Towards a Chemiresistive Sensor-Integrated Electronic Nose: A Review
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paper_title: Electronic noses: specify or disappear

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Abstract When the quality control is achieved by using GC or GC/MS, the apparatus must comply with the applicable norms, but what about “electronic noses”? End users demand for formal specifications for selectivity, sensitivity, repeatability and sample throughput. The behavioural modelling of electronic olfactometers may provide specifications for these required parameters. This will allow both the measure itself, and evaluate the influence of the experimental errors on the sample classification. Users may expect to find a methodology allowing the performances of systems to be checked before any final decision and during routine use. We have demonstrated that the system sensitivity and logarithmic baseline recovery after analysis can be well fitted, thus enabling high-accuracy measurements with controlled sample throughput. The selectivity versus temperature of the sensitive element is currently in characterisation using a GC/sensors coupling.
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paper_title: Electronic Noses as Flexible Tools to Assess Food Quality and Safety: Should We Trust Them?

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This paper presents three different applications of an electronic nose (EN) based on a metal oxide sensor array, in order to illustrate the broad spectrum of potential uses of the technique in food quality control. The following scenarios are considered: 1) the screening of a typical error that may occur during the processing of tomato pulp, which leads to sensory damage of the product; 2) the detection of microbial contamination by Alicyclobacillus spp. (ACB) affecting soft drinks; and 3) the proof of evidence of extra virgin olive oil fraudulently adulterated with hazelnut oil. In each case, the EN is able to identify the spoiled product by means of the alterations in the pattern of volatile compounds, reconstructed by principal component analysis of the sensor responses.
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paper_title: Correlation of surface acoustic wave device coating responses with solubility properties and chemical structure using pattern recognition

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Abstract : Twelve surface acoustic wave (SAW) device coatings were exposed to eleven chemical vapors and responses were correlated with solubility properties and coating structure to determine possible vapor/coating interaction mechanisms. Hydrogen bonding ability is implicated as a significant vapor/coating interaction mechanism. Pattern recognition schemes applied to the preliminary data aided in solubility property/response correlations. Principal component analysis demonstrated good separation of different classes of chemical vapors tested. Hierarchical clustering provided additional evidence of the correlations between solubility properties and the observed clustering. In addition, pattern recognition methods were used to determine potential selectivity of an array detector using these coatings. Learning techniques show that one fourth of the sensors can adequately separate compounds of interest from chemically similar interferences.
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paper_title: Spike Latency Coding in Biologically Inspired Microelectronic Nose

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Recent theoretical and experimental findings suggest that biological olfactory systems utilize relative latencies or time-to-first spikes for fast odor recognition. These time-domain encoding methods exhibit reduced computational requirements and improved classification robustness. In this paper, we introduce a microcontroller-based electronic nose system using time-domain encoding schemes to achieve a power-efficient, compact, and robust gas identification system. A compact (4.5 cm × 5 cm × 2.2 cm) electronic nose, which is integrated with a tin-oxide gas-sensor array and capable of wireless communication with computers or mobile phones through Bluetooth, was implemented and characterized by using three different gases (ethanol, carbon monoxide, and hydrogen). During operation, the readout circuit digitizes the gas-sensor resistances into a concentration-independent spike timing pattern, which is unique for each individual gas. Both sensing and recognition operations have been successfully demonstrated in hardware. Two classification algorithms (rank order and spike distance) have been implemented. Both algorithms do not require any explicit knowledge of the gas concentration to achieve simplified training procedures, and exhibit comparable performances with conventional pattern-recognition algorithms while enabling hardware-friendly implementation.
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paper_title: VLSI Implementation of a Bio-Inspired Olfactory Spiking Neural Network

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This paper presents a low-power, neuromorphic spiking neural network (SNN) chip that can be integrated in an electronic nose system to classify odor. The proposed SNN takes advantage of sub-threshold oscillation and onset-latency representation to reduce power consumption and chip area, providing a more distinct output for each odor input. The synaptic weights between the mitral and cortical cells are modified according to an spike-timing-dependent plasticity learning rule. During the experiment, the odor data are sampled by a commercial electronic nose (Cyranose 320) and are normalized before training and testing to ensure that the classification result is only caused by learning. Measurement results show that the circuit only consumed an average power of approximately 3.6 μW with a 1-V power supply to discriminate odor data. The SNN has either a high or low output response for a given input odor, making it easy to determine whether the circuit has made the correct decision. The measurement result of the SNN chip and some well-known algorithms (support vector machine and the K-nearest neighbor program) is compared to demonstrate the classification performance of the proposed SNN chip.The mean testing accuracy is 87.59% for the data used in this paper.
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paper_title: An artificial olfaction system based on the optical imaging of a large array of chemical reporters

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Abstract Electronic noses are object of research since more than two decades; nonetheless, the analogies between natural and olfaction systems are still limited to the selectivity properties of the receptors. The implementation of more sophisticated features such as the large number of receptors and the glomeruli layer have been hampered by technical difficulties related to the management of a large number of contemporaneous signals. As demonstrated in the past, optical imaging is a read-out technique for sensors development that can provide large sensor arrays. In this paper an artificial olfaction system based on the imaging of a continuous layer of chemical indicators is illustrated. The system incorporates an array of thousands of sensors, corresponding to the pixels of the image. The choice of Computer Screen Photoassisted Technology as a platform for optical interrogation of the sensing layer allows for the definition of a strategy for an automatic definition of a glomeruli layer based on the classification of the optical fingerprints of the image pixels. Chemical indicators were dissolved into a polymeric matrix providing the further property of odor diffusion mimicking the functions of the olfactory mucosa. The system has been tested in a simple experiment and data have been treated applying a lateral inhibition to the glomeruli layer resulting in a dynamic pattern resembling that observed in natural olfaction.
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paper_title: The evaluation of quality of post-harvest oranges and apples by means of an electronic nose

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Abstract The measure of quality of post-harvest fruits is considered a promising application field for electronic nose technology such as the detection of defects. Among the possible defects present in fruits those due to post-harvest treatment are particularly important. Among them defects like mealiness (due to post-harvest over-ripening), skin damage (due to mechanical or temperature stresses), and infections affect strongly the perception of consumers. They have to be avoided in order to achieve high quality products. In this paper, the study of the variations of aroma of oranges, during the storage, and apples, due to the presence of mealiness and skin damage by means of a thickness shear mode quartz resonators- (TSMR) based electronic nose, is illustrated and discussed. Results have evidenced that the electronic nose has enough sensitivity and resolution to distinguish among the various classes and to correctly predict the amount of defects (for apples) and storage days (for oranges).
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paper_title: Advances in Electronic-Nose Technologies Developed for Biomedical Applications

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The research and development of new electronic-nose applications in the biomedical field has accelerated at a phenomenal rate over the past 25 years. Many innovative e-nose technologies have provided solutions and applications to a wide variety of complex biomedical and healthcare problems. The purposes of this review are to present a comprehensive analysis of past and recent biomedical research findings and developments of electronic-nose sensor technologies, and to identify current and future potential e-nose applications that will continue to advance the effectiveness and efficiency of biomedical treatments and healthcare services for many years. An abundance of electronic-nose applications has been developed for a variety of healthcare sectors including diagnostics, immunology, pathology, patient recovery, pharmacology, physical therapy, physiology, preventative medicine, remote healthcare, and wound and graft healing. Specific biomedical e-nose applications range from uses in biochemical testing, blood-compatibility evaluations, disease diagnoses, and drug delivery to monitoring of metabolic levels, organ dysfunctions, and patient conditions through telemedicine. This paper summarizes the major electronic-nose technologies developed for healthcare and biomedical applications since the late 1980s when electronic aroma detection technologies were first recognized to be potentially useful in providing effective solutions to problems in the healthcare industry.
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paper_title: Aroma discrimination by pattern recognition analysis of responses from semiconductor gas sensor array

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The method was applied to discriminating coffee aromas, essential oils, and volatile compounds with different functional groups. To standardise sample introduction and to remove excess ethanol from volatile mixtures, headspace concentration utilizing a porous polymer trap was incorporated into the sensing system. Pattern recognition techniques such as discriminant analysis and cluster analysis were applied to the normalized response pattern. Two ground coffees, Coffea arabica and C.robusta, and freeze-dried and spray-dried commercial instant coffees were clearly separated by cluster analysis and linear discriminant analysis.
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paper_title: Development of a Portable Electronic Nose System for the Detection and Classification of Fruity Odors

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In this study, we have developed a prototype of a portable electronic nose (E-Nose) comprising a sensor array of eight commercially available sensors, a data acquisition interface PCB, and a microprocessor. Verification software was developed to verify system functions. Experimental results indicate that the proposed system prototype is able to identify the fragrance of three fruits, namely lemon, banana, and litchi.
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paper_title: A portable electronic nose based on embedded PC technology and GNU/Linux: hardware, software and applications

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This paper describes a portable electronic nose based on embedded PC technology. The instrument combines a small footprint with the versatility offered by embedded technology in terms of software development and digital communications services. A summary of the proposed hardware and software solutions is provided with an emphasis on data processing. Data evaluation procedures available in the instrument include automatic feature selection by means of SFFS, feature extraction with linear discriminant analysis (LDA) and principal component analysis (PCA), multi-component analysis with partial least squares (PLS) and classification through k-NN and Gaussian mixture models. In terms of instrumentation, the instrument makes use of temperature modulation to improve the selectivity of commercial metal oxide gas sensors. Field applications of the instrument, including experimental results, are also presented.
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paper_title: In-Situ Chemiresistor Sensor Package for Real-Time Detection of Volatile Organic Compounds in Soil and Groundwater

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This paper presents the development of a real-time microsensor-based monitoring system that can be used to detect and characterize volatile organic compounds in soil and groundwater. The system employs an array of polymer-based microsensors (chemiresistors) packaged in a waterproof housing that is designed to protect the sensor from harsh subsurface environments, including completely water-saturated conditions. The sensors and packaging have been tested in field and laboratory environments, and characterization methods are being developed that utilize contaminant-transport models and time-dependent, in-situ sensor data to identify the location of the contaminant source.
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paper_title: An electronic nose: a sensitive and discriminating substitute for a mammalian olfactory system

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The dram of a direct electronic analogue for a biological nose may still be some way from realisation, but considerable progress can be reported towards prototype computerised instruments capable of equivalent, or even better, performance in certain applications. The achievements are partly attributable to success in new circuit and systems approaches, as well as in developing sensing devices, with the prospect of further rapid progress based on the exploitation of materials and integrated sensor technology. Other important advances are being created in information processing, particularly in relation to pattern recognition. >
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paper_title: Design for smelling

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On our best days-without head colds, for example-and with a time out between sniffs, we can note the presence of and distinguish among 10000 airborne molecules or molecular compounds, sometimes when they amount to only a few molecules per trillion. Here, the authors present a quick tour of the route from molecule to smell. They correlate many of the discrete physiological steps with engineering ones, ranging from sampling, signal processing and amplification all the way to neural net computation.
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paper_title: A portable electronic nose system for the identification of cannabis-based drugs

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Abstract We report on a research aimed at evaluating the capacity of a simple, low-cost, portable electronic nose system based on commercially available metal oxide gas sensors to classify different types of drugs. Five drugs, namely cannabis buds, cannabis plants, hashish, snuff tobacco and tobacco leaves were employed. A dedicated real-time data acquisition system based on dynamic headspace sampling, a microcontroller and a laptop computer have been designed and constructed for this application. To demonstrate its discrimination capability, unsupervised and supervised classification models have been built and validated. Principal Component Analysis (PCA) of volatile profiles revealed five distinct groups corresponding to the five different drugs analyzed. This was further confirmed by a multivariate analysis of variance (MANOVA) test. Support Vectors Machines (SVMs) were applied to build a classifier and reached a 98.5% success rate in the recognition of the different drugs analyzed. This work demonstrates for the first time that the electronic nose technology could be successfully applied to the identification of illegal drugs.
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paper_title: A Wearable and Wireless Sensor System for Real-Time Monitoring of Toxic Environmental Volatile Organic Compounds

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An integrated volatile organic toxicants sensor with a Bluetooth device interface has been developed. The device is based on novel tuning fork sensor platform along with a wireless communication/interface technology taken in an integrated system approach. It features high sensitivity and selectivity. The sensitivity and selectivity are accomplished through the use of novel tuning fork sensor modified by design (molecularly imprinted) polymers and selective filtering. Experiments have shown that the device can detect toxic volatile organic compounds (VOCs) under high concentrations of common interferents from flavors and fragrances. Applications of the device for detection of BTEX in real-world situations such as outdoor and gas station VOCs have also been demonstrated. All these features make the device a promising candidate to be deployed in real-world applications, particularly in environmental health and air pollution studies.
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paper_title: Electronic nose: a useful tool for monitoring environmental contamination

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Abstract The advances in the technology of multisensor arrays and neural computation have allowed the development of “electronic noses”, which has enabled the discrimination of compounds by their odours and consequently, has played a fundamental role in the environmental monitoring. An electronic nose MOSES II (MOdular SEnsor System) with two arrays of eight (tin oxide and quartz microblance) sensors, each one manufactured by Lennartz Electronic/MoTech, was employed in this work. The aim of this research was to discriminate the following factors by odours: (a) small concentrations (ppm) of lindane and nitrobenzene in water, (b) dry solid insecticides (synthetic pyrethroids) such as permethrin, deltamethrin and cypermethrin, (c) mixtures of different quantities of cypermethrin in an inert substance, and (d) solutions of these pyrethroids in an appropriate organic solvent. Contaminating residues of insecticides (lindane and syntethic pyrethroids) and products from the leather manufacture (phenols, nitrobenzene, anilines) are often offloaded into streams or rivers — despite the prohibition regulations — in heedless disregard of the danger they present to the health of the population and the survival of fish and flora.
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paper_title: A Low-Power Electronic Nose Signal-Processing Chip for a Portable Artificial Olfaction System

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The bulkiness of current electronic nose (E-Nose) systems severely limits their portability. This study designed and fabricated an E-Nose signal-processing chip by using TSMC 0.18-μ m 1P6M complementary metal-oxide semiconductor technology to overcome the need to connect the device to a personal computer, which has traditionally been a major stumbling block in reducing the size of E-Nose systems. The proposed chip is based on a conductive polymer sensor array chip composed of multiwalled carbon nanotubes. The signal-processing chip comprises an interface circuit, an analog-to-digital converter, a memory module, and a microprocessor embedded with a pattern-recognition algorithm. Experimental results have verified the functionality of the proposed system, in which the E-Nose signal-processing chip successfully classified three odors, carbon tetrachloride (CCl4), chloroform (CHCl3), and 2-Butanone (MEK), demonstrating its potential for portable applications. The power consumption of this signal-processing chip was maintained at a very low 2.81 mW using a 1.8-V power supply, making it highly suitable for integration as an electronic nose system-on-chip.
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paper_title: The electronic nose applied to dairy products: a review

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The state-of-the-art and current trends in the development of “aroma” analysis with electronic noses are reviewed with special reference to applications to dairy-products. Some of the reported problems with electronic noses have recently been reduced, e.g. the correction/reduction of signal drift, the influence of humidity and temperature. New promising and reproducible sensor manufacturing techniques are being implemented, e.g. electro-spray for QMB sensor production. The development of more selective and sensitive sensors, especially of QMB and conducting polymer (CP) type, should improve their applicability. Interesting novel sampling techniques, such as SPME or SBSE, offer more possibilities for the analysis of semi-volatile compounds which are generally more odoriferous. However, standard calibration procedures and reference materials are not yet available. Although they are normally less powerful than human noses, electronic noses offer some significant advantages in the analysis of volatiles, for example, in instrumental classifications based on hedonic or sensory analyses and in potentially automated on-line monitoring of volatiles. Several groups have explored the application of different electronic noses in the investigation of various aspects of dairy products. The present review includes as examples the evaluation of Swiss and Cheddar cheese aroma, the assessment of the ripening of Pecorino Toscano cheese (ewe’s), the detection of mould in Parmesan cheese, the classification of milk by trademark, by fat level and by preservation process, the classification and the quantification of off-flavours in milk, the evaluation of Maillard reactions during heating processes in block-milk, as well as the identification of single strains of disinfectant–resistant bacteria in mixed cultures in milk. © 2003 Elsevier Science B.V. All rights reserved.
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paper_title: Multi-layer conducting polymer gas sensor arrays for olfactory sensing

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Conductivity sensors using the conducting polymer poly(pyrrole) and its derivatives have been prepared with a novel electrode design which allows the probing of resistance changes within zones of a single sensor. It was found that the application of principal component analysis to the sensor responses allowed methanol, ethanol and propanol to be distinguished. The use of layered conducting polymers improved the discrimination of the sensor. A sensor consisting of four electrode pairs and two polymer layers is capable of separating the response of certain alcoholic beverages.
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paper_title: Classification of multiple indoor air contaminants by an electronic nose and a hybrid support vector machine

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Abstract This paper presents a laboratory study of multi-class classification problem for multiple indoor air contaminants which belongs to a completely linear-inseparable case. Six kinds of indoor air contaminations (formaldehyde, benzene, toluene, carbon monoxide, ammonia and nitrogen dioxide) were recognized as indicators of air quality in this project. The effectiveness of the proposed HSVM model has been rigorously evaluated on the experimental E-nose data sets. In addition, we have also compared it with existing five methods including Euclidean distance to centroids (EDC), simplified fuzzy ARTMAP network (SFAM), multilayer perceptron neural network (MLP) based on back-propagation learning rule, individual FLDA and single SVM. Experimental results have demonstrated that the HSVM model outperforms other classifiers in general. Also, HSVM classifier preliminarily shows its superiority in solution to discrimination in various electronic nose applications.
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paper_title: Metal Oxide Sensors for Electronic Noses and Their Application to Food Analysis

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Electronic noses (E-noses) use various types of electronic gas sensors that have partial specificity. This review focuses on commercial and experimental E-noses that use metal oxide semi-conductors. The review covers quality control applications to food and beverages, including determination of freshness and identification of contaminants or adulteration. Applications of E-noses to a wide range of foods and beverages are considered, including: meat, fish, grains, alcoholic drinks, non-alcoholic drinks, fruits, milk and dairy products, olive oils, nuts, fresh vegetables and eggs.
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paper_title: Convergent, Self-Encoded Bead Sensor Arrays in the Design of an Artificial Nose

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We report a new approach to designing an artificial nose based on high-density optical arrays that directly incorporate a number of structural and operational features of the olfactory system. The arrays are comprised of thousands of microsphere (bead) sensors, each belonging to a discrete class, randomly dispersed across the face of an etched optical imaging fiber. Beads are recognized and classified after array assembly by their unique, "self-encoded" response pattern to a selected vapor pulse. The high degree of redundancy built into the array parallels that found in nature and affords new opportunities for chemical-sensor signal amplification. Since each bead is independently addressable through its own light channel, it is possible to combine responses from same-type beads randomly distributed throughout the array in a manner reminiscent of the sensory-neuron convergence observed in the mammalian olfactory system. Signal-to-noise improvements of approximately n1/2 have been achieved using this method.
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paper_title: Preliminary study of ion mobility based electronic nose MGD-1 for discrimination of hard cheeses.

