Multiple tunable six-peak graphene absorber for high-performance refractive index sensing

In the present study, a design of a novel metamaterial absorber is proposed. It consists of a gold substrate at the bottom, a dielectric layer filled with silica in the middle, and a top layer of specially patterned graphene as the covering. The absorber we designed has a straightforward structure, is convenient to fabricate, and has a period of 6.1 μm. As simulated by FDTD Solution, the absorber absorption peaks are located at 6.1328 THz, 10.7916 THz, 16.4188 THz, 20.8016 THz, 22.9118 THz, and 25.1303 THz. The absorptivity of the six absorption peaks were 95.82 %, 92.58 %, 96.31 %, 99.56 %, 93.67 %, and 99.62 %, respectively, and the average absorptivity reached 96.26 %. The absorber, additionally, shows insensitivity in both TE and TM polarization modes. We utilized impedance matching theory, electromagnetic field theory, and plasma resonance theory to analyze the resonance peaks of the absorber. The analysis demonstrates that adjusting the graphene's chemical potential and relaxation time can modulate the resonance frequency and absorptivity of the absorption peak. With the angle of incidence varying in the range of 0°–60°, the absorber can be found to be insensitive to the angle. As the ambient refractive index and SiO₂ refractive index changed, research was carried out on the Figure of Merit, sensitivity, and Q - Factor of each absorption peak. Finally, by comparing the absorber with other absorbers, the absorber performs well in terms of average absorptivity, FOM, sensitivity and Q-Factor. To sum up, there are potential applications for the absorber designed in this paper in the fields of photodetectors and solar cells.