Broadband solid cloak for underwater acoustics
  Application of transformation theory to underwater acoustics has been a challenging task because highly anisotropic density is unachievable in water. A possible strategy is to exploit anisotropic modulus rather than density, while has not been experimentally demonstrated. We present an annular underwater acoustic cloak designed from particular graded solid microstructures. The geometry tailored microstructures mimics meta-fluid with highly anisotropic modulus through substantially suppressed shear wave. Transient wave experiments are conducted with the cloak in a designed 2D underwater waveguide system and proved excellent cloaking performance for enclosed target over broadband frequency 9-15 kHz. This finding paves the way for controlling underwater acoustics using the structured anisotropic modulus meta-fluid. 
Yi Chen, Mingye Zheng, Xiaoning Liu, Yafeng Bi, Zhaoyong Sun, Ping   Xiang, Jun Yang, Gengkai Hu
physics.class-ph cond-mat.mtrl-sci