Broadband ventilated sound insulation based on acoustic consecutive multiple Fano resonances

Recently, with advances in acoustic metamaterial, the Fano resonance has been widely introduced into the field of noise reduction for simultaneous airborne soundproofing and airflow permeability. The conventional Fano-based mechanism, manifesting as an ultrasharp spectrum, just serves a narrow working-frequency range, which deviates from the demands of broadband sound insulation. Here, we theoretically present and experimentally demonstrate the concept of acoustic consecutive multiple Fano resonances (ACMFRs), unlocking an unprecedented soundproof bandwidth (80%) while maintaining highly efficient ventilation. We first develop an analytical model to analyze the transmission spectra of ACMFRs in the bilayer metamaterial. Owing to the superposition of multiorder Fano resonance modes, the response strength from the discrete and continuum states of ACMFRs remains quasibalanced over a broad frequency range, which can be further interpreted by a consecutive single-negative nature. Subsequently, we implement this concept with an ultraopen helical metamaterial, which yields broadband sound attenuation at 770--1768 Hz and high air permeability (90%) simultaneously. The experimental results coincide with both theoretical and numerical ones, validating the effectiveness of the proposed ACMFRs. Our work lays the groundwork for the next generation of Fano-based metamaterial applications, with far-reaching implications for noise control and related fields.