Fig. 1. Schematic diagram and equivalent circuit model of traditional SRR-based microwave sensor

Fig. 2. Schematic diagram and equivalent circuit model of ICS-SRR-based microwave sensor

Fig. 3. Distributions of electric fields

Fig. 4. Schematic diagram and equivalent circuit model of proposed microwave sensor

Fig. 5. A comparison between circuit model and simulation in terms of S-parameters

Fig. 6. The 3D model of proposed differential ICS-SRR-based microwave sensor

Fig. 7. Simulated transmission coefficients $S_{\mathrm{21}}$ for real permittivity of material under test altering from 1 to 80

Fig. 8. Simulated relative resonant frequency shift versus real permittivity

Fig. 9. Photograph of proposed differential microwave sensor

Fig. 10. Experimental photograph of proposed sensor

Fig. 11. Simulated and measured reflection coefficient and transmission coefficient for PDMS loaded and unloaded

Fig. 12. Measured S-parameters，resonant frequencies，and notched magnitudes for water concentration altering from 0% to 100% with a step of 20%

Fig. 13. Measured S-parameters，resonant frequencies，and notched magnitudes for water concentration altering from 10% to 90% with a step of 20%

Fig. 14. A comparison between reference value and measured complex permittivity

Fig. 15. A comparison between traditional SRR-based sensor and proposed ICS-SRR-based sensor in terms of sensitivity