Pole Localization and Impedance Measurement for Porous Layers with a Small Porosity

For acoustically thin porous layers, and acoustically thick porous layers with a sufficient high flow resistivity, a reformulation of the classical equations derived by Chien and Soroka [1] has been performed. A method based on this new formulation has been used to localize the pole of the reflection coefficient for an angle close to grazing incidence and to measure the surface impedance at this angle. A general condition of validity of the new formulation is presented. An illustration with simulations is given for media with a small porosity. Measurements are performed on a draining asphalt. It is shown that a method previously used in anechoic room presents some limitations when it is used outdoor.