Excitation of soft porous frame resonances and evaluation of rigidity coefficients

Recent works have been performed concerning the guided elastic waves in soft porous elastic frames and the related normal displacement of the surface generated by a mechanical excitation. In this work, the mechanical excitation is replaced by a monopole acoustic field in air above the porous structure. Two cases are considered: a frame bonded on a rigid impervious layer and a free frame. The normal and the radial velocity induced by the monopole field at the surface of the frame is predicted with the Biot theory and the Sommerfeld representation of the monopole field. Measurements are performed with a laser vibrometer on a urethane foam. It is shown that the characterization of the excited modes can lead to an evaluation of the rigidity coefficients of the frames at acoustical frequencies.