Wearable Antennas: A Review of Materials, Structures, and Innovative Features for Autonomous Communication and Sensing
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paper_title: Next Generation 5G Wireless Networks: A Comprehensive Survey

paper_content:

The vision of next generation 5G wireless communications lies in providing very high data rates (typically of Gbps order), extremely low latency, manifold increase in base station capacity, and significant improvement in users’ perceived quality of service (QoS), compared to current 4G LTE networks. Ever increasing proliferation of smart devices, introduction of new emerging multimedia applications, together with an exponential rise in wireless data (multimedia) demand and usage is already creating a significant burden on existing cellular networks. 5G wireless systems, with improved data rates, capacity, latency, and QoS are expected to be the panacea of most of the current cellular networks’ problems. In this survey, we make an exhaustive review of wireless evolution toward 5G networks. We first discuss the new architectural changes associated with the radio access network (RAN) design, including air interfaces, smart antennas, cloud and heterogeneous RAN. Subsequently, we make an in-depth survey of underlying novel mm-wave physical layer technologies, encompassing new channel model estimation, directional antenna design, beamforming algorithms, and massive MIMO technologies. Next, the details of MAC layer protocols and multiplexing schemes needed to efficiently support this new physical layer are discussed. We also look into the killer applications, considered as the major driving force behind 5G. In order to understand the improved user experience, we provide highlights of new QoS, QoE, and SON features associated with the 5G evolution. For alleviating the increased network energy consumption and operating expenditure, we make a detail review on energy awareness and cost efficiency. As understanding the current status of 5G implementation is important for its eventual commercialization, we also discuss relevant field trials, drive tests, and simulation experiments. Finally, we point out major existing research issues and identify possible future research directions.
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paper_title: Smart wearable systems: Current status and future challenges

paper_content:

Objective: Extensive efforts have been made in both academia and industry in the research and development of smart wearable systems (SWS) for health monitoring (HM). Primarily influenced by skyrocketing healthcare costs and supported by recent technological advances in micro- and nanotechnologies, miniaturisation of sensors, and smart fabrics, the continuous advances in SWS will progressively change the landscape of healthcare by allowing individual management and continuous monitoring of a patient's health status. Consisting of various components and devices, ranging from sensors and actuators to multimedia devices, these systems support complex healthcare applications and enable low-cost wearable, non-invasive alternatives for continuous 24-h monitoring of health, activity, mobility, and mental status, both indoors and outdoors. Our objective has been to examine the current research in wearable to serve as references for researchers and provide perspectives for future research. Methods: Herein, we review the current research and development of and the challenges facing SWS for HM, focusing on multi-parameter physiological sensor systems and activity and mobility measurement system designs that reliably measure mobility or vital signs and integrate real-time decision support processing for disease prevention, symptom detection, and diagnosis. For this literature review, we have chosen specific selection criteria to include papers in which wearable systems or devices are covered. Results: We describe the state of the art in SWS and provide a survey of recent implementations of wearable health-care systems. We describe current issues, challenges, and prospects of SWS. Conclusion: We conclude by identifying the future challenges facing SWS for HM.
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paper_title: Design and Characterization of Purely Textile Patch Antennas

paper_content:

In this paper, we present four purely textile patch antennas for Bluetooth applications in wearable computing using the frequency range around 2.4 GHz. The textile materials and the planar antenna shape provide a smooth integration into clothing while preserving the typical properties of textiles. The four antennas differ in the deployed materials and in the antenna polarization, but all of them feature a microstrip line as antenna feed. We have developed a manufacturing process that guarantees unaffected electrical behavior of the individual materials when composed to an antenna. Thus, the conductive textiles possess a sheet resistance of less than 1Omega/squarein order to keep losses at a minimum. The process also satisfies our requirements in terms of accuracy meeting the Bluetooth specifications. Our investigations not only characterize the performance of the antennas in planar shape, but also under defined bending conditions that resemble those of a worn garment. We show that the antennas can withstand clothing bends down to a radius of 37.5 mm without violating specifications
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paper_title: Stretchable nanoparticle conductors with self-organized conductive pathways

paper_content:

Stretchable conductors have many applications, from flexible electronics to medical implants; here polyurethane is filled with gold nanoparticles to give a composite with tunable viscoelastic properties arising from the dynamic self-organization of the nanoparticles under stress.
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paper_title: Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires

paper_content:

We demonstrate a class of microstrip patch antennas that are stretchable, mechanically tunable, and reversibly deformable. The radiating element of the antenna consists of highly conductive and stretchable material with screen-printed silver nanowires embedded in the surface layer of an elastomeric substrate. A 3-GHz microstrip patch antenna and a 6-GHz 2-element patch array are fabricated. Radiating properties of the antennas are characterized under tensile strain and agree well with the simulation results. The antenna is reconfigurable because the resonant frequency is a function of the applied tensile strain. The antenna is thus well suited for applications like wireless strain sensing. The material and fabrication technique reported here could be extended to achieve other types of stretchable antennas with more complex patterns and multilayer structures.
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paper_title: A Transparent and Flexible Polymer-Fabric Tissue UWB Antenna for Future Wireless Networks

paper_content:

A flexible and transparent ultrawideband (UWB) antenna that uses a transparent conductive fabric tissue on a polydimethylsiloxane (PDMS) substrate is presented in this letter. The fabric tissue is integrated onto the PDMS having a thickness of 2 mm to produce an efficient UWB antenna. To achieve this, first, a sheet of the conductive fabric tissue was attached to the upper and lower surface of a PDMS layer to produce a fabric panel with three layers. Then, the radiating elements were formulated precisely in the upper and lower layers, using a laser machine. The measured transparency of the fabric tissue and the PDMS can attain a value of more than 70% and 90%, respectively, in the visible spectrum. The antenna operates at a 2.2-25-GHz band with average efficiency of over 75% throughout the operating band and shows satisfactory gain and a good radiation pattern. It performs well under bending conditions, as ensured by its measurements. The proposed antenna's optical transparency, mechanical flexible properties, and seamless integration process indicate its promising potential in a variety of transparent antenna applications for future wireless networks.
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paper_title: Textile Materials for the Design of Wearable Antennas: A Survey

paper_content:

In the broad context of Wireless Body Sensor Networks for healthcare and pervasive applications, the design of wearable antennas offers the possibility of ubiquitous monitoring, communication and energy harvesting and storage. Specific requirements for wearable antennas are a planar structure and flexible construction materials. Several properties of the materials influence the behaviour of the antenna. For instance, the bandwidth and the efficiency of a planar microstrip antenna are mainly determined by the permittivity and the thickness of the substrate. The use of textiles in wearable antennas requires the characterization of their properties. Specific electrical conductive textiles are available on the market and have been successfully used. Ordinary textile fabrics have been used as substrates. However, little information can be found on the electromagnetic properties of regular textiles. Therefore this paper is mainly focused on the analysis of the dielectric properties of normal fabrics. In general, textiles present a very low dielectric constant that reduces the surface wave losses and increases the impedance bandwidth of the antenna. However, textile materials are constantly exchanging water molecules with the surroundings, which affects their electromagnetic properties. In addition, textile fabrics are porous, anisotropic and compressible materials whose thickness and density might change with low pressures. Therefore it is important to know how these characteristics influence the behaviour of the antenna in order to minimize unwanted effects. This paper presents a survey of the key points for the design and development of textile antennas, from the choice of the textile materials to the framing of the antenna. An analysis of the textile materials that have been used is also presented.
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paper_title: Effect of textile materials on wearable antenna performance: a case study of GPS antennas

paper_content:

Recently, textile antennas have been presented in international conferences. These studies have demonstrated that fabrics are suitable for microstrip antenna substrates. In this paper, our study focuses on the characterization of different synthetic fabrics suitable for circular polarized micro-strip antennas. Special attention is paid to GPS antennas. Five different synthetic textile materials are chosen for the comparison. The word textile is typically used for antenna class and fabric to describe a particular material. However, in many cases these words are interchangeable.
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paper_title: Textile UWB Antenna Bending and Wet Performances

paper_content:

The vision and ideas of wearable computing systems describe future electronic systems as an integral part of our everyday clothing that provides the wearer with such intelligent personal assistants. Recently, there has been growing interest in the antenna community to merge between wearable systems technology, ultrawideband (UWB) technology and textile technology. This work aimed to make closer steps towards real wearability by investigating the possibilities of designing wearable UWB antenna where textile materials are used for the substrate as well as the conducting parts of the designed antenna. Two types of conducting materials have been used for conducting parts, while a nonconducting fabric has been used as antenna substrate material. A set of comparative results of the proposed design were presented and discussed. Moreover, effects on the return loss by means of measurements for each fabricated antenna prototype under bent and fully wet conditions were discussed in more details.
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paper_title: Flexible and reversibly deformable radio-frequency antenna based on stretchable SWCNTs/PANI/Lycra conductive fabric

paper_content:

We demonstrated a flexible and reversibly deformable radio-frequency antenna based on SWCNTs/PANI/Lycra conductive fabric and semipermeable film for wireless wearable communications applications. The conductive fabric fabricated by using the 'dip and dry' process exhibits good flexibility, electrical stability, stretchability and mechanical properties, and a high electrical conductivity (with low sheet resistance of ~35 Ω/sq) was obtained based on the SWCNTs/PANI synergistic conductive network. The morphology of the semipermeable film was investigated to further illustrate the waterproof breathable features. Meanwhile, the modeling, fabrication procedure and radiating properties of the radio-frequency textile antenna worked at 2.45 GHz were systematically illustrated. The measured reflection coefficient, VSWR and the −10 dB bandwidth is ~−18.6 dB, 1.58 and ~270 MHz respectively, which agreed well with the simulation results. Furthermore, the results indicate that the design methodology for the radio-frequency textile antenna could have promising applications in flexible and reversibly deformable antennas for wearable wireless communications systems.
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paper_title: A Method to Realize Robust Flexible Electronically Tunable Antennas Using Polymer-Embedded Conductive Fabric

paper_content:

A new approach to realize robust, flexible, and electronically tunable wearable antennas is presented. Conductive fabric is used to form the conducting parts of the antenna on a polydimethylsiloxane (PDMS) substrate. Then the antenna and the lumped (active and passive) elements, required for electronic tuning and RF choking, are fully encapsulated with additional layers of PDMS. As a concept demonstration, a new frequency-reconfigurable antenna has been designed and fabricated. The details of the prototype manufacturing process are described. Two UWB human muscle equivalent phantoms were also fabricated for testing purposes. Furthermore, the antenna was subjected to several investigations on its RF performance (both in free space and on a flat phantom) and mechanical stability. The latter includes bending tests on several locations on a human-body shaped phantom and washing in a household washing machine. Good agreement between predicted and experimental results (both in free space and on the phantom) is observed, validating the proposed concept. The tests demonstrated that lumped components and other antenna parts remained intact and in working order even under extreme bending (to a bending radius of 28 mm) and after washing, thus maintaining the overall antenna performance including good frequency reconfigurability from 2.3 to 2.68 GHz. To the best of our knowledge, all these features have never been demonstrated in previously published electronically tunable antennas.
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paper_title: Highly stretchable electric circuits from a composite material of silver nanoparticles and elastomeric fibres.

paper_content:

Conductive electrodes and electric circuits that can remain active and electrically stable under large mechanical deformations are highly desirable for applications such as flexible displays, field-effect transistors, energy-related devices, smart clothing and actuators. However, high conductivity and stretchability seem to be mutually exclusive parameters. The most promising solution to this problem has been to use one-dimensional nanostructures such as carbon nanotubes and metal nanowires coated on a stretchable fabric, metal stripes with a wavy geometry, composite elastomers embedding conductive fillers and interpenetrating networks of a liquid metal and rubber. At present, the conductivity values at large strains remain too low to satisfy requirements for practical applications. Moreover, the ability to make arbitrary patterns over large areas is also desirable. Here, we introduce a conductive composite mat of silver nanoparticles and rubber fibres that allows the formation of highly stretchable circuits through a fabrication process that is compatible with any substrate and scalable for large-area applications. A silver nanoparticle precursor is absorbed in electrospun poly (styrene-block-butadiene-block-styrene) (SBS) rubber fibres and then converted into silver nanoparticles directly in the fibre mat. Percolation of the silver nanoparticles inside the fibres leads to a high bulk conductivity, which is preserved at large deformations (σ ≈ 2,200 S cm(-1) at 100% strain for a 150-µm-thick mat). We design electric circuits directly on the electrospun fibre mat by nozzle printing, inkjet printing and spray printing of the precursor solution and fabricate a highly stretchable antenna, a strain sensor and a highly stretchable light-emitting diode as examples of applications.
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paper_title: Conductive polymers: Towards a smart biomaterial for tissue engineering

paper_content:

Abstract Developing stimulus-responsive biomaterials with easy-to-tailor properties is a highly desired goal of the tissue engineering community. A novel type of electroactive biomaterial, the conductive polymer, promises to become one such material. Conductive polymers are already used in fuel cells, computer displays and microsurgical tools, and are now finding applications in the field of biomaterials. These versatile polymers can be synthesised alone, as hydrogels, combined into composites or electrospun into microfibres. They can be created to be biocompatible and biodegradable. Their physical properties can easily be optimized for a specific application through binding biologically important molecules into the polymer using one of the many available methods for their functionalization. Their conductive nature allows cells or tissue cultured upon them to be stimulated, the polymers’ own physical properties to be influenced post-synthesis and the drugs bound in them released, through the application of an electrical signal. It is thus little wonder that these polymers are becoming very important materials for biosensors, neural implants, drug delivery devices and tissue engineering scaffolds. Focusing mainly on polypyrrole, polyaniline and poly(3,4-ethylenedioxythiophene), we review conductive polymers from the perspective of tissue engineering. The basic properties of conductive polymers, their chemical and electrochemical synthesis, the phenomena underlying their conductivity and the ways to tailor their properties (functionalization, composites, etc.) are discussed.
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paper_title: Fabrication of highly conductive stretchable textile with silver nanoparticles

paper_content:

A method has been developed for the deposition of conductive metals onto fibers within textile structures. The resultant fabric exhibited full metal coverage with good adhesion to the fibers. As well as being conductive and extremely flexible with little effect on its handle and drape properties. In order to make a conductive fabric, cotton was first mercerized followed by immersion in poly(diallyldimethylammonium chloride) solution. Silver nitrate was then reduced on the surface of the fabric which allowed formation of silver nanoparticles. Scanning electron microscopy studies of the conductive fabric confirmed the deposition of the polymer resulted in more uniform attachment of nanosilver to the surface of fibers. The fabric was then electroless plated to obtain a surface resistivity less than 0.2 Ω/square. This method can be used for woven, non-woven and knitted types of fabric. It can be applied on to the fibers before or after being made into a textile.
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paper_title: A Stretchable RF Antenna With Silver Nanowires

paper_content:

A stretchable, flexible antenna fabricated with silver nanowires (AgNW) and polydimethylsiloxane (PDMS) is presented. Highly conductive AgNWs coupled with mechanically flexibility and durable PDMS are shown to produce promising results for RF sensing. The RF antenna is designed as a 1.5-GHz microstrip patch antenna using the transmission-line model. The resonance frequency of the antenna shifts in response to the applied force/strain, making the configuration suitable for wireless sensing applications.
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paper_title: A highly deformable conducting traces for printed antennas and interconnects: silver/fluoropolymer composite amalgamated by triethanolamine

paper_content:

Stretchable conducting traces are the key component to realize wearable healthcare electronics; a conductor material that can withstand high strain conditions can be crucial. Here, we describe a simple fabrication pathway to achieve stretchable conductive ink for printing. Specifically, silver flakes and fluorine rubber are amalgamated by the aid of triethanolamine (TEA), which enhanced the compatibility of the components in solution state where methylisobutylketone is the co-solvent. Moreover, TEA plasticizes the composites after the printing and drying of the solvent, causing the composite to deform freely without losing conductivity. The composite exhibits a conductivity value of 8.49 × 104 S m−1 at rest. The printed composite itself is not mechanically resilient after plastic deformation, but it has remarkable adhesion on elastomeric substrates. Thus, the printed ink on elastomers allows stretchable trace that can accommodate repeated stretching/releasing cycles. We fabricate and characterize stretchable printed antenna with three different designs (loop, patch, and bowtie) for the application of skin-adhesive electronics.
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paper_title: Design and fabrication of an E-shaped wearable textile antenna on PVB-coated hydrophobic polyester fabric

paper_content:

In this paper, we investigated the simulation and fabrication of an E-shaped microstrip patch antenna realized on multilayered polyester fabric suitable for WiMAX (Worldwide Interoperability for Microwave Access) applications. The main challenges while designing a textile antenna were to provide adequate thickness, surface uniformity and water wettability to the textile substrate. Here, three layers of polyester fabric were stacked together in order to obtain sufficient thickness, and were subsequently dip coated with polyvinyl butyral (PVB) solution. The PVB-coated polyester fabric showed a hydrophobic nature with a contact angle of 91°. The RMS roughness of the uncoated and PVB-coated polyester fabric was about 341 nm and 15 nm respectively. The promising properties, such as their flexibility, light weight and cost effectiveness, enable effortless integration of the proposed antenna into clothes like polyester jackets. Simulated and measured results in terms of return loss as well as gain were showcased to confirm the usefulness of the fabricated prototype. The fabricated antenna successfully operates at 3.37 GHz with a return loss of 21 dB and a maximum measured gain of 3.6 dB.
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paper_title: Polydimethylsiloxane-Embedded Conductive Fabric: Characterization and Application for Realization of Robust Passive and Active Flexible Wearable Antennas

paper_content:

