A technique for acoustic surface studies of nonpiezoelectric materials

Abstract

A technique is described for fluid coupling acoustic surface waves onto an arbitrary nonpiezoelectric material to allow the study of its surface properties. In these surface studies the relevant experimental information is contained in an induced phase change of the acoustic wave. For this reason, the primary concern was to develop a reliable technique by which this phase could be transmitted through the fluid interface. This issue has not been considered in previous work on fluid coupling. A simple physical model of the coupling mechanism is given, followed by a detailed description of the apparatus and procedure. Experimental studies of the phase change using the fluid-coupling technique are compared with results obtained by direct surface-wave excitation with interdigital transducers. The comparison shows that nonvolatile low-viscosity fluids (e.g., water, xylene, and o-dichlorobenzene) consistently reproduce the direct coupling results over a large variation of fluid-coupling parameters. We present an example of the application of this technique to a problem of current research interest: alkali-halide surface absorption of CO2 laser radiation.