Considerations on coupling-of-modes equations for shear horizontal type SAW

Shear horizontal type (SH-type) SAW on an interdigital transducer has the characteristics, back-scattering bulk radiation, and frequency-dependence of the electromechanical coupling, due to interaction with SH-bulk wave. Therefore, it cannot be appropriately expressed by the conventional COM equations. Plessky successfully derived simple COM equations to represent the dispersion characteristics of shear horizontal type SAW. These equations had not included transduction terms and an equation of busbar current. In this paper, by applying an energy conservation law which considered mode profile in the depth direction, Plessky´s COM equations are extended to include excitation and detection. An admittance of an infinitely long periodic transducer derived from the extended COM equations is in agreement with the Koskela´s admittance formula without inconsistency.