional structures. PSO and DE optimizers are used to solve the inverse scattering problem and both optimizers contain FDTD technique as their scattering problem solver.
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paper_title: Antenna Sensors in Passive Wireless Sensing Systems

paper_content:

Antenna sensors have received considerable interests in recent years due to their passive wireless operation, simple configuration, compact size, multiplexing capability, and multimodality sensitivity. Based on the principle of antenna backscattering, an antenna sensor can be wirelessly interrogated at middle range distances without an onboard battery. Since the antenna serves the dual function of sensing and communicating, an antenna sensor can be implemented with minimum number of components. As narrowband resonators, antenna sensors can be easily multiplexed based on the principle of frequency division multiplexing. In addition, different types of antenna sensors that are sensitive to a variety of physical measurands have been demonstrated. Due to these unique features, antenna sensor technology could play a vital role in our drive toward ubiquitous sensing. This chapter provides a comprehensive review of this exciting technology with detailed descriptions on the operational principle and wireless interrogation of batteryless antenna sensors. Four application examples of using antenna sensors for moisture, dynamic strain, temperature, and crack sensing are discussed. Future research directions and open problems are suggested.
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paper_title: UHF RFID Tag Antenna-Based Sensing for Corrosion Detection & Characterization Using Principal Component Analysis

paper_content:

The authors identified errors in [1, eq. (1)] , which states \begin{align*} P_{R\leftarrow T}[\Psi (\theta,\phi)]=\frac {1}{4\pi }& \left({\frac {\lambda _{0}}{4\pi d}}\right)^{2} \\ & \times \,P_{in}G_{R}^{2}(\theta,\phi)\eta ^{2}_{p}RCS[\Psi (\theta,\phi)].\end{align*} Knowing that the dimensions of $P_{R\leftarrow T}$ function, $\lambda _{0}$ , $ P_{\mathrm {in}}, ~d$ , and RCS function are watt, meter, watt, meter, and square meter, respectively, also $\eta _{p}$ and $G_{R}$ functions do not have any dimension—it is seen that both sides of [1, eq. (1)] are not in the same dimension. Looking at another reference, [2, eq. (3)] , it is seen that the mathematical power of $d$ is equal to 2 \begin{align*} P_{R\leftarrow T}[\Psi (\theta,\phi)]=\frac {1}{4\pi }& \left({\frac {\lambda _{0}}{4\pi d^{2}}}\right)^{2} \\[-1pt]&\times \,P_{in}G_{R}^{2}(\theta,\phi)\eta ^{2}_{p}RCS[\Psi (\theta,\phi)]\end{align*} and the mathematical power of $d$ is not 1 as given in [1, eq. (1)] . However, the rest of the paper and analysis given in [1] are still correct.
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paper_title: Characteristic Mode Based Tradeoff Analysis of Antenna-Chassis Interactions for Multiple Antenna Terminals

paper_content:

The design of multiple antennas in compact mobile terminals is a significant challenge, due to both practical and fundamental design tradeoffs. In this paper, fundamental antenna design tradeoffs of multiple antenna terminals are presented in the framework of characteristic mode analysis. In particular, interactions between the antenna elements and the characteristic modes and their impact on design tradeoffs are investigated in both theory and simulations. The results reveal that the characteristic modes play an important role in determining the optimal placement of antennas for low mutual coupling. Moreover, the ability of antenna elements to localize the excitation currents on the chassis can significantly influence the final performance. To demonstrate the effectiveness of the proposed approach, a dual-band, dual-antenna terminal is designed to provide an isolation of over 10 dB for the 900 MHz band without additional matching or decoupling structures. A tradeoff analysis of bandwidth, efficiency, effective diversity gain and capacity is performed over different antenna locations. Finally, three fabricated prototypes verify the simulation results for representative cases.
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paper_title: Self- and mutual-admittances of wire antennas in terms of characteristic modes

paper_content:

Particularly simple quadratic forms are derived for the self- and mutual-admittances of delta gaps in thin wire structures in terms of the characteristic currents of the structures. Results based on these forms are found to be in substantial agreement with those derived by other methods.
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paper_title: Eddy‐current interaction with an ideal crack. II. The inverse problem

paper_content:

Eddy‐current inversion is the process whereby the geometry of a flaw in a metal is derived from electromagnetic probe measurements. An inversion scheme is described for finding the shape and size of cracks from eddy‐current probe impedance measurements. The approach is based on an optimization scheme that seeks to minimize a global error function quantifying the difference between predicted and observed probe impedances. The error minimum is sought using a standard descent algorithm that requires a knowledge of the gradient of the error with respect to a variation of the flaw geometry. Computation of the gradient is based on a provisional flaw estimate, then the flaw estimate is updated in a ‘‘direction’’ that reduces the error. The process continues iteratively until a convergence criterion has been satisfied. Then the final flaw estimate should match the shape of the real defect. An equation for the gradient has been derived using an integral formulation of the ideal crack problem. Numerical estimates o...
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paper_title: RFID Grids: Part II—Experimentations

paper_content:

The RFID Grid is a model for generally coupled multitudes of tags including single-chip tags in close mutual proximity or a single tag with a plurality of embedded microchips. Some properties of this new entity, useful for passive Sensing and for Security, are the possibility to increase the read-range and to provide responses rather insensitive to the interrogation modalities. These recently introduced issues are here experimented for the first time with many real-world examples comprising multi-chip configurations designed for improved power scavenging and for passive sensing of things.
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paper_title: Internet of Things (IoT): A Vision, Architectural Elements, and Future Directions

paper_content:

Ubiquitous sensing enabled by Wireless Sensor Network (WSN) technologies cuts across many areas of modern day living. This offers the ability to measure, infer and understand environmental indicators, from delicate ecologies and natural resources to urban environments. The proliferation of these devices in a communicating-actuating network creates the Internet of Things (IoT), wherein sensors and actuators blend seamlessly with the environment around us, and the information is shared across platforms in order to develop a common operating picture (COP). Fueled by the recent adaptation of a variety of enabling wireless technologies such as RFID tags and embedded sensor and actuator nodes, the IoT has stepped out of its infancy and is the next revolutionary technology in transforming the Internet into a fully integrated Future Internet. As we move from www (static pages web) to web2 (social networking web) to web3 (ubiquitous computing web), the need for data-on-demand using sophisticated intuitive queries increases significantly. This paper presents a Cloud centric vision for worldwide implementation of Internet of Things. The key enabling technologies and application domains that are likely to drive IoT research in the near future are discussed. A Cloud implementation using Aneka, which is based on interaction of private and public Clouds is presented. We conclude our IoT vision by expanding on the need for convergence of WSN, the Internet and distributed computing directed at technological research community.
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paper_title: Electromagnetic Models for Passive Tag-to-Tag Communications

paper_content:

The UHF passive radio frequency identification technology generally enables an asymmetric interaction between the reader and the tag, the latter only being able to respond to the query of the reader through backscattering modulation. Very recently, some experiments put into evidence the possibility to set up a tag-to-tag communication by using a simple illuminator. The key issues and the physical limitation of such a cross-link are here investigated both theoretically and numerically by fully accounting for the mutual coupling among the tags, their radiation properties and the impedance modulation. The analysis reveals that the cross-link range may be optimized by a proper design of the tags' input impedance and that alignment of a multiplicity of tags could be able to communicate according to a simple routing strategy.
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paper_title: A Low-Power and Flexible Energy Detection IR-UWB Receiver for RFID and Wireless Sensor Networks

paper_content:

This paper presents an energy detection Impulse Radio Ultra-Wideband (IR-UWB) receiver for Radio Frequency Identification (RFID) and Wireless Sensor Networks (WSN) applications. An Application-Specific Integrated Circuit (ASIC) consisting of a 3-5 GHz analog front-end, a timing circuit and a high speed baseband controller is implemented in a 90 nm standard CMOS technology. A Field-Programmable Gate Array (FPGA) is employed as a reconfigurable back-end, enabling adaptive baseband algorithms and ranging estimations. The proposed architecture is featured by high flexibility that adopts a wide range of pulse rate (512 kHz-33 MHz), processing gain (0-18 dB), correlation schemes, synchronization algorithms, and modulation schemes (PPM/OOK). The receiver prototype was fabricated and measured. The power consumption of the ASIC is 16.3 mW at 1 V power supply, which promises a minimal energy consumption of 0.5 nJ/bit. The whole link is evaluated together with a UWB RFID tag. Bit error rate (BER) measurement displays a sensitivity of -79 dBm at 10 Mb/s with 10-3 BER achieved by the proposed receiver, corresponding to an operation distance over 10 meters under the FCC regulation.
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paper_title: RFID and sensor integration standards: State and future prospects

paper_content:

In the last few years, the standards development community has seen an increasing interest in the link between sensor and RFID standards. Standardization bodies such as the ISO/IEC and the IEEE are developing new specifications or updating their existing ones to reflect this interest. During this process, collaborations that span throughout several standardization documents and bodies have emerged in order to avoid the duplication of efforts and to speed up the standardization process. In the ever complex standardization world, this interconnection of standards makes the current status of the process difficult to understand, specially when most of the documents are still in development and constantly being updated. In this paper, we aim to provide a clearer view of the state of the sensor and RFID integration standardization activities, highlighting the collaboration among standardization bodies and discussing how these standardization processes are likely to evolve.
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paper_title: RFID: From Supply Chains to Sensor Nets

paper_content:

