Study of a Surface Acoustic Wave Microsensor for Gas Detection

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Currently a need exists for accurate, dependable microsensors which can communicate to the observer data associated with processes which may be at the molecular level or the parts per billion to trillion range. Surface acoustic wave (SAW) technology offers one of the most attractive methods to realize the microsensor. The SAW gas microsensor basically consists of twin SAW delay lines. Each line is configured as an oscillator and the propagation path of one contains a selectively sorbent film while the other is the uncoated reference. Phase delay changes induced by the gas sorbed on the film results in frequency shifts which are directly proportional to the gas concentration. An interdisciplinary effort which includes the theory, design, fabrication and testing of SAW devices and the physics and chemistry of surfaces is ongoing at the University of Maine to realize the potential of this sensor. The purpose of the present renewal project is to continue the ongoing experimental and theoretical study of the SAW gas microsensor. The sensing film being used is tungsten trioxide (WO3) and the gas being sensed is hydrogen sulfide (H2S). Microscopic and macroscopic experimental tools are being used in order to study and optimize sensor properties such as selectivity, sensitivity, operating range sensor signature, response time, recovery time, reproducibility and aging.