A low-frequency sound absorbing material with subwavelength thickness

TLDR

This work aims to stimulate research and applications in low‑frequency sound absorption. The authors propose an efficient low‑frequency sound‑absorbing material. The material consists of two axially coupled, co‑planarly coiled tubes whose geometry is tuned to overlap their absorption curves, broadening the bandwidth, and its design is validated by 3D‑printed experiments. The design achieves an absorption coefficient above 0.8 over a 36‑Hz bandwidth centered near 100 Hz, with a wavelength‑to‑thickness ratio of 38.5.

Abstract

We propose a sound absorbing material efficient for low frequency. This material is mainly composed of two axially coupled tubes in series, which are co-planarly coiled in a plane perpendicular to incident waves. By carefully designing the geometric parameters of the coupled tubes, we can overlap the absorption coefficient curves of each individual tube and are therefore able to broaden the frequency bandwidth within which the absorption coefficient is larger than a designed value. A material with an absorption coefficient greater than 0.8 over a frequency bandwidth of 36 Hz for a low frequency of around 100 Hz can be designed, and the wavelength to thickness ratio reaches as high as 38.5. The experiment measurement with the sample made by the 3D printing technique is also conducted to validate the proposed design method. This work may stimulate the research studies on and applications for low frequency sound absorption.