ELECTRICAL IMPEDANCE ANALYZER OF SENSOR CONVERTERS BASED ON POROUS SILICON

Abstract

A portable measuring and computing system for information signals processing of a multi-element sensor matrix based on porous silicon the IC5933A (Analog Devices) specialized impedance spectral converter integrated circuit was realized. This system of electrochemical impedance spectroscopy has been tested for character change of individual profiles problems of sensory elements impedance characteristics in the process of adsorption of different types water-containing gases molecules. During the investigation it was fixed that the selected scheme including of sensor elements and the nominal value of the resistance element sensor units Rsence = 150 KOm, the optimal frequency range of impedance measurement is in the range of 100 Hz - 10 kHz. Experimental data confirm the existence of functional dependence impedance spectra and partial sensitivities of individual sensors to individual gas component. These dependences are essentially analog converter characteristic gas sensors. The analysis of the nature of the change of the complex transfer coefficient module of each sensor allows to identify and numerically describe the adsorption processes of different types of gases, since they are characterized by individual frequency responses. On the set of the obtained experimental data, a method of constructing a mathematical model of the transformative characteristics of each sensory element is proposed. The method is realized on the real-time registration of the sensor impedance responses the to the external influence and an iterative algorithm of polynomial approximation of the obtained data array. Software for 3D visualization of measurement results is developed. Accuracy is done by comparing the real-element reference signal and its counterpart in the analytical method. At the end of each approximation cycle, a constant of the maximum approximation error for the given array is formed. The proposed approaches and the results obtained demonstrate the fundamental ability to identify the types of gases and calculate their concentrations, and can be the basis for the construction of systems for the express detection of molecules of CO, CO₂, H₂S, smoke, alcohols, propane and other hydrocarbons in the studied gas environments, as well as for environmental and biomedical monitoring.

Keywords: porous silicon, gas sensor, electrochemical impedance spectroscopy, Fourier analysis, approximation.