Effects of Piezoelectric Coupling on Bechmann's number for thickness-twish waves in a plate of hexagonal crystals

Solutions for thickness-twist waves in a piezoelectric plate of 6-mm crystals with surface mass layers are obtained. The solutions are used to determine Bechmann's number for designing electrode size of devices operating with these waves. This generalizes the existing knowledge on Bechmann's number by the inclusion of piezoelectric coupling. It is shown that this coupling plays a role as important as or more important than the electrode inertia. The results are of fundamental importance to resonator design, in particular thin film resonators of ZnO and AlN