Switchable trifunctional terahertz absorber for both broadband and narrowband operations

Tunable ultra-wideband graphene-based filter with a staggered structure

We present a tunable ultra-wideband band-stop filter utilizing graphene with a straightforward staggered structure. The transmission spectrum has been meticulously analyzed using the effective-index-based transfer matrix method (EIB-TMM). The results demonstrate that the filtering properties can be precisely tailored by manipulating the Fermi energy level of graphene. Importantly, we have successfully achieved a remarkable ultra-wideband stopband by optimizing the staggered parameters. Our exploration of redefining the staggered structure through adjustments to three critical parameters has revealed a crucial role in expanding bandwidth. This investigation deepens our understanding of how nonperiodic structures can effectively broaden bandwidth and holds great promise for the prospective design of ultra-wideband band-stop devices.

Switchable broadband/narrowband absorber based on a hybrid metasurface of graphene and metal structures

This paper proposes a switchable broadband/narrowband absorber based on a hybrid metasurface comprising graphene and metal in the millimeter-wave regime. The designed absorber achieves broadband absorption when the surface resistivity of graphene R_s = 450 Ω/◻ and narrowband absorption when R_s = 1300 Ω/◻ and 2000 Ω/◻. The physical mechanism behind the graphene absorber is explored by analyzing the distributions of power loss, electric field, and surface current densities. An equivalent circuit model (ECM) based on transmission-line theory is derived to theoretically investigate the performance of the absorber, with ECM results in good agreement with simulation results. Furthermore, we fabricate a prototype and evaluate its reflectivity by applying various biasing voltages. The results obtained from the experiment are also consistent with those obtained from the simulation. When the external bias voltage is changed from +1.4 V to -3.2 V, the proposed absorber has an average reflectivity ranging from -5 dB to -33 dB. The proposed absorber has potential applications in radar cross-section (RCS) reduction, antenna design, electromagnetic interference (EMI) shielding, and EM camouflage techniques.

Penrose tiling-inspired graphene-covered multiband terahertz metamaterial absorbers

In this work, we propose two different graphene-covered nanostructured metamaterial absorbers inspired by Penrose tiling. These absorbers allow spectrally tunable absorption within the terahertz spectrum corresponding to 0.2-20 THz. We have conducted finite-difference time-domain analyses to determine the tunability of these metamaterial absorbers. The proposed structures, Penrose models 1 and 2, perform differently from each other due to their design characteristics. Penrose model 2 reaches a perfect absorption at 8.58 THz. In addition, the relative absorption bandwidth calculated at full-wave at half-maximum in Penrose model 2 varies between 5.2% and 9.4%, which characterizes the metamaterial absorber as a wideband absorber. Also, we can observe that as we increase the Fermi level of graphene from 0.1 to 1 eV, the absorption bandwidth and relative absorption bandwidth both increase. Our findings show the high tunability of both models through varying graphene's Fermi level, the graphene's thickness, the substrate's refractive index, and the proposed structures' polarization. We can further observe multiple tunable absorption profiles that may find applications in designer infrared absorbers, optoelectronic devices, and THz sensors.