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Abstract Electronic nose presents a rapid method to determine quality characteristics of foodstuffs. Ion mobility spectrometry allows rapid and simple on-site determination of gaseous compounds. Ion mobility based electronic nose system “MGD-1” was used to determine the separation of various hard and extra-hard cheese samples via headspace analysis. The verification of the electronic nose system was performed for different applications such as the discrimination of Emmental cheeses based on either age or geographical origin, and the discrimination of different cheeses based on variety. Nine month ripened Emmental cheeses were successfully discriminated from Emmental cheeses with 3 or 6 month ripening time. The results obtained from Emmental cheeses and other hard and extra-hard cheese varieties showed that the MGD-1 system is of a significant potential for discrimination of the cheese samples.
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paper_title: Something in the air [electronic nose]

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No electronic nose can match the capabilities of its human counterpart. But, as the author reports in this paper, advances in sensor technology are transforming the capabilities of the all-electric hooter.
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paper_title: Strategies for qualitative and quantitative analyses with mass spectrometry-based electronic noses

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Abstract We review the state of the art and current trends in the development of strategies for qualitative and quantitative analysis with electronic noses based on mass spectrometry (MS), with special reference to applications in the environmental field. The “mass sensor” provides a fingerprint of the sample that is analyzed without prior chromatographic separation. The resulting spectrum is characteristic of the sample being analyzed. Suitable treatment of the signal by chemometric techniques is essential in order to extract the information contained in the signal profile. The question of the temporal stability of the signal is still important in the case of MS-based systems, although the problem is less pronounced than with conventional electronic noses. We compare and contrast four strategies to correct signal drift: internal normalization; internal standardization; gas standard addition; and, calibration transfer. In addition, we describe another strategy for solving this problem, based on support vector machines (SVMs). Most works carried out with this new generation of electronic noses successfully solve different classification problems. To date, there have been few contributions aimed at quantitative analyses, but the results obtained in this field show the potential of these instruments in quantification tasks. The present article reviews the main applications in this field.
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paper_title: A low-power micromachined MOSFET gas sensor

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This paper reports on the design, fabrication, and characterization of the first low-power consumption MOSFET gas sensor, The novel MOSFET array gas sensor has been fabricated using anisotropic bulk silicon micromachining. A heating resistor, a diode used as temperature sensor, and four MOSFETs are located in a silicon island suspended by a dielectric membrane. The membrane has a low thermal conductivity coefficient and, therefore, thermally isolates the electronic components from the chip frame. This low thermal mass device allows the reduction of the power consumption to a value of 90 mW for an array of four MOSFETs at an operating temperature of 170/spl deg/C. Three of the MOSFETs have their gate covered with thin catalytic metals and are used as gas sensors. The fourth one has a standard gate covered with nitride and could act as a reference. The sensor was tested under different gaseous atmospheres and has shown good gas sensitivities to hydrogen and ammonia. The low-power MOSFET array gas sensor presented is suitable for applications in portable gas sensor instruments, electronic noses, and automobiles.
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paper_title: Strategies for the development of reliable QA/QC methods when working with mass spectrometry-based chemosensory systems

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Abstract This paper relates to the MS-Sensor, a representative of a new generation of gas sensors: systems based on mass spectrometry. In this contribution, the strategy involved to achieve reliable applications for quality assessment and quality control when working with this device is discussed in detail.
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paper_title: Electronic Noses Sniff Success

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E-nose technology has quietly advanced during the past two decades. Commercial models equipped with sensor arrays came to market in the mid-1990s, and today they're used to distinguish wines, analyze food flavors, and sort lumber. Benchtop systems are also used in the pharmaceutical, food, cosmetics, and packaging industries, while smaller, portable units are used to monitor air quality. But these noses cost in the range of US $5000 to $100 000. A coming convergence between e-nose technology and advances in printed electronics will finally bring the price down; way down. Within a decade we'll see e-noses that cost tens of dollars and appear in smart packaging for high-end items like pharmaceuticals or as part of intelligent or interactive appliances- picture a refrigerator that knows when milk has gone bad. Prices could easily drop to under a dollar by 2020. The secret? Conducting polymers. Developers of both electronic noses and printed electronics are exploiting these materials, which can be sensitive to the chemicals that make up odors and are also capable of producing electrical signals. E-nose developers are concentrating on honing the sensing properties of conducting polymers, while the printed-electronics people are investigating ways of using these materials to fabricate ultralow-cost electronics. Combining the fruits of these two separate efforts will finally bring e-noses into our supermarkets, homes, and daily life.
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paper_title: TOWARDS AN INTEGRATED ELECTRONIC NOSE USING CONDUCTING POLYMER SENSORS

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Abstract This paper describes progress that has been made towards realizing an artificial nose based on arrays of conducting polymers. Electrically conducting organic polymers based on heterocyclic molecules display reversible changes in conductivity when exposed to polar volatile chemicals. In the sensor described, the polymers are interrogated for resistance changes by means of an application-specific integrated circuit (ASIC) realized in BiCMOS technology. The ASIC and the polymer array are housed on a single thick-film ceramic substrate.
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paper_title: The how and why of electronic noses

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Witnessing the swift advances in the electronic means of seeing and hearing, scientists and engineers scent a market for systems mimicking the human nose. Already commercial systems from several companies are targeting applications, present and potential, that range from quality assurance of food and drugs to medical diagnosis, environmental monitoring, safety and security and military use. Here, the authors outline the major transducer technologies-in one sense, the key component of an electronic nose.
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paper_title: Electronic gas and odour detectors that mimic chemoreception in animals

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Chemoreception in biological systems is carried out by arrays of sensors that have relatively broad specificity, but which interact with chemicals in the environment on the basis of size, shape and charge. This article focuses on the design of gas and odour sensor arrays with emphasis on new conducting polymer materials that may be used to mimic some aspects of the biological system, and the information processing methods that are applicable.
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paper_title: An electronic nose system for monitoring the quality of potable water

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A measurement system has been developed for the testing of cyanobacteria in water, and it consists of three main stages: the odour sampling system, an electronic nose (e-nose) and a CellFacts instrument that analyses liquid samples. The e-nose system, which employs an array of six commercial odour sensors, has been used to monitor not only different strains but also the growth phase of cyanobacteria (i.e. blue-green algae) in water over a 40-day period. Principal components analysis (PCA), multi-layer perceptron (MLP), learning vector quantisation (LVQ) and Fuzzy ARTMAP were used to analyse the response of the sensors. The optimal MLP network was found to classify correctly 97.1% of the unknown nontoxic and 100% of the unknown toxic cyanobacteria. The optimal LVQ and Fuzzy ARTMAP algorithms were able to classify 100% of both strains of cyanobacteria samples. The accuracy of MLP, LVQ and Fuzzy ARTMAP in terms of predicting four different growth phases of toxic cyanobacteria was 92.3%, 95.1% and 92.3%, respectively. These results show the potential application of neural network based e-noses to test the quality of potable water as an alternative to instruments, such as liquid chromatography or optical microscopy.
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paper_title: The electronic nose in Lilliput

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Electronic noses today are handy enough systems for detecting gaseous chemicals used in industrial cleaning or fabrication processes. Available from a half-dozen manufacturers, the instruments are desktop or laptop in size, depending on their features. The gases, called volatile organic compounds (VOCs), are toxic, carcinogenic and quick to evaporate in combination, a danger to their environs. Here, the authors describe how a miniature experimental system based on a CMOS chip is being readied to detect a range of gaseous compounds.
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paper_title: A Novel Breath Analysis System Based on Electronic Olfaction

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Certain gases in the breath are known to be indicators of the presence of diseases and clinical conditions. These gases have been identified as biomarkers using equipments such as gas chromatography (GC) and electronic nose (e-nose). GC is very accurate but is expensive, time consuming, and non-portable. E-nose has the advantages of low-cost and easy operation, but is not particular for analyzing breath odor and hence has a limited application in diseases diagnosis. This article proposes a novel system that is special for breath analysis. We selected chemical sensors that are sensitive to the biomarkers and compositions in human breath, developed the system, and introduced the odor signal preprocessing and classification method. To evaluate the system performance, we captured breath samples from healthy persons and patients known to be afflicted with diabetes, renal disease, and airway inflammation repectively and conducted experiments on medical treatment evaluation and disease identification. The results show that the system is not only able to distinguish between breath samples from subjects suffering from various diseases or conditions (diabetes, renal disease, and airway inflammation) and breath samples from healthy subjects, but in the case of renal failure is also helpful in evaluating the efficacy of hemodialysis (treatment for renal failure).
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paper_title: Automated odor-sensing system based on plural semiconductor gas sensors and computerized pattern recognition techniques

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Abstract Although odor is an inherent characteristic of chemical substances, no methods to measure or identify odor objectively have been available. A computerized method for classification and identification of odor is reported. Odors are detected by using eight semiconductor gas-sensor elements which have different sensing properties for gases; the output from the odor-detecting apparatus for a gas sample is represented by an 8-dimensional vector. The vectors for 30 substances were examined by clustering analysis and four obvious clusters were observed. These clusters corresponded to ethereal, etherealminty, ethereal-pungent and pungent substances.
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paper_title: Landmine Detection with an Electronic Nose Mounted on an Airship

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An Electronic Nose (EN) might be a promising alternative to sniffer dogs for detecting landmines on the basis of their characteristic gas ensemble. The latter does not only consist of the gas released by the explosive itself but to a larger extent of the gases produced by the explosive’s so-called by-products and mine packaging. The Karlsruhe Micronose KAMINA is a novel type of EN developed at the Karlsruhe Research Center. It has primarily been designed for use in consumer applications. The gas sensitivity of the thumbnail-sized microarray chip is based on a single semi-conducting metal oxide thin film. Its low price, weight and small size as well as its low power consumption combined with the appropriate analytical power provide an excellent basis for mine detection. The KAMINA mounted on a 9 m long radio-controlled airship allows the location and classification of objects with characteristic gas release such as landmines. First test results obtained with tin dioxide microarray chips detecting contaminated soil model samples showed that when using a 2 m long sniffing tube a maximum speed of 3 km/h was appropriate for a safe detection of gas emitting objects. When simply moving the KAMINA system a few centimeters above the ground (i.e. without using the sniffing tube) a maximum speed of even 6 km/h was found to be feasible. The spatial resolution of the micro-pump sampling was about 10 cm. The newly developed microarray with a nanogranular layer of tin dioxide showed an extremely high gas sensitivity. Laboratory tests with model gas exposures revealed detection limits of less than 1 ppb. Thus, microarray chips of this type provide an excellent basis for the delicate task of gas analytical landmine detection. The cheap and easy maneuverable radio-controlled airship seems to be an ideal platform for moving the EN over the terrain to be investigated.
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paper_title: Electronic nose for monitoring the flavour of beers

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The flavour of a beer is determined mainly by its taste and smell, which is generated by about 700 key volatile and non-volatile compounds. Beer flavour is traditionally measured through the use of a combination of conventional analytical tools (e.g., gas chromatography) and organoleptic profiling panels. These methods are not only expensive and time-consuming but also inexact due to a lack of either sensitivity or quantitative information. In this paper an electronic instrument is described that has been designed to measure the odour of beers and supplement or even replace existing analytical methods. The instrument consists of an array of up to 12 conducting polymers, each of which has an electrical resistance that has partial sensitivity to the headspace of beer. The signals from the sensor array are then conditioned by suitable interface circuitry and processed using a chemometric or neural classifier. The results of the application of multivariate statistical techniques are given. The instrument, or electronic nose, is capable of discriminating between various commercial beers and, more significantly, between standard and artificially-tainted beers. An industrial version of this instrument is now undergoing trials in a brewery.
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paper_title: Intelligent vapour discrimination using a composite 12-element sensor array

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Abstract A multisensor system has been developed that is capable of discriminating between complex vapours or gaseous mixtures. The system is based on an array of 12 discrete tin oxide semi-conductor sensing elements, each possessing different characteristics whilst being sensitive to a broad spectrum of gases. A weighted fault-tolerant least-squares method is used to analyse the multisensor data. Results show the multisensor system successfully discriminates (100%) between methanol, ethanol, propan-2-ol and butan-1-ol. Its overall ability to distinguish between beverages and spirits or mixtures is somewhat lower (83%) underpinning a need in this case for complementary sensing materials.
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paper_title: An electronic nose distinguishes exhaled breath of patients with Malignant Pleural Mesothelioma from controls.

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BACKGROUND ::: Malignant Pleural Mesothelioma (MPM) is a tumour of the surface cells of the pleura that is highly aggressive and mainly caused by asbestos exposure. Electronic noses capture the spectrum of exhaled volatile organic compounds (VOCs) providing a composite biomarker profile (breathprint). ::: ::: ::: OBJECTIVE ::: We tested the hypothesis that an electronic nose can discriminate exhaled air of patients with MPM from subjects with a similar long-term professional exposure to asbestos without MPM and from healthy controls. ::: ::: ::: METHODS ::: 13 patients with a histology confirmed diagnosis of MPM (age 60.9±12.2 year), 13 subjects with certified, long-term professional asbestos exposure (age 67.2±9.8), and 13 healthy subjects without asbestos exposure (age 52.2±16.2) participated in a cross-sectional study. Exhaled breath was collected by a previously described method and sampled by an electronic nose (Cyranose 320). Breathprints were analyzed by canonical discriminant analysis on principal component reduction. Cross-validated accuracy (CVA) was calculated. ::: ::: ::: RESULTS ::: Breathprints from patients with MPM were separated from subjects with asbestos exposure (CVA: 80.8%, sensitivity 92.3%, specificity 85.7%). MPM was also distinguished from healthy controls (CVA: 84.6%). Repeated measurements confirmed these results. ::: ::: ::: CONCLUSIONS ::: Molecular pattern recognition of exhaled breath can correctly distinguish patients with MPM from subjects with similar occupational asbestos exposure without MPM and from healthy controls. This suggests that breathprints obtained by electronic nose have diagnostic potential for MPM.
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paper_title: Chaos based neural network optimization for concentration estimation of indoor air contaminants by an electronic nose

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Abstract Electronic nose (E-nose), as an artificial olfactory system, can be used for estimation of gases concentration combined with a pattern recognition module. This paper studies the concentration estimations of indoor contaminants for air quality monitoring in dwellings using chaos based optimization artificial neural network integrated into our self-designed portable E-nose instrument. Back-propagation neural network (BPNN) has been recognized as the common pattern recognition. Considering the local optimal flaw of BPNN, this paper presents a novel chaotic sequence optimization BPNN method for improving the accuracy of E-nose prediction. Further comparison with particle swarm optimization is also employed, and maximum 26.03% and 16.4% prediction error decreased after using chaotic based optimization for formaldehyde and benzene concentration estimation. Experimental results demonstrate the superiority and efficiency of the portable E-nose instrument integrated with artificial neural network optimized by chaotic sequence based optimization algorithms in real-time monitoring of air quality in dwellings.
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paper_title: Electronic Noses and Tongues: Applications for the Food and Pharmaceutical Industries

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The electronic nose (e-nose) is designed to crudely mimic the mammalian nose in that most contain sensors that non-selectively interact with odor molecules to produce some sort of signal that is then sent to a computer that uses multivariate statistics to determine patterns in the data. This pattern recognition is used to determine that one sample is similar or different from another based on headspace volatiles. There are different types of e-nose sensors including organic polymers, metal oxides, quartz crystal microbalance and even gas-chromatography (GC) or combined with mass spectroscopy (MS) can be used in a non-selective manner using chemical mass or patterns from a short GC column as an e-nose or “Z” nose. The electronic tongue reacts similarly to non-volatile compounds in a liquid. This review will concentrate on applications of e-nose and e-tongue technology for edible products and pharmaceutical uses.
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paper_title: Review of Electronic-nose Technologies and Algorithms to Detect Hazardous Chemicals in the Environment

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Abstract Novel mobile electronic-nose (e-nose) devices and algorithms capable of real-time detection of industrial and municipal pollutants, released from point-sources, recently have been developed by scientists worldwide that are useful for monitoring specific environmental-pollutant levels for enforcement and implementation of effective pollution-abatement programs. E-nose devices are ideal instruments for measuring and monitoring carbon and greenhouse-gas emissions due to their sensitivity to a wide diversity of volatile organic compounds (VOCs). A large number of e-nose instrument types, based on a wide diversity of technologies and operational mechanisms, are available to monitor gaseous and particulate pollutants released into the atmosphere, or liquid and dissolved organic pollutants released into municipal and industrial waste-water systems. Some commonly used e-nose technologies include conducting polymers (CP), metal-oxide semiconductor (MOS), quartz crystal microbalance (QCM), and surface acoustic wave (SAW) sensors. Potential pollution-detection applications of e-noses range from atmospheric pollutant (gas-leak) detection of carbon emissions from biofuel production plants and fossil-fuel production sources in the oil and gas industry to VOC-releases from numerous other industries. E-nose technologies are potentially capable of monitoring all phases of industrial manufacturing processes to minimize production of pollutants and maintain efficient, clean production lines. E-nose devices are also useful in designing more environmentally-friendly, clean technologies for energy production, various industrial processes and product-manufacturing systems. This paper is a review of recent novel electronic-nose systems and algorithms, developed over the past decade, that have potential applications for detecting specific types of harmful VOC pollutants in the environment to meet carbon-capture and emission-reduction targets of worldwide environmental protection agencies.
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paper_title: Detection and identification of odorants using an electronic nose

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Gas sensing systems for detection and identification of odorant molecules are of crucial importance in an increasing number of applications. Such applications include environmental monitoring, food quality assessment, airport security, and detection of hazardous gases. We describe a gas sensing system for detecting and identifying volatile organic compounds (VOC), and discuss the unique problems associated with the separability of signal patterns obtained by using such a system. We then present solutions for enhancing the separability of VOC patterns to enable classification. A new incremental learning algorithm that allows new odorants to be learned is also introduced.
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paper_title: Odour Detection Methods: Olfactometry and Chemical Sensors

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The complexity of the odours issue arises from the sensory nature of smell. From the evolutionary point of view olfaction is one of the oldest senses, allowing for seeking food, recognizing danger or communication: human olfaction is a protective sense as it allows the detection of potential illnesses or infections by taking into account the odour pleasantness/unpleasantness. Odours are mixtures of light and small molecules that, coming in contact with various human sensory systems, also at very low concentrations in the inhaled air, are able to stimulate an anatomical response: the experienced perception is the odour. Odour assessment is a key point in some industrial production processes (i.e., food, beverages, etc.) and it is acquiring steady importance in unusual technological fields (i.e., indoor air quality); this issue mainly concerns the environmental impact of various industrial activities (i.e., tanneries, refineries, slaughterhouses, distilleries, civil and industrial wastewater treatment plants, landfills and composting plants) as sources of olfactory nuisances, the top air pollution complaint. Although the human olfactory system is still regarded as the most important and effective "analytical instrument" for odour evaluation, the demand for more objective analytical methods, along with the discovery of materials with chemo-electronic properties, has boosted the development of sensor-based machine olfaction potentially imitating the biological system. This review examines the state of the art of both human and instrumental sensing currently used for the detection of odours. The olfactometric techniques employing a panel of trained experts are discussed and the strong and weak points of odour assessment through human detection are highlighted. The main features and the working principles of modern electronic noses (E-Noses) are then described, focusing on their better performances for environmental analysis. Odour emission monitoring carried out through both the techniques is finally reviewed in order to show the complementary responses of human and instrumental sensing.
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paper_title: Meat and Fish Freshness Inspection System Based on Odor Sensing

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We propose a method for building a simple electronic nose based on commercially available sensors used to sniff in the market and identify spoiled/contaminated meat stocked for sale in butcher shops. Using a metal oxide semiconductor-based electronic nose, we measured the smell signature from two of the most common meat foods (beef and fish) stored at room temperature. Food samples were divided into two groups: fresh beef with decayed fish and fresh fish with decayed beef. The prime objective was to identify the decayed item using the developed electronic nose. Additionally, we tested the electronic nose using three pattern classification algorithms (artificial neural network, support vector machine and k-nearest neighbor), and compared them based on accuracy, sensitivity, and specificity. The results demonstrate that the k-nearest neighbor algorithm has the highest accuracy.
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paper_title: Embedded Electronic Nose and Supporting Software Tool for its Parameter Optimization

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Abstract This paper details the work done towards a low cost, small size, portable embedded electronic nose (e-nose) and its application for analysis of different VOC mixtures. The sensor array is composed of commercially available metal oxide semiconductor sensors by Figaro. The Embedded E-nose consists of an ADuC831 and has an RS 232 interface to Desktop PC for higher level data collection and NN training. An E-nose Software Package (ESP) Integrated Development Environment (IDE) is implemented for the design and development of Embedded E-nose. The IDE facilitates the parameter optimization of data acquisition, signal pre-processing, feature extraction and Multilayer Perceptron Neural Network (MLP NN) training. The optimized parameters are then downloaded onto Embedded E-nose by means of docking the device to the ESP tool via PC serial port. The Embedded E-nose is used for realization of both qualitative as well as quantitative analysis and their results are discussed.
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paper_title: Prediction of gas sensor response using basic molecular parameters

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The response of a silicone oil used as a gas sensor coating to a selection of gases and vapours was investigated by measurement of the mass change, due to sorption at the oil/gas interface, using a piezoelectric quartz crystal microbalance. The sensors were exposed to each of 26 test analytes and the frequency shifts were used to calculate the partition coefficients and hence the Gibbs free energy of absorption. Molecular physico-chemical properties of the analyte vapours were calculated using semi-empirical molecular orbital and molecular mechanics methods and were related to the observed partitioning by pattern recognition methods. The key molecular parameters that influence the sensor response were extracted to build mathematical models for the quantitative prediction of a gas sensor response to a limited number of analytes. The approach shows how a model can be developed to described the response of a gas sensor to an analyte based solely on its molecular descriptors.
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paper_title: A chemically diverse, conducting polymer-based "electronic noise"

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We describe a method for generating a variety of chemically diverse, broadly responsive, low power vapor sensors. A key to our ability to fabricate chemically diverse sensing elements is the preparation of processable, air stable films of electrically conducting organic polymers. An array of such sensing elements produces a chemically reversible, diagnostic pattern of electrical resistance changes upon exposure to different odorants. Such conducting polymer elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. In addition, these sensors yield a fairly rapid, low power, dc electrical signal in response to the vapor of interest, and their signals are readily integrated with software or hardware-based neural networks for purposes of analyte identification. Principle component analysis has demonstrated that such sensors can identify and quantify different airborne organic solvents, and can yield information on the components of gas mixtures.
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paper_title: Evaluation of unpleasant odor with a portable electronic nose

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An intelligent multi-sensor system with an entire autonomy, a low weight and a small size has been developed for in situ applications such as environmental pollutant gas detection or olfactory estimation. This portable electronic nose works with commercial metal oxide gas sensors and a microcontroller connected to a compact flash memory as intelligent unit. In this work we present the conception of this electronic nose, its laboratory validation, and a real application which concerns an outdoor air monitoring of a duck breeding. This application is developed in order to quantify continuously discomfort odor spread, causing neighbor complaints. The odor measurements were made using our electronic nose (Nepo) and results are compared to the simultaneous results obtained from other olfactometric techniques.
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paper_title: Examination of ammonia-polypyrrole interactions by piezoelectric and conductivity measurements

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The conducting polymer poly(pyrrole), electrochemically prepared and doped with anions, has been found to be a responsive coating for a piezoelectric gas detection system. Polymers doped with bromide, nitrate and sulphate ions were tested. It was found that samples of ammonia gas cause a measurable frequency decrease, interpreted as adsorption by the polymer coating of the quartz crystal; the linear range was 0.05–1% for mixtures of the gas in nitrogen. These signals were found to correspond to simultaneous conductivity changes of a similarly prepared poly(pyrrole) sample, showing analogies in the two sensing mechanisms. The duality of the poly(pyrrole) response increases the possibilities of using it as a gas sensor.
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paper_title: A real-time data acquisition system for a hand-held electronic nose (H2EN)

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This paper describes an approach towards the development of a portable E-nose device based on an array of metal oxide sensors (MOS) devices, for early on-site dry rot detection on building timbers. A dedicated real-time data acquisition system with a programmable voltage generator, self-calibration techniques and custom visual software programs for a desktop PC and a hand-held computer have been designed and constructed for this application. This paper also describes an example of software calibration to correct source errors for this data acquisition system. Experimental results show that this data acquisition system can accurately measure a large range of resistive sensor responses and is suitable for measuring both conducting polymer and MOS sensors. The custom software also allows users to easily capture, analyse and record measurement data. In addition, the constructed framework for a hand-held computer is based on real-time object-oriented methodology to carry out the functions of desktop PC based instrumentation software. This system presents an effective and user-friendly interface for portable applications.
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paper_title: Acetic Acid Detection Threshold in Synthetic Wine Samples of a Portable Electronic Nose

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Wine quality is related to its intrinsic visual, taste, or aroma characteristics and is reflected in the price paid for that wine. One of the most important wine faults is the excessive concentration of acetic acid which can cause a wine to take on vinegar aromas and reduce its varietal character. Thereby it is very important for the wine industry to have methods, like electronic noses, for real-time monitoring the excessive concentration of acetic acid in wines. However, aroma characterization of alcoholic beverages with sensor array electronic noses is a difficult challenge due to the masking effect of ethanol. In this work, in order to detect the presence of acetic acid in synthetic wine samples (aqueous ethanol solution at 10% v/v) we use a detection unit which consists of a commercial electronic nose and a HSS32 auto sampler, in combination with a neural network classifier (MLP). To find the characteristic vector representative of the sample that we want to classify, first we select the sensors, and the section of the sensors response curves, where the probability of detecting the presence of acetic acid will be higher, and then we apply Principal Component Analysis (PCA) such that each sensor response curve is represented by the coefficients of its first principal components. Results show that the PEN3 electronic nose is able to detect and discriminate wine samples doped with acetic acid in concentrations equal or greater than 2 g/L.
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paper_title: Biology and applications of olfactory sensing system: A review

