Stamatios A. Amanatiadis

On the Use of FDTD and Ray-Tracing Schemes in the Nanonetwork Environment

In this letter, the finite difference time-domain (FDTD) method and the ray-tracing (RT) technique are systematically revisited and compared as potential tools that can reliably characterize new protocols for emerging nanonetwork applications. To this aim, a set of efficient simulation schemes for the precise prediction of the reception quality in various communication scenarios is presented. In particular, each algorithm involves a similar configuration with a realistic transmitter/receiver model and multiple obstacles sized up to some micrometers. The proposed analysis reveals that, unlike conventional assessments, the RT approach can be successfully employed at nanoscale dimensions, with increasing accuracy at higher frequencies, as a tool for fast received-energy estimations, since its results are in acceptable agreement with the respective FDTD data. These significant deductions are, finally, substantiated by a theoretical formulation equivalent to that of frequency selective surfaces.

A Loss-Controllable Absorbing Boundary Condition for Surface Plasmon Polaritons Propagating Onto Graphene

The development of a robust terminating boundary scheme for the transverse magnetic surface plasmon polaritons, supported on graphene, is introduced in this paper and incorporated in the finite-difference time-domain (FDTD) method. First, the 2-D FDTD algorithm is adjusted to efficiently model the graphene sheet as a surface conductivity, and the effect of the scattering rate-the main loss mechanism of graphene-on the surface wave propagation properties, is thoroughly studied. Then, the new scheme is optimally formulated via the prior scattering rate and combined with the FDTD algorithm. Its enhanced performance is successfully validated for several 2-D setups and a 3-D configuration with a surface wave traveling on a graphene microribbon waveguide.

A Convolutional PML Scheme for the Efficient Modeling of Graphene Structures through the ADE-FDTD Technique

A new auxiliary differential equation finite-difference time-domain method, incorporating a rigorous convolutional perfectly matched layer, is presented in this paper for the termination of infinite graphene structures. The consistency and performance of the featured technique is substantiated via detailed comparisons with setups terminated by existing absorbing boundary conditions.

Radiation Efficiency Enhancement of Graphene THz Antennas Utilizing Metamaterial Substrates

The radiation efficiency improvement of graphene plasmonic antennas via synthesized substrates with metamaterial resonators is introduced in this letter. Graphene, represented as an ultrathin layer, can support highly confined surface waves of significantly decreased wavelength compared to the vacuum one. Although this concept yields more compact devices, its applicability to graphene antennas is limited, due to the degradation of radiation efficiency. Thus, the effect of a substrate material on the surface-wave wavelength is thoroughly examined, while radiators of larger dimensions and enhanced efficiency are designed for an epsilon-negative medium. Also, a novel realistic metamaterial substrate is developed for graphene terahertz (THz) antennas, successfully verifying all theoretical estimations. Numerical results are extracted via an accurate finite-difference time-domain algorithm that treats graphene as an efficient surface boundary condition.

Surface plasmon polariton waves onto graphene's surface over an anisotropic metamaterial substrate

The present work investigates the propagation properties of the surface plasmon polariton wave supported on graphene surface over an anisotropic substrate at far-infrared frequencies. Initially, the surface wave’s propagation on isotropic media substrate is studied and verified with the theoretical estimation, including the noteworthy epsilon-near-zero case. Moreover, after utilizing theoretical substrate media and examining anisotropy relative to the normal to graphene’s surface, direction, the anisotropy is enforced to the tangential direction revealing the significant influence of the substrate on the surface wave that is propagating on graphene. Additionally, the more realistic implementation with graphene’s substrate consisting of metamaterial resonators is thoroughly investigated. Numerical results are extracted through a reliable finite-difference time-domain (FDTD) algorithm, focalising, mainly, on the wavelength of graphene’s surface wave.

