Showing papers in "IEEE Sensors Journal in 2005"
TL;DR: In this paper, the authors examined the parameters that control the accuracy, latency, and signal to noise ratio for SSTDR and sequence time domain reflectometry for aircraft wires carrying typical signals in flight.
Abstract: Spread spectrum time domain reflectometry (SSTDR) and sequence time domain reflectometry have been demonstrated to be effective technologies for locating intermittent faults on aircraft wires carrying typical signals in flight. This paper examines the parameters that control the accuracy, latency, and signal to noise ratio for these methods. Both test methods are shown to be effective for wires carrying ACpower signals, and SSTDR is shown to be particularly effective at testing wires carrying digital signals such as Mil-Std 1553 data. Results are demonstrated for both controlled and uncontrolled impedance cables. The low test signal levels and high noise immunity of these test methods make them well suited to test for intermittent wiring failures such as open circuits, short circuits, and arcs on cables in aircraft in flight.
337 citations
TL;DR: In this article, a principal component analysis-based feature extraction that provides orthogonal information for multiple sensor fusion has been introduced and investigated using the features of multiple projection coefficients, 3-D surface flaws can be measured and reconstructed.
Abstract: This paper proposes the use of multiple sensors in pulsed eddy-current detection for three-dimensional (3-D) subsurface flaw imaging. A normalization technique has been proposed to eliminate the characteristic variation among the Hall devices used in the probe and lift off effects. A principal component analysis-based feature extraction that provides orthogonal information for multiple sensor fusion has been introduced and investigated. Using the features of multiple projection coefficients, 3-D surface flaws can be measured and reconstructed. The experimental tests have illustrated that the proposed method has delivered more defect information than the conventional peak value and time for pulsed eddy-current sensors.
193 citations
TL;DR: A series of laboratory experiments have been performed highlighting the potential of laser-induced breakdown spectroscopy (LIBS) as a versatile sensor for the detection of terrorist threats as discussed by the authors.
Abstract: A series of laboratory experiments have been performed highlighting the potential of laser-induced breakdown spectroscopy (LIBS) as a versatile sensor for the detection of terrorist threats. LIBS has multiple attributes that provide the promise of unprecedented performance for hazardous material detection and identification. These include: 1) real-time analysis, 2) high sensitivity, 3) no sample preparation, and 4) the ability to detect all elements and virtually all hazards, both molecular and biological. We have used LIBS to interrogate a variety of different target samples, including explosives, chemical warfare simulants, biological agent simulants, and landmine casings. We have used the acquired spectra to demonstrate discrimination between different chemical warfare simulants, including those on soil backgrounds. A linear correlation technique permits discrimination between an anthrax surrogate and several other biomaterials such as molds and pollens. We also use broadband LIBS to identify landmine casings versus other plastics and environmental clutter materials. A new man-portable LIBS system developed as a collaborative effort between the U.S. Army Research Laboratory and Ocean Optics, Inc., is described and several other schemes for implementing LIBS sensors for homeland security and force protection are discussed.
185 citations
TL;DR: In this article, a novel approach based on the selective etching along the grating region has been analyzed, leading to high-sensitivity refractive index sensors based on intensity measurements.
Abstract: In this work, highly sensitive refractive index measurements have been experimentally demonstrated by using thinned fiber Bragg grating (FBG) sensors. When the cladding diameter is reduced, significant changes in the effective refractive index occur due to surrounding medium refractive index modifications, leading to Bragg wavelength shifts. Uniformly thinned FBGs have been obtained by using wet chemical etching in hydrofluoric acid solutions. In order to prove sensor sensitivity, experimental tests have been carried out by using glycerine solutions with well-known refractive indices. Obtained results agree well with the numerical analysis carried out by using the three-layer fiber model. If the cladding layer is completely removed, resolutions of /spl ap/10/sup -5/ and /spl ap/10/sup -4/ for the outer refractive index around 1.450 and 1.333, respectively, are possible. Finally, a novel approach based on the selective etching along the grating region has been analyzed, leading to high-sensitivity refractive index sensors based on intensity measurements.