The next generation internet will be the internet of things (and not just of computing devices like PCs, PDAs); this is presumed to be enabled by integrating simple computing plus communications capabilities into common objects of everyday use. Radio-frequency identification (RFID) is a compelling technology for creation of such pervasive sensor networks due to its potential for ubiquitous, low-cost/low-maintenance use. However, the current drivers for RFID deployment emphasize supply chain management using passive tags, implying that RFID sensor nets require advances beyond the components and system designs aimed at supply chain applications. This work provides a glimpse of how this may be achieved.
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paper_title: Low-Cost, Ubiquitous RFID-Tag-Antenna-Based Sensing

paper_content:

Radio-frequency identification (RFID) has been well established as an effective technology for track and trace applications. In this paper, we go beyond the ID in RFID, and discuss the potential for RFID tags to be used as low-cost sensors by mapping a change in some physical parameter of interest to a controlled change in RFID tag antenna electrical properties. We will also show that it is possible to design the tag antenna to suffer a permanent change in case of violation of a critical threshold in the parameter of interest thereby creating a low-cost threshold sensing mechanism. This can be achieved by inducing controlled changes to the tag antenna geometry parameters or to the antenna boundary conditions, in effect creating a nonelectric memory to monitor state. After identifying the application space for which this class of sensing is well suited, we present details into the design and testing of three different kinds of sensors based on this sensing paradigm. We demonstrate how we use this concept to sense displacements, temperature thresholds, and fluid levels. We will show that RFID-tag-antenna-based sensing has the potential to revolutionize application domains in which there is a need for low-cost, long-lasting, ubiquitous sensors.
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paper_title: RFID-Grids for deformation sensing

paper_content:

This contribution explores the possibility to monitor structural deformations by means of grids of antennas. Deformations, occurring in engineering structures due to unexpected loading conditions and to ageing, may lead to potentially dangerous events. By engineering the electromagnetic interaction among the elements of a grid of UHF Radiofrequency Identification (RFID) tags, it is possible to extract various measureable indicators useful to track the local as well the overall deformation of the body on which the antennas are attached on, and hence to monitor the “health” of sensitive structures.
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paper_title: A delay-tolerant framework for integrated RSNs in IoT

paper_content:

The Internet of Things (IoT) represents an evolutionary vision that promises to identify and connect physical objects and devices. This vision faces many challenges in terms of integrating technologies, especially RFID-sensor networks (RSNs). In this paper, we introduce a framework for node deployment and delay-tolerance in RSNs under the IoT paradigm. Our framework is comprised of two components. The first is SIWR, a novel Smart Integrated WSNs and RFIDs architecture that classifies nodes into light nodes and super integrated nodes. SIWR employs an optimal linear programming formulation to cost-efficiently place integrated RFID readers. However, integrated IoT architectures face significant connectivity challenges. IoT settings assume no guaranteed contemporaneous end-to-end path between node pairs. To this end, in the second part of our framework, we introduce DIRSN, an optimized delay-tolerant approach for integrated RFID-sensor networks. This is a novel scheme for data routing and courier nodes' selection in RSNs. DIRSN's formulation minimizes delay across the network without violating the main dense-deployment and load-balancing requirements. In addition, DIRSN builds on SIWR's novel architecture to locate the best set of couriers that promise to provide connectivity. Our combined approach is compared to three types of RSN integration architectures and the results show that our architecture and courier selection approaches perform substantially better than other architectures in terms of minimizing delay, cost, packet loss, and in handling extensive traffic demands.
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paper_title: Internet of Things in Industries: A Survey

paper_content:

Internet of Things (IoT) has provided a promising opportunity to build powerful industrial systems and applications by leveraging the growing ubiquity of radio-frequency identification (RFID), and wireless, mobile, and sensor devices. A wide range of industrial IoT applications have been developed and deployed in recent years. In an effort to understand the development of IoT in industries, this paper reviews the current research of IoT, key enabling technologies, major IoT applications in industries, and identifies research trends and challenges. A main contribution of this review paper is that it summarizes the current state-of-the-art IoT in industries systematically.
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paper_title: A Battery-Assisted Sensor-Enhanced RFID Tag Enabling Heterogeneous Wireless Sensor Networks

paper_content:

This paper presents the design, realization, and experimental validation of a battery-assisted radio frequency identification (RFID) tag with sensing and computing capabilities conceived to explore heterogeneous RFID-based sensor network applications. The tag (hereafter called mote) features an ultra-low-power ferroelectric random-access-memory microcontroller, a LED, temperature and light sensors, three-axis accelerometer, non-volatile storage, and a new-generation I2C-RFID chip for communication with standard UHF EPCglobal Class-1 Generation-2 readers. A preliminary RFID mote prototype, fabricated on a printed circuit board using low-cost discrete components and equipped with a small 225-mAh coin battery, provides an estimated lifetime of 3 years when sensing and computing tasks are performed every 30 s. In addition, the reliable RFID communication range up to 22 m achieved in an indoor scenario represents, to the best of our knowledge, the longest distance ever reported for similar sensor-enhanced RFID tags.
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paper_title: An Efficient Small Data Transmission Scheme in the 3GPP NB-IoT System

paper_content:

This letter proposes an efficient small data transmission scheme in the narrow band (NB)-Internet of Things (IoT) system. For the efficient use of radio resources, the proposed scheme enables devices in an idle state to transmit a small data packet without the radio resource control connection setup process. This can improve the maximum number of supportable devices in the NB-IoT system which has insufficient radio resources. Numerical results have shown that the proposed scheme can increase the maximum number of supportable devices by about 60% compared with the conventional scheme.
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paper_title: Efficient RFID Tag Identification Exploiting Hybrid UHF-UWB Tags and Compressive Sensing

paper_content:

In this paper, we propose a novel tags identification protocol based on compressive sensing (CS) and ultra-wideband (UWB) for radio frequency identification (RFID) systems. In a hybrid RFID system, ultra-high-frequency (UHF) reader-to-tag communications are combined with the UWB transceivers for localization and ranging purposes. Here, the UWB information of such a hybrid UHF-UWB architecture is exploited to reduce the ID search space of a UHF-CS decoding scheme. Simulation results prove that our solution significantly decreases the amount of bits required for successful tags identification, compared with the state-of-the-art protocols.
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paper_title: RFID Sensor-Tags Feeding a Context-Aware Rule-Based Healthcare Monitoring System

paper_content:

Along with the growing of the aging population and the necessity of efficient wellness systems, there is a mounting demand for new technological solutions able to support remote and proactive healthcare. An answer to this need could be provided by the joint use of the emerging Radio Frequency Identification (RFID) technologies and advanced software choices. This paper presents a proposal for a context-aware infrastructure for ubiquitous and pervasive monitoring of heterogeneous healthcare-related scenarios, fed by RFID-based wireless sensors nodes. The software framework is based on a general purpose architecture exploiting three key implementation choices: ontology representation, multi-agent paradigm and rule-based logic. From the hardware point of view, the sensing and gathering of context-data is demanded to a new Enhanced RFID Sensor-Tag. This new device, de facto, makes possible the easy integration between RFID and generic sensors, guaranteeing flexibility and preserving the benefits in terms of simplicity of use and low cost of UHF RFID technology. The system is very efficient and versatile and its customization to new scenarios requires a very reduced effort, substantially limited to the update/extension of the ontology codification. Its effectiveness is demonstrated by reporting both customization effort and performance results obtained from validation in two different healthcare monitoring contexts.
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paper_title: RFID Grids: Part I—Electromagnetic Theory

paper_content:

The close displacement of UHF RFID tags can be considered as an electromagnetic interconnected system having specific properties. The so denoted RFID Grid includes single-chip tags in close mutual proximity or a single tag with a multiplicity of embedded microchips. A multi-port scattering framework is used to derive the macroscopic parameters governing the system response which could be optimized for the specific application. Moreover, unique features are introduced, such as the possibility to improve the power scavenging and the generation of analog identifiers and fingerprint. The last ones are electromagnetic responses independent on the position and orientation of the reader and on the nearby environment, with great relevance for Sensing and Security.
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paper_title: E2MAC: An energy efficient MAC for RFID-enhanced wireless sensor networks

paper_content:

