Tunable Asymmetric Acoustic Absorption in Ventilated Metasurfaces

TL;DR

This paper introduces a tunable asymmetric ventilated acoustic system using coupled resonators, achieving high absorption and reflection asymmetry, with adjustable properties via simple rotation, suitable for broadband applications.

Contribution

It presents a novel, tunable asymmetric acoustic metasurface with coupled resonators that allows for adjustable absorption and reflection properties through simple rotation.

Findings

Achieves 99% absorption for left-incident waves and 98% reflection for right-incident waves.

Rotation of the resonator causes an 11 dB attenuation, functioning as an acoustic switch.

Broadband absorption from 325 to 375 Hz exceeding 0.8 efficiency.

Abstract

Asymmetric sound absorption is essential for advanced acoustic manipulation. However, current frequency modulation and broadbanding highly depend on geometric reconfiguration, leading to inevitable structural complexity that impedes their practical applications. Here, we propose a tunable, highly efficient, asymmetric ventilated acoustic system comprising two heterogeneous resonators. Specifically, it couples a highly dissipative space-coiling resonator (SCR) as a dark mode for energy consumption, alongside a weakly damped Helmholtz resonator as a bright mode acting as a reflective soft boundary. Theoretical and numerical analyses reveal strong asymmetry within the deep-subwavelength region (with a resonator size of approximately \lambda/9.4), achieving 99% absorption for left-incident waves and 98% reflection for right-incident ones. Furthermore, the SCR introduces an interesting degree of freedom for acoustic tuning. Simply rotating the resonator induces a 92% absorption drop (~11 dB attenuation), functioning as an "Acoustic Switch". Moreover, this rotation significantly shifts the operating band. By parallel-coupling multi-angle isomorphic resonators, we achieve efficient broadband absorption (>0.8) from 325 to 375 Hz, offering an attractive paradigm for tunable acoustic metasurfaces and ventilated absorbers.