Using a Second Order Sigma-Delta Control to Improve the Performance of Metal-Oxide Gas Sensors

Controls of surface potential have been proposed to accelerate the time response of MOX gas sensors. These controls use temperature modulations and a feedback loop based on first-order sigma-delta modulators to keep constant the surface potential. Changes in the surrounding gases, therefore, must be compensated by average temperature produced by the control loop, which is the new output signal. The purpose of this paper is to present a second order sigma-delta control of the surface potential for gas sensors. With this new control strategy, it is possible to obtain a second order zero of the quantization noise in the output signal. This provides a less noisy control of the surface potential, while at the same time some undesired effects of first order modulators, such as the presence of plateaus, are avoided. Experiments proving these performance improvements are presented using a gas sensor made of tungsten oxide nanowires. Plateau avoidance and second order noise shaping is shown with ethanol measurements.Postprint (author's final draft

Identification of Tequila with an Array of ZnO Thin Films: A Simple and Cost-Effective Method

Se trata de identificar calidad de bebidas alcohólicasAn array of ZnO thin film sensors was obtained by thermal oxidation of physical vapor deposited thin Zn films. Different conditions of the thermal treatment (duration and temperature) were applied in view of obtaining ZnO sensors with different gas sensing properties. Films having undergone a long thermal treatment exhibited high responses to low ethanol concentrations, while short thermal treatments generally led to sensors with high ethanol sensitivity. The sensor array was used to distinguish among Tequilas and Agave liquor. Linear discriminant analysis and the multilayer perceptron neural network reached 100% and 86.3% success rates in the discrimination between real Tequila and Agave liquor and in the identification of Tequila brands, respectively. These results are promising for the development of an inexpensive tool offering low complexity and cost of analysis for detecting fraud in spirits.Beca CONACyT- Bilateral de estudios de Doctorad

Analysis of the conductance transient in thick film tin oxide gas sensors

In this paper, we analyse the conductance transient of a Taguchi TGS-822 sensor under a step change in the vapour concentration. A diffusion-limited range in the conductance transient is observed. Adjustments between the theoretical calculations based on a non-linear diffusion-reaction model and the experimental results alloy a constant, t', to be estimated, which is independent of the final conductance value and depends, among other parameters, on the effective diffusion coefficients of vapours in the porous tin oxide sensor. From transient measurements of organic solvents (benzene and o-xylene) we have obtained t' values that are independent of concentration and characteristic for each vapour. This new parameter can give useful information for gas/vapour recognition.Peer Reviewe

Localized aerosol-assisted CVD of nanomaterials for the fabrication of monolithic gas sensor microarrays

Abstract The self-heating capability of MEMS-based devices is used to grow locally into the sensing active area of monolithic gas sensor microarrays differently-functionalized materials via aerosol-assisted CVD. Results derived from SEM, TEM, XRD and Raman demonstrate the integration of non-functionalized (WO3-x) and functionalized nanostructures with gold (WO3-x/Au) or platinum (WO3-x/Pt) NPs into the array. Tests of these microarrays toward various concentrations of reducing gases show stable and reproducible responses, with the highest responses (R) for WO3-x to carbon monoxide (e.g. R = 4.3-80 ppm), for WO3-x/Au to ethanol (e.g. R = 7-80 ppm) and for WO3-x/Pt to hydrogen (e.g. R = 3.6-80 ppm). Principal component analysis of the sensor response replicates to each gas and concentration suggest that the differences in the sensing properties of each element of the array provide the complementary information to discriminate H2 and EtOH from CO. © 2015 Elsevier B.V. All rights reserved

Using a Second Order Sigma-Delta Control to Improve the Performance of Metal-Oxide Gas Sensors

Controls of surface potential have been proposed to accelerate the time response of MOX gas sensors. These controls use temperature modulations and a feedback loop based on first-order sigma-delta modulators to keep constant the surface potential. Changes in the surrounding gases, therefore, must be compensated by average temperature produced by the control loop, which is the new output signal. The purpose of this paper is to present a second order sigma-delta control of the surface potential for gas sensors. With this new control strategy, it is possible to obtain a second order zero of the quantization noise in the output signal. This provides a less noisy control of the surface potential, while at the same time some undesired effects of first order modulators, such as the presence of plateaus, are avoided. Experiments proving these performance improvements are presented using a gas sensor made of tungsten oxide nanowires. Plateau avoidance and second order noise shaping is shown with ethanol measurements

An ultrasensitive room-temperature H2S gas sensor based on 3D assembly of Cu2O decorated WS2 nanomaterials

Herein, we report for the first time on the fabrication of a hybrid material consisting of Cu2O nanoparticlesdecoratedmultilayeredtungstendisulfide nanostructuresand demonstrate their remarkable gas sensing characteristics towards hydrogen sulfide gas. In the first step, a continuous film of WS2 was deposited directly on commercial alumina substrate by adopting a facile route combining aerosol-assisted chemical vapor deposition with H2 free atmospheric pressure CVD technique. For functionalization an additional step of synthesis was added where copper oxide nanoparticles were grown and deposited directly over as-grown tungsten disulfide at low temperature (i.e., 150 ◦C) using a simple and cost-effective technique. The morphological, structural and chemical characteristicswere investigatedusing FESEM, TEM, and EDX spectroscopy.The gas-sensing studies performed shows that this hybrid nanomaterial has excellent sensitivity towards hydrogen sulfide (11-times increase in response compared to that of pristine WS2 sensor) at moderate temperature (150 ◦C). Additionally, functionalization of pristine WS2 sensor with Cu2O nanoparticles further enhances the gas sensing performance towards the targeted gas even at room temperature (13-times increase in response compared with that of pristine WS2 sensor). Moreover, results obtained from humidity cross-sensitivity of Cu2O-WS2 sensor indicates superior gas sensing response (with a negligible decrease in response) as compared to pristine WS2 sensor, when ambient humidity is increased to 50%, which is rarely found in metal oxide-based sensors. This study could add a significant research value in the gas sensor domain