Broadband Near-Perfect Absorption at Low Frequencies by Coupling Coiled-up Structures

Broadband sound absorption in the low-frequency range remains a significant challenge in acoustics. Traditional sound-absorbing structures are constrained by bulky volumes, while acoustic metamaterials often involve complicated structural designs. In this work, we propose an acoustic metasurface by coupling multiple coiled-up structures, in order to achieve broadband near-perfect absorption in the low-frequency range. Capitalizing on complex frequency plane analysis, each coiled-up unit is tuned to critical damping, enabling perfect sound absorption. Through an interleaved arrangement of four coiled-up units with distinct parameters, the proposed metasurface achieves near-perfect absorption α>0.9 within 261~372 Hz. The total thickness of the structure is 50 mm, corresponding to 1/26 of the wavelength at the lowest absorption frequency. Theoretical and simulated results confirm that sound waves at respective resonant frequencies can be captured and dissipated by the corresponding coiled-up units. Impedance tube experiments validate the accuracy of the adopted methodology, and demonstrate the potential of this metasurface for practical acoustic applications.