Fig. 1. Proposed terahertz multifunctional device. (a) 3D structural schematic; (b) top view; (c) fabrication process

Fig. 2. Results of FDTD simulation and process of theoretical analysis. (a)‒(c) Transmission spectra of individual G1, individual G2, and their combination G1+G2, with insets showing magnetic field (H_z) distributions in graphene layer corresponding to resonance valleys; (d) schematic diagram of CMT

Fig. 3. Transmission spectra and quality factor of PIT at different E_F. (a) Transmission spectra of simulation results and theoretical calculations at different E_F; (b) fitting parameter values of Q_in and Q_tn as a function of E_F

Fig. 4. Transmission spectrum obtained by simulating structure with only VO₂ layer present

Fig. 5. Evolution of transmission spectrum obtained through simulations as E_F continuously changes

Fig. 6. Variations of phase shift and group delay with frequency at E_F=1.1 eV, and the group delay of PIT response under different E_F. (a) Variation of phase shift with frequency; (b) variation of group delay with frequency; (c) group delay of PIT response under different E_F

Fig. 7. Transmission spectra and group delay for different σ when E_F=1.1 eV. (a) Transmission spectra; (b) group delay

Fig. 8. Simulated absorption spectra and theoretical analysis results. (a) Absorption spectra versus E_F of graphene from 0.9 eV to 1.1 eV; (b) elative impedance under quad-narrowband perfect absorption when E_F is 1.1 eV

Fig. 9. Physical mechanism of perfect absorption. (a)‒(d) Distributions of electric field (E) in the x-y plane at frequencies of 2.31, 3.90, 6.02, and 7.91 THz; (e)‒(g) distributions of z-direction component of electric field (E_z) in x-z plane at frequencies of 2.31, 3.90, and 6.02 THz; (h) distribution of E_z in y-z plane at frequency of 7.91 THz; (i)‒(l) distributions of magnetic field (H) in the x-z plane at frequencies of 2.31, 3.90, 6.02, and 7.91 THz

Fig. 10. Absorption spectra for different E_F when VO₂ is in metallic state (σ=200000 S/m)

Fig. 11. Transmission spectra and absorption spectra at different polarization angles when E_F=1.1 eV. (a) Transmission spectra; (b) absorption spectra