Acoustic absorption properties of a composite structure of stepped micro-perforated plates with double-layer foam metal

A novel composite sound-absorbing structure comprising a micro-perforated plate (MPP) combined with double-layer foam metal (MPDF) is proposed in this study. Theoretical analysis and numerical simulations were employed to predict the sound absorption coefficients of the structure, and experimental validation was conducted to verify the accuracy of the results. The MPDF exhibits an effective absorption bandwidth spanning 560 ~ 2395 Hz, demonstrating significant superiority over homogeneous foam metal and conventional MPP structures. To further broaden the absorption bandwidth, a stepped configuration of the MPP with double-layer foam metal (SMPDF) was developed. The SMPDF achieves three distinct absorption peaks at 880 Hz, 1660 Hz, and 2720 Hz, with corresponding absorption coefficients of 0.77, 0.87, and 0.92, respectively. Its effective absorption bandwidth extends from 520 Hz to 3500 Hz, with an average absorption coefficient of 0.71 across the 0 ~ 3500 Hz frequency range. The sound absorption mechanisms were investigated through analysis of acoustic pressure and energy dissipation distributions, clarifying the origin of the absorption peaks. Furthermore, parametric studies reveal that the rear cavity depth of the MPP significantly affects the absorption bandwidth, while the thickness of the metal foam primarily influences the amplitude and frequency of the absorption peaks, and the thickness of the rear cavity behind the foam metal governs the first absorption peak.