Acoustic absorption properties of granular silica aerogels

Aerogels are a class of synthetic materials derived using supercritical drying to extract the liquid component of a gel and replacing it with a gas. This process results in the formation of an ultra-lightweight nanoporous solid composed of up to 99.98% air by volume. Here, we characterize the absorption properties of commercially available aerogel granules using a two-microphone impedance tube. Four different aerogels with granule diameters ranging from 2- to 4000 μm and granule densities ranging 120 to 180 kg/m3 are tested. The results show that the aerogel granules are highly effective in absorbing sound over a wide frequency range. Further, we use an inverse characterization approach to obtain their acoustic transport properties and explore the possibility of modelling them as an equivalent rigid-frame porous material within the frequency range of interest.