The primary aim of any anti-collision protocols is to identify tags quickly, as doing so ensures that a Radio Frequency IDentification (RFID) reader incurs minimal energy wastage and achieves high identification rate. To date, researchers have proposed various protocols to minimize tag collisions and idle slots-key factors that determine a reader's read rate and energy expenditure. Most of these protocols, however, are designed for single reader systems. To this end, we propose E^2MAC, an energy efficient, distributed Medium Access Control (MAC) protocol for identifying and monitoring tags in RFID-enhanced wireless sensor networks. E^2MAC exploits the low power capability of a ultra-wideband transceiver and distinct pulses to address the reader collision problem. In addition, it uses ResMon, an enhanced dynamic frame slotted Aloha protocol to read and monitor tags. Lastly, E^2MAC uses a novel load balancing algorithm to amortize the cost of reading and monitoring tags to multiple readers. These E^2MAC features ensure that the contention level at each reader is kept at a minimum and distributed fairly. As a result, E^2MAC has a high reading rate and low energy consumption. In addition, E^2MAC helps in minimizing the impact of the tag orientation problem, where a tag becomes unreadable if its antenna is parallel to a reader's field lines. In particular, the use of multiple readers increases spatial diversity and hence increases the likelihood that a tag is readable by at least one reader. Our simulation results show E^2MAC to have very low energy consumption, reading delay and per-reader collision. More importantly, system designers have the flexibility to lower these metrics further with additional readers, bigger frame sizes, or by dividing tags into small groups.
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paper_title: Enhanced UHF RFID Sensor-Tag

paper_content:

A cost-effective integration of passive UHF RFID tags and sensors is still a challenge. In such a field, authors have already proposed a label-type multi-antenna Sensor-Tag, an RFID device accepting as input a generic sensor and allowing the transmission of the measured data towards a standard RFID reader. In this work a new enhanced version of Sensor-Tag is presented. It is based on optimized tag antennas designed by taking into account both size constraints and coupling effects. Compared with the old version, an appreciable size reduction is obtained and the working distance doubled, being now as good as a long range passive UHF tag.
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paper_title: Data Cleaning for RFID and WSN Integration

paper_content:

Today's manufacturing environments are very dynamic and turbulent. Traditional enterprise information systems (EISs) have mostly been implemented upon hierarchical architectures, which are inflexible to adapt changes and uncertainties promptly. Next-generation EISs must be agile and adaptable to accommodate changes without significant time delays. It is essential for an EIS to obtain real-time data from the distributed and dynamic manufacturing environment for decision making. Wireless sensor networks (WSNs) and radio-frequency identification (RFID) systems provide an excellent infrastructure for data acquisition, distribution, and processing. In this paper, some key challenges related to the integration of WSN and RFID technologies are discussed. A five-layer system architecture has been proposed to achieve synergistic performance. For the integration of WSN and RFID, one of the critical issues is the low efficiency of communication due to redundant data as redundant data increases energy consumption and causes time delay. To address it, an improved data cleaning algorithm has been proposed; its feasibility and effectiveness have been verified via simulation and a comparison with a published algorithm. To illustrate the capacity of the developed architecture and new data cleaning algorithm, their application in relief supplies storage management has been discussed.
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paper_title: Tag-based cooperative data gathering and energy recharging in wide area RFID sensor networks

paper_content:

The Wireless Identification and Sensing Platform (WISP) conjugates the identification potential of the RFID technology and the sensing and computing capability of the wireless sensors. Practical issues, such as the need of periodically recharging WISPs, challenge the effective deployment of large-scale RFID sensor networks (RSNs) consisting of RFID readers and WISP nodes. In this view, the paper proposes cooperative solutions to energize the WISP devices in a wide-area sensing network while reducing the data collection delay. The main novelty is the fact that both data transmissions and energy transfer are based on the RFID technology only: RFID mobile readers gather data from the WISP devices, wirelessly recharge them, and mutually cooperate to reduce the data delivery delay to the sink. Communication between mobile readers relies on two proposed solutions: a tag-based relay scheme, where RFID tags are exploited to temporarily store sensed data at pre-determined contact points between the readers; and a tag-based data channel scheme, where the WISPs are used as a virtual communication channel for real time data transfer between the readers. Both solutions require: (i) clustering the WISP nodes; (ii) dimensioning the number of required RFID mobile readers; (iii) planning the tour of the readers under the energy and time constraints of the nodes. A simulative analysis demonstrates the effectiveness of the proposed solutions when compared to non-cooperative approaches. Differently from classic schemes in the literature, the solutions proposed in this paper better cope with scalability issues, which is of utmost importance for wide area networks.
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paper_title: Fundamental Characteristics of Electro-Textiles in Wearable UHF RFID Patch Antennas for Body-Centric Sensing Systems

paper_content:

Electro-textiles feature excellent radio frequency (RF) performance. They have an enormous potential to be widely accepted in body-centric sensing systems as wearable antenna materials. However, the RF community lacks comprehensive knowledge of electro-textile fundamental characteristics. This paper provides critical electro-textile design parameters for wearable radio frequency identification (RFID) ultra-high-frequency (UHF) patch antennas. For the first time, modeling parameters for embroidered antenna ground plane and patch structures are established and verified. The results highlight a new unprecedented fundamental characteristic of embroidered antennas: all embroidered structures, modeled as uniform and infinitely thin textile layer, have an existing imaginary part in their sheet impedance modeling parameter. It accounts for the antenna input inductance contributed from the electro-textile. Ideally, such as for highly conductive fabrics and pure conductors, the imaginary part is negligible. Utilizing the proposed design guidelines, a fully wearable and flexible embroidered RFID patch antenna is for the first time realized. Its performance may be considered as a benchmark for future designs. The design parameters and findings form an important milestone in the development towards wearable intelligence and foster industrial developments of garment-integrated RFID antennas.
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paper_title: Detecting Vital Signs with Wearable Wireless Sensors

paper_content:

The emergence of wireless technologies and advancements in on-body sensor design can enable change in the conventional health-care system, replacing it with wearable health-care systems, centred on the individual. Wearable monitoring systems can provide continuous physiological data, as well as better information regarding the general health of individuals. Thus, such vital-sign monitoring systems will reduce health-care costs by disease prevention and enhance the quality of life with disease management. In this paper, recent progress in non-invasive monitoring technologies for chronic disease management is reviewed. In particular, devices and techniques for monitoring blood pressure, blood glucose levels, cardiac activity and respiratory activity are discussed; in addition, on-body propagation issues for multiple sensors are presented.
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paper_title: Toward Graphene-Based Passive UHF RFID Textile Tags: A Reliability Study

paper_content:

This paper discusses the fabrication, wireless performance, and reliability of graphene-based passive ultrahigh-frequency radio-frequency identification (RFID) tags on a fabric substrate. The conductive ink comprising functionalized graphene nanoplatelets is deposited directly on a cotton fabric substrate to fabricate the tag antennas. After attaching the chips, the tag performance is evaluated through wireless tag measurements before and after high-humidity conditions, bending, and stretching. Initially, the peak read range of the tag is about 1.6 m, which increases to 3.2 m in 100% humidity conditions. Additionally, after drying, the performance of the tag returns back to normal. In a bending test, the read range of a bent tag decreases below 1 m. Furthermore, the read range of the tag in a nonbended state gradually decreases and is about 1.1 m after 100 bending cycles. According to our measurements, stretching has a serious detrimental effect on these tags and they cannot be considered stretchable. However, these initial results show that this low-cost and eco-friendly graphene RFID tag has a remarkable and unique response to moisture and high reliability in harsh bending conditions. Overall, it also has a strong potential to be used in future wearable sensor applications.
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paper_title: Low-Cost, Ubiquitous RFID-Tag-Antenna-Based Sensing

paper_content:

Radio-frequency identification (RFID) has been well established as an effective technology for track and trace applications. In this paper, we go beyond the ID in RFID, and discuss the potential for RFID tags to be used as low-cost sensors by mapping a change in some physical parameter of interest to a controlled change in RFID tag antenna electrical properties. We will also show that it is possible to design the tag antenna to suffer a permanent change in case of violation of a critical threshold in the parameter of interest thereby creating a low-cost threshold sensing mechanism. This can be achieved by inducing controlled changes to the tag antenna geometry parameters or to the antenna boundary conditions, in effect creating a nonelectric memory to monitor state. After identifying the application space for which this class of sensing is well suited, we present details into the design and testing of three different kinds of sensors based on this sensing paradigm. We demonstrate how we use this concept to sense displacements, temperature thresholds, and fluid levels. We will show that RFID-tag-antenna-based sensing has the potential to revolutionize application domains in which there is a need for low-cost, long-lasting, ubiquitous sensors.
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paper_title: Battery-free multichannel digital ECG biotelemetry using UHF RFID techniques

paper_content:

We propose to leverage UHF RFID techniques to yield a continuously wearable, battery-free wireless multichannel ECG telemetry device that is potentially disposable, low-cost and suitable for integration with multiple electrodes in a flexible circuit assembly. Such a device could have broad applicability, ranging from initial patient assessment by first responders, to continuous monitoring in various clinical settings. We employ a recently described single-chip data acquisition system including RF power harvesting to eliminate the need for a battery. The single-chip system includes 14 channels of integrated biopotential amplification, an 11-bit ADC, and a 5 Mbps digital backscatter telemetry link. We present an initial characterization of the telemetry chip in this application including battery-free, wireless 3 and 5 channel ECG recordings made from an ambulatory human subject at a range of ≈ 1 meter.
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paper_title: On-Body Performance of a Wearable Single-Layer RFID Tag

paper_content:

