Transmission and reflection bidirectional terahertz coding metasurface based on thermally switchable materials

Metasurface, with its powerful and flexible terahertz(THz) wave manipulation capability, has become a key component of beamforming and imaging systems in the THz band. However, its practical application is limited by fixed properties and propagation mode on a single metasurface. In this paper, we propose a coding metasurface with tunable characteristics and bidirectional working modes. The complete 2π phase compensation can be realized by rotating the InSb unit according to the Pancharatnam-Berry phase concept, and eight meta-atoms are selected to regulate the wavefront of terahertz waves using phase compensation. By increasing the temperature of the InSb from 290 K to 370 K, the working frequency permits wideband coverage from 1.7 to 4.5 THz. As the temperature reaches 341.15 K, which is required for vanadium dioxide's(VO2) phase transition, the metasurface's propagation direction mode will switch from transmission to reflection. The proposed metasurface can perform beam deflecting, splitting, and focusing functions when VO2 is in a dielectric state. Meanwhile, beam deflecting, splitting, and radar scattering surface (RCS) reduction can also be achieved when VO2 is in a metallic state. Furthermore, a near-field image of the letter P is presented as verification. Numerous potential applications for the reconfigurable metasurfaces include polarization beam splitters, imaging, and terahertz switching.