Showing papers on "Computational electromagnetics published in 2020"

Fundamental implicit fdtd schemes for computational electromagnetics and educational mobile apps (invited review)

Abstract: This paper presents an overview and review of the fundamental implicit finite-difference time-domain (FDTD) schemes for computational electromagnetics (CEM) and educational mobile apps. The fundamental implicit FDTD schemes are unconditionally stable and feature the most concise update procedures with matrix-operator-free right-hand sides (RHS). We review the developments of fundamental implicit schemes, which are simpler and more efficient than all previous implicit schemes having RHS matrix operators. They constitute the basis of unification for many implicit schemes including classical ones, providing insights into their inter-relations along with simplifications, concise updates and efficient implementations. Based on the fundamental implicit schemes, further developments can be carried out more conveniently. Being the core CEM on mobile apps, the multiple one-dimensional (M1-D) FDTD methods are also reviewed. To simulate multiple transmission lines, stubs and coupled transmission lines efficiently, the M1-D explicit FDTD method as well as the unconditionally stable M1-D fundamental alternating direction implicit (FADI) FDTD and coupled line (CL) FDTD methods are discussed. With the unconditional stability of FADI methods, the simulations are fast-forwardable with enhanced efficiency. This is very useful for quick concept illustrations or phenomena demonstrations during interactive teaching and learning. Besides time domain, many frequency-domain methods are well-suited for further developments of useful mobile apps as well.

Artificial neural network models for radiowave propagation in tunnels

Abstract: The authors present a machine learning approach for the extraction of radiowave propagation models in tunnels. To that end, they discuss three challenges related to the application of machine learning to general wireless propagation problems: how to efficiently specify the input to the model, which learning method to use and what output functions to seek. The input that any propagation modelling tool (be it a ray-tracer, a full-wave method or a parabolic equation solver) uses, can be considered as visual, in the form of an image or a point cloud of the environment under consideration. Therefore, they propose an artificial neural network structure that generalises well to various geometries. The desired output can be values of the electromagnetic field components across the channel or just a path loss model. They apply these ideas to the case of arched tunnels for the first time. They consider cases where the geometric parameters of the tunnel, the position of the receiver and the frequency of operation are parts of a model trained by a vector parabolic equation solver. The model is evaluated using solver-generated as well as measured data. The numerical results demonstrate that this approach combines computational efficiency with high accuracy.

Quantum information preserving computational electromagnetics

Abstract: We present a computational framework for canonical quantization in arbitrary inhomogeneous dielectric media by incorporating quantum electromagnetic effects into complex solutions of quantum Maxwell's equations. To do so, the proposed algorithm integrates and performs (1) numerical computation of normal modes and (2) evaluation of arbitrary products of ladder operators acting on multimode Fock states. The former is associated with Hermitian-Helmholtz linear systems using finite-element or finite-difference methods; consequently, the complete set of numerical normal modes diagonalizes the Hamiltonian operators up to floating-point precision. Its Hermiticity is retained, allowing its quantization. Then, we perform quantum numerical simulations of two-photon interference occurring in a 50:50 beam splitter to observe the Hong-Ou-Mandel effect. Our prototype model is useful for numerical analyses on various narrow-band quantum-optical multiphoton systems such as quantum metasurfaces, quantum-optical filters, and quantum electrodynamics in open optical cavities.