157 citations
TL;DR: In this article, the effect of mechanical thermal noise on a vibrational microelectromechanical system gyroscope, including the angle of random walk, the noise equivalent rotation rate, and the spectral density of the noise component of the rate measurement, was derived.
Abstract: We derive expressions for the effect of mechanical thermal noise on a vibrational microelectromechanical system gyroscope, including the angle of random walk, the noise equivalent rotation rate, and the spectral density of the noise component of the rate measurement. We explicitly calculate and compare the output signal due to rotation and the output due to noise. We avoid several ambiguities in the literature concerning bandwidth and correctly observe a factor of two reduction in noise power due to synchronous demodulation. We use stochastic averaging to obtain an approximate "slow" system that clarifies the effect of thermal noise and shows the effect of frequency mismatch between the drive and sense axes. We compute the noise equivalent rate for both open-loop and force-to-rebalance operation of the gyroscope.
149 citations
TL;DR: In this paper, a bend-sensor consisting of one LPFG induced by a UV laser and two LPFGs induced by high-frequency CO/sub 2/ laser pulses is proposed and demonstrated.
Abstract: A novel long period fiber-grating (LPFG) sensor that can not only measure curvature directly, but also determine every bend-direction within the circular range of 0/spl deg/-360/spl deg/, is proposed and demonstrated in this paper. Such a bend-sensor consists of one LPFG induced by a UV laser and two LPFGs induced by high-frequency CO/sub 2/ laser pulses. The curvature is measured by the UV laser-induced LPFG whose bend-sensitivity is independent of the bend-directions, and the bend-direction is determined by the CO/sub 2/ laser-induced LPFGs whose bend-sensitivities depend strongly on the curved directions. In addition, the unique bend-characteristics of LPFGs induced by high-frequency CO/sub 2/ laser pulses are demonstrated.
142 citations
TL;DR: In this article, a push-pull differential resonant accelerometer with double-ended-tuning-fork (DETF) as the inertial force sensor was designed and tested.
Abstract: We present the design, fabrication, and testing of a push-pull differential resonant accelerometer with double-ended-tuning-fork (DETF) as the inertial force sensor. The accelerometer is fabricated with the silicon-on-insulator microelectromechanical systems (MEMS) technology that bridges surface micromachining and bulk micromachining by integrating the 50-/spl mu/m-thick high-aspect ratio MEMS structure with the standard circuit foundry process. Two DETF resonators serve as the force sensor measuring the acceleration through a frequency shift caused by the inertial force acting as axial loading. Two-stage microleverage mechanisms with an amplification factor of 80 are designed for force amplification to increase the overall sensitivity to 160 Hz/g, which is confirmed by the experimental value of 158 Hz/g. Trans-resistance amplifiers are designed and integrated on the same chip for output signal amplification and processing. The 50-/spl mu/m thickness of the high-aspect ratio MEMS structure has no effect on the amplification factor of the mechanism but contributes to a greater capacitance force; therefore, the resonator can be actuated by a much lower ac voltage comparing to the 2-/spl mu/m-thick DETF resonators. The testing results agree with the designed sensitivity for static acceleration.
138 citations
TL;DR: In this paper, the authors demonstrate the application of terahertz (THz) time-of-flight tomographic imaging to identify the distribution of defects in foam materials.
Abstract: We demonstrate the application of terahertz (THz) time-of-flight tomographic imaging to identify the distribution of defects in foam materials. Based on THz time-domain spectroscopy technology, THz imaging probes targets with picosecond pulses of broad-band radiation in the frequency range from 100 GHz to 3 THz. The reflected THz wave from the target is measured using electrooptic sampling, which provides two-dimensional images with phase and amplitude information, as well as the spectroscopic properties of the object. The depth information is recorded in the THz time-domain waveform. Several reconstruction models are developed for tomographic imaging of defects inside foam. Foam insulation of space shuttle fuel tanks, with prebuilt defects, are investigated with THz tomographic imaging. Most prebuilt defects are pinpointed and models used to identify different kinds of defects are discussed.
138 citations
TL;DR: Preliminary in vitro operational stability tests performed with the microdisc array lactate biosensor demonstrated retention of 80% initial biosensor response after five days of continuous operation in buffer under physiologic conditions of pH and temperature.
