In this paper, a tunable multilayer metamaterial absorber is proposed, which is composed of VO2-graphene mixed structure layer, PDMS dielectric layer, VO2 layer, PDMS dielectric layer and bottom metal film layer. The simulation results show that when VO2 is in the insulating phase and the Fermi level of graphene is 0.9 eV, the absorption peak of 0.75–1.15 THz is generated by the interaction resonance of graphene and bottom metal. When VO2 is in metal phase and the Fermi level of graphene is 0 eV, the absorption peak of 2.5–4.5 THz is generated by the resonance of vanadium dioxide. Therefore, the tunable switching between two different frequency bands can be realized. Moreover, the dual regulation of both vanadium dioxide conductivity and graphene Fermi energy level can also modulate the absorption amplitude and broaden absorption band. In order to explain the mechanism of VO2-graphene on the absorption performance, the electric field distribution and equivalent impedance of the absorber are discussed and analyzed in this paper. In addition, the absorption performances at variable incidence angles for both TE and TM polarizations are investigated and the absorber is insensitive to polarization. Therefore, the absorber has potential application value in the terahertz field.

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We propose a bulk negative refractive index (NRI) metamaterial composed of periodic array of tightly coupled metallic cross-pairs printed on the six sides of a cube for applications of superlenses. The structural characteristics of the three-dimensional (3D) metamaterial consist in the high symmetry and the superposition of metallic cross-pairs, which can increase the magnetic inductive coupling between adjacent cross-pairs and realize a broadband and isotropic NRI. The proposed 3D structure is simulated using the CST Microwave Studio 2006 to verify the design validity. The simulation results show that the proposed structure can not only realize simultaneously an electric and magnetic response to an incident electromagnetic (EM) wave, but also exhibit a broadband NRI whose relative bandwidth can reach up to 56.7%. In addition, the NRI band is insensitive to the polarization and the incident angle of the incident EM wave. Therefore, the proposed metamaterial is a good candidate material as three-dimensional broadband isotropic NRI metamaterial.