Polarization-independent Perfect Absorber Research Articles

Polarization-Independent Perfect Absorption in Monolayer Black Phosphorus Metasurfaces at Terahertz Frequencies via Critical Coupling.

Two-dimensional (2D) materials, which possess rich underlying physical properties that can provide the potential for designing more efficient and compact optoelectronic devices, have attracted great interest among scientists. Due to the atomic-scale thickness and the anisotropy of in-plane conductivity, 2D black phosphorus (BP) exhibits a polarization-dependent absorption spectrum with low absorption, which limits its further development in polarization-independent applications such as light absorbers and sensors. In this paper, a polarization-independent perfect absorber in the terahertz band is proposed, which is composed of a patterned BP monolayer deposited on a lossless photonic crystal (PC) slab with a back reflection mirror. The absorption of the patterned BP monolayer can reach 100% at resonant frequencies through the critical coupling mechanism of guided resonance. Moreover, the absorber exhibits polarization-independent absorption characteristics for vertically incident light, which are attributed to the 4-fold rotational symmetry of the PC substrate and the patterned BP monolayer deposited on it. This work opens up the possibility of fabricating optically polarization-independent devices based on single-layer 2D anisotropic materials.

Polarization-independent perfect metamaterial absorber for C, X and, Ku band applications

In this paper, a polarization-independent perfect absorber with near-zero index metamaterial (NZIM) property is proposed. Conventional FR4 substrate without any lumped or substrate-embedded elements has been used with a unique patch of the swastika-shaped capacitive gap along with inductive tails at 90-degree rotational symmetry. The simulation results for both the unit cell and the array for co-polarized waves at normal and oblique incidences up to 90° has shown near unity absorptions at 4.238, 7.836, 10.482, 11.014 and 13.352 GHz along with near zero values of permittivity, permeability, and refractive index. The cross-polarization analysis has proved its perfect absorption capability. The absorber has shown 14 GHz of near-zero refractive index at the entire operating frequency range. The equivalent circuit analysis and measurement of both the array and the unit cell were in good agreement with simulation results, which proved it as a perfect NZIM absorber to enhance antenna gain and directivity and other sensing applications at C, X and Ku band.

Tunable Extraordinary Transmission through a Graphene-Covered Hole Array: an Analytical Equivalent-Circuit Modeling Approach

We study two-dimensional (2D) hole arrays drilled into a perfect conductor slab covered with a graphene sheet. Such arrays support the extraordinary transmission of electromagnetic waves and allow tunability via graphene properties. We investigate the effect of graphene on transmission spectra by proposing an accurate analytical circuit model for the structure, where the graphene contributes an admittance component at the interface. The model demonstrates how extraordinary transmission can be tuned via the graphene conductivity. We study the free-standing structure, where the hole array is covered by a graphene sheet on both sides of the conductor slab, and a substrate-bound hole array covered by graphene on the exposed slab surface. The results are compared to full-wave simulations, yielding good agreement. In addition, thanks to the proposed circuit model, we demonstrate a polarization-independent perfect absorber by tuning the surface conductivity of graphene.