Abstract: The design, fabrication, and in-vitro evaluation of an amperometric biochip that is designed for the continuous in vivo monitoring of physiological analytes is described. The 2 /spl times/4 /spl times/0.5 mm biochip contains two platinum working enzyme electrodes that adopt the microdisc array design to minimize diffusional limitations associated with enzyme kinetics. This configuration permits either dual analyte sensing or a differential response analytical methodology during amperometric detection of a single analyte. The working enzyme electrodes are complemented by a large area platinized platinum counter electrode and a silver reference electrode. The biorecognition layer of the working electrodes was fabricated from around 1.0-/spl mu/m-thick composite membrane of principally tetraethylene glycol (TEGDA) cross-linked poly(2-hydroxyethyl methacrylate) that also contained a derivatized polypyrrole component and a biomimetic methacrylate component with pendant phosphorylcholine groups. These two additional components were introduced to provide interference screening and in vivo biocompatibility, respectively. This composite membrane was used to immobilize glucose oxidase and lactate oxidase onto both planar and microdisc array electrode designs, which were then used to assay for in vitro glucose and lactate, respectively. The glucose biosensor exhibited a dynamic linear range of 0.10-13.0 mM glucose with a response time (t/sub 95/) of 50 s. The immobilized glucose oxidase within the hydrogel yielded a K/sub m(app)/ of 35 mM, not significantly different from that for the native, solution-borne enzyme (33 mM). The microdisc array biosensor displayed linearity for assayed lactate up to 90 mM, which represented a 30-fold increase in linear dynamic lactate range compared to the biosensor with the planar electrode configuration. Preliminary in vitro operational stability tests performed with the microdisc array lactate biosensor demonstrated retention of 80% initial biosensor response after five days of continuous operation in buffer under physiologic conditions of pH and temperature.
126 citations
TL;DR: A new control algorithm is described that can track down a gas source within the distance of 2 m in 32 s, even though semiconductor gas sensors with a long recovery time (>60 s) are used.
Abstract: Gas sensors provide an artificial sense of smell for a mobile robot to track an airborne gas/odor plume and locate its source. However, a slow response of gas sensors has been the major factor limiting the development of plume-tracking robots. This paper describes a new control algorithm that breaks the limitation. The basic idea is to detect onsets of gas sensor response and starts of recovery by monitoring the relative change in each sensor output. Fast plume tracking is accomplished by making the robot take appropriate actions immediately when the sensor outputs start changing from one state to another. Growing sensor outputs evoke an increase in the robot speed for further acceleration of plume tracking, whereas insufficient sensor outputs slow down the robot to avoid degrading the search success rate. In contrast to the previous algorithm, based on the absolute sensor output levels, the detection of output change also leads to reliable plume detection, since it is insusceptible to drift in the gas sensor outputs. Experimental results have shown that the robot can track down a gas source within the distance of 2 m in 32 s, even though semiconductor gas sensors with a long recovery time (>60 s) are used.
120 citations
TL;DR: In this paper, a fiber-optic-based humidity sensor was fabricated using a fiber Bragg grating (FBG) coated with a moisture-sensitive polymer, which was used to measure the humidity.
Abstract: A fiber-optic-based humidity sensor has been fabricated using a fiber Bragg grating (FBG) coated with a moisture-sensitive polymer. The sensing concept exploits the inherent characteristics of the FBG and is based on the strain effect induced in the Bragg grating through the swelling of the polymer coating. A direct indication of the humidity level is given by the shift of the Bragg wavelength caused by the expansion of the sensing material. The FBG sensor used in this work has an approximate coating thickness of 33 /spl mu/m and was exposed to different humidity levels at room temperature. The sensitivity of the sensor was estimated to be about 4.5 pm/%RH at a wavelength of 1535 nm, this being obtained through a process of linear regression. The resulting uncertainty in the measurement is /spl plusmn/4%RH and the response time of the sensor and the moisture expansion coefficient of polyimide were obtained from a series of experimental investigations and cross compared with the results of previous work.
TL;DR: In this paper, a resonant cantilever beam is used to detect chemical vapors and gases at trace concentrations using complementary metal-oxide semiconductor (CMOS) technology.