The effects of the human body on a wearable radio frequency identification (RFID) tag at 866 MHz are presented. We concentrate on the effect of the varying antenna-body separation distance on the antenna properties. The results of the three-dimensional radiation pattern measurements are presented. A 6-m read range, -6 dBi realized gain, and 12% antenna efficiency are achieved when this antenna is worn on the body.
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paper_title: Design, Calibration and Experimentation of an Epidermal RFID Sensor for Remote Temperature Monitoring

paper_content:

An epidermal radiofrequency identification technology (RFID) sensor consists of a flexible antenna provided with a radiofrequency identification and sensing microchip directly stuck over the human skin by means of a sub-millimeter bio-compatible membrane. A compact-size epidermal RFID thermometer is here proposed and extensively experimented concerning its electromagnetic and thermal performance in case of battery-less and battery-assisted configurations. The antenna element embeds a mechanism for a post-manufacturing frequency retuning in order to adapt its response to the specific placement over the body. When attached over the skin, the sensor is readable from up to 0.7 m in battery-less mode and 2.3 m in battery-assisted mode. A calibration procedure improved the accuracy of the IC sensor down to 0.18 °C. The time constant evaluated by the first-order response of the IC to impulse heating (photo-flash) resulted in 4.3 s. The epidermal wireless thermometer was experimented in both supervised applications (manual reading) and in un-supervised architectures where users were continuously monitored by a fixed remote antenna or during the crossing of a surveillance gate. In all the considered cases, the reliability of the interrogation link was experimentally quantified and resulted robust for health monitoring applications in clinical and domestic settings and even for the automatic detection of anomalous temperature peaks of people walking within airports and at country border crossing.
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paper_title: Electromagnetic characterisation of self-tuning UHF RFID tags for sensing application

paper_content:

Recently introduced self-tuning UHF RFID microchips offer interesting possibility for low-cost sensing. We have investigated the response of such a chip embedded into a meandered-dipole tag versus the interrogation modalities, the frequency and the variable boundary conditions. A simple impedance model has permitted to accurately reproduce the tag behaviour during the monitoring of the filling level of a box.
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paper_title: Feasibility of Body-Centric Systems Using Passive Textile RFID Tags

paper_content:

Recent progresses in the design of wearable RFID-tag antennas stimulate the idea of passive body-centric systems, wherein the required power to drive the wearable tags is directly scavenged from the interrogation signal emitted by the reader unit. While active body-centric links have been extensively investigated, the feasibility of passive systems is still questionable, due to the poor sensitivity of the tags and due to the modest reading distances. This paper describes a systematic measurement campaign involving low-profile wearable textile tags in the UHF RFID band. It was demonstrated that both on-body and off-body links are affordable, with a power budget fully compliant with the available technology and the safety standards. The experiments permitted identifying the most-efficient tag placements, and proposing some quantitative and general guidelines useful to characterize and design this kind of new system.
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paper_title: An Irreversible Single-Use Humidity-Threshold Monitoring Sensor Principle for Wireless Passive Sensor Solutions

paper_content:

Monitoring environmental parameters, which have negative effects on goods (e.g., temperature and relative humidity) to determine threshold or dosage violations, is of strong interest throughout their life cycle. The task is challenging if there is no continuous supply of electric energy available, and lowest cost monitoring solutions are required. These are two common application constraints when passive sensor-enhanced RFID tags are used to fulfill this monitoring task. A sensor principle is proposed in which the exceedance of a humidity threshold followed by critical exposure leads to a permanent change in an electric sensor parameter, i.e., a pronounced electric resistance decrease in the presented case. The sensor principle is based on the phenomena deliquescence of salts for humidity threshold detection and sensor activation mechanism and salt solution dissemination processes in porous media as well as chemical liquid phase sintering of metal nanoparticles under ambient temperature conditions as an irreversible state change mechanism. The sensor principle deduced arrangement is fully compatible with printed electronics manufacturing technologies as exemplified by a sample fabrication via inkjet printing. The proposed sensors can serve as humidity-triggered switches in electric circuits, which permanently close due to critical humidity exposure above a humidity threshold. Presented are experimental results demonstrating the feasibility of the proposed sensor concept. Also given are application examples not only demonstrating the suitability of the sensor concept for sensor enhanced RFID tags via an integration into a freely programmable RFID UHF transponder tag but also for wireless passive sensors exemplified via integration into an inductively coupled resonant sensor tag.
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paper_title: A Sub-$\mu$ W Embedded CMOS Temperature Sensor for RFID Food Monitoring Application

paper_content:

An ultra-low power embedded CMOS temperature sensor based on serially connected subthreshold MOS operation is implemented in a 0.18 μm CMOS process for passive RFID food monitoring applications. Employing serially connected subthreshold MOS as sensing element enables reduced minimum supply voltage for further power reduction, which is of utmost importance in passive RFID applications. Both proportional-to-absolute-temperature (PTAT) and complimentary-to-absolute-temperature (CTAT) signals can be obtained through proper transistor sizing. With the sensor core working under 0.5 V and digital interfacing under 1 V, the sensor dissipates a measured total power of 119 nW at 333 samples/s and achieves an inaccuracy of + 1/-0.8°C from - 10°C to 30°C after calibration. The sensor is embedded inside the fabricated passive UHF RFID tag. Measurement of the sensor performance at the system level is also carried out, illustrating proper sensing operation for passive RFID applications.
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paper_title: Conformal Magnetic Composite RFID for Wearable RF and Bio-Monitoring Applications

paper_content:

This paper introduces for the first time a novel flexible magnetic composite material for RF identification (RFID) and wearable RF antennas. First, one conformal RFID tag working at 480 MHz is designed and fabricated as a benchmarking prototype and the miniaturization concept is verified. Then, the impact of the material is thoroughly investigated using a hybrid method involving electromagnetic and statistical tools. Two separate statistical experiments are performed, one for the analysis of the impact of the relative permittivity and permeability of the proposed material and the other for the evaluation of the impact of the dielectric and magnetic loss on the antenna performance. Finally, the effect of the bending of the antenna is investigated, both on the S-parameters and on the radiation pattern. The successful implementation of the flexible magnetic composite material enables the significant miniaturization of RF passives and antennas in UHF frequency bands, especially when conformal modules that can be easily fine-tuned are required in critical biomedical and pharmaceutical applications.
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paper_title: Printed Humidity Sensor With Memory Functionality for Passive RFID Tags

paper_content:

This paper presents a printed UHF radio frequency identification (RFID) sensor solution that indicates whether a passive RFID tag has been exposed to a certain degree of humidity. The printed sensor operates as a write-once read-many-times resistive memory as it permanently changes its resistance from about 2 ${\rm k}\Omega$ to less than 50 $\Omega$ after exposure to humidity or water. The change of the sensor resistance is used to modulate the properties of a UHF RFID tag antenna by changing antenna input impedance and also introducing or removing ohmic losses in the antenna structure. The final result is reflected in the change of the minimum transmit power required to power-up the RFID tag. Both the sensor and the tag antenna are printed horizontally on a paper substrate. Different geometric combinations of sensor and antenna structures are investigated. Typical applications include noninvasive methods for detecting wetness or humidity levels in hidden locations, such as within construction structures. The sensor setup can also serve to provide information as to whether a package sent over a supply chain has exceeded a certain level of humidity during its route.
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paper_title: Sensor-Enabled RFID System for Monitoring Arm Activity: Reliability and Validity

paper_content:

After stroke, capacity to complete tasks in the treatment setting with the more-affected arm is an unreliable index of actual use of that extremity in daily life. Available objective methods for monitoring real-world arm use rely on placing movement sensors on patients. These methods provide information on amount but not type of arm activity, e.g., functional versus nonfunctional movement. This paper presents an approach that places sensors on patients and household objects, overcoming this limitation. An accelerometer and the transmitter component of a radio-frequency proximity sensor are attached to objects; the receiver component is attached to the arm of interest. The receiver triggers an on-board radio-frequency identification tag to signal proximity when that arm is within 23 cm of an instrumented object. In benchmark testing, this system detected perfectly which arm was used to move the target object on 200 trials. In a laboratory study with 35 undergraduates, increasing the amount of time target objects were moved with the arm of interest resulted in a corresponding increase in system output (p <; 0.0001) . Moreover, measurement error was low (≤2.5%). The results support this system's reliability and validity in individuals with unimpaired movement; testing is now warranted in stroke patients.
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paper_title: A Multifrequency Passive Sensing Tag With On-Chip Temperature Sensor and Off-Chip Sensor Interface Using EPC HF and UHF RFID Technology

paper_content:

