Derivation of COM equations for the SAW IDT

Abstract

A general approach for the consistent derivation of coupling-of-modes (COM) equations for an IDT with electrodes of finite thickness is proposed. This approach is based on the surface impedance method and the exact analytic solution of the electrostatic problem in the presence of an arbitrary external electric field. Firstly, the scalar self-consistent equation for the electric potential of the acoustic waves in the arbitrary gratings of electrodes is obtained. For the periodic structure this equation is reduced to the form of COM equations for slowly varying amplitudes. These equations include naturally the NSPUDT effect description. The dissipation and storage energy terms may be introduced empirically. The solution of the COM equations is represented in the form of a P-matrix with elements written in a convenient form. The relations among the elements of the P-matrix are found. A simple formula for calculating the location of maximum transducer frequency response is proposed