Abstract: The design, fabrication, and testing of a resonant cantilever beam in complementary metal-oxide semiconductor (CMOS) technology is presented in this paper. The resonant cantilever beam is a gas-sensing device capable of monitoring hazardous vapors and gases at trace concentrations. The new design of the cantilever beam described here includes interdigitated fingers for electrostatic actuation and a piezoresistive Wheatstone bridge design to read out the deflection signal. The reference resistors of the Wheatstone bridge are fabricated on auxiliary beams that are immediately adjacent to the actuated device. The whole device is fabricated using a 0.6-/spl mu/m, three-metal, double-poly CMOS process, combined with subsequent micromachining steps. A custom polymer layer is applied to the surface of the microcantilever beam to enhance its sorptivity to a chemical nerve agent. Exposing the sensor with the nerve agent simulant dimethylmethylphosphonate (DMMP), provided a demonstrated detection at a concentration of 20 ppb or 0.1 mg/m/sup 3/. These initial promising results were attained with a relatively simple design, fabricated in standard CMOS, which could offer an inexpensive option for mass production of a miniature chemical detector, which contains on chip electronics integrated to the cantilever beam.
TL;DR: In this article, the authors present a new electrical impedance tomography system for online measurement of two-phase flows with axial velocities up to 10 ms/sup -1/.
Abstract: This paper presents the development of a new electrical impedance tomography system for online measurement of two-phase flows with axial velocities up to 10 ms/sup -1/. The system is designed in a modular fashion and can consist of several data acquisition modules and computing modules. The data acquisition module includes a voltage controlled current source with a direct-current-restoration circuit, an equal-width pulse synthesizer unit and a synchronized digital demodulation unit. A new concept of current switching scheme is developed to enhance the ac coupling speed. The computing module includes a digital signal processor (TMS320C6202/6713) with memory, multichannel buffered serial ports and an IEEE1394 communication interface. Several DSP modules can be pipelined for a series of tasks ranging from measurement control to image reconstruction to flow velocity implementation. The performances have been tested and some trial results are reported. A data acquisition speed of 1164 dual-frames (2.383 million data points) per second has been achieved with a root mean square error less than 0.6% at 80 kHz in static test application. An application in the measurement of vertical oil-in-water pipe flow is reported.
TL;DR: Test results indicate that spread spectrum methods have significant promise for locating intermittent faults on wires as they occur in flight or other modes of operation, such as landing and takeoff, taxiing, and other critical times when possible vibration, etc., may cause intermittent faults.
Abstract: Spread spectrum methods are an important emerging class of sensors that have the potential to locate small, intermittent faults on energized aircraft power circuit wires. Previous work has demonstrated the use of these methods for hard faults (open and short circuits). This paper extends that work to the location of typical intermittent faults that plague aircraft maintainers. Test results on 200-ft-long realistic aircraft wires demonstrate the feasibility of these techniques to locate both wet and dry arcs while the system is powered with 400-Hz 115-V ac power running a variety of aircraft lighting loads. The capability of the system to function with either the aircraft structure or a paired wire as the return path to ground is demonstrated. These results indicate that spread spectrum methods have significant promise for locating intermittent faults on wires as they occur in flight or other modes of operation, such as landing and takeoff, taxiing, and other critical times when possible vibration, etc., may cause intermittent faults.
TL;DR: In this article, an artificial olfactory system can be used as a nondestructive instrument to measure fruit maturity and a good correlation between sensor signals and some fruit quality indicators was also found.
Abstract: The main goal of our study was to see whether an artificial olfactory system can be used as a nondestructive instrument to measure fruit maturity. In order to make an objective comparison, samples measured with our electronic nose prototype were later characterized using fruit quality techniques. The cultivars chosen for the study were peaches, nectarines, apples, and pears. With peaches and nectarines, a PCA analysis on the electronic nose measurements helped to guess optimal harvest dates that were in good agreement with the ones obtained with fruit quality techniques. A good correlation between sensor signals and some fruit quality indicators was also found. With pears, the study addressed the possibility of classifying samples regarding their ripeness state after different cold storage and shelf-life periods. A PCA analysis showed good separation between samples measured after a shelf-life period of seven days and samples with four or less days. Finally, the electronic nose monitored the shelf-life ripening of apples. A good correlation between electronic nose signals and firmness, starch index, and acidity parameters was found. These results prove that electronic noses have the potential of becoming a reliable instrument to assess fruit ripeness.
