"Fast" quasilongitudinal sagittally polarized surface waves in layer-substrate structures

The propagation of surface sagittally polarized waves on the plated surface of a semi-infinite medium with the phase velocity exceeding that of bulk quasitransverse sagittally polarized waves in the substrate is studied analytically and numerically. Such a surface wave is shown to exist in nonpiezoelectric and piezoelectric composites provided both the sagittal plane and the interface are planes of elastic symmetry of the layer and substrate. In the case of a nonpiezoelectric structure, the "fast" surface wave is one-component, involving only the quasi-longitudinal nonuniform mode in the substrate. In piezoelectrics this wave is two-component and incorporates the quasilongitudinal mode and the mode of electrical potential in the substrate. The "fast" wave exists at definite values of the velocity nuF and the layer thickness/wavelength ratio (h/lambda)F. It has been found that one or two surface waves can arise for the same direction of propagation at different nuF and (h/lambda)F, in the case of two surface solutions, both the values of (h/lambda)F being small. The approximate expressions are derived which allow one to elucidate whether the structure under consideration can support the "fast" surface wave and to estimate the corresponding nuF and (h/lambda)F. A comparison is performed of numerical and analytical results.