Electromechanically tunable graphene-based terahertz metasurface

For reconfigurable terahertz (THz) devices, graphene is a promising platform; however, most of the proposed designs exploit the gate-tunability of graphene's chemical potential. In this paper, we propose a new way of tuning graphene-based THz metasurfaces using the electromechanical method. Our proposed metasurface consists of a free-standing graphene layer supported by an oxide grating on a gold substrate. While electromechanically, the metasurface acts as a variable capacitor, electromagnetically, it is a frequency -dependent tunable absorber. Any potential difference between the graphene layer and the gold substrate causes a deflection in the free-standing regions of the graphene layer, which in turn causes a shift in the resonance wavelength of the metasurface. Our numerical simulation confirms continuous tunability of the resonant frequency over a frequency range of 0.5 THz for the applied external potential of only 20 V. We further demonstrate the application of our proposed metasurface in THz modulation. From the frequency response analysis, we have shown the maximum bandwidth of operation of the modulator is 353 kHz, which is mainly limited by the resonance frequency of the free-standing membrane. At the operating frequency of 5.49 THz, we have obtained an extinction ratio of 4.67 dB for a drive voltage of 20 V. As a new method of tunable THz metasurface, such implementation will find promising applications in optical MEMS-based sensors, actuators, beam steering applications etc.