Multi-scale acoustic metamaterial for low-frequency broadband sound insulation

• The proposed multi-scale acoustic metamaterial enables low-frequency broadband sound insulation. • Excellent frequency and amplitude tunability in the low-frequency range is achieved via the introduction of particles. • The multi-scale energy dissipation mechanism of macroscopic locally resonant units and microscopic particles is revealed. • Diffuse field experimental measurements on large-scale structures validate the feasibility of engineering applications. Multi-scale design of metamaterials can effectively enhance their acoustic performance without sacrificing structural dimensions, which has been validated in the design of vibration and sound absorption structures. Based on this, this study constructs a multi-scale acoustic metamaterial (MSAM) for low-frequency broadband sound insulation by using a double-layer thin-plate-type locally resonant acoustic metamaterial as the carrier and replacing homogeneous masses with particle-filled masses in locally resonant units. By leveraging the resonance and anti-resonance effects of macroscopic locally resonant units, together with the mass and damping effects introduced by microscopic particles, MSAM can achieve multi-scale energy dissipation, effectively improving the low-frequency sound insulation performance of thin-plate-type acoustic metamaterials. Meanwhile, the in-plane non-uniform distribution broadens the working frequency band. The research on MSAM shows that the introduction of particles introduces additional design parameters for thin-plate-type acoustic metamaterials. By adjusting the particle filling ratio, the mass and damping effects of MSAM can be modulated, enabling excellent frequency and amplitude tunability in the low-frequency range. Experimental measurements on large-scale structures validate the engineering feasibility of MSAM. Owing to its thin thickness, low surface mass density, good structural stability, and excellent low-frequency broadband sound insulation performance, MSAM has promising applications in practical noise control engineering.