TL;DR: A biosensor for the detection of pathogenic bacteria was developed for biosecurity applications and incorporates heterobifunctional crosslinkers and immobilized antibodies that detected the change in impedance caused by the presence of bacteria immobilized on interdigitated gold electrodes.
Abstract: A biosensor for the detection of pathogenic bacteria was developed for biosecurity applications. The sensor was fabricated using photolithography and incorporates heterobifunctional crosslinkers and immobilized antibodies. The sensor detected the change in impedance caused by the presence of bacteria immobilized on interdigitated gold electrodes and was fabricated from (100) silicon with a 2-/spl mu/m layer of thermal oxide as an insulating layer. The sensor has a large active area of 9.6 mm/sup 2/ and consists of two interdigital gold electrode arrays each measuring 0.8 /spl times/ 6 mm. Pathogenic Escherichia coli and Salmonella infantis were tested in serially diluted pure culture. Analyte specific antibodies were immobilized to the oxide between the electrodes to create a biological sensing surface. After immersing the biosensor in solution, the impedance across the interdigital electrodes was measured. Bacteria cells present in the sample solution attached to the antibodies and became tethered to the electrode array thereby causing a change in measured impedance. The biosensor was able to discriminate between different cellular concentrations from 10/sup 4/ - 10/sup 7/ CFU/mL (colony-forming units per milliliter) in solution. The sample testing process, including data acquisition, required 5 min. The design, fabrication, and testing of the biosensor is discussed along with the implications of these findings toward further biosensor development.
TL;DR: In this article, a comparative study of noise and resolution is presented with respect to the frequency and the quality factor of the microbalance oscillator for damping media, and it is shown that when working below the maximum quality factor, for similar values, the resolution can be improved by elevating the work frequency.
Abstract: The use of quartz-crystal oscillators as high-sensitivity microbalance sensors is limited by the frequency noise present in the circuit. To characterize the behavior of the sensors, it is not enough to determine their experimental sensitivity, but, rather, it is essential to study the frequency fluctuations in order to establish the sensor resolution. This is fundamental in the case of oscillators for damping media, because the level of noise rises due to the strong decline of the quality factor of the resonator. In this paper, a comparative study of noise and resolution is presented with respect to the frequency and the quality factor. The study has been made using four oscillators designed to be used in quartz-crystal microbalance sensors in damping media. The four circuits have been designed at increasing frequencies in order to improve the sensitivity or frequency change per unit of measurand. Also, the present theoretical resolution limit or best resolution achievable with a microbalance oscillator using an AT resonator is determined, since this does not depend on frequency. However, when operating in liquid, the damping of the resonator makes the resolution diminish due to a worsening of the quality factor. The relationship between the resolution limit and the frequency and characteristics of the liquid medium is determined. The resolution worsens when the density and viscosity of the liquid is increased. However, in this case, an increase in frequency implies a small increase in resolution. Therefore, we find that when working below the maximum quality factor, for similar values, the resolution can be improved by elevating the work frequency.
TL;DR: In this paper, the authors present a cost-effective concurrent test methodology for droplet-based microelectrofluidic systems for real-time polymerase chain reaction application.
Abstract: Recent events have heightened the need for fast, accurate, and reliable biological/chemical sensor systems for critical locations. As droplet-based microelectrofluidic sensor systems become widespread in these safety-critical biomedical applications, reliability emerges as a critical performance parameter. In order to ensure the operational health of such safety-critical systems, they need to be monitored for defects, not only after manufacturing, but also during in-field operation. In this paper, we present a cost-effective concurrent test methodology for droplet-based microelectrofluidic systems. We present a classification of catastrophic and parametric faults in such systems and show how faults can be detected by electrostatically controlling and tracking droplet motion. We then present a fault simulation approach based on tolerance analysis using Monte-Carlo simulation to characterize the impact of parameter variations on system performance. Finally, we present experimental results on a droplet-based microelectrofluidic system for a real-time polymerase chain reaction application.
