Acoustic extreme asymmetry with a passive <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="script">P</mi><mi mathvariant="script">T</mi></mrow></math>-symmetric metasurface

Fangfang Ju; Bogang Huang; Xin Wang; Ye Tian; Shibei Xue; Shengyou Qian; Xiaojun Liu

doi:10.1103/s9km-73gf

Acoustic extreme asymmetry with a passive $P T$ -symmetric metasurface

Fangfang Ju ¹, Bogang Huang¹, Xin Wang¹, Ye Tian², Shibei Xue ³, Shengyou Qian^1,*, and Xiaojun Liu ^4,†

¹School of Physics and Electronics, Hunan Normal University, Changsha 410081, China
²School of Physics and Information Technology, Shaanxi Normal University, Xi’an 710062, China
³Department of Automation, Shanghai Jiao Tong University, Shanghai 200240, China
⁴Institute of Acoustics, Department of Physics, Nanjing University, Nanjing 210093, China

^*Contact author: syqian@hunnu.edu.cn
^†Contact author: liuxiaojun@nju.edu.cn

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Phys. Rev. Applied 25, 044020 – Published 8 April, 2026

DOI: https://doi.org/10.1103/s9km-73gf

Abstract

In this article, we propose a passive parity-time ( $P T$ )-symmetric metasurface mirror composed of only a lossy stepped waveguide per period, exhibiting perfect retroflection for positive incidence (PI) but perfect absorption for negative incidence (NI) at the exceptional point. The mechanism underlying the extreme asymmetry is the unilateral excitation of the evanescent wave and the waveguide mode. In addition, by combining two pieces of the established passive $P T$ -symmetric metasurface mirrors, the incident wave for NI absorbed by one of the established passive $P T$ -symmetric metasurface mirrors can be recovered by the other. Thus, a passive $P T$ -symmetric metasurface with balanced “loss” and “gain” is constructed, exhibiting perfect retroflection for PI but perfect transmission for NI. This work extensively simplifies the design of the $P T$ -symmetric metasurface, and may stimulate the development of asymmetric response engineering in compact acoustic devices.

Physical Review Applied

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Acoustic extreme asymmetry with a passive PT-symmetric metasurface

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Acoustic extreme asymmetry with a passive $P T$ -symmetric metasurface