A Rayleigh acoustic wave travelling on the surface of a semi-infinite piezoelectric medium may be changed by interaction with carriers and diffused gas in an adjacent semiconductor. The configuration, which uses a thin semiconductor film supported by a catalytic layer (Pd), is described in detail and the theoretical results of gas-sensor layer interaction are presented.
In the paper a new theoretical model for analyzing a surface acoustic wave gas sensor is presented. Basing on the electric load of the piezoelectric acoustic line the effect of surface acoustic wave velocity changes vs. surface conductivity is predicted which depends on the profile concentration of gas molecules diffused into the porous film. Inside the sensor layer Knudsen's model of gas diffusion was used.
In the paper a new sensor structure for surface acoustic wave gas system is presented. A bilayer structure WO 3 -Pd thin films may be useful for hydrogen detection in low concentration in air. A bilayer sensor structure of tungsten oxide WO 3 with a very thin catalytic film of palladium on the top has been studied for gas-sensing application at room temperature (about 25• C) in surface acoustic wave system. The bilayer structure of WO 3 layers with a thickness of about 50 nm, 100 nm and 150 nm was made onto a LiNbO 3 Y -cut Z-propagating substrate by means of the vacuum sublimation method using a special aluminum mask. The vapor source consisted of commercially available WO3 powder (Fluka 99.9%) and molybdenum heater. The thin palladium (Pd) layer (about 10 nm) was made separately on each WO3 layer by means of vapor deposition in high vacuum. There have been investigated three structures: 50 nm WO3 + 10 nm Pd, 100 nm WO3 + 10 nm Pd and 150 nm WO3 + 10 nm Pd in three canal surface acoustic wave system with reference oscillator. Numerical results obtained by analysis of the surface acoustic wave gas sensor model have been compared with experimental results.
The paper presents the results of an analysis of gaseous sensors based on a surface acoustic wave (SAW) by means of the equivalent model theory. The applied theory analyzes the response of the SAW sensor in the steady state affected by carbon monoxide (CO) in air. A thin layer of WO3 has been used as a sensor layer. The acoustical replacing impedance of the sensor layer was used, which takes into account the profile of the concentration of gas molecules in the layer. Thanks to implementing the Ingebrigtsen equation, the authors determined analytical expressions for the relative changes of the velocity of the surface acoustic wave in the steady state. The results of the analysis have shown that there is an optimum thickness of the layer of CO sensor at which the acoustoelectric effect (manifested here as a change in the acoustic wave velocity) is at its highest. The theoretical results were verified and confirmed experimentally.
The paper presents the numerical results of investigations of the layered gas surface acoustic waves sensor. The base electric load of the piezoelectric acoustic line is predicted by the effect of surface acoustic waves velocity changes vs. surface conductivity, which depends on the profile concentration by gas diffused molecules into the porous film. Inside the sensor layer Knudsen's model of gas diffusion was used.
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