State-of-the-art passive RFID tags are limited in terms of functionality and operating range due to the limited power that can be converted from the electromagnetic field. This is why state-of-the-art wireless sensor systems are mostly battery-based if a high operating range is required. The proposed ultralow-power on-chip sensor unit and off-chip sensor interface which provides enough energy to supply various sensors with a power consumption up to the milliwatt range make it possible to remotely power the proposed RFID tag and use it as wireless sensor node. Equipping sensor nodes with RFID functionality not only enables identification and logistic applications but also an easy integration of the sensing tag into existing RFID systems. Exploiting the different characteristics of HF and UHF RFID systems, namely the large operating range in UHF and the high available power in HF, increases the flexibility and applicability of wireless sensor nodes. This paper presents a remotely powered multifrequency sensing tag according to the EPC HF and EPC Class 1 Gen 2 UHF standard developed in a 0.13-μm low-cost CMOS process. Input powers of -10.3 or -7.9 dBm at a frequency of 900 MHz are necessary to operate the sensing tag with activated on-chip sensor unit or off-chip sensor interface, respectively.
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paper_title: A system-on-chip EPC Gen-2 passive UHF RFID tag with embedded temperature sensor

paper_content:

This paper presents a system-on-chip passive RFID tag with an embedded temperature sensor for the EPC Gen-2 protocol in the 900-MHz UHF frequency band. A dual-path clock generator is proposed to support both applications with either very accurate link frequency or very low power consumption. On-chip temperature sensing is accomplished with a time-readout scheme to reduce the power consumption. Moreover, a gain-compensation technique is proposed to reduce the temperature sensing error due to process variations by using the same bandgap reference of the tag to generate bias currents for both the current-to-digital converter and the clock generator of the sensor. Also integrated is a 128-bit one-time-programmable (OTP) memory array based on gate-oxide antifuse without extra mask steps. Fabricated in a standard 0.18- μm CMOS process with analog options, the 1.1-mm2 tag chip is bonded onto an antenna using flip-chip technology to realize a complete tag inlay, which is successfully demonstrated and evaluated in real-time wireless communications with commercial RFID readers. The tag inlay achieves a sensitivity of -6 dBm and a sensing inaccuracy of ±0.8° C (3 σ inaccuracy) over operating temperature range from -20°C to 30°C with one-point calibration.
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paper_title: Automatic Antenna Tuning Unit to Improve RFID System Performance

paper_content:

Systems for radio-frequency identification (RFID) realize a bidirectional wireless communication between a reader device and cheap passive tags (e.g., an RFID chip with an antenna printed on badges for access-control systems) in the near field of an antenna. This paper deals with the automatic and fast tuning of the resonant reader antennas in the widely used 13.56-MHz frequency band, resulting in a performance improvement and an increased read/write range. A novel RFID reader system is proposed with a tuning transformer for the automatic adjustment of the resonant circuit center frequency. This is achieved by shifting the magnetic operating point (i.e., the biasing direct-current (dc) magnetization) of a Ni-Zn ferrite transformer by means of an additional dc winding. The operation principle and the performance potential of this device are demonstrated by measurements on a prototypical RFID system.
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paper_title: Multi-Chip RFID Antenna Integrating Shape-Memory Alloys for Detection of Thermal Thresholds

paper_content:

Low-cost wireless measurement of objects' temperature is one of the greatest expectation of radiofrequency identification technology for the so many applications in cold supply-chain control and safety assessment in general. In this context, the paper proposes a dual-chip UHF tag embedding shape memory alloys (SMA) able to transform the variation of the tagged item's temperature into a permanent change of antenna radiation features. This event-driven antenna is hence able to selectively activate the embedded microchips according to the temperature above or below a given threshold. A general design methodology for the resulting two-ports tag antenna is here introduced and then applied to prototypes able to work at low (around 0°C) and high (80°C) temperatures.
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paper_title: Smart sensing and data logging using RFID

paper_content:

A Class-1 Generation-2 compliant UHF RFID tag board, capable of smart sensing and data logging is introduced in this paper. The new tag has the ability to autonomously sense, process and store data over prolonged periods of time until the tag comes within range of an RFID reader. The logging operation is intelligently controlled to effectively utilize the memory, thereby enabling the tag to incorporate sensors to give more information than existing RFID tags.
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paper_title: Enhanced UHF RFID Sensor-Tag

paper_content:

A cost-effective integration of passive UHF RFID tags and sensors is still a challenge. In such a field, authors have already proposed a label-type multi-antenna Sensor-Tag, an RFID device accepting as input a generic sensor and allowing the transmission of the measured data towards a standard RFID reader. In this work a new enhanced version of Sensor-Tag is presented. It is based on optimized tag antennas designed by taking into account both size constraints and coupling effects. Compared with the old version, an appreciable size reduction is obtained and the working distance doubled, being now as good as a long range passive UHF tag.
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paper_title: A communication link analysis based on biological implant wireless body area networks

paper_content:

The rapid growth in remote healthcare services and biomedical demands has seen novel developments in wireless body area networks (WBANs). The WBAN can be seen as an integration of intelligent networks, which permits devices and sensors to work together to obtain a series of critical physiological parameters, such as blood flow velocity and heartbeat frequency. Analysis of WBAN radio frequency communication systems is the key factor and the critical research challenge that determines system performance, such as achievable transmission distance, data rate and so forth. The human head is an area of particular potential in WBAN design that is worthy of attracting more attention than its limited literature to date. This paper is primarily focused on the one of the most detailed comprehensive multi-modal imagingbased anatomical human head models. This is a multimodal imaging-based detailed anatomical model, denoted by the acronym MIDA, this features 153 structures at a high resolution of up to 500 μm, including numerous distinct muscles, bones and skull layers in the license-free 2.4 GHz industrial, scientific, and medical (ISM) band. It presents and compares a set of advanced simulation methods and then proposes a path loss simulation flat phantom, semi-empirical path loss models for typical homogeneous tissues and the anatomical human head MIDA model. The bit error rate (BER) performances of the MIDA model fading channel using Binary Phase Shift Keying (BPSK) and Pulse-Amplitude Modulation (PAM) are obtained. Furthermore, achievable transmission distances for several data rates for predetermined acceptable BERs are accomplished. The results show that PAM promises longer transmission distances than BPSK when using both high and low data rates. The proposed communication systems can be applied to optimize implantation communication system scenarios and biotelemetry applications.
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paper_title: RFID: From Supply Chains to Sensor Nets

paper_content:

The next generation internet will be the internet of things (and not just of computing devices like PCs, PDAs); this is presumed to be enabled by integrating simple computing plus communications capabilities into common objects of everyday use. Radio-frequency identification (RFID) is a compelling technology for creation of such pervasive sensor networks due to its potential for ubiquitous, low-cost/low-maintenance use. However, the current drivers for RFID deployment emphasize supply chain management using passive tags, implying that RFID sensor nets require advances beyond the components and system designs aimed at supply chain applications. This work provides a glimpse of how this may be achieved.
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paper_title: Improvement in Robustness and Recognizability of RCS Response of U-Shaped Strip-Based Chipless RFID Tags

paper_content:

This letter presents significant improvement in robustness and recognizability of radar cross section (RCS) response of the two topologically rearranged 20-bit U-shaped strip-based tags for spectral signature-based chipless RFID systems. The space rearrangement of individual tag scatterers in the array reduces the interelement mutual coupling and, thus, significantly enhances the frequency and amplitude robustness of their RCS. In comparison to the original arrangement of scatterers, the measurement of tags designed for 2–4-GHz frequency band showed a significantly improved homogeneity of the RCS curve, which results in a more reliable recognition of coded information.
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paper_title: Wireless Hydrogen Smart Sensor Based on Pt/Graphene-Immobilized Radio-Frequency Identification Tag

paper_content:

Hydrogen, a clean-burning fuel, is of key importance to various industrial applications, including fuel cells and the aerospace and automotive industries. However, hydrogen gas is odorless, colorless, and highly flammable; thus, appropriate safety protocol implementation and monitoring are essential. Highly sensitive hydrogen-gas leak detection and surveillance systems are needed; additionally, the ability to monitor large areas (e.g., cities) via wireless networks is becoming increasingly important. In this report, we introduce a radio frequency identification (RFID)-based wireless smart-sensor system, composed of a Pt-decorated reduced graphene oxide (Pt_rGO)-immobilized RFID sensor tag and an RFID-reader antenna-connected network analyzer to detect hydrogen gas. The Pt_rGOs, produced using a simple chemical reduction process, were immobilized on an antenna pattern in the sensor tag through spin coating. The resulting Pt_rGO-based RFID sensor tag exhibited a high sensitivity to hydrogen gas at unprecede...
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paper_title: A Fully Inkjet-Printed Wireless and Chipless Sensor for CO2 and Temperature Detection

paper_content:

A study on a low-cost wireless fully inkjet-printed chipless sensor on a flexible laminate with three different inks is presented. It is based on two split ring resonator 90° oriented between each other to allow for independent responses on two polarizations. A deposit of a polymer/single walled carbon nanotube composite ink is used to allow for the detection of CO ::: 2 ::: as well as temperature. In this paper, it is shown that the inkjet printing of a polymer-based coating on top of the sensing/reactive deposit can significantly reduce the sensitivity to CO ::: 2 ::: , whereas the temperature sensitivity stays at same. Simulations and experimental results verify the repeatability of this topology.
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paper_title: Directly Printable Moisture Sensor Tag for Intelligent Packaging

paper_content:

