Showing papers on "Computational electromagnetics published in 2018"

Electromagnetic Modeling of Self-Tuning RFID Sensor Antennas in Linear and Nonlinear Regimes

Abstract: Multistate chips for an UHF radio frequency identification ensure self-compensation of the variations in antenna impedance. This self-tuning capability can provide a digital information about the change in local boundary conditions within the vicinity of the tag. This feature can be exploited further for low-cost wireless sensing applications. An electromagnetic model of the tag in linear and nonlinear regimes allows prediction of analog and digital responses of the device depending on the boundary conditions that cause the variation of the antenna impedance and/or gain. In addition, the model provides estimation of the degradation in communication performance of the tag due to imperfect retuning of the chip impedance. The theoretical findings of the model are verified in sensing applications using a reference self-tuning tag. Sensing measurements of liquid compounds in linear regime and of the water-filling level of a box in nonlinear regime are demonstrated as a practical application of the proposed mathematical model.

A Finite-Element Method Framework for Modeling Rotating Machines With Superconducting Windings

Abstract: Electrical machines employing superconductors are attractive solutions in a variety of application domains. Numerical models are powerful and necessary tools to optimize their design and predict their performance. The electromagnetic modeling of superconductors by the finite-element method is usually based on a power-law resistivity for their electrical behavior. The implementation of such constitutive law in conventional models of electrical machines is quite problematic: the magnetic vector potential directly gives the electric field and requires using a power-law depending on it. This power-law is a nonbounded function that can generate enormous uneven values in the low electric field regions that can destroy the reliability of solutions. The method proposed here consists in separating the model of an electrical machine in two parts, where the magnetic field is calculated with the most appropriate formulation: the H -formulation in the part containing the superconductors and the A -formulation in the part containing conventional conductors (and possibly permanent magnets). The main goal of this work is to determine and to correctly apply the continuity conditions on the boundary separating the two regions. Depending on the location of such boundary—in the fixed or rotating part of the machine—the conditions that one needs to apply are different. In addition, the application of those conditions requires the use of Lagrange multipliers satisfying the field transforms of the electromagnetic quantities in the two reference systems, the fixed and the rotating one. In this paper, several exemplary cases for the possible configurations are presented. In order to emphasize and capture the essential point of this modeling strategy, the discussed examples are rather simple. Nevertheless, they constitute a solid starting point for modeling more complex and realistic devices.

SKA aperture array verification system: electromagnetic modeling and beam pattern measurements using a micro UAV

Abstract: In this paper we present the electromagnetic modeling and beam pattern measurements of a 16-elements ultra wideband sparse random test array for the low frequency instrument of the Square Kilometer Array telescope. We discuss the importance of a small array test platform for the development of technologies and techniques towards the final telescope, highlighting the most relevant aspects of its design. We also describe the electromagnetic simulations and modeling work as well as the embedded-element and array pattern measurements using an Unmanned Aerial Vehicle system. The latter are helpful both for the validation of the models and the design as well as for the future instrumental calibration of the telescope thanks to the stable, accurate and strong radio frequency signal transmitted by the UAV. At this stage of the design, these measurements have shown a general agreement between experimental results and numerical data and have revealed the localized effect of un-calibrated cable lengths in the inner side-lobes of the array pattern.

The ICVSIE: A General Purpose Integral Equation Method for Bio-Electromagnetic Analysis

Abstract: Objective: An internally combined volume surface integral equation (ICVSIE) for analyzing electromagnetic (EM) interactions with biological tissue and wide ranging diagnostic, therapeutic, and research applications, is proposed Method: The ICVSIE is a system of integral equations in terms of volume and surface equivalent currents in biological tissue subject to fields produced by externally or internally positioned devices The system is created by using equivalence principles and solved numerically; the resulting current values are used to evaluate scattered and total electric fields, specific absorption rates, and related quantities Results: The validity, applicability, and efficiency of the ICVSIE are demonstrated by EM analysis of transcranial magnetic stimulation, magnetic resonance imaging, and neuromuscular electrical stimulation Conclusion: Unlike previous integral equations, the ICVSIE is stable regardless of the electric permittivities of the tissue or frequency of operation, providing an application-agnostic computational framework for EM-biomedical analysis Significance: Use of the general purpose and robust ICVSIE permits streamlining the development, deployment, and safety analysis of EM-biomedical technologies

Stochastic Collocation Applications in Computational Electromagnetics

Abstract: The paper reviews the application of deterministic-stochastic models in some areas of computational electromagnetics. Namely, in certain problems there is an uncertainty in the input data set as some properties of a system are partly or entirely unknown. Thus, a simple stochastic collocation (SC) method is used to determine relevant statistics about given responses. The SC approach also provides the assessment of related confidence intervals in the set of calculated numerical results. The expansion of statistical output in terms of mean and variance over a polynomial basis, via SC method, is shown to be robust and efficient approach providing a satisfactory convergence rate. This review paper provides certain computational examples from the previous work by the authors illustrating successful application of SC technique in the areas of ground penetrating radar (GPR), human exposure to electromagnetic fields, and buried lines and grounding systems.

