Use of multilayer SAWMG program to determine partial second order contributions to interdigital transducers

A method of obtaining partial second order contributions to the reflection coefficient and velocity shift of periodic interdigital transducers is developed for a piezoelectric substrate and isotropic overlay material. A periodic IDT with a rectangular finger grating with metallization η, in the limit η→1 becomes loaded with a thin metal layer for which the simplified boundary conditions allow an exact calculation of SAW velocity as a function of layer height. In this limit contributions to velocity shift of an arbitrary finger grating may be calculated by a multilayer program. Since this relies on modelling the IDT with a metal layer, only those second order contributions which are nonzero in the η→1 limit may be calculated by this method. The total solution for an arbitrary geometry must be obtained by other methods. Data for YZ LiNbO₃, 112° LiTaO₃, and ST X quartz are displayed. Also included is a discussion of the validity of the perturbative approach for these materials