The self-collimation effect induced by non-Hermitian acoustic systems

Abstract

With the proposal of the concept of parity-time-symmetry, more and more exotic properties are being unearthed in non-Hermitian systems. In this work, we investigate the related acoustic feature and phenomenon in two-dimensional phononic crystals with a complex modulus by introducing the balanced loss and gain. Different from Hermitian properties, partial band degeneracy has occurred in the dispersion diagram, leading to higher density of states, and self-collimated wave propagation has been predicted at the merged frequency. More importantly, the input locations of the point source have a significant impact not only on the direction of self-collimation waves but also on the intensity profiles of the pressure field, which is not achieved in self-collimation of Hermitian systems. We also propose a digital single-pole double-throw switch, which corresponds to two special self-collimating situations. Our finding provides an effective approach for controlling the wave direction and designing more digital acoustic functional devices in non-Hermitian systems.