Multilayer structures for high-intensity sound energy absorption in low-frequency range

Although small-amplitude sound absorption problems have been comprehensively studied over the past decades, the high-intensity sound absorption problem in the low-frequency range remains unresolved. This paper is concerned with the design of a multilayer structure consisting of a main pore and hierarchical absorption layers to realize perfect absorption of high-intensity sound energy in the low-frequency range. The multilayer structure has enhanced energy dissipation ability in the high-intensity noise excitation environment due to vortex shed-ding in the sub-slits of the structure. An analytical model based on the equivalent fluid method is established for computing the nonlinear sound absorption coefficient of the structure. Effects of geometrical parameters on the sound absorption coefficient of the multilayer structure are investigated. It is found that under high-intensity sound excitation (e.g., 140 dB), the resistance of the multilayer structure grows along with the sound ampli-tude and renders a higher absorption coefficient, leading to great sound energy attenuation for high-intensity acoustic waves. The effective sound absorption coefficient of the designed structure is also studied by experi-ments based on an impedance tube. Noise reduction of a scaled-down payload fairing equipped with multilayer structures is investigated by experiments in a high-intensity sound pressure reverberation chamber in order to confirm the great noise control performance of the proposed structure. The results show that the sound pressure levels inside the fairing can be significantly suppressed by the multilayer structure in broadband, and the maximum reduction of the average sound pressure level is more than 17.5 dB.