Scattering of SAW at discontinuities: some numerical experiments

In developing models to characterize the metallic-finger step discontinuity in SAW devices on piezoelectric substrates it is important to estimate the SAW reflection coefficients and the effect of other modes at step discontinuities. In the literature perturbation approximations, finite element methods and various phenomenological parameter-fitting using experimental data are among the techniques which have been exploited. In this paper, a non-perturbation approximation method, which attempts to parallel some well-established techniques used in solving electromagnetic waveguide-discontinuity problems, is developed as an alternate numerical procedure for calculating SAW reflections. Implementing such method requires that the full solution to SAW propagation in the free and in the layered regions be obtained. Thus, for a free-to-metallized discontinuity, the two SAW phase velocities, the total SAW power flow in the free region and in the layered region, and the electroacoustic fields, must be calculated. The reflection problem is formulated as an optimization problem subject to the necessary scattering parameter constraints. Numerical experiments are described, and the results of calculations for reflectivity are compared to perturbation approximations, non-perturbation approximations and the available experimental data for the effects of energy storage