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Abstract Various metal oxide and conducting polymer-based sensors have been used in electronic nose systems for the detection of volatile organic compounds (VOCs). Some of the major constrains of these sensor materials are their sensitivity and selectivity. Recently, much research has been towards the development of biosensors that mimic biological olfactory mechanism. The sensing materials based on biological olfactory system can be well adapted to detect low concentrations of VOCs as it exhibits high selectivity/specificity, fast response time, high sensitivity, simplicity in fabrication, and are not toxic resulting from their biocompatibility and rapid biodegradability. A better understanding of human olfactory system can aid in the development of an artificial olfactory sensing system. The application domain of such sensors/systems could be potentially expanded for rapid and accurate detection of VOCs in environment and other biological media. Therefore, this paper provides a brief overview of the biology, associated mechanisms, and the functional principles of the olfactory sensing system in humans. Moreover, it summarizes the recent research on the development of an olfactory sensor utilizing olfactory receptors, odorant binding proteins and olfactory epithelium for the detection of different VOCs, and research needs in this area.
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paper_title: Sensors and sensory systems for an electronic nose

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1. Odours -- The Stimulus for an Electronic Nose G.H. Dodd, P.N. Bartlett, J.W. Gardner. 2. Biophysical Properties of Olfactory Receptor Neurones H.A. Schultens, D. Schild. 3. Molecular Modeling and the Selective Sensor Response M. Thompson, D.C. Strone. 4. Odour Sensors for an Electronic Nose P.N. Bartlett, J.W. Gardner. 5. Fundamentals and Recent Developments of Homogeneous Semiconducting Sensors D. Kohl. 6. Fine-Tuning of Electron- and Ion-Conducting Materials for Sensor Arrays W. Gopel, K-D. Schierbaum, S. Vaihinger, U. Weimar. 7. Microsensors Based on Modulation of Work Function J. Janata. 8. Studies of Interactions Between Organic Vapours and Organic Semiconductors Aplications to Chemical Sensing M. Josowicz, P. Topart. 9. Silicon Based Surface Acoustic Wave Gas Sensors M.S. Nieuwenhuizen, A.J. Nederlof. 10. Miniaturisation of Gas Sensor Substrates. Problems and Benefits of Microelectronic Technology U. Dibbern. 11. Pattern Recognition in Odour Sensing J.W. Gardner, P.N. Bartlett. 12. Desired and Achieved Characteristics of Sensor Arrays G. Horner, R. Muller. 13. Use of Pattern Recognition Techniques Applied to Signals Generated by a Multielement Gas Sensor Array as a Means of Compensating for Poor Individual Element Response A.W.J. Cranny, J.K. Atkinson. 14. Pattern Recognition in Electronic Noses by Artificial Neural Network Models T. Moruzumi, T. Nakamoto, Y. Sakuraba. 15. Sensor Arrays Using Conducting Polymers for an Artificial Nose K.C. Persaud, P. Pelosi. 16. Monitoring ofFish Freshness Using Tin Oxide Sensors R. Olafsson, E. Martinsdottir, G. Olafsdottir, P.I. Sigfusson, J.W. Gardner. 17. Chemical Sensor Arrays: Practical Insights and Examples J.R. Stetter. 18. Electronic Noses Based on Field Effect Structures I. Lundstrom, E. Hedborg, A. Spetz, H. Sundgren, F. Winquist. Index.
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paper_title: A Wireless Electronic Nose System Using a Fe2O3 Gas Sensing Array and Least Squares Support Vector Regression

paper_content:

This paper describes the design and implementation of a wireless electronic nose (WEN) system which can online detect the combustible gases methane and hydrogen (CH4/H2) and estimate their concentrations, either singly or in mixtures. The system is composed of two wireless sensor nodes—a slave node and a master node. The former comprises a Fe2O3 gas sensing array for the combustible gas detection, a digital signal processor (DSP) system for real-time sampling and processing the sensor array data and a wireless transceiver unit (WTU) by which the detection results can be transmitted to the master node connected with a computer. A type of Fe2O3 gas sensor insensitive to humidity is developed for resistance to environmental influences. A threshold-based least square support vector regression (LS-SVR)estimator is implemented on a DSP for classification and concentration measurements. Experimental results confirm that LS-SVR produces higher accuracy compared with artificial neural networks (ANNs) and a faster convergence rate than the standard support vector regression (SVR). The designed WEN system effectively achieves gas mixture analysis in a real-time process.
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paper_title: A brief history of electronic noses

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The human nose is still the primaryinstrument' used to assess the smell or flavour of various industrial products today, despite considerable and sustained attempts to develop new electronic instrumentation capable of mimicking its remarkable ability . In this paper we review the research effort that has been carried out over the past 25 years or so to create an electronic nose . Indoing so, we first provide a definition for the term electronic nose, and then discuss some of the technologies that have been explored in what is essentially an intelligent chemical array sensor systemwe summarize the applications of electronic noses to date and suggest where future applications may lie .
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paper_title: Exploitation of a low-cost electronic system, designed for low-conductance and wide-range measurements, to control metal oxide gas sensors with temperature profile protocols

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Abstract This work is the continuation of two previous works: in the former we developed a WO 3 based gas sensor featuring high sensitivity to NO 2 but with the drawbacks of low conductance values (below 1 nS) and long recovery times (over 20 min); in the latter we developed a low-cost control electronic circuit suited to measure a wide range of conductance values (10 pS–100 μS). Here, we use this electronic system to control this WO 3 sensor according to temperature profile protocols, with the aim to show the possibility to handle such low conductance devices by means of cheap instrumentation, featuring at the same time reduce response times and a degree of selectivity arising from the temperature profile protocol. In particular, we focus on two target applications: detection of NO 2 and detection of reducing gases, namely ethanol and methane, in different humidity conditions, showing the usefulness of time constants extrapolated from the response dynamics for the purpose.
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paper_title: Development of a Portable Electronic Nose System for the Detection and Classification of Fruity Odors

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In this study, we have developed a prototype of a portable electronic nose (E-Nose) comprising a sensor array of eight commercially available sensors, a data acquisition interface PCB, and a microprocessor. Verification software was developed to verify system functions. Experimental results indicate that the proposed system prototype is able to identify the fragrance of three fruits, namely lemon, banana, and litchi.
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paper_title: A portable electronic nose based on embedded PC technology and GNU/Linux: hardware, software and applications

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This paper describes a portable electronic nose based on embedded PC technology. The instrument combines a small footprint with the versatility offered by embedded technology in terms of software development and digital communications services. A summary of the proposed hardware and software solutions is provided with an emphasis on data processing. Data evaluation procedures available in the instrument include automatic feature selection by means of SFFS, feature extraction with linear discriminant analysis (LDA) and principal component analysis (PCA), multi-component analysis with partial least squares (PLS) and classification through k-NN and Gaussian mixture models. In terms of instrumentation, the instrument makes use of temperature modulation to improve the selectivity of commercial metal oxide gas sensors. Field applications of the instrument, including experimental results, are also presented.
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paper_title: Design for smelling

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On our best days-without head colds, for example-and with a time out between sniffs, we can note the presence of and distinguish among 10000 airborne molecules or molecular compounds, sometimes when they amount to only a few molecules per trillion. Here, the authors present a quick tour of the route from molecule to smell. They correlate many of the discrete physiological steps with engineering ones, ranging from sampling, signal processing and amplification all the way to neural net computation.
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paper_title: A New Low-Cost Electronic System to Manage Resistive Sensors for Gas Detection

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In this paper, a new electronic system for gas detection is presented. Particular attention is focused on electronic noses that employ several resistive sensors. New resistive sensors may have high value due to new substances (TiO2) or to low-cost fabrication process and, supposing to use these sensors together with traditional ones (SnO2), a novel instrument to manage high-value resistive sensors varying over a wide range, from kilohms to gigohms is required. The proposed hardware approach is a modular architecture which takes advantage from an improved resistance-to-period converter, where sensors are DC powered. Experimental results show a relative standard deviation below 0.01% and a relative displacement to the reference line less than 1% over six decades if commercial resistors are considered. A prototype has been realized to manage up to eight sensors, detect and estimate substance concentrations, and communicate results to the Internet.
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paper_title: A portable electronic nose system for the identification of cannabis-based drugs

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Abstract We report on a research aimed at evaluating the capacity of a simple, low-cost, portable electronic nose system based on commercially available metal oxide gas sensors to classify different types of drugs. Five drugs, namely cannabis buds, cannabis plants, hashish, snuff tobacco and tobacco leaves were employed. A dedicated real-time data acquisition system based on dynamic headspace sampling, a microcontroller and a laptop computer have been designed and constructed for this application. To demonstrate its discrimination capability, unsupervised and supervised classification models have been built and validated. Principal Component Analysis (PCA) of volatile profiles revealed five distinct groups corresponding to the five different drugs analyzed. This was further confirmed by a multivariate analysis of variance (MANOVA) test. Support Vectors Machines (SVMs) were applied to build a classifier and reached a 98.5% success rate in the recognition of the different drugs analyzed. This work demonstrates for the first time that the electronic nose technology could be successfully applied to the identification of illegal drugs.
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paper_title: How the olfactory system makes sense of scents

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The human nose is often considered something of a luxury, but in the rest of the animal world, from bacteria to mammals, detecting chemicals in the environment has been critical to the successful organism. An indication of the importance of olfactory systems is the significant proportion — as much as 4% — of the genomes of many higher eukaryotes that is devoted to encoding the proteins of smell. Growing interest in the detection of diverse compounds at single-molecule levels has made the olfactory system an important system for biological modelling.
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paper_title: A Concept of a Sensor System for Determining Composition of Organic Solvents

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This paper presents the results of work on a gas sensor system for determining qualitative and quantitative composition of organic solvents. The system performs the analysis of gaseous mixtures, which are obtained by evaporating liquid solvents and therefore directly represent their composition. The system utilizes gas sensor array, which is built of Taguchi gas sensors (TGS). It provides patterns of measured solvents which are analyzed by pattern recognition module. The module employs multivariate statistical tools like discriminant function analysis (DFA) and partial least squares (PLS) regression. The determination of solvent composition is organized in a hierarchical structure. The concept of the system was experimentally verified using the example of two-component solvents. It was here demonstrated that the proposed system is capable of determining qualitative and quantitative composition of liquid solvents.
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paper_title: Analyzing the Responses of a Thermally Modulated Gas Sensor Using a Linear System Identification Technique for Gas Diagnosis

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A novel approach to the problem of diagnostic data extraction from the responses of a thermally modulated resistive gas sensor (RGS) is presented. The RGS affected by a target gas (TG) is considered a black box dynamic system. The input to the system is the time-varying voltage applied to the heating element of the RGS, and the transient response of the RGS is the output. The structure of the defined system varies with the nature and concentration of the prevailing TG, and the parametric system identification techniques employed reveal system parameters differentiated only by the existing dissimilarities between the TGs. The discriminative information content of these parameters is, then, extracted by standard mathematical tools and utilized for TG recognition. Air contaminated with four different combustible vapors, methanol, ethanol, 2-propanol, and 1-butanol, each at 13 different contamination levels, was used to define 52 different systems. In each case, the transient response of the system to a staircase voltage waveform input was recorded. Computer modeling, based on autoregressive moving average with exogenous input (ARMAX) model, rendered different sets of system parameters which afforded feature extraction and TG classification by standard mapping tools. The method was verified by the successful classification of unknown TGs at undetermined contamination levels.
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paper_title: Portable electronic nose system based on the carbon black–polymer composite sensor array

paper_content:

Abstract A portable electronic nose system based on personal digital apparatus has been developed by using the vapor detection array made of carbon black–polymer composites and the user software, such as data acquisition and pattern recognition. The gas sensor array is possible to have maximum 16 sensing elements integrated on the same silicon substrate. The individual element has a Si bulk-micromachined well which allows the polymer-carbon black composite solution to be placed reproducibly in a specific and well-constrained area during the drop-coating process. Preliminary results show that our portable electronic nose system has successfully classified simple volatile organic compounds, and the complex liquor samples of brandy and whiskey.
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paper_title: A Novel Breath Analysis System Based on Electronic Olfaction

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Certain gases in the breath are known to be indicators of the presence of diseases and clinical conditions. These gases have been identified as biomarkers using equipments such as gas chromatography (GC) and electronic nose (e-nose). GC is very accurate but is expensive, time consuming, and non-portable. E-nose has the advantages of low-cost and easy operation, but is not particular for analyzing breath odor and hence has a limited application in diseases diagnosis. This article proposes a novel system that is special for breath analysis. We selected chemical sensors that are sensitive to the biomarkers and compositions in human breath, developed the system, and introduced the odor signal preprocessing and classification method. To evaluate the system performance, we captured breath samples from healthy persons and patients known to be afflicted with diabetes, renal disease, and airway inflammation repectively and conducted experiments on medical treatment evaluation and disease identification. The results show that the system is not only able to distinguish between breath samples from subjects suffering from various diseases or conditions (diabetes, renal disease, and airway inflammation) and breath samples from healthy subjects, but in the case of renal failure is also helpful in evaluating the efficacy of hemodialysis (treatment for renal failure).
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paper_title: A hybrid chemiresistive sensor system for the detection of organic vapors

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A five node sensor array, consisting of three films of gold nanoparticles functionalized with p-terphenylthiol, dodecanethiol and mercapto-(triethylene glycol) methyl ether, and films of poly(3hexylthiophene) and polypyrrole, was integrated into a portable, microprocessor-based system. The system was evaluated for the detection of chloroform, diisopropyl methylphosphonate (DIMP), ethanol, hexane, methanol, and toluene vapors. Direct comparison of the five sensor films with respect to sensitivity, response time and recovery time was made by measurement of the resistance changes upon simultaneous exposure to each analyte. In general, the sensor films responded, with greatest sensitivity, to organic analyte molecules with similar chemical functionality (e.g., polarity). For example, the dodecanethiol-functionalized gold nanoparticle film sensor excelled at detecting hexane, while the mercapto-(triethylene glycol) methyl ether-functionalized nanoparticle film exhibited superb detection of ethanol and chloroform. Although the poly(3-hexylthiophene) film was very sensitive to polar analytes, including DIMP, in many cases it suffered from relatively long recovery times. Following training of the sensor system, successful differentiation and detection of the analytes were realized using a relatively simple algorithm based on “minimization of the squares of differences” method. The ability of the system to optimally differentiate these analytes is considered within the context of principal component analysis, and the effects of long-term sensor drift are discussed. © 2011 Published by Elsevier B.V.
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paper_title: Intelligent gas-mixture flow sensor

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A simple way to realize a gas-mixture flow sensor is presented. The sensor is capable of measuring two parameters from a gas flow. Both the flow rate and the helium content of a helium-nitrogen gas mixture are measured. The sensor exploits two measurement principles in combination with (local) information handling in an artificial neural network. An analysis of the measurement principles is given and the IC-compatible realization process is described. The sensor is simple to integrate with other micro gas-handling components such as valves, pressure sensors, etc. The sensing elements are combined with a small electronic circuit in which the artificial neural network is implemented. The experimental results are very promising.
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paper_title: Vinegar Classification Based on Feature Extraction and Selection From Tin Oxide Gas Sensor Array Data

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Tin oxide gas sensor array based devices were often cited in publications dealing with food products. However, during the process of using a tin oxide gas sensor array to analysis and identify different gas, the most important and difficult was how to get useful parameters from the sensors and how to optimize the parameters. Which can make the sensor array can identify the gas rapidly and accuracy, and there was not a comfortable method. For this reason we developed a device which satisfied the gas sensor array act with the gas from vinegar. The parameters of the sensor act with gas were picked up after getting the whole acting process data. In order to assure whether the feature parameter was optimum or not, in this paper a new method called “distinguish index”(DI) has been proposed. Thus we can assure the feature parameter was useful in the later pattern recognition process. Principal component analysis (PCA) and artificial neural network (ANN) were used to combine the optimum feature parameters. Good separation among the gases with different vinegar is obtained using principal component analysis. The recognition probability of the ANN is 98 %. The new method can also be applied to other pattern recognition problems.
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paper_title: Chaos based neural network optimization for concentration estimation of indoor air contaminants by an electronic nose

paper_content:

Abstract Electronic nose (E-nose), as an artificial olfactory system, can be used for estimation of gases concentration combined with a pattern recognition module. This paper studies the concentration estimations of indoor contaminants for air quality monitoring in dwellings using chaos based optimization artificial neural network integrated into our self-designed portable E-nose instrument. Back-propagation neural network (BPNN) has been recognized as the common pattern recognition. Considering the local optimal flaw of BPNN, this paper presents a novel chaotic sequence optimization BPNN method for improving the accuracy of E-nose prediction. Further comparison with particle swarm optimization is also employed, and maximum 26.03% and 16.4% prediction error decreased after using chaotic based optimization for formaldehyde and benzene concentration estimation. Experimental results demonstrate the superiority and efficiency of the portable E-nose instrument integrated with artificial neural network optimized by chaotic sequence based optimization algorithms in real-time monitoring of air quality in dwellings.
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paper_title: Electronic noses — development and future prospects

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Abstract The human olfactory system is still regarded as the most important ‘analytical instrument’ for the assurance of odour quality in many industries, such as food and drinks. Until recently, there has been no major advance in the analytical methods employed to assess odour. Now, research on artificial olfaction in the late 1980s and early 1990s has led to significant advances in this field and to the launch of commercial instruments (called ‘electronic noses’) being used in a variety of industries (including food, water and brewing). An electronic nose comprises an array of chemical sensors, where each sensor has only partial specificity to a wide range of odorant molecules, coupled with a suitable pattern recognition system. This paper briefly reviews the development of artificial olfaction and discusses future trends in electronic nose technology.
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paper_title: Design and development of a metal oxide based electronic nose for spoilage classification of beef

paper_content:

Abstract A metal oxide sensor-based electronic nose system consisting of nine sensors was designed and used to analyze the volatile compounds emanating from beef strip loins (M. Longisimmus lumborum ) stored at 4 °C and 10 °C. Two statistical techniques, i.e., linear discriminant analysis (LDA) and quadratic discriminant analysis (QDA) were used to develop classification models from the collected sensor signals. The performances of the developed models were validated by two different methods, i.e., leave-1-out cross validation and bootstrapping. Also, each classification model was developed using 6 and 10 features. The classification models classified meat samples based on the microbial population into “unspoiled” (microbial counts 10 cfu/g) and “spoiled” (microbial counts ≥ 6 log 10 cfu/g). For the meat samples stored at 10 °C, the highest classification accuracies obtained by LDA method with leave-1-out and bootstrapping validations were 83.8% and 89.1%, respectively. On the other hand, classification by QDA and subsequent validation by leave-1-out and bootstrapping provided highest accuracies of 81.5% and 93.2%, respectively. For samples stored at 4 °C, the LDA method provided highest classification accuracies of 80% and 86.6% using leave-1-out and bootstrapping validation, respectively. The highest classification accuracies obtained for the samples stored at 4 °C were 85% and 96% by using QDA method with leave-1-out and bootstrapping validations, respectively.
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paper_title: An electronic nose based on solid state sensor arrays for low-cost indoor air quality monitoring applications

paper_content:

The occurrence of illnesses related with poor ventilation has driven an increasing attention towards indoor air quality monitoring. In buildings equipped with climate control systems, the diseases related to the air quality can be significantly reduced if smart intervening procedures, aiming to control the concentration of pollutants in the indoor air, can be implemented in the heating, ventilation air conditioning unit. When reliable information about both the indoor and outdoor air quality is made available, the climate control system can provide the most appropriate amount of ventilation, ensuring safe and comfortable living conditions. In this paper, a dedicated, miniaturized, low-cost electronic nose based on state-of-the-art metal oxide sensors and signal processing techniques was developed. The proposed device is targeted to the quantification of carbon monoxide and nitrogen dioxide in mixtures with relative humidity and volatile organic compounds by using an optimized gas sensor array and highly effective pattern recognition techniques. The electronic nose was tested in an environment reproducing real operating conditions. Exploiting the unique response patterns of the different sensors in the array and the capability of a simple fuzzy-logic system it was possible to identify and discriminate concentrations as low as 20 ppb for NO2 and 5 ppm for CO in the test gas environment, allowing to reach the necessary sensitivity towards the target pollutants together with the selectivity towards the typical interfering gas species. © 2004 Elsevier B.V. All rights reserved.
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paper_title: Embedded Electronic Nose and Supporting Software Tool for its Parameter Optimization

paper_content:

Abstract This paper details the work done towards a low cost, small size, portable embedded electronic nose (e-nose) and its application for analysis of different VOC mixtures. The sensor array is composed of commercially available metal oxide semiconductor sensors by Figaro. The Embedded E-nose consists of an ADuC831 and has an RS 232 interface to Desktop PC for higher level data collection and NN training. An E-nose Software Package (ESP) Integrated Development Environment (IDE) is implemented for the design and development of Embedded E-nose. The IDE facilitates the parameter optimization of data acquisition, signal pre-processing, feature extraction and Multilayer Perceptron Neural Network (MLP NN) training. The optimized parameters are then downloaded onto Embedded E-nose by means of docking the device to the ESP tool via PC serial port. The Embedded E-nose is used for realization of both qualitative as well as quantitative analysis and their results are discussed.
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paper_title: Evaluation of unpleasant odor with a portable electronic nose

paper_content:

An intelligent multi-sensor system with an entire autonomy, a low weight and a small size has been developed for in situ applications such as environmental pollutant gas detection or olfactory estimation. This portable electronic nose works with commercial metal oxide gas sensors and a microcontroller connected to a compact flash memory as intelligent unit. In this work we present the conception of this electronic nose, its laboratory validation, and a real application which concerns an outdoor air monitoring of a duck breeding. This application is developed in order to quantify continuously discomfort odor spread, causing neighbor complaints. The odor measurements were made using our electronic nose (Nepo) and results are compared to the simultaneous results obtained from other olfactometric techniques.
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paper_title: A real-time data acquisition system for a hand-held electronic nose (H2EN)

paper_content:

