A surface generated acoustic wave liquid microsensor

The properties of the acoustic waves in a fluid overlay on a piezoelectric substrate are investigated. Acoustic wave properties such as velocity and attenuation are obtained as a function of the thickness and physical properties of the fluid layer. It is shown that subtle changes in fluid properties modify the acoustic wave properties, which can then be used as the sensing element in a fluid microprocessor. Various liquids containing different concentrations of solutes were studied. Both the velocity and the attenuation of the acoustic mode varied in a predictable fashion as the fluid properties changed. The sensor exhibited high sensitivity to minute variations in solute concentrations. The sensor response was not extremely sensitive to geometric factors such as the parallelism of the two solids. This type of acoustic sensor may have applications in such diverse areas as water pollution control, chemical sensors, and biosensors. >