A hybrid design based on alternating layered fluids for the cloaking of elastic cylinders

With the combination of two critical features from Cummer-Schurig, acoustic cloaking and the scattering cancellation technique, this study reports a hybrid design for the cloaking of elastic cylinders using alternating layered fluids (the effective density to be anisotropic), which are achieved by alternately immersing HGM (a syntactic foam, light solid material with high sound velocity) and Pb (lead, a heavy solid material) in the background fluid medium. The cloaking performance of the proposed design is investigated both by the numerical simulation and by experimental measurement. For a lead cylinder of radius 50 mm, the measured visibility reduction below -5 dB is obtained in the frequency range from 18 kHz to 23 kHz. Compared with the scattering cancellation by the thin elastic shell, the proposed cloaking can be obtained at shorter wavelengths due to the suppression of more higher-order scattering. In addition, the performance of cloaking has no dependence on the incident angles, which has an advantage over the scattering cancellation using scatters distributed unevenly. This is the first experiment using layered fluids to obtain the cloaking of an elastic cylinder, which has potential application in underwater acoustic stealth.