Nature-inspired orbital angular momentum beam generator using aperiodic metasurface

This article presents the design of reflective nature-inspired metasurfaces for generation of wideband and high purity circularly polarized (CP) orbital angular momentum (OAM) waves. It has been shown in this article that the breaking of the transitional periodicity and the combination of aperiodic nature-inspired distribution of sub-wavelength sized meta-atoms based on Pancharatnam-Berry (PB) phase theory can lead to OAM beams of high purity with improved bandwidth. The distribution of the PB anisotropic meta-atoms across the proposed metasurface aperture is non-uniform and distributed along logarithmic spirals similar to sunflower seeds, i.e. outwardly logarithmic spiral lattices of no transitional periodicity. The proposed reflective CP-OAM beam generator metasurface diameter is 140 mm, thickness approximate to 0.11 lambda (17GHz) and has 600 anisotropic spatially rotated PB meta-atoms of sub-wavelength size of 5 mm approximate to 0.28 lambda (17GHz). Four OAM metasurface generators have been designed to produce OAM waves of various modes from 1 to 4. Both simulation and experimental results have demonstrated that the proposed metasurfaces can efficiently generate CP-OAM beams from 13.1 GHz to 20.5 GHz (BW = 44%) with high mode purity >90%.