Propagation of gap waves between two functionally graded piezoelectric half-spaces

We analyze the propagation of gap waves between two half-spaces of functionally graded piezoelectric materials (FGPM). The material properties of the half-spaces vary in the direction perpendicular to their surfaces. It is found that there exist waves that can propagate in the gap and near the surfaces of the half-spaces. The speed of these waves is sensitive to the thickness of the gap and the material property variation of the FGPM.