Numerical Methods for Engineering: An introduction using MATLAB® and computational electromagnetics examples

Abstract: The revised and updated second edition of this textbook teaches students to create modeling codes used to analyze, design, and optimize structures and systems used in wireless communications, microwave circuits, and other applications of electromagnetic fields and waves. Worked code examples are provided for key algorithms using the MATLAB technical computing language. The book begins by introducing the field of numerical analysis and providing an overview of the fundamentals of electromagnetic field theory. Further chapters cover basic numerical tasks, finite difference methods, numerical integration, integral equations and the method of moments, solving linear systems, the finite element method, optimization methods, and inverse problems. Developing and using numerical methods helps students to learn the theory of wave propagation in a concrete, visual, and hands-on way. This book fills the missing space of current textbooks that either lack depth on key topics or treat the topic at a level that is too advanced for undergraduates or first-year graduate students. Presenting the topic with clear explanations, relevant examples, and problem sets that move from simple algorithms to complex codes with real-world capabilities, this book helps its readers develop the skills required for taking a mathematical prescription for a numerical method and translating it into a working, validated software code, providing a valuable resource for understanding the finite difference method, the method of moments, the finite element method, and other tools used in the RF and wireless industry.

A Maxwell's Equations Based Deep Learning Method for Time Domain Electromagnetic Simulations

Abstract: In this study, we discuss an unsupervised deep learning approach for time-domain electromagnetic simulations. Our method, based on physics informed neural network, encodes initial conditions, boundary conditions as well as governing equations as the constraints when training the network, turning an electromagnetic simulation problem into an optimization process. High prediction accuracy of the electromagnetic fields, without discretization or interpolation in space or in time, can be achieved with limited numbers of layers and neurons in each layer of the neural network. We analyze three aspects that influence the performance of the deep learning method. First, we discuss the applicability of this network in the homogeneous media and the relative error can be less than 0.1%. Then, we analyze the relationship between accuracy and network architecture in training. Testing results show that increasing the number of hidden layers and neurons per layer can improve prediction accuracy. Finally, we study numerical examples of the inhomogeneous medium.

Electromagnetic Modeling Techniques for Switched Reluctance Machines: State-of-the-Art Review

Abstract: Switched Reluctance Machines (SRMs) are gaining more attention due to their simple, and rugged construction, low manufacturing cost, and high-speed operation capability. An electromagnetic model of the machine is needed in the design, and analysis processes. The required accuracy level of the model depends mainly on the application. A high-fidelity model is required to achieve a good design, and predict the performance accurately. However, it requires high computational cost, and longer simulation time. Other fast, and less-comprehensive models with less computational burden could be utilized in the design, and analysis of the motor drives. This paper extensively analyzes various electromagnetic modeling techniques of SRMs. Analytical, numerical, and hybrid models are considered. The paper investigates analytical models that are based on Maxwell's equations in addition to interpolation, and curve fitting techniques. Numerical techniques such as Finite Element Method (FEM), and Boundary Element Method (BEM) are presented. Moreover, Magnetic Equivalent Circuit (MEC) method is discussed. Finally, potential research areas are proposed for the electromagnetic modeling of SRMs.

An Efficient Preconditioner for 3-D Finite Difference Modeling of the Electromagnetic Diffusion Process in the Frequency Domain

Abstract: Krylov subspace solvers for frequency-domain electromagnetic forward modeling problems converge remarkably more slowly as the period increases. In this article, we present an efficient four-color cellblock Gauss Seidel (GS) preconditioner for finite-difference (FD) electromagnetic modeling in geophysical applications. Rather than updating the FD electromagnetic (EM) equation edge by edge, as in a traditional GS scheme, we renew six edge components attached to one node simultaneously (i.e., in cellblock manner) effectively enforcing a local divergence free condition for currents. To improve implementation efficiency, we reorder the nodes on the FD grid into four colors so that nodes in each color are uncoupled, allowing the use of highly parallel vectorized algorithms. The four-color cellblock GS preconditioner is implemented in the MATLAB code, in conjunction with a BiCGstab solver. It is compared, in terms of iteration number and computing time, with other three commonly used preconditioners [GS, symmetric successive overrelaxation (SSOR) and incomplete lower and upper triangular matrix decomposition (ILU)] on three models—two synthetic and one modified from the version of real data inversion. The comparison indicates that the proposed algorithm is extremely stable and efficient compared with the other three preconditioners tested, over a range of periods (1-1000 s). Especially at long periods, the improvement of our proposed algorithm is substantial. In addition, a parallel implementation of the cellblock GS preconditioner is straightforward due to the independence of nodes in each color.

