Anomalous correction in absorption coefficient measurements

The acoustical characterization of isotropic thin samples by electrical imp edancemetry methods shows anomalies in absorption coefficient measurements. This coefficient increases when the thickness decreases. In this paper, we will try to explain this phenomenon by developping a material characteriza tion method based on die electrical admittance measurements of the transduc er alone and loaded taking into account the layer coupling the transducer t o the sample constituing the load. We determine the absorption coefficient for different thicknesses of PMMA (polymethyl-methacrylate) realised in the same plate.