Study of the noise reduction performance of acoustic enclosures with ultra-thin bending labyrinth metasurfaces

Abstract

This study proposes a bending labyrinth metasurface (BLM) that integrates an embedded aperture with bending channels. Adopting the thermal-viscous model and the transfer matrix method, a theoretical model for solving the absorption coefficient of the BLM unit was established. Adopting the complex frequency plane method (CFPM) and the principle of critical coupling, a 12-mm thick BLM unit was investigated and found to exhibit perfect absorption (absorption coefficient α > 0.95) specifically at a frequency of 562 Hz. Subsequently, to achieve low-frequency broadband noise reduction, the regulation principle of the sound absorption coefficient of the BLM unit was studied through multi-parameter variation. BLM units that can achieve perfect absorption at multiple discrete frequencies are proposed. Furthermore, to ensure the uniform discrete distribution of the perfect sound absorption frequency of the BLM unit, 12 BLM units were selected and coplanar connected in parallel to constitute panels with equal-height and variable-height BLMs. These panels exhibit highly efficient sound absorption within broadband ranges of 397–706 Hz and 307–706 Hz, respectively. Finally, five identical metasurface panels were bonded together to form a rectangular box-shaped acoustic enclosure, and the noise reduction performance of this enclosure was experimentally studied. The results indicate that within the frequency range of 200–1000 Hz, the average noise reduction improvements for acoustic enclosures with variable-height and equal-height BLMs are 8.3 and 8.2 dB, respectively, compared with the acoustic enclosure with a homogeneous double layer. The frequency range over which the noise reduction is improved matches the frequency range of efficient absorption of the BLM panels. This work provides both a theoretical reference and a practical guide for engineering applications for controlling low-frequency broadband noise in compact spaces.