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1 – 10 of 819Zhi Gong and Shiyou Yang
The purpose of this work is to develop a computational paradigm for performance analysis of low-frequency electromagnetic devices containing both magnetic metamaterials (MTMs) and…
Abstract
Purpose
The purpose of this work is to develop a computational paradigm for performance analysis of low-frequency electromagnetic devices containing both magnetic metamaterials (MTMs) and natural media.
Design/methodology/approach
A time domain finite element method (TDFEM) is proposed. The electromagnetic properties of the MTMs are modeled by a nonstandard Lorentz model. The time domain governing equation is derived by converting the one from the frequency domain into the time domain based on the Laplace transform and convolution. The backward difference is used for the temporal discretization. An auxiliary variable is introduced to derive the recursive formula.
Findings
The numerical results show good agreements between the time domain solutions and the frequency domain solutions. The error convergence trajectory of the proposed TDFEM conforms to the first-order accuracy.
Originality/value
To the best knowledge of the authors, the presented work is the first one focusing on TDFEMs for low-frequency near fields computations of MTMs. Consequently, the proposed TDFEM greatly benefits the future explorations and performance evaluations of MTM-based near field devices and systems in low-frequency electrical and electronic engineering.
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Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community…
Abstract
Gives introductory remarks about chapter 1 of this group of 31 papers, from ISEF 1999 Proceedings, in the methodologies for field analysis, in the electromagnetic community. Observes that computer package implementation theory contributes to clarification. Discusses the areas covered by some of the papers ‐ such as artificial intelligence using fuzzy logic. Includes applications such as permanent magnets and looks at eddy current problems. States the finite element method is currently the most popular method used for field computation. Closes by pointing out the amalgam of topics.
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Irene Woyna, Erion Gjonaj and Thomas Weiland
– The purpose of this paper is to present a time domain discontinuous Galerkin (DG) approach for modeling wideband frequency dependent surface impedance boundary conditions.
Abstract
Purpose
The purpose of this paper is to present a time domain discontinuous Galerkin (DG) approach for modeling wideband frequency dependent surface impedance boundary conditions.
Design/methodology/approach
The paper solves the Maxwellian initial value problem in a computational domain, which is spatially discretized by the higher order DG method. On the boundary of the computational domain the paper applies a suitable impedance boundary condition (IBC). The frequency dependency of the impedance function is modeled by auxiliary differential equations (ADE).
Findings
The authors will study the resonance frequency and the Q factor of different types of cavity resonators including lossy materials. The lossy materials are modeled by means of IBCs. The authors will compare the results with analytical results, as well as numerical results obtained by direct calculations where lossy materials are included explicitly into the numerical model. Several convergence studies are performed which demonstrate the accuracy of the approach.
Originality/value
Modeling of frequency dependent boundary conditions in time domain with finite difference time domain method (FDTD) method is considered in numerous papers, as well as in frequency domain finite element method (FEM), and in a few papers also time domain FEM. However, FDTD method is only first order accurate and fails in modeling of complicated surfaces. FEM allows for high order accuracy, but time domain modeling is numerically extremely expensive. In frequency domain, broadband modeling of frequency dependent boundary conditions requires several simulations as opposed to the time domain, where a single simulation is needed. The time domain DG method proposed in this paper allows to overcome the difficulties. The authors introduce a broadband surface impedance formulation based on the ADE approach for the higher order DG method.
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Zhongming Bai, Xikui Ma, Xu Zhuansun and Qi Liu
The purpose of the paper is to introduce a perfectly matched layer (PML) absorber, based on Berenger's split field PML, to the recently proposed low-dispersion precise integration…
Abstract
Purpose
The purpose of the paper is to introduce a perfectly matched layer (PML) absorber, based on Berenger's split field PML, to the recently proposed low-dispersion precise integration time domain method using a fourth-order accurate finite difference scheme (PITD(4)).
Design/methodology/approach
The validity and effectiveness of the PITD(4) method with the inclusion of the PML is investigated through a two-dimensional (2-D) point source radiating example.
Findings
Numerical results indicate that the larger time steps remain unchanged in the procedure of the PITD(4) method with the PML, and meanwhile, the PITD(4) method employing the PML is of the same absorbability as that of the finite-difference time-domain (FDTD) method with the PML. In addition, it is also demonstrated that the later time reflection error of the PITD(4) method employing the PML is much lower than that of the FDTD method with the PML.
Originality/value
An efficient application of PML in fourth-order precise integration time domain method for the numerical solution of Maxwell's equations.
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Hooman Razmjoo and Masoud Movahhedi
In this paper, a modified meshless method, as one of the numerical techniques that has recently emerged in the area of computational electromagnetics, is extended to solving…
Abstract
Purpose
In this paper, a modified meshless method, as one of the numerical techniques that has recently emerged in the area of computational electromagnetics, is extended to solving time-domain wave equation. The paper aims to discuss these issues.
Design/methodology/approach
In space domain, the fields at the collocation points are expanded into a series of new Shepard's functions which have been suggested recently and are treated with a meshless method procedure. For time discretization of the second-order time-derivative, two finite-difference schemes, i.e. backward difference and Newmark-β techniques, are proposed.
