Latticed underwater acoustic Luneburg lens

This letter describes a theoretical and experimental study of an underwater acoustic Luneburg lens made of isotropic metamaterial. The designed lens is found to be capable of focusing plane waves over a broad range from 160 to 210 kHz. The measured lateral width of the focal spot is 5.5 mm, an ideal size that is close to the Rayleigh resolution limit. The functionality of the underwater lens is realized by an artificial structure. Different from those rigid-scatterers-based devices, the working mechanism of the proposed structure is by introducing waterborne ultrasound waves into the solid structures and manipulating mechanical waves.