TL;DR: The DMS has shown promise as a detector for chemical weapon agents, and the ability of the DMS to detect nerve and blister agent simulants at clinically relevant levels is demonstrated.
Abstract: With international concern growing over the potential for chemical and biological terrorism, there is an urgent need for a sensor that can quickly and accurately detect chemical and biological agents. Such a sensor needs to be portable, robust, and sensitive, with fast sample analysis time. We will demonstrate the use of a micromachined differential mobility spectrometer (DMS) with these characteristics that can detect multiple agents simultaneously on a time scale of seconds. In this study, we have demonstrated the ability of the DMS to detect Bacillus subtilis spores, a surrogate for Bacillus anthracis spores, the causative agent of anthrax. Pyrolysis was used as the sample introduction method to volatilize the spores before introducing material into the DMS. Additionally, we examined the effect of pyrolysis on B. subtilis spores suspended in sterile water using SDS-PAGE. These experiments showed that the spores must be heated at 650/spl deg/C or greater for 5 s or at 550/spl deg/C for at least 10 s to be fragmented into particles considerably smaller than 10 kDa, which the DMS can detect. Several major biomarkers can be easily distinguished above the background of the sterile water in which the spores are suspended, and we hypothesize that additional biomarkers could be liberated by further optimizing conditions. The DMS also has shown promise as a detector for chemical weapon agents, and we have demonstrated the ability of the DMS to detect nerve and blister agent simulants at clinically relevant levels.
TL;DR: In this paper, the development of inexpensive, highly selective, and extremely sensitive sensors to help combat terrorism is discussed, and the critical requirements for a single, miniature sensor platform have been met and the realization of an integrated, widely deployable MEMS sensor is near.
Abstract: An urgent need exists for the development of inexpensive, highly selective, and extremely sensitive sensors to help combat terrorism. If such sensors can be made miniature, they could be deployed in virtually any situation. Terrorists have a wide variety of potential agents and delivery means to choose from for chemical, biological, radiological, or explosive attacks. Detecting terrorist weapons has become a complex and expensive endeavor, because a multitude of sensor platforms is currently needed to detect the various types of threats. The ability to mass produce and cost effectively deploy a single type of sensor that can detect a wide range of threats is essential in winning the war on terrorism. Silicon-based microelectromechanical sensors (MEMS) represent an ideal sensor platform for combating terrorism because these miniature sensors are inexpensive and can be deployed almost anywhere. Recently, the high sensitivity of MEMS-based microcantilever sensors has been demonstrated in the detection of a variety of threats. Therefore, the critical requirements for a single, miniature sensor platform have been met and the realization of an integrated, widely deployable MEMS sensor could be near.
TL;DR: In this paper, a modified Newton-Raphson method was used to adjust the conductivity profile to fit a set of multifrequency inductances in a least-squared sense.
Abstract: This paper presents an inverse method for determining the conductivity distribution of a flat, layered conductor using a multifrequency electromagnetic sensor. Eddy-current sensors are used in a wide range of nondestructive testing applications. Single-frequency sensors are very common; however, the potential of an eddy-current sensor with spectroscopic techniques offers the ability to extract depth profiles and examine more fully the internal structure of the test piece. In this paper, the forward solution for a small right-cylindrical air-cored coil placed next to a layered conductor is based on the analytic solution provided by the transfer matrix approach. For an inverse solution, a modified Newton-Raphson method was used to adjust the conductivity profile to fit a set of multifrequency inductances in a least-squared sense. The approximate Jacobian matrix (sensitivity matrix) was obtained by the perturbation method. Numerical results of the forward solution are provided for cases of step, continuous conductivity profiles. Good estimates for the conductivity profile were obtained. Experimental eddy-current tests are performed by taking the difference in inductance of the coil when placed next to a reference conductor and next to a layered conductor over the range 100 kHz - 1 MHz. Inverse results based on experimental and simulated data verified this method.
TL;DR: In this paper, parallel arrays of Pd nanowires were fabricated by electrodeposition from an aqueous plating solution onto the surface of highly oriented pyrolytic graphite (HOPG).
