Pixelated liquid crystal programmable metasurface enabled multi-functional terahertz near-field wavefront manipulation

Reconfigurable intelligent surface (RIS) technology is believed to effectively solve the dilemma of terahertz wireless communication in non-line-of-sight scenarios. Notably, the deployment of large-scale RIS arrays at high frequencies brings about significant near-field effects, resulting in extensive near-field areas, which provides the possibility for the application of near-field communication. In this paper, a pixelated liquid crystal programmable metasurface (PLCPM) is proposed to effectively manipulate terahertz waves in the near-field region. Leveraging the tunability of liquid crystal (LC) materials, the proposed PLCPM achieves 1-bit phase coding capability within the 104–110 GHz frequency band. Subsequently, by combining lithography machining with printed circuit board (PCB) manufacturing technology, the pixelated controllability of the PLCPM is realized. The simulation and experimental results demonstrate that the proposed PLCPM can perform multi-functional near-field beam control for terahertz waves, including focusing beams for different distances and positions, near-field orbital angular momentum (OAM) beams for large-capacity communication, and Bessel beams for long-distance propagation. These results verify the effectiveness of the proposed PLCPM in flexibly controlling near-field beams, paving the way for the application of RIS in terahertz near-field communication.