SURFACE ACOUSTIC WAVES IN LAYER - SUBSTRATE STRUCTURES OF ARBITRARY ANISOTROPY

The existence of surface acoustic waves in a semi-infinite substrate with a solid layer is theoretically investigated. The substrate and the layer are not piezoelectrics, but can belong to any class of crystallographic symmetry. By presenting the dispersion equation as a condition on the substrate and layer impedance matrices, it is possible to determine, using the properties of impedances, the maximum allowable number of surface waves depending on the type of contact and the ratio between the velocities of the bulk waves in the substrate and the layer materials. In addition, a dispersion equation is derived for the symmetrical orientation of an orthorhombic substrate with a deposited monoatomic layer and the possibility of a purely flexure surface acoustic wave in the case of a very hard surface layer, for example, a monolayer of graphene on a soft polymer substrate, is shown.