A multiband tunable metamaterial terahertz absorber based on VO2 material is introduced and studied. The absorber consists of gold planes and periodic metallic materials. The first layer is gold plane, the second layer is polyimide, the third layer is silicon film, and the fourth layer is super surface. From the simulation results, we can see that the phase transition occurs when the temperature of VO2 is greater than or equal to 68°C. After the phase transition, there are three absorption peaks, and the absorption rates are more than 99% at 2.53, 5.7, and 8.67 THz, realizing perfect absorption. When the temperature of VO2 is less than 68°C, the maximum absorption rate is 30.4%, which fails to meet the absorption requirements. By increasing the thickness of polyimide, the absorption spectrum moves slightly to the low frequency band to achieve redshift. Compared with most of the proposed multiband absorbers, the metamaterial absorber with adjustable absorption spectrum has better application prospects. VO2 is a phase change material with insulator metal phase transition characteristics and reversible process. By using the phase transition characteristics of VO2, the absorber has a switching function and is conducive to the flexible regulation of the absorption spectrum.
A metamaterial- and graphene-based broadband terahertz (THz) electromagnetic wave absorber that is composed of a stack of patterned gold film layer, patterned graphene layer, polyimide layer, and silicon layers was studied in detail. Our study is based on numerical simulations and electromagnetic absorption level higher than 90% over 2.09 THz band was demonstrated. The absorption frequency band significantly depends on the thickness of the polyimide layer and red shifts in parallel with its thickness. The major role of the added patterned graphene layer is to introduce frequency tunability property to the almost perfect absorption. As the Fermi level of graphene changed from 0 to 0.6 eV, the center frequency of the absorption band blueshifts from 6.19 to 8.15 THz. We also investigated incoming beam angle of incidence dependence and polarization sensitivity of the absorption. Metamaterial-based tunable absorbers prospected to be utilized in high-performance THz devices as a performance boosting critical element.
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