Fig. 1. Diagram of open-end coaxial probe measurement principle

Fig. 2. Experimental device. (a) Measurement equipment; (b) open-end coaxial probe; (c) network analyzer

Fig. 3. Dielectric properties of glucose aqueous solution with different concentrations. (a) Dielectric constant; (b) conductivity

Fig. 4. Fitting relation between Debye parameters and glucose aqueous solution concentration. (a) ε∞; (b) Δε; (c) τ

Fig. 5. Single-order Debye model fitting of glucose aqueous solution with concentration of 200 mg·dl^-1. (a) Dielectric constant; (b) conductivity

Fig. 6. Dielectric properties of five aqueous glucose solutions reconstructed by single-order Debye model. (a) Dielectric constant; (b) conductivity

Fig. 7. Five-layer earlobe electromagnetic model and transceiver antenna

Fig. 8. Single-order Debye model of skin and fat. (a) Dielectric constant; (b) conductivity

Fig. 9. Microwave signal transmitted by transmitting antenna. (a) Time domain diagram; (b) frequency domain diagram

Fig. 10. Changes of S₂₁ at different glucose concentrations. (a) S₂₁; (b) S₂₁ difference; (c) absolute value of S₂₁ difference

Fig. 11. Relationship between absolute value of S₂₁ difference and glucose concentration at different frequency points. (a) 1.35 GHz; (b) 1.63 GHz; (c) 3.25 GHz; (d) 4 GHz

Fig. 12. Experimental environment. (a) Experimental device; (b) earlobe model and antenna

Fig. 13. Experimental measurement results. (a) S₂₁; (b) S₂₁ difference; (c) absolute value of S₂₁ difference

Fig. 14. Relationship between absolute value of S₂₁ difference and glucose concentration at different frequency points