Structure design and experimental research on underwater micro-perforated absorbers

Based on the theory of micro-perforated panel (MPP) by academician MAA Dah-You,an underwater micro-perforated absorber was built by adding a micro-perforated panel in the cavity of sandwich composite structure.According to the general theory of micro-perforated panel and the peculiarity of underwater acoustic stealth structures, the structure of underwater micro-perforated panel of under water absorber were designed,by considering the effect of cavity depth,panel thickness,perforated diameter and rate.The absorption coefficient of specimens of underwater micro-perforated absorbers was studied by a pulse tube experimental system.The results showed that the low frequency band was broaden by adding a micro-perforated panel,and the influence of panel parameters suited to the result of theoretical analysis.The experimental results also showed that the cavity number,shape and resonant characters,of the underwater micro-perforated absorbers with several absorption mechanisms,were as well as important factors of absorption properties.So the matching designing in the engineering application must be done according to the concerned frequency band.