Showing papers in "IEEE Sensors Journal in 2006"

Magnetic sensors and their applications

Abstract: Magnetic sensors can be classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. Here, we describe and compare most of the common technologies used for magnetic field sensing. These include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors. The usage of these sensors in relation to working with or around Earth's magnetic field is also presented

Optimization of inertial micropower Generators for human walking motion

Abstract: Micropower generators, which have applications in distributed sensing, have previously been classified into architectures and analyzed for sinusoidal driving motions. However, under many practical operating conditions, the driving motion will not be sinusoidal. In this paper, we present a comparison of the simulated performance of optimized configurations of the different architectures using measured acceleration data from walking motion gathered from human subjects. The sensitivity of generator performance to variations in generator parameters is investigated, with a 20% change in generator parameters causing between a 3% and 80% drop in generator power output, depending upon generator architecture and operating condition. Based on the results of this investigation, microgenerator design guidelines are provided. The Coulomb-force parametric generator is the recommended architecture for generators with internal displacement amplitude limits of less than /spl sim/0.5 mm and the velocity-damped resonant generator is the recommended architecture when the internal displacement amplitude can exceed /spl sim/0.5 mm, depending upon the exact operating conditions. Maximum power densities for human powered motion vary between 8.7 and 2100 /spl mu/W/cm/sup 3/, depending upon generator size and the location of the body on which it is mounted.

Recent advancements in the gas-phase MicroChemLab

Abstract: Sandia's hand-held MicroChemLab system uses a micromachined preconcentrator, a gas chromatography channel, and a quartz surface acoustic wave array detector for sensitive/selective detection of gas-phase chemical analytes. Requisite system size, performance, power budget, and time response mandate microfabrication of the key analytical system components. In the fielded system, hybrid integration has been employed, permitting optimization of the individual components. Recent improvements in the hybrid-integrated system, using plastic, metal, or silicon/glass manifolds, is described, as is system performance against semivolatile compounds and toxic industrial chemicals. The design and performance of a new three-dimensional micro-preconcentrator is also introduced. To further reduce system dead volume, eliminate unheated transfer lines, and simplify assembly, there is an effort to monolithically integrate the silicon PC and GC with a suitable silicon-based detector, such as a magnetically-actuated flexural plate wave sensor or a magnetically-actuated pivot plate resonator

Human Tracking With Wireless Distributed Pyroelectric Sensors

Abstract: This paper presents a wireless pyroelectric sensor system, composed of sensing modules (slaves), a synchronization and error rejection module (master), and a data fusion module (host), to perform human tracking. The computation workload distribution among slave, master, and host is investigated. The performances and costs of different signal-processing and target-tracking algorithms are discussed. A prototype system is described containing pyroelectric sensor modules that are able to detect the angular displacement of a moving thermal target. Fresnel lens arrays are used to modulate the sensor field of view. The sensor system has been used to track a single human target

The invisible fray: a critical analysis of the use of reflectometry for fray location

Abstract: Significant international research and development efforts have been devoted to methods and equipment for locating wiring faults, particularly those on aging aircraft. Several reflectometry methods that send high frequency signals down the line and analyze the returned reflections have risen to the forefront of these technologies. While these methods are proving to be accurate for location of "hard" faults (open and short circuits), the location of "soft" faults such as frays and chafes remains elusive. This paper analyzes the impedance of several types of soft faults and their resultant reflectometry returns, which are shown to be smaller than returns from other sources of physical and electrical noise in the system. Through numerical simulations verified by measurement, it is shown that soft faults are virtually impossible to locate using today's reflectometry methods including time domain reflectometry, frequency domain reflectometry, and spread spectrum time domain reflectometry. The methods used in this analysis can be extended to other types of reflectometry as they emerge

