Surface Wave Propagation on Piezoelectric Materials

Abstract

Surface waves (Rayleigh and Love) are the normal propagating modes of vibration on a free surface. Propagation on anisotropic piezoelectric materials can only occur along certain crystallographic directions for which the piezoelectric matrix gives a direct method of determining the principal ones. Surface waves been generated on nonpiezoelectric Al2O3 by depositing thin films of piezoelectric ZNS or CdS. Some discussion is given of the practical arrangement of electrodes for generating surface waves with reference to frequency response. Evidence has been accumulated to suggest that in quartz, for instance, bulk shear and compressional waves are always generated in addition to the surface wave. This is one factor limiting the ultimate conversion efficiency of electrical energy to surface sound energy. Conversion efficiencies of 100% or greater are achievable in semiconducting piezoelectric materials under conditions of acoustic amplification. Results are presented of attenuation measurements of Rayleigh waves in quartz to demonstrate a general T4 phonon-phonon type of scattering present at low temperatures. The application of surface waves in electronic signal processing is illustrated by way of a delay line, directional coupler, and waveguide.