Vanadium Dioxide-Based Terahertz Metamaterial Devices Switchable between Transmission and Absorption

Two bits dual-band switchable terahertz absorber enabled by composite graphene and vanadium dioxide metamaterials

This article presents the design of a 2-bit dual-band switchable terahertz absorber using a stacked combination of graphene and vanadium dioxide (VO2) metamaterials. For the first time, the proposed absorber design offers four switchable states by controlling the conductivity of graphene and VO2 metamaterial layers. The lower absorption band is produced by the graphene metamaterial, whereas the upper band is implemented by the VO2 metamaterial pattern. The structure shows two absorption bands (State 11) at 0.745-0.775 THz and 2.3-5.63 THz, when the Fermi graphene level of graphene is 0.2 eV and the VO2 is in the metallic phase. The lower absorption band is turned off, while keeping the upper band (State 01), when the graphene Fermi level is 0 eV and the VO2 layer is in the metallic phase. The upper absorption band is turned off, while preserving the lower absorption band (State 10) by switching the VO2 into the insulator phase and keeping the graphene Fermi level at 0.2 eV. Finally, both of the absorption bands are turned off by setting the graphene Fermi level to 0 eV and switching the VO2 into the insulating phase. Equivalent circuit modelling analysis and full-wave electromagnetic simulations are used to explain the operation principle of the proposed absorber. Very good agreement is obtained between the theoretical analysis and the simulations confirming the presented design principle for the 2-bit switchable absorber.

Switchable bi-functional metasurface for absorption and broadband polarization conversion in terahertz band using vanadium dioxide and photosensitive silicon

We proposed a bi-functional switchable metasurface based on vanadium dioxide (VO2) and photosensitive silicon. The metasurface functions as a transmissive polarization converter in its insulating state with asymmetric transmission characteristics. It attains a remarkable polarization conversion rate (PCR) surpassing 90% and a notable maximum asymmetric transmission (AT) parameter value of 0.73. This performance is observed within the frequency range from 4.31 to 7.86 THz. Dynamic regulation of PCR and AT can be achieved by adjusting the conductivity of photosensitive silicon. To illustrate the underlying factor behind the broadband polarization conversion, the surface current distribution is analyzed at 5.96 THz and 6.08 THz. On the other hand, when VO2is in the metallic state, the metasurface transforms into a bidirectional absorber with near-perfect absorption in both illumination directions. Under forward incidence of terahertz waves, the absorption rates for the transverse electric and transverse magnetic waves are 99.3% at 3.54 THz and 93% at 3.56 THz, respectively. The physical mechanism of near-perfect absorption is explained using impedance matching theory and the electric field distribution. This research expands the applications of transmissive polarization converters within multifunctional metasurfaces, providing new avenues for their practical implementation.