Performance Of Such Sensors Research Articles

Piezoresistive Composite Silicon Dioxide Nanocantilever Surface Stress Sensor: Design and Optimization.

In this paper, we present the design and optimization of a rectangular piezoresistive composite silicon dioxide nanocantilever sensor. Unlike the conventional design approach, we perform the sensor optimization by not only considering its electro-mechanical response but also incorporating the impact of self-heating induced thermal drift in its terminal characteristics. Through extensive simulations first we comprehend and quantify the inaccuracies due to self-heating effect induced by the geometrical and intrinsic parameters of the piezoresistor. Then, by optimizing the ratio of electrical sensitivity to thermal sensitivity defined as the sensitivity ratio (υ) we improve the sensor performance and measurement reliability. Results show that to ensure υ ≥ 1, shorter and wider piezoresistors are better. In addition, it is observed that unlike the general belief that high doping concentration of piezoresistor reduces thermal sensitivity in piezoresistive sensors, to ensure υ ≥ 1 doping concentration (p) should be in the range: 1E18 cm-3 ≤ p ≤ 1E19 cm-3. Finally, we provide a set of design guidelines that will help NEMS engineers to optimize the performance of such sensors for chemical and biological sensing applications.

Impact of Isolation and Immobilization Layers on the Electro-Mechanical Response of Piezoresistive Nano Cantilever Sensors.

In the last decade, piezoresistive nano cantilever sensors have been extensively explored, especially for chemical and biological sensing applications. Piezoresistive cantilever sensors are multi-layer structures with different constituent materials. Performance of such sensors is a function of their geometry and constituent materials. For a fixed material set, the pre-requisite for optimizing the performance of a composite piezoresistive cantilever sensor is careful geometrical design of its constituent layers. Even though, treatise encompasses various designs of such sensors, typically for computational simplicity the functional layers i.e., the isolation and immobilization layers are neglected in the modeling stages. In this paper, we elucidate the impact of the functional layers on the electro-mechanical response of composite piezoresistive nano cantilever sensors. Systematic and detailed computations are performed using theoretical models and numerical simulations. Results show that both the isolation and immobilization layers play a critical role in governing the sensor performance. Simulation results depict that compared to a sensor with an isolation layer of thickness 100 nm, a sensor without isolation layer has 36.29% and 42.51% better deflection sensitivity and electrical sensitivity respectively. Furthermore, it is found that when an immobilization layer of thickness 40 nm is added atop the isolation layer, the deflection sensitivity and electrical sensitivity reduces by 12.98% and 15.83% respectively. Through our investigation it is shown that the isolation and immobilization layers not only play a vital role in determining the stability and electro-mechanical response of the sensor but their negligence in the design stages can be detrimental. Apart from investigating the impact of the immobilization layer thickness, to model the sensor closer to real time operational conditions, we have performed analysis to understand the impact of non-uniformity in the immobilization layer thickness and non-uniform surface stress loading on the electro-mechanical response of the sensor. Results and inferences obtained from this study will help NEMS engineers to optimize the performance of piezoresistive nano cantilever sensors and to design multi-layer cantilever platform structures for other transducers.

A novel surface-integrated spray-on thermocouple for heat transfer measurements

A novel manufacturing process for surface-integrated thermocouples is presented and its potential for heat transfer experiments is demonstrated. The presented manufacturing approach allows finely structured and reproducible thermocouples produced as part of the object under study. Therefore a fine channel is milled inside the investigated Perspex wall and gradually filled with conductive paints using spray cans of copper and nickel paint. High flexibility in adapting the sensor design to the requirements of a given experiment is offered by this approach as it involves only low-cost materials and standard manufacturing machinery. The paper details the characteristics and performance of such sensors, i.e. durability, reliability and operational range. Furthermore, an analytical, one-dimensional heat conduction model is used to describe the two layer arrangement of the sensor and underlying support substrate. For a step change in fluid temperature, this model in combination with a multipoint optimization procedure allows to determine the local heat transfer coefficient and the corresponding reference temperature. It is shown that this is possible without knowledge of the thermal properties of the sensor resulting in no additional calibration requirements. The obtained results are validated against measurements with thermochromic liquid crystals and commercial thermocouples. Deviations are within the uncertainty of the reference showing that the new device is competitive to state of the art techniques. Potential applications are seen for all kind of heat transfer experiments, especially when optical access for conventional techniques is restricted. Another possible field is the in-situ calibration of planar measurement techniques such as infrared thermography or thermochromic liquid crystals.

