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Description
Broadband, low to mid-frequency sound absorption with thin, compact structures presents a significant challenge in acoustical engineering. This work presents a novel acoustic metasurface based on weakly coupled parallel Helmholtz resonators (HRs). The design begins with an optimized dual-cavity HR unit, where a small inter-cavity perforation bridges two resonance peaks to create a continuous absorption band. By extending this principle to a network of several cavities interconnected via carefully designed perforations, multiple overlapping resonance modes can be created, effectively covering a continuous and wider frequency range. This scaled-up weak-coupling network allows for superior impedance matching across a broader spectrum, maintaining the near-optimal condition where dimensionless reactance approaches zero, and resistance approaches unity over an expanded interval. Based on this mechanism, a nine-HRs acoustic metamaterial unit cell (four perforated pairs and one single resonator), achieving an average absorption coefficient of 0.82 between 750 Hz to 3000 Hz, with individual peaks above 0.9. By coupling five such unit cells, a mixed multi-cavity parallel-arranged HRs based acoustic metasurface is realized, attaining an average absorption of 0.87 from 650 Hz to 3000 Hz with only 57 mm total thickness. The design was optimized via finite element analysis (FEM), fabricated using Low-Force Stereolithography (LFS), and validated experimentally with an impedance tube based on the two-microphone method. Excellent agreement between simulation and measurement confirms the design's accuracy and robustness, demonstrating a compact, high-performance solution for practical noise-control applications.