Acoustic imaging by three-dimensional acoustic Luneburg meta-lens with lattice columns

A three-dimensional acoustic Luneburg lens, or acoustic Luneburg ball, has the advantage of refracting sound waves for all incident angles and concentrating higher sound pressure compared to a two-dimensional lens. A lens with a radius of 60 mm was designed with thousands of unit atoms comprising lattice columns to maintain its shape. The focusing performance of the lens was simulated using COMSOL Multiphysics, a finite element analysis program. Acoustic imaging was performed at a frequency of 10 kHz using a microphone, transducer, three-axis linear stage, and LabVIEW-based measurement program for a plastic lens made by a selective laser sintering 3D printer. The omnidirectional property was confirmed by measuring the sound pressure level while rotating the lens. The sound pressure level gain was defined to represent the frequency-dependent performance of the lens, and the maximum values were measured at approximately 20 dB and 15 dB in the numerical simulation and the experiment, respectively, at a frequency of 16 kHz. The results suggest that acoustic meta-lenses can be used for acoustic communication, imaging systems, and energy harvesting.