Findings
Both schemes are implicit and always stable and have unconditional stability with different orders of accuracy and numerical dispersion. The unconditional stability of the proposed methods is analytically proven and numerically verified. Moreover, two numerical examples for electromagnetic field computation are also presented to investigate characteristics of the proposed methods.
Originality/value
The paper presents two unconditionally stable schemes for meshless methods in time-domain electromagnetic problems.
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Athanasios N. Papadimopoulos, Stamatios A. Amanatiadis, Nikolaos V. Kantartzis, Theodoros T. Zygiridis and Theodoros D. Tsiboukis
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…
Abstract
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.
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A. Bouquet, C. Dedeban and S. Piperno
The use of the prominent finite difference time‐domain (FDTD) method for the time‐domain solution of electromagnetic wave propagation past devices with small geometrical details…
Abstract
Purpose
The use of the prominent finite difference time‐domain (FDTD) method for the time‐domain solution of electromagnetic wave propagation past devices with small geometrical details can require very fine grids and can lead to unmanageable computational time and storage. The purpose of this paper is to extend the analysis of a discontinuous Galerkin time‐domain (DGTD) method (able to handle possibly non‐conforming locally refined grids, based on portions of Cartesian grids) and investigate the use of perfectly matched layer regions and the coupling with a fictitious domain approach. The use of a DGTD method with a locally refined, non‐conforming mesh can help focusing on these small details. In this paper, the adaptation to the DGTD method of the fictitious domain approach initially developed for the FDTD is considered, in order to avoid the use of a volume mesh fitting the geometry near the details.
Design/methodology/approach
Based on a DGTD method, a fictitious domain approach is developed to deal with complex and small geometrical details.
Findings
The fictitious domain approach is a very interesting complement to the FDTD method, since it makes it possible to handle complex geometries. However, the fictitious domain approach requires small volume elements, thus making the use of the FDTD on wide, regular, fine grids often unmanageable. The DGTD method has the ability to handle easily locally refined grids and the paper shows it can be coupled to a fictitious domain approach.
Research limitations/implications
Although the stability and dispersion analysis of the DGTD method is complete, the theoretical analysis of the fictitious domain approach in the DGTD context is not. It is a subject of further investigation (which could provide important insights for potential improvements).
Originality/value
This is believed to be the first time a DGTD method is coupled with a fictitious domain approach.
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Valerio De Santis, Mauro Feliziani and Francescaromana Maradei
The aim of the paper is to apply a numerical dosimetry procedure to a biological tissue with an embedded discrete vascularisation in order to evaluate the temperature increase…
Abstract
Purpose
The aim of the paper is to apply a numerical dosimetry procedure to a biological tissue with an embedded discrete vascularisation in order to evaluate the temperature increase produced by radio‐frequency (RF) exposure.
Design/methodology/approach
The blood temperature inside thin vessels is analysed by a 1D finite difference procedure to solve the convection‐dominated heat problem. The tissue temperature inside the remaining 3D domain governed by the heat diffusion equation is calculated by the finite element method. Then, the two separate numerical methods are coupled by an iterative time domain procedure.
Findings
The main advantage of the proposed hybrid method is found to be the considerable reduction of the number of unknowns respect to other traditional numerical techniques.
Research limitations/implications
In this paper, only the numerical model of the new hybrid procedure has been proposed. In future work realistic biological regions will be examined and the proposed model will be improved by considering the artery/vein coupled structure.
Originality/value
The originality of the proposed method regards the solution of the bio‐heat equation by means of a new hybrid finite element/finite difference procedure. This procedure is applied inside a vascularized region considering a discrete blood vessel structure.
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Jiawei Wang, Feng Chen, Jinghui Shao, Weichen Zhang and Xikui Ma
This paper aims to present a novel hybrid time integration approach for efficient numerical simulations of multiscale problems involving interactions of electromagnetic fields…
Abstract
Purpose
This paper aims to present a novel hybrid time integration approach for efficient numerical simulations of multiscale problems involving interactions of electromagnetic fields with fine structures.
Design/methodology/approach
The entire computational domain is discretized with a coarse grid and a locally refined subgrid containing the tiny objects. On the coarse grid, the time integration of Maxwell’s equations is realized by the conventional finite-difference technique, while on the subgrid, the unconditionally stable Krylov-subspace-exponential method is adopted to breakthrough the Courant–Friedrichs–Lewy stability condition.
Findings
It is shown that in contrast with the conventional finite-difference time-domain method, the proposed approach significantly reduces the memory costs and computation time while providing comparative results.
Originality/value
An efficient hybrid time integration approach for numerical simulations of multiscale electromagnetic problems is presented.
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N.V. Kantartzis, E.E. Kriezis and T.D. Tsiboukis
The FDTD approach is rapidly becoming one of the most widely used computational methods in electromagnetics. It is a marching‐in‐time procedure which simulates the continuous…
Abstract
The FDTD approach is rapidly becoming one of the most widely used computational methods in electromagnetics. It is a marching‐in‐time procedure which simulates the continuous actual waves by sampled data numerical analogues propagating in a data space stored in a computer. Thus it leads to a complete understanding of near fields and transient effects. In this paper, the study of the propagating modes and the calculation of the energy forced in the interior of a terminated waveguide is performed with an iterative FDTD technique. Results are obtained and compared with the theoretical ones. Their agreement is almost perfect.