Multi-Mode P-Matrix Models for the Description of Interacting Modes in TCSAWand LSAW Devices

A multi-mode P-matrix formalism accounting for energy conservation, causality and reciprocity is presented. The P-matrix of an electrode is represented as product of P-matrices for propagation, excitation and reflection. Reflection considers the interaction of forward and backward propagating waves of the same mode as well as different modes. Model parameters are determined by fitting to dispersion relation [1] and harmonic admittance, both obtained from finite element (FEM) computations. For a temperature compensated SAW (TCSAW) system a two-mode model of interacting Rayleigh and shear horizontal (SH) mode is determined. It is shown that the excitation of the SH mode is mainly determined by mode interaction, rather than direct excitation of the mode. A multi-mode model for leaky SAW (LSAW) systems is set up by considering the interaction of a single guided mode and a quasicontinuum of bulk acoustic wave (BAW) modes. In this way the surface bulk hybrid (SBH) mode and other characteristic features of LSAW devices automatically emerge in the simulation result.