Experimental and numerical acoustic characterization of ultrasonically absorptive porous materials

Abstract

The paper addresses the experimental and numerical acoustic characterization of ultrasonically absorptive porous materials with random microstructure such as carbon fiber reinforced carbon ceramic C/C or C/C-SiC. The present study carries on a preceding experimental study of the authors by improving and extending the established experimental method and by conducting complementary numerical studies. The latter uses a new inverse Helmholtz Solver associated with an incident planar acoustic wave to estimate the complex acoustic impedance at the open surface of an arbitrarily shaped cavity. The experimental approach is complemented by high speed schlieren visualization and Mach-Zehnder Interferometer measurements to qualitatively and quantitatively assess the interaction between an ultrasonic wave packet and a porous surface. The main emphasis of the paper is to assess the potential and the limitations of the experimental methods and the comparison of the experimental results to the numerically obtained absorption characteristics.