The Acoustical Properties of Air Saturated Aerogel Powders

There is a general lack of understanding of the acoustical behaviour of air-saturated aerogel powders in the audible frequency range. It is unclear what physical processes control the acoustic absorption and /or attenuation mechanisms in a very light, loose granular mix in which the grain diameter is comparable to a micron. This work attempts to fit a Biot-type viscoelastic model to predict the absorption coefficient of two aerogel powder mixes with the particle diameter in the range of 1 - 40 microns. it is shown that these materials behave like a highly flexible, viscoelastic layer. It is found that the absorption coefficient for these materials depends strongly on the root mean square pressure in the incident wave. It is also found that the loss coefficient which accounts for the energy dissipation due to vibration of the elastic frame is a key model parameter. The value of this parameter reduces progressively with the frequency and sound pressure. Other parameters in the adopted Biot-type viscoelastic model, e.g. the storage module of the elastic frame and pore size, are relatively independent of the frequency and amplitude of the incident wave. It is shown that this material can be a very efficient resonance absorber in the low frequency range