Accurate EMC Engineering on Realistic Platforms Using an Integral Equation Domain Decomposition Approach

Abstract: This article investigates the efficiency, accuracy and versatility of a surface integral equation (SIE) multisolver scheme to address very complex and large-scale radiation problems including multiple scale features, in the context of realistic electromagnetic compatibility (EMC)/electromagnetic interference (EMI) studies. The tear-and-interconnect domain decomposition (DD) method is applied to properly decompose the problem into multiple subdomains attending to their material, geometrical, and scale properties, while different materials and arbitrarily shaped connections between them can be combined by using the so-called multiregion vector basis functions. The SIE-DD approach has been widely reported in the literature, mainly applied to scattering problems or small radiation problems. Complementarily, in this article, the focus is placed on realistic radiation problems, involving tens of antennas and sensors and including multiscale ingredients and multiple materials. Such kind of problems are very demanding in terms of both convergence and computational resources. Throughout two realistic case studies, the proposed SIE-DD approach is shown to be a powerful electromagnetic modeling tool to provide the accurate and fast solution which is indispensable to rigorously accomplish real-life EMC/EMI studies.

SLIM: A Well-Conditioned Single-Source Boundary Element Method for Modeling Lossy Conductors in Layered Media

Abstract: The boundary element method (BEM) enables the efficient electromagnetic modeling of lossy conductors with a surface-based discretization. Existing BEM techniques for conductor modeling require either expensive dual basis functions or the use of both single- and double-layer potential operators to obtain a well-conditioned system matrix. The computational cost is particularly significant when conductors are embedded in stratified media, and the expensive multilayer Green's function (MGF) must be used. In this letter, a novel single-source BEM formulation is proposed, which leads to a well-conditioned system matrix without the need for dual basis functions. The proposed single-layer impedance matrix formulation does not require the double-layer potential to model the background medium, which reduces the cost associated with the MGF. The accuracy and efficiency of the proposed method are demonstrated through realistic examples drawn from different applications.

Numerical Methods for Electromagnetic Modeling of Graphene: A Review

Abstract: Graphene’s remarkable electrical, mechanical, thermal, and chemical properties have made this the frontier of many other 2-D materials a focus of significant research interest in the last decade. Many theoretical studies of the physical mechanisms behind these properties have been followed by those investing the graphene’s practical use in various fields of engineering. Electromagnetics, optics, and photonics are among these fields, where potential benefits of graphene in improving the device/system performance have been studied. These studies are often carried out using simulation tools. To this end, many numerical methods have been developed to characterize electromagnetic field/wave interactions on graphene sheets and graphene-based devices. In this article, most popular of these methods are reviewed and their advantages and disadvantages are discussed. Numerical examples are provided to demonstrate their applicability to real-life electromagnetic devices and systems.

TEM cell for Testing Low-profile Integrated Circuits for EMC

Abstract: The paper presents the results of development of TEM cell with a working volume of $30\times 30\times 5 mm^{3}$ for measuring radiated immunity and electromagnetic emissions of low-profile integrated circuits. A solid model of the TEM cell was developed based on the analysis of various designs for matching transitions using analytical estimation and electrodynamic simulation. A research prototype of the cell was built and its S-parameters measurements were performed.

Domain Uncertainty Quantification in Computational Electromagnetics

Abstract: We study the numerical approximation of time-harmonic, electromagnetic fields inside a lossy cavity of uncertain geometry. Key assumptions are a possibly high-dimensional parametrization of the unc...

A Gradient Weighted Finite Element Method (GW-FEM) for Static and Quasi-Static Electromagnetic Field Computation

Abstract: This paper presented a Gradient Weighted Finite Element Method (GW-FEM) for solving electromagnetic problems. First, the analysis domain is discretized into a set of triangular or tetrahedral eleme...

