A bifunctional metamaterial is proposed based on a hybrid graphene and vanadium dioxide (VO2) configuration, which can realize a dynamic switch between beam steering and broadband absorption. The structure consists of a VO2 square, graphene patch, topas spacer, VO2 film, topas spacer, and metal substrate. When VO2 is in the metallic state, the structure serves as a coding metamaterial. By engineering different sizes of the top VO2 square and adjusting the Fermi energy level of graphene, the incident wave is scattered in different patterns. When VO2 is in the dielectric state, the structure serves as a broadband absorber. By changing the Fermi energy level of graphene from 0.0 eV to 0.9 eV, absorptance can be gradually changed and working bandwidth widens. There is an absorption band with near 100% absorptance from 0.9 THz to 1.35 THz when the Fermi energy level is 0.73 eV. And the designed broadband absorber is polarization-insensitive within the incident angle of 50°. Our work may show great potential in applications such as terahertz switching and modulation.

As an emerging material, graphene has been widely applied in the field of active metasurface. Recently, researchers employed graphene to achieve dynamical control of electromagnetic wavefront. In this work, graphene-based reflective metasurface is presented to realize dynamical wavefront reconfiguration for terahertz wave. Using a hybrid structure of cross-shaped graphene and metal patch, the designed metasurface has 360° phase modulation capability. Its wavefront is reconfigurable and can realize multiple functions. In order to verify this, three examples are designed to demonstrate the phenomenon of wavefront reconstruction. They are gradient metasurface, vortex beam generator, and focusing mirror, respectively. First of all, Fermi level of graphene is used to reconstruct the reflected wavefront of gradient metasurface, and then realize switching between positive and negative reflections. Secondly, a vortex beam generator is implemented, and it can reconstruct the mode number of orbital angular momentum through Fermi level. Finally, a reflective lens is proposed and verified, whose focus can appear or disappear with the tuning of Fermi level. The proposed functions have potential applications in the fields of terahertz switching, communication, and focusing.

Coding metasurfaces incorporated with reconfigurable elements can dynamically control electromagnetic waves to realize reconfigurable multiple functionalities. The mostly existing active devices usually work in microwave band and have little ability to dynamically control terahertz waves. Here, a graphene-based coding metasurface (GBCM) is presented to realize dynamic beam steering for terahertz waves. The coding state "1" of the proposed GBCM can be continuously tuned to "0" by Fermi level of an integral graphene film. In order to verify the working principle, two examples are designed to demonstrate the dynamic tunability of the proposed GBCM for terahertz waves. One is dynamic multi-beam switching and another is dynamic diffusion switching. Under the normal illumination of terahertz waves, a 1D periodic-sequence GBCM produces dual-, tri-and single-beam by setting Fermi level as 0.05 eV, 0.15 eV and 0.70 eV, respectively. Similarly, a 2D periodic-sequence GBCM produces quad-, penta-and single-beam by setting Fermi level as 0.05 eV, 0.11 eV and 0.70 eV, respectively. In the case of aperiodic coding sequence, reflected waves can be dynamically switched from diffusion to mirror reflection by increasing Fermi level from 0.05 eV to 0.70 eV. The above functionalities are well verified by theoretical calculations and numerical simulations.

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A new dual‐band bandpass filter (BPF) using two very simple coupled microstrip rings is proposed in this paper. The two identical 3λg/2 microstrip rings are coupled each other with λg/2 coupled length, resulting in the generation of dual frequency bands with multiple transmission zeros (TZs). Theoretical deduction is presented to verify the proposed structure. The center frequencies and bandwidths of the two passbands can be tuned by controlling the impedance parameters of the microstrip rings. For demonstration, a prototype example of this dual‐band BPF is fabricated and characterized. The measured results show that it has high selectivity and great return losses of passbands with multiple TZs at the stopband.