Calibration and assessment of electrochemical air quality sensors by co-location with regulatory-grade instruments

Abstract. The use of low-cost air quality sensors for air pollution research has outpaced our understanding of their capabilities and limitations under real-world conditions, and there is thus a critical need for understanding and optimizing the performance of such sensors in the field. Here we describe the deployment, calibration, and evaluation of electrochemical sensors on the island of Hawai`i, which is an ideal test bed for characterizing such sensors due to its large and variable sulfur dioxide (SO2) levels and lack of other co-pollutants. Nine custom-built SO2 sensors were co-located with two Hawaii Department of Health Air Quality stations over the course of 5 months, enabling comparison of sensor output with regulatory-grade instruments under a range of realistic environmental conditions. Calibration using a nonparametric algorithm (k nearest neighbors) was found to have excellent performance (RMSE < 7 ppb, MAE < 4 ppb, r2 > 0.997) across a wide dynamic range in SO2 (< 1 ppb, > 2 ppm). However, since nonparametric algorithms generally cannot extrapolate to conditions beyond those outside the training set, we introduce a new hybrid linear–nonparametric algorithm, enabling accurate measurements even when pollutant levels are higher than encountered during calibration. We find no significant change in instrument sensitivity toward SO2 after 18 weeks and demonstrate that calibration accuracy remains high when a sensor is calibrated at one location and then moved to another. The performance of electrochemical SO2 sensors is also strong at lower SO2 mixing ratios (< 25 ppb), for which they exhibit an error of less than 2.5 ppb. While some specific results of this study (calibration accuracy, performance of the various algorithms, etc.) may differ for measurements of other pollutant species in other areas (e.g., polluted urban regions), the calibration and validation approaches described here should be widely applicable to a range of pollutants, sensors, and environments.

A Route to Superior Performance of a Nanoplasmonic Biosensor: Consideration of Both Photonic and Mass Transport Aspects

Optical biosensors based on plasmonic nanostructures present a promising alternative to conventional biosensing methods and provide unmatched possibilities for miniaturization and high-throughput analysis. Previous works on the topic, however, have been overwhelmingly directed toward elucidating the optical performance of such sensors, with little emphasis on the topic of mass transport. To date, there exists no examination, experimental nor theoretical, of the bioanalytical performance of such sensors (in terms of detection limits) that simultaneously addresses both optical and mass transport aspects in a quantitative manner. In this work we present a universal model that describes the smallest concentration that can be detected by a nanoplasmonic biosensor. Accounting for both optical and mass transport aspects, this model establishes a relationship between bioanalytical performance and the biosensor’s design parameters. We employ the model to optimize the performance of a nanoplasmonic DNA biosensor co...