This paper describes an approach towards the development of a portable E-nose device based on an array of metal oxide sensors (MOS) devices, for early on-site dry rot detection on building timbers. A dedicated real-time data acquisition system with a programmable voltage generator, self-calibration techniques and custom visual software programs for a desktop PC and a hand-held computer have been designed and constructed for this application. This paper also describes an example of software calibration to correct source errors for this data acquisition system. Experimental results show that this data acquisition system can accurately measure a large range of resistive sensor responses and is suitable for measuring both conducting polymer and MOS sensors. The custom software also allows users to easily capture, analyse and record measurement data. In addition, the constructed framework for a hand-held computer is based on real-time object-oriented methodology to carry out the functions of desktop PC based instrumentation software. This system presents an effective and user-friendly interface for portable applications.
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paper_title: Olfactory receptors: molecular basis for recognition and discrimination of odors

paper_content:

The daunting task of our nose to detect and discriminate among thousands of low-molecular-weight organic compounds with diverse chemical structures and properties requires an enormous molecular recognition capacity. This is based on distinct proteins, capable of recognizing and binding odorous compounds, including odorant-binding proteins, which are supposed to shuttle odorous compounds through the nasal mucus, and most notably the odorant receptors, which are heptahelical membrane proteins coupling via G-proteins onto intracellular transduction cascades. From more than a thousand genes each olfactory neuron is supposed to express only one receptor subtype. Receptors appear to be selective but rather non-specific-i.e. a distinct odorant activates multiple receptors and individual receptors respond to multiple odorants. It is the molecular receptive range of its receptor type which determines the reaction spectrum of a sensory neuron. Populations of cells equipped with the same receptor type project their axons to common glomeruli, thereby transmitting the molecular receptive range of a receptor type into the receptive field of glomerulus. Recent insight into the molecular basis of odor recognition and the combinatorial coding principles of the olfactory system may provide some clues for the design and development of technical sensors, electronic noses. In this review more emphasis has been placed on physiological rather than analytical aspects.
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paper_title: Biology and applications of olfactory sensing system: A review

paper_content:

Abstract Various metal oxide and conducting polymer-based sensors have been used in electronic nose systems for the detection of volatile organic compounds (VOCs). Some of the major constrains of these sensor materials are their sensitivity and selectivity. Recently, much research has been towards the development of biosensors that mimic biological olfactory mechanism. The sensing materials based on biological olfactory system can be well adapted to detect low concentrations of VOCs as it exhibits high selectivity/specificity, fast response time, high sensitivity, simplicity in fabrication, and are not toxic resulting from their biocompatibility and rapid biodegradability. A better understanding of human olfactory system can aid in the development of an artificial olfactory sensing system. The application domain of such sensors/systems could be potentially expanded for rapid and accurate detection of VOCs in environment and other biological media. Therefore, this paper provides a brief overview of the biology, associated mechanisms, and the functional principles of the olfactory sensing system in humans. Moreover, it summarizes the recent research on the development of an olfactory sensor utilizing olfactory receptors, odorant binding proteins and olfactory epithelium for the detection of different VOCs, and research needs in this area.
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paper_title: Chemical sensors for portable, handheld field instruments

paper_content:

A review of three commonly used classes of chemical sensor technologies as applicable to implementation in portable, handheld field instruments is presented. Solid-state gas and chemical sensors have long been heralded as the solution to a wide variety of portable chemical sensing system applications. However, advances in optical sensing technology have reduced the size of supporting infrastructure to be competitive with their solid-state counterparts. Optical, solid-state, and hybrid arrays of sensors have application for portable instruments, but issues of insufficient selectivity and sensitivity continue to hamper the widespread introduction of these miniaturized sensors for solving chemical sensing problems in environments outside the laboratory. In this article, we evaluate three of the major classes of compact chemical sensors for portable applications: (solid-state) chemiresistors, (solid-state) CHEMFETs, and (optical) surface plasmon resonance sensors (SPR). These sensors are evaluated and reviewed, according to the current state of research, in terms of their ability to operate at low-power, small-size, and relatively low-cost in environments, with numerous interferents and variable ambient conditions.
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paper_title: Identification of CO and NO2 using a thermally resistive microsensor and support vector machine

paper_content:

Levels of carbon monoxide and nitrogen dioxide in air are currently monitored using two different thick-film resistive gas sensors. The resultant high power consumption of thick-film-based gas sensors is problematic for portable multi-gas monitors. The use of a single low-power thermally-modulated resistive gas sensor to monitor simultaneously both gases is reported. The silicon micromachined Substrate not only reduces the DC power consumption to 100mW Lit 300degreesC but also permits AC temperature modulation through a small thermal mass. Uniquely, a Support vector machine is employed to classify the wavelet coefficients of the AC resistive signal. This simple method permits the rapid classification of CO/NO2, gas mixtures with a high level of confidence (94% or better) using just one low-power gas microsensor. Thus demonstrating the potential application of a single low-power thermally-modulated resistive gas sensor in portable multi-gas monitors.
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paper_title: A monolithic CMOS microhotplate-based gas sensor system

paper_content:

A monolithic CMOS microhotplate-based conductance-type gas sensor system is described. A bulk micromachining technique is used to create suspended microhotplate structures that serve as sensing film platforms. The thermal properties of the microhotplates include a 1-ms thermal time constant and a 10/spl deg/C/mW thermal efficiency. The polysilicon used for the microhotplate heater exhibits a temperature coefficient of resistance of 1.067/spl times/10/sup -3///spl deg/C. Tin(IV) oxide and titanium(IV) oxide (SnO/sub 2/,TiO/sub 2/) sensing films are grown over postpatterned gold sensing electrodes on the microhotplate using low-pressure chemical vapor deposition (LPCVD). An array of microhotplate gas sensors with different sensing film properties is fabricated by using a different temperature for each microhotplate during the LPCVD film growth process. Interface circuits are designed and implemented monolithically with the array of microhotplate gas sensors. Bipolar transistors are found to be a good choice for the heater drivers, and MOSFET switches are suitable for addressing the sensing films. An on-chip operational amplifier improves the signal-to-noise ratio and produces a robust output signal. Isothermal responses demonstrate the ability of the sensors to detect different gas molecules over a wide range of concentrations including detection below 100 nanomoles/mole.
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paper_title: Micro gas sensor array with neural network for recognizing combustible leakage gases

paper_content:

A micro gas sensor array, consisting of four porous tin oxide thin films added with noble metal catalysts on a micro-hotplate, was designed and fabricated. The micro-hotplate was designed to obtain a uniform thermal distribution along with a low-power consumption and fast thermal response. The sensing properties of the sensors toward certain combustible gases, i.e., propane, butane, LPG, and carbon monoxide, were evaluated. A multilayer neural network was then used to classify the gas species. The results demonstrated that the proposed micro sensor array, plus multilayer neural network employing a backpropagation learning algorithm, was very effective in recognizing specific kinds and concentration levels of combustible gas below their respective threshold limit values.
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paper_title: Resistance characteristics of conducting polymer films used in gas sensors

paper_content:

Abstract The measurement of the resistance of thin films of conducting polymer deposited between microelectrodes is discussed. Attention is drawn to the severity of self-heating effects which may perturb the measurement unless the measuring power is kept low. The conduction mechanism is nonohmic at frequencies below 1 MHz, but considerably more ohmic at frequencies of tens of MHz. Noise measurements show that the passage of d.c. current generates a high level of excess noise with a 1/ƒ characteristic. This result, taken with the high-frequency data, is consistent with a model picture of a film conductivity which is dominated by intergranular contact at low frequencies although electrode contact effects cannot be completely excluded. Due to the 1/ƒ noise, accurate resistance measurements are best made using a.c. techniques.
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paper_title: Applications and Advances in Electronic-Nose Technologies

paper_content:

Electronic-nose devices have received considerable attention in the field of sensor technology during the past twenty years, largely due to the discovery of numerous applications derived from research in diverse fields of applied sciences. Recent applications of electronic nose technologies have come through advances in sensor design, material improvements, software innovations and progress in microcircuitry design and systems integration. The invention of many new e-nose sensor types and arrays, based on different detection principles and mechanisms, is closely correlated with the expansion of new applications. Electronic noses have provided a plethora of benefits to a variety of commercial industries, including the agricultural, biomedical, cosmetics, environmental, food, manufacturing, military, pharmaceutical, regulatory, and various scientific research fields. Advances have improved product attributes, uniformity, and consistency as a result of increases in quality control capabilities afforded by electronic-nose monitoring of all phases of industrial manufacturing processes. This paper is a review of the major electronic-nose technologies, developed since this specialized field was born and became prominent in the mid 1980s, and a summarization of some of the more important and useful applications that have been of greatest benefit to man.
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paper_title: A review of gas sensors employed in electronic nose applications

paper_content:

This paper reviews the range of sensors used in electronic nose (e‐nose) systems to date. It outlines the operating principles and fabrication methods of each sensor type as well as the applications in which the different sensors have been utilised. It also outlines the advantages and disadvantages of each sensor for application in a cost‐effective low‐power handheld e‐nose system.
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paper_title: Metal Oxide Semi-Conductor Gas Sensors in Environmental Monitoring

paper_content:

Metal oxide semiconductor gas sensors are utilised in a variety of different roles and industries. They are relatively inexpensive compared to other sensing technologies, robust, lightweight, long lasting and benefit from high material sensitivity and quick response times. They have been used extensively to measure and monitor trace amounts of environmentally important gases such as carbon monoxide and nitrogen dioxide. In this review the nature of the gas response and how it is fundamentally linked to surface structure is explored. Synthetic routes to metal oxide semiconductor gas sensors are also discussed and related to their affect on surface structure. An overview of important contributions and recent advances are discussed for the use of metal oxide semiconductor sensors for the detection of a variety of gases—CO, NOx, NH3 and the particularly challenging case of CO2. Finally a description of recent advances in work completed at University College London is presented including the use of selective zeolites layers, new perovskite type materials and an innovative chemical vapour deposition approach to film deposition.
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paper_title: Employment of Electric Potential to Build a Gas-Selective Response of Metal Oxide Gas Sensor Array

paper_content:

This paper presents an approach to design multisensor microarrays for electronic nose instruments employing a metal oxide thin film whose spatial gas-sensitive properties are locally differentiated by electric potential. The measurement of local potential as a sensor signal over the metal oxide film serves to build a gas discriminating pattern which can be selectively identified by pattern recognition techniques. The gas sensitivity studies have revealed a higher gas response on the film areas, which are activated by positive potential, than that at earth potential. The gas-recognition capability of potential patterns is, at least, comparable with the one of conductance patterns recorded at the same microarrays differentiated by nonhomogeneous spatial heating. The experimental data are discussed in terms of oxide surface charging by adspecies coming through the ambient air. The suggested approach could be considered for designing reproducible multisensor systems on a single-chip platform.
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paper_title: Metal Oxide Nanowire and Thin-Film-Based Gas Sensors for Chemical Warfare Simulants Detection

paper_content:

This work concerns with metal oxide (MOX) gas sensors based on nanowires and thin films. We focus on chemical warfare agents (CWAs) detection to compare these materials from the functional point-of-view. We work with different chemicals including simulants for Sarin nerve agents, vescicant gases, cyanide agents, and analytes such as ethanol, acetone, ammonia, and carbon monoxide that can be produced by everyday activities causing false alarms. Explorative data analysis has been used to demonstrate the different sensing performances of nanowires and thin films. Within the chosen application, our analysis reveal that the introduction of nanowires inside the array composed by thin films can improve its sensing capability. Cyanide simulants have been detected at concentrations close to 1 ppm, lower than the Immediately Dangerous for Life and Health (IDLH) value of the respective warfare agent. Higher sensitivity has been obtained to simulants for Sarin and vescicant gases, which have been detected at concentrations close or even lower than 100 ppb. Results demonstrate the suitability of the proposed array to selectively detect CWA simulants with respect to some compounds produced by everyday activities.
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paper_title: The tin oxide gas sensor and its applications

paper_content:

Abstract After a brief introduction to the operation of the semiconductor gas sensor, details of its construction and characteristics are presented. These are followed by a review of the performance of the device in terms of sensitivity and selectivity to various gases, and of the problems presented by its response to changes in ambient temperature and humidity. Practical points relevant to its use in gas alarm and gas monitoring instruments are included.
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paper_title: Integration of MOX gas sensors on polyimide hotplates

paper_content:

In this communication, we report on the integration of metal-oxide gas sensors on polymeric micro-hotplates made on polyimide and silicon substrates. Low-power consumption micro-hotplates with platinum electrodes and heaters were fabricated on polyimide membranes. Their thermal behavior was optimized using temperature probing at the micro-scale level coupled with thermal simulations. Tin oxide thick films were successfully integrated on these polyimide micro-hotplates using the drop coating technique. The annealing process of the tin oxide drops on the polyimide substrate was investigated and gas measurements are presented. Compared to the polyimide hotplates on silicon substrates, the hotplates made on polyimide sheets are simpler to process and more robust, and therefore, they are more suitable for the integration of metal-oxide films. Finally, a wafer level packaging technique using multiple polyimide layers was developed and led to a polymeric platform for metal oxide sensors. The technology is also promising for the integration of polyimide humidity sensors, of resistive and capacitive gas-sensitive polymeric films to realise fully flexible gas sensor arrays.
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paper_title: Air quality monitoring and fire detection with the Karlsruhe electronic micronose KAMINA

paper_content:

An indoor air monitoring device is one of the most prominent consumer applications of an electronic nose (EN). Integral gas analysis similar to biogenic odor perception can be a versatile tool to obtain continuous information about pollutants, odors, and air compositions indicating gaseous precursors of dangers such as fires. However, an EN to be used as a common household device has to combine high sensitivity and excellent gas discrimination power with inexpensiveness, small size, and low power consumption. A special gas sensor microarray of thumbnail size has been developed at the Forschungszentrum Karlsruhe based on metal-oxide technology to meet these requirements. The microarray is produced by simply partitioning a monolithic metal-oxide layer with parallel electrode strips allowing low cost fabrication. A temperature gradient and a membrane thickness gradient (on metal-oxide layer) are responsible for differentiation between the individual sensor segments and thus for the conductivity patterns that are accordingly produced. The two membranes form the basis of gas discrimination power, reliability self checks, and online noise reduction. Model gas exposures usually show detection limits lower than 1 ppm. Successful practical tests are reported on the detection of overheated wire insulation for fire prevention as well as on air quality analysis for air conditioning purposes (e.g., air quality control during a meeting).
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paper_title: Portable e-nose to classify different kinds of wine

paper_content:

To address the problem of the wine quality measurement a portable electronic nose (e-nose) has been developed. Two different micromachined resistive sensor arrays are developed for this portable e-nose, one with a polysilicon integrated heater and the other with a platinum one. The nose is tested with four different wines coming of Madrid region (Malvar, Airen, Garnacha, and Tempranillo). The principal component analysis (PCA) plots show a slight overlapping of the responses for the sensor array with Platinum heater and an 88% of classification result is obtained with a probabilistic neural network (PNN). With the sensor array with polysilicon heater a good separation is achieved by the PCA and the PNN classification success is 100%.
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paper_title: Microsensors in Dynamic Backgrounds: Toward Real-Time Breath Monitoring

paper_content:

We evaluated a microelectromechanical systems (MEMS) microsensor array with temperature-controlled chemi-resistive elements for use as a noninvasive clinical diagnostic tool to detect the presence or absence of trace amounts of disease biomarkers in simulated breath samples. The microsensor environment was periodically altered between air (78% N2, 21% O2 by volume, 20% relative humidity) and simulated breath (77% N2, 16% O2, 4% CO2 by volume, 80% relative humidity) samples creating a dynamic background. Acetone, a disease marker for diabetes, was spiked into select simulated breath samples at relevant concentrations ( 0.5 ?mol/mol to 8 ?mol/mol) to pose a diagnostic problem for the sensor array. Using standard statistical dimensionality reduction and classification algorithms, we compared the ability of a variety of sensing materials to detect and recognize the disease marker. Our analyses indicate that the porous, doped nanoparticle materials (Sb:SnO2 microshell films and Nb :TiO2 nanoparticle films) are best for the recognition problem (acetone present versus absent), but that WO3 and SnO2 films are better at the quantification task (high versus low concentrations of acetone).
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paper_title: Micro-machined resistive micro-heaters for high temperature gas sensing applications

paper_content:

Presented for the first time is the design and fabrication of novel high temperature, low power consumption, and good thermal uniformity micro-heaters for environmental gas sensors. A O/N/O (SiO2/SixNy/SiO2) structure of membrane was used for stress compensation and thermal isolation. A Wheatstone-bridge type resistive Pt heating structure and a multi-ringed heat spreading structure was applied to enhance the thermal uniformity. Results show that these fabricated heaters can operate at a high temperature, have low power consumption and good thermal uniformity. The thermal efficiency of the fabricated micro-heaters is 36°C/mW.
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paper_title: ZnO nanowire-based oxygen gas sensor

paper_content:

We report growth of vertically well-aligned ZnO nanowires on ZnO:Ga/glass templates and the fabrication of resistive ZnO nanowire-based oxygen gas sensor. It was found that the ZnO nanowires are grown preferred oriented in the (002) direction with a small X-ray diffraction full-width-half-maximum. From high resolution transmission electron microscopy, scanning electron microscopy and micro-Raman measurements, it was found that the ZnO nanowires prepared in this study are single crystalline with good crystal quality. It was also found that measured sample resistance increased logarithmically as the oxygen gas pressure in the chamber was increased. Such a relationship suggests that the device is potentially useful for resistive oxygen gas sensing at room temperature.
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paper_title: Chemical Sensors and Electronic Noses Based on 1-D Metal Oxide Nanostructures

paper_content:

The detection of chemicals such as industrial gases and chemical warfare agents is important to human health and safety. Thus, the development of chemical sensors with high sensitivity, high selectivity, and rapid detection is essential and could impact human beings in significant ways. 1-D metal oxide nanostructures with unique geometric and physical properties have been demonstrated to be important candidates as building blocks for chemical sensing applications. Chemical sensors composed of a wide range of pristine 1-D metal oxide nanostructures, such as In2O3, SnO2, ZnO, TiO2, and CuO, have been fabricated, and exhibited very good sensitivity in the detection of important industrial gases, chemical warfare agents, and human breath. In this review, we provide an overview of this chemical sensing field. Various key elements of the topics will be reviewed, including 1-D metal oxide nanostructure synthesis, electronic properties of nanowire-based FETs, and their chemical sensing behaviors. In addition, this paper provides a review of the recent development of electronic nose systems based on metal oxide nanowires, which indicate great potential for the improvement of sensing selectivity.
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paper_title: Synthesis and integration of tin oxide nanowires into an electronic nose

paper_content:

Abstract Single crystal nanostructures of semiconducting tin oxides have been fabricated and characterized as sensing materials for implementation in an electronic nose. The nanowires exhibit exceptional crystalline quality and a very high length-to-width ratio, resulting in enhanced sensing capability as well as long-term material stability for prolonged operation. A sensing device based on SnO 2 nanowires has been fabricated and comparatively tested in an array of chemical sensor with conventional thin film sensing device. Preliminary measurements ethanol/water mixtures demonstrate that nanowire-based sensors can be favourably implemented in the electronic nose and that they perform comparably with the conventional thin film layers.
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paper_title: Miniaturised arrays of tin oxide gas sensors on single microhotplate substrates fabricated by micromolding in capillaries

paper_content:

Abstract The concept of producing one gas sensor on one microhotplate is extended towards a gas sensor array consisting of several sensors on one hotplate. Twelve miniaturised gas sensors of nanoparticulate tin oxide were integrated as an array on a single microhotplate by using soft lithography, i.e. micromolding in capillaries. Soft lithography is a microfabrication technique based on elastomeric molds of poly-dimethylsiloxane (PDMS) for pattern transfer. It is ideally suited to directly micro-shape liquid materials, including suspensions of oxidic powders. PDMS molds containing recessed microchannels could be placed directly—and removed after processing—on freestanding silicon nitride membranes of 250 nm thickness without causing damage. Tin oxide microlines were generated after applying a suspension droplet at the entrance of the microchannels and filling them by capillary force action. A single sensor was shrunk on a minimal area of 10 μm ×30 μm. In gas sensitivity experiments with carbon monoxide concentrations from 100 to 2000 ppm, a maximal sensitivity to carbon monoxide of 600 ppm was obtained. The heating power required to operate the whole array is reduced by at least one order of magnituede compared to the power that is usually required to run an array of multiple (>10) micromachined gas sensors.
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paper_title: Temperature Gradient Effect on Gas Discrimination Power of a Metal-Oxide Thin-Film Sensor Microarray

paper_content:

The paper presents results concerning the effect of spatial inhomogeneous operating temperature on the gas discrimination power of a gas-sensor microarray, with the latter based on a thin SnO2 film employed in the KAMINA electronic nose. Three different temperature distributions over the substrate are discussed: a nearly homogeneous one and two temperature gradients, equal to approx. 3.3 °C/mm and 6.7 °C/mm, applied across the sensor elements (segments) of the array. The gas discrimination power of the microarray is judged by using the Mahalanobis distance in the LDA (Linear Discrimination Analysis) coordinate system between the data clusters obtained by the response of the microarray to four target vapors: ethanol, acetone, propanol and ammonia. It is shown that the application of a temperature gradient increases the gas discrimination power of the microarray by up to 35 %.
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paper_title: A Neuro-Fuzzy Classifier-Cum-Quantifier for Analysis of Alcohols and Alcoholic Beverages Using Responses of Thick-Film Tin Oxide Gas Sensor Array

paper_content:

A novel neuro-fuzzy classifier-cum-quantifier is presented. The proposed classifier retrieves both qualitative and quantitative information simultaneously from the steady-state responses of thick-film tin oxide gas sensor array when it was exposed to seven different kinds of alcohols and alcoholic beverages. The individual concentration bands were represented in the output feature space by fuzzy subsethood measure. The qualitative and quantitative classifications were done by training an artificial neural network (ANN) with backpropagation algorithm. Each output neuron of the network represented one out of the seven alcohols and alcoholic beverage classes and was trained to fire at the fuzzy subsethood value of the particular concentration band of a particular alcohol or alcoholic beverage whose sample was presented to the network. The proposed network gave satisfactory performance and simultaneous qualitative and quantitative classification of the alcohols and alcoholic beverages was obtained using a single neural network.
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paper_title: Recognition of olive oils by means of an integrated sol–gel SnO2 Electronic Nose

paper_content:

