Experimental acoustic radiation from an elastic plate covered with a porous layer

In this work the sound radiation of a rectangular plate covered with a porous layer was analyzed experimentally. The vibratory energy in these types of structures is dissipated by several mechanisms, sound radiation being one of them. Once the porous layer is in contact with the plate, the plate vibration induce vibrations not only in the fluid, but also in the solid phase of the porous material, providing propagating waves in both phases simultaneously. The structure analyzed in this work consists of a simply supported base plate covered with a foam layer and with an extra thin cover plate. The surface velocity of the system was measured scanning the surface with a transducer and using phonoscopy, a particular case of near-field acoustical holography. It was observed that the radiation efficiency of the structure is not too much affected by the presence of the porous layer.