### ASA 127th Meeting M.I.T. 1994 June 6-10

## 2aPA1. A transmission method for estimating the specific acoustic
impedance of a porous material: Modelization.

**Celse K. Amedin
**

**
Yvan Champoux
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**
Alain Berry
**

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

*
*
A new method is suggested for the characterization of porous materials; it
is based on a measurement of the sound transmission through a layer of the
material. This paper presents two theoretical models to evaluate the potential
of the method. In these models, a thin layer of the material lies on a
horizontal baffle; the acoustic source is a waveguide mounted vertically under
the baffle with its end flush to the baffle and the sound is transmitted
through the layer to the half-space above the layer. The two models calculate
the transfer function between the volume velocity of the waveguide and the
sound pressure over the layer. The first model is based on the integral method
and collocation in which the appropriate Green's functions are used to describe
the sound field. The second model uses a method of decomposition into plane
waves. The details of each model are described; results, comparisons, and
validations are presented. Finally, the potential of the method to evaluate the
characteristics of the porous layer is discussed.