Sensing Tilt With MEMS Accelerometers

Abstract: A miniature tilt sensor made of standard microelectromechanical systems accelerometers and with an accuracy of 0.3deg over the full measurement range of pitch and roll is presented. Such sensor performance has been achieved, owing to the application of an original method of determining tilt angles, which is described in this paper. Experimental studies performed on a physical model of the sensor are discussed, and ways on improving the performance of the sensor are briefly introduced

A Programmable 0.18- $\mu\hbox{m}$ CMOS Electrochemical Sensor Microarray for Biomolecular Detection

Abstract: A configurable electrochemical sensor microarray system-on-a-chip fabricated in a standard digital 0.18-mum complementary metal-oxide-semiconductor (CMOS) process is presented. Each pixel within this 5times10 array occupies a 160 mumtimes120 mum area and contains a differential electrochemical transducer with a programmable sensor. The sensor has a digitally configurable topology capable of performing different electroanalytical measurements for a variety of affinity-based biomolecular sensing applications. The main modes of operation for this system are impedance spectroscopy, voltammetry, potentiometry, and field-effect sensing

Fabrication and testing of bulk micromachined silicon carbide piezoresistive pressure sensors for high temperature applications

Abstract: This paper explores the development of high-temperature pressure sensors based on polycrystalline and single-crystalline 3C-SiC piezoresistors and fabricated by bulk micromachining the underlying 100-mm diameter (100) silicon substrate. In one embodiment, phosphorus-doped APCVD polycrystalline 3C-SiC (poly-SiC) was used for the piezoresistors and sensor diaphragm, with LPCVD silicon nitride employed to electrically isolate the piezoresistor from the diaphragm. These piezoresistors fabricated from poly-SiC films deposited at different temperatures and doping levels were characterized, showing -2.1 as the best gauge factor and exhibited a sensitivities up to 20.9-mV/V*psi at room temperature. In a second embodiment, epitaxially-grown unintentionally nitrogen-doped single-crystalline 3C-SiC piezoresistors were fabricated on silicon diaphragms, with thermally grown silicon dioxide employed for the piezoresistor electrical isolation from the diaphragm. The associated 3C-SiC/SiO/sub 2//Si substrate was fabricated by bonding a (100) silicon wafer carrying the 3C-SiC onto a silicon wafer with thermal oxide covering its surface. The 3C-SiC handle wafer was then etched away in KOH. The diaphragm was fabricated by time etching the silicon substrate. The sensors were tested at temperatures up to 400/spl deg/C and exhibited a sensitivity of 177.6-mV/V*psi at room temperature and 63.1-mV/V*psi at 400/spl deg/C. The estimated longitudinal gauge factor of 3C-SiC piezoresistors along the [100] direction was estimated at about -18 at room temperature and -7 at 400/spl deg/C.

Electrical Capacitance Tomography—Sensor Models, Design, Simulations, and Experimental Verification

Abstract: This paper summarizes the theory and principles of electrical capacitance tomography (ECT) with focus on illuminating the design criteria involved in the radial and axial dimensions of different electrodes used in ECT sensors. After addressing the basic principles, the focus shifts to design and modeling of ECT sensors and culminates in experimental verifications. Different aspects of ECT sensor design and some principles of image reconstruction are addressed. The concept of capacitance, which is the property measured, and how this is related to the field quantities are reviewed. In addition, the reasons for the form and location of guard electrodes are also given in a pertinent way based on field theoretical simulations. This perspective is useful for both academia and industry

MEMS-Capacitive Pressure Sensor Fabricated Using Printed-Circuit-Processing Techniques

Abstract: Microelectromechanical systems (MEMS)-based capacitive pressure sensors are typically fabricated using silicon-micromachining techniques. In this paper, a novel liquid-crystal polymer (LCP)-based MEMS-capacitive pressure sensor, fabricated using printed-circuit-processing technique, is reported. The pressure sensor consists of a cylindrical cavity formed by a sandwich of an LCP substrate, an LCP spacer layer with circular holes, and an LCP top layer. The bottom electrode and the top electrode of the capacitive pressure sensor are defined on the top side of the LCP substrate and the bottom side of the top-LCP layer, respectively. An example pressure sensor with a diaphragm radius of 1.6 mm provides a total capacitance change of 0.277 pF for an applied pressure in the range of 0-100 kPa

