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Owing to the large losses in the conversion process of traditional polarization converters , there is an increasing demand for metasurfaces with excellent transmission performance. In this work, an efficient polarization conversion metasurface is proposed based on electromagnetically induced transparency-like (EIT-like) effect in the terahertz band. The multi-level bright mode paths are excited by an asymmetric structure to obtain orthogonal circular polarization conversion windows. The transmission window is generated by the mutual interference of two sets of bright modes with similar resonant frequencies. Then an asymmetric structure is constructed to achieve transmission window shift under TE polarization and TM polarization, thereby realizing dual-frequency polarization conversion. The metamaterial unit structure consists of four open metal resonant rings and four metal resonant strips. The working mechanism is explored by analyzing the surface current distribution, frequency response, and incident angle characteristics. The results show that electromagnetically induced transparency can be achieved under different polarizations. Furthermore, based on the EIT resonance between the two incident polarizations, the conversion from linear polarization to right-hand circular polarization is achieved at 0.692 THz, and the conversion from linear polarization to left-hand circular polarization is realized at 0.782 THz, transmission coefficients are 0.7 and 0.68 respectively. According to the Stokes parameters, the corresponding ellipticity η values are 96% and 98%, respectively. This EIT-based polarization conversion metasurface with low loss and ultra-thin characteristics has great potential applications in compact antennas, derived radar phased arrays, and military detectors.
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Keywords:
- metamaterials /
- electromagnetic induced transparency effect /
- polarization conversion /
- filters
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图 1 所提出的单元结构 (a) 功能示意图; (b) 单元结构图
Figure 1. Proposed unit structure: (a) Functional diagram; (b) cell structure diagram.
图 2 不同单元结构的透射谱 (a) TM极化波下的不同基本结构透射谱、表面电流以及磁场图分布图; (b) TE极化波下的不同结构透射谱、表面电流以及磁场图分布图; (c) 整体结构的透射谱; (d) 类EIT效应的能级系统
Figure 2. Transmission spectra of different unit structures: (a) Transmission spectra, surface currents, and magnetic field maps of different basic structures under TM polarized waves; (b) transmission spectra, surface currents, and magnetic field maps of different structures under TE polarized waves; (c) transmission spectrum of the overall structure; (d) energy level systems of class EIT effects.
图 3 磁场以及电流图
Figure 3. Magnetic field (absolute value) and current diagram.
图 4 极化转换点的表面电流以及磁场图
Figure 4. Surface current and magnetic field (absolute value) of the polarization transition point.
图 5 重要指标图 (a) 透射曲线和相位; (b) 透射曲线的轴比; (c) 透射曲线的椭圆度; (d) 透射曲线的极化方位角
Figure 5. Important indicators: (a) Transmission curve and phase; (b) axial ratio of transmission curve; (c) ellipticity of the transmission curve; (d) polarization azimuth of the transmission curve.
图 6 极化转换示意图 (a) 45°线极化入射波; (b) 0.692 THz透射波模拟极化; (c) 0.782 THz透射波模拟极化
Figure 6. Schematic diagram of polarization conversion: (a) 45° linearly polarized incident wave; (b) simulated polarization of 0.692 THz transmitted wave; (c) simulated polarization of 0.782 THz transmitted wave.
图 7 不同入射角度所对应透射谱的变化
Figure 7. Changes of transmission spectrum corresponding to different incidence angles.
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