Interdigital Transducer Interaction with SAWS and BAWS

Abstract

The aim of this work is a rigorous approach to the two-dimensional analysis of excitation, propaga- tion and detection of acoustic waves. For the efficient computation of the dynamic charge distribution on IDTs we use the concept of Green's function and the method of moments. Since no restrictions are imposed on the transducer potentials, even multistrip couplers, multi- phase transducers and metal reflectors can be analysed. First we apply the formalism in the sagittal plane to in- vestigate BAW excitation. We detail the effect of BAW- excitation on IDT end-fingers and present radiation pat- terns in YZ-LiNbOs. Next we extend the formalism and treat SAW excitation and diffraction on the surface rigorously. We take into account the two-dimensional charge distribution and the anisotropy of both slowness and coupling-coefficient, I. Introduction The calculation of the interaction of interdigital transducers (IDTs) with acoustic waves in piezoelectric materials is ba- sically a problem of solving the coupled electric and acoustic field equations. The computation of the field distributions requires the solution of a boundary value problem for a set of linear partial differential equations (l). Treating linear boundary value problems, the primary task is to construct the associated Green's function. The latter is the response of the medium due to a point excitation. Applying the superposition principle, any electrical and mechanical field quantity $(F) can be written as the convolution of Green's function G(F - F') with the spatial distribution of the ex- citing physical quantity u(Ff): $(F) = G(F - Ff)u(Ff)dFf