We present our study on polydimethylsiloxane (PDMS)-embedded conductive fabric, which we propose as a simple yet effective solution to the challenging issue of poor PDMS-metal adhesion, allowing for a relatively easy realization of robust flexible antennas for wearable applications. The method combines the use of conductive fabric as a radiator with PDMS, which acts as the substrate and a protective encapsulation simultaneously. For the first time, a holistic study on the mechanical and electrical properties of the proposed combination of materials is presented thoroughly using a number of fabricated samples. As concept demonstrations, a microstrip patch and a reconfigurable patch antenna are fabricated using the proposed technique to validate the idea. The inclusion of a PDMS-ceramic composite as part of the antenna’s substrate, which leads to over 50% reduction in the size compared with a pure PDMS, is also demonstrated to showcase further the versatility of the proposed technique. The fabricated antennas are tested in several wearable scenarios and consistent performance including reconfigurability is obtained even after the antennas are exposed to harsh environments, i.e., extreme bending and machine-washing.
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paper_title: Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires

paper_content:

We demonstrate a class of microstrip patch antennas that are stretchable, mechanically tunable, and reversibly deformable. The radiating element of the antenna consists of highly conductive and stretchable material with screen-printed silver nanowires embedded in the surface layer of an elastomeric substrate. A 3-GHz microstrip patch antenna and a 6-GHz 2-element patch array are fabricated. Radiating properties of the antennas are characterized under tensile strain and agree well with the simulation results. The antenna is reconfigurable because the resonant frequency is a function of the applied tensile strain. The antenna is thus well suited for applications like wireless strain sensing. The material and fabrication technique reported here could be extended to achieve other types of stretchable antennas with more complex patterns and multilayer structures.
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paper_title: A wearable tracking device inkjet-printed on textile

paper_content:

Despite the abundance of localization applications, the tracking devices have never been truly realized in E-textiles. Standard printed circuit board (PCB)-based devices are obtrusive and rigid and hence not suitable for textile based implementations. An attractive option would be direct printing of circuit layout on the textile itself, negating the use of rigid PCB materials. However, high surface roughness and porosity of textiles prevents efficient and reliable printing of electronics on textile. In this work, by printing an interface layer on the textile first, a complete localization circuit integrated with an antenna has been inkjet-printed on the textile for the first time. Printed conductive traces were optimized in terms of conductivity and resolution by controlling the number of over-printed layers. The tracking device determines the wearer's position using WiFi and this information can be displayed on any internet-enabled device, such as smart phone. The device is compact (55mm45mm) and lightweight (22g with 500mAh battery) for people to comfortably wear it and can be easily concealed in case discretion is required. The device operates at 2.4GHz communicated up to a distance of 55m, with localization accuracy of up to 8m.
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paper_title: Sol–gel synthesis of transition-metal doped ferrite compounds with potential flexible, dielectric and electromagnetic properties

paper_content:

A compact and flexible dielectric substrate with efficient electromagnetic performances both in flat and bending conditions are presented in this paper. The proposed substrates, for potential microwave radiator applications have been fabricated from Mn doped zinc ferrite compounds by sol–gel method. Prepared MnxZn(1−x)Fe2O4, (x = 0.0, 0.2, 0.4, 0.6, 0.8) substrates were analysed structurally by X-ray diffraction spectroscopy and morphologically studied by scanning electron microscopy. We studied the optical and dielectric properties in the microwave range to evaluate the new material as a dielectric substrate for microwave applications. The prepared flexible substrates exhibit high dielectric permittivity and low dielectric loss in the microwave frequency range. For the proof of concept, the electromagnetic performances both at flat and bending conditions were verified by loading an electromagnetic radiator. We report the detailed measured performances of the reflection coefficient below −10 dB, average efficiency above 73% and average realized gain above 1.5 dBi within the operational bandwidth for the first time. The measured stable omnidirectional radiation patterns both in flat and bending conditions also confirm the potential of the proposed material to be used as a new flexible dielectric substrate.
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paper_title: Flexible and reversibly deformable radio-frequency antenna based on stretchable SWCNTs/PANI/Lycra conductive fabric

paper_content:

We demonstrated a flexible and reversibly deformable radio-frequency antenna based on SWCNTs/PANI/Lycra conductive fabric and semipermeable film for wireless wearable communications applications. The conductive fabric fabricated by using the 'dip and dry' process exhibits good flexibility, electrical stability, stretchability and mechanical properties, and a high electrical conductivity (with low sheet resistance of ~35 Ω/sq) was obtained based on the SWCNTs/PANI synergistic conductive network. The morphology of the semipermeable film was investigated to further illustrate the waterproof breathable features. Meanwhile, the modeling, fabrication procedure and radiating properties of the radio-frequency textile antenna worked at 2.45 GHz were systematically illustrated. The measured reflection coefficient, VSWR and the −10 dB bandwidth is ~−18.6 dB, 1.58 and ~270 MHz respectively, which agreed well with the simulation results. Furthermore, the results indicate that the design methodology for the radio-frequency textile antenna could have promising applications in flexible and reversibly deformable antennas for wearable wireless communications systems.
---
paper_title: A Method to Realize Robust Flexible Electronically Tunable Antennas Using Polymer-Embedded Conductive Fabric

paper_content:

A new approach to realize robust, flexible, and electronically tunable wearable antennas is presented. Conductive fabric is used to form the conducting parts of the antenna on a polydimethylsiloxane (PDMS) substrate. Then the antenna and the lumped (active and passive) elements, required for electronic tuning and RF choking, are fully encapsulated with additional layers of PDMS. As a concept demonstration, a new frequency-reconfigurable antenna has been designed and fabricated. The details of the prototype manufacturing process are described. Two UWB human muscle equivalent phantoms were also fabricated for testing purposes. Furthermore, the antenna was subjected to several investigations on its RF performance (both in free space and on a flat phantom) and mechanical stability. The latter includes bending tests on several locations on a human-body shaped phantom and washing in a household washing machine. Good agreement between predicted and experimental results (both in free space and on the phantom) is observed, validating the proposed concept. The tests demonstrated that lumped components and other antenna parts remained intact and in working order even under extreme bending (to a bending radius of 28 mm) and after washing, thus maintaining the overall antenna performance including good frequency reconfigurability from 2.3 to 2.68 GHz. To the best of our knowledge, all these features have never been demonstrated in previously published electronically tunable antennas.
---
paper_title: A highly deformable conducting traces for printed antennas and interconnects: silver/fluoropolymer composite amalgamated by triethanolamine

paper_content:

Stretchable conducting traces are the key component to realize wearable healthcare electronics; a conductor material that can withstand high strain conditions can be crucial. Here, we describe a simple fabrication pathway to achieve stretchable conductive ink for printing. Specifically, silver flakes and fluorine rubber are amalgamated by the aid of triethanolamine (TEA), which enhanced the compatibility of the components in solution state where methylisobutylketone is the co-solvent. Moreover, TEA plasticizes the composites after the printing and drying of the solvent, causing the composite to deform freely without losing conductivity. The composite exhibits a conductivity value of 8.49 × 104 S m−1 at rest. The printed composite itself is not mechanically resilient after plastic deformation, but it has remarkable adhesion on elastomeric substrates. Thus, the printed ink on elastomers allows stretchable trace that can accommodate repeated stretching/releasing cycles. We fabricate and characterize stretchable printed antenna with three different designs (loop, patch, and bowtie) for the application of skin-adhesive electronics.
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paper_title: Silicones for Stretchable and Durable Soft Devices: Beyond Sylgard-184.

paper_content:

This paper identifies and characterizes silicone elastomers that are well-suited for fabricating highly stretchable and tear-resistant devices that require interfacial bonding by plasma or UV ozone treatment. The ability to bond two or more pieces of molded silicone is important for creating microfluidic channels, chambers for pneumatically driven soft robotics, and other soft and stretchable devices. Sylgard-184 is a popular silicone, particularly for microfluidic applications. However, its low elongation at break (∼100% strain) and moderate tear strength (∼3 N/mm) make it unsuitable for emerging, mechanically demanding applications of silicone. In contrast, commercial silicones, such as Dragon Skin, have excellent mechanical properties yet are difficult to plasma-bond, likely because of the presence of silicone oils that soften the network yet migrate to the surface and interfere with plasma bonding. We found that extracting silicone oligomers from these soft networks allows these materials to bond but only when the Shore hardness exceeds a value of 15 A. It is also possible to mix highly stretchable silicones (Dragon Skin and Ecoflex) with Sylgard-184 to create silicones with intermediate mechanical properties; interestingly, these blends also only bond when the hardness exceeds 15 A. Eight different Pt-cured silicones were also screened; again, only those with Shore hardness above 15 A plasma-bond. The most promising silicones from this study are Sylgard-186 and Elastosil-M4130 and M4630, which exhibit a large deformation (>200% elongation at break), high tear strength (>12 N/mm), and strong plasma bonding. To illustrate the utility of these silicones, we created stretchable electrodes by injecting a liquid metal into microchannels created using such silicones, which may find use in soft robotics, electronic skin, and stretchable energy storage devices.
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paper_title: Polydimethylsiloxane-Embedded Conductive Fabric: Characterization and Application for Realization of Robust Passive and Active Flexible Wearable Antennas

paper_content:

We present our study on polydimethylsiloxane (PDMS)-embedded conductive fabric, which we propose as a simple yet effective solution to the challenging issue of poor PDMS-metal adhesion, allowing for a relatively easy realization of robust flexible antennas for wearable applications. The method combines the use of conductive fabric as a radiator with PDMS, which acts as the substrate and a protective encapsulation simultaneously. For the first time, a holistic study on the mechanical and electrical properties of the proposed combination of materials is presented thoroughly using a number of fabricated samples. As concept demonstrations, a microstrip patch and a reconfigurable patch antenna are fabricated using the proposed technique to validate the idea. The inclusion of a PDMS-ceramic composite as part of the antenna’s substrate, which leads to over 50% reduction in the size compared with a pure PDMS, is also demonstrated to showcase further the versatility of the proposed technique. The fabricated antennas are tested in several wearable scenarios and consistent performance including reconfigurability is obtained even after the antennas are exposed to harsh environments, i.e., extreme bending and machine-washing.
---
paper_title: Sol–gel synthesis of transition-metal doped ferrite compounds with potential flexible, dielectric and electromagnetic properties

paper_content:

A compact and flexible dielectric substrate with efficient electromagnetic performances both in flat and bending conditions are presented in this paper. The proposed substrates, for potential microwave radiator applications have been fabricated from Mn doped zinc ferrite compounds by sol–gel method. Prepared MnxZn(1−x)Fe2O4, (x = 0.0, 0.2, 0.4, 0.6, 0.8) substrates were analysed structurally by X-ray diffraction spectroscopy and morphologically studied by scanning electron microscopy. We studied the optical and dielectric properties in the microwave range to evaluate the new material as a dielectric substrate for microwave applications. The prepared flexible substrates exhibit high dielectric permittivity and low dielectric loss in the microwave frequency range. For the proof of concept, the electromagnetic performances both at flat and bending conditions were verified by loading an electromagnetic radiator. We report the detailed measured performances of the reflection coefficient below −10 dB, average efficiency above 73% and average realized gain above 1.5 dBi within the operational bandwidth for the first time. The measured stable omnidirectional radiation patterns both in flat and bending conditions also confirm the potential of the proposed material to be used as a new flexible dielectric substrate.
---
paper_title: Textile Materials for the Design of Wearable Antennas: A Survey

paper_content:

In the broad context of Wireless Body Sensor Networks for healthcare and pervasive applications, the design of wearable antennas offers the possibility of ubiquitous monitoring, communication and energy harvesting and storage. Specific requirements for wearable antennas are a planar structure and flexible construction materials. Several properties of the materials influence the behaviour of the antenna. For instance, the bandwidth and the efficiency of a planar microstrip antenna are mainly determined by the permittivity and the thickness of the substrate. The use of textiles in wearable antennas requires the characterization of their properties. Specific electrical conductive textiles are available on the market and have been successfully used. Ordinary textile fabrics have been used as substrates. However, little information can be found on the electromagnetic properties of regular textiles. Therefore this paper is mainly focused on the analysis of the dielectric properties of normal fabrics. In general, textiles present a very low dielectric constant that reduces the surface wave losses and increases the impedance bandwidth of the antenna. However, textile materials are constantly exchanging water molecules with the surroundings, which affects their electromagnetic properties. In addition, textile fabrics are porous, anisotropic and compressible materials whose thickness and density might change with low pressures. Therefore it is important to know how these characteristics influence the behaviour of the antenna in order to minimize unwanted effects. This paper presents a survey of the key points for the design and development of textile antennas, from the choice of the textile materials to the framing of the antenna. An analysis of the textile materials that have been used is also presented.
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paper_title: Multilayer Stretchable Conductors on Polymer Substrates for Conformal and Reconfigurable Antennas

paper_content:

Multilayer stretchable conductors (SCs) are demonstrated for the first time as an alternative cost-effective method for implementing conformal and reconfigurable antennas over flexible substrates. Structurally, these SCs are realized on polydimethylsiloxane (PDMS) substrate via single or double copper layers deposited around a commercially available conductive rubber. The dc measurements demonstrate the stretchability of the multilayer SCs up to 25% and 22.5 times larger conductivity as compared to the standalone conductive rubber. The RF performance of these multilayer SCs is first characterized in the 1–5-GHz range by measuring the insertion loss in 50- $\Omega$ microstrip lines. As compared to a standalone conductive rubber, the triple-layer SC has shown 58% less insertion loss. To demonstrate their use in reconfigurable and flexible conformal antennas, an aperture-coupled patch antenna is designed, fabricated, and tested. Specifically, it is shown that the antenna can be tuned from 2.97 to 2.69 GHz when stretched by 9%. Additionally, the patch antenna implemented from the multilayer SC exhibits 6.18 dB realized gain. This gain is 3.71 dB better than that of a patch antenna implemented from a standalone conductive rubber layer, and only 0.4 dB lower than that of a conventional patch.
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paper_title: Silicones for Stretchable and Durable Soft Devices: Beyond Sylgard-184.

paper_content:

This paper identifies and characterizes silicone elastomers that are well-suited for fabricating highly stretchable and tear-resistant devices that require interfacial bonding by plasma or UV ozone treatment. The ability to bond two or more pieces of molded silicone is important for creating microfluidic channels, chambers for pneumatically driven soft robotics, and other soft and stretchable devices. Sylgard-184 is a popular silicone, particularly for microfluidic applications. However, its low elongation at break (∼100% strain) and moderate tear strength (∼3 N/mm) make it unsuitable for emerging, mechanically demanding applications of silicone. In contrast, commercial silicones, such as Dragon Skin, have excellent mechanical properties yet are difficult to plasma-bond, likely because of the presence of silicone oils that soften the network yet migrate to the surface and interfere with plasma bonding. We found that extracting silicone oligomers from these soft networks allows these materials to bond but only when the Shore hardness exceeds a value of 15 A. It is also possible to mix highly stretchable silicones (Dragon Skin and Ecoflex) with Sylgard-184 to create silicones with intermediate mechanical properties; interestingly, these blends also only bond when the hardness exceeds 15 A. Eight different Pt-cured silicones were also screened; again, only those with Shore hardness above 15 A plasma-bond. The most promising silicones from this study are Sylgard-186 and Elastosil-M4130 and M4630, which exhibit a large deformation (>200% elongation at break), high tear strength (>12 N/mm), and strong plasma bonding. To illustrate the utility of these silicones, we created stretchable electrodes by injecting a liquid metal into microchannels created using such silicones, which may find use in soft robotics, electronic skin, and stretchable energy storage devices.
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paper_title: Flexible Uniplanar Electrically Small Directive Antenna Empowered by a Modified CPW-Feed

paper_content:

A flexible printed near-field resonant parasitic (NFRP) GPS L1 antenna that is a compact, efficient, directive radiator is demonstrated. The simple uniplanar design incorporates a capacitively loaded loop (CLL) resonator, which acts as the NFRP element, and a coplanar waveguide (CPW)-fed semi-loop antenna. A set of slots is introduced into the CPW feedline ground strips. The resulting meander-line-shaped CPW ground strips act as a driven dipole element that is capacitively coupled to the NFRP element in such a manner that when they are properly tuned, nearly complete matching to the 50-Ω source is achieved with no matching circuit, and the pair acts as a two-element endfire array. Parameter studies are reported to illustrate the nuances of the design and its operating mechanisms. The experimental results are in good agreement with their simulated values. The endfire realized gain is 3.57 dBi with a 13.44-dB front-to-back-ratio (FTBR) at its resonance frequency: 1.574 GHz (GPS L1), where the electrical size ka = 0.97. The flexibility of the proposed antenna is demonstrated both numerically and experimentally by mounting it on several cylindrical structures whose curvatures vary over a large range and by confirming that there is little impact on its operational frequency, impedance matching, bandwidth, and radiation characteristics.
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paper_title: Design and fabrication of an E-shaped wearable textile antenna on PVB-coated hydrophobic polyester fabric

paper_content:

