Theoretical Determination of Equivalent Circuit Parameters for Double Electrode SAW Interdigital Transducers

Abstract

A theoretical method for determining circuit parameters of equivalent circuits is described for the analysis of excitation and reflection characteristics of double electrode SAW interdigital transducers (DIDT). Admittance mismatch for single electrode SAW interdigital transducers, dispersion characteristics of an infinite arrary corresponding to an electrically shorted or opened DIDT and static capacitance for one pair of DIDT, which are necessary for determining circuit parameters, are calculated by using the finite-element method. Therefore in this approach, all the effects of piezoelectric perturbation, mechanical perturbation, ecergy storage, and anisotropy of substrate are taken into account. Numerical examples are presented for the circuit parameters of DIDTs on several piezoelectric substrates. For a 128° Y-X LiNbO₃ substrate, excitation and reflection characteristics are calculated and the computed results agree well with the experimental results.