A broadband switchable metamaterial absorber is investigated in this paper. The switchable response is achieved by utilizing the phase transition property of vanadium dioxide (VO 2) that is thermally controlled. A novel band extension scheme is presented by introducing capacitive coupling effects among the resonators. By exploiting the coupling effect, near octave bandwidth is achieved when referred to an absorptivity of 90%. Further, by integrating the temperature controlled VO 2 film into the dielectric layer, the proposed absorber can be switched between a frequency band from 0.32 THz to 0.56 THz and another band from 0.356 THz to 0.682 THz that is achieved by changing the operation temperature. Due to the symmetrical structure, the studied absorber features polarization insensitive and a wide incident angle of up to 50 •. The broadband and switchable properties are discussed based on the resonant structure, surface current distributions, electric field distributions and impedance matching. It is noted the presented method can be scaled to other adjacent THz frequency band. INDEX TERMS Broadband, metamaterial absorber, phase change material, switchable bandwidth.

In this paper, a broadband and highly efficient reflective polarization converter based on Z-shaped metasurface is demonstrated at sub-terahertz (THz) frequencies. The polarizer can convert a linearly polarized (LP) wave to its cross-polarized wave at three resonant frequencies, which can also convert a LP wave to a circularly polarized(CP) wave at other two frequencies. The polarization conversion efficiency for normal incidence larger than 80% is obtained from 0.116THz to 0.26THz. The surface current distributions are demonstrated to investigate the physical mechanism. Furthermore, the performance under oblique incidence shows the broad bandwidth can be sustained as incident angle increases to o 45. The polarizer could be useful for enhancing the efficiency of polarization conversion in THz regime.

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