The acoustical background for submerged elastic targets and resonance scattering phenomena

Abstract

The pioneering paper on resonant acoustical scattering from elastic solids by Flax etal. [J. Acoust. Soc. Am. 63, 723–731 (1978)] (FDU) formed the basis for resonance scattering theory; proposing the decomposition of the elastic response into resonance and nonresonance ‘‘background’’ components. The resonance component was equivalent to the Breit–Wigner form from quantum mechanics, in which Flax and Uberall were trained. The ‘‘background’’ for elastic solids was that of a rigid scatterer. In a series of papers, FDU introduced many resonance classification schemes based on actual physical mechanisms. The FDU development bore much fruit in target classification physics in over a decade of lively research. Flax, also interested in elongated targets and elastic shells, initiated theoretical studies involving Waterman’s T-matrix method. Here, some recent work stemming from Flax’s interests stimulated by our early interaction with him is reported. The best backgrounds for generally shaped evacuated and fluid-filled elastic shells are discussed; and their use to interpret complicated resonance phenomena are outlined. Also demonstrated is that the FDU theory can be derived formally from an abstract mathematical structure. [Work sponsored by the Naval Research Laboratory 6.1 Program Element 0601153N.]