Discrete Electromagnetic Model for the Evaluation of Wideband Bistatic Scattering Responses and Statistics of Chaff Clouds

Abstract: A method, hereinafter referred to as discrete chaff cloud model (DCCM), for the electromagnetic modeling of general chaff clouds is presented, with which harmonic or wideband impulse scattering responses can be evaluated. The model applies to a wide range of scenarios, for any combination of illumination and observation angles and polarizations. The technique considers the geometry of the cloud and the statistical distributions of the elements, both in density and orientation. After a 1-D discretization of the cloud, the complete statistical response or single-experiment observations can be evaluated. The model is formulated in a very general form to extend its applicability as much as possible. Its limitations have been identified and assessed in relevant scenarios. Validation cases have been included, comparing results obtained with DCCM, other published formulations, and full-wave simulations.

The Impact of Connection Failure of Bonding Wire on Signal Transmission in Radio Frequency Circuits

Abstract: Bonding wires are widely used in microwave circuits and chip packaging. The exposure to harsh environments may lead to connection failure in these wires. In this article, the impact of such failures on signal transmission was studied using model analysis and experimental testing. The effects of gold bonding wire failure on both the dc and high frequency characteristics were analyzed. Signal reflection and loss caused by failed gold bonding wire at different positions and a number of failed gold bonding wire were also investigated. Based on computational electromagnetics and transmission line theory, a 3-D electromagnetic field numerical calculation model and a distributed parameter circuit model were developed. The electromagnetic field model results are in good agreements with those obtained from the distributed parameter circuit model. The results obtained by the model simulation are validated using experimental tests. The results of this investigation provide a better understanding of the influence of the position and the number of failed bonding wires on the signal integrity of the circuit and theoretical support for identifying failure features in fault diagnosis.

On Applications of Fractional Derivatives in Electromagnetic Theory

Abstract: In this paper, concepts of fractional-order (FO) derivatives are analysed from the point of view of applications in the electromagnetic theory. The mathematical problems related to the FO generalization of Maxwell’s equations are investigated. The most popular formulations of the fractional derivatives, i.e., Riemann-Liouville, Caputo, Grunwald-Letnikov and Marchaud definitions, are considered. Properties of these derivatives are evaluated. It is demonstrated that some of formulations of the FO derivatives have limited applicability in the electromagnetic theory. That is, the Riemann-Liouville and Caputo derivatives with finite base point have a limited applicability whereas the Grunwald-Letnikov and Marchaud derivatives lead to reasonable generalizations of Maxwell’s equations.

Electromagnetic Modeling of Superconductors with Commercial Software: Possibilities with Two Vector Potential-Based Formulations

Abstract: In recent years, the $H$ formulation of Maxwell's equation has become the de facto standard for simulating the time-dependent electromagnetic behavior of superconducting applications with commercial software. However, there are cases where other formulations are desirable, for example for modeling superconducting turns in electrical machines or situations where the superconductor is better described by the critical state than by a power-law resistivity. In order to accurately and efficiently handle those situations, here we consider two published approaches based on the magnetic vector potential: the $T$-$A$ formulation of Maxwell's equations (with power-law resistivity) and Campbell's implementation of the critical state model. In this contribution, we extend the $T$-$A$ formulation to thick conductors so that large coils with different coupling scenarios between the turns can be considered. We also revise Campbell's model and discuss it in terms of its ability to calculate AC losses: in particular, we investigate the dependence of the calculated AC losses on the frequency of the AC excitation and the possibility of using quick one-step (instead of full cycle) simulations to calculate the AC losses.

Fundamental properties of solutions to fractional-order Maxwell's equations

Abstract: In this paper, fundamental properties of solutions to fractional-order (FO) Maxwell's equations are analysed. As a starting point, FO Maxwell's equations are introduced in both time and frequency d...

