(a) Schematic diagram of the graphene and metallic grating-based reflective THz modulator gated by the ion gel (top panel) and the side view of the device (low panel). Measured reflection spectra under different gate voltages (b) without the metallic grating and (e) with the metallic grating. The resonance frequency and charge neutral points (CNP) are plotted by the white and gray dash lines. Extracted reflection coefficient under different gate voltages at resonance frequency (c) without the metallic grating and (f) with the metallic grating. Calculated absorbance and modulation depth at resonance frequency (d) without the metallic grating and (g) with the metallic grating.^[58] Figure reprinted with permission: Ref. [58], ©2019 by the John Wiley and Sons.