In this paper, we investigated the simulation and fabrication of an E-shaped microstrip patch antenna realized on multilayered polyester fabric suitable for WiMAX (Worldwide Interoperability for Microwave Access) applications. The main challenges while designing a textile antenna were to provide adequate thickness, surface uniformity and water wettability to the textile substrate. Here, three layers of polyester fabric were stacked together in order to obtain sufficient thickness, and were subsequently dip coated with polyvinyl butyral (PVB) solution. The PVB-coated polyester fabric showed a hydrophobic nature with a contact angle of 91°. The RMS roughness of the uncoated and PVB-coated polyester fabric was about 341 nm and 15 nm respectively. The promising properties, such as their flexibility, light weight and cost effectiveness, enable effortless integration of the proposed antenna into clothes like polyester jackets. Simulated and measured results in terms of return loss as well as gain were showcased to confirm the usefulness of the fabricated prototype. The fabricated antenna successfully operates at 3.37 GHz with a return loss of 21 dB and a maximum measured gain of 3.6 dB.
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paper_title: Embroidery and Related Manufacturing Techniques for Wearable Antennas: Challenges and Opportunities

paper_content:

This paper will review the evolution of wearable textile antennas over the last couple of decades. Particular emphasis will be given to the process of embroidery. This technique is advantageous for the following reasons: (i) bespoke or mass produced designs can be manufactured using digitized embroidery machines; (ii) glue is not required and (iii) the designs are aesthetic and are integrated into clothing rather than being attached to it. The embroidery technique will be compared to alternative manufacturing processes. The challenges facing the industrial and public acceptance of this technology will be assessed. Hence, the key opportunities will be highlighted.
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paper_title: Inkjet-Printed Wideband Antenna on Resin-Coated Paper Substrate for Curved Wireless Devices

paper_content:

A low-cost, inkjet-printed multiband monopole antenna for conformal wireless applications is presented for the first time. The antenna is implemented on a low-cost resin-coated paper substrate which can be used for conformal devices. The antenna developed here is composed of four branch lines on the radiator and three L-shaped slots on the ground plane that help to generate multiple bands without increasing the size of the antenna. The antenna has a compact size, making it suitable for handheld and wearable wireless devices. Details of the inkjet printing fabrication processes and related issues are presented. The antennas were characterized under flat and bent conditions, and the results indicate that the antennas can cover most bands for mobile and wireless applications such as PCS, UMTS, GSM1900, and WLAN.
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paper_title: Innovative SIW components on paper, textile, and 3D-printed substrates for the Internet of Things

paper_content:

This paper presents an overview of the recent achievements in the developments of novel components and innovative materials for the future Internet of Things (IoT). The development of substrate integrated waveguide (SIW) components and antennas is discussed, with particular emphasis on the use of paper substrates for eco-friendly wireless systems, textile for wearable components, and 3D-printed substrates for fully-3D cost-effective structures. Several prototypes are presented to validate the proposed fabrication technologies and show the potential of integrated microwave systems for IoT applications.
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paper_title: Review of substrate-integrated waveguide circuits and antennas

paper_content:

Substrate-integrated waveguide (SIW) technology represents an emerging and very promising candidate for the development of circuits and components operating in the microwave and millimetre-wave region. SIW structures are generally fabricated by using two rows of conducting cylinders or slots embedded in a dielectric substrate that connects two parallel metal plates, and permit the implementation of classical rectangular waveguide components in planar form, along with printed circuitry, active devices and antennas. This study aims to provide an overview of the recent advances in the modelling, design and technological implementation of SIW structures and components.
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paper_title: Wearable tri-band SIW based antenna on leather substrate

paper_content:

A compact substrate integrated waveguide (SIW) based wearable tri-band leather antenna, designed for optimal on-body performance in the 2.4 GHz (ISM), 3.51 GHz (WiMAX) and 4.69 GHz (Military application) bands is proposed. By using brass eyelets and a combination of conducting and non-conductive leather materials, a substrate integrated waveguide cavity with a ground plane is realised. The antenna is very compact, flexible and directs radiation away from the wearer. Additional miniaturisation is achieved by introducing slits. The free space performance in the bands is found satisfactory with measured impedance bandwidths of 11, 7 and 5%, maximal measured free-space gains of 1.1, 0.9 and 2.1 dBi, and efficiencies of 71.3%, 68.2% and 76.5% achieved for the proposed antenna.
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paper_title: Ultraminiaturized Metamaterial-Inspired SIW Textile Antenna for Off-Body Applications

paper_content:

This letter introduces a novel miniaturized cavity-backed substrate integrated waveguide textile antenna for off-body applications in the 2.45 GHz industrial, scientific, and medical radio band. The use of metamaterial-inspired slots reduces the antenna size by 80% compared to previous works, and the radiation pattern is broadside toward the normal direction. The simulated and measured results are presented for both free space and the human body, and show good impedance matching for both normal and curved models. The measured gain and efficiency of the structure were 5.35 dBi and 74.3%, respectively, and the effect of the antenna on the human body was measured using a skin equivalent phantom. The maximum numerically calculated specific absorption rate in the human body model over 10 g of tissue was 0.38 W/kg, on average, for 500 mW of input power, which is less than the 2 W/kg European limit. The design and configuration of the antenna make it a suitable choice for off-body applications.
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paper_title: Wearable Passive E-Textile UHF RFID Tag Based on a Slotted Patch Antenna with Sewn Ground and Microchip Interconnections

paper_content:

We present a wearable passive UHF RFID tag based on a slotted patch antenna comprising only textile materials (e-textile, textile substrate, and conductive yearn). As a novel manufacturing approach, we realize the patch-to-ground and antenna-to-IC interfaces using only conductive thread and a sewing machine. We outline the electromagnetic optimization of the antenna for body-worn operation through simulations and present a performance comparison between the e-textile tag and a tag produced using regular electronics materials and methods. The measured results show that the textile tag achieves the electrical performance required in practical applications and that the slotted patch type antenna provides stable electromagnetic performance in different body-worn configurations.
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paper_title: Design and fabrication of an E-shaped wearable textile antenna on PVB-coated hydrophobic polyester fabric

paper_content:

In this paper, we investigated the simulation and fabrication of an E-shaped microstrip patch antenna realized on multilayered polyester fabric suitable for WiMAX (Worldwide Interoperability for Microwave Access) applications. The main challenges while designing a textile antenna were to provide adequate thickness, surface uniformity and water wettability to the textile substrate. Here, three layers of polyester fabric were stacked together in order to obtain sufficient thickness, and were subsequently dip coated with polyvinyl butyral (PVB) solution. The PVB-coated polyester fabric showed a hydrophobic nature with a contact angle of 91°. The RMS roughness of the uncoated and PVB-coated polyester fabric was about 341 nm and 15 nm respectively. The promising properties, such as their flexibility, light weight and cost effectiveness, enable effortless integration of the proposed antenna into clothes like polyester jackets. Simulated and measured results in terms of return loss as well as gain were showcased to confirm the usefulness of the fabricated prototype. The fabricated antenna successfully operates at 3.37 GHz with a return loss of 21 dB and a maximum measured gain of 3.6 dB.
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paper_title: Reliability evaluation of wearable radio frequency identification tags: Design and fabrication of a two-part textile antenna

paper_content:

Passive radio frequency identification-based technology is a convincing approach to the achievement of versatile energy- and cost-efficient wireless platforms for future wearable applications. By u...
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paper_title: Conformal Load-Bearing Spiral Antenna on Conductive Textile Threads

paper_content:

We present a novel load-bearing spiral antenna on conductive textile threads (E-threads) for conformal applications. The textile spiral exhibits a nearly 10:1 bandwidth (0.3–3 GHz) with circularly polarized gain of 6.5 dBi across the 1–3 GHz bandwidth. Such performance is unique for textiles and flexible surfaces. An important aspect of this letter is the demonstration of repeatable performance for this textile spiral antenna. Also, mechanical tests for the spiral showed no appreciable changes in performance, even after 300 flexing cycles. The spiral is a cavity-backed configuration with its ground plane also embroidered using very thin (diameter = 0.12 mm) Elektrisola E-threads. These threads can achieve geometrical precision down to 0.1 mm. To enhance robustness, high-strength Kevlar fabric was employed as the substrate. Overall, the proposed spiral is very attractive for several wideband, conformal, and load-bearing applications, such as airborne and wearables.
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paper_title: Embroidered Metamaterial Antenna for Optimized Performance on Wearable Applications

paper_content:

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim In this work, an embroidered metamaterial monopole antenna based on a split ring resonator electromagnetic bandgap shielding structure is designed, simulated, and tested. This work investigates the impact of different types of embroidering metamaterial patterns on the antenna performance, shielding effect in terms of human safety through specific absorption rate analysis and degree of material wearability, in comparison with the standard antenna topologies. The proposed antenna design presents a full compact embroidered metamaterial device manufactured in felt textile substrate and requires a 85 × 70 mm2area, operating at 2.45 GHz. On-voxel analysis reveals that specific absorption standards are satisfied for both public and occupational sector with a significant safety margin whereas the antenna performance in terms of gain and directivity are significantly optimized with regard to standard wearable materials.
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paper_title: Embroidery and Related Manufacturing Techniques for Wearable Antennas: Challenges and Opportunities

paper_content:

This paper will review the evolution of wearable textile antennas over the last couple of decades. Particular emphasis will be given to the process of embroidery. This technique is advantageous for the following reasons: (i) bespoke or mass produced designs can be manufactured using digitized embroidery machines; (ii) glue is not required and (iii) the designs are aesthetic and are integrated into clothing rather than being attached to it. The embroidery technique will be compared to alternative manufacturing processes. The challenges facing the industrial and public acceptance of this technology will be assessed. Hence, the key opportunities will be highlighted.
---
paper_title: Porous Textile Antenna Designs for Improved Wearability

paper_content:

Textile antennas are an integral part of the next generation personalized wearable electronics system. However, the durability of textile antennas are rarely discussed in the literature. Typical textile antennas are prone to damage during normal wearable user scenarios, washing, and heat cycling over time. Fabricating a durable, washable, flexible, and breathable (like textile materials) antenna is challenging due to the incompatibility of the mechanical properties of conductive materials and soft textile materials. This paper describes a scalable screen printing process on an engineered nonwoven substrate to fabricate microstrip patch antennas with enhanced durability. This work used an Evolon® nonwoven substrate with low surface roughness (~Ra = 18 μm) and high surface area (~2.05 mm2 mm−2 of fabric area) compared to traditional textile materials, which allows the ink to penetrate evenly in the fiber bulk with its strong capillary wicking force and enhances print resolution. The composite layer of ink and fiber is conductive and enables the antennas to maintain high mechanical flexibility without varying its RF (Radio Frequency) properties. Additionally, the antennas are packaged by laminating porous polyurethane web to make the device durable and washable. The fully packaged antennas maintain the structural flexibility and RF functionality after 15 cycles of washing and drying. To improve the air permeability and enhance flexibility the antenna is also modified by incorporating holes in the both patch and ground layer of the antenna. The antennas were analyzed before and after submerging in water to observe the effect of wetting and drying with respect to frequency response. The porous antenna with holes recovered 3x times faster than the one without holes (solid) from fully wet state (saturated with water) to the dry state, demonstrating its potential use as a moisture sensor system.
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paper_title: Fabrication of highly conductive stretchable textile with silver nanoparticles

paper_content:

A method has been developed for the deposition of conductive metals onto fibers within textile structures. The resultant fabric exhibited full metal coverage with good adhesion to the fibers. As well as being conductive and extremely flexible with little effect on its handle and drape properties. In order to make a conductive fabric, cotton was first mercerized followed by immersion in poly(diallyldimethylammonium chloride) solution. Silver nitrate was then reduced on the surface of the fabric which allowed formation of silver nanoparticles. Scanning electron microscopy studies of the conductive fabric confirmed the deposition of the polymer resulted in more uniform attachment of nanosilver to the surface of fibers. The fabric was then electroless plated to obtain a surface resistivity less than 0.2 Ω/square. This method can be used for woven, non-woven and knitted types of fabric. It can be applied on to the fibers before or after being made into a textile.
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paper_title: Embroidery manufacturing techniques for textile dipole antenna applied to wireless body area network

paper_content:

This paper addresses the design, simulation, manufacturing, and experimental test of textile dipole antennas based on advanced embroidery techniques. The proposed dipoles are intended to operate at...
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paper_title: Performance characterization of screen printed radio frequency identification antennas with silver nanopaste

paper_content:

The era of wireless communication has come and it is going to flourish in the form of radio frequency identification (RFID) tags. The employment of RFID tags in daily commodities, however, is constrained due to the manufacturing cost. Therefore, industries in the field have sought for alternative manufacturing methods at an ultra low cost and various printing processes have been considered such as inkjet, gravure, flexo, off-set and screen. Although such printing processes are age-old, their applications have been mainly limited to graphic arts and design rules for electronic appliances have not been fully established yet. In this paper, the selection of ink and printing process to fabricate RFID antennas is discussed. The developed silver nanopaste in the range of 20 to 50 nm without the inclusion of microparticles and flakes was sintered at 120 °C for 1 min, which is lower than that of conventional silver paste with microparticles and flakes, and its resistivity was found to be approximately 3 μΩ cm. The radiation performances of various screen printed RFID antennas with silver nanopaste were found comparable to those of copper etched ones.
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paper_title: Copper deposition on textiles via an automated dispensing process for flexible microstrip antennas

paper_content:

A three-axis automatic robot was coupled with a precision liquid dispenser to deposit copper on fabrics to be used as the conductive layer for assembly of textile-based flexible microstrip patch antennas. Two reactive solutions, copper sulfate and sodium borohydride, were sequentially dispensed on fabrics and a conductive copper was produced in situ and in real time, through a simple redox mechanism. Driving pressure, the number of dispensing cycles, concentration and composition (i.e. the addition of a complexing agent sodium citrate to the copper sulfate solution) of the reactive solutions were studied to optimize the dispensing process in favor of rapid copper deposition. The electrical performance of the resulting copper deposit and its adhesion to the textile substrates were characterized. A copper coating of about 0.2 ohm/□ sheet resistance could be prepared in less than 1 hour under a 45 kPa driving pressure, at a 200 mm·s−1 moving speed, and within 60 dispensing cycles.
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paper_title: Design and fabrication of an E-shaped wearable textile antenna on PVB-coated hydrophobic polyester fabric

paper_content:

In this paper, we investigated the simulation and fabrication of an E-shaped microstrip patch antenna realized on multilayered polyester fabric suitable for WiMAX (Worldwide Interoperability for Microwave Access) applications. The main challenges while designing a textile antenna were to provide adequate thickness, surface uniformity and water wettability to the textile substrate. Here, three layers of polyester fabric were stacked together in order to obtain sufficient thickness, and were subsequently dip coated with polyvinyl butyral (PVB) solution. The PVB-coated polyester fabric showed a hydrophobic nature with a contact angle of 91°. The RMS roughness of the uncoated and PVB-coated polyester fabric was about 341 nm and 15 nm respectively. The promising properties, such as their flexibility, light weight and cost effectiveness, enable effortless integration of the proposed antenna into clothes like polyester jackets. Simulated and measured results in terms of return loss as well as gain were showcased to confirm the usefulness of the fabricated prototype. The fabricated antenna successfully operates at 3.37 GHz with a return loss of 21 dB and a maximum measured gain of 3.6 dB.
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paper_title: Design and Fabrication of Compact Inkjet Printed Antennas for Integration Within Flexible and Wearable Electronics

paper_content:

The demand for flexible and wearable wireless systems is increasing exponentially in today's information-oriented society. These systems are extremely beneficial and applied in a wide spectrum of fields, such as personal communication, medicine, military, firefighting, entertainment, aeronautics, and radio frequency identification. In this paper, the design constraints, fabrication process, flexibility tests, and measurement of flexible and wearable antennas are discussed in detail. Furthermore, the design, fabrication, and testing of a compact flexible ultrawideband antenna are presented. The proposed design has the merits of light weight, ultralow profile (50.8 μm), wideband width, mechanical robustness, compactness, and high efficiency. The antenna is also tested against bending effects to characterize its performance in a realistic setup since it is expected to be conformed on curved surfaces and/or flexed during operation.
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paper_title: Porous Textile Antenna Designs for Improved Wearability

paper_content:

