Fig. 1. Structure diagrams of proposed metamaterial sensor. (a) 3D array diagram ; (b) unit structure diagram (h=50 μm, p=500 μm, l=300 μm, r=60 μm, a=294 μm, and b=60 μm); (c) cross sectional view of the unit structure filled with silk fibroin, and the thickness of silk fibroin film is 15 μm

Fig. 2. Transmission spectra obtained by scanning different structure parameters via the simulation software in the 0-0.8 THz band. (a) Total length a of the dumbbell shaped hole; (b) thickness h of the stainless-steel plate; (c) width l of the stainless-steel plate; (d) period p of the stainless-steel plate; (e) radius r of the two circles of the dumbbell shaped hole

Fig. 3. Transmission curve of proposed metamaterial sensor with optimized structural parameters (total length a=294 μm, thickness h=50 μm, period p=500 μm, width l=300 μm, circle radius r=60 μm, and middle width b=60 μm)

Fig. 4. Surface current distribution and magnetic field intensity distribution at the frequency of 0.47 THz. (a) Top view of surface current distribution; (b) magnetic field intensity distribution in the xoz plane

Fig. 5. Simulation results of transmission spectra and linear fitting curve of the relationship between transmission frequency of resonance peak and relative humidity for proposed metamaterial sensor. (a) Transmission spectra; (b) linear fitting curve

Fig. 6. Physical photos of proposed sensor. (a) Fabricated metamaterial humidity sensor; (b) microscopy pictures of the unit cell

Fig. 7. Schematic and physical device diagram of humidity control system. (a) Schematic; (b) physical device diagram

Fig. 8. Measurement results of transmission spectra and linear fitting curve of the relationship between transmission frequency of resonance peak and relative humidity for proposed metamaterial sensor. (a) Transmission spectra; (b) linear fitting curve