A compact, high-absorption bending labyrinth metasurface for blade passing noise control

Abstract Air-cooled systems are widely used in equipment that requires effective thermal management, including computers and workstations. While removing heat, the spinning fans in these systems also introduce extra noise. This noise is mainly concentrated at the fan blade-passing frequency and its harmonics, resulting in low-frequency, narrowband noise. Accordingly, effective noise reduction can be achieved by selective absorption at these discrete frequencies. To fix this issue, we introduce a bi-frequency bending labyrinth metasurface (BiBLM) that combines four L-shaped folded BLM units with a single square-folded unit in a compact arrangement. An acoustoelectric circuit model was then developed to evaluate its absorption performance. Based on this model, the Non-dominated Sorting Genetic Algorithm (NSGA-II) was employed to optimize the geometric parameters to balance compactness and absorption performance. Finite Element Analysis (FEA) further reveals that the dual absorption bands originate from cooperative interactions among the constituent units. To validate the optimized design, impedance tube measurements were conducted, giving absorption coefficients of 0.916 at 410.2 Hz and 0.956 at 820.3 Hz. In practical application tests on a reinforced computer within the anechoic chamber, BiBLM achieved noise reductions of 4.42 dB(A) and 10.04 dB(A) at the targeted frequencies. The compactness, strong acoustic performance, and straightforward fabrication make it a promising option for engineering applications.