基于开口椭圆环的高效超宽带极化旋转超表面

High-efficiency ultra-wideband polarization conversion metasurfaces based on split elliptical ring resonators

电磁波的极化态在信号传输和灵敏度测量中有非常重要的应用价值.本文设计、仿真并实验验证了微波频段基于开口椭圆环谐振器的极化旋转超表面.理论上,将多阶表面等离子谐振和高阻抗表面相结合,解释了多谐振点、高效率极化旋转的物理机理.数值上,通过对结构参数的仿真分析,给出了运用开口椭圆环结构设计多频段、超宽带高效极化旋转超表面的方法.所设计和制作的超表面能够在相对带宽104.5%的频率范围内实现大于85%的极化旋转效率.这些工作将为极化操控超表面的设计和应用提供重要帮助.

Polarization state of electromagnetic waves plays a significant role in the fields of signal transmission and sensitive measurements. High-e？ciently manipulating and controlling polarization state by two-dimensional flat metamaterials over a wider bandwidth has been turned into hot issues in recent years. A polarization conversion metasurface based on the split elliptical ring resonator is designed, simulated, and experimentally validated in the microwave regime. The proposed metasurface can convert a linear polarization state into its orthogonal one with a high e？ciency for an ultra-wide band. Theoretically, the mechanism of polarization conversion is explained by the theoretical models of high-impedance surface and multi-plasmonic resonances. The metasurface has a strong anisotropy, which behaves as a high-impedance surface, and serves as a metal sheet in orthogonal orientation in the vicinity of the resonant frequencies. The reflection phase has a delay ofπfor one of the two electric field components and remains unchanged for the other. As a result, the polarization angle of the synthesized reflection electric field rotates byπ/2. The fourth-order plasmonic resonances are generated by the electric and magnetic resonances, which contribute to the bandwidth expansion of cross-polarization reflection. Numerically, by means of simulation and analysis on the axial ratio and flare angle of the split elliptical ring resonators, the influences of these structure parameters on the bandwidth and e？ciency of the polarization conversion are clarified. And then the design method of multi-peaks and wideband polarization conversion metasurfaces with split elliptic ring resonators is proposed for different kinds of applications. Experimentally, the geometry is implemented within the currently available printing circuit techniques, and a free space method is adopted to measure the scattering coe？cients. A polarization conversion ratio of the fabricated sample is larger than 85%at a relative bandwidth of 104.5%, and approximately 100%of the polarization conversion ratio can be achieved around the resonant frequencies. Experimental results are in good consistency with the simulation results. Compared with the anterior polarization conversion metasurfaces, the proposed metasurface broadens the cross-polarization bandwidth greatly with little e？ciency expenses. These works provide beneficial guidance for manipulating and controlling polarization states of electromagnetic waves, and have potential applications in modern radar and communication systems, signal detection systems, and sensitivity measurement systems, etc.