Acoustic Metal

TL;DR

This paper introduces 'acoustic metal', a novel material using resonator arrays with dissipative components that strongly interact with sound across wide frequencies, enabling noise blocking without airflow obstruction.

Contribution

It presents the design and realization of an acoustic metal that achieves strong sound coupling and noise blocking, a property previously absent in acoustic materials.

Findings

Achieved 99% noise reduction in an acoustic Faraday cage setup.

Demonstrated the volume requirement for acoustic metal based on causality.

Showed potential for high-performance audio device applications.

Abstract

Metal reflects electromagnetic waves because of the large conductivity that is responsible for dissipation. During which the waves undergo a 180$^\circ$ phase change that is independent of the frequency. There is no counterpart material for acoustic waves. Here we show that by using an array of acoustic resonators with a designed high-density dissipative component, an "acoustic metal" can be realised that strongly couples with sound over a wide frequency range not otherwise attainable by conventional means. In particular, we show the acoustic Faraday cage effect that when used as a ring covering an air duct, 99% of the noise can be blocked without impeding the airflow. We further delineate the underlying volume requirement for an acoustic metal based on the constraint of the causality principle. Our findings complement the missing properties of acoustic materials and pave the way to the strong wave-material couplings that are critical for the applications as high-performance audio devices.