A compact, flexible 24-b dual-polarized chipless radio frequency identification tag with a size of 20.6mm × 19.9mm is realized. The tag structure is optimized and analyzed for Taconic, Kapton TIN and organic substrate. The prototype fabricated on TIP photopaper with silver nanoparticles-based conductive ink is exhibiting a behavior of moisture sensor. The proposed moisture sensor tag has a bandwidth of 13.5GTIz. The direct printability of moisture sensor tag makes it suitable for intelligent packaging and various low-cost applications.
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paper_title: High-Resolution, Far-Field, and Passive Temperature Sensing up to 700 °C Using an Isolated ZST Microwave Dielectric Resonator

paper_content:

This paper presents a high-resolution, wireless and passive temperature measurement system up to 700 °C. The sensor is based on a metallization-free monolithic microwave dielectric resonator composed of zirconium tin titanate (Zr0.8Sn0.2TiO4) operating at 2.37 GHz. The external electromagnetic fields of the tracked single mode are adequate for the far-field coupling without the need to use any conducting part on the sensor surface. The measurements are conducted in a light weight refractory bricks oven at a distance of 1.20 m between the sensor and a reader planar antenna connected to a time-domain RADAR-based interrogation unit. This method allows to retain a quality factor ( $Q$ ) higher than 670 at 700 °C, while the $Q$ -factor from other electromagnetic cavity or microwave dielectric resonators degrades below 100, hence limiting the sensing resolution and increasing the sensitivity to the environmental echoes. The effect of temperature on the tracked sensor resonance frequency, signal-to-noise ratio, $Q$ -factor, thermal expansion, and sensing resolution is presented. The concept is suitable for applications working in extreme environments, such as aerospace applications.
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paper_title: High-Capacity Chipless RFID Tag Insensitive to the Polarization

paper_content:

Designing a reader for chipless RFID is a hard task since both the polarization and operating frequency agility have to be implemented. The new tag design proposed in this paper is polarization independent, making the design of the reader easier since only linear polarization is needed to detect the tag. The proposed chipless tag is based on multiple circular ring patch resonators. The coding capacity of this tag reaches 19 bits within a compact surface of cm . Further, the frequency band is within 3.1 to 10.6 GHz to be compliant with FCC and ECC regulations for UWB. This new design is experimentally validated in the frequency domain using bi-static measurement set-up. Both amplitude and group delay responses of the tag are investigated and carried out.
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paper_title: A Cost-Effective SDR Platform for Performance Characterization of RFID Tags

paper_content:

The rigorous characterization of ultrahigh-frequency passive radio-frequency identification (RFID) tags is a challenging but mandatory task. Indeed, tags are the most critical devices in RFID systems: their performance should be adequately good, although stringent requirements in terms of compactness, used materials, and costs must be satisfied. Factors such as the goodness of the conjugate impedance matching between the chip and the antenna, the chip sensitivity, and the quality of the backscattered signal affect tag performance. Tag sensitivity and differential radar cross section (RCS) are the most significant metrics for tag characterization: they define the forward (from the reader to the tag) and the backward (from the tag to the reader) link reliability, respectively. Nevertheless, measurement of such metrics cannot be approached with conventional methods based on vector network analyzers or conventional RFID readers. Vice versa, commercially available instrumentation and solutions are very expensive and not totally flexible. In this paper, a novel approach for performance characterization of RFID tags is explored. To this end, we developed a very cheap (below $1000) and flexible tool based on software-defined radio, which enables measurement of tag sensitivity and differential RCS. An exhaustive experimental campaign has been carried out on ten commercial and four built-in laboratory RFID tags. Achieved results demonstrate the flexibility, accuracy, and appropriateness of the proposed approach.
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paper_title: Wireless Passive Temperature Sensors Using Integrated Cylindrical Resonator/Antenna for Harsh-Environment Applications

paper_content:

Wireless passive temperature sensors for harsh-environment applications based on cylindrical microwave cavity resonators are presented herein. Slot antennas are integrated with sensors with zero additional volume. The resonant frequencies of the sensors are determined by the dielectric constants of the ceramic materials, which monotonically increase versus temperature. Silicoboron carbonitride (SiBCN) ceramic materials, which are very robust inside harsh environments featuring high temperatures and corrosive gases, are optimized in this paper to reduce dielectric losses and increase sensing ranges and accuracies. A robust interrogation antenna is developed to wirelessly measure the sensors up to 1300 °C. Two sensors based on Si ::: 6 ::: B ::: 1 ::: and Si ::: 4 ::: B ::: 1 ::: ceramics are measured up to 1050 °C and 1300 °C, respectively, with a sensitivity of ~0.78 MHz/°C at 1050 °C. This type of wireless, passive, and robust sensor can be used for many harsh-environment applications, such as gas turbines.
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paper_title: Inline SAW RFID tag using time position and phase encoding

paper_content:

Surface acoustic wave (SAW) radio-frequency iden- tification (RFID) tags are encoded according to partial reflections of an interrogation signal by short metal reflectors. The standard encryption method involves time position encoding that uses time delays of response signals. However, the data capacity of a SAW RFID tag can be significantly enhanced by extracting additional phase information from the tag responses. In this work, we have designed, using FEM-BEM simulations, and fabricated, on 128 ◦ -LiNbO3, inline 2.44-GHz SAW RFID tag samples that combine time position and phase encoding: each reflective echo has four possible time positions and, additionally, a phase of 0 ◦ ,- 90 ◦ , -180 ◦ , or -270 ◦ . This corresponds to 16 different
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paper_title: Stretchable RFID for Wireless Strain Sensing With Silver Nano Ink

paper_content:

Flexible and stretchable inductor-capacitor (LC) resonator-based chipless radio frequency identification (RFID) tags have been fabricated by the direct stamping with silver nano ink. The tags are optimized based on the sympathetic oscillation of LC circuit at specifically designed resonant frequencies ranged from 1.12 to 1.7 GHz by adjusting dimensions of the inductor and capacitor in a tag. Pressure applied to the layer of silver nano ink during the stamping procedure helps densification of silver nanoparticles inside trenches of the stamp before heat-annealing of them. Transfer stamping process is simulated to demonstrate stress distribution across the layer of silver nanoparticles. Compaction of silver nanoparticles, in turn, positively affects mechanical strength of the final silver electrode and enables RFID strain sensors on polydimethylsiloxane to be stretchable up to 7%. By the stretchable RFID strain sensors, wireless strain sensing is demonstrated with a gauge factor of 0.51. Multiple encoded identifications with combination of double tags and stretching behavior of fabricated tags are also demonstrated. This stretchable RFID sensor is promising for biomedical applications such as real-time monitoring of motion detection.
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paper_title: Single-shot and single-sensor high/super-resolution microwave imaging based on metasurface

paper_content:

High-resolution or super-resolution imaging is a long sought-after goal in various imaging applications, where both real-time data acquisition and low-cost hardware are desired. Three types of active imaging systems have been developed for data acquisition in the past decades, namely, the real-aperture (RA) system1, the synthetic-aperture (SA) system2, and the random-pattern-based computational imager3,4,5,6. The RA system composed of a large amount of antenna elements in a large aperture is more flexible in measurement modes but suffers from the big size, heavy weight, high power, and high expense of hardware. The SA system, by contrast, belongs to the category of single-sensor systems. The completion of imaging relies on the mechanical movement of a single sensor to form virtually a large scanning aperture and subsequent data post-processing. ::: ::: Inspired by the compressive sensing (CS) theory proposed about one decade ago, the single-pixel imaging systems have been developed to reduce the number of measurements while keeping acceptable imaging quality at optical3,4, terahertz5,6,7 and millimeter-wave8 frequencies. The key idea behind these imaging systems is to project the object’s information into the single-pixel detector through a set of spatial light modulators (SLMs) with quasi-random patterns at a single frequency. Apparently, the CS-based imaging apparatus falls into the category of multi-shot and single-sensor systems. Usually, the number of required SLMs is in the order of the sparsity degree of the probed object, and a sparsity-driven convex optimization problem must be solved to retrieve the information of the probed object. The series of random SLMs are manipulated in a sequential manner, suffering from low-efficiency data acquisition. ::: ::: Recently, several excellent contributions on single-sensor imaging have been made by using single-resonant metamaterials9 or multi-resonant metamaterials10,11, which are typically spatio-temporal dispersive, combined with a sparsity-regularized reconstruction algorithm to treating the sparse microwave scene. Since such dispersive metamaterial can produce random radiation patterns over a broad frequency band excited by a broadband source, this system works as a single-shot and single-sensor imager9,10,11. However, the sparsity-regularized computational reconstruction algorithm involved only treats the imaging of well-separated sparse objects in the sense of the Rayleigh criterion, hence it is a low resolution imaging system10. In a later contribution by the same group, the imaging resolution problem has been addressed12, in which four-time shots of electromagnetic waves are required to collect enough measurement data. Therefore, it is a multi-shot and single-sensor system. More recently, a similar concept of passive single-sensor imager composed of a fan-like metamaterial waveguide was presented for detecting well-separated sparse acoustic sources13. This design also requires solving a sparsity-regularized convex optimization problem, making it a passive single-sensor system for low-resolution imaging. ::: ::: In this work, we propose the first broadband single-shot and single-sensor microwave imager for the super-resolution imaging with the aid of a spatio-temporal dispersive metasurface, capable of coupling the evanescent modes into the propagating modes. During the past decade, metamaterials and metasurfaces have shown great promises to control electromagnetic waves in flexible ways, as evidenced in the demonstration of a number of interesting devices and applications, such as ultrathin flat lenses14, analogy signal processing15, switchable plasmon coupler16, high-resolution hologram17, and various other functionalities18,19,20,21. Recently, we have demonstrated that a well-designed metasurface can make conversions among different wave components, either propagating or evanescent waves, resulting from the localized surface plasmon resonances22,23. In this sense, it is expected that the spatial information of the probed object can be sufficiently embodied into the data acquired by a single sensor fixed in the far-field region. ::: ::: We demonstrate to get the acceptable image quality through the procedure of simple data processing such as the standard minimum least square reconstruction algorithm, instead of using the sparsity-promoted iterative reconstruction algorithms3,4,5,6,7,8,9,10,11. The efficient conversion of evanescent waves to propagating waves can be achieved, which enables the super-resolution imaging by even using one single far-field sensor along with a single-shot excitation. In fact, the desired imaging resolution can be obtained by adjusting the distance between the probed object and the metasurface. When the object is placed in the vicinity of the metasurface, the super resolution is achieved. We show that the broadband single-shot and single-sensor imager brings us an expedient far-field super-resolution imaging scheme, which is capable of producing an image with resolution up to 0.2λ. Moreover, we experimentally demonstrate that the single-shot and single-sensor microwave imaging system has the unique ability to perform real-time data acquisition, and is capable of generating high-resolution images without mechanical scanning or antenna arrays.
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paper_title: Listening to Tags: Uplink RFID Measurements With an Open-Source Software-Defined Radio Tool

