Fig. 1. Schematic diagrams of the tunable and scalable metamaterial ultra-broadband absorber with the VO2 spacer in the (a) insulating phase and (b) metallic phase. Here, a group of multi-width Cr−VO2 sub-cells is placed directly on the surface of a uniform Cr substrate. Parameters are set as p=1900  nm, w1=200  nm, w2=300  nm, w3=400  nm, w4=500  nm, t1=300  nm, t2=260  nm, t3=30  nm, g1=80  nm, g2=120  nm, g3=140  nm. The surrounding material is air.

Fig. 2. Calculated absorbance spectra. BW, bandwidth; AA, average absorption.

Fig. 3. Electric and magnetic field distributions of the TSMA with the VO2 under the insulating state.

Fig. 4. Electric and magnetic field distributions of the TSMA with the VO2 under the metallic state.

Fig. 5. (a), (b) Spectral comparison between the proposed TSMA and planar films with different top metals. (c), (d) Spectral comparison between TSMAs with different top and bottom metals.

Fig. 6. (a) Real parts of the refractive indices for Cr and VO2. (b) Imaginary parts of the refractive indices for Cr and VO2. (c) Temperature-dependent absorption spectra of the VO2-based TSMA.

Fig. 7. Scalability demonstration of the VO2-TSMA with 3-width (black line) and 5-width (blue line) sub-cells, compared with the proposed reference structure with 4-width sub-cells (red line).

Fig. 8. Absorption spectra of the VO2-TSMA with various thicknesses of top-Cr and VO2, calculated at 25°C and 80°C.

Fig. 9. Angular dispersions of the TSMA under VO2 (I) as well as VO2 (M) for both TE and TM polarizations.