Textile antennas are an integral part of the next generation personalized wearable electronics system. However, the durability of textile antennas are rarely discussed in the literature. Typical textile antennas are prone to damage during normal wearable user scenarios, washing, and heat cycling over time. Fabricating a durable, washable, flexible, and breathable (like textile materials) antenna is challenging due to the incompatibility of the mechanical properties of conductive materials and soft textile materials. This paper describes a scalable screen printing process on an engineered nonwoven substrate to fabricate microstrip patch antennas with enhanced durability. This work used an Evolon® nonwoven substrate with low surface roughness (~Ra = 18 μm) and high surface area (~2.05 mm2 mm−2 of fabric area) compared to traditional textile materials, which allows the ink to penetrate evenly in the fiber bulk with its strong capillary wicking force and enhances print resolution. The composite layer of ink and fiber is conductive and enables the antennas to maintain high mechanical flexibility without varying its RF (Radio Frequency) properties. Additionally, the antennas are packaged by laminating porous polyurethane web to make the device durable and washable. The fully packaged antennas maintain the structural flexibility and RF functionality after 15 cycles of washing and drying. To improve the air permeability and enhance flexibility the antenna is also modified by incorporating holes in the both patch and ground layer of the antenna. The antennas were analyzed before and after submerging in water to observe the effect of wetting and drying with respect to frequency response. The porous antenna with holes recovered 3x times faster than the one without holes (solid) from fully wet state (saturated with water) to the dry state, demonstrating its potential use as a moisture sensor system.
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paper_title: Inkjet-printing deposition of silver electro-conductive layers on textile substrates at low sintering temperature by using an aqueous silver ions-containing ink for textronic applications

paper_content:

Abstract The main problem in preparing stable and printable inks for the inkjet printing of textile substrates is in overcoming their roughness and high sintering temperature. In this study, the modified Tollens’ process for the preparation of a suitable water-soluble ink containing silver for the inkjet printing of textile substrates as a tool for textronic applications was adopted. The choice of this type of ink ensured inkjet printability of textile surfaces with simultaneous sintering at low temperature not exceeding 90 °C. The surface resistance of the inkjet-printed silver layers on all the textile fabrics studied steadily decreased with the number of silver layers deposited. In the case of 8 prints on synthetic textiles made of polyacrylonitrile, polypropylene, polyester and basalt fibres the surface resistance in the range 0.155–0.235 Ω/sq. was achieved. For some textile substrates made of natural fibres and their blends with synthetic fibres, to achieve the proper conductivity an interlayer of acrylic copolymer containing resin was applied. The surface resistance for the same number of prints was in the range of 0.389–0.622 Ω/sq. The study confirmed the usefulness of ink applied in printing silver electrodes and their resistance to bending, washing and dry-cleaning processes. On the basis of these findings, some potential applications in textronic systems, e.g., capacitors, textile heating actuators, textile patch antennas, and high-frequency transmission lines were proposed.
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paper_title: Shape-programmed inkjet-printed silver electro-conductive layers on textile surfaces

paper_content:

The inkjet-printing technique was used to deposit a commercial silver nanoparticle ink in order to fabricate the electro-conductive layers directly on the different natural, synthetic, blend and mi...
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paper_title: A wearable tracking device inkjet-printed on textile

paper_content:

Despite the abundance of localization applications, the tracking devices have never been truly realized in E-textiles. Standard printed circuit board (PCB)-based devices are obtrusive and rigid and hence not suitable for textile based implementations. An attractive option would be direct printing of circuit layout on the textile itself, negating the use of rigid PCB materials. However, high surface roughness and porosity of textiles prevents efficient and reliable printing of electronics on textile. In this work, by printing an interface layer on the textile first, a complete localization circuit integrated with an antenna has been inkjet-printed on the textile for the first time. Printed conductive traces were optimized in terms of conductivity and resolution by controlling the number of over-printed layers. The tracking device determines the wearer's position using WiFi and this information can be displayed on any internet-enabled device, such as smart phone. The device is compact (55mm45mm) and lightweight (22g with 500mAh battery) for people to comfortably wear it and can be easily concealed in case discretion is required. The device operates at 2.4GHz communicated up to a distance of 55m, with localization accuracy of up to 8m.
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paper_title: Conductive Inks with a “Built-In” Mechanism That Enables Sintering at Room Temperature

paper_content:

At present there is no metallic ink that enables formation of conductive patterns at room temperature by a single printing step. Printing conductive features by metallic nanoparticle-based inks must be followed by sintering while heating to elevated temperatures, thus preventing their utilization on most plastic substrates used in plastic electronics. In this report we present a new silver nanoparticle-based conductive ink, having a built-in sintering mechanism, which is triggered during drying of the printed pattern. The nanoparticles that are stabilized by a polymer undergo self-sintering spontaneously, due to the presence of a destabilizing agent, which comes into action only during drying of the printed pattern. The destabilizing agent, which contains Cl− ions, causes detachment of the anchoring groups of the stabilizer from the nanoparticles’ surface and thus enables their coalescence and sintering. It was found that the new metallic ink leads to very high conductivities, by a single printing step: u...
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paper_title: Design and Fabrication of Compact Inkjet Printed Antennas for Integration Within Flexible and Wearable Electronics

paper_content:

The demand for flexible and wearable wireless systems is increasing exponentially in today's information-oriented society. These systems are extremely beneficial and applied in a wide spectrum of fields, such as personal communication, medicine, military, firefighting, entertainment, aeronautics, and radio frequency identification. In this paper, the design constraints, fabrication process, flexibility tests, and measurement of flexible and wearable antennas are discussed in detail. Furthermore, the design, fabrication, and testing of a compact flexible ultrawideband antenna are presented. The proposed design has the merits of light weight, ultralow profile (50.8 μm), wideband width, mechanical robustness, compactness, and high efficiency. The antenna is also tested against bending effects to characterize its performance in a realistic setup since it is expected to be conformed on curved surfaces and/or flexed during operation.
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paper_title: Low-Cost Printed Flexible Antenna by Using an Office Printer for Conformal Applications

paper_content:

A low-cost inkjet printing method for antenna fabrication on a polyethylene terephthalate (PET) substrate is presented in this paper. An office inkjet printer is used to have desired patterns of silver nanoparticle ink on the PET substrate without any postprocessing. Silver nanoparticle ink cures instantly as soon as it is ejected from the printer on a chemically treated PET substrate. The thickness of the silver nanoparticle layer was measured to be 300 nm with a sheet resistance of as low as 0.3 Ω/sq and a conductivity around 1.11 × 107 S/m with single layer deposition. A coplanar waveguide- (CPW-) fed Z-shape planar antenna on the PET substrate achieved the measured radiation efficiency of 62% and the IEEE gain of 1.44 dBi at 2.45 GHz. The printed antenna is also tested in bending conditions to ascertain its performance for the Internet of things (IoT) conformal applications for the future 5G network.
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paper_title: A Compact Kapton-Based Inkjet-Printed Multiband Antenna for Flexible Wireless Devices

paper_content:

A low-cost inkjet-printed multiband antenna envisioned for integration into flexible and conformal mobile devices is presented. The antenna structure contains a novel triangular iterative design with coplanar waveguide (CPW) feed, printed on a Kapton polyimide-based flexible substrate with dimensions of $ 70\times 70\times 0.11~\hbox{mm}^{\bf 3}$ . The antenna covers four wide frequency bands with measured impedance bandwidths of 54.4%, 14%, 23.5% and 17.2%, centered at 1.2, 2.0, 2.6 and 3.4 GHz, respectively, thus, enabling it to cover GSM 900, GPS, UMTS, WLAN, ISM, Bluetooth, LTE 2300/2500 and WiMAX standards. The antenna has omnidirectional radiation pattern with a maximum gain of 2.1 dBi. To characterize the flexibility of the antenna, the fabricated prototype is tested in convex and concave bent configurations for radii of 78 mm and 59 mm. The overall performance remains unaffected, except a minor shift of 20 MHz and 60 MHz in S11, for concave bending at both radii. The compact, lightweight and conformal design as well as multiband performance in bent configurations, proves the suitability of the antenna for future electronic devices.
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paper_title: Inkjet-Printed Microstrip Patch Antennas Realized on Textile for Wearable Applications

paper_content:

This letter introduces a new technique of inkjet printing antennas on textiles. A screen-printed interface layer was used to reduce the surface roughness of the polyester/cotton material that facilitated the printing of a continuous conducting surface. Conducting ink was used to create three inkjet-printed microstrip patch antennas. An efficiency of 53% was achieved for a fully flexible antenna with two layers of ink. Measurements of the antennas bent around a polystyrene cylinder indicated that a second layer of ink improved the robustness to bending.
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paper_title: A miniaturized wearable button antenna for Wi-Fi and Wi-Max application using transparent acrylic sheet as substrate

paper_content:

A compact miniaturized wearable antenna with the appearance of a button on clothing for Wi-Fi and Wi-Max applications as well as used for body centric communication is presented. The radiating elements of the antenna are made of copper tape, while the substrate is given a property of transparent acrylic fiber sheet material and fed by a coaxial line through the ground plane. The proposed antenna is simulated by Ansoft HFSS finite element method based simulation software and has been optimized to operate within the Wi-Fi and Wi-Max frequency bands with center frequency of 5.5 GHz (5250–5850 MHz). The measured peak gain of this antenna is 2.92 dBi. There is a good matching between the simulated and the measured result. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:45–49, 2015
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paper_title: Compact, Highly Efficient, and Fully Flexible Circularly Polarized Antenna Enabled by Silver Nanowires for Wireless Body-Area Networks

paper_content:

A compact and flexible circularly polarized (CP) wearable antenna is introduced for wireless body-area network systems at the 2.4 GHz industrial, scientific, and medical (ISM) band, which is implemented by employing a low-loss composite of polydimethylsiloxane (PDMS) and silver nanowires (AgNWs). The circularly polarized radiation is enabled by placing a planar linearly polarized loop monopole above a finite anisotropic artificial ground plane. By truncating the anisotropic artificial ground plane to contain only 2 by 2 unit cells, an integrated antenna with a compact form factor of 0.41 λ 0 × 0.41 λ 0 × 0.045 λ 0 is obtained, all while possessing an improved angular coverage of CP radiation. A flexible prototype was fabricated and characterized, experimentally achieving S 11 <− 15 dB, an axial ratio of less than 3 dB, a gain of around 5.2 dBi, and a wide CP angular coverage in the targeted ISM band. Furthermore, this antenna is compared to a conventional CP patch antenna of the same physical size, which is also comprised of the same PDMS and AgNW composite. The results of this comparison reveal that the proposed antenna has much more stable performance under bending and human body loading, as well as a lower specific absorption rate. In all, the demonstrated wearable antenna offers a compact, flexible, and robust solution which makes it a strong candidate for future integration into body-area networks that require efficient off-body communications.
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paper_title: Bending and On-Arm Effects on a Wearable Antenna for 2.45 GHz Body Area Network

paper_content:

Three types of flexible textile antennas for 2.45 GHz body area network (BAN) are compared in this letter. Two types of conducting materials are used to form radiation patch and ground plane; they are called copper foil tape (CFT, 0.05 mm thickness) and Shieldex (SH, 0.13 mm thickness, 0.009 Ohm surface resistivity). The substrate is a thin felt with relative permittivity of 1.2 and the thickness of 2 mm. In order to satisfy these requirements of small frequency shifting when the antenna is bent and placed on human body, two shorting probes are used to connect the radiation patch and ground plane. Compared to the antenna without shorting probes, the size of proposed antenna is reduced from 96 ×47 to 70 ×25 mm 2 , and the measured minimum value of S11 in free space is also decreased from -14.59 to -33.30 dB. Furthermore, an antenna with smaller size of 46 ×25 mm 2 is designed by modifying the proposed structure, and it can act as a wearable antenna as well.
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paper_title: A Miniaturized Patch Antenna by Using a CSRR Loading Plane

paper_content:

This paper presents a design methodology for the implementation of a miniaturized square patch antenna and its circuit model for 5.15 GHz ISM band. The miniaturization is achieved by employing concentric complementary split ring resonator (CSRR) structures in between the patch and ground plane. The results are compared with the traditional square patch antenna in terms of area, bandwidth, and efficiency. The area is reduced with a ratio of 1/4 with respect to the traditional patch. The miniaturized square patch antenna has an efficiency, bandwidth, and reflection coefficient of 78%, 0.4%, and −16 dB, respectively. The measurement and circuit modeling results show a good agreement with the full-wave electromagnetic simulations.
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paper_title: A Low-Profile Wearable Antenna Using a Miniature High Impedance Surface for Smartwatch Applications

paper_content:

A novel antenna structure enabled by a miniature high impedance surface (HIS) is proposed for smartwatch applications. The smartwatch antenna must be low-profile, highly directive, low specified absorption rate (SAR), and robust to the loading effect due to a human body. HISs are particularly suitable to cope with these design goals. However, an HIS is usually too electrically large to fit into the design space of smartwatch applications. Furthermore, the characterization of HISs is determined by observing the reflection phase of a unit cell, but this method becomes improper for finite-size and miniaturized HISs. In this letter, a new design method is presented. By using fractional factorial designs (FFD), the antenna performances are significantly enhanced even though the size of the HIS is only $0.3{\lambda _0}\times 0.3{\lambda _0}$ . Accordingly, the dimensions of the proposed antenna are $38 \times 38 \times 3 ~\hbox{mm}^3$ (at 2.4 GHz), which is the most compact HIS structure to date. The directivity of the antenna is 6.3 dBi, and the maximum 1 g averaged SAR value is only 0.29 W/kg for an input power of 100 mW; moreover, the radiation efficiency and impedance matching are very robust against the loading effect due to wrist tissue.
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paper_title: A Miniaturized Flexible Antenna Printed on a High Dielectric Constant Nanopaper Composite

paper_content:

A high-dielectric-constant and flexible cellulose nanopaper composite is prepared by mixing a small amount of silver nanowires with cellulose nanofibers. The nanopaper antenna is downsized by about a half when using the nanopaper substrate. The nanopaper antenna has potential in wearable wireless communication devices.
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paper_title: A Compact, Low-Profile Metasurface-Enabled Antenna for Wearable Medical Body-Area Network Devices

paper_content:

We propose a compact conformal wearable antenna that operates in the 2.36-2.4 GHz medical body-area network band. The antenna is enabled by placing a highly truncated metasurface, consisting of only a two by two array of I-shaped elements, underneath a planar monopole. In contrast to previously reported artificial magnetic conducting ground plane backed antenna designs, here the metasurface acts not only as a ground plane for isolation, but also as the main radiator. An antenna prototype was fabricated and tested, showing a strong agreement between simulation and measurement. Comparing to previously proposed wearable antennas, the demonstrated antenna has a compact form factor of 0.5 λ ::: 0 ::: ×0.3 λ ::: 0 ::: ×0.028 λ ::: 0 ::: , all while achieving a 5.5% impedance bandwidth, a gain of 6.2 dBi, and a front-to-back ratio higher than 23 dB. Further numerical and experimental investigations reveal that the performance of the antenna is extraordinarily robust to both structural deformation and human body loading, far superior to both planar monopoles and microstrip patch antennas. Additionally, the introduced metal backed metasurface enables a 95.3% reduction in the specific absorption rate, making such an antenna a prime candidate for incorporation into various wearable devices.
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paper_title: Wearable Textile Half-Mode Substrate-Integrated Cavity Antenna Using Embroidered Vias

paper_content:

A wearable textile antenna based on the fundamental mode of a half-mode substrate-integrated semicircular cavity is presented. The antenna operates around 5 GHz and is manufactured with two layers of silver fabric conductors, on the top and bottom of a low-permittivity low-loss foam with minimal water absorption. The vias are realized with five passes of conductive yarn with a diameter of 0.12 mm placed every 1 mm. Their precise arrangement is obtained using computerized embroidery. Compared to other antenna concepts, this design features minimal manufacturing complexity as it does not require accurate patterned cutting of textile conductors. Good isolation from the human body and robustness in terms of deformation are further key characteristics of this structure. This letter provides design guidelines and investigates realistic issues associated with the manufacturing technique. A good agreement between simulated and measured performance with a gain of 7.2 dB validates the concept.
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paper_title: Textile antenna with EBG structure for body surface wave enhancement

paper_content:

A textile antenna with an electric bandgap (EBG) structure for body surface wave enhancement is proposed. The proposed antenna is composed of a centre-fed circular patch to generate the TM01 mode and an EBG structure near the patch to guide the TM wave along the horizontal surface (θ = 90°). Considering the wearability, the antenna has been fabricated using only textile materials such as conductive textiles, conductive thread, and a leather substrate, and has an enhanced radiated field along the surface direction in the 5.8 GHz industrial, scientific, and medical (ISM) band for on-body communication. The proposed antenna has a diameter of 1.98λ 0 and a thickness of 0.058λ 0 at 5.8 GHz.
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paper_title: Paired Snap-On Buttons Connections for Balanced Antennas in Wearable Systems

paper_content:

A pair of commercial snap-on buttons is demonstrated as a detachable radio frequency (RF) balanced connection between a garment-integrated textile dipole antenna and a passive sensor-enabled radio frequency identification (RFID) tag in a wearable wireless system. This arrangement offers reliable, low-cost, and easily detachable RF coupling and feeding connections for balanced antennas, as conceptualized in simulations and validated through measurements. In addition, a back-to-back balanced transmission-line structure has been designed and measured to characterize the RF performance of the proposed snap-on button connection. The resulting $S$ -parameters indicate the good performance of the snap-on buttons as RF connectors for balanced antennas/transmission lines at least up to 5 GHz with insertion loss better than 0.8 dB.
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paper_title: A Miniaturized CSRR Loaded Wide-Beamwidth Circularly Polarized Implantable Antenna for Subcutaneous Real-Time Glucose Monitoring

paper_content:

