Abstract
Piezoelectric semiconductors such as cadmium sulfide exhibit a strong coupling between conduction electrons that are present in the substance and acoustic waves that are propagated along certain directions in the material. This energy exchange mechanism is highly nonlinear, and thus the simultaneous introduction of several collinear acoustic waves into the substance generates new signals at the conbination (sum and difference) frequencies. A theoretical explanation of this interaction mechanism, based on consideration of the nonlinear cross term present in the current-density equation, has been developed, and the validity of this method of analysis has been tested and qualitatively confirmed through experimentation.