Micropreconcentrator for Enhanced Trace Detection of Explosives and Chemical Agents

Abstract: The design, fabrication, and testing of a sorbent-coated microfabricated preconcentrator device in complementary metal-oxide-semiconductor is presented. As a sorbent-coated device, the preconcentrator is used to collect, concentrate, and deliver analyte sampled from air for analysis with a detector. The preconcentrator in this paper is based on a perforated flowthrough microhotplate structure that is coated with a sorbent layer to maximize vapor trapping efficiency. The coating sorbs the analytes of interest during the collection phase at ambient temperatures. A thermal desorption cycle is then used to rapidly heat the preconcentrator to 180 degC in 40 ms to release a concentrated wave of analyte. A finite-volume method was used to simulate the temperature distribution on a microhotplate and to model the time to reach the steady-state temperature. The experimental electrical measurements of the device were found to be in good agreement with the predicted values obtained using the finite-volume method. The preconcentrator device was demonstrated by interfacing to the front end of a handheld chemical agent detector and a handheld trace explosives detector. The preliminary results showed signal enhancement for the detection of the nerve agent simulant dimethylmethylphosphonate and the explosive 2,4,6-trinitrotoluene

Ultrasonic Transmission-Mode Tomography Imaging for Liquid/Gas Two-Phase Flow

Abstract: This paper details the development of noninvasive ultrasonic tomography for imaging liquid and gas flow. The transmission-mode approach has been used for sensing the liquid/gas two-phase flow, which is a kind of strongly inhomogeneous medium. Sixteen pairs of ultrasonic sensors have been used. By using low excitation voltage of 20 V, fan-shaped beam ultrasonic transmitters will emit ultrasonic pulses to the receivers. The investigations were based on the transmission and the reception of ultrasonic sensors that were mounted circularly on the surface of the experimental vessel. The algorithms used to reconstruct the concentration profile for two-phase flow using a fan-shaped beam scanning geometry were presented. By using a hybrid-binary reconstruction algorithm, real-time ultrasonic transmission-mode tomography has been developed. Experiments show that performance is acceptable with an image-reconstruction speed of 10 frames/s. The results of the experiments and possible future improvements were also discussed

Design principles for multichannel fringing electric field sensors

Abstract: This paper presents general rules and principles for designing multichannel fringing electric field (FEF) sensors. A detailed analysis on how the design parameters, especially sensor geometry, affect the performance of FEF sensors is provided. Tradeoffs among different design objectives are explained, and qualitative design rules for balancing these tradeoffs are presented. The rules are illustrated with the design examples of two concentric FEF sensors. The effects of shielding electrode width and substrate thickness on sensor performance were evaluated through finite element simulations. In addition, the performance of the two sensors was compared based on the numerical calculations of penetration depth and signal strength. The comparison proves that the addition of shielding electrodes can improve the penetration depth of FEF sensors.

Experimental modal analysis of an aircraft model wing by embedded fiber Bragg grating sensors

Abstract: A critical issue in practical structural health monitoring is related to the capability of proper sensing systems integrated within the host structures to detect, identify, and localize damage generation. To this aim, many techniques have been proposed involving dynamic measurements such as modal analysis, acoustic emission, and ultrasonics. This paper relies on the use of embedded fiber Bragg grating sensors for performing an experimental modal analysis on a wing of an aircraft model. Time domain response of the embedded fiber-optic sensors induced by hammer impacts were acquired and transformed into the frequency domain. Using a classical technique based on the frequency transfer function, the first displacement and strain mode shapes of the wing have been retrieved in terms of natural frequencies and amplitudes. Experimental results confirm the excellent performances of this class of sensing devices to determine the modal behavior within complex structures compared with conventional accelerometer-based detection systems.