A single-fed miniaturized wide-beamwidth circularly polarized implantable antenna, operating in the Industrial, Scientific, and Medical band (2.40–2.48 GHz), is designed and experimentally verified for subcutaneous real-time glucose monitoring applications. The proposed antenna features a very good miniaturization with the dimensions of ${\mathbf 8.5 \times 8.5 \times 1.27 \; \text{mm}^{3}}$ by employing four C-shaped slots and a complementary split-ring resonator (CSRR). Meanwhile, by adjusting the slits of CSRR, circular polarization is realized. The simulation results in a three-layer phantom demonstrate that the impedance bandwidth is 12.2% (2.32–2.62 GHz) with a peak gain of −17 dBi, and the 3-dB axial-ratio bandwidth is 2.4% (2.42–2.48 GHz) with a wide beamwidth of around 140°. An in vitro test was carried out in a pork slab, and the measured impedance bandwidth is 13% (2.31–2.63 GHz) with ${\boldsymbol S_{11} , confirming the simulated results. The specific absorption rate distribution has been evaluated for the consideration of health safety, and the calculated link margin shows that the reliable communication can be guaranteed within 10 m in free space.
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paper_title: Wearable Antenna Integrated into Military Berets for Indoor/Outdoor Positioning System

paper_content:

A wearable antenna integrated into a military beret for an indoor/outdoor positioning system is proposed. The antenna consists of a truncated patch and a circular ring patch with four conductive threads. The truncated patch antenna is designed for the Global Positioning System (GPS) L1 band for use in outdoor situations, and the circular ring patch antenna with four conductive threads operates at the TM41 higher-order resonance mode (915 MHz) with a monopole-like radiation characteristic for indoor positioning systems. The antenna is fabricated using textile materials and is integrated into a military beret. The effects of the antenna deformation due to the shape of the military beret and the effects of the human head are analyzed via both simulation and measurement. The simulated and measured 10-dB return-loss bandwidths of the antenna on the head phantom fully cover the 915-MHz industrial, science, and medical band and the 1.575-GHz GPS L1 band.
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paper_title: Dual-Polarized Dual-Band Patch Antenna Loaded With Modified Mushroom Unit Cell

paper_content:

In this letter, novel designs of a triple-band linearly polarized patch antenna as well as a dual-band dually polarized patch antenna are proposed. A square slot is etched out along the diagonal of a conventional patch antenna, which is further loaded with a modified mushroom unit cell to achieve a triple-band operation. The lower-order modes are combined to achieve a circularly polarized mode, thus leading to the design of a dual-band dually polarized patch antenna. Both the triple- and dual-band prototypes of a modified mushroom loaded patch are fabricated to validate the results obtained in simulation. The results obtained in both the electromagnetic (EM) simulations and measurements are in good agreement.
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paper_title: Flexible Uniplanar Electrically Small Directive Antenna Empowered by a Modified CPW-Feed

paper_content:

A flexible printed near-field resonant parasitic (NFRP) GPS L1 antenna that is a compact, efficient, directive radiator is demonstrated. The simple uniplanar design incorporates a capacitively loaded loop (CLL) resonator, which acts as the NFRP element, and a coplanar waveguide (CPW)-fed semi-loop antenna. A set of slots is introduced into the CPW feedline ground strips. The resulting meander-line-shaped CPW ground strips act as a driven dipole element that is capacitively coupled to the NFRP element in such a manner that when they are properly tuned, nearly complete matching to the 50-Ω source is achieved with no matching circuit, and the pair acts as a two-element endfire array. Parameter studies are reported to illustrate the nuances of the design and its operating mechanisms. The experimental results are in good agreement with their simulated values. The endfire realized gain is 3.57 dBi with a 13.44-dB front-to-back-ratio (FTBR) at its resonance frequency: 1.574 GHz (GPS L1), where the electrical size ka = 0.97. The flexibility of the proposed antenna is demonstrated both numerically and experimentally by mounting it on several cylindrical structures whose curvatures vary over a large range and by confirming that there is little impact on its operational frequency, impedance matching, bandwidth, and radiation characteristics.
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paper_title: Smart wearable systems: Current status and future challenges

paper_content:

Objective: Extensive efforts have been made in both academia and industry in the research and development of smart wearable systems (SWS) for health monitoring (HM). Primarily influenced by skyrocketing healthcare costs and supported by recent technological advances in micro- and nanotechnologies, miniaturisation of sensors, and smart fabrics, the continuous advances in SWS will progressively change the landscape of healthcare by allowing individual management and continuous monitoring of a patient's health status. Consisting of various components and devices, ranging from sensors and actuators to multimedia devices, these systems support complex healthcare applications and enable low-cost wearable, non-invasive alternatives for continuous 24-h monitoring of health, activity, mobility, and mental status, both indoors and outdoors. Our objective has been to examine the current research in wearable to serve as references for researchers and provide perspectives for future research. Methods: Herein, we review the current research and development of and the challenges facing SWS for HM, focusing on multi-parameter physiological sensor systems and activity and mobility measurement system designs that reliably measure mobility or vital signs and integrate real-time decision support processing for disease prevention, symptom detection, and diagnosis. For this literature review, we have chosen specific selection criteria to include papers in which wearable systems or devices are covered. Results: We describe the state of the art in SWS and provide a survey of recent implementations of wearable health-care systems. We describe current issues, challenges, and prospects of SWS. Conclusion: We conclude by identifying the future challenges facing SWS for HM.
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paper_title: An active wearable dual-band antenna for GPS and Iridium satellite phone deployed in a rescue worker garment

paper_content:

An active wearable dual-band circularly polarized microstrip patch antenna for Global Positioning System and Iridium satellite phone applications is presented. It is constructed using flexible foam and fabric substrates, combined with copper-on-polyimide film conductors. A low-noise amplifier chip is integrated directly underneath the antenna patch. The antenna's performance is examined under bending and on-body conditions. The active antenna gain is higher than 25 dBi and the 3dB axial ratio bandwidth exceeds 183 MHz in free-space conditions. The antenna performance is robust to bending and on-body placement.
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paper_title: A Sleeve-Badge Circularly Polarized Textile Antenna

paper_content:

A circularly polarized sleeve-badge antenna is proposed for a 2.45 GHz frequency band. The proposed antenna is small and thin enough to fit within a standard jacket sleeve badge, while the assembly is based on the standard off-the-shelf parts, which enables simple and cost-effective mass production. A wide beamwidth and a 5.6% impedance bandwidth provide practical properties.
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paper_title: Built-in antenna design for 2.4 GHz ISM band and GPS operations in a wrist-worn wireless communication device

paper_content:

A compact monopole and inverted-F antenna design for 2.4 GHz ISM band (2400–2485 MHz) and 1.575 GHz GPS operations suitable to be embedded within a wrist-worn wireless communication device is presented. Those antennas are fabricated on a polycarbonate and acrylonitrile-butadiene-styrene blend substrate with a three-dimensional etching process for irregular plastic materials. The wrist-worn device with and without a solid hand phantom model is evaluated. The radiation efficiency of the antennas can reach 80% for the ISM band and 63% for the GPS band without the hand phantom model. With the hand phantom model, the radiation efficiency reduces in half for both the ISM and GPS bands due to lossy materials in the phantom model. Good agreements between simulations and measurements are obtained. Moreover, the specific absorption rate of the device for the ISM band is measured and the results are much lower than the limit required by the FCC. This build-in antenna design can be applied in the wearable wireless communication device.
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paper_title: A Novel 1.575-GHz Dual-Polarization Textile Antenna for GPS Application

paper_content:

This article presents a novel dual-polarization textile antenna (DPTA) for Global Positioning System applications. In this design, four sector radiating elements are centrally fed by a coaxial probe. A novel antenna structure is successfully achieved by integrating electronic components into a wearable textile antenna. Silver loaded epoxy adhesive is used in embedding four PIN diode switches on ShieldIt super textile of the proposed antenna. The activation of certain PIN diode switches configuration determines the polarization of DPTA. Dimension-wise, this antenna is compact and small where it consists of 40-mm radius .The proposed DPTA design successfully generated dual-polarization omnidirectional radiation pattern with maximum gain 1.81 dB at angle of 0°/360°, 90°, 180°, and 270°. Its small size, flexible, and wearable features enables this DPTA to be easily integrated onto safety jacket and rain coat for tracking, search, and rescue applications. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2414–2420, 2013
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paper_title: A Miniaturized CSRR Loaded Wide-Beamwidth Circularly Polarized Implantable Antenna for Subcutaneous Real-Time Glucose Monitoring

paper_content:

A single-fed miniaturized wide-beamwidth circularly polarized implantable antenna, operating in the Industrial, Scientific, and Medical band (2.40–2.48 GHz), is designed and experimentally verified for subcutaneous real-time glucose monitoring applications. The proposed antenna features a very good miniaturization with the dimensions of ${\mathbf 8.5 \times 8.5 \times 1.27 \; \text{mm}^{3}}$ by employing four C-shaped slots and a complementary split-ring resonator (CSRR). Meanwhile, by adjusting the slits of CSRR, circular polarization is realized. The simulation results in a three-layer phantom demonstrate that the impedance bandwidth is 12.2% (2.32–2.62 GHz) with a peak gain of −17 dBi, and the 3-dB axial-ratio bandwidth is 2.4% (2.42–2.48 GHz) with a wide beamwidth of around 140°. An in vitro test was carried out in a pork slab, and the measured impedance bandwidth is 13% (2.31–2.63 GHz) with ${\boldsymbol S_{11} , confirming the simulated results. The specific absorption rate distribution has been evaluated for the consideration of health safety, and the calculated link margin shows that the reliable communication can be guaranteed within 10 m in free space.
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paper_title: A Compact Circularly Polarized Slotted Patch Antenna for GNSS Applications

paper_content:

A compact circularly polarized (CP) square-ring slotted patch antenna with vias is proposed for global navigation satellite systems (GNSS). Four square-ring-shaped slots are cut symmetrically onto a square patch radiator along its diagonals for wide-angle CP radiation and miniaturization. The antenna size is further reduced by grounding the central patches surrounded by the square-ring-shaped slots. An antenna prototype with an overall size of 60 mm 60 mm 5m m shows a measured 10-dB return loss bandwidth of 90.0 MHz (1.565-1.655 GHz) with a maximum gain of 4.65 dBic. The measured 3-dB axial ratio (AR) bandwidth is 35.0 MHz (1.57-1.605 GHz) with a 3-dB AR beamwidth of more than 140 across the bandwidth. Index Terms—Circularly polarized antenna, global navigation satellite systems (GNSS), miniaturization, patch antenna, slotted patch radiator, via.
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paper_title: Flexible and Compact AMC Based Antenna for Telemedicine Applications

paper_content:

We present a flexible, compact antenna system intended for telemedicine applications. The design is based on an M-shaped printed monopole antenna operating in the Industrial, Scientific, and Medical (ISM) 2.45 GHz band integrated with a miniaturized slotted Jerusalem Cross (JC) Artificial Magnetic Conductor (AMC) ground plane. The AMC ground plane is utilized to isolate the user's body from undesired electromagnetic radiation in addition to minimizing the antenna's impedance mismatch caused by the proximity to human tissues. Specific Absorption Rate (SAR) is analyzed using a numerical human body model (HUGO) to assess the feasibility of the proposed design. The antenna expresses 18% impedance bandwidth; moreover, the inclusion of the AMC ground plane increases the front to back ratio by 8 dB, provides 3.7 dB increase in gain, in addition to 64% reduction in SAR. Experimental and numerical results show that the radiation characteristics, impedance matching, and SAR values of the proposed design are significantly improved compared to conventional monopole and dipole antennas. Furthermore, it offers a compact and flexible solution which makes it a good candidate for the wearable telemedicine application.
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paper_title: Flexible 16 Antenna Array for Microwave Breast Cancer Detection

paper_content:

Radar-based microwave imaging has been widely studied for breast cancer detection in recent times. Sensing dielectric property differences of tissues has been studied over a wide frequency band for this application. We design single- and dual-polarization antennas for wireless ultrawideband breast cancer detection systems using an inhomogeneous multilayer model of the human breast. Antennas made from flexible materials are more easily adapted to wearable applications. Miniaturized flexible monopole and spiral antennas on a 50-μm Kapton polyimide are designed, using a high-frequency structure simulator, to be in contact with biological breast tissues. The proposed antennas are designed to operate in a frequency range of 2–4 GHz (with reflection coefficient (S11) below –10 dB). Measurements show that the flexible antennas have good impedance matching when in different positions with different curvature around the breast. Our miniaturized flexible antennas are 20 mm × 20 mm. Furthermore, two flexible conformal 4 × 4 ultrawideband antenna arrays (single and dual polarization), in a format similar to that of a bra, were developed for a radar-based breast cancer detection system. By using a reflector for the arrays, the penetration of the propagated electromagnetic waves from the antennas into the breast can be improved by factors of 3.3 and 2.6, respectively.
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paper_title: Smart Coat with a Fully-Embedded Textile Antenna for IoT Applications

paper_content:

The Internet of Things (IoT) scenario is strongly related with the advance of the development of wireless sensor networks (WSN) and radio frequency identification (RFID) systems. Additionally, in the WSN context, for a continuous feed, the integration of textile antennas for energy harvesting into smart clothing is a particularly interesting solution when the replacement of batteries is not easy to practice, such as in wearable devices. This paper presents the E-Caption: Smart and Sustainable Coat. It has an embedded dual-band textile antenna for electromagnetic energy harvesting, operating at global system for mobile communication (GSM) 900 and digital cellular system (DCS) 1800 bands. This printed antenna is fully integrated, as its dielectric is the textile material composing the coat itself. The E-Caption illustrates the innovative concept of textile antennas that can be manipulated as simple emblems. Seven prototypes of these “emblem” antennas, manufactured by lamination and embroidering techniques are also presented. It is shown that the orientation of the conductive fabric does not influence the performance of the antenna. It is also shown that the direction and number of the stitches in the embroidery may influence the performance of the antenna. Moreover, the comparison of results obtained before and after the integration of the antenna into cloth shows the integration does not affect the behavior of the antenna.
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paper_title: Low SAR Ferrite Handset Antenna Design

paper_content:

This article was published in the journal, IEEE Transactions on Antennas and Propagation[© IEEE], and is available at: http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=8 ::: Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.
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paper_title: Investigations on SAR and Thermal Effects of a Body Wearable Microstrip Antenna

paper_content:

Wearable technology has emerged as a hot topic in contemporary years around the globe and the interest in this sector continues to develop and will dominate in the future as well. This research work presents a microstrip-based multi-band monopole antenna for body wearable wireless devices (WWD) used for various body centric wireless communication applications. The designed antenna works at multi bands resonating at 1.8, 2.4, 5.0 and 8.9 GHz covering wireless and UWB based communication technologies. The electromagnetic (EM) effects of radiation absorption are investigated in terms of specific absorption rate and its biological manifestation as heating effect. EM computations and measurements are used to analyze the biological effects when placed on different sites on the body. Thermal effects for short term exposures and steady state conditions are evaluated using analytical methods. Experimental techniques using infrared thermography has been used for finding out the temperature elevation at three specific regions of the body. Simulated, analytical and experimental results of the heating effect are compared and are in good agreement. Further, the rise in temperature is found to be compliant with international safety regulations.
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paper_title: Wearable slot antenna at 2.45 GHz for off-body radiation: Analysis of efficiency, frequency shift, and body absorption.

paper_content:

The interaction of body-worn antennas with the human body causes a significant decrease in antenna efficiency and a shift in resonant frequency. A resonant slot in a small conductive box placed on the body has been shown to reduce these effects. The specific absorption rate is less than international health standards for most wearable antennas due to small transmitter power. This paper reports the linear relationship between power absorbed by biological tissues at different locations on the body and radiation efficiency based on numerical modeling (r = 0.99). While the -10 dB bandwidth of the antenna remained constant and equal to 12.5%, the maximum frequency shift occurred when the antenna was close to the elbow (6.61%) and on the thigh (5.86%). The smallest change was found on the torso (4.21%). Participants with body-mass index (BMI) between 17 and 29 kg/m2 took part in experimental measurements, where the maximum frequency shift was 2.51%. Measurements showed better agreement with simulations on the upper arm. These experimental results demonstrate that the BMI for each individual had little effect on the performance of the antenna. Bioelectromagnetics. 39:25-34, 2018. © 2017 Wiley Periodicals, Inc.
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paper_title: A Low-Profile Wearable Antenna Using a Miniature High Impedance Surface for Smartwatch Applications

paper_content:

A novel antenna structure enabled by a miniature high impedance surface (HIS) is proposed for smartwatch applications. The smartwatch antenna must be low-profile, highly directive, low specified absorption rate (SAR), and robust to the loading effect due to a human body. HISs are particularly suitable to cope with these design goals. However, an HIS is usually too electrically large to fit into the design space of smartwatch applications. Furthermore, the characterization of HISs is determined by observing the reflection phase of a unit cell, but this method becomes improper for finite-size and miniaturized HISs. In this letter, a new design method is presented. By using fractional factorial designs (FFD), the antenna performances are significantly enhanced even though the size of the HIS is only $0.3{\lambda _0}\times 0.3{\lambda _0}$ . Accordingly, the dimensions of the proposed antenna are $38 \times 38 \times 3 ~\hbox{mm}^3$ (at 2.4 GHz), which is the most compact HIS structure to date. The directivity of the antenna is 6.3 dBi, and the maximum 1 g averaged SAR value is only 0.29 W/kg for an input power of 100 mW; moreover, the radiation efficiency and impedance matching are very robust against the loading effect due to wrist tissue.
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paper_title: A High-Fidelity All-Textile UWB Antenna With Low Back Radiation for Off-Body WBAN Applications

paper_content:

