Validation of a numerical method for extracting liner impedance

We report the initial results of a test series to evaluate a method for extracting the normal incidence impedance of a locally reacting, acoustically absorbing liner located on the lower wall of a duct in a grazing incidence, multimodal, nonprogressive acoustic wave environment without flow. This initial evaluation tests the method's ability to converge to the known normal-incidence impedance of a solid steel plate, and to the normal-incidence impedance of an absorbing test specimen whose impedance has been measured In a conventional normal-incidence tube. The method converges to the normal-incident impedance values and thus is an adequate tool for extracting the impedance of specimens in a grazing-incidence, multimodal, nonprogressive acoustic wave environment for a broad range of source frequencies.