Resonator exhibiting uniform motional output

An ultrasonic resonator of generally rectangular cross-section dimensioned to operate as a half wavelength resonator at a predetermined frequency of sound travelling longitudinally therethrough from an input surface to an oppositely disposed output surface and through a medially disposed nodal region and including a pair of laterally spaced longitudinal slots disposed in said resonator and extending generally from a region near said input surface to a region near said output surface and passing through said nodal region for interrupting Poisson couplings, and including means for applying vibrations of predetermined frequency at a central portion of said input surface, the improvement comprising:

• a respective pad disposed at the lateral portions of said input surface for increasing the mass of said resonator at said lateral portions with respect to the central portion of said resonator for achieving substantially uniform motional amplitude along the output surface of the resonator.