3D underwater acoustic Luneburg lens based on gradient face-centered-cubic phononic crystals

Abstract

A Luneburg lens is a gradient refractive index lens that can focus plane waves on a point at the perimeter without aberration. Three-dimensional (3D) Luneburg lens for airborne sound has been well investigated in recent years. However, constructing a 3D Luneburg lens for underwater sound is a challenging task due to the difficulties in the designing and fabricating of the desired isotropic underwater acoustic materials. This work presents the practical implementation of a 3D Luneburg lens for underwater sound. Such a 3D Luneburg lens is designed based on 3D gradient face-centered-cubic phononic crystals, which have quasi-isotropic refractive index patterns and can be fabricated with photosensitive resin by 3D printing. The experimental results show that the lens can realize the omnidirectional imaging of underwater sound from 30 to 38 kHz. This 3D underwater acoustic Luneburg lens may prompt the potential applications in underwater acoustic wide-angle retroreflectors, sonars, and biomedical imaging devices.