Ultra-ventilated sound-absorbing lamina metamaterial via nonlocal coherent coupling of weakly resonant folded-loop-neck Helmholtz resonators

Abstract Conventional acoustic metamaterials often struggle to simultaneously achieve efficient ventilation, heat dissipation, and noise reduction. To address this, an ultra-ventilated sound-absorbing lamina metamaterial (LMM) constructed from unique folded-loop-neck Helmholtz resonator unit cells is proposed. Benefiting from the nonlocal coherent coupling among ultrathin weakly resonant unit cells (resonators with low absorption coefficients), the LMM effectively suppresses anti-resonance and overcomes the typical absorption dips within the absorption band that arise from the coupling of conventional strong-resonance structural units. The lamina has a thickness of only 39.8 mm (with a ventilation area ratio of 73%), and experiments demonstrate excellent ventilation performance with a wind velocity ratio of 0.90. Meanwhile, it achieves broadband, high-efficiency sound absorption under grazing incidence of sound waves, with experimentally measured absorption coefficients exceeding 0.9 over the frequency range of 542–653 Hz. This work represents a new breakthrough in metamaterial design for achieving broadband and highly efficient sound absorption under the constraint of ultra-ventilated performance.