Acoustic properties of cellular vitreous carbon foams

Abstract

The present work deals with acoustic properties of highly porous rigid foams derived from flavonoid tannins. Such cellular solids derived from renewable resources were investigated before and after pyrolysis, the latter leading to cellular, vitreous, carbon foams. It is demonstrated here that these lightweight materials have a high air flow resistivity, which depends on the density of the foam. Vitreous carbon foams, especially, have rather low performances for sound absorption. Using a simple model, their sound absorption coefficients were predicted and found to be in very good agreement with measurements in all the investigated frequency range, 50–4300Hz. However, we have shown that carbon foams are very appropriate materials to apply the double porosity concept since they can produce a high permeability contrast. This paper shows how vitreous carbon foams can become excellent sound-absorbing materials in a targeted frequency range by using the double porosity concept.