A tunable acoustic coil structure coupled with porous material linings for customized perfect absorption

Achieving continuous high absorption at low frequencies remains a persistent challenge in acoustics. Conventional sound-absorbing structures struggle to mitigate low-frequency noise within limited spatial constraints. To address this, we propose an acoustic metasurface based on coupled acoustic coils, which is capable of customized absorption bandwidth performance in the low-frequency range. Each acoustic coil incorporates porous material linings on its inner walls, whose thickness can be tuned to precisely modulate damping properties, resulting in perfect absorption. By arranging multiple coils in parallel, the metasurface generates continuous absorption peaks across low frequencies, and the parameters such as the truncation ratio enable precise band customization. A theoretical model grounded in double porosity theory is established to analyze the acoustic performance of the proposed metasurface. The complex frequency plane analysis method is employed to characterize the system damping behavior. Results demonstrate that adjusting the thickness of the porous linings can readily induce critical damping behavior and perfect absorption. Parametric studies of entrance length and truncation ratio confirm the exceptional tunability of the coils. This leads to a coupled absorber achieving near-perfect absorption α>0.9 at frequencies as low as 295–355 and 229–264 Hz with a compact thickness of 45 mm. The proposed structure and its design methodology are expected to advance the development of acoustic metasurfaces.