Device configuration and experiment photos. (a) Schematic illustration of the Al₂O₃/Si gated graphene-loaded metal wire grating device. (b) Side view of the device on a 120 degree high-resistance Si prism and a 30 degree super critical incident angle at the surface of metal grating/air. The polarization of the THz light is out-of-paper. (c) Experimental setup of the TIR measurement. A 5×5 mm size graphene is transferred to the metal grating surface. The gate voltage between graphene and HR-Si was swept from -3 V to 3 V. (d) The photo of graphene metal wire grating on Al₂O₃/Si substrate. The period of the metal wire grating is 20 μm and gap width is 4 μm.