A novel all-textile UWB antenna with full-ground plane and high on-body fidelity is presented in this work. Due to the combined requirements of backward radiation reduction in WBANs and high-fidelity prerequisite for UWB pulse transmission/reception, a multilayered structure is implemented. The structure consists of two patches and a ground plane implemented on two layers of 2-mm-thick substrate. The full ground plane on the lower layer shields users against on-body radiation. Numerical and experimental evaluations both in free space and on human body prove the antenna operation within the FCC UWB bandwidth of 3.1–10.6 GHz. Its high-measured on-body system fidelity values of between 95% and 97% at a distance of 1 m show that the textile UWB antenna is suitable for body-worn UWB impulse radio communication.
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paper_title: Investigation of Flexible Textile Antennas and AMC Reflectors

paper_content:

In this paper, two different methods for fabric characterization are presented: a single frequency method and a broadband method. Felt and denim fabrics are characterized, and patch antennas are designed using these substrates to test both methods. Prototypes of the antennas on felt and denim are manufactured using conductive textile (called electrotextile) aiming to obtain fully flexible antennas. The prototypes are characterized in anechoic chamber to be compared and obtain conclusions related to the characterization methods. A new dual-band hexagonal AMC reflector combinable with antennas is also proposed to improve their performance and reduce the backward radiation to the human body. A novel broadband CPW-fed monopole antenna is designed to be combined with the AMC. The resulted prototype is characterized and compared with the performance of the CPW-fed antenna alone.
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paper_title: A Low Profile, Dual-band, Dual Polarized Antenna for Indoor/Outdoor Wearable Application

paper_content:

A planar, low-profile, dual-band and dual-polarized antenna on a semi-flex substrate is proposed in this paper. The antenna is fabricated on Rogers substrate with a thickness of 3.04 mm and sized at 70.4×76.14×3.11 mm ::: 3 ::: (0.37λ ::: 0 ::: ×0.40λ ::: 0 ::: ×0.016λ ::: 0 ::: ) only. The circular polarization property is enabled in the global navigation satellite system (GNSS) L1/E1 (lower) band by introducing a complementary split ring resonator on the antenna patch. Meanwhile, the antenna operates in the second (upper) 2.45 GHz WLAN band is enabled by etching a U-shaped slot on its ground plane. This simultaneous, dual-band and dual-polarized operation enables the proposed antenna to be applied in the indoor/outdoor wearable application. To isolate the antenna against the influence of the human body, a multiband artificial magnetic conductor (AMC) plane is added on the reverse side of the dual-band radiator. Comparison of the antenna without AMC in free space and when evaluated on the chest of a human body backed by AMC showed improved gain; from 3-5.1 dBi in the lower band, and from 1.53-5.03 dBi in the upper band. Besides that, the front-to-back ratio of the AMC backed monopole antenna also improved from 11-21.88 dB and from 2.5-24.5 dB in the GNSS and WLAN bands, respectively. Next, the specific absorption rate (SAR) of the monopole antenna with and without the AMC plane is assessed. Evaluation results indicate that the maximum SAR value decreased by up to 89.45 % in comparison with the antenna without AMC in the lower band. This indicates the effectiveness of the AMC array in increasing gain and FBR, besides reducing EM absorption in the human body.
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paper_title: A Wearable Wideband Circularly Polarized Textile Antenna for Effective Power Transmission on a Wirelessly-Powered Sensor Platform

paper_content:

In this communication, the simulation and experimental results of a novel wideband wearable circularly polarized textile antenna for low-power transmission in the 2.45 GHz ISM band are presented. The wide impedance and axial ratio bandwidths make it perfect for low microwave power transmission to a wearable sensor system. The antenna is flexible, robust and light weight so that it can be easily integrated into clothes. It is shown that the circularly polarized textile antenna has a 3-dB axial ratio bandwidth of 564 MHz (23%) and a -10dB impedance bandwidth of 1086 MHz (44%) on a human body with the maximum gain of 4.9 dBic. Lastly, the textile antenna is employed on the battery-less temperature sensor system on a human arm to demonstrate the effective power transmission over a metre distance.
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paper_title: Textile Soft Surface for Back Radiation Reduction in Bent Wearable Antennas

paper_content:

A textile soft surface is proposed to reduce back radiation of a textile patch antenna, and the performance is analyzed when the antenna is placed on a bent surface. This surface is assumed to be c ...
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paper_title: CPW-fed monopole antenna with reduced radiation hazards toward human head using metallic thin-wire mesh for 802.11ac applications

paper_content:

This article presents a planar monopole antenna with reduced radiation hazard toward human head using thin-wire mesh which is needed in smart phone (mobile) for less crowded 801.11ac (5 GHz Wi-Fi) applications. The antenna consists of a rectangular radiating element with a particular rectangular part being removed from it to increase the electrical length of the antenna for miniaturization. CPW—feed and radiating element are printed on the topside of the double sided PCB. Radiation hazards toward human head has been reduced using a metallic thin-wire mesh in the backside of the PCB. Orientation of metallic thin wire mesh play a vital role. It has been placed in such a way to disturb the fringing field coupled toward head direction (positive X direction). The proposed antenna offers an impedance bandwidth of 1.47 GHz from 4.35 GHz to 5.82 GHz with resonant frequency 5.18 GHz when it printed on an FR4-epoxy substrate with dielectric constant (er) of 4.4. It is over all in dimension of 21.7 × 25.5 × 1.6 mm3. It has been designed and optimized using parametric study on the geometrical dimensions are investigated using electromagnetic simulation software HFSS 13.0 (High Frequency Structure Simulator). © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2684–2687, 2015
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paper_title: Conformal dual-band textile antenna with metasurface for WBAN application

paper_content:

This paper presents the design of a dual-band wearable planar slotted dipole integrated with a metasurface. It operates in the 2.45 GHz (lower) and 5.8 GHz (upper) bands and made fully using textiles to suit wireless body area network applications. The metasurface in the form of an artificial magnetic conductor (AMC) plane is formed using a rectangular patch incorporated with a diamond-shaped slot to generate dual-phase response. This plane is then integrated with the planar slotted dipole antenna prior to its assessment in free space and bent configurations. Simulations and measurements indicated a good agreement, and the antenna featured an impedance bandwidth of 164 and 592 MHz in the lower and upper band, respectively. The presence of the AMC plane also minimized the backward radiation toward the human body and enhanced realized gains by up to 3.01 and 7.04 dB in the lower and upper band.
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paper_title: Wearable AMC Backed Near-Endfire Antenna for On-Body Communications on Latex Substrate

paper_content:

A near-endfire, artificial magnetic conductor (AMC) backed wearable antenna is proposed in this paper for wireless body area networks operating in the 2.4-GHz industrial, scientific and medical (ISM) radio band. The latex substrate permittivity has accurately been characterized for realizing a flexible planar Yagi-Uda antenna printed on it using a large-area screenprinting process. The bidirectional-endfire radiation of Yagi- Uda antenna is changed to an off-axis near-endfire radiation using an AMC reflector also printed on latex. The antenna is separated from the upper AMC surface using flexible Styrofoam of thickness 0.044λ 0 at 2.4 GHz for the best compromise between keeping the antenna structure low profile and achieving an off-axis beam-tilt radiation of ~74° toward the endfire direction. The 0° reflection phase single-layered AMC and double-layered AMC (D-AMC) surfaces are proposed to reduce the body-absorbed radiation and, consequently, minimize the peak specific absorption rate (SAR) level for 2.4-GHz frequency band. Antenna performance in terms of return loss, radiation efficiency, extent of frequency detuning, gain, and SAR level is studied for free space as well as the CST MWS tissue-equivalent voxel model for all the proposed antenna designs. Antenna deformation bending study when placed on the human body is also performed in this paper. The antenna design is first optimized and fabricated on printed circuit board to verify the concept and then designed over the latex for actual human on-body all-flexible configuration. The Yagi-Uda antenna backed with D-AMC reflector demonstrates the measured return loss bandwidth of 45 MHz (2.425-2.47 GHz) and the gain of 0.12 dBi in the endfire direction with an improved on-body (chest) radiation efficiency of 78.97% and a reduced peak SAR level of 0.714 W/kg (average over 10-g tissue) for the compact overall flexible latex antenna volume of 0.4λ 0 ×0.4λ 0 ×0.076λ 0 at 2.4 GHz. To the best of our knowledge, this is the first latex-based endfire antenna for on-body 2.4-GHz wireless communications backed with an AMC periodic metamaterial surface.
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paper_title: Bending impact on a flexible ultra-wideband conductive polymer antenna

paper_content:

This paper presents a numerical and experimental study of the impact of bending on the characteristics of a flexible ultra-wide band (UWB) conductive polymer antenna. The antenna under investigation is highly flexible and designed for high radiation efficiency. It consists of a planar structure made entirely of non-metallic materials including a thin PEDOT polymer sheet as conducting materials and sticky tape as substrate. Importantly for a flexible antenna, possible performance degradations in various bending conditions need to be investigated, including variations in matching and radiation characteristics. The results indicate that the antenna still performs well in terms of impedance matching even with considerable bending angles whereas degradation due to bending has to be taken into account for polarization.
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paper_title: A Wideband Textile Antenna with a Ring-slotted AMC Plane

paper_content:

A wideband microstrip-based textile planar antenna with artificial magnetic conductor (AMC) plane is presented. The antenna is initially designed using the combination of two rectangular microstrip antennas operating at 1.5 and 2.5 GHz before being further optimized for wideband operation using various broadbanding techniques. This optimized radiator is then placed over an array of unit elements forming an AMC plane. Each unit element is formed using a square patch slotted using a circular ring and is designed to resonate at 2 GHz. To validate the contribution of the AMC plane in reducing backward radiation toward the human user, the performance of the proposed antenna is compared to a similar antenna without the AMC plane. This investigation indicated that the proposed antenna is capable of reducing backlobe while simultaneously increasing gain to 3.38 dB and improving bandwidth up to 52%.
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paper_title: Dual-Band EBG Integrated Monopole Antenna Deploying Fractal Geometry for Wearable Applications

paper_content:

This letter presents the design of a dual-band wearable fractal-based monopole patch antenna integrated with an electromagnetic band-gap (EBG) structure. The prototype covers the GSM-1800 MHz and ISM-2.45 GHz bands. The EBG structure reduces the radiation into the human body over 15 dB. It also reduces the effect of frequency detuning due to the human body. The performance of the antenna under bending, crumpling, and on-body conditions has been studied and presented. Specific absorption rate (SAR) assessment has also been performed to validate the antenna for its usefulness in wearable applications.
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paper_title: Wearable Antenna Integrated into Military Berets for Indoor/Outdoor Positioning System

paper_content:

A wearable antenna integrated into a military beret for an indoor/outdoor positioning system is proposed. The antenna consists of a truncated patch and a circular ring patch with four conductive threads. The truncated patch antenna is designed for the Global Positioning System (GPS) L1 band for use in outdoor situations, and the circular ring patch antenna with four conductive threads operates at the TM41 higher-order resonance mode (915 MHz) with a monopole-like radiation characteristic for indoor positioning systems. The antenna is fabricated using textile materials and is integrated into a military beret. The effects of the antenna deformation due to the shape of the military beret and the effects of the human head are analyzed via both simulation and measurement. The simulated and measured 10-dB return-loss bandwidths of the antenna on the head phantom fully cover the 915-MHz industrial, science, and medical band and the 1.575-GHz GPS L1 band.
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paper_title: Wearable Flexible Reconfigurable Antenna Integrated With Artificial Magnetic Conductor

paper_content:

This letter presents a wearable flexible reconfigurable folded slot antenna. The antenna is composed of a folded slot and a stub where the reconfigurability is achieved by turning a p-i-n diode on and off , which alters the radiation characteristics of the stub. The operating frequency and polarization of the slot and stub are different. Hence, a polarization-dependent dual-band artificial magnetic conductor (AMC) surface is integrated with the antenna to improve its radiation performance and to reduce the specific absorption rate (SAR). The antenna is designed and fabricated on a flexible substrate, and its performance is measured for both flat and curved configurations. The measurements show an excellent agreement with the simulations. To examine its performance as a wearable antenna, it is measured on a human body. Simulations show that the SAR level is reduced when the AMC surface is used as an isolator. The proposed wearable antenna structure can be used for wireless body area network (WBAN) and Worldwide Interoperability for Microwave Access (WiMAX) body-worn wireless devices.
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paper_title: Compact, Highly Efficient, and Fully Flexible Circularly Polarized Antenna Enabled by Silver Nanowires for Wireless Body-Area Networks

paper_content:

A compact and flexible circularly polarized (CP) wearable antenna is introduced for wireless body-area network systems at the 2.4 GHz industrial, scientific, and medical (ISM) band, which is implemented by employing a low-loss composite of polydimethylsiloxane (PDMS) and silver nanowires (AgNWs). The circularly polarized radiation is enabled by placing a planar linearly polarized loop monopole above a finite anisotropic artificial ground plane. By truncating the anisotropic artificial ground plane to contain only 2 by 2 unit cells, an integrated antenna with a compact form factor of 0.41 λ 0 × 0.41 λ 0 × 0.045 λ 0 is obtained, all while possessing an improved angular coverage of CP radiation. A flexible prototype was fabricated and characterized, experimentally achieving S 11 <− 15 dB, an axial ratio of less than 3 dB, a gain of around 5.2 dBi, and a wide CP angular coverage in the targeted ISM band. Furthermore, this antenna is compared to a conventional CP patch antenna of the same physical size, which is also comprised of the same PDMS and AgNW composite. The results of this comparison reveal that the proposed antenna has much more stable performance under bending and human body loading, as well as a lower specific absorption rate. In all, the demonstrated wearable antenna offers a compact, flexible, and robust solution which makes it a strong candidate for future integration into body-area networks that require efficient off-body communications.
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paper_title: Bending and On-Arm Effects on a Wearable Antenna for 2.45 GHz Body Area Network

paper_content:

Three types of flexible textile antennas for 2.45 GHz body area network (BAN) are compared in this letter. Two types of conducting materials are used to form radiation patch and ground plane; they are called copper foil tape (CFT, 0.05 mm thickness) and Shieldex (SH, 0.13 mm thickness, 0.009 Ohm surface resistivity). The substrate is a thin felt with relative permittivity of 1.2 and the thickness of 2 mm. In order to satisfy these requirements of small frequency shifting when the antenna is bent and placed on human body, two shorting probes are used to connect the radiation patch and ground plane. Compared to the antenna without shorting probes, the size of proposed antenna is reduced from 96 ×47 to 70 ×25 mm 2 , and the measured minimum value of S11 in free space is also decreased from -14.59 to -33.30 dB. Furthermore, an antenna with smaller size of 46 ×25 mm 2 is designed by modifying the proposed structure, and it can act as a wearable antenna as well.
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paper_title: A Modular Textile Antenna Design Using Snap-on Buttons for Wearable Applications

paper_content:

An antenna design concept with detachable radiation elements offering modular geometry reconfigurabilities for wearable applications is presented. By utilizing snap-on buttons, both as the radio-frequency (RF) connection and mechanical holding mechanism, different modularly interchangeable microstrip patches are employed to demonstrate geometry reconfigurabilities in terms of polarization and resonance frequency. The uniqueness of the design arises from the fact that all configurations share one common feed structure which consists of a two-layered substrate including snap-on buttons, a ground plane, and a proximity coupled feed. To show the concept, modular realizations with different functionalities in terms of polarization or resonance frequency are demonstrated in this paper. First, a detachable patch offering interchangeable right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) at 5 GHz is proposed. Second, a demonstration of a planar inverted-F antenna (PIFA) concept offering interchangeable resonance frequencies for the 2.4- and 5.3-GHz bands of wireless local area networks (WLAN) is given. Finally, a patch module designed for 8-GHz operation is presented to show the versatility in frequency modularity. Experimental results of the fabricated antennas in free space, worn by a torso phantom and in bending conditions, validate the concept and prove that this type of modular design offers convenient, passive, low cost, and versatile system reconfigurabilities, which can benefit wearable applications.
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paper_title: Wearable Circularly Polarized Antenna for Personal Satellite Communication and Navigation

paper_content:

Integrating antennas into fabrics is a potential way for facilitating many applications, such as health monitoring of patients, fire-fighting, rescue work, and space and military personal communications. This paper studies possibilities to construct a flexible, lightweight and mechanically robust textile antenna for dual-band satellite use: Iridium and GPS. Different textile materials were characterized and the most promising materials were used to design, construct, and test a rectangular patch antenna. The gain and axial ratio for both bands is compliant with specifications and relatively stable under most bending conditions. The developed antenna solution allows integration into clothing.
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paper_title: Effect of lamination on the bending fatigue life of copper coated PET substrate

paper_content:

