  A three-dimensional acoustic Luneburg meta-lens has the advantage of
refracting sound waves for all incident angles and focusing higher sound
pressure compared to a two-dimensional lens. The lens made of plastic with a
diameter of 120 mm was designed with thousands of lattice column-shaped
meta-atoms to maintain its three-dimensional shape. The lens's
three-dimensional focusing performance and acoustic imaging were simulated and
measured at the frequency range of 5 kHz ~ 20 kHz. The omnidirectional property
was confirmed by rotating the lens to change the incident angle and measuring
the sound pressure. The development of these spherical Luneburg meta-lenses is
expected to improve the performance of devices that require acoustic focusing.
