Fig. 1. Relationship between conductivity and frequency under different chemical potentials. (a) Relationship between the real part of conductivity and frequency; (b) relationship between the imaginary part of conductivity and frequency

Fig. 2. Relationship between bias voltage and chemical potential of graphene

Fig. 3. Geometric structure of the antenna. (a) Top view; (b) bottom view

Fig. 4. Echo parameters in switch mode

Fig. 5. Radiation pattern of the antenna in switch mode. (a) E side; (b) H side

Fig. 6. Current distribution on the back of the antenna. (a) state 2; (b) state 5

Fig. 7. Echo parameters in fine-tuning mode

Fig. 8. Radiation pattern of the antenna in fine-tuning mode. (a) E side; (b) H side

Fig. 9. Current distribution on the back of the antenna. (a) state 5.1; (b) state 5.2; (c) state 5.3; (d) state 5.4; (e) state 5.5