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Sandwich structures are widely used in several fields because of their mechanical performance with low weight. In this paper, a sandwich panel made of a core and a top and a back panel is investigated using the finite element method. The core consists of 33 hexagonal cells and each cell is connected to a micro-perforation. To improve the sound absorption, inhomogeneous micro-perforations are considered within the top panel. It is shown that with homogenous micro-perforations made of the same diameter, the sound absorption coefficient presents only one resonant peak. When 2, 3, and 6 different sets of micro-perforation diameters are considered, the sound absorption coefficient presents, respectively, 2, 3, and 6 resonance peaks where the surface impedance is close to that of the air. When each micro-perforation diameter is different resulting in inhomogeneous distribution of micro-perforations within the top panel, the sound absorption frequency band is widened and the absorption coefficient value increases while without micro-perforations the absorption coefficient of the sandwich panel is zero over the entire frequency range. The studied structure can offer high mechanical stiffness and good sound absorption performance.
Laly et al. (Fri,) studied this question.