An impedance-decoupled tube-bundle metamaterial with porous lining for deep-subwavelength broadband low-frequency absorption

This paper proposes a novel embedded tube-bundle panel with porous lining acoustic metamaterial for high-efficiency broadband sound absorption in the sub-500 Hz regime at deep-subwavelength scales. A physics-informed analytical model based on double-porosity theory and the transfer-matrix method is developed and validated through finite element simulations. An impedance decoupling strategy is introduced to independently regulate acoustic resistance and reactance by tuning the geometric parameters of the tube bundles under a constant panel perforation ratio, thereby enabling flexible control of both the resonance frequency and absorption bandwidth. The effects of tube diameter, tube length, porous lining thickness, and the static flow resistivity of the porous material on sound absorption performance are systematically investigated. The results show that the tube bundles modulate low-frequency resonance to localize acoustic energy, while the porous-lined back cavity provides dominant dissipation; their synergistic resonance–dissipation mechanism leads to efficient broadband absorption. Using the proposed impedance decoupling strategy, a parallel multi-unit absorber with a total thickness of only 50 mm (1/26 of the wavelength) is constructed and experimentally validated. The absorber achieves continuous high-efficiency absorption, with an average coefficient of 0.941 over 259–480 Hz (α > 0.9). This work provides a physics-informed and scalable design framework for compact and tunable acoustic metamaterials targeting broadband low-frequency noise control.