Characterisation of porous materials viscoelastic properties involving the vibroacoustical behaviour of coated panels

Porous materials are widely used for noise control. Often attached to a structure subjected to vibration, the porous layer contributes to diminish vibration by increasing structural damping and also reduce noise level in cavities by sound absorption. For optimal design, it is often necessary to know the viscoelastic properties of these materials in the frequency range relevant to their application. At these frequencies and for most of porous materials the viscoelastic properties can not be determined by standard methods because of the strong coupling with air. The method proposed is based on measurements representative of industrial use (car, aircraft, train): acoustic radiation of vibrating coated panel and transmission loss of coated panel. The use of an inverse methode based on analytical models to determined the viscoelatic properties insure a good simulation of the porous material behaviour in the required context.