Research and Design of Unequal Cavity Depth Structures for Porous Materials and Micro-perforated Plates

To overcome the frequency band limitations of a single material or structure, this paper proposes a parallel composite structure comprising micro-perforated plates and porous acoustic materials, thereby achieving optimized mid-to-high-frequency sound absorption performance through collaborative coupling of two distinct absorption mechanisms. Based on the Johnson–Champoux–Allard (JCA) model, the porous material’s parameters were fitted, and the validity of these parameters was verified via impedance tube measurements. Simulation results showed excellent agreement with experimental data across the 200–6000 Hz frequency range. For the parallel configuration with unequal cavity depths, a theoretical model was established using the electro-acoustic analogy method; through a folding design, the overall structural thickness was reduced from 70 mm to 50 mm, significantly improving space utilization. Parametric simulations of the acoustic absorption structure were conducted using COMSOL Multiphysics^®, and experimental validation was subsequently performed to verify the rationality of the design. Results demonstrate that the composite structure achieves a sound absorption coefficient exceeding 0.6 over the 520–4000 Hz band—fulfilling wideband absorption requirements. Notably, within the 1300–2500 Hz range, the coefficient reaches 0.8 or higher. The proposed composite structure thus offers a novel strategy for broadband noise control.