Theoretical design of a reconfigurable broadband integrated metamaterial terahertz device

Abstract

An actively reconfigurable broadband terahertz (THz) metamaterial functional device based on the phase-change material vanadium dioxide (VO2) and two-dimensional graphene material is theoretically proposed and demonstrated. The device has excellent tolerance under oblique incidence. When the VO2 is in the metallic state, and the Fermi energy of graphene is fixed at 0.1 eV, the designed device acts as a broadband THz absorber in the transverse magnetic (TM) polarization mode. The absorptance bandwidth exceeds 0.55 THz with a complete absorption intensity of more than 90%. In this state, the absorber operates as a broadband modulator with the total modulation depth exceeding 91.5% as the continually decreased conductivity of VO2 from 200000 S/m to 10 S/m. In the transverse electric (TE) polarization process, the structure behaves as a dual-band absorber with two perfect absorption peaks. When the conductivity of VO2 is changed, the tunable absorber can also be regarded as an absorptance modulator, with a maximum modulation intensity of 92.1%. Alternatively, when VO2 behaves as an insulator at room temperature in the TE polarization mode, a strong broadband electromagnetically induced transparency (EIT) window is obtained, with a bandwidth exceeding 0.42 THz in the transmittance spectrum. By varying the Fermi energy of graphene from 0 to 0.9 eV, the EIT-like window or broadband transmission spectrum (in TM mode) can be switched. The results indicate that the device can also be operated as a modulator in the transmission mode. The impedance matching theory is used, and electric field distributions are analyzed to quantify the physical mechanism. An advantage of the manipulation of the polarization angle is that the modulation performance of the proposed multi-functional THz device can be regulated after fabricated.

Terahertz Reconfigurable Intelligent Surfaces (RISs) for 6G Communication Links

“…Optical control usually modulates the whole surface with a laser pump, but localization may be possible through an additional coding mask [101]. Tuning elements can be combined to add additional reconfigurable freedom [111,112]. Other reconfigurable methods, such as mechanical [113] and microfluid-based [114] tuning, are also feasible.…”

A VO2 film-based multifunctional metasurface in the terahertz band

“…The middle layer is polyimide with the permittivity of ε = 3.5 and the loss tangle of 0.002. For the 200 nm thick VO 2 film, the insulatorto-metal transition properties of VO 2 can be described by different values of conductivity to realize the switchability of multiple functions [21,[27][28][29][30][31][32] . In our research, the conductivity of VO 2 is set as 200 S/m and 2 × 10 5 S=m to mimic insulating state and metallic state, respectively [27,31] .…”

“…For the 200 nm thick VO 2 film, the insulatorto-metal transition properties of VO 2 can be described by different values of conductivity to realize the switchability of multiple functions [21,[27][28][29][30][31][32] . In our research, the conductivity of VO 2 is set as 200 S/m and 2 × 10 5 S=m to mimic insulating state and metallic state, respectively [27,31] . In the following, we will show the multifunctional properties of the designed metasurface based on the tunability of the VO 2 .…”

“…Song et al [21] presented a bifunctional design of a broadband absorber and a broadband polarization converter based on the insulator-to-metal phase transition of vanadium dioxide (VO 2 ), in which the 90% absorption bandwidth and 90% crosspolarized reflectance are 79% and 85%, respectively. Li et al [27] combined VO 2 and graphene to design an actively reconfigurable THz functional device with tunable absorption and electromagnetically induced transparency (EIT) window effect.…”

Circularly Polarized Manipulations with VO2‐Doped Dielectric Electromagnetically Induced Transparency and Absorption

“…Assume that the equivalent impedance of this device (Z eff ) matches that of free space (Z 0 ) in a certain resonance frequency, where the normalized complex impedance Z r = Z eff /Z 0 will be computed equal to 1, and the perfect absorption is feasible. Z eff can be derived from the inversion of S-parameters: [40,46]…”