Systems of Differential Algebraic Equations in Computational Electromagnetics

Abstract: Starting from space-discretisation of Maxwell’s equations, various classical formulations are proposed for the simulation of electromagnetic fields. They differ in the phenomena considered as well as in the variables chosen for discretisation. This contribution presents a literature survey of the most common approximations and formulations with a focus on their structural properties. The differential-algebraic character is discussed and quantified by the differential index concept.

3D transient electromagnetic modeling using a shift-and-invert Krylov subspace method

Abstract: We present a fast and efficient algorithm for simulation of a three-dimensional (3D) transient electromagnetic (TEM) response using a modified shift-and-invert Krylov subspace method. The mimetic finite volume method with a staggered grid is carried out for spatial discretization of the time-domain Maxwell's equations. The transient electromagnetic response then can be expressed as a matrix exponential function with an analytic initial magnetic field for a step-off loop source. The shift-and-invert Krylov subspace method can be used to solve the matrix exponential function. However, it requires solving dozens of large sparse linear equations at every time point to reconstruct the Krylov subspace, which makes the conventional shift-and-invert Krylov subspace method time-consuming. By analyzing the characteristics of the optimal shift and shift-and-invert Krylov subspace dimension in detail, we proposed a fast substitute approach to obtain the optimal shift and subspace order by using single optimal shift and constant subspace order with a useful stopping criterion, and developed an efficient modified shift-and-invert Krylov subspace method. Only one LU factorization of a shift coefficient matrix and hundreds of times backward substitutions are required to obtain the results of the TEM modeling data. Time savings are considerable, and this approach makes it possible to compute the response at any time point in the given time interval within the given residual easily and accurately. This is illustrated by using synthetic examples both in layered models and in a 3D complicated model.

Computational Electromagnetics with MATLAB, Fourth Edition

Abstract: This fourth edition of the text reflects the continuing increase in awareness and use of computational electromagnetics and incorporates advances and refinements made in recent years. Most notable among these are the improvements made to the standard algorithm for the finite-difference time-domain (FDTD) method and treatment of absorbing boundary conditions in FDTD, finite element, and transmission-line-matrix methods. It teaches the readers how to pose, numerically analyze, and solve EM problems, to give them the ability to expand their problem-solving skills using a variety of methods, and to prepare them for research in electromagnetism. Includes new homework problems in each chapter. Each chapter is updated with the current trends in CEM. Adds a new appendix on CEM codes, which covers commercial and free codes. Provides updated MATLAB code.

Electromagnetic Modeling of Vital Sign Detection and Human Motion Sensing Validated by Noncontact Radar Measurements

Abstract: Technology to analyze human motion has significantly advanced over the last few years. Locomotion studies have proved useful and have been practically applicable to some gait analysis. However, its use has been hampered by the amount of data generated and the limitations to the interpretation capabilities of this massive data. New techniques need to be developed to capture data rapidly, accurately, efficiently, and preferably remotely using noninvasive techniques. It is our goal to develop modeling capabilities and experimentally validate results to succeed in establishing models and practical ways to interpret this collected data. In this paper, electromagnetic models have been developed and validated using a software-defined radar to analyze different human motion sensing scenarios. Encouraging preliminary results have been achieved, and efforts will continue to analyze and model more motion scenarios.

Waveport modeling for the DGTD simulation of electromagnetic devices

Abstract: The issue of waveport modeling for the numerical simulation of electromagnetic devices using the discontinuous Galerkin time-domain (DGTD) method is investigated. A new implementation of the waveport boundary condition (WPBC) is presented along with a fast evaluation of the required convolution. The performance of the WPBC for the DGTD simulation is then compared with that of the first-order absorbing boundary condition and the uniaxial perfectly matched layer (UPML). Two numerical examples are presented to demonstrate the waveport modeling for the DGTD simulation of electromagnetic devices based on the WPBC and UPML.