paper_content:

We present the software-defined radio (SDR) implementation of a Radio Frequency IDentification (RFID) Listener, a passive receive-only device that decodes the signals exchanged between the RFID Reader and the interrogated Tag following the Electronic Product Code Class-1 Generation-2 standard. Our RFID Listener is based on the open-source project GNU Radio. It provides complete flexibility and full control over the entire protocol stack down to the physical layer. As such, it can be used as a powerful but inexpensive tool for testing and measuring the performance of RFID systems in real operating conditions. In this paper, we leverage the SDR Listener for a number of experiments that, taken collectively, are illustrative of the potential of such tool for RFID research. First, we use it to test comparatively different timing recovery schemes for the reception of the Tag signal in uplink, through the analysis of bit-error statistics measured experimentally. We find that the scheme proposed by Harris and Rice based on polyphase filter bank displays excellent performance in this context, very close to the theoretical bound and with a gain of 5 dB over the more common Mueller and Muller scheme. Second, we use the Listener to evaluate the impact of frequency nulls in the uplink RFID channel for different indoor scenarios. We find that frequency nulls are pronounced particularly in the presence of metal objects and obstructions of the Fresnel zone, but frequency hopping is effective in counteracting the problem. Our experiments show that the signal backscattered by a passive Tag can be correctly received up to a distance of 35 m, with low-cost equipment and without highly directional antennas.
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paper_title: A Review of the Radio Frequency Non-destructive Testing for Carbon-fibre Composites

paper_content:

Abstract The purpose of this paper is to review recent research on the applications of existing non-destructive testing (NDT) techniques, especially radio frequency (RF) NDT, for carbon-fibre reinforced plastics (CFRP) composites. Electromagnetic properties of CFRP composites that are associated with RF NDT are discussed first. The anisotropic characteristic of the conductivity and the relationship between the penetration depth and conductivity should be paid much attention. Then, the well-established RF NDT including eddy current technique, microwave technique and RF-based thermography are well categorised into four types (i.e. electromagnetic induction, resonance, RF-based thermography and RF wave propagation) and demonstrated in detail. The example of impact damage detection using the induction and resonance methods is given. Some discussions on the development (like industrial-scale automated scanning, three-dimensional imaging, short-range ultra-wideband (UWB) imaging and the radio frequency identification technology (RFID)-based NDT) are presented.
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paper_title: Plasmonic Gas Sensing Using Nanocube Patch Antennas

paper_content:

© 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim. The ability of individual nanocube patch antennas, consisting of a silver nanocube separated from an Ag sheet by a thin fluoropolymer spacer, to act as subwavelength sensing elements is demonstrated. An increase in relative humidity (RH) causes the spacer to expand, which alters the resonance of the plasmon cavity mode formed between the cube and the sheet. Using bottom-up fabrication techniques, sensitivities up to 0.57 nm/% RH are recorded, and a resolution of better than 1% RH achieved with a rapid response time, making this the most effective single nanoparticle plasmonic humidity sensor to date. Finite-difference time-domain simulations are conducted to understand the effects of particle geometry on the sensitivity. This platform could be utilized to detect a variety of gases with an appropriate choice of spacer material, and could be scaled up to create a large-area metamaterial sensor, or used as a subwavelength sensing element with the potential for integration into plasmonic circuitry.
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paper_title: Current deflection NDE for the inspection and monitoring of pipes

paper_content:

Abstract Routine inspection of oil and gas pipes for time dependent degradation is essential. Pipelines are most commonly inspected using In-Line Inspection (ILI), however restrictions from pipe geometry, features or flow rate can prevent its use. Facility pipework rarely facilitates ILI, and external inspection often warrants the undesirable removal of the pipe insulation and cladding. This work investigates the applicability of a current deflection non-destructive evaluation technique for both the detection and growth monitoring of defects, particularly focusing on corrosion. Magnetic sensors are used to monitor variations in the spatial distribution of the induced magnetic flux density outside a pipe that arise from deflection of an injected electric current around inner or outer wall defects. An array of orthogonal magnetoresistive sensors has been used to measure the magnetic flux density surrounding six-inch schedule 40 seamless and welded carbon steel and austenitic steel pipes. The measurements were stable and repeatable to the order of 100 pT which suggests that the defect detection or growth monitoring of corrosion-type defects may be possible with a few amps of injected current when measurements are taken at around 50 mm lift-off. The sensitivity of the technique is dependent on factors including defect geometry, sensor lift-off, bends, variations in nominal pipe geometry or material properties, and the presence of ferromagnetic objects, each of which were investigated using either experiment or a validated finite element model.
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paper_title: Through-life Engineering for Nuclear Plant

paper_content:

Abstract Nuclear power stations are very capital intensive and need high load factors for economic operation. They and plants used for waste management and fuel cycle operations present unique challenges for operation, maintenance and repair constrained by hostile environments, shielding and radioactive contamination. It is therefore not surprising that this area was chosen for one of the first feasibility studies commissioned by the EPSRC Centre for Innovative Manufacture in Through-life Engineering Services. This paper summarises the outcome of that feasibility study. The main issues on materials and component degradation are described for current and future nuclear systems. The focus was on UK nuclear plant, in order to maximise industrial involvement and access to operational data, but the study is equally applicable to all nuclear plant around the world and there is scope for international collaboration. Recommendations are made on how degradation can be monitored and the specific challenges of the nuclear environment. Data management and processing are both key to implementation of optimised operation and maintenance and the decisions on repair and replacement of components. This information is also critical in establishing operational safety cases and applications for life extension and ultimately it also has to be used in new designs so that the economics of the plant can be optimised on the basis of through-life costs. Recommendations are made for future research programmes.
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paper_title: Toward Graphene-Based Passive UHF RFID Textile Tags: A Reliability Study

paper_content:

This paper discusses the fabrication, wireless performance, and reliability of graphene-based passive ultrahigh-frequency radio-frequency identification (RFID) tags on a fabric substrate. The conductive ink comprising functionalized graphene nanoplatelets is deposited directly on a cotton fabric substrate to fabricate the tag antennas. After attaching the chips, the tag performance is evaluated through wireless tag measurements before and after high-humidity conditions, bending, and stretching. Initially, the peak read range of the tag is about 1.6 m, which increases to 3.2 m in 100% humidity conditions. Additionally, after drying, the performance of the tag returns back to normal. In a bending test, the read range of a bent tag decreases below 1 m. Furthermore, the read range of the tag in a nonbended state gradually decreases and is about 1.1 m after 100 bending cycles. According to our measurements, stretching has a serious detrimental effect on these tags and they cannot be considered stretchable. However, these initial results show that this low-cost and eco-friendly graphene RFID tag has a remarkable and unique response to moisture and high reliability in harsh bending conditions. Overall, it also has a strong potential to be used in future wearable sensor applications.
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paper_title: Graphene Nanoflakes Printed Flexible Meandered-Line Dipole Antenna on Paper Substrate for Low-Cost RFID and Sensing Applications

paper_content:

