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