Ultra-broadband acoustic absorption with inhomogeneous high-order Fabry-Pérot resonances

We present an ultra-broadband acoustic metamaterial with inhomogeneous high-order Fabry-Perot (FP) resonances that achieves near-perfect continuous absorption in the range of 400-10000 Hz. The unit is composed of multiple FP channels with inhomogeneous cross-sectional areas, allowing for flexible adjustment of the impedance characteristics of each channel. This approach prevents the high-order peaks' resistances from increasing rapidly and ensures a smooth resistance characteristic across a broad frequency range. As a result, the absorption performance in the high-frequency range above 3000 Hz can be significantly enhanced, eliminating the need for conventional porous materials. The inhomogeneous high-order absorption mechanism is investigated thoroughly by theoretical calculations and finite element simulations. By critically coupling the FP channels, a 27-cell broadband metamaterial is obtained with an average absorption coefficient above 90% over 400-10000 Hz, which is verified by experiments in a square impedance tube and an alpha-cabin reverberation room, respectively. Characterized by its extraordinary performance and easy-fabricated structure, this metamaterial has great potential in noise control engineering applications, especially in environments with low temperature, high humidity, or significant dustiness.(c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/).