Generation of broadband non-diffraction millimeter-wave airy beams based on high-efficiency tri-layer metasurfaces

Airy beams based on the Airy function, exhibiting a special curved parabolic trajectory, can effectively alleviate diffraction along its propagation and hold potential in many interesting applications. However, to date, the broadband and high-efficiency generation of non-diffraction Airy beams has remained largely unexplored, especially in the millimeter-wave range that is full of great application potential. In this paper, broadband 1-D and 2-D Airy beam generators utilizing high-efficiency tri-layer metasurfaces operating from 55 to 67 GHz are presented. The metasurfaces consist of elaborately tailored meta-atoms that can independently realize complete amplitude modulation from 1% to 98% and binary phase tuning of 0 and π. The Airy beam generators are engineered and verified by simulations and experiments, which demonstrate the broadband quasi-non-diffraction feature and curved trajectory of the Airy beam. Compared to the 1-D Airy beam generator, the measured quasi-non-diffraction propagation property of the 2-D Airy beam can be maintained by greater than 160 free-space wavelengths across the entire bandwidth. Self-reconstruction property of the 2-D Airy beam is also experimentally validated in the presence of metallic and dielectric obstacles. This work may benefit novel applications of Airy beams in millimeter-wave imaging and detection.