Dynamic energy dissipation and wave attenuation mechanisms in bio-inspired series-parallel coupled metastructures

Controlling broadband wave propagation and achieving efficient dynamic energy dissipation within spatially confined structures remains a fundamental challenge in structural dynamics and solid mechanics. Inspired by the multi-scale hierarchical topology of natural banana stems (concentric layered leaf sheaths and internal parenchyma cellular tissue), this study investigates the dynamic energy dissipation mechanisms of a novel bio-inspired Sandwich Honeycomb-core Network Acoustic Metamaterial (SHNAM). The proposed metastructure establishes a hybrid energy dissipation paradigm by integrating cascaded micro-perforated panels (series coupling) with hierarchical nested network cavities (parallel coupling), facilitating continuous, ultra-broadband acoustic impedance matching. A rigorous theoretical model based on the acoustic-electrical analogy is developed to formulate the multi-modal acoustic response, which is systematically validated through thermoviscous acoustic finite element simulations and impedance tube experiments on SLA 3D-printed specimens. The theoretical and experimental results demonstrate that this hybrid series-parallel coupling significantly suppresses the deep absorption valleys inherent in pure parallel configurations. Operating within a strict sub-wavelength regime, the proposed metastructure achieves a high average absorption coefficient of 0.71, a half-absorption bandwidth proportion of 74%, and a high-efficiency absorption bandwidth proportion (α ≥ 0.8) of 65% across the targeted 0-4 kHz spectrum. Furthermore, comprehensive analyses elucidate the frequency-dependent spatial energy allocation and the multi-modal resonance behaviors driven by hierarchical scaling effects. By uncovering the dynamic synergy between multi-scale geometries and acoustic wave control, this study provides a new theoretical framework and a physically predictable metastructure solution for advanced broadband noise attenuation covering the low-frequency spectrum.