Piezoelectric interfacial waves in directions of vanishing slowness curvature

Abstract

Piezoelectric interfacial waves can propagate in a piezoelectric body along the conducting plane embedded in it (that is, at the bonding of two metallized pieces of a crystal); its velocity is close to one of the shear bulk waves. The wave-field penetration depth depends on the shear wave slowness curvature. At investigated propagation directions of vanishing curvature, the wave decays at about two or more wavelengths. There are only a handful of such points in investigated crystals: 12 distinct ones in quartz and 6 in lithium niobate. They are analyzed applying Stroh formalism (the case of fourfold defective matrix), and using the recently developed ‘‘papal’’ approximation to the planar harmonic Green’s function. In almost all cases, the approximation evaluated at a given wave number is accurate enough for application in a sufficiently wide wave number domain. This is beneficial for physical interpretation of numerical results. (The method can also be adopted for analysis of Rayleigh and pseudo surface waves in anisotropic crystals.) Possible applications of the investigated waves include: (a) low-temperature investigations of materials or superconducting layers (propagating inside the crystal, the wave is well protected from an adverse environment), (b) validation of material constants, and (c) in surface acoustic wave devices.