First-order velocity shift and reflection coefficient for surface acoustic wave propagation

Design of surface acoustic wave (SAW) devices requires accurate values of velocity shift q and reflection coefficient r associated with finger overlays placed on the substrate material. In previous treatments variational and perturbative approaches have been developed for calculating first-order reflection coefficients and velocity shifts; however, the anisotropic substrate materials have until now been modeled by an effective isotropic substrate. We extend the variational and perturbative calculations of the first-order quantities to fully anisotropic crystals for several standard SAW substrate and overlay materials. Moreover, we report results obtained with both electrically free and shorted trial functions, and suggest optimum parametrizations of q and r, to first order in h/lambda, where h is the finger thickness and lambda is the Rayleigh wavelength. (C) 1996 American Institute of Physics.