Propagation of Surface Waves at the Boundary Between a Piezoelectric Crystal and a Fluid Medium

The propagation of surface waves at the boundary between a piezoelectric crystal and an ideal fluid is investigated. The effect of the fluid on the character of the waves is studied and it is found that for the particular examples considered, propagating waves take the form of leaky waves transfering energy to the fluid medium. The numerical solution for the complex leaky wave velocity is obtained by two methods. One is a straightforward solution of the complex characteristic equation for the velocity; the other is a perturbation scheme that treats the leaky wave as a first-order perturbation on the nonleaky wave associated with surface-wave propagation when the mechanical properties of the fluid are neglected. Comparison of the two methods reveals that the perturbation procedure is very accurate over a broad range of fluid parameters. As an example, the leaky wave phase velocity and attenuation are obtained as functions of direction of propagation on X, Y, and Z cuts of lithium niobate.