Bidirectional acoustic negative refraction based on a pair of metasurfaces with both local and global PT-symmetries

TL;DR

This paper introduces a loss-free, bidirectional acoustic negative refraction system using a pair of PT-symmetric metasurfaces, overcoming traditional limitations of acoustic metamaterials in imaging and wave manipulation.

Contribution

It presents a novel PT-symmetric metasurface system that achieves loss-free, bidirectional negative refraction with switchable states between absorption and amplification.

Findings

Realizes loss-free bidirectional negative refraction

Achieves switching between CPA and amplifier states

Provides a new physical mechanism for bidirectional functions

Abstract

Negative refraction plays an important role in acoustic wave manipulation and imaging. However, conventional systems based on acoustic metamaterials suffer from the limits induced by loss-related and resolution issues. In this work, a parity-time (PT)-symmetric system is introduced to realize loss-free bidirectional acoustic negative refraction. The system is composed of a pair of locally PT-symmetric multi-layer metasurfaces sandwiching a region of free space, which also forms a global PT-symmetry. The property of bidirectional negative refraction, which is rare for regular PT-symmetric structures, is related to the coexistence of amplification and absorption in the locally PT-symmetric metasurfaces at their PT broken phases. Such metasurfaces can freely switch their states between coherent perfect absorber (CPA) and amplifier depending on the direction of incidence. Our results provide a new physical mechanism for realizing bidirectional functions in PT-symmetric systems.