Boundary Element Method Analysis of Interdigital Transducers Having Arbitrary Metallisation Ratio

Abstract

The paper describes the use of weighted Tchebycheff-polynomials as the expansion functions for the boundary element method, by which SAW-IDTs with arbitrary metallisation ratio r (finger width relative to finder periodicity) were analysed. First, it is shown that the order of the polynomials N should be increased with r to keep the accuracy within a specified value: N=2 results in negligible error for commonly employed IDTs with r of less than 0.9. Secondly, the r dependence of IDT input admittance was analysed and IDT behaviours were characterised at both fundamental and harmonic frequencies.