Electromagnetic modeling for FSS with anisotropic substrate by using a hybrid-accelerated VSIE method

Abstract: An efficient and simple-to-implement volume surface integral equation method is presented to simulate electromagnetic properties of periodic structures involving anisotropic media. The algorithm starts with the periodic Green's function, thus only a unit cell of the object is needed to be calculated. Moreover, the Ewald method is used to expedite the computation of the near region while the linear interpolation is implemented to expedite the computation of the far region. In this manner, the matrix filling time can be saved significantly. The study on the reflection characteristics of several frequency selective surfaces with anisotropic dielectric substrate is presented to demonstrate the accuracy, efficiency and flexibility of the proposed method. And the anisotropic effect of dielectric substrate is also studied through a FSS with liquid crystal substrate.

Determination of the Effective Electromagnetic Parameters of Complex Building Materials for Numerical Analysis of Wireless Transmission Networks

Abstract: In this paper, we present the method for determination of effective electromagnetic parameters of complex building materials. By application of the proposed algorithm, it is possible to analyze electromagnetic field distribution for large-scale problems with heterogeneous materials. The two-dimensional numerical model of building components (hollow brick) with periodic boundary conditions was solved using the finite-difference time-domain method (FDTD) and discussed. On this basis, the resultant transmission coefficient was found and then the equivalent relative permeability and electric conductivity of heterogeneous dielectric structures, in the developed homogenization algorithm, were identified. The homogenization of material properties was achieved by performing a multi-variant optimization scheme and finally, selecting optimal electric parameters. Despite the analysis of heterogeneous building materials, the presented algorithm is shown as a tool for the homogenization of complex structures when scattering of a high-frequency electromagnetic field is considered.

Parallel FDTD modelling of nonlocality in plasmonics

Abstract: As nanofabrication techniques become more precise, with ever smaller feature sizes, the ability to model nonlocal effects in plasmonics becomes increasingly important. While nonlocal models based on hydrodynamics have been implemented using various computational electromagnetics techniques, the finite-difference time-domain (FDTD) version has remained elusive. Here we present a comprehensive FDTD implementation of nonlocal hydrodynamics, including for parallel computing. As a sub-nanometer step size is required to resolve nonlocal effects, a parallel implementation makes the computational cost of nonlocal FDTD more affordable. We first validate our algorithms for small spherical metallic particles, and find that nonlocality smears out staircasing artifacts at metal surfaces, increasing the accuracy over local models. We find this also for a larger nanostructure with sharp extrusions. The large size of this simulation, where nonlocal effects are clearly present, highlights the importance and impact of a parallel implementation in FDTD.

Numerical 3D Simulation of a Full System Air Core Compulsator-Electromagnetic Rail Launcher

Abstract: Multiphysics problems represent an open issue in numerical modeling. Electromagnetic launchers represent typical examples that require a strongly coupled magnetoquasistatic and mechanical approach. This is mainly due to the high velocities which make comparable the electrical and the mechanical response times. The analysis of interacting devices (e.g., a rail launcher and its feeding generator) adds further complexity, since in this context the substitution of one device with an electric circuit does not guarantee the accuracy of the analysis. A simultaneous full 3D electromechanical analysis of the interacting devices is often required. In this paper a numerical 3D analysis of a full launch system, composed by an air-core compulsator which feeds an electromagnetic rail launcher, is presented. The analysis has been performed by using a dedicated, in-house developed research code, named “EN4EM” (Equivalent Network for Electromagnetic Modeling). This code is able to take into account all the relevant electromechanical quantities and phenomena (i.e., eddy currents, velocity skin effect, sliding contacts) in both the devices. A weakly coupled analysis, based on the use of a zero-dimensional model of the launcher (i.e., a single loop electrical equivalent circuit), has been also performed. Its results, compared with those by the simultaneous 3D analysis of interacting devices, show an over-estimate of about 10–15% of the muzzle speed of the armature.