Fig. 1. Electrical simulation results. (a) Schematic of electrically tunable ITO metasurface, the MOS structure consists of a gold back plane, a thin ITO film, a thin Al₂O₃ film, and gold stripe nanoantenna array; (b) spatial distribution of the carrier concentration under different applied voltages; (c)(d) distribution diagrams of the permittivity of ITO at different voltages and depths at a wavelength of 1470 nm

Fig. 2. MOS structure with charge accumulation (dash) and charge depletion (solid). (a) Schematic of MOS structure; (b) energy-band diagram; (c) carrier density curve; (d) as the carrier density increases or decreases at the interface, the real part of the permittivity changes from positive to negative

Fig. 3. Optical simulation results of adjustable metasurface. (a) Reflection phase as a function of voltage and wavelength; (b) reflectance as a function of voltage and wavelength; (c)‒(e) spatial distribution of the electric field E_y at 1470-nm wavelength under applied bias of 0, 2.5, 5 V, respectively

Fig. 4. Practical applications of deflection and focusing. (a) Schematic of the electrically tunable reflectarray antenna; (b) simulated electric field distribution with the bending angle of -18^o; (c) simulated relationship between the reflection amplitude and the angle; (d) electric field distribution at focal length of 6λ

Fig. 5. Double-gated metasurface. (a) Schematic of the unit cell of the double-gated metasurface, the thicknesses of the antenna array, the gate dielectrics, the ITO layer, and the back reflector are t₁= 50 nm, t₂=9.5 nm, t₃=5 nm, and t₄= 80 nm, respectively, and the electrode width is w₂=170 nm; (b) simulated result of charge carrier distribution; (c) real part of the dielectric permittivity of the ITO as a function of the applied voltage and position; (d) maximum phase achieved under different voltages at λ=1500 nm

Table 1. Phase and voltage values of each antenna in deflection applications