Finite cylinder mode identification in scattering using finite elements, Fourier decomposition, and background subtraction.

Abstract

Finite elements are widely used for calculating the acoustic scattering by objects for which a partial wave series solution is not available. When interpreting the results of such calculations for the purpose of developing signal processing methods, it can be helpful to identify the elastic modes of the object excited by the incident sound. One approach to this is examined here for a finite metallic circular cylinder. Since the object is rotationally symmetric it is convenient to use a Fourier basis to speed up the calculations [Zampolli et al., J. Acoust. Soc. Am. 122, 1472–1485 (2007)]. This also has the advantage of using the scattering amplitude associated with a given Fourier index to extract mode information. It is also helpful to subtract from the computed complex amplitude the corresponding scattering by a rigid or nearly rigid object having the same size and shape as the cylinder. For some situations this can be compared with quantitative ray theory and experimental results using reversible synthetic aperture sonar processing. [Work supported by ONR.]