Ultralight micro-perforated sandwich panel with double-layer hierarchical square honeycomb core for broadband sound absorption

The micro-perforated panel (MPP) has only one sound absorption peak, and the sound absorption performance is poor in the wide frequency range. Besides, the stiffness and strength of MPP are insufficient, so it can not bear the external load. In this study, double layers of hierarchical square honeycomb are placed within the air-back cavity of MPP to produce a sandwich structure. On the one hand, hierarchical honeycombs divide the air-back cavity into several sub-cavities. The perforations on the panel together with the sub-cavities form a series-parallel system of Helmholtz resonators. The sound absorption curve of the structure has multiple peaks and the half-absorption bandwidth is extensively widened. On the other hand, the hierarchical honeycomb with excellent load-bearing properties can strongly support the MPP to resist external loads. This new structure possesses both sound absorption and load bearing capabilities, and has practical application value in the noise reduction of high-speed trains and civil aircraft. Through theoretical and simulation analysis, the sound absorption performance of the structure is systematically studied and the influence of key parameters is quantified, providing guidance for the design of noise reduction materials.