Acoustic self-localization in a distributed sensor network

Abstract: The purpose of this paper is to present a technique for determining the coordinate locations of nodes in a distributed sensor network. This technique is based on the time difference of arrival (TDOA) of acoustic signals. In this scheme, several sound sources of known locations transmit while each node in the sensor network records the wave front time-of-arrival. Data from the nodes are transmitted to a central processor and the nonlinear TDOA equations are solved. Computational simulation results are presented in order to quantify the solution behavior and its sensitivity to likely error sources. Results based on experimentally collected data are also presented in order to demonstrate the potential for this approach in solving the self-localization problem.

A Handheld Neutron-Detection Sensor System Utilizing a New Class of Boron Carbide Diode

Abstract: A handheld neutron-detection sensor application is described in this paper. The sensor system utilizes a new class of boron carbide diode that interacts with incoming neutrons. To interface with the boron carbide diode, an integrated front end is designed in a 1.5-mum standard CMOS technology. With the diode and front-end microchip, a handheld neutron-detection system was realized with an embedded microcontroller for real-time processing. The handheld detector operation was then tested with a plutonium-beryllium neutron source. Test and measurement results confirm the validity of the approach and the functionality of the design

Capacitance Sensors for Void-Fraction Measurements and Flow-Pattern Identification in Air–Oil Two-Phase Flow

Abstract: The design methodology of capacitance sensors for void-fraction measurement in adiabatic two-phase flow systems is presented in this paper. The effect of design parameters on the capacitance output has been theoretically and experimentally investigated for two types of sensor configurations: concave and ring types. Experiments were performed using air-oil two-phase flow to determine the signal-to-noise ratio, sensitivity, and time response of the capacitance sensors. The results show that the ring-type sensors are more sensitive to the void-fraction signal than the concave type for the same spatial resolution. The predictions from the theoretical model for the ring-type sensors are in better agreement with the experimental results than for the concave type. The mean value, time trace, power spectral density (PSD), and the probability density function (PDF) of the void-fraction signal from the capacitance sensors are used to objectively identify the flow pattern. The method was validated using high-speed video images of the flow and comparing the results to those from the signal analysis

Ferrite-Piezoelectric Multilayers for Magnetic Field Sensors

Abstract: A magnetic field sensor based on magnetoelectric effects in a ferrite-piezoelectric layered sample is proposed. Such sensors are passive, provide direct conversion of magnetic fields into an electrical signal, and allow measurements of both ac and dc magnetic fields. A multilayer sample of nickel zinc ferrite-lead zirconate titanate has been used to characterize the sensor response to ac and dc fields, field orientations, frequency, and temperature. The sample shows a linear response for dc fields up to a maximum of 1750 Oe. The sensor output is temperature independent over 273-337 K, but is dependent on frequency of the ac excitation field. Operating at electromechanical resonance for the element enhances the sensor sensitivity by an order of magnitude. For ac magnetic field sensors, the output varies linearly with amplitude

Immobilization of cytochrome c oxidase into electrode-supported lipid bilayer membranes for in vitro cytochrome c sensing

Abstract: Blood and tissue biochemical oxidation-reduction (redox) reactions are ubiquitous and are reflective of many important biological processes in the body, ranging from the state of cellular oxygenation to the overall antioxidant status. It is likely that, similar to acid-base balance, the body optimally operates within a narrow redox potential range made possible by various homeostatic mechanisms, and that deviation from this range will occur in tissue damage. A means to monitor the redox potential of blood or tissue would be valuable in both the diagnosis and treatment of diseases or conditions that adversely affect the body's redox potential. The biosensor described herein involves the immobilization of bovine cytochrome c oxidase (CCO) into electrode-supported lipid bilayer membranes. As a first proof of concept, the biosensor was used to potentiometrically monitor the concentration ratio of a redox pair (oxidized and reduced cytochrome c) in an in vitro system. The response of this modified electrode is reproducible and exhibits Nernstian behavior consistent with the four-electron reduction of the CCO. The oxidase-modified electrode can also operate as an amperometric biosensor for the detection of solution-resident ferrocytochrome c at concentrations as low as 0.1 /spl mu/M. Because this biosensor uses an electron sensor native to the body, it may be of future value to explore the biosensor as a point of care test to measure blood redox potential or perhaps as an implantable sensor to measure tissue redox potential in many settings.

