Spurious bulk waves in SAW filters with apodized transducers

The authors report the simulation of the bulk wave transmission characteristics of planar acoustic devices on arbitrary substrates. Starting from the basic acoustoelectric differential equations, the analysis is based on the Green´s function formalism and the Ritz-Galerkin method. In contrast to previously published papers, the authors apply these methods to devices with large apodized IDTs (interdigital transducers) and treat the interaction with bulk waves rigorously during generations as well as reception. They derive a CPIM (charge potential interrelation matrix) formulation of the voltage weighting analysis method for apodized IDTs and compare it with the track-by-track analysis method. Finally, simulation results of the spurious bulk wave responses of a TV filter with 170 IDT fingers are presented