Low-frequency broadband acoustic absorption characteristics of honeycomb-type gradient perforated porous acoustic metamaterials paired with embedded necks

Conventional acoustic structures struggle to achieve a balance between low-frequency and broadband absorption while preserving structural compactness at frequencies below 500 Hz. In this paper, a novel honeycomb-type gradient perforated porous acoustic metamaterial paired with an embedded neck is proposed. An analytical model of the sound absorption coefficient of metamaterials is developed based on the homogenized equivalent method, with a comparison between finite elements and experimental results. The results indicate that a new energy compensation mechanism is discovered in this structure: the porous material with gradual perforation replaces the neck as the main dissipation source, which greatly increases the tunable acoustic absorption of the metamaterial. In addition, the proposed metamaterial achieves excellent acoustic absorption at low frequency 265 Hz with a relative absorption bandwidth of 58.5 % while maintaining a compact structure thickness of just 52 mm. Compared with the perforated plate structure, the embedded neck design reduces the thickness of the metamaterial structure by 21.2 %. The acoustic absorption coefficient α > 0.9 within the frequency range of 268 Hz to 473 Hz was achieved through the connection of seven cells in parallel. The acoustic metamaterials presented in this paper provide an innovative solution for low-frequency noise control on the sub-wavelength scale.