SH-waves with zero energy-flux velocity in plate of superstrong piezoelectric KNbO3

The problem of the existence of pure-shear backward waves and zero-group velocity waves is studied for plates of X-cut and Y-cut potassium niobate. The last mentioned waves are promising for development of new acoustoelectronic devices of the hybrid class. The secular equations are derived in explicit analytical form and they are studied numerically. It is shown that the backward waves and waves with zero energy-flux velocity exist only in the X-cut plate. This is explained by the effect of concavity on the slowness surface for shear bulk waves in locality of the X axis of potassium niobate.