In this paper, we report a specific application of a semiconductor thin films based sensor array for the discrimination of different olive oils. The active elements of the sensor array were undoped and Ni, Pd, Pt, Os-doped SnO thin films prepared by 2 sol–gel technique. Olive oil samples were randomly selected. They included commercial olive oils of different qualities (extravirgin, virgin and husk oils) and non-commercial local olive oils (deriving from different zone of the Salento region in Apulia) with different degrees of acidity. The sensor array coupled with a principal component analysis allows discrimination between different olive oils. In particular good separation between commercial and local products was obtained. 2002 Elsevier Science B.V. All rights reserved.
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paper_title: Gas Identification Based on Committee Machine for Microelectronic Gas Sensor

paper_content:

Gas identification represents a big challenge for pattern recognition systems due to several particular problems such as nonselectivity and drift. The purpose of this paper is twofold: 1) to compare the accuracy of a range of advanced and classical pattern recognition algorithms for gas identification for the in-house sensor array signals and 2) to propose a gas identification ensemble machine (GIEM), which combines various gas identification algorithms, to obtain a unified decision with improved accuracy. An integrated sensor array has been designed with the aim of identifying combustion gases. The classification accuracy of different density models is compared with several neural network architectures. On the gas sensors data used in this paper, Gaussian mixture models achieved the best performance with higher than 94% accuracy. A committee machine is implemented by assembling the outputs of these gas identification algorithms through advanced voting machines using a weighting and classification confidence function. Experiments on real sensors' data proved the effectiveness of the system with an improved accuracy over the individual classifiers. An average performance of 97% was achieved using the proposed committee machine
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paper_title: Discrimination Effects in Zeolite Modified Metal Oxide Semiconductor Gas Sensors

paper_content:

The use of zeolites to enhance the response and discriminating power of solid state metal oxide semiconductor gas sensors is demonstrated. Thick film sensors were prepared by screen printing layers of chromium titanium oxide (CTO) or tungsten trioxide with various zeolites as over-layers. The sensors gas response was tested against two similar gases; ethanol and isopropyl alcohol. The modified sensors effectively discriminated between the two gases. An understanding of this discriminating behavior is elucidated through computer modeling of diffusion and reaction processes occurring in the zeolite transformation layer and sensor element. Our analysis suggests that the discrimination is the result of the size and shape selective behavior.
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paper_title: A Radial Basis Function Neural Network Classifier for the Discrimination of Individual Odor Using Responses of Thick-Film Tin-Oxide Sensors

paper_content:

This paper presents a novel approach to odor discrimination of alcohols and alcoholic beverages using published data obtained from the responses of thick film tin oxide sensor array fabricated at our laboratory and employing a combination of transformed cluster analysis and radial basis function neural network. The performance of the new classifier was compared with others based on backpropagation (BP) algorithm. The new model has superior discrimination power with a much lower discrimination error. Also, it was found to be less sensitive to the variations in learning parameters apart from being significantly faster than the conventional models based on BP algorithm. Both raw data and data preprocessed by transformed cluster analysis (TCA) were used to train radial basis function neural network (RBFNN) and backpropagation network (BPN). Superior learning and classification performance was obtained using proposed model constituting TCA processed data and RBF network.
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paper_title: Nanosensor and Breath Analyzer for Ammonia Detection in Exhaled Human Breath

paper_content:

The detection and monitoring of gases in exhaled human breath up to date has been limited by the lack of appropriate materials and technologies which could rapidly and selectively identify the presence and monitor the concentration of trace levels of specific analytes-biomarkers. We present a metal oxide-based nanosensor that is highly specific to ammonia gas in breath-simulating environments at low part-per-billion concentrations. The design of a handheld breath analyzer for gas detection in exhaled human breath is described. Semiconducting ceramics are presented as suitable sensor materials for easy and affordable noninvasive diagnostics.
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paper_title: Nanostructured Metal Oxide Gas Sensors, a Survey of Applications Carried out at SENSOR Lab, Brescia (Italy) in the Security and Food Quality Fields

paper_content:

In this work we report on metal oxide (MOX) based gas sensors, presenting the work done at the SENSOR laboratory of the CNR-IDASC and University of Brescia, Italy since the 80s up to the latest results achieved in recent times. In particular we report the strategies followed at SENSOR during these 30 years to increase the performance of MOX sensors through the development of different preparation techniques, from Rheotaxial Growth Thermal Oxidation (RGTO) to nanowire technology to address sensitivity and stability, and the development of electronic nose systems and pattern recognition techniques to address selectivity. We will show the obtained achievement in the context of selected applications such as safety and security and food quality control.
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paper_title: Characterization of Integrated Tin Oxide Gas Sensors With Metal Additives and Ion Implantations

paper_content:

Post-treatment of the sensing film in tin oxide gas sensor arrays is widely used to improve the selectivity in gas recognition applications. This letter describes the characterization study of an integrated tin oxide gas sensor array chip in which the sensing films are modified using metal additives and ion implantations. Measurement results reveal that metal additives present a higher impact on the sensor sensitivity compared with ion implantations. The latter has no significant effect on the sensing properties. The drift is increased for the sensors with only ion implantation compared with the ones with metal additives. An array combining both post-treatment techniques is expected to improve the overall recognition performance.
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paper_title: An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array

paper_content:

This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibility. However, limited sacrificial layer thickness usually leads to higher power consumption. In this work, a convex MHP structure is developed to increase the thermal efficiency, which is critical for large dimension and low-power gas sensor array integration. Before the structure release process, 700degC-950degC annealing process was carried out on the 190 times190 mum2 MHP with 2.8 mum polysilicon sacrificial layer. It is shown that higher annealing temperature leads to lower tensional stress of the MHP membrane and larger curvature of the released structure, which enables higher thermal efficiency. Among the four annealing temperatures, the 950degC annealed MHP has the largest curvature of 2.438 cm-1 and the highest thermal efficiency of 13degC/mW. Experimental results showing the responses of the sensor array to different combustible gases are also illustrated in this paper. Comparison of power consumption with other designs reported in the literature illustrates the effectiveness of the proposed process.
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paper_title: Use of Compatible Polymer Blends To Fabricate Arrays of Carbon Black−Polymer Composite Vapor Detectors

paper_content:

Compatible blends of poly(vinyl acetate) and poly(methyl methacrylate) have been used to produce a series of electrically conducting carbon black composites whose resistance is sensitive to the nature and concentration of an analyte in the vapor phase. The dc electrical resistance response of the composites was found to be a nonlinear function of the mole fraction of poly(vinyl acetate) in the blend. These compatible blend composite detectors provided additional analyte discrimination information relative to a reference detector array that only contained composites formed using the pure polymer phases. The added discrimination power provided by the compatible blend detectors, and thus the added diversity of the enhanced detector array, was quantified through use of a statistical metric to assess the performance of detector arrays in various vapor classification tasks.
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paper_title: A bio-inspired two-layer multiple-walled carbon nanotube-polymer composite sensor array and a bio-inspired fast-adaptive readout circuit for a portable electronic nose.

paper_content:

We report a fully integrated, portable, battery-operated electronic nose system comprising a bio-inspired two-layer multiple-walled carbon nanotube (MWNT)-polymer composite sensor array, a bio-inspired fast-adaptive readout circuit, and a microprocessor embedded with a pattern recognition algorithm. The two-layer MWNT-polymer composite sensor is simple to operate, and the membrane quality can be easily controlled. These two-layer membranes have improved sensitivity and stability. The fast-adaptive readout circuit responds to the sensor response, while tuning out the long-term constant background humidity, temperature, and odors. This portable electronic nose system successfully classified four complex alcohol samples 40 times for each sample; these samples were sake, sorghum liquor, medical liquor, and whisky.
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paper_title: Gas Sensors Based on Conducting Polymers

paper_content:

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.
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paper_title: Hydroxyapatite/polymer composite flame-sprayed coatings for orthopedic applications.

paper_content:

The complex biological and mechanical requirements for implant materials in the human body generally cannot be furnished by one single material. In the present study, hydroxyapatite/polymer composite coatings with different contents of hydroxyapatite were produced using a flame spray system. This processing route is intended to obtain a coating with an optimal combination of biological and mechanical properties of these two materials for skeletal implants. The composite coatings were produced from a mechanical blend of hydroxyapatite and ethylene methacrylic acid copolymer powders, which were delivered from a fluidized bed powder feeder. Characterization of the coating surface morphology, polished coating cross-sections, and fracture surface morphology was conducted by scanning electron microscopy. The dissolution behavior of the coatings was evaluated with a calcium-specific ion meter. The stress-strain behavior was investigated by tensile testing. The biological and mechanical properties were found to b...
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paper_title: Microheater-integrated single gas sensor array chip fabricated on flexible polyimide substrate

paper_content:

Abstract A microheater-integrated sensor substrate for the single 16-channel sensor array chip was prepared from a polyimide film by modifying the fabrication processes used in the flexible printed circuit technology. Conductive copper layers were patterned to form interdigitated detection electrodes and a resistive heating line at front and backsides, respectively. The microheater was found to have the power consumption of 1.35 mW mm −2 at an operation temperature of 40 °C and was possible to act as a thermometer, simultaneously, possessing the temperature coefficient of resistance of 37 × 10 −4 °C −1 . Vapor-sensing materials were deposited on the detection electrodes by casting of carbon black–polymer composite solutions. Their ethanol-sensing characteristics have been investigated carefully as a function of the analyte concentration and the operation temperature. The response magnitude linearly intensified with increasing the ethanol concentration in the wide range of 60–8000 ppm in air and generally decreased as the operation temperature goes from 22 to 60 °C. This temperature dependence could be explained with the variation in analyte solubility induced by the thermodynamic enthalpy change during the sensing process. By using the sensor array chip and the principal component analysis, classification was successfully made among the three different volatile organic compounds of ethanol, toluene and benzene.
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paper_title: Quantitative study of the resolving power of arrays of carbon black-polymer composites in various vapor-sensing tasks.

paper_content:

A statistical metric, based on the magnitude and standard deviations along linear projections of clustered array response data, was utilized to facilitate an evaluation of the performance of detector arrays in various vapor classification tasks. This approach allowed quantification of the ability of a 14-element array of carbon black-insulating polymer composite chemiresistors to distinguish between members of a set of 19 solvent vapors, some of which vary widely in chemical properties (e.g., methanol and benzene) and others of which are very similar (e.g., n-pentane and n-heptane). The data also facilitated evaluation of questions such as the optimal number of detectors required for a specific task, whether improved performance is obtained by increasing the number of detectors in a detector array, and how to assess statistically the diversity of a collection of detectors in order to understand more fully which properties are underrepresented in a particular set of array elements. In addition, the resolving power of arrays of carbon black-polymer composites was compared to the resolving power of specific collections of bulk conducting organic polymer or tin oxide detector arrays in a common set of vapor classification tasks.
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paper_title: An electronic nose employing dual-channel odour separation columns with large chemosensor arrays for advanced odour discrimination

paper_content:

Here we report on an improved concept for electronic noses (e-noses) that combines three large chemosensor arrays (300 resistive elements per array) with two micro-packages, each containing a column inspired by our study of the human olfactory mucosa and nasal cavity. In this novel system, a sample odour passes over the first chemoresistive array giving "spatial" response data, equivalent to a traditional sensor-based e-nose. The odour is then divided evenly and passes through two further micro-packages (and thus columns) simultaneously. As the odour pulse travels along these columns chemical components within it are selectively delayed, thus the second and third array, placed after the micro-packages, provide both temporal retentive and spatial information. This combination of a front-end sensor array with back-end second and third arrays, coupled with appropriate pattern analysis algorithms, is shown to enhance significantly the system's ability to discriminate between complex odours. The columns were coated with non-polar and polar compounds to maximise the discrimination ability of the system. We believe that this combination of an initial sensor array, creating spatial data with the spatio-temporal data from the second array significantly enhances the ability of e-noses to discriminate complex odours.
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paper_title: Controlling percolation in field-structured particle composites: Observations of giant thermoresistance, piezoresistance, and chemiresistance

paper_content:

Composites of conductive particles in an insulating phase are conductive if the particle volume fraction exceeds the percolation threshold. Composites prepared slightly above the percolation threshold have a conductivity that is sensitive to small volume changes, and thus have potential as temperature, pressure, or chemical sensors. In practice it is difficult to prepare composites close to the percolation threshold, and the critical current-carrying path gives a rather low sample conductivity. We find that magnetic-field-structured composites, consisting of gold-coated magnetic particle chains in a polymeric resin, can be reproducibly brought to the percolation threshold, regardless of particle concentration. The low-dimensionality conducting chains form a dense population of critical current paths with extreme sensitivity to composite volume changes. These field-structured composites thus exhibit giant thermoresistance, piezoresistance, and chemiresistance, and should be useful as sensor materials.
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paper_title: Chemical sensors for portable, handheld field instruments

paper_content:

A review of three commonly used classes of chemical sensor technologies as applicable to implementation in portable, handheld field instruments is presented. Solid-state gas and chemical sensors have long been heralded as the solution to a wide variety of portable chemical sensing system applications. However, advances in optical sensing technology have reduced the size of supporting infrastructure to be competitive with their solid-state counterparts. Optical, solid-state, and hybrid arrays of sensors have application for portable instruments, but issues of insufficient selectivity and sensitivity continue to hamper the widespread introduction of these miniaturized sensors for solving chemical sensing problems in environments outside the laboratory. In this article, we evaluate three of the major classes of compact chemical sensors for portable applications: (solid-state) chemiresistors, (solid-state) CHEMFETs, and (optical) surface plasmon resonance sensors (SPR). These sensors are evaluated and reviewed, according to the current state of research, in terms of their ability to operate at low-power, small-size, and relatively low-cost in environments, with numerous interferents and variable ambient conditions.
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paper_title: Polymers in sensor applications

paper_content:

Abstract Because their chemical and physical properties may be tailored over a wide range of characteristics, the use of polymers is finding a permanent place in sophisticated electronic measuring devices such as sensors. During the last 5 years, polymers have gained tremendous recognition in the field of artificial sensor in the goal of mimicking natural sense organs. Better selectivity and rapid measurements have been achieved by replacing classical sensor materials with polymers involving nano technology and exploiting either the intrinsic or extrinsic functions of polymers. Semiconductors, semiconducting metal oxides, solid electrolytes, ionic membranes, and organic semiconductors have been the classical materials for sensor devices. The developing role of polymers as gas sensors, pH sensors, ion-selective sensors, humidity sensors, biosensor devices, etc., are reviewed and discussed in this paper. Both intrinsically conducting polymers and non-conducting polymers are used in sensor devices. Polymers used in sensor devices either participate in sensing mechanisms or immobilize the component responsible for sensing the analyte. Finally, current trends in sensor research and also challenges in future sensor research are discussed.
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paper_title: Studies of the vapor-induced sensitivity of hybrid composites fabricated by filling polystyrene with carbon black and carbon nanofibers

paper_content:

Abstract A conductive composite with good gas sensitivity was fabricated by filling polystyrene (PS) with hybrid fillers composed of vapor grown carbon nanofiber (VGCNF) and carbon black (CB) introduced by solution mixing. The composite’s electrical and gas sensitive properties were tested. The combined effect of the VGCNF and CB enormously ameliorated the conductivity of the hybrid composites due to the formation of special conductive pathways in the matrix. The composite obtained showed good gas sensitivity in many organic vapors. The sensitivity was affected by the total amount and the ratio of VGCNF to CB in the matrix, and also by the thickness of the composite’s film. The gas sensitivity, upon exposure to vapors, of the composites containing the hybrid fillers is greater and more stable than that of the composites filled only with CB in vapors. These hybrid composites are very promising gas sensing materials and they can be used to make sensors to detect and discriminate many organic vapors.
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paper_title: Integrated and microheater embedded gas sensor array based on the polymer composites dispensed in micromachined wells

paper_content:

Abstract This paper reports a new fabrication method and a performance of miniaturized and temperature-controllable gas sensor array constructed on 5 in. double side polished (1 0 0) silicon wafer. The films of polymer-carbon black composite were used as gas sensors. Both silicon process and bulk micromachining technology were employed to fabricate sensor array equipped with an interdigitated electrode pair, microheater, and micromachined well of an area of 2 mm ×2 mm. During dispensing a polymer composite–solvent solution on the electrode, micromachined well helped the sensor film be placed in a constrained area and be formed reproducibly from a constant volume of the polymer composite–solvent solution. The dimension of a sensor array chip consisting of 16 separate sensors is 30 mm ×14 mm. The sensors of polymer-carbon black composite responded diversely when they were dispensed in micromachined wells and exposed to various chemical vapors. Principal component analysis (PCA) clearly demonstrated that the gas sensor array could identify various chemical vapors. Pt microheater consumed 7 mW to heat sensor film at the operating temperature of 40 °C, and temperature reached a steady maximum value promptly because of its small heat capacity and effective thermal isolation. The electrical resistance of polymer composite sensor and the partition coefficients for sensor–vapor interactions showed to be considerably affected by the substrate temperature.
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paper_title: Effect of Hygroscopicity of Insulating Unit of Polymer Composites on Their Response to Relative Humidity

paper_content:

The effect of hygroscopicity of the insulating unit of polymer composites on their response to relative humidity has been investigated. The composites examined were the poly(o-aminophenol) (PoAP) composites with poly(vinyl pyrrolidone) (PVP), poly(acrylic acid) (PAA), poly(ethylene oxide) (PEO), and poly(methyl methacrylate) (PMMA) in which the hygroscopicity of these insulating polymers decreases in the sequence PAA>PVP>PEO>PMMA. The electrical conductivity of the PoAP/PVP composite was proportional to relative humidity covering more than four orders of magnitude. This result is explained on the basis of salt-base transition of conducting polymer in the composite which on reflection depends on the presence of weakly and strongly bound water. The PoAP composite with hydrophilic PAA holds a large amount of strongly bound water, and as a consequence PoAP is completely transformed to the salt form at humidity higher than 70%, resulting in the approach to a constant conductivity at the high level of conduction. On the other hand, the nonlinear dependence of the conductivity upon the change in humidity was observed for the PoAP/PEO and PoAP/PMMA composites on the first run of measurement, which was attributed to a lesser amount of strongly bound water in the composite.
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paper_title: Differential Detection of Enantiomeric Gaseous Analytes Using Carbon Black-Chiral Polymer Composite, Chemically Sensitive Resistors

paper_content:

Carbon black−chiral polymer composites were used to provide diagnostic differential resistance responses in the presence of enantiomers of chiral gaseous analytes. Vapors of (+)-2-butanol and (−)-2-butanol, (+)-α-pinene and (−)-α-pinene, (+)-epichlorohydrin and (−)-epichlorohydrin, and methyl (+)-2-chloropropionate and methyl (−)-2-chloropropionate were generated and passed over a chemically sensitive carbon black−poly((R)-3-hydroxybutyrate-co-(R)-3-hydroxyvalerate) (77% butyrate) composite resistor. Each enantiomer of a pair produced a distinct relative differential resistance change on the chiral detector, whereas both enantiomers of a set produced identical signals on achiral carbon black−poly(ethylene-co-vinyl acetate) (82% ethylene) detectors.
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paper_title: RESPONSE OF A POLY(PYRROLE) RESISTIVE MICRO-BRIDGE TO ETHANOL VAPOUR

paper_content:

In this paper the authors describe the behaviour of a silicon micro-bridge fabricated with four conducting polymer resistive elements (two active) in a CMOS-compatible process. The poly(pyrrole) (PPy) bridges were characterised using a precision analogue interface circuit with the constant-current drive and voltage off-set set by a Labview Virtual Instrument. The responses of eight polymer micro-bridges to ethanol vapour were recorded at different temperatures and humidity’s. The output voltage of the bridge circuit followed the classical Langmuir adsorption isotherm in concentration and generally fell with increasing temperature and humidity. A typical bridge sensitivity to ethanol of ca. 30 mV:ppm was observed at room temperature with the linear temperature coefficient of the operation being relatively high at 2.8 10 2 :°C. © 1998 Elsevier Science S.A. All rights
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paper_title: A highly selective chemical gas sensor based on functionalization of multi-walled carbon nanotubes with poly(ethylene glycol)

paper_content:

A novel highly selective gas sensor was fabricated by a chemical modification of multi-walled carbon nanotubes containing carboxyl groups (MWNT-COOH) with poly(ethylene glycol) (PEG) in the presence of N,N-dicyclohexylcarbodiimide (DCC). The resistance responsiveness of the film samples against various organic vapors was investigated. The graft percentage and vibration spectra were characterized by a thermo-gravimetric analyzer (TGA), a Fourier transform infrared spectroscope (FTIR) and a Raman spectrometer. The experimental results showed that the sensors obtained displayed high chemical selectivity, fast response and good reproducibility or long stability to chloroform vapor, which are attributed to the properties of MWNTs grafted PEG polymers. In addition, a hydrogen bond interaction and a swelling theory were utilized to illuminate the responsiveness.
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paper_title: Conducting polymer-based chemical sensor: Characteristics and evaluation of polyaniline composite films

paper_content:

A conducting polymer-based chemical sensor was fabricated by depositing a film containing polyaniline blended with polyethylene oxide and doped with copper chloride onto interdigitated electrodes in a surface cell configuration. It was found to be very sensitive to alcoholic vapours, especially methanol. Its characteristics such as response time (tr), recovery time (td), sensitivity factor (σmax/σ0), etc. have been studied with respect to film composition, chemical vapour dosage, etc. It was found that the sensitivity was maximum and tr minimum at a certain concentration of polyaniline in the film matrix. Although the response was quite fast (tr < 10 s), the recovery was slow and in many cases followed a two-step process. The two components in the recovery were clearly delineated in log-log plots, from which one could be associated with diffusion and the other with selective residual adsorption of the chemical vapour by the conducting polymer moieties. These results have been discussed in the light of the charge transport mechanism and the formation of interfacial barriers between polyaniline domains.
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paper_title: The sensibility of the composites fabricated from polystyrene filling multi-walled carbon nanotubes for mixed vapors

paper_content:

In this paper, the gas sensitivity of the composites fabricated by polystyrene (PS) filling multi-walled carbon nanotubes (MWCNT) was studied in mixed vapors of THF and water. It is very significant to study the resistance change of MWCNT/PS composites in the mixed vapors including water, because the water vapor almost exists anywhere and anytime. In experiments, a strange phenomenon of resistance rise of MWCNT/PS composites is observed when the composites are transferred into the dried air after their resistances reach the maximum in the mixed vapors with water. The different water vapor partial pressures will result in different resistance changes. Therefore, a new mechanism of parallel electrocircuit was brought forward to explain the phenomenon. Some additional experiments verify the reasonability of the mechanism. These findings would help to understand electrical response mechanism of the composites as promising gas-sensing materials.
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paper_title: Large-Scale Chemical Sensor Array Testing Biological Olfaction Concepts

paper_content:

Biological olfactory systems are characterized by a large number of sensors with broad overlapping specificities. The sensitivity and selectivity of the system may be enhanced by the huge redundancy of the olfactory receptor neurons (ORNs). A European project, NEUROCHEM, was devoted to test computational models of the olfactory system of vertebrates and insects. To test these models, a realistic artifact of the olfactory epithelium was developed as a large sensor array mimicking some features of biological ORNs, in particular, the broad and overlapping selectivity to many odors, the combinatorial response, the high level of redundancy, and the different dynamic ranges exhibited by same types of ORNs. The sensor array is composed of 16 384 elements arranged in four smaller arrays of 64 × 64 interdigitated electrodes deposited on a borosilicate substrate. To mimic the redundancy of the biological ORNs, tens of organic conductive polymers were chosen as active sensing materials because of their broad and diverse, but overlapping, specificity to different classes of volatile organic compounds. These sensors were characterized by their responses to varying concentrations of test analytes. The collected sensor data were processed with standard multivariate techniques and the results are reported in this paper.
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paper_title: Carbon nanotube screen-printed electrochemical sensors

paper_content:

The fabrication, and evaluation of carbon-nanotube (CNT)-derived screen-printed (SP) electrochemical sensors based on a CNT ink are reported. The fabricated CNT strips combine the attractive advantages of CNT materials and disposable screen-printed electrodes. Such thick-film CNT sensors have a well-defined appearance, are mechanically stable, and exhibit high electrochemical reactivity.
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paper_title: Grafting of branched polymers onto the surface of vapor grown carbon fiber and their electric properties

paper_content:

The grafting of branched polymers onto vapor grown carbon fiber (VGCF) surface and their electric properties of the composite prepared from the branched polymer-grafted VGCF were investigated. In the first step, the grafting of copolymers having pendant peroxy groups onto VGCF was achieved by the copolymerization of 1-(t-butylperoxy-i-propyl)-3-i-propenylbenzene (BPPB) with vinyl monomers initiated by the system consisting of Mo(CO)6 and trichloroacetyl groups previously introduced onto the surface. In the second step, the postpolymerization of vinyl monomers was initiated by pendant peroxy groups of grafted poly(vinyl monomer-co-BPPB) on the surface to give branched vinyl polymer-grafted VGCF. The dispersibility of VGCF in THF was remarkably improved by grafting of branched polymers onto the surface. The electric resistance of composites prepared from the branched polymer-grafted VGCF suddenly increased when the composites were transferred into solvent vapors and suddenly decreased when they were transferred to dry air.
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paper_title: Current-mode multiplexer for interrogating resistive sensor arrays

paper_content:

A current-mode multiplexer for interrogating resistive sensor arrays has been fabricated in a commercial 2 mu m BiCMOS process under the EUROCHIP initiative. The multiplexer allows a programmable voltage to be forced across the required sensor(s) and the resulting current can be offset by a programmable current source. Control of the device is via a simple serial digital interface. >
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paper_title: Investigation into the vapor sensing behavior and mechanism of a reactive hydroxyl-terminated polybutadiene liquid rubber/carbon black conductive film

paper_content:

An electrically conductive composite of polyurethane pre-polymers was prepared by an intramolecular hydrogen transfer reaction using a reactive hydroxyl-terminated polybutadiene (HTPB) liquid rubber oligopolymer as a reactant, toluene diisocyanate (TDI) as a curing agent and carbon black (CB) as a conductive filler. The influence of the component ratios, types of carbon black particles, curing temperatures and chain-extending agents such as glycerine and triethanolamine on the responsiveness and reversibility of HTPB/TDI/CB composite films was investigated. The structural characterization of the curing materials was conducted on a FT-IR spectrometer. The experimental results indicated that a higher response behavior of HTPB/TDI/CB composite films occurred in non-polar solvent vapors than with polar solvent vapors. The response intensity of the composite films enhanced with increased TDI content and the introduction of chain-extending agents. The responsivity of the films to benzene vapor reached 106 times the original value, but the responsive time and recovery time were prolonged at higher curing temperatures. The response mechanism for the films was elucidated based on the relationship between soft chain segments and hard chain segments.
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paper_title: Portable electronic nose system based on the carbon black–polymer composite sensor array

paper_content:

Abstract A portable electronic nose system based on personal digital apparatus has been developed by using the vapor detection array made of carbon black–polymer composites and the user software, such as data acquisition and pattern recognition. The gas sensor array is possible to have maximum 16 sensing elements integrated on the same silicon substrate. The individual element has a Si bulk-micromachined well which allows the polymer-carbon black composite solution to be placed reproducibly in a specific and well-constrained area during the drop-coating process. Preliminary results show that our portable electronic nose system has successfully classified simple volatile organic compounds, and the complex liquor samples of brandy and whiskey.
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paper_title: Conductive silicone/acetylene black composite film as a chemical vapor sensor

paper_content:

The changes of electrical resistance of the polymer composites on exposure to chemical vapors have been applied for the production of vapor sensors. In this study, to confirm the ability of silicone rubber as chemical vapors sensors, silcone/acetylene black (AB) composite film was prepared by compounding and compression molding. The responses of this elastomer composite film for various organic vapors (polar aprotic, polar protic, and non-polar solvents) were calculated by monitoring the change in the resistance of the composite film when exposed to the organic vapors. The changes of electrical resistance of the composite films are explained on the basis of volume expansion as swelling and polar interaction of various vapors on the composite. The experimental results showed that the behaviors to organic solvent vapors were considerably influenced by the temperature of the solvents and the silicone/AB composite sensor was appropriate for the detection of polar aprotic and non-polar solvents at moderate temperature.
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paper_title: Temperature dependence of conductivity of mixed-phase composite polymer solid electrolytes

paper_content:

Abstract This paper describes the conductivity data obtained for various polymeric electrolytes containing dispersed inorganic and organic fillers. For all of the systems studied an increase in ambient temperature conductivity in comparison with pristine poly(ethylene oxide)-based electrolytes was achieved. The temperature dependence of the conductivity data can be described by the Arrhenius equation below and above the melting point of the polymer crystalline phase. The relationship between the conductivity pre-exponential factor and the activation energy is discussed according to the Meyer-Neldel rule.
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paper_title: Novel molecularly imprinted polymer (MIP) composite membranes via controlled surface and pore functionalizations

paper_content:

Molecular imprinting of polymers, a cross-linking polymerization of functional monomers in presence of a template, yields synthetic materials mimicking the function of biological receptors [1]. The controlled photoinitiated synthesis of thin layers of molecularly imprinted polymers (MIPs) [2] offers many possibilities for development of novel composite materials for affinity technologies (Fig. 1). Molecularly imprinted membranes have a very large, but almost unexplored potential for substance-specific separation, analytics or catalysis [3]. Our aim is the rational design of structure and function of MIP affinity membranes. Our main approach is the controlled functionalization of porous polymeric, especially microfiltration and track-etched membranes to synthesize novel MIP composite membranes (Fig 2).
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paper_title: Morphology and gas-sensitive properties of polymer based composite films

paper_content:

Abstract Morphology and gas sensitive properties of composite films have been studied. Graphite/silicone rubber composite system exhibits better gas-sensitive response properties than those of carbon-black/silicone rubber system. Analysis of composite morphology indicates poor gas-sensitive response properties of carbon-black/silicone rubber system may be due to the presence of carbon gel, because carbon gel would hamper swelling effect of composite. It shows that gas-sensitive properties of composite film are related to their microstructures. Porous structure in composite film would aid diffusion and therefore decrease the response time
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paper_title: Estimation of chemical and physical characteristics of analyte vapors through analysis of the response data of arrays of polymer-carbon black composite vapor detectors

paper_content:

Analysis of the signals produced by a collection of organic polymer-carbon black composite vapor detectors has been performed to assess the ability to estimate various chemical and physical properties of analyte vapors based on information contained in the response patterns of the detector array. A diverse array of composite chemiresistive vapor detectors was exposed to a series of 75 test analytes that had been selected from among five different chemical classes: alcohols, halogenated hydrocarbons, aromatics, unsubstituted hydrocarbons, and esters. The algorithmic task of interest was to use the resulting array of response data to assign one of the five chemical class labels to a test analyte, despite having left that analyte out of the model used to generate the class labels. Algorithms evaluated for this purpose included principal components analysis (PCA) and k-nearest neighbor (k-NN) analysis employing either Euclidean or Mahalanobis distance calculations. Each data cluster that was produced by replicate exposures to an individual analyte was well resolved from all of the other 74 analyte clusters. Furthermore, with the exception of the halide cluster, the analyte response clusters could be robustly grouped into supersets such that each of the five individual chemical classes was well-separated from every other class of analytes in principal component space. Accordingly, using either of the k-nearest neighbor algorithms, in excess of 85% of the non-halide test analyte exposures were correctly assigned to their chemical classes, and halides were only routinely confused with aromatics or esters but not with alcohols or hydrocarbons. The detector array response data also was found to contain semi-quantitative information regarding physicochemical properties of the members of the test analyte series, such as the degree of unsaturation of the carbon chain, the dipole moment, the molecular weight, the number of halogen atoms, and type of aromatic ring in the test analytes. The performance in these types of tasks is relevant for applications of a semi-selective array of vapor detectors in situations when no prior knowledge of the analyte identity is available and when there is no assurance that the test analyte will have been contained in the training set database produced by a compiling a library of responses from the detector array.
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paper_title: Temperature dependence of the conductivity in conducting polymer composites

paper_content:

The temperature dependence of the electrical conductivity of a conducting polymer composite is reported from 77 to 450 K. The relationship between the temperature dependence of the conductivity and the structure of the composite is discussed. The low-temperature electrical resistivity of low-density polyethylene/polypyrrole composite was also investigated and a linear relationship between the resistivity and T--1/4 was found in the liquid-nitrogen temperature range.
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paper_title: Micromachined polymer-based chemical gas sensor array

paper_content:

We have developed a miniature polymer-based chemical gas sensor array on silicon using micromachining technology. The sensors are polymer‐carbon black composite films, which swell reversibly and cause a resistance change upon exposure to a wide variety of gases. We have fabricated two types of devices which can measure this resistance change using a ‘‘well’’ design. These ‘‘wells’’ contain the polymer‐ carbon black‐solvent liquid volume present during deposition and allow the sensor film to be placed reproducibly in a specific and wellconstrained area. After deposition, the solvents evaporate and leave behind a polymer‐carbon black residue crust between metal leads on each side of the ‘‘well’’. Two types of devices, a bulk micromachined sensor and a patterned thick-film sensor, have been fabricated, ranging in size from 500mm 600m mt o 100mm 100 mm. Since the composite film sensors are not specific to any one gas, an array of these sensors, each with a different sensing film, is used to identify gases and gas mixtures through the pattern response of the array. Six polymer‐carbon black composite films were deposited into the sensor array and exposed to three chemical gases at five different concentration levels. The sensors were able to uniquely detect these gas vapors and demonstrated a linear response to concentration levels between 2000 and 10,000 ppm. Results also indicate that a reduction in sensor area by an order of magnitude (from 4.32 to 0.30 mm 2 ) does not reduce sensor response. This design allows the integration of circuits to process the changes in resistance which will permit the realization of a completely integrated miniature gas sensor. # 2001 Published by Elsevier Science B.V.
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paper_title: Integrated Arrays of Gas Sensors Using Conducting Polymers with Molecular Sieves

paper_content:

Abstract The concept of an electronic nose, mimicking the mammalian olfactory organ, is now well established. An essential feature of the man-made system is an array of odour-sensing elements, each of which responds differently to a range of gaseous molecules. The present paper describes efforts to produce an integrated array of such sensors using the conducting polymer polypyrrole as the sensing material, but avoiding a procedure in which at each step every element is treated differently, since this would be expensive and prone to faults. The technique explored here involves aiming to produce on ceramic tiles an array of electrochemically deposited sensors which are initially identical and then to modify their characteristics individually by coating each with layers of arachidic acid applied as Langmuir-Blodgett (L-B) films. These layers are subsequently skeletonized by a salting process, which leaves holes in the films comparable in size to the molecules of gases for whose discrimination the underlying polymer is designed, thus providing a molecular sieve. Testing for the effectiveness of the sieves is carried out by means of a static rig.
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paper_title: Design of a very large chemical sensor system for mimicking biological olfaction

paper_content:

Olfactory receptor neurons in the mammalian olfactory system transduce the odour information into electrical signals and project these into the olfactory bulb. In the biological system the huge redundancy and the massive convergence of the olfactory receptor neurons to the olfactory bulb are thought to enhance the sensitivity and selectivity of the system. To explore this concept a polymeric chemical sensor array consisting of 216 (65,536) sensors comprising tens of different types will be built in the frame of the FP7 NEUROCHEM project. To interface such a large sensor array, a topological array configuration with n rows and m columns has been adopted in order to reduce the total wiring connections to n + m. A detailed numerical analysis of the electrical crosstalk deriving from such a configuration has been carried out for elucidating advantages and limitations of the scanning algorithm. A prototype of the transducing array has been designed and an electronic scanning system capable of reading the 65,536 sensing elements array has been realized.
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paper_title: The preparation and vapor-induced response of a conductive nanocomposite based on poly(methyl acrylic acid)/expanded graphite by in situ polymerization

paper_content:

A poly(methyl acrylic acid)/expanded graphite (PMAA/EG) conductive nanocomposite was prepared by means of in situ intercalation polymerization using expanded graphite (EG) as conductive fillers and acrylic acid (MAA) as a monomer. The electrical resistance response of the model material was investigated upon exposure to several solvent vapors. The crystalline, morphology and functional group changes on the graphite surface were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT-IR). The experimental results showed that the electrical resistance increases as the model material is exposed to such solvent vapors as tetrahydrofuran (THF), N,N-dimethylformamide (DMF), chloroform and acetone. In particular, PMAA/EG intercalation composite film displays an optimal responsiveness to chloroform vapor, exhibiting a selective positive vapor coefficient effect (PVC). Expanded graphite with more polar groups, micropores and large basal spacing is in favor of the diffusion and absorption in organic solvent vapors. Meanwhile graphite nanosheets with a large aspect ratio (ratio of diameter to thickness) are more propitious to the formation of PMAA/EG composite conductive networks. The existence of an ionic bond between the graphite and the chloroform molecules, and a hydrogen bond between the PMAA and the chloroform molecules as well as the charge repulsion interaction are all responsible for improving the responsiveness of the PMAA/EG intercalation composite film to chloroform vapor.
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paper_title: Conducting polymers in chemical sensors and arrays.

paper_content:

The review covers main applications of conducting polymers in chemical sensors and biosensors. The first part is focused on intrinsic and induced receptor properties of conducting polymers, such as pH sensitivity, sensitivity to inorganic ions and organic molecules as well as sensitivity to gases. Induced receptor properties can be also formed by molecularly imprinted polymerization or by immobilization of biological receptors. Immobilization strategies are reviewed in the second part. The third part is focused on applications of conducting polymers as transducers and includes usual optical (fluorescence, SPR, etc.) and electrical (conductometric, amperometric, potentiometric, etc.) transducing techniques as well as organic chemosensitive semiconductor devices. An assembly of stable sensing structures requires strong binding of conducting polymers to solid supports. These aspects are discussed in the next part. Finally, an application of combinatorial synthesis and high-throughput analysis to the development and optimization of sensing materials is described.
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paper_title: Metal–polymer composite sensors for volatile organic compounds: Part 1. Flow-through chemi-resistors

paper_content:

Abstract A new type of chemi-resistor based on a novel metal–polymer composite is described. The composite contains nickel particles with sharp nano-scale surface features, which are intimately coated by the polymer matrix so that they do not come into direct physical contact. No conductive chains of filler particles are formed even at loadings above the percolation threshold and the composite is intrinsically insulating. However, when subjected to compression the composite becomes conductive, with sample resistance falling from ≥10 12 Ω to R / R 0 ≥ 10 7 , are observed when saturated vapours are passed through the chemi-resistor. Rapid response allows real time sensing of VOCs and the initial state is recovered in a few seconds by purging with an inert gas stream. The variation in response as a function of VOC concentration is determined.
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paper_title: The effect of aggregation on the electrical conductivity of spin-coated polymer/carbon nanotube composite films.

paper_content:

This paper considers the feasibility of replacing indium tin oxide (ITO) with spin-coated, polymer-based composite films that are filled with multiwalled carbon nanotubes (MWNTs). The coating mixture consists of a solvent with low volatility, a dissolved thermoplastic polymer, and MWNTs. The high aspect ratio of MWNTs and their good electrical conductivity enable electrical percolation at very low concentrations, so that films can be prepared that conduct electricity while retaining good optical transparency. Although the MWNTs are driven to aggregate by Van der Waals interactions, the high viscosity of the polymer/solvent solution enables the preparation of metastable, homogeneous dispersions. However, exposing the mixtures to shear leads to aggregation, the magnitude of which depends on the duration of the shear. This effect could be observed directly in spin-coated films using both optical microscopy and conductivity measurements, with aggregation causing a drop in conductivity at high nanotube loading, and more complex non-monotonic behavior at concentrations approaching the percolation threshold.
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paper_title: A chemically diverse, conducting polymer-based "electronic noise"

paper_content:

We describe a method for generating a variety of chemically diverse, broadly responsive, low power vapor sensors. A key to our ability to fabricate chemically diverse sensing elements is the preparation of processable, air stable films of electrically conducting organic polymers. An array of such sensing elements produces a chemically reversible, diagnostic pattern of electrical resistance changes upon exposure to different odorants. Such conducting polymer elements are simply prepared and are readily modified chemically to respond to a broad range of analytes. In addition, these sensors yield a fairly rapid, low power, dc electrical signal in response to the vapor of interest, and their signals are readily integrated with software or hardware-based neural networks for purposes of analyte identification. Principle component analysis has demonstrated that such sensors can identify and quantify different airborne organic solvents, and can yield information on the components of gas mixtures.
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paper_title: Polymer/carbon nanotube composite patterns via laser induced forward transfer

paper_content:

Direct and high spatial resolution printing of polymer/carbon nanotube (CNT) composite layers has been demonstrated by means of laser induced forward transfer (LIFT). Laser irradiation of composite target materials, such as poly(acrylic acid)/CNT and polyvinylpyrrolidone/CNT, enabled dry deposition of well resolved composite pixels onto glass substrates. The dispersion of the CNT into the deposited composite pixels was investigated by transmission electron microscopy. The LIFT technique was also employed for the accurate deposition of polymer/CNT composite pixels onto aluminum microelectrodes for the fabrication of chemical sensors based on polymer/CNT compounds.
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paper_title: Trends in odor intensity for human and electronic noses: Relative roles of odorant vapor pressure vs. molecularly specific odorant binding

paper_content:

Response data were collected for a carbon black-polymer composite electronic nose array during exposure to homologous series of alkanes and alcohols. The mean response intensity of the electronic nose detectors and the response intensity of the most strongly driven set of electronic nose detectors were essentially constant for members of a chemically homologous odorant series when the concentration of each odorant in the gas phase was maintained at a constant fraction of the odorant’s vapor pressure. A similar trend is observed in human odor detection threshold values for these same homologous series of odorants. Because the thermodynamic activity of an odorant at equilibrium in a sorbent phase is equal to the partial pressure of the odorant in the gas phase divided by the vapor pressure of the odorant and because the activity coefficients are similar within these homologous series of odorants for sorption of the vapors into specific polymer films, the data imply that the trends in detector response can be understood based on the thermodynamic tendency to establish a relatively constant concentration of sorbed odorant into each of the polymeric films of the electronic nose at a constant fraction of the odorant’s vapor pressure. Similarly, the data are consistent with the hypothesis that the odor detection thresholds observed in human psychophysical experiments for the odorants studied herein are driven predominantly by the similarity in odorant concentrations sorbed into the olfactory epithelium at a constant fraction of the odorant’s vapor pressure.
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paper_title: Electrical response and adsorption performance of novel composites from polystyrene filled with carbon aerogel in organic vapors

paper_content:

As a new nano-sized carbon material, carbon aerogels (CA) with specific properties have been applied in many fields. In this paper, new conductive polymer composites fabricated by polystyrene (PS) filled with carbon aerogels were reported. Their electrical property, gas responsivity and adsorption behaviors in organic vapors were studied. The experimental results showed that carbon aerogels were well qualified for the candidates to make gas sensing conductive polymer composites. The resistance responses were affected not only by the content of carbon aerogels in the matrix, but by the adsorption phenomena of vapors on the composites and the fillers. Compared with carbon black/polystyrene (CB/PS) composites, the carbon aerogel/polystyrene (CA/PS) composites showed better gas responsivity. This is attributed mainly to the much more CA capacity of CA to organic vapors than CB due to the specific structure of CA.
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paper_title: CMOS Interfacing for Integrated Gas Sensors: A Review

paper_content:

Modern gas sensor technology is becoming an important part of our lives. It has been applied within the home (monitoring CO levels from boilers), the workplace (e.g., checking levels of toxic gases) to healthcare (monitoring gases in hospitals). However, historically the high price of gas sensors has limited market penetration to niche applications, such as safety in mines or petrochemical plants. The high price may be attributed to several different components: (1) cost of a predominantly manual manufacturing process; (2) need for interface circuitry in the form of discrete components on a PCB; and (3) fireproof packaging, making the cost of gas detection instruments typically many hundreds of dollars. Consequently, there has been a considerable effort over the past 20 years, towards the goal of low-cost ($1-$5) gas sensors, employing modern microelectronics technology to manufacture both the sensing element and the signal conditioning circuitry on a single silicon chip. In this paper, we review the emerging field of CMOS gas sensors and focus upon the integration of two main gas-sensing principles, namely, resistive and electrochemical and associated circuitry by CMOS technology. We believe that the combination of CMOS technology with more recent MEMS processing is now mature enough to deliver the exacting demands required to make low-power, low-cost smart gas sensors in high volume and this should result in a new generation of CMOS gas sensors. These new integrated, mass-produced gas sensors could open up mass markets and affect our everyday lives through application in cars, cell phones, watches, etc.
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paper_title: TOWARDS AN INTEGRATED ELECTRONIC NOSE USING CONDUCTING POLYMER SENSORS

paper_content:

Abstract This paper describes progress that has been made towards realizing an artificial nose based on arrays of conducting polymers. Electrically conducting organic polymers based on heterocyclic molecules display reversible changes in conductivity when exposed to polar volatile chemicals. In the sensor described, the polymers are interrogated for resistance changes by means of an application-specific integrated circuit (ASIC) realized in BiCMOS technology. The ASIC and the polymer array are housed on a single thick-film ceramic substrate.
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paper_title: CMOS Baseline Tracking and Cancellation Instrumentation for Nanoparticle-Coated Chemiresistors

paper_content:

Chemiresistor (CR) sensors and sensor arrays coated with thiolate-monolayer-protected gold nanoparticle (MPN) interfaces show great promise as detectors in gas-chromatographic microsystems with applications in biomedical and environmental analysis including breath biomarkers of disease. This paper describes a new readout circuit that overcomes the wide range of baseline resistances and drift in baseline values inherent to MPN-coated CRs to achieve a 57 ppm readout resolution. The 0.5-mum CMOS circuit operates at 5 V and provides a response resolution of 74 muV. It can cancel baseline voltages from 0.3 to 4.3 V with an accuracy of 4.2 mV and can track and compensate for drifts up to 30 mV/min. Performance was verified with MPN-coated CRs, where drift was measured and effectively cancelled. The circuit topology and size support an on-chip MPN-coated CR sensor array.
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paper_title: High-precision intelligent interface for a hybrid electronic nose

paper_content:

Abstract At present all commercial electronic noses may be described as monotype, that is, they rely on a single class of sensing material and transduction principle such as conducting polymers or semiconducting oxides chemoresistors. However, in order to meet the emerging needs of the industry, we need to design superior instruments and to this end we have developed a multitype programmable electronic instrument. First, it can handle a wide range of sensor baseline values (e.g., three orders of magnitude of resistance). Secondly, it has a high resolution and stability with, if desired, embedded numerical temperature compensation. Thirdly, sensor signals can be mathematically pre-processed in order to enhance the discrimination power of the electronic nose. The instrument can employ resistive and piezoelectric sensors in arrays, either paired or on integrated devices, to make a multitype or hybrid electronic nose with improved dynamic characteristics.
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paper_title: A new generation of integrated electronic noses

paper_content:

Abstract At Eurosensors VII the authors discussed the feasibility of integrating the UMIST artificial electronic nose. A tentative sensor deposition technique was reported along with the development of an application specific integrated circuit (ASIC) to perform the analogue signal processing. The following paper reports further progress in achieving this goal. The integrated nose employs two ASICs; a current multiplexer and a current amplifier. Current-mode signal processing has been utilized where appropriate. Arrays of conducting organic polymers have been successfully fabricated. Results are presented on the dynamics, reproducibility and matching of the sensing elements.
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paper_title: TOWARDS AN INTEGRATED ELECTRONIC NOSE USING CONDUCTING POLYMER SENSORS

paper_content:

Abstract This paper describes progress that has been made towards realizing an artificial nose based on arrays of conducting polymers. Electrically conducting organic polymers based on heterocyclic molecules display reversible changes in conductivity when exposed to polar volatile chemicals. In the sensor described, the polymers are interrogated for resistance changes by means of an application-specific integrated circuit (ASIC) realized in BiCMOS technology. The ASIC and the polymer array are housed on a single thick-film ceramic substrate.
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paper_title: A Fully-Analog Lock-In Amplifier With Automatic Phase Alignment for Accurate Measurements of ppb Gas Concentrations

paper_content:

A novel fully-analog lock-in amplifier for the accurate measurements of low quantities of gas in sensor applications is here presented. When compared with commercial lock-in and other solutions available in the literature, the proposed system implements an automatic alignment of the relative phase between input and reference signals, both at power-on and for any variation of the input signal phase and amplitude during the working time, so allowing to detect, accurately and in a continuous way, the mean value of the input signal coming from sensors (typically buried into noise). The circuit has been optimized to operate at a specified reference frequency, in particular 77 Hz; this value is suitable for gas sensor applications, since it avoids also any kind of interferences at 50 Hz net frequency and its harmonics. Experimental results have confirmed the correct functionality of the system, also tested for both carbon monoxide (CO) and ethylene glycol detections. With respect to the simpler resistive gas sensor interface, implemented by a resistive voltage divider, the improvement experimentally given by the proposed automatic lock-in amplifier, in terms of resolution, has been of a factor of about 100 for the CO and 230 for the ethylene glycol measurements, so allowing a theoretical gas detection in the order of ppb.
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paper_title: A 160 dB Equivalent Dynamic Range Auto-Scaling Interface for Resistive Gas Sensors Arrays

paper_content:

In this paper an integrated wide-dynamic-range interface circuit for resistive gas-sensors arrays is presented. The proposed device consists of a multiscale transresistance continuous time amplifier followed by a 13-bit incremental A/D converter. The circuit selects automatically the scale to use for each measurement and includes two digital-to-analog converters for the calibration of offset and gain of each scale. The proposed interface circuit achieves a measurement accuracy almost always better than 0.1 % over a sensor resistance range of more than 5 decades [100 Omega-20 MOmega], leading to an equivalent dynamic range of about 160 dB. The chip has been realized with a 0.35 mum CMOS technology and occupies an area of 3.1 mm2 consuming 6 mW from a 3.3 V power supply.
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paper_title: A portable integrated wide-range gas sensing system with smart A/D front-end

paper_content:

In this paper, the development of a portable environmental monitoring system based on a gas sensor array is proposed. The most critical issues related to the microsensor, the interface circuit and the data analysis have been addressed. The complete system is designed to exhibit high precision and large dynamic range. Experimental results on a prototype, obtained by injecting ethanol on a microsensor coated with Pd-doped SnO2, have confirmed the theoretical expectations, demonstrating that the system is suitable for high-precision gas sensing applications.
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paper_title: Towards a Real-Time Transduction and Classification of Chemoresistive Sensor Array Signals

paper_content:

Recently, a growing interest in artificial implementations of biological systems has been arising. In particular, several research groups have been working in mimicking the mammalian olfactory system with the so-called electronic noses (e-noses). The e-noses, which are based on a sensor array, a fluid-dynamic system, and a data processing unit, are systems devoted to detecting and analyzing volatiles, where a deep knowledge of the target application is needed. In order to achieve effective results the sampling system, the measurement protocols, the sensor array, and the pattern recognition techniques have to be carefully designed. The increasing complexity of such design poses issues in sensory feature extraction and fusion, drift compensation, and data processing, especially when high efficiency is required for real-time applications. The interconnection and cooperation of several modules devoted to processing different tasks, such as control, data acquisition, data filtering interfaces, feature selection, and pattern analysis, are already mandatory. Moreover, heterogeneous techniques used to implement such tasks may introduce module interconnection and cooperation issues. In this paper, we address the development of a dedicated instrument able to perform real-time transduction, fusion, and processing of chemoresistive sensor array signals. In particular, this instrument realizes a dynamic and efficient management of data processing techniques and automatically controls the measurement protocols and the sampling system. An array of conducting poly (alkoxy-bithiophenes) sensors, the fluid-dynamic system, the electronic section, the framework's base architecture, and the implementation of dedicated application processes are described. The classification task is based on a self-organizing map where models for artificial neurons and connections were derived from the base structures available in the framework core. According to the target application, this instrument is portable and easily tailored, calibrated, and trained. Classification of olive oil headspaces supports its utility in supplying high-efficiency routine for volatile organic compounds detection and analysis
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paper_title: The effects of signal conditioning and quantization upon gas and odour sensing system performance

paper_content:

Abstract The effects of signal conditioning and quantization during data acquisition in multisensor arrays applied to gas and odour sensing is often given little attention. Aspects such as sensor technology and pattern recognition are often considered more important. However, if multisensor system performance is to be optimized, the signal conditioning and data acquisition must complement the sensor technology and pattern recognition techniques. It will be shown that system sensitivity and the sensor information content can be severely restricted by inappropriate signal conditioning. Also, the analogue to digital converter (ADC) is seen to be very important when considering the limitations of a system. The resolution will determine the upper limit of patterns and hence odour fingerprints that can be identified. In considering these limitations, allowances are also be made for the concentration dependence of the sensors upon the measurands and the pattern recognition pre-processing procedures. In a practical situation, the sensor reproducibility is usually the limiting factor when determining the level of overall system performance. This reproducibility is treated as a fractional variation of the ADC dynamic range, effectively reducing the quantization resolution. Estimates are made of the size of the multisensor array required to identify any given number of measurands.
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paper_title: A Programmable Interface Circuit for an Ultralow Power Gas Sensor

paper_content:

Abstract-An electronic system based on a microcontroller architecture, devoted to interfacing a three-terminal, ultralow power (ULP) Metal OXide (MOX) gas sensor is presented. The sensor features a novel three-terminal configuration where the microheater is not galvanically isolated with respect to the MOX sensor. The system provides both control of the operating temperature and management of the acquired data. A Pulse Width Modulation (PWM) signal with variable duty cycle is used to provide power to the heating resistor in order to set the desired operating temperature. The heating resistance value is measured in the range (100-300) Ω with a relative error of less than 1%. The circuit devoted to measuring the gas concentration is based on a logarithmic amplifier which measures the current flowing in the sensing layer of the sensor. The measurand range is 30 nA to 60 mA and the relative error of the measured current is less than 0.6%. The data acquisition system was successfully tested by acquiring data of a three-terminal ULP gas sensor located in an automatically controlled environmental chamber under benzene and NO2 flow.
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paper_title: A 141-dB Dynamic Range CMOS Gas-Sensor Interface Circuit Without Calibration With 16-Bit Digital Output Word

paper_content:

In this paper, we present the design and the characterization of a wide-dynamic-range interface circuit for resistive gas-sensors able to operate without calibration. The circuit is based on resistance-to-frequency conversion, which guarantees low complexity. The state-of-the-art of this measurement method has been improved first by separating the Resistance value Controlled Oscillator circuit (RCO) from the sensing device, thus leading to higher linearity performance, and then by exploiting a novel digital frequency measurement system. Measurement results on a silicon prototype, designed in a 0.35-μm CMOS technology, show that the circuit achieves, without calibration, a precision in resistance measurement of 0.4% over a range of 4 decades and better than 0.8% over 5 decades (dynamic range, DR = 141 dB). Furthermore, after calibration, it reaches a precision of 0.4% for resistance values ranging between 1 kΩ and 1 GΩ, thus leading to a DR of 168 dB. The prototype chip consumes less than 15 mW from a 3.3-V supply.
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paper_title: A New Low-Cost Electronic System to Manage Resistive Sensors for Gas Detection

paper_content:

In this paper, a new electronic system for gas detection is presented. Particular attention is focused on electronic noses that employ several resistive sensors. New resistive sensors may have high value due to new substances (TiO2) or to low-cost fabrication process and, supposing to use these sensors together with traditional ones (SnO2), a novel instrument to manage high-value resistive sensors varying over a wide range, from kilohms to gigohms is required. The proposed hardware approach is a modular architecture which takes advantage from an improved resistance-to-period converter, where sensors are DC powered. Experimental results show a relative standard deviation below 0.01% and a relative displacement to the reference line less than 1% over six decades if commercial resistors are considered. A prototype has been realized to manage up to eight sensors, detect and estimate substance concentrations, and communicate results to the Internet.
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paper_title: Uncalibrated integrable wide-range single-supply portable interface for resistance and parasitic capacitance determination

paper_content:

Abstract In this paper an uncalibrated fully integrable interface for wide-range resistance determination is presented. The proposed circuit, which implements a resistance-to-time conversion, is able to reveal more than six decades of resistance values (from 100 KΩ to more than 100 GΩ), typical of some resistive gas sensors, as well as to determine the sensor parallel capacitive component (in the order of few pF). The proposed front-end has been designed both to work with a single-supply voltage (3.3 V), so it is suitable in low-cost portable applications, and to simplify the integration in a standard CMOS technology together with the digital components needed for the time measurement. Post-layout simulations on the designed integrated solution (in a standard CMOS technology) and experimental results, using a discrete-component prototype, both on passive components and on real sensors (MoW-based metal oxide sensors) have shown high linearity and reduced percentage error with respect to the theoretical expectations.
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paper_title: A New and Fast-Readout Interface for Resistive Chemical Sensors

paper_content:

The main issue concerning metal oxide (MOX) gas sensors is mostly related to the wide range of resistive values that the sensors can show. In addition, some sensors could have baseline resistive values up to tens of gigohms. To avoid the use of expensive picoammeters or the use of circuits adopting scaling factors, different solutions have recently been proposed, exploiting the resistance-to-time conversion (RTC) technique. They show good linearity and are suitable for the integration in a chip together with the elaboration unit, but they may require long measurement time (tens of seconds) if high resistance values need to be estimated. In addition, they may suffer the influence of a sensor parasitic capacitance, in parallel with the resistive component. In this paper, a new method is proposed to reduce the measuring time, keeping the advantages offered by the RTC approach and including a parasitic capacitance estimation feature. Particularly, an effective architecture, based on moving thresholds, has been proposed, simulated, and experimentally tested with commercial resistors (values between 1 M? and 100 G?) and capacitors (values between 1 and 47 pF). Finally, a fast sensor transient, due to a rapid change in the heating power, has been acquired with the proposed instrument and compared with a similar transient analyzed with a classical RTC approach. This test has shown the applicability of the interface for solutions requiring detailed information of the sensor response, such as the characterization of new sensors (e.g., nanowires) or the behavior analysis during nonstandard thermal profiles.
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paper_title: A CMOS integrated low-voltage low-power time-controlled interface for chemical resistive sensors

paper_content:

Abstract In this paper, an innovative integrated interface circuit, suitable for wide range resistive sensors, such as chemical devices for gas sensing, is presented. The key characteristic is the ability to overcome the main limit of the circuits based on the resistance-to-time ( R – T ) conversion, that is the long measuring time occurring in the evaluation of high-value resistances. The proposed solution is based on a tricky oscillating circuit architecture performing a sort of “compression” of the higher part of the resistive range, thus limiting the measuring time. The interface is oriented to the development of a single chip for resistive chemical sensor applications, thus it is designed to be as simple as possible, utilizing only operational amplifiers ( OAs ) and passive components. The proposed front-end is capable to estimate both the sensor resistance over a wide range (five decades) and, through the AC excitation voltage of the sensor, the in-parallel parasitic capacitance, for diagnosis purposes or to provide a more complete characterization of the sensor. Preliminary experimental measurements, conducted through a fabricated discrete component prototype PCB and utilizing commercial sample resistors and capacitors to emulate sensor behaviour, have shown the feasibility of the proposed approach in a wide resistive range. Further experimental results, achieved through the fabricated integrated circuit, developed in 0.35 μm standard CMOS technology, have shown good performance both for resistance and capacitance estimations. The on-chip integrated solution, requiring a silicon area of about 0.9 mm 2 , supplied at 1.8 V and showing a low power consumption (lower than 600 μW), results to be suitable for resistive sensor array configurations and portable applications, as also witnessed by an experimental test with CO gas and a sample commercial sensor.
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paper_title: A CCII-Based Low-Voltage Low-Power Read-Out Circuit for DC-Excited Resistive Gas Sensors

paper_content:

In this paper, we propose a low-voltage (LV) low-power (LP) oscillating circuit suitable for the read-out of DC-excited resistive gas sensors, based on Second Generation Current Conveyors (CCIIs). This low-cost fully integrable front-end is able to evaluate the resistive behavior of gas sensors, without any preliminary calibration, operating a Resistance to Time ( R-T) conversion and exciting the sensor with a DC voltage. Through the use of CCIIs, all the Current-Mode (CM) benefits in LV LP integrated architecture design are achieved. The developed interface, designed at transistor level, is able to operate with a low supply voltage (plusmn0.75 V), showing a low power consumption of about 700 muW, and, hence, it is suitable for portable applications. Both CADENCE simulations on the designed integrated solution and experimental results, achieved using a PCB prototype, have shown a linear characteristic and a good agreement with theoretical expectations, for more than four decades of resistive variation. Experimental measurements, conducted employing low cost commercial components (AD844 as CCII and Figaro TGS 2600 device as resistive gas sensor), have confirmed the good performances of the developed read-out circuit as resistive gas sensor interface.
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paper_title: An Electronic System to Heat MOX Sensors With Synchronized and Programmable Thermal Profiles

paper_content:

Metal oxide (MOX) sensors are widely used in several application fields: environmental monitoring, home automation, food control, and so on. Research activities in this topic are oriented toward new materials and nanotechnologies, thus requiring new instruments for the sensor characterization and management. Often, in order to improve selectivity, sensitivity, stability, the sensor is heated according to purposely designed profiles. The repeatability of the measurement conditions strongly depends on the ability to perform a sensor resistance measurement in a synchronous fashion with respect to the imposed thermal profile. This work proposes an electronic equipment for a complete management of a generic MOX sensor. The system is able to estimate the sensor resistance in a range varying from tens of kilohms up to tens of gigohms, while driving the sensor heater with a thermal profile designed by the user. Thanks to the short readout time (10 ms) and to the synchronism between the heater management and the sensor resistance measurement, the system is suitable for monitoring fast transients and thermal dynamics of the sensors. In addition, an estimation of the sensor parasitic capacitance, modeled in parallel with the resistive part and on the order of few picofarads, is provided for diagnostic purposes. Experimental results conducted on both commercial resistors/capacitors emulating the sensor, and on a real SnO2 nanowire-based sensor for carbon monoxide detection have demonstrated the validity of the proposed approach. Broad topic: 17. Measurement Techniques.
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paper_title: A single-chip integrated interfacing circuit for wide-range resistive gas sensor arrays

paper_content:

Abstract In this work, we present novel experimental results on a single-chip integrated interface for wide-range resistive gas sensors. The proposed circuit has been proved to be able to reveal more than five decades of resistance variation (about 1% of relative error in the range 470 kΩ–50 GΩ) and, at the same time, to estimate the sensor parasitic capacitance (about 0.3 pF of estimation error in the range 0–33 pF). The fabricated integrated circuit has shown good performances in a wide range of environmental temperature (from −20 °C to 80 °C). The suitability for sensor applications has been proved by interfacing a high-value resistance MOX sensor and monitoring both the resistance and the parasitic capacitance values during a fast thermal transient of the sensor. Moreover, the front-end has been utilized, as an example, for the detection of hydrogen by means of a Figaro TGS 2600 sensor. An on/off modulation has been applied during the fluxing of two gas mixtures, constituted by both hydrogen and nitrogen, with a hydrogen concentration of 40 ppm and 80 ppm, respectively. Compared to other solutions presented in the literature, the implementation and fabrication as integrated circuit in a standard CMOS technology allows the whole interface to be considered as a simple and low-cost solution for wide-range resistive sensor arrays.
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paper_title: A CMOS Integrable Oscillator-Based Front End for High-Dynamic-Range Resistive Sensors

paper_content:

A new oscillating circuit is proposed to estimate the resistance and parallel parasitic capacitance of resistive chemical sensors. The circuit is able to reveal the resistance in a wide range (from tens of kiloohms to more than 100 GOmega) due to the adopted resistance-to-time technique. In addition, the parallel capacitance (up to 50 pF) can be estimated. The circuit, which does not need any initial calibration, is very simple and compact and is suitable to be integrated with a standard CMOS technology to obtain a low-cost and low-power device for a sensor array interface. Different kinds of post layout simulations concerning the CMOS integrated implementation have been conducted. Experimental results obtained using a discrete prototype board, both on passive components and on real sensors (metal-oxide sensors), have shown good linearity and reduced percentage error with respect to the theoretical expectations.
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paper_title: Bread baking aromas detection by low-cost electronic nose

paper_content:

In this work we propose a low-cost electronic nose based on a resistance to period converter readout system, suitable to handle a wide range of resistance values (from kΩ up to tens of GΩ) with high accuracy (<1%). An array composed of four metal oxide based gas sensors, with baseline resistance spreading on the above range has been used to validate the system. The electronic nose has been applied to the detection of key aromas peculiar of different stages of the bread baking process has been chosen as target application, revealing the suitability of the proposed electronic nose to distinguish these volatiles in an ordered manner reflecting the different baking step they represent.
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paper_title: An electronic nose employing dual-channel odour separation columns with large chemosensor arrays for advanced odour discrimination

paper_content:

Here we report on an improved concept for electronic noses (e-noses) that combines three large chemosensor arrays (300 resistive elements per array) with two micro-packages, each containing a column inspired by our study of the human olfactory mucosa and nasal cavity. In this novel system, a sample odour passes over the first chemoresistive array giving "spatial" response data, equivalent to a traditional sensor-based e-nose. The odour is then divided evenly and passes through two further micro-packages (and thus columns) simultaneously. As the odour pulse travels along these columns chemical components within it are selectively delayed, thus the second and third array, placed after the micro-packages, provide both temporal retentive and spatial information. This combination of a front-end sensor array with back-end second and third arrays, coupled with appropriate pattern analysis algorithms, is shown to enhance significantly the system's ability to discriminate between complex odours. The columns were coated with non-polar and polar compounds to maximise the discrimination ability of the system. We believe that this combination of an initial sensor array, creating spatial data with the spatio-temporal data from the second array significantly enhances the ability of e-noses to discriminate complex odours.
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paper_title: Integrating Metal-Oxide-Decorated CNT Networks with a CMOS Readout in a Gas Sensor

paper_content:

We have implemented a tin-oxide-decorated carbon nanotube (CNT) network gas sensor system on a single die. We have also demonstrated the deposition of metallic tin on the CNT network, its subsequent oxidation in air, and the improvement of the lifetime of the sensors. The fabricated array of CNT sensors contains 128 sensor cells for added redundancy and increased accuracy. The read-out integrated circuit (ROIC) was combined with coarse and fine time-to-digital converters to extend its resolution in a power-efficient way. The ROIC is fabricated using a 0.35 µm CMOS process, and the whole sensor system consumes 30 mA at 5 V. The sensor system was successfully tested in the detection of ammonia gas at elevated temperatures.
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paper_title: Large-Scale Chemical Sensor Array Testing Biological Olfaction Concepts

paper_content:

Biological olfactory systems are characterized by a large number of sensors with broad overlapping specificities. The sensitivity and selectivity of the system may be enhanced by the huge redundancy of the olfactory receptor neurons (ORNs). A European project, NEUROCHEM, was devoted to test computational models of the olfactory system of vertebrates and insects. To test these models, a realistic artifact of the olfactory epithelium was developed as a large sensor array mimicking some features of biological ORNs, in particular, the broad and overlapping selectivity to many odors, the combinatorial response, the high level of redundancy, and the different dynamic ranges exhibited by same types of ORNs. The sensor array is composed of 16 384 elements arranged in four smaller arrays of 64 × 64 interdigitated electrodes deposited on a borosilicate substrate. To mimic the redundancy of the biological ORNs, tens of organic conductive polymers were chosen as active sensing materials because of their broad and diverse, but overlapping, specificity to different classes of volatile organic compounds. These sensors were characterized by their responses to varying concentrations of test analytes. The collected sensor data were processed with standard multivariate techniques and the results are reported in this paper.
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paper_title: Design of a very large chemical sensor system for mimicking biological olfaction

paper_content:

Olfactory receptor neurons in the mammalian olfactory system transduce the odour information into electrical signals and project these into the olfactory bulb. In the biological system the huge redundancy and the massive convergence of the olfactory receptor neurons to the olfactory bulb are thought to enhance the sensitivity and selectivity of the system. To explore this concept a polymeric chemical sensor array consisting of 216 (65,536) sensors comprising tens of different types will be built in the frame of the FP7 NEUROCHEM project. To interface such a large sensor array, a topological array configuration with n rows and m columns has been adopted in order to reduce the total wiring connections to n + m. A detailed numerical analysis of the electrical crosstalk deriving from such a configuration has been carried out for elucidating advantages and limitations of the scanning algorithm. A prototype of the transducing array has been designed and an electronic scanning system capable of reading the 65,536 sensing elements array has been realized.
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paper_title: A new discrete circuit for readout of resistive sensor arrays

paper_content:

Abstract In this paper, we present a method that simplifies the interconnect complexity of N × M resistive sensor arrays from N × M to N + M . In this method, we propose to use two sets of interconnection lines in row–column fashion with all the sensor elements having one of their ends connected to a row line and other end to a column line. This interconnection overloading results in crosstalk among all the elements. This crosstalk causes the spreading of information over the whole array. The proposed circuit in this method takes care of this effect by minimizing the crosstalk. The circuit makes use of the concept of virtual same potential at the inputs of an operational amplifier in negative feedback to obtain a sufficient isolation among various elements. We theoretically present the suitability of the method for small/moderate sized sensor arrays and experimentally verify the predicted behavior by lock-in-amplifier based measurements on a light dependent resistor (LDR) in a 4 × 4 resistor array. Finally, we present a successful implementation of this method on a 16 × 16 imaging array of LDR.
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paper_title: Microfabrication techniques for chemical/biosensors

paper_content:

Microfabrication processes for chemical and biochemical sensors are reviewed. Standard processing steps originating from semiconductor technology are detailed, and specific micromachining steps to fabricate three-dimensional mechanical structures are described. Fundamental chemical sensor principles are briefly abstracted and corresponding state-of-the-art examples of microfabricated chemical sensors and biosensors are given. The advantages and disadvantages of either fabricating devices in IC fabrication technology with additional microfabrication steps, or of using custom-designed nonstandard microfabrication process flows are debated. Finally, monolithic integrated chemical and biological microsensor systems are presented, which include transducer structures and operation circuitry on a single chip.
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paper_title: Microsensor Integration Into Systems-on-Chip

paper_content:

Sensing systems-on-chip (SSoCs), combining micromachined sensing structures and microelectronic building blocks on a single chip, are reviewed. While single-chip pressure and inertial sensing systems have been commercially available for more than a decade, the recent expansion of SSoC into new application areas, ranging from chemical and biochemical sensing to atomic force microscopy, demonstrates the full potential of this microsensor integration approach. Available fabrication processes for integrated sensing systems are summarized, categorizing them into pre-, intra-, and post-CMOS approaches depending on the way the micromachining module is merged with the integrated circuit (IC) technology. Examples of SSoCs are presented to highlight the different integration options, ranging from cointegration of micromachined sensors with purely analog signal chains to microsystems with cointegrated digital signal processors and digital interfaces.
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paper_title: Chip-Scale Integration of Data-Gathering Microsystems

paper_content:

Integrated microsystems merging embedded computing with sensing and actuation are poised to dramatically expand our ability to gather information from the nonelectronic world. Examples include a microassembled multichip electronic interface to the brain, an integrated electrofluidic gas chromatography system for environmental monitoring, and a wireless intra-arterial microsystem for pressure and flow measurements. In general, such microsystems will consist of a few chips, integrated in generic platforms that are customized for a given application by the sensors selected and by software. This paper illustrates this approach with a 0.15-cm/sup 3/ multisensor microsystem for autonomously sensing and storing environmental and biological data. The microsystem is formed using on-board pressure/temperature/humidity sensors, off-board strain gauges and neural/EMG electrodes, a custom sensor-interface chip, a mixed-signal microcontroller, and a nonvolatile memory. These components allow the acquisition and storage of multidomain data at low power levels (< 50 /spl mu/W reading capacitive sensors at 1 Hz). The system is programmable in gain (0.4-3.2 mV/fF), offset (10b), accuracy (14b), and sampling rate (0.1 Hz-10 kHz) and is integrated in a micromachined silicon platform that implements through-wafer interconnects, solder-based microconnectors, and recessed cavities for chip-stacking. The microsystem is realized in 9.5 mm/spl times/7.6 mm/spl times/2.0 mm (0.15 cm/sup 3/) (< 0.5 cm/sup 3/ with a lithium battery).
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paper_title: A bio-inspired two-layer multiple-walled carbon nanotube-polymer composite sensor array and a bio-inspired fast-adaptive readout circuit for a portable electronic nose.

paper_content:

We report a fully integrated, portable, battery-operated electronic nose system comprising a bio-inspired two-layer multiple-walled carbon nanotube (MWNT)-polymer composite sensor array, a bio-inspired fast-adaptive readout circuit, and a microprocessor embedded with a pattern recognition algorithm. The two-layer MWNT-polymer composite sensor is simple to operate, and the membrane quality can be easily controlled. These two-layer membranes have improved sensitivity and stability. The fast-adaptive readout circuit responds to the sensor response, while tuning out the long-term constant background humidity, temperature, and odors. This portable electronic nose system successfully classified four complex alcohol samples 40 times for each sample; these samples were sake, sorghum liquor, medical liquor, and whisky.
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paper_title: CMOS Baseline Tracking and Cancellation Instrumentation for Nanoparticle-Coated Chemiresistors

paper_content:

Chemiresistor (CR) sensors and sensor arrays coated with thiolate-monolayer-protected gold nanoparticle (MPN) interfaces show great promise as detectors in gas-chromatographic microsystems with applications in biomedical and environmental analysis including breath biomarkers of disease. This paper describes a new readout circuit that overcomes the wide range of baseline resistances and drift in baseline values inherent to MPN-coated CRs to achieve a 57 ppm readout resolution. The 0.5-mum CMOS circuit operates at 5 V and provides a response resolution of 74 muV. It can cancel baseline voltages from 0.3 to 4.3 V with an accuracy of 4.2 mV and can track and compensate for drifts up to 30 mV/min. Performance was verified with MPN-coated CRs, where drift was measured and effectively cancelled. The circuit topology and size support an on-chip MPN-coated CR sensor array.
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paper_title: A Low-Power Electronic Nose Signal-Processing Chip for a Portable Artificial Olfaction System

paper_content:

The bulkiness of current electronic nose (E-Nose) systems severely limits their portability. This study designed and fabricated an E-Nose signal-processing chip by using TSMC 0.18-μ m 1P6M complementary metal-oxide semiconductor technology to overcome the need to connect the device to a personal computer, which has traditionally been a major stumbling block in reducing the size of E-Nose systems. The proposed chip is based on a conductive polymer sensor array chip composed of multiwalled carbon nanotubes. The signal-processing chip comprises an interface circuit, an analog-to-digital converter, a memory module, and a microprocessor embedded with a pattern-recognition algorithm. Experimental results have verified the functionality of the proposed system, in which the E-Nose signal-processing chip successfully classified three odors, carbon tetrachloride (CCl4), chloroform (CHCl3), and 2-Butanone (MEK), demonstrating its potential for portable applications. The power consumption of this signal-processing chip was maintained at a very low 2.81 mW using a 1.8-V power supply, making it highly suitable for integration as an electronic nose system-on-chip.
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paper_title: A wearable Electronic Nose SoC for healthier living

paper_content:

The Electronic nose (E-Nose) system has the potential for personal healthcare applications but is restricted by size and cost. This study reports the world's first E-Nose system-on-chip (SoC), which fully integrates the sensor array and signal processing circuit. The E-Nose SoC has been designed and fabricated using TSMC 0.18µm 1P6M CMOS technology. The sensor array is coated with multiple-walled carbon nanotubes (MWNTs) conducting polymers. The signal processing circuit is composed of interface circuitry, analog-to-digital converter, memory, and microprocessor embedded with a pattern recognition algorithm. The power consumption of the chip was measured at 1.05mW, making it very suitable for a wearable device. The E-Nose SoC has been integrated in a prototype, and successfully recognized eight odors emulating decayed fish, liver damage, careinogen and industrial solvent.
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paper_title: A Digital CMOS Architecture for a Micro-Hotplate Array

paper_content:

A monolithic gas sensor array fabricated in industrial CMOS technology combined with post-CMOS micromachining is presented. The device comprises an array of three metal-oxide-coated micro-hotplates with integrated MOS transistor heaters and the needed driving and signal-conditioning circuitry. Three digital PID controllers enable individual temperature regulation for each hotplate. The operating temperature of the SnO2 metal-oxide sensors may amount up to 350degC. A serial interface and the temperature control units have been implemented digitally. Emphasis was put on designing a modular system with the required analog circuitry reduced to a minimum. With its small overall size of 5.5times4.5 \ mm2, its digital interface and its good hotplate thermal efficiency of 6degC/mW, the system represents a significant development on the way to low-cost mobile gas sensor systems. The limit of detection at constant temperatures has been assessed to be below 1 ppm for CO and approximately 100 ppm for CH4. The mainly digital implementation with a maximum sampling rate of 9.3 kHz for all three sensors offers the advantage to apply a power-saving mode and temperature modulation techniques to enhance the analyte discrimination capability
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paper_title: On-line novelty detection by recursive dynamic principal component analysis and gas sensor arrays under drift conditions

paper_content:

Leakage detection is a common chemical-sensing application. Leakage detection by thresholds on a single sensor signal suffers from important drawbacks when sensors show drift effects or when they are affected by other long-term cross sensitivities. In this paper, we present an adaptive method based on a recursive dynamic principal component analysis (RDPCA) algorithm that models the relationships between the sensors in the array and their past history. In normal conditions, a certain variance distribution characterizes sensor signals, however, in the presence of a new source of variance the PCA decomposition changes drastically. In order to prevent the influence of sensor drift, the model is adaptive, and it is calculated in a recursive manner with minimum computational effort. The behavior of this technique is studied with synthetic and real signals arising by oil vapor leakages in an air compressor. Results clearly demonstrate the efficiency of the proposed method
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paper_title: A real-time data acquisition system for a hand-held electronic nose (H2EN)

paper_content:

This paper describes an approach towards the development of a portable E-nose device based on an array of metal oxide sensors (MOS) devices, for early on-site dry rot detection on building timbers. A dedicated real-time data acquisition system with a programmable voltage generator, self-calibration techniques and custom visual software programs for a desktop PC and a hand-held computer have been designed and constructed for this application. This paper also describes an example of software calibration to correct source errors for this data acquisition system. Experimental results show that this data acquisition system can accurately measure a large range of resistive sensor responses and is suitable for measuring both conducting polymer and MOS sensors. The custom software also allows users to easily capture, analyse and record measurement data. In addition, the constructed framework for a hand-held computer is based on real-time object-oriented methodology to carry out the functions of desktop PC based instrumentation software. This system presents an effective and user-friendly interface for portable applications.
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paper_title: Towards a Wearable Electronic Nose Chip

paper_content:

An electronic nose chip which uses three carbon black polymer sensors as its input is fabricated and tested. Results of longitudinal testing, response to analyte mixtures, temperature dependence, and power dissipation are discussed in the paper. Future work towards a fully integrated wearable electronic nose chip is discussed at the end of the paper.
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paper_title: An Integrated Surface Micromachined Convex Microhotplate Structure for Tin Oxide Gas Sensor Array

paper_content:

This paper describes the fabrication process for a novel convex microhotplate (MHP) structure using surface micromachining technology. The process is used to fabricate an integrated 4times4 tin oxide gas sensor array. Surface micro-machining is selected for its simplified process and CMOS compatibility. However, limited sacrificial layer thickness usually leads to higher power consumption. In this work, a convex MHP structure is developed to increase the thermal efficiency, which is critical for large dimension and low-power gas sensor array integration. Before the structure release process, 700degC-950degC annealing process was carried out on the 190 times190 mum2 MHP with 2.8 mum polysilicon sacrificial layer. It is shown that higher annealing temperature leads to lower tensional stress of the MHP membrane and larger curvature of the released structure, which enables higher thermal efficiency. Among the four annealing temperatures, the 950degC annealed MHP has the largest curvature of 2.438 cm-1 and the highest thermal efficiency of 13degC/mW. Experimental results showing the responses of the sensor array to different combustible gases are also illustrated in this paper. Comparison of power consumption with other designs reported in the literature illustrates the effectiveness of the proposed process.
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paper_title: A CMOS Single-Chip Gas Recognition Circuit for Metal Oxide Gas Sensor Arrays

paper_content:

This paper presents a CMOS single-chip gas recognition circuit, which encodes sensor array outputs into a unique sequence of spikes with the firing delay mapping the strength of the stimulation across the array. The proposed gas recognition circuit examines the generated spike pattern of relative excitations across the population of sensors and looks for a match within a library of 2-D spatio-temporal spike signatures. Each signature is drift insensitive, concentration invariant and is also a unique characteristic of the target gas. This VLSI friendly approach relies on a simple spatio-temporal code matching instead of existing computationally expensive pattern matching statistical techniques. In addition, it relies on a novel sensor calibration technique that does not require control or prior knowledge of the gas concentration. The proposed gas recognition circuit was implemented in a 0.35 μm CMOS process and characterized using an in-house fabricated 4 × 4 tin oxide gas sensor array. Experimental results show a correct detection rate of 94.9% when the gas sensor array is exposed to propane, ethanol and carbon monoxide.
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paper_title: Electronic nose and artificial neural network.

paper_content:

Gas sensor array technology combined with multivariate data processing methods as artificial neural network has been demonstrated to have a promising potential for rapid nondestructive analysis of odour and flavour in foods. It may be applicable in quality control of raw material, food processing or products. This technique cannot completely replace reference methods like the use of sensory panels as the technique requires a frequent calibration against some valid reference method. As with all new techniques there remain some basic problems to be solved concerning sample handling and instrumental performance. The emerging research activity in the development of chemical sensors including hardware and software combined with applied research makes it realistic to expect applications with this technique implemented on-line in the food industry in near future. In particular, promising applications on meat seem to be within the field of spoilage, off-flavour, sensory analysis and fermentation processes.
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paper_title: VLSI Implementation of a Bio-Inspired Olfactory Spiking Neural Network

paper_content:

This paper presents a low-power, neuromorphic spiking neural network (SNN) chip that can be integrated in an electronic nose system to classify odor. The proposed SNN takes advantage of sub-threshold oscillation and onset-latency representation to reduce power consumption and chip area, providing a more distinct output for each odor input. The synaptic weights between the mitral and cortical cells are modified according to an spike-timing-dependent plasticity learning rule. During the experiment, the odor data are sampled by a commercial electronic nose (Cyranose 320) and are normalized before training and testing to ensure that the classification result is only caused by learning. Measurement results show that the circuit only consumed an average power of approximately 3.6 μW with a 1-V power supply to discriminate odor data. The SNN has either a high or low output response for a given input odor, making it easy to determine whether the circuit has made the correct decision. The measurement result of the SNN chip and some well-known algorithms (support vector machine and the K-nearest neighbor program) is compared to demonstrate the classification performance of the proposed SNN chip.The mean testing accuracy is 87.59% for the data used in this paper.
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paper_title: An Analog Multilayer Perceptron Neural Network for a Portable Electronic Nose

paper_content:

This study examines an analog circuit comprising a multilayer perceptron neural network (MLPNN). This study proposes a low-power and small-area analog MLP circuit to implement in an E-nose as a classifier, such that the E-nose would be relatively small, power-efficient, and portable. The analog MLP circuit had only four input neurons, four hidden neurons, and one output neuron. The circuit was designed and fabricated using a 0.18 μm standard CMOS process with a 1.8 V supply. The power consumption was 0.553 mW, and the area was approximately 1.36 × 1.36 mm2. The chip measurements showed that this MLPNN successfully identified the fruit odors of bananas, lemons, and lychees with 91.7% accuracy.
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paper_title: Synthesis and integration of tin oxide nanowires into an electronic nose

paper_content:

Abstract Single crystal nanostructures of semiconducting tin oxides have been fabricated and characterized as sensing materials for implementation in an electronic nose. The nanowires exhibit exceptional crystalline quality and a very high length-to-width ratio, resulting in enhanced sensing capability as well as long-term material stability for prolonged operation. A sensing device based on SnO 2 nanowires has been fabricated and comparatively tested in an array of chemical sensor with conventional thin film sensing device. Preliminary measurements ethanol/water mixtures demonstrate that nanowire-based sensors can be favourably implemented in the electronic nose and that they perform comparably with the conventional thin film layers.
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paper_title: Analog VLSI Circuit Implementation of an Adaptive Neuromorphic Olfaction Chip

paper_content:

In this paper, we present the analog circuit design and implementation of the components of an adaptive neuromorphic olfaction chip. A chemical sensor array employing carbon black composite sensing materials with integrated signal processing circuitry forms the front end of the chip. The sensor signal processing circuitry includes a dc offset cancellation circuit to ameliorate loss of measurement range associated with chemical sensors. Drawing inspiration from biological olfactory systems, the analog circuits used to process signals from the on-chip odor sensors make use of temporal "spiking" signals to act as carriers of odor information. An on-chip spike time dependent learning circuit is integrated to dynamically adapt weights for odor detection and classification. All the component subsystems implemented on chip have been successfully tested in silicon
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paper_title: Application of ANN with extracted parameters from an electronic nose in cigarette brand identification

paper_content:

The Chinese cigarette industry is losing millions of dollars per year due to counterfeit cigarettes. Detecting illegal cigarettes in the field is difficult, but may be possible using portable electronic noses (E-noses). However, the differences between odours from counterfeit and genuine cigarettes are small and detection may prove difficult. In this study we propose a practical approach to increase the performance of E-noses in cigarette brand identification. A portable E-nose was employed to collect and classify aroma signals from different brands of cigarettes. Artificial neural networks (ANNs) were employed and trained with raw data and extracted features from the data collected by the E-nose to identify the cigarettes. This preliminary investigation succeeded in identifying four different types of cigarettes in the laboratory. The identification results obtained from the neural network trained with extracted parameters were better than the ones obtained directly from the E-nose.
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paper_title: Electronic Noses Sniff Success

paper_content:

E-nose technology has quietly advanced during the past two decades. Commercial models equipped with sensor arrays came to market in the mid-1990s, and today they're used to distinguish wines, analyze food flavors, and sort lumber. Benchtop systems are also used in the pharmaceutical, food, cosmetics, and packaging industries, while smaller, portable units are used to monitor air quality. But these noses cost in the range of US $5000 to $100 000. A coming convergence between e-nose technology and advances in printed electronics will finally bring the price down; way down. Within a decade we'll see e-noses that cost tens of dollars and appear in smart packaging for high-end items like pharmaceuticals or as part of intelligent or interactive appliances- picture a refrigerator that knows when milk has gone bad. Prices could easily drop to under a dollar by 2020. The secret? Conducting polymers. Developers of both electronic noses and printed electronics are exploiting these materials, which can be sensitive to the chemicals that make up odors and are also capable of producing electrical signals. E-nose developers are concentrating on honing the sensing properties of conducting polymers, while the printed-electronics people are investigating ways of using these materials to fabricate ultralow-cost electronics. Combining the fruits of these two separate efforts will finally bring e-noses into our supermarkets, homes, and daily life.
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Title: Towards a Chemiresistive Sensor-Integrated Electronic Nose: A Review

Section 1: Introduction
Description 1: This section provides an introduction to artificial olfaction and electronic noses, outlining their history, applications, and importance.

Section 2: Portable Chemiresistive Sensors Based Electronic Nose System
Description 2: This section describes the structure and components of portable electronic nose systems based on chemiresistive sensors, including their design and applications.

Section 3: Chemiresistive Sensors
Description 3: This section provides an overview of chemiresistive sensors, including their types, properties, advantages, and disadvantages.

Section 4: Metal-Oxide Semiconductor Gas Sensor
Description 4: This section discusses the properties, applications, and fabrication of metal-oxide semiconductor gas sensors in electronic noses.

Section 5: Conductive-Polymer Gas Sensor
Description 5: This section covers conductive-polymer gas sensors, their mechanism, advantages, disadvantages, and developments in sensor technology.

Section 6: Interface of the Chemiresistive Sensors
Description 6: This section explains the purpose and design considerations of interfaces for chemiresistive sensors, focusing on sensor signal conversion and processing.

Section 7: ADC-Based Sensor Interface
Description 7: This section describes ADC-based sensor interfaces, their operation, design, and applications in electronic nose systems.

Section 8: PWM-Based Sensor Interface
Description 8: This section discusses PWM-based sensor interfaces, including their principles, advantages, and implementations.

Section 9: Large Amounts of Sensor Interfaces
Description 9: This section details interfaces designed for large sensor arrays in biomimetic olfactory systems and discusses row-column readout structures.

Section 10: Highly Integrated ASIC/SoC for Electronic Nose
Description 10: This section covers the development of ASIC and SoC technologies for integrated electronic nose systems, focusing on sensor front-end design and electronic nose SoCs.

Section 11: Sensing Front End ASIC and Electronic Nose SoC
Description 11: This section presents the integration of sensor arrays with circuits in a single chip and discusses the applications of highly integrated sensor front-end ASICs and SoCs.

Section 12: Very Large Scale Integration of Artificial Neural Networks
Description 12: This section explores the use of artificial neural networks for pattern recognition in electronic noses and discusses the VLSI implementation of these networks.

Section 13: Conclusions
Description 13: This section summarizes the review, highlighting the potential of chemiresistive sensor-integrated electronic noses to become small, fast, and inexpensive devices suitable for daily use.