Non-Hermitian Acoustic Metamaterials: the role of Exceptional Points in sound absorption

TL;DR

This paper explores how non-Hermitian acoustic metamaterials, utilizing PT-symmetry and exceptional points, can be engineered to achieve enhanced and broadband sound absorption, offering new mechanisms for acoustic control.

Contribution

It introduces a framework using effective non-Hermitian Hamiltonians to design acoustic metamaterials with tunable absorption properties based on exceptional points and PT-symmetry.

Findings

Perfect absorption at multiple frequencies via PT-symmetry

Broadband absorption at exceptional points

Enhanced absorption using gain in acoustic systems

Abstract

Effective non-Hermitian Hamiltonians are obtained to describe coherent perfect absorbing and lasing boundary conditions. PT -symmetry of the Hamiltonians enables to design configurations which perfectly absorb at multiple frequencies. Broadened and flat perfect absorption is predicted at the exceptional point of PT -symmetry breaking while, for a particular case, absorption is enhanced with the use of gain. The aforementioned phenomena are illustrated for acoustic scattering through Helmholtz resonators revealing how tailoring the non-Hermiticity of acoustic metamaterials leads to novel mechanisms for enhanced absorption.