Low-frequency sound absorption enhancement in multi-layer honeycomb metamaterials with embedded long-curved-neck Helmholtz resonators

Abstract

<p>To overcome the narrow absorption bandwidth of conventional Helmholtz resonator-based acoustic metamaterials in the low-frequency range, this study proposes a multi-layer honeycomb acoustic metamaterial with embedded long-curved-neck Helmholtz resonators (ELCN-HR). A comprehensive methodology integrating theoretical analysis, numerical simulations, and experimental testing is employed to systematically investigate the modulation of resonance frequency by neck geometric parameters and the multi-resonance mode superposition mechanism induced by hierarchical coupling. The results show that the micro-perforation diameter contributes the most in all parameters. Furthermore, the elongated ELCN-HR design substantially reduces resonance frequencies while improving acoustic wave dissipation efficiency. Additionally, the multi-layered coupling architecture excites localized resonance peaks across adjacent frequency bands, facilitating continuous spectral coupling. Optimized simulations demonstrate that the proposed metamaterial achieves a half-absorption bandwidth of 448 Hz (285–733 Hz), representing a 32% enhancement compared to conventional single-layer Helmholtz coupled structures (340 Hz). Moreover, the onset frequency for α > 0.5 is reduced from 720 Hz to 285 Hz, significantly extending low-frequency absorption performance. Mechanistic analysis confirms that multi-scale acoustic impedance gradient matching plays a critical role in enhancing broadband energy dissipation. These findings provide a novel design paradigm for developing low-frequency broadband sound-absorbing metamaterials.</p>