Ultrathin arch-like labyrinthine acoustic metasurface for low-frequency sound absorption.

• An acoustic metasurface containing coplanar arch-like channels (ALC) is proposed. • The channel with nonuniform cross section can effectively lower the absorption peak frequency. • A unit with multiple different branches is introduced to achieve a wide absorption band. • Varying channel width enables to tailor the absorption band. In this study, a novel compact design for an acoustic metasurface containing coplanar arch-like channels (ALC) is proposed. The ALC is squeezed within a compact disk-shaped volume with a small thickness of 1/94th wavelength for absorbing undesired sound energy at low frequencies in limited-volume circumstances. An impedance-based analytical model is proposed and used for determining the absorption characteristics of arch-like channels with high accuracy. Compared with a uniform cross-section, varied channel widths can effectively lower the operating frequency. Furthermore, using multiple branches with different width arrangements can create a multi-peak absorption profile and effectively broaden the absorption bandwidth. The 3D printing technique is employed to fabricate test samples. The analytical and finite element predictions are verified by comparing those results with experimental measurements. The proposed structure has great potential for applications in noise abatement. [ABSTRACT FROM AUTHOR]