Abstract: Palladium (Pd) nanowires, synthesized by template-nanomanufacturing techniques, has been studied for hydrogen gas-sensing applications at room temperature. In this study, parallel arrays of Pd nanowires were fabricated by electrodeposition from an aqueous plating solution onto the surface of highly oriented pyrolytic graphite (HOPG). The nanowires were then transferred onto a polystyrene film and silver electrical contact pads were fabricated by shadow masking. The morphology of the nanowires was analyzed using atomic force microscope (AFM) in noncontact mode and the diameter of the observed nanowires was measured to be approximately 250 nm. Scanning electron microscope (SEM) images revealed that the nanowires fabricated by this procedure were parallel and continuous. Electrodes were patterned by shadow masking and the I-V characteristics of the nanowires were studied. Experimental results indicated that the sensors are highly sensitive to hydrogen, showing a two-order change in conductance. The morphology of the nanowires was analyzed using SEM and AFM in order to understand the properties responsible for the high sensitivity of the nanowires. SEM images showed that the nanowires contain nanogaps in absence of H/sub 2/. Upon exposure to H/sub 2/, the Pd absorbed hydrogen, resulting in the expansion of Pd grains. This expansion results in the closing of the nanogaps. The expansion occurred due to the phase transition from /spl alpha/ to /spl beta/ and the Pd lattice expansion.
TL;DR: In this paper, a magnetostriction-based, passive optical current sensing device for highvoltage applications was developed and tested, with a useable linear range of 100-1000 A with a measured phase shift of around 30/spl deg/ for a steady-state 60Hz excitation.
Abstract: The authors have developed and tested a prototype magnetostriction-based, passive optical current sensing device for high-voltage applications. The sensor contains a ferromagnetic yoke, a modulator of magnetostrictive Terfenol-D that responds to the magnetic field, and a fiber Bragg grating that converts this response into a wavelength-modulated optical signal and transmits it via an optical fiber to ground-level electronics. To linearize the output, the modulator material was subjected to both mechanical and magnetic biases. The prototype CT was found to have a useable linear range of 100-1000 A with a measured phase shift of around 30/spl deg/ for a steady-state 60-Hz excitation. Both the gain and the phase response have been found to be dependent on mechanical prestress and magnetic bias. The authors also report on materials characterization and modeling that support the actual design process.
TL;DR: In this paper, surface-enhanced Raman scattering spectra of chemical and biological agent simulants, such as dimethyl methylphonate, pinacolyl methylphosphonate and diethyl phosphoramidate, 2-chloroethyl ethylsulfide, bacillus globigii, erwinia herbicola, and Bacillus thuringiensis were obtained from silver-oxide film-deposited substrates.
Abstract: Surface-enhanced Raman scattering spectra of chemical and biological agent simulants, such as dimethyl methylphonate, pinacolyl methylphosphonate, diethyl phosphoramidate, 2-chloroethyl ethylsulfide, bacillus globigii, erwinia herbicola, and bacillus thuringiensis were obtained from silver-oxide film-deposited substrates. Thin AgO films ranging in thickness from 50 to 250 nm were produced by chemical bath deposition onto glass slides. Further Raman intensity enhancements were noticed in UV irradiated surfaces due to photo-induced Ag nanocluster formation, which may provide a possible route to producing highly useful plasmonic sensors for the detection of chemical and biological agents upon visible-light illumination.
TL;DR: In this paper, the authors have discussed the construction, sensing, and applications of capacitive fiber-meshed transducers and their applications, and used capacitive and resistive measurement techniques for the detection.
Abstract: Capacitive sensing is used in manufacturing E-textiles for touch and proximity-sensing applications. The common approach is to construct electrodes on top of a nonconductive fabric structures. Woven and knitted fabric structures are used for the construction; metallic wire and conductive coated fibers are primarily used. Due to the performance degradation and poor comfort of these constructions, we have constructed electrodes with inherently conductive polymers and multifilament metallic fibers by integrating them into fiber-meshed structures such that the electrodes are a part of the nonconductive base structure. We have used capacitive and resistive measurement techniques for the detection. Out of many mechanical methods of fiber-integrating processors, we have used flat bed-knitting technology and Jacquard weaving technology. In this paper, we have discussed the construction, sensing, and applications of capacitive fiber-meshed transducers and their applications.
