Fig. 1. Schematic of MIM structure

Fig. 2. Simulation results of MIM structure. (a) Reflectance spectra; (b) distribution of electric field

Fig. 3. Control of geometric parameters on the resonance wavelength. (a) Effect of PVA film thickness on the resonance wavelength; (b) effect of top Ag film thickness on the resonance wavelength; (c) effect of PVA refractive index on the resonance wavelength

Fig. 4. Process of proposed MIM structure fabrication

Fig. 5. PVA aqueous solution preparation process and smoothness characterization after spin-coating. (a) Preparation process of PVA aqueous solution; (b) SEM image of PVA film

Fig. 6. Experimental testing results under different PVA film thicknesses. (a) Reflectance spectra; (b) CIE 1931 chromaticity diagram

Fig. 7. Experimental testing results under different top Ag film thicknesses. (a) Reflectance spectra; (b) CIE 1931 chromaticity diagram

Fig. 8. Experimental optical images under different PVA thicknesses and top Ag film thicknesses

Fig. 9. Relative humidity testing system

Fig. 10. Relative humidity testing reflectance spectra and linear fitting curves. (a)(b) Sample 1, PVA thickness h=90 nm; (c)(d) sample 2, PVA thickness h=110 nm

Fig. 11. Calculation results of the color, RGB values, chromaticity coordinates (x, y), and color variation path in the CIE 1931 color space for sample 1 under different relative humidity values

Fig. 12. Calculation results of the color, RGB values, chromaticity coordinates (x, y), and color variation path in the CIE 1931 color space for sample 2 under different relative humidity values