Proposal of cheap microperforated panel absorbers manufactured by infiltration

Microperforated panels (MPPs) are tunable systems providing sound absorption in a couple of octaves frequency band. Their absorption curve can be reliably predicted by using well established models, such as the Maa and fluid equivalent models, which depend on the perforation diameter, the perforation ratio, and the panel and air gap thicknesses. However, while MPP absorbers can be soundly designed by these models, their widespread use in noise control applications is dissuaded due to their high manufacturing cost. MPPs usable in the frequency range of noise control applications require thousands of sub-millimetric holes which are usually done by a laser technology, this in turn resulting in a rather expensive absorption system. Here we propose a fabrication technique which significantly lowers the manufacturing cost of MPP absorbers. This technique consists of mixing common salt grains of controlled size with a commercial epoxy resin. The mixture is introduced into a mould. When the epoxy cures, the sample is released and introduced into a water tank to dissolve the salt grains appearing holes with the shape of the grains. The parameters of the resulting MPP are controlled by the size and percentage of salt grains in the initial mixture. Preliminary experimental results demonstrate the viability of this cheap technique to manufacture MPP absorbers.