Flat ultrasonic metalens with ultra-wide field-of-view

Acoustic metalenses have demonstrated outstanding focusing abilities, while most lenses still suffer from a limited field of view (FOV) due to angle-induced aberration. In this paper, we propose a flat ultrasonic metalens (UML) with an ultra-wide FOV. The metalens follows a discrete quadratic phase profile. Variations in the angle of incidence (AOI) can be translated into transverse shifts of the focus in the absence of rapid phase gradients. The flat UML is realized using a metal plate with slits and a resin phase grating. Numerical simulations demonstrate that the proposed UML can achieve ultrasonic focusing when the AOI ranges from 0° to ∼ 60°. Furthermore, deep subwavelength structures are unnecessary, as the FOV is robust to slit width. Finally, we fabricate a sample using stereolithography 3D printing techniques and verify its ultra-wide FOV of ∼ 120° through experiments. The proposed UML may have potential applications in energy harvesting, ultrasonic imaging, and nondestructive inspection.