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… Show more
“…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.…”
The forthcoming sixth generation (6G) communication network is envisioned to provide ultra-fast data transmission and ubiquitous wireless connectivity. The terahertz (THz) spectrum, with higher frequency and wider bandwidth, offers great potential for 6G wireless technologies. However, the THz links suffers from high loss and line-of-sight connectivity. To overcome these challenges, a cost-effective method to dynamically optimize the transmission path using reconfigurable intelligent surfaces (RISs) is widely proposed. RIS is constructed by embedding active elements into passive metasurfaces, which is an artificially designed periodic structure. However, the active elements (e.g., PIN diodes) used for 5G RIS are impractical for 6G RIS due to the cutoff frequency limitation and higher loss at THz frequencies. As such, various tuning elements have been explored to fill this THz gap between radio waves and infrared light. The focus of this review is on THz RISs with the potential to assist 6G communication functionalities including pixel-level amplitude modulation and dynamic beam manipulation. By reviewing a wide range of tuning mechanisms, including electronic approaches (complementary metal-oxide-semiconductor (CMOS) transistors, Schottky diodes, high electron mobility transistors (HEMTs), and graphene), optical approaches (photoactive semiconductor materials), phase-change materials (vanadium dioxide, chalcogenides, and liquid crystals), as well as microelectromechanical systems (MEMS), this review summarizes recent developments in THz RISs in support of 6G communication links and discusses future research directions in this field.
“…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.…”
The forthcoming sixth generation (6G) communication network is envisioned to provide ultra-fast data transmission and ubiquitous wireless connectivity. The terahertz (THz) spectrum, with higher frequency and wider bandwidth, offers great potential for 6G wireless technologies. However, the THz links suffers from high loss and line-of-sight connectivity. To overcome these challenges, a cost-effective method to dynamically optimize the transmission path using reconfigurable intelligent surfaces (RISs) is widely proposed. RIS is constructed by embedding active elements into passive metasurfaces, which is an artificially designed periodic structure. However, the active elements (e.g., PIN diodes) used for 5G RIS are impractical for 6G RIS due to the cutoff frequency limitation and higher loss at THz frequencies. As such, various tuning elements have been explored to fill this THz gap between radio waves and infrared light. The focus of this review is on THz RISs with the potential to assist 6G communication functionalities including pixel-level amplitude modulation and dynamic beam manipulation. By reviewing a wide range of tuning mechanisms, including electronic approaches (complementary metal-oxide-semiconductor (CMOS) transistors, Schottky diodes, high electron mobility transistors (HEMTs), and graphene), optical approaches (photoactive semiconductor materials), phase-change materials (vanadium dioxide, chalcogenides, and liquid crystals), as well as microelectromechanical systems (MEMS), this review summarizes recent developments in THz RISs in support of 6G communication links and discusses future research directions in this field.
“…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] .…”
Section: Design and Resultsmentioning
confidence: 99%
“…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 .…”
Section: Design and Resultsmentioning
confidence: 99%
“…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.…”
“…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]…”
Section: Parameters Discussion and Revisionsmentioning
Superior analogs for electromagnetically induced transparency (EIT) and absorption (EIA) in metasurfaces (MSS) are universal, but fewer integrate both effects in one device, let alone contribute to polarization manipulations. Here, note that asymmetrical EITs are rigorously demonstrated under both polarization incidences in dielectric orthogonal dumbbell‐shaped structures, with a maximum group delay of 335 ps. The transverse magnetic (TM) mode excited EIT holds a transparent window at 1.318 THz close to the transverse electric (TE) mode excited that of 1.358 THz, which triggers the linear‐to‐circular polarization conversion at 1.339 THz with an optimized transmittance of 0.67, validated via the axial ratio. Additionally, asymmetrical EIAs are presented with an embedded metal‐phase VO2 plate, holding a common absorption of 0.51 at 1.340 THz, of which the insulating state affects little to the circular‐polarization output. Given the detuning of two frequencies (1.339 and 1.340 THz) can be compensated by the dispersion properties, it can be understood as the original converted circularly polarized propagating light decays with 0.5‐absorption via phase‐tuned VO2, operating as a temperature‐driven switch. The circular‐polarization transmission and absorption are integrated respectively based on EIT and EIA with the different states of VO2, promising broad prospects in multifunctional devices.
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