FDTD subcell graphene model beyond the thin-film approximation

Abstract

A subcell technique for calculation of optical properties of graphene with the finite-difference time-domain (FDTD) method is presented. The technique takes into account the surface conductivity of graphene which allows the correct calculation of its dispersive response for arbitrarily polarized incident waves interacting with the graphene.The developed technique is verified for a planar graphene sheet configuration against the exact analytical solution. Based on the same test case scenario, we also show that the subcell technique demonstrates a superior accuracy and numerical efficiency with respect to the widely used thin-film FDTD approach for modeling graphene. We further apply our technique to the simulations of a graphene metamaterial containing periodically spaced graphene strips (graphene strip-grating) and demonstrate good agreement with the available theoretical results.

Electrodynamic models of 2D materials: can we match thin film and single sheet approaches?

“…Notably, a high value of ∆T is observed on a vertical line corresponding to Re [χ s ] = d f , for which the real part of the permittivity ε = 1 − χ s /d f vanishes. This shows, similarly to what was reported in [21], that an artificial plasmonic resonance is predicted by an isotropic thin film model, due to the artificial metallic nature of the out-of-plane component of the permittivity tensor. This unphysical resonance could have dramatic effects on the prediction of the optical properties.…”

“…In particular, it confirms that in the limit d f = 0, both models agree, as reported in [32]. More importantly, this also resolves the apparent contradiction between the conclusions of [32], and those of [18,19,21] on the equivalence (or not) of both models for d f → 0. Indeed, (19) shows that, if we model graphene by means of a thicker layer so that χ s…”

“…The results for the anisotropic thin film cannot be distinguished from those of the anisotropic single sheet, and are therefore not plotted. The thickness d f = 5 nm is commonly used in discrete numerical simulations to avoid prohibitive numerical cost [21]. As expected, at normal incidence, all curves are superimposed and the anisotropy does not play any role.…”

“…However, these two approaches (a purely 2D surface conductivity and a 3D isotropic thin film) do not match as demonstrated analytically and numerically [18,19] and give model-dependent interpretation of ellipsometric data [20]. This is particularly true for oblique incidence and TM (p-polarised) EM radiation [21]. Indeed, considering only a purely inplane 2D conductivity means that the out-of-plane response of the layer is neglected, while for an isotropic thin film, both the in-plane and out-of-plane responses are linked.…”

Development of a miniature microwave radiothermograph for monitoring the internal brain temperature

“…To calculate EF E(r), it is necessary to carry out numerical modeling in the program of electrodynamic modeling taking into account electrical losses and the antenna design. Computations were performed using the HIPERCONE FDTD program [25] based on the EMTL (Electromagnetic Template Library) interface [26,27]. The high-performance core of Hipercone uses a new class of asynchronous vectorized updates of the calculation grid.…”