A fast accurate method for calculating the SAW and bulk wave radiation admittance of a SAW transducer

A fast accurate method which relies on fast Fourier transform routines is described for calculating the bulk wave admittance of a SAW (surface acoustic wave) transducer. The method relies on knowledge of the SAW radiation conductance and of the bulk wave portion of the effective permittivity. Also, an expression is derived which relates the static transducer capacitance to the integral of the SAW radiation conductance. In addition, expressions for the SAW input admittance are given which are based on the assumption that the electric field under a SAW transducer is approximated by the electrostatic electric field. This assumption is noted to be more accurate than the traditional modeling methods which assume that the surface charge density is well approximated by the electrostatic charge density. Finally, the accuracy of this model has been verified by comparison to careful experimental measurements of a 5-λ split-electrode transducer on 128° LiNbO₃