Inverse boundary and finite element formulations for the determination of high‐frequency specific impedance.

Abstract

Material databases for consulting acousticians require accurate determination of specific impedance. Such data are typically gathered from the composition of data sets obtained from impedance tubes. In such tubes, the restriction of frequencies under test to those that satisfy a plane wave assumption for the tube geometry in question allows for the application of a one‐dimensional transfer function analysis. Such tubes rarely achieve accuracy at the upper and lower ends of their operating spectra. Thus, the compositing of detailed data sets may produce significant error. For researchers of wave based methods of acoustic wave propagation, this represents a severe limitation. However, these data sets may be re‐purposed for an extension of frequencies under test by the application of an inverse problem formulation of the boundary element method. The method accurately predicts data obtained within a larger impedance tube and further well extrapolates to data observed in a smaller impedance tube. Moreover, the...