Hydrogen gas sensor using Pd nanowires electro-deposited into anodized alumina template

Abstract: This paper demonstrates a new kind of hydrogen sensor using palladium (Pd) nanowires. Hydrogen sensors using Pd metal have usually been utilizing the incremental change in electrical resistance of Pd upon hydrogen incorporation. Unlike the conventional Pd hydrogen sensors, however, the electrical resistance of the present Pd nanowire sensor decreases when hydrogen is incorporated into Pd nanowires. It is considered to be due to swelling of the nanowires as the result of hydrogen incorporation and subsequent narrowing of gaps between the nanowires, even though each nanowire should have had the higher resistance inherently. Because of extraordinarily high surface area of nanowires, the performance of sensing the hydrogen concentration was found to superior by far to the conventional Pd sensors. The response and recovery times are quite fast to be about 0.7 and 20 s, respectively and the sensing range of 0.2 ~ 1% 1% hydrogen concentration is suitable for the hydrogen safety sensors. The sensor introduced in this paper is unique with regard to both the sensing mechanism and performance

Development and analysis of a PCB vector 2-D magnetic field sensor system for electronic compasses

Abstract: A high-sensitivity vector two-dimensional (2-D) magnetic sensor system for low magnetic field measurements has been realized and tested. The system, made in PCB technology, consists of a double-axis Fluxgate magnetic sensor and the readout electronic circuitry, based on second-harmonic detection. The amorphous magnetic materials Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick) were used as the ferromagnetic core of the sensor. By applying a sinusoidal excitation current having a 450-mA peak at 10 kHz with Vitrovac 6025Z, the measured magnetic sensitivity was about 1.25 mV//spl mu/T. This value seems to be adequate for the Earth's magnetic field detection (/spl plusmn/60 /spl mu/T). The full-scale linearity error was about 1.5%. By using the thicker Vitrovac 6025X and a sinusoidal excitation current having a 600-mA peak at 10 kHz, a maximum sensitivity of approximately 1.68 mV//spl mu/T with a linearity error of about 1.55% full scale in the range of /spl plusmn/60 /spl mu/T were measured. Due to the use of commercially available ferromagnetic materials, the vector 2-D magnetic sensor system presented is characterized by a very simple fabrication process, thus allowing low-cost devices to be designed.

The van der Pauw stress sensor

Abstract: Piezoresistive sensors fabricated on (100) and (111) silicon surfaces are capable of measuring from four to all six components of the stress state at a point on the surface of an integrated circuit die. Such resistor-based sensors have been successfully designed and fabricated on these wafer planes and have been used successfully for measurement of die stresses in electronic packages by many research teams. In this paper, classical van der Pauw (VDP) structures, traditionally used for sheet resistance measurement, are shown to provide more than three times the sensitivity of standard resistor sensors. A single four-terminal VDP device replaces two resistor rosette elements and inherently utilizes the high-accuracy four-wire resistance measurement method. Theoretical expressions are developed for the change in resistance of the VDP device as a function of the individual stress components resolved in wafer coordinate systems on both the (100) and (111) silicon surfaces, and it is predicted theoretically that VDP devices will exhibit more than three times higher sensitivity to stress than standard resistor sensors. Design, fabrication, and experimental characterization of VDP and resistor test structures are presented for both silicon surfaces, and numerical simulation is used to help resolve discrepancies between theory and experiment. Sources of experimental error are identified, and the 3.16 times sensitivity enhancement of the VDP device is confirmed.

