GAUSSIAN CURVATURE OF THE SLOWNESS SURFACE FOR PIEZOELECTRIC SURFACE-WAVES ON A CUBIC-CRYSTAL

The Gaussian curvature of the slowness surface for piezoelectric surface waves propagating on the Z-cut metal-coated surface of a semi-infinite cubic crystal (class 4̄3m or 23) is calculated. It is shown numerically that the points of zero curvature on the slowness surface correspond to the cusps in the wave surface. It is also shown analytically and numerically that these points correspond to the points satisfying ∂ε/∂cursive-theta sign=-1 on the ε-cursive-theta sign curve, where cursive-theta sign is the phase propagation angle and ε is the deviation angle, i.e., the angle which the phase velocity vector makes with the energy velocity vector.