Observation of Ultrabroadband Acoustic Focusing Based on V-Shaped Meta-Atoms

Acoustic focusing has extensive applications in medical ultrasound and nondestructive detection. The recent rapid development of acoustic metamaterials and metasurfaces has provided various mechanisms for designing advanced focusing lenses. However, the realization of acoustic focusing lenses with ultrabroad bandwidth still remains a challenge. To overcome it, ultrabroadband acoustic focusing lens based on phased unit cells composed of different numbers of same V-shaped meta-atoms is theoretically proposed and experimentally realized. By using eight types of unit cells, the fractional bandwidth of the acoustic lens can reach about 1.12 with a high focusing performance. Moreover, based on two types of unit cells with a phase difference of pi, the fractional bandwidth of the focusing lens still reaches about 0.76 with the same criteria, showing a high robustness characteristic. The proposed acoustic focusing lenses have the advantages of ultrabroad bandwidths, simple fabrication and assembly, and high robustness, which provide diverse routes to construct ultrabroadband sound devices for medical ultrasound and nondestructive detection.