A Sound‐Absorbing Metamaterial With Tree‐Inspired Bionic Helmholtz Resonators

Abstract To alleviate the cavity dependence of Helmholtz resonators, this work designs a Helmholtz resonator incorporating porous materials, cover plates, multilayer embedded necks, and cavities, inspired by the structural configuration of tree canopies, trunks, roots, and soil. The sound absorption characteristics and underlying physical mechanisms of the structure are elucidated through impedance matching theory and finite element simulations. The results demonstrate that the introduction of multilayer thin walls induces a velocity modulation phenomenon of sound waves at the necks, causing the surface acoustic impedance and energy dissipation characteristics of the Helmholtz resonator to vary with the number and arrangement of the thin walls. A sound‐absorbing acoustic metamaterial composed of tree‐inspired bionic Helmholtz resonators, along with two sound‐absorbing arrays composed of conventional Helmholtz resonators, is designed. Experimental results show good agreement with both theoretical predictions and simulation outcomes. Compared with the traditional Helmholtz resonator array, the proposed sound‐absorbing metamaterial achieves effective absorption within the range of 230–424 Hz, with a nearly 50% reduction in maximum neck length, thereby mitigating the constraint of cavity thickness on neck design and improving the scalability of low‐frequency sound absorption. This work provides a strategy for the design of deep subwavelength low‐frequency absorbers.