Prototype microwave acoustic fluid sensors

The properties of the acoustic wave in a fluid overlay on a piezoelectric substrate are investigated for two different geometries: bounce mode and waveguide mode. Acoustic wave properties such as velocity and attenuation are obtained as a function of the fluid layer thickness and the physical properties of the fluid layer. It is shown that subtle changes in fluid properties will modify the acoustic waves. One or more of these acoustic wave properties can then be used as the sensing element in a fluid microsensor. Very promising results were obtained in the case of the bounce-mode geometry. Both the velocity and the attenuation of the acoustic mode varied in a predictable fashion as the fluid properties changed. In the case of the waveguide geometry the experimental and theoretical values of the velocity agreed quite well. However, the acoustic wave properties were found to be extremely sensitive to geometric factors such as the parallelism of the two solids.<>