Ce doped NiO nanoparticles as selective NO2 gas sensor

Metal oxide gas sensors are promising portable gas detection devices because of their advantages such as low cost, easy production and compact size. The performance of such sensors is strongly dependent on material properties such as morphology, structure and doping. In the present study, we report the effect of cerium (Ce) doping on nickel oxide (NiO) nano-structured thin film sensors towards various gases. Bare NiO and Ce doped NiO nanoparticles (Ce:NiO) were synthesized by sol-gel method. To understand the effect of Ce doping in nickel oxide, various molar percentages of Ce with respect to nickel were incorporated. The structure, phase, morphology and band-gap energy of as-synthesized nanoparticles were studied by XRD, SEM, EDAX and UV–vis spectroscopy. Thin film gas sensors of all the samples were prepared and subjected to various gases such as LPG, NH3, CH3COCH3 and NO2. A systematic and comparative study reveals an enhanced gas sensing performance of Ce:NiO sensors towards NO2 gas. The maximum sensitivity for NO2 gas is around 0.719% per ppm at moderate operating temperature of 150 °C for 0.5% Ce:NiO thin film gas sensor. The enhanced gas sensing performance for Ce:NiO is attributed to the distortion of crystal lattice caused by doping of Ce into NiO.

Binding Affinity of a Highly Sensitive Au/Ag/Au/Chitosan-Graphene Oxide Sensor Based on Direct Detection of Pb2+ and Hg2+ Ions.

The study of binding affinity is essential in surface plasmon resonance (SPR) sensing because it allows researchers to quantify the affinity between the analyte and immobilised ligands of an SPR sensor. In this study, we demonstrate the derivation of the binding affinity constant, K, for Pb2+ and Hg2+ ions according to their SPR response using a gold/silver/gold/chitosan–graphene oxide (Au/Ag/Au/CS–GO) sensor for the concentration range of 0.1–5 ppm. The higher affinity of Pb2+ to binding with the CS–GO sensor explains the outstanding sensitivity of 2.05 °ppm−1 against 1.66 °ppm−1 of Hg2+. The maximum signal-to-noise ratio (SNR) upon detection of Pb2+ is 1.53, and exceeds the suggested logical criterion of an SNR. The Au/Ag/Au/CS–GO SPR sensor also exhibits excellent repeatability in Pb2+ due to the strong bond between its functional groups and this cation. The adsorption data of Pb2+ and Hg2+ on the CS–GO sensor fits well with the Langmuir isotherm model where the affinity constant, K, of Pb2+ and Hg2+ ions is computed. The affinity of Pb2+ ions to the Au/Ag/Au/CS–GO sensor is significantly higher than that of Hg2+ based on the value of K, 7 × 105 M−1 and 4 × 105 M−1, respectively. The higher shift in SPR angles due to Pb2+ and Hg2+ compared to Cr3+, Cu2+ and Zn2+ ions also reveals the greater affinity of the CS–GO SPR sensor to them, thus supporting the rationale for obtaining K for these two heavy metals. This study provides a better understanding on the sensing performance of such sensors in detecting heavy metal ions.

Experimental comparison of homodyne demodulation algorithms for phase fiber-optic sensor

Subject of Research. The paper presents the results of experimental comparative analysis of homodyne demodulation algorithms based on differential cross multiplying method and on arctangent method under the same conditions. The dependencies of parameters for the output signals on the optical radiation intensity are studied for the considered demodulation algorithms. Method. The prototype of single fiber optic phase interferometric sensor has been used for experimental comparison of signal demodulation algorithms. Main Results. We have found that homodyne demodulation based on arctangent method provides greater (by 7 dB at average) signal-to-noise ratio of output signals over the frequency band of acoustic impact from 100 Hz to 500 Hz as compared to differential cross multiplying algorithms. We have demonstrated that no change in the output signal amplitude occurs for the studied range of values of the optical pulses amplitudes. Obtained results indicate that the homodyne demodulation based on arctangent method is most suitable for application in the phase fiber-optic sensors. It provides higher repeatability of their characteristics than the differential cross multiplying algorithm. Practical Significance. Algorithms of interferometric signals demodulation are widely used in phase fiber-optic sensors. Improvement of their characteristics has a positive effect on the performance of such sensors.

