### ASA 125th Meeting Ottawa 1993 May

## 3aEA8. Integral method for modeling the sound field above a porous
material.

**Celse K. Amedin
**

**
Alain Berry
**

**
Yvan Champoux
**

**
**
*G.A.U.S., Mech. Eng. Dept., Univ. de Sherbrooke, Sherbrooke, PQ J1K 2R1,
Canada
*

*
*
A new concept of a transmission technique for the characterization of
porous material is presented. It is based on the accurate modeling of the sound
field above the layer of material that rests on an horizontal infinite baffle.
The sound field is generated by a waveguide mounted vertically under the baffle
with its termination flush to the baffle. The waveguide is assumed to create a
uniform distribution of particle velocity at the termination. The field in the
material is expressed using a Green's function that accounts for the multiple
reflections on the baffle and at the upper surface of the material. The field
above the material is formulated in terms of the pressure gradient distribution
over the upper surface. Starting with the boundary conditions at the upper
surface (continuity of the sound pressure and normal particle velocity), the
collocation method is used to solve for the pressure gradient at a mesh on this
surface. This, in turn, allows one to calculate the sound pressure above the
material and the transfer function between the volume velocity of the source
and this sound pressure. Numerical results are presented, and the potential of
this technique for the characterization of porous material is discussed.