Generation and regulation of two-dimensional autofocusing Airy beams based on holographic metasurfaces

This paper proposes a new method to generate a two-dimensional (2D) Airy beam and Airy autofocusing beam by using the scalar holographic metasurface with amplitude-phase modulation in the microwave band. The proposed holographic metasurface comprises subwavelength patch unit cells with a period of fewer than 1/8 wavelengths, which means that it has the finer sampling for electromagnetic waves and can simultaneously achieve precise modulations for the amplitude and phase of electromagnetic waves. Firstly, the 2D-Airy beam with quasi-non-diffraction and self-bending characteristics is generated, from which the holographic metasurface is designed to realize four different 2D-Airy beams with the same focus, achieving the 2D-Airy autofocusing beam in the microwave frequency. The holographic metasurface for Airy beam generation has high efficiency and an ultra-lower profile. Meanwhile, for applying the Airy beam in wireless power transfer (WPT), the efficiency of the generated Airy beam and Airy autofocusing beam is calculated for the first time in the microwave field. The simulation results show that the efficiency of the 2D-Airy beam can reach 66% at 150 ​mm away from the metasurface, while the efficiency of the 2D-Airy autofocusing beam at the focus, which is 280 ​mm from the metasurface, can reach 35%. The theoretical, simulated, and measured results show that the proposed method and holographic metasurfaces can flexibly achieve the special characteristics of self-autofocusing and self-bending Airy beams in the microwave domain, providing an effective path for wireless power transfer (WPT) scenario with radial obstructions.