Precise Modeling of Magnetically Biased Graphene Through a Recursive Convolutional FDTD Method

An efficient and consistent technique to implement numerically a magnetically biased graphene layer is introduced in this paper. Through the novel scheme and after applying a magnetic bias perpendicular to graphene, its surface conductivity presents anisotropic behavior and this effect is systematically modeled and incorporated in terms of the recursive convolution formulation in the finite-difference time-domain algorithm. The extracted numerical results are comprehensively compared with the corresponding analytical expressions to validate the significant performance of the proposed method over a wide frequency range.

Evaluation of magnetic field’s uniformity inside electromagnetic coils using graphene

The distribution of the magnetic field in electromagnetic coils, such as those employed in magnetic resonance imaging (MRI), is evaluated in this paper, through graphene gyrotropic properties. Initially, the rotation of an incident linearly polarized plane wave, due to an infinite graphene layer, is studied theoretically via the extraction of the perpendicular, to the polarization, electric component of the transmitted wave. Moreover, the influence of the magnetic bias field strength on this component is, also, examined, indicating the eligibility of graphene to detect magnetostatic field variations. To this aim, a specific device is proposed, consisting of a high frequency source, an electric field detector, and a finite graphene sheet that differs from the infinite one of the analytical case. To quantify the distance that the gyrotropic effects are detectable, the effective region is introduced and extracted via a properly modified finite-difference time-domain (FDTD) algorithm. The featured device is v...

Graphene sheet modeling with an efficient unconditionally-stable hybrid approach

The combination of two versions of a split-step finite-difference time-domain (FDTD) algorithm is proposed for the efficient simulation of waves supported by graphene sheets. A dispersive scheme based on the auxiliary differential equation (ADE) approach is used for the graphenes surface conductivity, while an optimized technique featuring specially designed spatial approximations is applied at free-space grid points. The involved equation updates are unconditionally stable, providing a useful as well as efficient tool for the investigation of graphene-based configurations.

Rigorous time-domain analysis of statistically oriented graphene sheet fluctuations

Purpose Important statistical variations are likely to appear in the propagation of surface plasmon polariton waves atop the surface of graphene sheets, degrading the expected performance of real-life THz applications. This paper aims to introduce an efficient numerical algorithm that is able to accurately and rapidly predict the influence of material-based uncertainties for diverse graphene configurations. Design/methodology/approach Initially, the surface conductivity of graphene is described at the far infrared spectrum and the uncertainties of its main parameters, namely, the chemical potential and the relaxation time, on the propagation properties of the surface waves are investigated, unveiling a considerable impact. Furthermore, the demanding two-dimensional material is numerically modeled as a surface boundary through a frequency-dependent finite-difference time-domain scheme, while a robust stochastic realization is accordingly developed. Findings The mean value and standard deviation of the propagating surface waves are extracted through a single-pass simulation in contrast to the laborious Monte Carlo technique, proving the accomplished high efficiency. Moreover, numerical results, including graphene’s surface current density and electric field distribution, indicate the notable precision, stability and convergence of the new graphene-based stochastic time-domain method in terms of the mean value and the order of magnitude of the standard deviation. Originality/value The combined uncertainties of the main parameters in graphene layers are modeled through a high-performance stochastic numerical algorithm, based on the finite-difference time-domain method. The significant accuracy of the numerical results, compared to the cumbersome Monte Carlo analysis, renders the featured technique a flexible computational tool that is able to enhance the design of graphene THz devices due to the uncertainty prediction.

A convolutional PML scheme for the efficient modeling of graphene structures through the ADE-FDTD technique

The development of an accurate convolutional perfectly matched layer for the efficient termination of infinite graphene structures is introduced in this paper. Initially, the popular 2-D material receives the appropriate theoretical analysis, which reveals the necessity of a flexible terminating condition that can enhance the performance of existing absorbing schemes and offer sufficient truncation rates for the graphene’s strongly confined surface waves. The consistency and behavior of the novel technique are substantiated via comprehensive comparisons with setups truncated by conventional absorbing boundary conditions. Finally, a graphene microribbon waveguide is addressed to indicate the capabilities of featured algorithm in complex structures.