Dynamic Nonreciprocity in Loss-Compensated Piezophononic Media

In controlling sound, it is not trivial to engineer a device that can strongly break the reciprocity (symmetry under time reversal) of acoustic wave propagation. Despite significant progress, it is still difficult to obtain a large contrast ratio between the allowed (passing) and forbidden propagation directions, over a broad frequency range, without distortion or attenuation of the signal in the passing direction. The authors propose an approach, based on the acousto-electric effect in piezoelectric semiconductors, that could achieve all of these goals for acoustic waves in elastic solids, to the benefit of noise control, energy harvesting, and transducer technology in general.