Terahertz metasurfaces for absorber or reflectarray applications

A terahertz (THz) metasurface, with the unit cells consisting of double metal loops and a metallic back film on both sides of the dielectric layer, is investigated to find the connection between reflectivity and pattern geometry. An equivalent circuit of the unit cell is also given to ease the analysis and predication of the reflection coefficient and also to provide a guideline for tuning the impedance of the metasurface. An absorber and a reflectarray, as two typical applications of the metasurface that need low and high reflection efficiency, respectively, are demonstrated at 0.9 THz by varying dimensional parameters of the metal loops. The absorber can reach 0.102-THz bandwidth for reflectivity below -10 dB under normal incidence and also shows independence on polarization and incident angle, while the reflectarray antenna gain can reach 22 dBi at 0.875 THz. Finally, an absorber and a reflective surface prototype were fabricated and measured. Factors affecting the reflectivity and resonances introduced in the fabrication process are identified, which provides an important reference to design other kinds of THz devices.