TL;DR: In this article, an active fiber Bragg grating temperature and flow sensor based on self-heated optical hot wire anemometry is presented, which is directly powered by optical energy carried by optical fibers.
Abstract: This paper presents an active fiber Bragg grating temperature and flow sensor based on self-heated optical hot wire anemometry. The grating sensors are directly powered by optical energy carried by optical fibers. In-fiber diode laser light at 910 nm was leaked out from the fiber and absorbed by the surrounding metallic coating to raise the temperature and change the background refractive index distribution of the gratings. When the diode laser is turned off, the grating is used as a temperature sensor. When the diode laser is turned on, the resonance wavelength and spectral width change of the self-heated grating sensor is used to measure the gas flow velocity. The grating flow sensors have been experimentally evaluated for different grating length and input laser power. The grating flow sensors have demonstrated a 0.35- m/s sensitivity for nitrogen flow at atmosphere pressure.
TL;DR: In this paper, the metal-insulator silicon-carbide field effect transistor (MISiC-FET) sensor has been tested for this application and has been shown to be sensitive to NH/sub 3/.
Abstract: One way to decrease the emitted levels of NO/sub x/ from diesel engines is to add NH/sub 3/ in the form of urea to the exhausts after combustion. NH/sub 3/ will react with NO/sub x/ in the catalytic converter to form N/sub 2/ and water, which is called selective catalytic reduction (SCR). The amount of NH/sub 3/ added may be regulated through closed-loop control by using an NH/sub 3/ sensor. The metal-insulator silicon-carbide field-effect transistor (MISiC-FET) sensor has previously been tested for this application and has been shown to be sensitive to NH/sub 3/. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N/sub 2/O and NO/sub 2/, and studies concerning the influence of water vapor have been performed in the laboratory. The difference between Ir and Pt films, with regard to catalytic activity, has also been investigated. The sensors were found to be sensitive to NH/sub 3/ in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH/sub 3/ in a stair-like fashion to the system and detect it with the MISiC-FET sensors. The presence of water vapor was shown to have the largest effect on the sensors at low levels and the NH/sub 3/ response was slightly decreased by a background level of NO/sub 2/.
TL;DR: In this paper, a low-power, two-axis fluxgate magnetometer is presented, where a planar sensor is integrated in a standard CMOS process, which provides metal layers for the coils and electronics for the signal extraction and processing.
Abstract: In this paper, we present a low-power, two-axis fluxgate magnetometer. The planar sensor is integrated in a standard CMOS process, which provides metal layers for the coils and electronics for the signal extraction and processing. The ferromagnetic core is placed diagonally above the four excitation coils by a compatible photolithographic post process, performed on a whole wafer. The sensor works using the single-core principle, with a modulation technique to lower the noise and the offset at the output. In contrast to traditional fluxgate approaches, the sensor features a high degree of integration and minimal power consumption at 2.5 V of supply voltage that makes it suitable for portable applications. A novel digital feedback principle is integrated to linearize the sensor characteristics and to extend the linear working range.
TL;DR: In this article, a multiplexed optical fiber Bragg sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346m road bridge in Norway, for design verification and structural integrity monitoring purposes.
Abstract: A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized (/spl sim/0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of <10 /spl mu//spl epsiv/ over the test period with a precision of /spl plusmn/5 /spl mu//spl epsiv/ and a resolution of /spl plusmn/1 /spl mu//spl epsiv/. The readings from the FBG sensors were comparable to those from the foil gauge sensors to within /spl plusmn/4 /spl mu//spl epsiv/.
TL;DR: In this article, the authors review the physics of nuclear detection, and point out areas where improvements can be anticipated, via case studies of technologies such as gamma-ray imaging, advanced radiography, large-area detectors, and active interrogation.
Abstract: Countering clandestinely delivered nuclear and radiological threats requires a multielement, global, civil/military, system-of-systems approach. One important element is geographically layered, sensor-based detection of threat objects, including radiation detection systems. An effective defense against these threats should take advantage of the latest developments in radiation detection technology. This paper reviews the physics of nuclear detection, and points out areas where improvements can be anticipated, via case studies of technologies such as gamma-ray imaging, advanced radiography, large-area detectors, and active interrogation.