Fluid-structure effects of cloaking a submerged spherical shell

Abstract

Backscattering from a cloaked submerged spherical shell is analyzed in the low, mid, and high frequency regimes. Complex poles of the scattered pressure amplitudes using Cauchy residue theory are evaluated in an effort to explain dominant features of the scattered pressure and how they are affected by the introduction of a cloak. The methodology used is similar to that performed by Sammelmann and Hackman [J. Acoust. Soc. Am. 85, 114-124 (1989); J. Acoust. Soc. Am. 89, 2096Am. 89, -2103Am. 89, (1991; J. Acoust. Soc. Am. 90, 2705Am. 90, -2717Am. 90, (1991] in a series of papers written on scattering from an uncloaked spherical shell. In general, it is found that cloaking has the effect of diminishing the amplitude and shifting tonal backscatter responses. Extreme changes of normal and tangential fluid phase velocities at the fluid-solid interface when cloaking is employed leads to elimination of the "mid-frequency enhancement" near the coincidence frequency for even modestly effective cloaks, while reduction of the "high-frequency enhancement" resulting from the "thickness quasi-resonance" near the cut-off frequency of the symmetric (S B 2 ) mode requires more effective cloaking, but can be practically eliminated by employing a cloak that creates tangential acoustic velocities in excess of the S B 2 mode phase speed near cutoff.

Optimized cloaking design in moving fluid based on the scattering analysis method

“…Intense changes of fluid phase velocities at the submerged cloak's fluid-solid interface have been studied in the literature. 1 In this work, we assume that the cloak of interest is rigid and impervious to fluid but is transparent to sound waves. This assumption simplifies the problem of fluid-solid interface and could be implemented by mounting a cloth on the surface of the cloak.…”

A novel smart hybrid multimorph piezoelectric spherical shell cloak for broadband near-perfect underwater acoustic camouflage applications

“…configuration is also considered as a generic three dimensional acoustic cloaking device that can elegantly minimize or totally eradicate the acoustic traces of enclosed arbitrary-shaped three dimensional objects against incident sound waves [8][9][10][11][12][13][14] . In particular, the spherical cloak has the significant ability of concealing irregular objects from detection in any arbitrary incidence direction owing to the unique spherical symmetry (i.e., the so-called all-angle invisibility or omnidirectionality).…”