  A straightforward criterion to determine the limp model validity for porous
materials is addressed here. The limp model is an "equivalent fluid" model
which gives a better description of the porous behavior than the well known
"rigid frame" model. It is derived from the poroelastic Biot model assuming
that the frame has no bulk stiffness. A criterion is proposed to identify the
porous materials for which the limp model can be used. It relies on a new
parameter, the Frame Stiffness Influence FSI based on porous material
properties. The critical values of FSI under which the limp model can be used,
are determined using a 1D analytical modeling for a specific boundary set:
radiation of a vibrating plate covered by a porous layer.
