Abstract
An exact approach is used to investigate the propagation of Bleustein-Gulyaev waves in a functionally graded piezoelectric substrate carrying a finite-thickness metal layer. The piezoelectric material is polarized in the direction perpendicular to the wave propagation plane and the material properties change gradually with the depth of the substrate. We here assume that all material properties of the substrate have the same exponential function distribution along the depth direction. The dispersion relation for the existence of the waves with respect to phase velocity is obtained analytically. The effects of the material gradient on the phase velocity and group velocity are discussed in detail. The displacement, electric potential, and stress distributions along the depth of the structure are calculated and plotted. Numerical examples show that the material gradient has a significant effect on the starting part of the wave mode and appropriate gradient distribution of the material properties can not only make the waves propagate along the surface but also decrease the interfacial stresses of the layered structure, which is in favor of designing acoustic wave devices with better performance. The existence condition of the waves at all values of wave number has also been obtained theoretically.