Capacitive Soot Sensor

A capacitive soot sensor was built up on basis of a known resistive device by covering the electrode area with a thin but dense alumina layer manufactured by the aerosol-deposition-method (ADM). Deposited soot cannot short-circuit the electrodes but leads to an increasing capacitance of the sensor. Experiments were conducted in real exhaust. Increasing soot concentrations lead to a more fast and sharp increase of the capacitance and the blind time of the sensor decreased to almost zero. The performance of such sensors could be enhanced when a voltage is applied at the electrodes during soot collection.

Guidelines for the Design and Optimization of Wireless Sensors Based on the Modulated Scattering Technique

This paper presents the guidelines for the development and optimization of wireless sensors based on the modulated scattering technique (MST). In particular, this paper is focused on the design and optimization of different MST tag prototypes with different modulation techniques. In addition, it is shown how to obtain the best performance of such sensors in terms of communication range and load efficiency. The preliminary measurements obtained with different experimental tag prototypes demonstrate that these MST sensors are able to measure and to correctly send data without an expensive radio frequency (RF) transmitter or a bulky wired connection. The results obtained show that such sensors could be an interesting alternative to standard RF identifier and wireless sensors.

Tailoring magnetic and microwave absorption properties of glass-coated soft ferromagnetic amorphous microwires for microwave energy sensing

A comparative study of the magnetic softness, giant magnetoimpedance (GMI) effect, and microwave absorption capacity of glass-coated amorphous Co64.63Fe4.97B16Si11Cr3.4Ni0.02 and Co68B15Si10Mn7 microwires has been performed. We find that the Mn-containing sample exhibits a softer magnetic property, a larger GMI ratio, and a higher microwave absorption capacity as compared to those with a Fe-Cr-Ni composition. As a result, the Mn-containing microwire is shown to be a better microwave absorber for fabrication of a new class of microwave energy sensor based on Fiber Bragg Grating. Our study emphasizes a correlation between the magnetic softness, GMI, and microwave absorption in the microwires and paves the way to improving the performance of such sensors by tailoring their soft magnetic properties.

Molecular manipulations for enhancing luminescent bioreporters performance in the detection of toxic chemicals.

Microbial whole-cell bioreporters are genetically modified microorganisms that produce a quantifiable output in response to the presence of toxic chemicals or other stress factors. These bioreporters harbor a genetic fusion between a sensing element (usually a gene regulatory element responsive to the target) and a reporter element, the product of which may be quantitatively monitored either by its presence or by its activity. In this chapter we review genetic manipulations undertaken in order to improve bioluminescent bioreporter performance by increasing luminescent output, lowering the limit of detection, and shortening the response time. We describe molecular manipulations applied to all aspects of whole-cell bioreporters: the host strain, the expression system, the sensing element, and the reporter element. The molecular construction of whole-cell luminescent bioreporters, harboring fusions of gene promoter elements to reporter genes, has been around for over three decades; in most cases, these two genetic elements are combined "as is." This chapter outlines diverse molecular manipulations for enhancing the performance of such sensors.

Precision Gravity Tests with Atom Interferometry in Space

Atom interferometry provides extremely sensitive and accurate tools for the measurement of inertial forces. Operation of atom interferometers in microgravity is expected to enhance the performance of such sensors. This paper presents two possible implementations of a dual 85Rb-87Rb atom interferometer to perform differential gravity measurements in space, with the primary goal to test the Weak Equivalence Principle. The proposed scheme is in the framework of two projects of the European Space Agency, namely Q-WEP and STE-QUEST. The paper describes the baseline experimental configuration, and discusses the technology readiness, noise and error budget for the two proposed experiments.

A full ellipsometric approach to optical sensing with Bloch surface waves on photonic crystals

We report on the investigation on the resolution of optical sensors exploiting Bloch surface waves sustained by one dimensional photonic crystals. A figure of merit is introduced to quantitatively assess the performance of such sensors and its dependency on the geometry and materials of the photonic crystal. We show that the figure of merit and the resolution can be improved by adopting a full ellipsometric phase-sensitive approach. The theoretical predictions are confirmed by experiments in which, for the first time, such type of sensors are operated in the full ellipsometric scheme.

