An Analysis of Surface-Acoustic-Wave Devices Using Coupling-of-Mode Theory and Finite-Element Method

A coupling-of-mode theory is described for the analysis of excitation characteristics of interdigital transducers (IDT) for surface acoustic waves (SAW) and of reflection characteristics of SAW gratings. Coupling and transduction coefficients of coupled mode equations can be theoretically determined by applying the finite-element method (FEM) to an infinite array corresponding to an electrically shorted or open IDT. The FEM is also used to calculate the static capacitance for one pair of IDTs. Examples are computed for various types of IDTs and metallic gratings on a 128° Y-X LiNbO3 substrate.