Physical and chemical sensing applications of acoustic devices

Abstract

Acoustic devices are finding a number of applications as physical and chemical sensors. Thickness-shear mode resonators, for example, can be operated in a fluid to measure properties such as density and viscosity. These devices are being developed for in situ monitoring applications, including engine oil for condition-based maintenance. The surface acoustic wave (SAW) device serves as a versatile platform for constructing gas-phase chemical sensors. These devices serve as extremely sensitive gravimetric detectors with chemical selectivity conferred by depositing a chemically sensitive film onto the device surface. Selectivity can be further enhanced by using arrays of chemical sensors combined with a pattern recognition algorithm. Flexural plate wave (FPW) devices, consisting of a self-supporting membrane in which acoustic waves are excited, can be used in a number of sensing applications. These devices are sensitive to either mass accumulation or a change in membrane tension. Chemical sensors can be constructed by depositing a chemically sensitive film onto the membrane surface; species absorption leads to a change in the membrane’s areal mass density. Alternatively, sensors for pressure and acceleration can be constructed which rely on the device’s sensitivity to membrane tension. Sensor systems using these various sensor platforms will be described.