MEMS Gas-Sensor Array for Monitoring the Perceived Car-Cabin Air Quality

Abstract: Microelectromechanical-system (MEMS) metal-oxide gas sensors have reached a mature stage, which makes mass market applications in the automotive area possible. In contrast to the already established flap-control system, which controls the access of (combustion) gases from outside the vehicle to the car cabin, the system studied here detects odor events created within the car cabin. The events under study have been cigarette smoke, fast-food odor, manure, and bioeffluents (flatulence). As the reference cannot be a "simple analytical measurement," a human test panel for assessing the hedonic impression on a scale from 0 to 5 is used as reference. The technical system is a MEMS metal-oxide-sensor array consisting of three different sensors. The data-evaluation approach used here is combining the human-sensory data and the MEMS sensor data. The task is performed by the combination of two independent algorithms, where one is related to the normalized conductance and the other to signal variance. Using a combined approach has the advantage that "false" events are suppressed. After the algorithm was successfully transferred onto a microcontroller, real-life data were recorded and classified. Several practical examples are given in this paper. The overall gas-sensor system reaches good accordance with the human-sensory impression, which is represented by air quality levels. This enables the design of a demand-controlled ventilation system

Nano Chemical Sensors With Polymer-Coated Carbon Nanotubes

Abstract: A simple sensor platform consisting of an interdigitated electrode (IDE) pattern has been fabricated for sensing gas and organic vapors. Purified single-walled carbon nanotubes (SWNTs) in the form of a network laid on the IDE by solution casting serve as the sensor material. The electrical conductivity of the SWNT network changes reproducibly upon exposure to various gases and vapors. Selectivity to specific gases, for example, chlorine and hydrochloric acid vapor, is demonstrated by coating the SWNTs with polymers such as chlorosulfonated polyethylene and hydroxypropyl cellulose

Tilt sensor with FBG technology and matched FBG demodulating method

Abstract: A tilt measurement structure and signal detection method is proposed based on a self-demodulated fiber-Bragg grating (FBG) sensor, which consists of a couple of matched FBGs and a cantilever-based pendulum clinometer. Compared by the typical matched FBGs demodulating method, of which a sensing FBG and a demodulating filter FBG is placed separately, both matched FBGs of this tilt sensor are attached on the upper and lower surface of only one single pendulum-type cantilever element for simultaneous sensing and demodulating. So the received light power will change due to the split of the two reflected spectrum of FBGs, which is corresponding to the tilt angle. In addition, the cross-sensitivity effect of the FBG-based sensor is automatically solved due to a differential signal process method. Experimental results indicate the feasibility of the proposed idea.

Nonlinear forward problem solution for electrical capacitance tomography using feed-forward neural network

Abstract: A new technique for solving the forward problem in electrical capacitance tomography sensor systems is introduced. The new technique is based on training a feed-forward neural network (NN) to predict capacitance data from permittivity distributions. The capacitance data used in training and testing the NN is obtained from preprocessed and filtered experimental measurements. The new technique has shown better results when compared to the commonly used linear forward projection (LFP) while maintaining fast prediction speed. The new technique has also been integrated into a modified iterative linear back projection (Landweber) reconstruction algorithm. Reconstruction results are found to be in favor of the NN forward solver when compared to the widely used Landweber reconstruction technique with LFP forward solver.

