Nonreciprocal Elastic Wave Beaming in Dynamic Phased Arrays

Abstract

Beam forming using phased arrays forms the basis of several sonar communication and biomedical imaging techniques. However, to date, such arrays remain constrained by wave reciprocity in addition to being confined to their operational frequency; two limitations that have severely hindered imaginative advancements in this domain. In the context of sound propagation, nonreciprocity typically refers to unidirectional elastic and surface acoustic wave devices. However, a breakage of reciprocity in phased arrays manifests itself in reception and transmission patterns, which can be independently tuned, which has thus far been elusive. This work reports on a class of nonreciprocal phased arrays, which operate independently and simultaneously within different directions and frequency channels, thus breaking transmission-reception symmetry and offering enhanced capabilities in guided wave engineering. The system comprises an array of transceiving piezoelectric wafer discs bonded to an elastic medium and incorporates a prescribed dynamic modulation on top of a static phase gradient, which enables concurrent phononic transitions in energy and momentum spaces that mitigate the constraints imposed by Lorentz reciprocity. Following the theory and predictive analysis, the entire array and its associated capabilities are demonstrated experimentally.