Absorbers with spin-selection based on metasurface

Abstract

In recent years, due to their features nonexistent in natural matirials, the perfect absorbers based on metasurfaces have become a hot research point. Although great progress has been made, the absorbers with spin-selection are rarely reported. However, the absorbers with spin-selection have more widespread applications in chiral sensors and satellite communication. Therefore, a spin-selection absorber based on the metasurface with modified square split-ring structure is proposed. Firstly, the theoretical conditions for generating the spin-selection absorption are analyzed theoretically, and then the qualified metasurface unit cell is designed under the guidance of the theory. We design an asymmetric modified square split-ring resonator to break both the <i>n</i>-fold (<i>n</i>>2) rotational symmetry and mirror symmetry. The unit cell is composed of three layers, i.e. the top layer, which is a modified square split-ring, the middle layer, which is an FR4 dielectric plate with a thickness of 4 mm, and the bottom layer, which is an all-metal plate acting as the reflecting incident wave. In order to obtain the optimal performance, the designed meta-atom is optimized by CST Microwave Studio, a well-known commercial full wave simulation software.The numerical simulation results show that the unit cell can selectively absorb the right-handed circularly polarized waves and reflect left-handed circularly polarized waves at 7.2 GHz. A maximum absorption rate for the absorption of right-handed circularly polarized (RCP) waves reaches a value higher than 90%, while the absorption rate of the other spin state is kept lower than 19%. In addition, to meet the need of practical applications, the absorption performance is also further investigated under different oblique incident angles, with the wave vectors confined in the <i>x-z</i> plane and <i>y-z</i> plane, respectively. Finally, to further understand the mechanism of spin-selection absorber, the surface current distributions are also simulated for LCP and RCP wave, respectively. The different surface current distributions are obtained for incident LCP and RCP wave, which is a solid evidence for spin-selection absorption. This paper offers a reference for the generation of spin-selection absorber. The proposed method not only is suitable for microwave region, but also can be extended to higher frequencies, and hopefully it can be widely used in the field of communication.