Hierarchical Tri-Hex re-entrant honeycomb acoustic metamaterial for enhanced low-frequency sound absorption

To address the shortcomings of conventional honeycomb sandwich structures in low-frequency sound absorption, a hierarchical Tri-hex re-entrant honeycomb (ThrH) acoustic metamaterial was developed. Its acoustic performance was comprehensively investigated through theoretical analysis, experimental validation, and numerical simulations. A comprehensive investigation of its acoustic properties was conducted through theoretical analysis, experimental validation, and numerical simulations. Parametric studies revealed that when the micropore diameter is set to 0.7, 1.0, and 1.2 mm, the resonance peak of the Tri-hex re-entrant honeycomb shifts downward by approximately 190, 330, and 380 Hz, respectively. Furthermore, reducing the micropore–wall contact configuration from three-side contact to no contact resulted in a 33.6% increase in the resonance frequency. Comparative studies confirm that, under identical macroscopic geometric parameters, the proposed re-entrant design substantially enhances mid- and low-frequency sound absorption relative to conventional honeycomb-based structures.