Sound directivity by PT-symmetric acoustic dipoles

Abstract

The new physics of open-dissipative, non-Hermitian systems have become a fruitful playground to uncover novel physical phenomena, even in exotic or counterintuitive ways, especially in optics and, more recently, also in acoustics. In this work, we propose a non-Hermitian metasystem in acoustics for the control of the sound field in two dimensions. The building blocks, or meta-atoms composing the arrangements, are pairs of identical Helmholtz resonators with different gain or loss functions. Such Helmholtz resonator dipoles may be designed to hold asymmetric scattering, as was theoretically analyzed and experimentally confirmed. Furthermore, aiming to create a complicated directivity, we explored different ensembles of Helmholtz resonator dipoles and numerically demonstrated a sound concentration with various configurations. The proposed non-Hermitian parity-time- symmetric dipoles made of a pair of Helmholtz resonators may be a potential artificial element for the creation of complex sound fields.