Method for continuous nondisturbing monitoring of blood pressure by magnetoelastic skin curvature sensor and ECG

Abstract: This paper concerns continuous nondisturbing estimation of blood pressure using mechanical plethysmography in connection with standard electrocardiography (ECG). The plethysmography is given by a novel magnetoelastic skin curvature sensor (SC-sensor) applied on the neck over the carotid artery. The sensor consists of a magnetoelastic bilayer partly enclosed by a coil. Bending the bilayer causes large changes of magnetic permeability which can be measured by the coil. The SC-sensor signal and the ECG signal are adaptively processed in order to estimate blood pressure according to a specifically established theoretical model. The model uses estimated vessel radius changes and pulse transit time as parameters. The results show cross correlation coefficients in the range 0.8 up to 0.9 between reference and estimated values of systolic blood pressure, diastolic blood pressure, and systolic/diastolic blood pressure change, whereas the estimation error was below 4 +/- 7 mmHg at rest and increased with the stress level. Limitations of the model applicability are given by a hysteretic behavior of both model parameters due to inert changes in artery stiffness. The SC-sensor and the ECG electrodes cause minimal inconvenience to the patient and offer an approach for a continuous nondisturbing monitoring of blood pressure changes, as being relevant for sleep monitoring or biomechanic feedback

A High-Precision NDIR $\hbox{CO}_{2}$ Gas Sensor for Automotive Applications

Abstract: A new high-precision spectroscopic gas sensor measuring carbon dioxide (CO2) for harsh environmental conditions of automotive applications is presented. The carbon dioxide concentration is the primary parameter for sensing in cabin air quality, as well as an important safety parameter when R744 (carbon dioxide) is used as the refrigerant in the air conditioning system. The automotive environment challenges the potential sensor principles because of the wide temperature range from -40degC to +85degC, the atmospheric pressure from 700 to 1050 mbar, and relative humidity from 0% to 95%. The presented sensor system is based on the nondispersive infrared principle with new features for reaching high precision criteria and for enhancing long-term stability. A second IR source is used for internal recalibration of the primary IR source, redundancy purposes, and software plausibility checks. The CO2 sensor system achieves an accuracy of better than plusmn5.5% over the whole temperature, pressure, and humidity ranges, with a resolution below 15 ppm and a response time shorter than 5 s. The operating time of the sensor system is more than 6000 h over a corresponding lifetime of more than 15 years. Experimental results show outstanding results for the intended automotive applications

A time-based VLSI potentiostat for ion current measurements

Abstract: A time-based CMOS integrated potentiostatic control circuit has been designed and fabricated. The design maintains a constant bias potential between the reference and working electrodes for an amperometric chemical sensor. A technique of converting input currents into time for amperometric measurements is proposed. This technique eliminates current amplifying circuitry, reduces matching problems, and increases dynamic range while saving on area and power consumption. Redox currents ranging from 1 pA to 200 nA can be measured with a maximum nonlinearity of /spl plusmn/0.1% over this range. The design can be used to generate cyclic voltammograms for an electrochemical reaction by sweeping the voltages across a range specified by the user. Analog inputs are processed and digital outputs are generated without requiring a power-hungry A/D converter. A prototype chip has been fabricated in the 0.5-/spl mu/m AMI CMOS process. Experimental results are reported showing the performance of the circuit as a chemical sensor.

Identification of typical wine aromas by means of an electronic nose

Abstract: In the field of electronic noses (e-noses), it is not very usual to find many applications to wine detection. Most of them are related to the discrimination of wines in order to prevent their illegal adulteration and detection of off-odors, but their objective is not the identification of wine aromas. In this paper, an application of an e-nose for the identification of typical aromatic compounds present in white and red wines is shown. The descriptors of these compounds are fruity, floral, herbaceous, vegetative, spicy, smoky, and microbiological, and they are responsible for the usual aromas in wines; concentrations differ from 2-8/spl times/ the threshold concentration humans can smell. Some of the measured aromas are pear, apple, peach, coconut, rose, geranium, cut green grass, mint, vanilla, clove, almond, toast, wood, and butter. Principal component analysis and linear discriminant analysis show that datasets of these groups of compounds are clearly separated, and a comparison among several types of artificial neural networks has been also performed. The results confirm that the system has good performance in the classification of typical red and white wine aromas.