SURFACE ACOUSTIC-WAVE PROBE FOR CHEMICAL-ANALYSIS .1. INTRODUCTION AND INSTRUMENT DESCRIPTION

Surface acoustic waves are easily propagated along a quartz or lithium niobate surface. Interdigitized finger transducers serve as transmitters of 30-60 MHz SAW waves toward an equivalent detector. Surface molecules predictably affect the wave propagation. Circuitry has been built to measure such interactions by changes in amplitude or phase-angle shift of the SAW, or the alteration of the resonance frequency when the device is part of a “tank” circuit. Amplitude response is proportional to the pressure of gaseous molecules in the environment. For a given gas, the response factor is proportional to (molecular weight)1/2. Large linear frequency shifts were noted as ambient pressures changed. Amplitude measurements on quartz have the best S/N ratio (566). Limited data suggest that LiNbO3 devices have considerably better S/N ratios. © 1979, American Chemical Society. All rights reserved.