Transverse surface waves in functionally graded piezoelectric materials with exponential variation

For a functionally graded piezoelectric substrate with exponential variation, the existence and propagation behavior of transverse surface waves is studied by analytical technique. The dispersion equations for the existence of the transverse surface waves with respect to phase velocity are obtained for both electrically open and short conditions. A detailed investigation of the effect of gradient coefficient on dispersion relation, phase velocity, group velocity and electromechanical coupling factor is carried out. It is found by numerical examples that adjusting gradient coefficient makes the electromechanical coupling factor of the transverse surface waves achieve quite high values at some appropriate wavenumber, and at the same time, the penetration depth can be reduced to the same order as the wavelength under electrically short case. Because of the negligible initial stress in functionally graded piezoelectric materials, this model could serve as an excellent substitute for the typical layered piezoelectric structures used in surface acoustic wave (SAW) devices, thus providing a theoretical foundation for designing SAW devices with high performance.