Surface Acoustic Wave Propagation Characterisation by Finite-Element Method and Spectral Domain Analysis

Abstract

This paper proposes a method of deriving the discrete Green function for the analysis of surface acoustic wave (SAW) propagation and excitation under metallic-grating structures with finite thickness. The method uses the finite-element method (FEM) for the analysis of the grating electrode region, while the spectral domain analysis (SDA) is used for the analysis of the substrate region. This approach takes account of the mass-loading effect of grating electrodes as part of electrical quantities in a substrate, and makes it possible to employ Blφtekjær et al.'s theory for rapid computation. Rayleigh SAWs and leaky SAWs propagating under metallic-grating structures on 128°YX- LiNbO3 and 36°YX- LiTaO3 (36-LT), respectively, were analysed. The dispersion relation calculated by the present method agreed very well with that obtained by the perturbation theory. It is also shown that the electromechanical coupling factor for leaky SAWs on 36-LT increases with the thickness of grating electrodes, which is primarily due to the change in the SAW energy concentration near the surface.