While today's display technology is mainly based on rigid-based substrate, flexible display technology has been ::: significantly growing since the last decade. However, Flexible displays are susceptible to many types of stresses during ::: processing and usage. Thin films on flexible substrate are sensitive to ambient conditions. Therefore devices are usually ::: laminated with a protective layer. In this study high cyclic bending fatigue experiments were conducted on 2000 oA thick ::: copper thin films sputter deposited on 127 μm polyethylene terephthalate (PET) substrate laminated with another 127 μm ::: PET layer. High magnification images were used to observe crack initiation and propagation in the thin film layer. Initial ::: results showed a great influence of laminate layer on stress reduction in the thin film. Furthermore, a lamination layer ::: causes cracks to spread out on a larger area with fine cracks and therefore reduce the chance of the cracks to meet and ::: grow.
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paper_title: A Compact, Low-Profile Metasurface-Enabled Antenna for Wearable Medical Body-Area Network Devices

paper_content:

We propose a compact conformal wearable antenna that operates in the 2.36-2.4 GHz medical body-area network band. The antenna is enabled by placing a highly truncated metasurface, consisting of only a two by two array of I-shaped elements, underneath a planar monopole. In contrast to previously reported artificial magnetic conducting ground plane backed antenna designs, here the metasurface acts not only as a ground plane for isolation, but also as the main radiator. An antenna prototype was fabricated and tested, showing a strong agreement between simulation and measurement. Comparing to previously proposed wearable antennas, the demonstrated antenna has a compact form factor of 0.5 λ ::: 0 ::: ×0.3 λ ::: 0 ::: ×0.028 λ ::: 0 ::: , all while achieving a 5.5% impedance bandwidth, a gain of 6.2 dBi, and a front-to-back ratio higher than 23 dB. Further numerical and experimental investigations reveal that the performance of the antenna is extraordinarily robust to both structural deformation and human body loading, far superior to both planar monopoles and microstrip patch antennas. Additionally, the introduced metal backed metasurface enables a 95.3% reduction in the specific absorption rate, making such an antenna a prime candidate for incorporation into various wearable devices.
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paper_title: Wearable EBG antenna bending and crumpling

paper_content:

In this paper, we present the performance of a dual-band textile CPW antenna under different bending and crumpling conditions. The performance of the antenna is presented together with an electromagnetic band gap material (EBG) to improve the wearable antenna performance. The input impedance and radiation pattern are investigated based on numerical and experimental methods at 2.45 GHz and 5.8 GHz.
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paper_title: Textile antennas: effects of antenna bending on input matching and impedance bandwidth

paper_content:

How the performance of wearable textile antennas is affected on the antenna bending is described herein. The authors focus on the resonance frequency fluctuation and input-match bandwidth variation due to the antenna bending. The results are given for three different antennas, namely, a conventional patch, EBG, and dual-band U-slot antennas
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paper_title: Recent progress on liquid metals and their applications

paper_content:

AbstractGallium-based liquid metals show excellent thermal and electrical conductivities with low viscosity and non-toxicity. Their melting points are either lower than or close to room temperature, which endows them with additional advantages in comparison to the solid metals; for example, they are flexible, stretchable and reformable at room temperature. Recently, great improvements have been achieved in developing multifunctional devices by using Ga-based liquid metals, including actuators, flexible circuits, bio-devices and self-healing superconductors. Here, we review recent research progress on Gallium-based liquid metals, especially on the applications aspects. These applications are mainly based on the unique properties of liquid metals, including low melting point, flexible and stretchable mechanical properties, excellent electrical and thermal conductivities and biocompatibility.
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paper_title: Wearable Flexible Reconfigurable Antenna Integrated With Artificial Magnetic Conductor

paper_content:

This letter presents a wearable flexible reconfigurable folded slot antenna. The antenna is composed of a folded slot and a stub where the reconfigurability is achieved by turning a p-i-n diode on and off , which alters the radiation characteristics of the stub. The operating frequency and polarization of the slot and stub are different. Hence, a polarization-dependent dual-band artificial magnetic conductor (AMC) surface is integrated with the antenna to improve its radiation performance and to reduce the specific absorption rate (SAR). The antenna is designed and fabricated on a flexible substrate, and its performance is measured for both flat and curved configurations. The measurements show an excellent agreement with the simulations. To examine its performance as a wearable antenna, it is measured on a human body. Simulations show that the SAR level is reduced when the AMC surface is used as an isolator. The proposed wearable antenna structure can be used for wireless body area network (WBAN) and Worldwide Interoperability for Microwave Access (WiMAX) body-worn wireless devices.
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paper_title: Graphene-based multimode inspired frequency reconfigurable user terminal antenna for satellite communication

paper_content:

This study proposes a graphene conductive ink printed textile-based microstrip antenna capable of switching between S-band (3.03 GHz, TM ::: 10 ::: mode) and C-band (5.17 GHz, TM ::: 02 ::: mode and 6.13 GHz, TM ::: 20 ::: mode). The graphene conductive ink printed textile shows surface resistance of 2.7 Ω Sq. ::: -1 ::: , conductivity of 0.37 × 105 Sm ::: -1 ::: and excellent microstructural characteristics, which makes it suitable to be used as a metal sheet to fabricate the antenna structure. To overcome the low-conductivity issue of graphene conductive ink, a multilayered substrate approach is utilised to improve radiation performances of the antenna. A peak realised gain of 2.09 dBi and radiation efficiency of 74% is achieved at the dominant mode (3.03 GHz). The frequency reconfigurability is introduced by exciting the higher order modes, TM ::: 02 ::: and TM ::: 20 ::: through two different feeding locations. The excitation of ports is controlled through a radio frequency (RF) pin diode switch integrated microstrip transmission line. Subsequently, the proposed structure is further designed using copper foil of thickness (17 μm) and a comparative analysis of graphene-based and copper-based antennas is presented. The proposed antenna performs substantially well in terms of peak realised gain and radiation efficiency compared with that of the existing graphene-based antenna and the performance deviation with respect to the copper based antenna is lowered significantly.
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paper_title: Inkjet-Printed Flexible Reconfigurable Antenna for Conformal WLAN/WiMAX Wireless Devices

paper_content:

A new flexible reconfigurable antenna based on the concept of folded slot antennas is reported. The device is designed on a flexible polyethylene terephthalate substrate, and inkjet-printing technology is used to fabricate the prototype. One p-i-n diode is incorporated on the antenna surface to redirect and redistribute the surface current resulting in a reconfigurable antenna in terms of frequency and polarization. When the p-i-n diode is forward biased ( ON ), the antenna has a single band at 2.42 GHz for WLAN wireless devices. However, when the p-i-n diode is reversed biased ( OFF ), the antenna is dual-band with different polarizations at 2.36 and 3.64 GHz for WLAN and WiMAX wireless devices, respectively. The proposed antenna is simulated, fabricated, and tested for both flat and curved geometries, such as circumferential and axial cylindrical configurations, with good agreement between measurements and simulations.
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paper_title: Textile Antenna With Simultaneous Frequency and Polarization Reconfiguration for WBAN

paper_content:

This paper proposes the design of a reconfigurable circularly polarized textile antenna. The circular polarization feature in the proposed antenna is generated by the edge truncation of a rectangular patch and the incorporation of a slotted ground plane, whilst the frequency reconfigurability feature is realized by slot size modification via the use of three embedded RF p-i-n diode switches. Consequently, the antenna operation can be switched between six frequencies (1.57, 1.67, 1.68, 2.43, 2.50, and 2.55 GHz) depending on the seven switch configurations. The proposed antenna is validated experimentally to be operable within the WBAN, WLAN, and GPS range in a compact and wearable format, with gains of up to 4.8 dBi.
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paper_title: A Miniaturized Frequency Reconfigurable Antenna With Single Bias, Dual Varactor Tuning

paper_content:

Frequency reconfigurable antenna designs often suffer from limited tuning ranges and complex bias networks. This paper describes a dual varactor-tuned miniaturized antenna with a single bias introduced through the RF feed that addresses these challenges. The dual varactors provide a large tuning range (410–990 MHz, 2.1–3.5 GHz; ${\bf{VSWR}} = {\bf{2:1}}$ ), while the single bias voltage applied to both varactors greatly simplifies the bias network. The introduction of the bias through the RF feed eliminates the need for separate bias lines. As a result, when the electrical size of the antenna is decreased through tuning, undesired bias line coupling and radiation effects are nonexistent. The design highlights the radiation efficiency limitations associated with the desirable planar topology for electrically small antennas with very wide tuning range requirements. An overview of the antenna’s geometry and operation is presented along with detailed measurements to characterize its performance.
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paper_title: Miniature and Reconfigurable CPW Folded Slot Antennas Employing Liquid-Metal Capacitive Loading

paper_content:

Microfluidic channels filled with liquid metal are used to realize miniature and reconfigurable CPW folded slot antennas. The method is based on employing the reactive loading effect of fluid metal bridges on top of the CPW slot antenna. As a result of this reactive loading, the frequency of the antenna reduces and the antenna is miniaturized by a factor of 85%. Also, by changing the configuration of filled and empty channels, each channel can be used as a switch. By using two pairs of microfluidic channels, three different frequency bands of 2.4, 3.5, and 5.8 GHz can be achieved. This translates to a switching ratio ( $\bm{f}_{\bm{TR}}=\bm{f}_{\mathbf{2}}/\bm{f}_{\mathbf{1}}$ ) of more than 2.5. The antenna is realized using common PCB techniques for the antenna circuit board and three-dimensional (3-D) printing technology for PDMS-based microfluidics structure. The antenna circuit board and the PDMS structure are bonded to each other using a very thin spin-coated PDMS layer. Design methodology, simulation, and measurement results of both antenna prototypes are presented. Both the miniature and reconfigurable antennas have similar radiation patterns to a normal CPW folded slot antenna and show low cross-polarization levels at all operating frequencies.
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paper_title: Frequency Reconfigurable Antenna for Wireless Communications Using GaAs FET Switch

paper_content:

A compact frequency reconfigurable antenna which could be easily switched between a narrowband state and a dual-band state is presented in this letter. The narrowband covers the WLAN (2.4-2.48 GHz) and WiMAX (2.5-2.69 GHz), while the dual-band supports the PCS (1.85-1.99 GHz) and WiMAX (3.4-3.69 GHz). The reconfigurability is achieved by using a single GaAs field effect transistor switch to change the length of the current flow path. The switch can be directly driven by digital signal, and no bias network is needed. The simulated results are in agreement well with the measured results. The proposed antenna is well suited to be integrated within the wireless handheld devices.
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paper_title: A Reconfigurable Inkjet-Printed Antenna on Paper Substrate for Wireless Applications

paper_content:

An inkjet-printed reconfigurable multiband antenna printed on a low-cost commercial photo paper substrate using two p-i-n diodes is proposed for the first time. A main radiator is designed to operate at 3.4 GHz band, whereas L-shaped and U-shaped radiating elements are designed to operate at 1.9 and 2.4 GHz, respectively. The antenna has a size of 30 × 40 × 0.44 mm3 and can cover most of the mobile and wireless bands between 1.5 and 4 GHz. A prototype of the proposed antenna is fabricated and measured. Measured and simulated results of S 11, radiation pattern, gain, and efficiency are in good agreement. Measured results show that the antenna has a gain and efficiency of 2 dBi and 50%, respectively. A parametric study is proposed as a guidance to design the antenna for operating in other bands between 1.5 and 4 GHz.
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paper_title: Design of a Reconfigurable Patch Antenna Using the Movement of Liquid Metal

paper_content:

A polarization-agility antenna using liquid metal (eutectic gallium indium) with high radiation efficiency is proposed in this letter. This design approach offers possibilities to use the minimum amount of liquid metal as well as elastomer, so that a higher-radiation-efficiency liquid metal antenna can be realized. The proposed design is based on an aperture-coupled patch antenna composed of both liquid metal alloy and copper tape. The polarization of this antenna is controlled by the position of the pressure-driven liquid metal encased in four triangle cavities constructed by both the elastic dielectric material (i.e., Ecoflex) and polyethylene terephthalate film. A prototype is demonstrated with a center frequency of 2.45 GHz. Three kinds of polarization including left-hand circular polarization, right-hand circular polarization, and linear polarization are successfully demonstrated. A radiation efficiency higher than 90% is observed in the measurement.
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paper_title: A Flexible 2.45-GHz Power Harvesting Wristband With Net System Output From −24.3 dBm of RF Power

paper_content:

This paper presents a flexible 2.45-GHz wireless power harvesting wristband that generates a net dc output from a −24.3-dBm RF input. This is the lowest reported system sensitivity for systems comprising a rectenna and impedance-matching power management. A complete system has been implemented comprising: a fabric antenna, a rectifier on rigid substrate, a contactless electrical connection between rigid and flexible subsystems, and power electronics impedance matching. Various fabric and flexible materials are electrically characterized at 2.45 GHz using the two-line and the T-resonator methods. Selected materials are used to design an all-textile antenna, which demonstrates a radiation efficiency above 62% on a phantom irrespective of location, and a stable radiation pattern. The rectifier, designed on a rigid substrate, shows a best-in-class efficiency of 33.6% at −20 dBm. A reliable, efficient, and wideband contactless connection between the fabric antenna and the rectifier is created using broadside-coupled microstrip lines, with an insertion loss below 1 dB from 1.8 to over 10 GHz. A self-powered boost converter with a quiescent current of 150 nA matches the rectenna output with a matching efficiency above 95%. The maximum end-to-end efficiency is 28.7% at −7 dBm. The wristband harvester demonstrates net positive energy harvesting from −24.3 dBm, a 7.3-dB improvement on the state of the art.
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paper_title: Energy Harvesting Circuit on a One-Sided Directional Flexible Antenna

paper_content:

The present letter describes the design of an energy harvesting circuit on a one-sided directional flexible planar antenna. The circuit is composed of a flexible antenna with an impedance matching circuit, a resonant circuit, and a booster circuit for converting and boosting radio frequency power into a dc voltage. The proposed one-sided directional flexible antenna has a bottom floating metal layer that enables one-sided radiation and easy connection of the booster circuit to the metal layer. The simulated output dc voltage is 2.89 V for an input of 100 mV and a 50 Ω power source at 900 MHz, and power efficiency is 58.7% for 1.0 × 107 Ω load resistance.
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paper_title: A Novel Ultra-Lightweight Multiband Rectenna on Paper for RF Energy Harvesting in the Next Generation LTE Bands

paper_content:

This paper introduces a novel compact ultralightweight multiband RF energy harvester fabricated on a paper substrate. The proposed rectenna is designed to operate in all recently released LTE bands (range 0.79–0.96 GHz; 1.71–2.17 GHz; and 2.5–2.69 GHz). High compactness and ease of integration between antenna and rectifier are achieved by using a topology of nested annular slots. The proposed rectifier features an RF-to-dc conversion efficiency in the range of 5%–16% for an available input power of −20 dBm in all bands of interest, which increases up to 11%–30% at −15 dBm. The rectenna has been finally tested both in laboratory and in realistic scenarios featuring a superior performance to other state-of-the-art RF harvesters on flexible substrates.
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paper_title: Design and realization of a wearable multi-frequency RF energy harvesting system

paper_content:

In this paper a novel wearable, triple-band ring-antenna, designed to harvest RF energy from GSM 900, GSM 1800 and WiFi sources available in the ambient, is introduced. It consists of a single annular ring suitable modified with appropriate slots to be operated as a resonant radiator at all the bands of interest. This choice allows us to achieve high radiation efficiency and circular polarization in compact dimensions, compatible with technology garments. A rectenna is then designed by the concurrent use of harmonic-balance technique and electromagnetic simulation to predict the real rectified power in general operating conditions. A multilayer configuration is exploited making use of textiles and flexible substrates whose integration issues are also discussed.
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paper_title: Circularly polarized strips integrated microstrip antenna for energy harvesting applications

paper_content:

A circularly polarized (CP) microstrip antenna with four strips is proposed for wide beamwidth and RF energy harvesting applications. Four strips along the diagonal directions are integrated symmetrically onto a square patch radiator for CP radiation with wide beamwidth. To improve the impedance matching of the antenna, a stub is integrated along the orthogonal direction of the patch radiator. The antenna is designed on FR4 substrate and an antenna prototype shows a measured 10-dB return loss bandwidth of 120 MHz (2.53–2.65 GHz) with a maximum gain of 4.6 dBic. The measured 3-dB axial ratio (AR) bandwidth is 65 MHz (2.540–2.605 GHz) with a 3-dB AR beamwidth of around 180° across the band. Overall antenna volume is 0.475λo× 0.475λo × 0.013λo at 2.5 GHz. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:1044–1049, 2016
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paper_title: UHF Wearable Rectenna on Textile Materials

paper_content:

A wearable rectenna for operation in the ultra high frequency (UHF) band is presented. The proposed device consists of a compact patch antenna and a full-wave bridge rectifier, both fabricated with textile materials. The patch antenna has been realized by using an adhesive conductive fabric on a bi-layer substrate made of pile and jeans. As for the rectifier, it is on a layer of jeans on the back-face of the antenna. Experimental data referring both to the patch antenna and to the rectenna are reported and discussed. From measurements performed with an incident power density of 14 μ/cm2, it is demonstrated that the rectenna here presented exhibits a conversion efficiency higher than 20% over the frequency range 860-918 MHz with a maximum of about 50% at 876 MHz.
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paper_title: Conformal Hybrid Solar and Electromagnetic (EM) Energy Harvesting Rectenna

paper_content:

