Broadband and High-efficiency Circular-polarized Terahertz Frequency Scanning Metasurface

Due to the inefficiency of effective wave modulation components and dynamical metamaterial in terahertz (THz) range, an alternative approach of frequency sweeping for beam scanning based on a metasurface structure is proposed here. Aiming at broadband and high-efficiency circular-polarized terahertz frequency-scanning, we start with combining Pancharatnam-Berry scheme and generalized Snell's law to initiate the fundamental schematic design. The hybrid structural unit is composed of an I-shaped dipole and two rectangular dipoles for multi-resonance leading to broadband width. In order to realize directional deflection, the metasurface is arranged through eight rotated units with a fixed π/4 phase differences between adjacent units to reach 2π consecutive phase shift. A 45° phase difference among eight units adjacent in x axis keep in excellent linear maintenance with a bandwidth from 1 THz to 2.1 THz. The simulation result verifies the reflection efficiency of the unit reaches 90% in the operating frequency range. Under right-handed circular polarized normal incident wave, the frequency bandwidth is 1.1 THz (from 1 to 2.1 THz) with a scanning angle range from 17° to 38°. The simulation result is in good agreement with the theoretical analysis. In addition, the reflection efficiency of the scanning beam is more than 50% in the operating frequency range, and the maximum reflection efficiency of the scanning beam achieves 88% at 1.6 THz, which indicates the remarkable inhibition of the unwanted diffraction. The metasurface presented here features the advantages of a wide operating bandwidth and high efficiency, which has potential applications in fast THz imaging, moving target detection and wireless communication.