Effects of buffer composition and dilution on nanowire field-effect biosensors

Nanowire-based field-effect transistors (FETs) can be used as ultra-sensitive and label-free biosensors for detecting protein–protein interactions. A way to increase the performance of such sensors is to dilute the sensing buffer drastically. However, we show here that this can have an important effect on the function of the proteins. Moreover, it is demonstrated that this dilution significantly affects the pH stability of the sensing buffer, which consequently impacts the charge of the protein and thus the response and signal-to-noise ratio in the sensing experiments. Three model systems are investigated experimentally to illustrate the impact on ligand–protein and protein–protein interactions. Simulations are performed to illustrate the effect on the performance of the sensors. Combining various parameters, the current study provides a means for evaluating and selecting the most appropriate buffer composition for bioFET measurements.

Comparison of immobilization strategies for Cryptosporidium parvum immunosensors

Cryptosporidium is a waterborne protozoan parasite, which is problematic for the water industry due to widespread environmental presence, low infectious dose and resistance to chlorine disinfection. To replace the existing, slow regulatory monitoring procedure, immunosensors have been proposed. The performance of such sensors is often limited by the antibody immobilization. The aim of this article was to determine the immobilization protocol offering the highest oocyst capture efficiency. Four methods were tested both under static and convective conditions: physisorption, cysteamine–glutaraldehyde linkage, 3-aminopropyl-triethoxysilane functionalization and protein G linkage. The protein G protocol was shown to present the highest recovery rates in both conditions. For the protein G protocol, different antibody concentrations were tested and it was concluded that there is little difference in the recovery rates when the concentration of IgG antibody is higher than 20μg/mL. Additionally, operation under convective rather than static conditions increased the recovery for every protocol. These results can be useful to inform the design of future biosensor systems, using antibodies as the detection element, for Cryptosporidium.

Performance Analysis of Correlated Multiple Antenna Spectrum Sensing Cognitive Radio

We derive probability of detection Pd and false alarm Pf for spectrum sensing cognitive devices, employing correlated multiple antenna elements using linear test statistic. Detection performance of such sensors is severely degraded due to the correlation among antennas, in addition to that fading channel conditions may further deteriorate the performance. We propose a simple hard decision fusion strategy at the secondary Base Station to improve the performance by exploiting collaborative gain. Region of Convergence (ROC) is also evaluated under OR based fusion strategy. Numerical results certify the proposed proposal.

Investigation on the Magnetic Noise of Stacked Magnetostricitive-Piezoelectric Laminated Composites

The performance of multi-segments magneto-electric (ME) layered sensors as charge sources has been investigated by using a typical charge amplifier. We found that the intrinsic performance of such sensors consisting of several (namely 3 and 5) segments, is the same whether these segments are connected in parallel or in series. Both, the signal detecting capacity and the intrinsic noise source of ME layered sensors depend on the volume of sensor. We have measured an equivalent magnetic noise of about 1 nT√Hz at 1 Hz and as low as 10 pT√Hz in the white noise region

Metal oxide nanostructures and their gas sensing properties: a review.

Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called “small size effect”, yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them. In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion. Besides, doping is also an effective method to decrease particle size and improve gas sensing properties. Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article. The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

Diffusion in annealing of nanocrystalline Ni<SUB align="right">80Fe<SUB align="right">20/Cu composite wires

Weak magnetic field sensors have always been an area of great interest due to their immense potential applications in a wide array of fields such as magnetic anomaly detectors (MAD) in defence-related industry or bio-magnetic field sensors in biomedical industry. The performance of such sensors greatly depends on the magnetic softness of the sensing elements. Thus, optimisation of the post-heat treatment process is crucial as it serves to release stresses induced during the deposition process. In this study, furnace annealing was carried out on Ni