This paper presents the design of a cost effective, hybrid energy harvesting circuit combining a solar cell and a rectenna capable to harvest ambient electromagnetic energy. Electromagnetic analysis is used to model and optimize the designed circuits in order to allow the antenna and solar cell to share the same area leading to a compact structure. Nonlinear harmonic balance optimization is used to maximize the RF-to-DC conversion efficiency of the rectenna circuitry in the presence of the solar cell and both wideband and multiband topologies are presented. Furthermore, a low cost and flexible polyethylene terephthalate PET substrate and a flexible amorphous silicon solar cell are chosen, providing for both a low cost and conformal structure. A prototype able to generate a maximum DC power of 56 mW when the solar cell is illuminated with 100 mW/cm2 solar irradiance, and a dual band rectenna demonstrating an efficiency of 15% around 850 MHz and 1850 MHz when illuminated by a microwave signal of available power is presented.
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paper_title: A Flexible 2.45-GHz Power Harvesting Wristband With Net System Output From −24.3 dBm of RF Power

paper_content:

This paper presents a flexible 2.45-GHz wireless power harvesting wristband that generates a net dc output from a −24.3-dBm RF input. This is the lowest reported system sensitivity for systems comprising a rectenna and impedance-matching power management. A complete system has been implemented comprising: a fabric antenna, a rectifier on rigid substrate, a contactless electrical connection between rigid and flexible subsystems, and power electronics impedance matching. Various fabric and flexible materials are electrically characterized at 2.45 GHz using the two-line and the T-resonator methods. Selected materials are used to design an all-textile antenna, which demonstrates a radiation efficiency above 62% on a phantom irrespective of location, and a stable radiation pattern. The rectifier, designed on a rigid substrate, shows a best-in-class efficiency of 33.6% at −20 dBm. A reliable, efficient, and wideband contactless connection between the fabric antenna and the rectifier is created using broadside-coupled microstrip lines, with an insertion loss below 1 dB from 1.8 to over 10 GHz. A self-powered boost converter with a quiescent current of 150 nA matches the rectenna output with a matching efficiency above 95%. The maximum end-to-end efficiency is 28.7% at −7 dBm. The wristband harvester demonstrates net positive energy harvesting from −24.3 dBm, a 7.3-dB improvement on the state of the art.
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paper_title: Energy Harvesting Circuit on a One-Sided Directional Flexible Antenna

paper_content:

The present letter describes the design of an energy harvesting circuit on a one-sided directional flexible planar antenna. The circuit is composed of a flexible antenna with an impedance matching circuit, a resonant circuit, and a booster circuit for converting and boosting radio frequency power into a dc voltage. The proposed one-sided directional flexible antenna has a bottom floating metal layer that enables one-sided radiation and easy connection of the booster circuit to the metal layer. The simulated output dc voltage is 2.89 V for an input of 100 mV and a 50 Ω power source at 900 MHz, and power efficiency is 58.7% for 1.0 × 107 Ω load resistance.
---
paper_title: A Novel Ultra-Lightweight Multiband Rectenna on Paper for RF Energy Harvesting in the Next Generation LTE Bands

paper_content:

This paper introduces a novel compact ultralightweight multiband RF energy harvester fabricated on a paper substrate. The proposed rectenna is designed to operate in all recently released LTE bands (range 0.79–0.96 GHz; 1.71–2.17 GHz; and 2.5–2.69 GHz). High compactness and ease of integration between antenna and rectifier are achieved by using a topology of nested annular slots. The proposed rectifier features an RF-to-dc conversion efficiency in the range of 5%–16% for an available input power of −20 dBm in all bands of interest, which increases up to 11%–30% at −15 dBm. The rectenna has been finally tested both in laboratory and in realistic scenarios featuring a superior performance to other state-of-the-art RF harvesters on flexible substrates.
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paper_title: A Watch Strap Antenna for the Applications of Wearable Systems

paper_content:

A wearable antenna based on the metal watch strap is proposed. A prototype of a TISSOT classic watch is used for the demonstration. The width of the strap has only a little impact on the radiation patterns. However, the variations of the feeding location would dramatically influence the resonance frequency and the matching performance. The shapes and the graphic patterns of the wristband have contributions on the reflection coefficients as well as the radiation patterns. A fractional bandwidth of 77.8% could be obtained when feeding to the right of the dial at 2.46 GHz, which falls into the ISM (industrial, scientific, and medical) band. The main lobe is fairly wide in both $E$ - and $H$ -planes, which would enable the strap antenna to have a good adaptation for the various postures of the arm. The measurement results show good agreement with that of the simulations, which indicates it a potential option for the applications of wearable systems.
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paper_title: Transparent and Flexible Antenna for Wearable Glasses Applications

paper_content:

This paper aims to design, fabricate, and analyze transparent and flexible monopole antennas for an application in wearable glasses. A multilayer electrode film composed of 100-nm-thick indium–zinc–tin oxide (IZTO)/Ag/IZTO (IAI), a type of transparent conducting oxide electrodes, is selected as the conductors of antennas and ground planes of the wearable glasses. The average transparency of the proposed antennas is measured to be 81.1% in the visible wavelength, and the electrical conductivity of the proposed antennas is measured to be 2 000 000 S/m. The proposed antennas are fabricated with physical vapor deposition process in high vacuum. Moreover, nontransparent antennas made of a 40-nm-thick silver (Ag) thin film are designed and fabricated to compare their performances with the transparent IAI antennas. To reduce the electromagnetic field absorption of the human head, we introduced and analyzed three configurations (types A–C) of monopole antennas having different directions of radiation patterns. The fabricated IAI antennas show the average efficiency of 40% and 4-dBi peak gain at 2.4–2.5 GHz. Furthermore, they have a specific absorption rate lower than 1.6 W/kg, which complies with the Federal Communications Commission standard, when the input power is 15 dBm, which is Google Glass’s.
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paper_title: Wearable Button Antenna for Dual-Band WLAN Applications With Combined on and off-Body Radiation Patterns

paper_content:

A new type of wearable button antenna for wireless local area network (WLAN) applications is proposed. The antenna is composed of a button with a diameter of circa 16 mm incorporating a patch on top of a dielectric disc. The button is located on top of a textile substrate and a conductive textile ground that are to be incorporated in clothing. The main characteristic feature of this antenna is that it shows two different types of radiation patterns, a monopole type pattern in the 2.4 GHz band for on-body communications and a broadside type pattern in the 5 GHz band for off-body communications. A very high efficiency of about 90% is obtained, which is much higher than similar full textile solutions in the literature. A prototype has been fabricated and measured. The effect of several real-life situations such as a tilted button and bending of the textile ground have been studied. Measurements agree very well with simulations.
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paper_title: Wearable monopole zip antenna

paper_content:

The design of a novel textile monopole antenna based on a zip at 2.5 GHz is presented. A prototype is manufactured and characterised based on return loss and radiation pattern. The bandwidth and radiation characteristics obtained make the zip antenna suitable to be used for WiFi applications in the band from 2.4 to 2.7 GHz.
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paper_title: A Cavity-Backed Annular Slot Antenna With High Efficiency for Smartwatches With Metallic Housing

paper_content:

A cavity-backed annular slot antenna designed for the use in smartwatches in the 2.4-GHz Wi-Fi band is proposed. The cavity is metallic and has a cylindrical shape with a volume of $\pi \times 21^{2}\times10$ mm3. An annular slot is cut along the edge of the top surface (as the smartwatch screen) of the cavity. The circumference of the annular slot is about $1\lambda$ , making the design small enough for the smartwatch applications. The resonant modes, current distribution, and transverse mode of the cavity-backed annular slot antenna are studied using simulations and the results are used to design a smartwatch antenna. The proposed smartwatch is studied in free space, on a computer hand model, and on a phantom hand using simulations and measurements. Measured results show that the antenna has an efficiency of 57%–66% on a phantom hand. To study the antenna in a more realistic environment, the electronic components inside the smartwatch are modeled as a metallic block. For health risk concerns related to exposure to an electromagnetic radiation, the specific absorption rate for the smartwatch in the wrist-worn and next-to-mouth conditions is also studied using simulations.
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paper_title: Button-shaped radio-frequency identification tag combining three-dimensional and inkjet printing technologies

paper_content:

A ‘button-shaped’ three-dimensional (3D) radio-frequency identification (RFID) tag combining 3D printing and inkjet printing technologies in fabrication for the first time is proposed. The button shape facilitates the tag's integration with clothes for the purposes of identification and access control. The proposed tag features a compact size (radius 15 mm, height 7.5 mm) and a good performance with a measured maximum reading range of 2.1 m (4.0 W equivalent isotropically radiated power) in the RFID Federal Communications Commission band (902–928 MHz). Furthermore, the combination of the 3D printing and inkjet printing technologies reduces the fabrication time and cost.
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paper_title: 60 GHz Patch Antenna Array With Parasitic Elements for Smart Glasses

paper_content:

A 60 GHz patch antenna array with parasitic elements for smart glasses is proposed. The antenna is composed of a patch antenna array with feedlines, parasitic elements, and a ground. The antenna has a fan-beam radiation pattern with simulated 3 dB and 10 dB beamwidths of 38.9° and 142.9°, respectively. To demonstrate the antenna performance in a practical wearable environment, the antenna characteristics were simulated on a 60 GHz head phantom. The electromagnetic exposure on the head phantom was verified using specific absorption rate and power density.
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paper_title: A Shoelace Antenna for the Application of Collision Avoidance for the Blind Person

paper_content:

A shoelace antenna for the application of collision avoidance for the blind person is proposed for the first time. A thin flexible metal wire is used to fabricate the antenna, which can run along with the shoelace without destroying the shoe or adding extra big structures. According to the investigations, to put the feeding probe at the bottom of the cross point is better than the locations around the string bowknot. To make the shoelace tighter or looser will influence the performance with an affordable variation. The effect of the biological tissues has been taken into account during the performance evaluation of the antenna. The measured fractional bandwidth is 11% with a resonance of 2.43 GHz in the ISM Band. The main lobe of the antenna points to the upper front direction with an angle of about 20°, which is suitable for the detecting of the anterior obstacles when walking. The measured results indicate reasonable performance for the shoelace antenna to serve as a tool for the blind person.
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paper_title: Dual-Band Dual-Mode Button Antenna for On-Body and Off-Body Communications

paper_content:

A dual-band dual-mode button antenna for body centric communications is presented. At the lower band, a spiral inverted-F antenna is designed with omnidirectional radiation pattern for on-body communication. At the upper band, the high-order mode of the inverted-F antenna is utilized together with a metal reflector to realize broadside radiation for off-body communication. For demonstration, a prototype is implemented. The measured peak gains on the phantom at the lower and upper bands are −0.6 and 4.3 dBi, respectively. The antenna operating on the phantom has measured efficiencies of 46.3% at the lower band and 69.3% at the upper band. The issue of specific absorption rate (SAR) is studied. The maximum transmitted power under the SAR regulation of 1.6 W/kg is found to be 26.4 dB·m, which is high enough for body centric communications. In addition, the transmission performance between two proposed antennas mounted on the body is investigated by measuring the transmission loss. With an overall miniaturized size, the robust button antenna could be integrated in clothes and be a potential candidate for wireless body area network applications.
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paper_title: Conformal Hybrid Solar and Electromagnetic (EM) Energy Harvesting Rectenna

paper_content:

This paper presents the design of a cost effective, hybrid energy harvesting circuit combining a solar cell and a rectenna capable to harvest ambient electromagnetic energy. Electromagnetic analysis is used to model and optimize the designed circuits in order to allow the antenna and solar cell to share the same area leading to a compact structure. Nonlinear harmonic balance optimization is used to maximize the RF-to-DC conversion efficiency of the rectenna circuitry in the presence of the solar cell and both wideband and multiband topologies are presented. Furthermore, a low cost and flexible polyethylene terephthalate PET substrate and a flexible amorphous silicon solar cell are chosen, providing for both a low cost and conformal structure. A prototype able to generate a maximum DC power of 56 mW when the solar cell is illuminated with 100 mW/cm2 solar irradiance, and a dual band rectenna demonstrating an efficiency of 15% around 850 MHz and 1850 MHz when illuminated by a microwave signal of available power is presented.
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paper_title: A Handbag Zipper Antenna for the Applications of Body-Centric Wireless Communications and Internet of Things

paper_content:

The idea of making use of the metal zipper on the handbag to serve as an off-body antenna is proposed, and the simulations together with measurements have been carried out. The feeding point can be located at the bottom of the zipper, and to be more specific, around one of the teeth. The excitation at certain tooth of the zipper would bring variations in the reflection coefficients as well as the radiation patterns. No matter the zipper is totally closed, quarterly opened, half opened, or is even totally opened, the antenna can operate with acceptable performance, though the common status of the handbag zipper is closed. Thus, it is to some extent reconfigurable, especially for radiation patterns. A fractional bandwidth of 4.92% at 2.44 GHz of the industrial, scientific, and medical band with a gain of about 5 dBi has been achieved. The impact of the human body has been evaluated. It is noticeable but affordable. The measured results indicate reasonable agreements to that of the simulations in both the matching performance and the radiation feature for the zipper antenna, which seems to be a promising candidate for body-centric wireless communications and the Internet of Things.
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paper_title: Dual-Antenna Concept With Complementary Radiation Patterns for Eyewear Applications

paper_content:

A dual-antenna concept to be integrated in a smart eyewear device is presented. The two antennas are printed on FR4 substrate and placed inside an Acrylonitrile butadiene styrene dielectric eyewear frame manufactured using 3-D printing technology. One of the two antennas is a monopole situated at the back of the eyewear with a specifically shaped ground plane underneath. The second antenna is a balanced-fed loop antenna placed in front of the eyewear with an integrated balun circuit. Both antennas are designed to operate in the 2.4 GHz band of the 802.11b/g/n standard. When compared to a reference single monopole antenna usually used in commercial eyewear, higher gain and complementary radiation patterns are obtained in several useful directions using our dual-antenna solution: 1) in front of the eyewear to communicate with a laptop; 2) in the side direction of the eyewear to communicate with a fixed hotspot access point; and 3) in downward direction of the eyewear to communicate with a peripheral smartphone in the pocket of the user. S-parameters and radiation pattern measurements are given with the eyewear placed over a specific anthropomorphic mannequin head phantom to validate the advantages of this novel dual-antenna concept. Specific absorption rate simulation results are presented showing the proposed antennas stay within the authorized limits.
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Title: Wearable Antennas: A Review of Materials, Structures, and Innovative Features for Autonomous Communication and Sensing

Section 1: INTRODUCTION
Description 1: Introduce the importance and potential applications of wearable antennas, highlighting key technologies like 5G and IoT, and providing an overview of the wearable device market and design challenges.

Section 2: FLEXIBLE MATERIALS FOR WEARABLE ANTENNAS
Description 2: Discuss the different types of conductive and dielectric materials used in wearable antennas, including conductive nano materials, substrates, and the requirements for flexibility and durability under various conditions.

Section 3: FABRICATION TECHNIQUES FOR WEARABLE ANTENNAS
Description 3: Describe the various fabrication methods for wearable antennas, such as substrate integrated waveguides (SIW), stitching and embroidery, screen printing, and inkjet printing, along with their advantages and limitations.

Section 4: MINIATURIZATION TECHNIQUES FOR WEARABLE ANTENNAS
Description 4: Explore the techniques used to miniaturize wearable antennas for better performance in lower frequency bands, addressing space constraints, structural deformation, and efficiency.

Section 5: WEARABLE SINGLE AND DUAL POLARIZED ANTENNAS
Description 5: Detail the design and functionality of circularly-polarized antennas for outdoor location tracking systems, including the techniques for generating circular polarization and examples of single/dual band applications.

Section 6: EFFECTS OF THE HUMAN BODY ON WEARABLE ANTENNAS
Description 6: Investigate how the human body affects the performance of wearable antennas, including issues of reflection, radiation characteristics, and compliance with SAR standards to ensure safety.

Section 7: EFFECTS OF BENDING ON WEARABLE ANTENNAS
Description 7: Examine the impact of mechanical deformation like bending on the performance of wearable antennas, and discuss design methods to alleviate these effects.

Section 8: RECONFIGURABLE WEARABLE ANTENNAS
Description 8: Present various reconfigurable antenna designs that offer switching capabilities for frequency, polarization, and radiation direction, enhancing the versatility and functionality of wearable devices.

Section 9: ENERGY-HARVESTING WEARABLE RECTENNAS
Description 9: Discuss the integration of energy-harvesting elements into wearable antennas to achieve battery autonomy, and review examples of rectenna systems for sustainable power sources.

Section 10: UNIQUE WEARABLE ANTENNA TECHNIQUES
Description 10: Highlight innovative antenna design techniques for specific applications and placements, such as button antennas, zipper antennas, shoelace antennas, and antennas integrated into everyday items like glasses and watches.

Section 11: SUMMARY
Description 11: Summarize the key findings from the review, stressing the importance of flexible materials, effective fabrication methods, design challenges, and innovative features for future wearable antenna technologies.