Gradient distributed absorber for efficient broadband absorption and hierarchical dissipation

How to realize broadband sound absorption in microperforated plate (MPP) structure and reduce the thickness of the structure has been the focus of research. In this paper, a solution for broadband sound absorption and lightweight design of MPP is proposed. Based on the conventional MPP acoustic structure, the built-in double-layer and triple-layer gradient microperforated plates (DL-GMPP and TL-GMPP, collectively referred to as GMPP) were designed by gradient distribution of the multilayer MPP resonators. Compared to the conventional MPP acoustic structure, the configuration of gradient MPP resonators within the cavity facilitates the confinement of sound waves of different frequencies within discrete spatial domains. Thus, the spatial separation of different frequencies is realized. Furthermore, the structural parameters of TL-GMPP with different thicknesses were optimized through the application of the particle swarm optimization (PSO) algorithm. The results show that TL-GMPP is adequate to attain varying degrees of sound absorption, contingent on the total thickness of the structure. Finally, the experiments verified the accuracy of the theoretical model and the simulation prediction results. The results show that the absorption efficiencies of DL-GMPP and TL-GMPP with a thickness of 35 mm in the frequency range of 540–1600 Hz are greater than 73% and 80%, respectively, indicating superior broadband sound absorption performance.