In this letter, a graphene nanoflakes printed antenna is presented. Graphene nanoflakes conductive ink has been screen-printed on paper substrate and compressed to achieve the conductivity of $\text{0.43} \times {\text{10}^{\text{5}}} \hbox{\,S/m}$ . Low-profile meandered-line dipole antenna has been fabricated as a proof of concept due to its electrically small size and simple structure. The maximum gain is measured to be ${-}\hbox{4 dBi}$ , the ${-} \hbox{10-dB}$ bandwidth ranges from 984 to 1052 MHz (6.67%), and the radiation pattern is verified as being typical radiation patterns of a dipole-type antenna. The radiation efficiency is 32%. The measurement results reveal that graphene nanoflakes printed antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns for mid- and short-range RFID, and sensing applications. Furthermore, screen-printing technique employed in this work is of extremely low cost and capable of producing antennas in mass production.
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paper_title: Directly Printable Moisture Sensor Tag for Intelligent Packaging

paper_content:

A compact, flexible 24-b dual-polarized chipless radio frequency identification tag with a size of 20.6mm × 19.9mm is realized. The tag structure is optimized and analyzed for Taconic, Kapton TIN and organic substrate. The prototype fabricated on TIP photopaper with silver nanoparticles-based conductive ink is exhibiting a behavior of moisture sensor. The proposed moisture sensor tag has a bandwidth of 13.5GTIz. The direct printability of moisture sensor tag makes it suitable for intelligent packaging and various low-cost applications.
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paper_title: RFID Tag as a Sensor - A Review on the Innovative Designs and Applications

paper_content:

Abstract The Radio Frequency Identification (RFID) technology has gained interests in both academia and industry since its invention. In addition to the applications in access control and supply chain, RFID is also a cost-efficient solution for Non-Destructive Testing (NDT) and pervasive monitoring. The battery free RFID tags are used as independent electromagnetic sensors or energy harvesting and data transmission interface of sensor modules for different measurement purposes. This review paper aims to provide a comprehensive overview of the innovative designs and applications of RFID sensor technology with new insights, identify the technical challenges, and outline the future perspectives. With a brief introduction to the fundamentals of RFID measurement, the enabling technologies and recent technical progress are illustrated, followed by an extensive discussion of the novel designs and applications. Then, based on an in-depth analysis, the potential constraints are identified and the envisaged future directions are suggested, including printable/wearable RFID, System-on-Chip (SoC), ultra-low power, etc. The comprehensive discussion of RFID sensor technology will be inspirational and useful for academic and industrial communities in investigating, developing, and applying RFID for various measurement applications.
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paper_title: Sensor-Enabled RFID System for Monitoring Arm Activity: Reliability and Validity

paper_content:

After stroke, capacity to complete tasks in the treatment setting with the more-affected arm is an unreliable index of actual use of that extremity in daily life. Available objective methods for monitoring real-world arm use rely on placing movement sensors on patients. These methods provide information on amount but not type of arm activity, e.g., functional versus nonfunctional movement. This paper presents an approach that places sensors on patients and household objects, overcoming this limitation. An accelerometer and the transmitter component of a radio-frequency proximity sensor are attached to objects; the receiver component is attached to the arm of interest. The receiver triggers an on-board radio-frequency identification tag to signal proximity when that arm is within 23 cm of an instrumented object. In benchmark testing, this system detected perfectly which arm was used to move the target object on 200 trials. In a laboratory study with 35 undergraduates, increasing the amount of time target objects were moved with the arm of interest resulted in a corresponding increase in system output (p <; 0.0001) . Moreover, measurement error was low (≤2.5%). The results support this system's reliability and validity in individuals with unimpaired movement; testing is now warranted in stroke patients.
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paper_title: The opportunities and challenges associated with wireless interconnects in aircraft

paper_content:

Utilizing wireless data buses in aircraft has the potential to increase reliability, reduce weight, and improve flexibility and adaptability. In this article, the implementation of wirelessly connected interconnects in aircraft is introduced from a broad perspective, considering the issues of radio systems, propagation, antennas, and applications. Existing avionics systems are discussed briefly in order to understand the requirements placed on a wireless system and the specification it must meet. A review of existing wireless protocols and commercial off the shelf systems is provided, explaining where systems including ZigBee and IEEE 802.11 are suitable and unsuitable for a wireless aircraft application, and it is found that no existing system can be used exclusively. It is shown quantitatively that the propagation environment is expected to have high delay spreads and the negative impact of this on system reliability is shown through simulation and measurements. The application and benefits of a direct write, in-situ, metallic deposition procedure are dis- cussed for the placement of antennas, sensors, and their associated electronics. By writing electronics onto a surface, fitting and retrofitting are made much easier without the need to affect the aircraft structure, and this enables a more flexible wireless system. The opportunities, advantages and challenges for such a technology within the wireless aircraft are discussed.
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paper_title: Experimental study on a feasibility of using electromagnetic wave cylindrical cavity sensor to monitor the percentage of water fraction in a two phase system

paper_content:

This study proposed a microwave sensor system to monitor single and two phase flow systems. The microwave sensing technology in this study utilises the resonant frequencies that occur in a cylindrical cavity and monitor the changes in the permittivity of the measured phases to differentiate between the volume fractions of air, water and oil. The sensor system used two port configuration S21 (acted as transmitter and receiver) to detect the fluids inside the pipe. In principle, the strong polarity of water molecules results in higher permittivity in comparison to other materials. A tiny change of water fraction will cause a significant frequency shift. Electromagnetic waves in the range of 5 GHz to 5.7 GHz have been used to analyse a two phase air-water and oil-water stratified flow in a pipeline. The results demonstrated the potential of a microwave sensing technique to be used for the two phase systems monitoring. A significant shift in the frequency and change in the amplitude clearly shows the percentage fraction change of water in the pipe. The temperature study of water also demonstrated the independence of microwave analysis technique to the temperature change. This is accounted to overlapping modes negating the affect. Statistical analysis of the amplitude data for two phase systems shows a linear relationship of the change in water percentage to the amplitude. The electromagnetic wave cavity sensor successfully detected the change in the water fraction inside the pipe between 0-100%. The results show that the technique can be developed further to reduce the anomalies in the existing microwave sensor.
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Title: A Review of Passive RFID Tag Antenna-Based Sensors and Systems for Structural Health Monitoring Applications

Section 1: Introduction
Description 1: Introduce the topic of structural health monitoring (SHM) and the importance of using passive RFID tag antenna-based sensors for this purpose.

Section 2: Methodology and Categorization
Description 2: Explain the research methodology employed for examining the adoption of RFID in SHM, including literature review and systematic study.

Section 3: Context and Content
Description 3: Discuss the design and development challenges of passive antenna sensors and systems, focusing on the tradeoff among sensing, communication, resolution, sensitivity, size, read range, and robustness.

Section 4: Communication Issues and Solutions
Description 4: Present a detailed discussion on backscattered signals from passive antenna sensors, measurable parameters, and challenges and solutions for wireless communication.

Section 5: Sensing-Oriented Issues and Solutions
Description 5: Explore challenges and state-of-the-art progress in passive antenna sensors from four aspects: defect types and antenna topologies, materials and manufacturing technologies, sensing variable and measurement uncertainties, and feature extraction and characterization.

Section 6: Defect Types and Antenna Topologies
Description 6: Describe various defect types and antenna topologies for passive antenna sensors, highlighting design considerations and variations.

Section 7: Strain Detection and Characterization
Description 7: Summarize the recent advancements in strain detection using passive antenna sensors and describe various designs and their sensitivities.

Section 8: Crack Detection and Characterization
Description 8: Provide an overview of the development of crack detection and characterization using passive antenna sensors, focusing on different techniques and their effectiveness.

Section 9: Corrosion Detection and Characterization
Description 9: Discuss methods and advancements in corrosion detection using passive antenna sensors and summarize key developments.

Section 10: Materials and Manufacturing Technologies
Description 10: Examine the materials and manufacturing technologies relevant to passive antenna sensors, including printing technologies and their benefits.

Section 11: Sensing Variables and Measurement Uncertainties
Description 11: Discuss the measurement uncertainties and challenges associated with sensing variables in passive antenna sensor systems.

Section 12: Feature Extraction and Characterization
Description 12: Explain the process of feature extraction from sensing variables and discuss methods to mitigate multiple influences for robust sensing.

Section 13: Future Trends and Perspectives
Description 13: Explore the future trends and perspectives for passive antenna sensors and systems, categorizing into three directions: networking and standardization, more ubiquitous and adaptable, and more simple and reliable systems.

Section 14: Integration and Standardization
Description 14: Discuss the significance of integration and standardization of passive antenna sensors within broader sensor networks and IoT infrastructure.

Section 15: More Ubiquitous and Adaptable
Description 15: Discuss potential developments for making passive antenna sensors more ubiquitous and adaptable for various applications, including health monitoring and environmental sensing.

Section 16: More Simple and Reliable
Description 16: Present approaches to simplify and increase the reliability of passive antenna sensors, highlighting innovations such as SDR and chipless systems.

Section 17: UK Highlights
Description 17: Provide an overview of the current research and future directions for passive antenna sensors in the UK, including specific applications and potential collaborations.

Section 18: Conclusions
Description 18: Summarize the main findings of the review, discussing the potential of passive antenna sensors for SHM and other applications, and identify future research directions.