Quad-band terahertz metamaterial absorber enabled by an asymmetric I-type resonator formed from three metallic strips for sensing application

A quad-band near-perfect terahertz absorber employing an asymmetric metamaterial element is demonstrated.

Ultrahigh-Q Tunable Terahertz Absorber Based on Bulk Dirac Semimetal with Surface Lattice Resonance

In this paper, we present an easy-to-implement metamaterial absorber based on bulk Dirac semimetal (BDS). The proposed device not only obtains an ultrahigh quality factor (Q-factor) of 4133 and dynamic adjustability at high absorption, but also exhibits an excellent sensing performance with a figure of merit (FOM) of 4125. These outstanding properties are explained by the surface lattice resonance, which allows us to improve the quality factor significantly and control resonance wavelength precisely by tuning the unit cell periods, Fermi energy of the BDS, and structural parameters. Our findings can provide high-performance applications in terahertz filtering, detection, and biochemical sensing.

Narrowband-to-broadband switchable and polarization-insensitive terahertz metasurface absorber enabled by phase-change material

A terahertz absorber with controllable and switchable bandwidth and insensitive to polarization is of great interest. Here, we propose and demonstrate a metasurface absorber with switchable bandwidth based on a phase-change material of vanadium dioxide (VO2) and verify its performance by the finite element method simulations. The metasurface absorber is composed of a hybrid cross fractal as a resonator separated from a gold ground-plane by a polyimide spacer. Switching from narrowband to broadband absorber is achieved via connecting VO2 patches to the gold first-order cross fractal converting the resonator to a third-order cross fractal. In the insulator phase of VO2, the main narrowband absorption occurs at the frequency of 6.05 THz with a 0.99 absorption and a full-width half-maximum (FWHM) of 0.35 THz. Upon insulator-to-metal transition of VO2, the metasurface achieves a broadband absorption with the FWHM of 6.17 THz. The simulations indicate that by controlling the partial phase-transition of VO2, we can tune the bandwidth and absorption level of the absorber. Moreover, the designed absorber is insensitive to polarization due to symmetry and works well for a very wide range of incident angles. In the metallic state of VO2, the absorber has an absorption exceeding 0.5 in the 3.57-8.45 THz frequency range with incident angles up to 65°.

Electrically Tunable Perfect Terahertz Absorber Using Embedded Combline Graphene Layer

Graphene is a powerful 2-D matter with the capability of extraordinary transparency, and tunable conductivity is employed in emerging optoelectronics devices. In this article, the design of an electrically tunable graphene-based perfect terahertz absorber is proposed and evaluated numerically. The introduced structure is composed of two graphene layers with a sharp absorption peak in the terahertz band. These graphene layers are combline and stripline separated by the insulator substrate. The position of the absorption peak is tunable on the absorption band by means of manipulation in geometric parameters of the combline graphene layer. Furthermore, the intensity and frequency of the absorption peak can be flexibly modulated by varying Fermi potential of the combline graphene layer, which can be controlled through external DC voltages without the need of changing the geometry of the structure. It is shown that the absorption band can be tuned in the bandwidth from 5 to 15 in terahertz. The findings of this paper can promote a new perspective in designing perfect ribbon absorbers based on graphene properties that can be utilized for future photodetectors, solar cells, and thermal sensors with an absorption intensity above 2 × 105(nm2) with narrow absorption bandwidth of 0.112 THz.