A more accurate electromagnetic modeling of WBG power modules

Abstract: A major requirement for further development of wide-band gap (WBG) power devices and their applications is the optimization of packages and PCB layouts to enable fast-switching capabilities. Electromagnetic modelling allows the prediction of parasitic inductances, capacitances, and resistances of the current paths within power modules, which cannot be easily approached in measurements. As a result, electromagnetic-circuit-coupled modeling enables the optimization of package layouts and interconnections before manufacturing actual power modules. The accuracy and limitations of present numerical techniques for three-dimensional (3D) electromagnetic modeling of power modules is still neither well understood nor verified. This paper presents the extraction of parasitics of power semiconductor packages using two electromagnetic modelling approaches. The first approach is based on a well-established 3D electromagnetic quasi-static solver, ANSYS Q3D Extractor. For the second approach, a numerical solver based on the Partial Element Equivalent Circuit (PEEC) method is developed and assessed in terms of modelling accuracy required by fast switching WBG-based power converters. The PEEC method is presented as a promising numerical technique, which can potentially be used to overcome the limitations of the EM modeling based on the ANSYS Q3D Extractor.

Adaptive finite element for 3D time-domain airborne electromagnetic modeling based on hybrid posterior error estimation

Abstract: Airborne electromagnetic (AEM) forward modeling has been extensively developed in past years. However, not much attention has been paid to the adaptive numerical algorithms for time-domain ...

Dual Compressed Sensing Method for Solving Electromagnetic Scattering Problems by Method of Moments

Abstract: Rapid and accurate calculation of electromagnetic scattering problems over a wide incident angle range is a difficult but valuable subject in computational electromagnetics (CEM). Traditional methods need to calculate repeatedly at each finer angle step, which leads to low efficiency. Based on the recently proposed compressed sensing (CS) method in CEM, a new scheme is proposed to further improve the computation efficiency, in which CS is used two times to form an undetermined equation model and incident sources including much information of incident angles simultaneously. Theoretical frame and specific formulas are derived in detail, and numerical results verify that it provides an efficient technical route for solving electromagnetic scattering problems.

Modeling the atmospheric propagation of electromagnetic waves in 2D and 3D using fourier and wavelet transforms

Abstract: The long-range propagation of electromagnetic waves is a major issue in telecommunication, navigation, and surveillance. The objective of this Ph.D. thesis is to develop fast and accurate modeling methods for the tropospheric propagation in 2D and 3D. In this work, two main contributions towards this objective are achieved. Firstly, self-consistent methods, i.e. based on the discrete electromagnetic theory, are developed in 2D and 3D. Secondly, a fast wavelet-based 2D method is proposed. For simulating the electromagnetic wave propagation in a 2D atmosphere, the split-step Fourier method (SSF) is widely used. The computation is performed marching on in distances taking into account a variable refractivity, an irregular relief, and the electric characteristics of the ground. At each step, the signal is transformed from the spatial to the spectral domains. The phase screens method is applied to model refraction. Besides, to model an impedance ground, the discrete mixed Fourier transform (SSF-DMFT) is used. The concept of the self-consistent electromagnetic theory implies that the use of discrete Maxwell equations for numerical simulations does not lead to spurious solutions. In the widely used SSF-DMFT, the spectral transform is based on the discrete impedance boundary condition, while the propagator is derived from the continuous equation. To overcome this inconsistency, a discrete formulation of SSF-DMFT is proposed, denoted as DSSF-DMFT. The spectral transform and propagator are both derived from the discrete equations to achieve self-consistency. Numerical tests show that SSF-DMFT has spurious oscillations in certain simulation conditions, whereas DSSF-DMFT remains accurate. Indeed, the self-consistency prevents from numerical instabilities. To simulate the propagation in 3D environments, the previous methods are extended to 3D. First, 3D-SSF is presented as a natural extension of SSF. Then, 3D-DSSF is derived from discrete equations. To consider an impedance ground, 3D-DSSF-DMFT is developed leading to new expressions for the propagators. These methods are tested for several configurations, including a refractivity profile extracted from measurements. Results show that they have a high accuracy. They notably consider lateral effects. However, for the propagation in a large computation domain, time and memory occupations become the main concern. To improve the computation burden, a split-step wavelet method (SSW) is proposed in 2D as an alternative to SSF. It is based on the fast wavelet transform, which complexity is weak and which allows for data compression. The propagation is performed by means of a linear combination of wavelets that are individually propagated. Data compression is applied to increase the efficiency. A new local image source method dedicated to wavelet propagation is proposed to consider the ground reflection. Numerical tests show that this method has a higher computational efficiency than SSF while keeping a good accuracy.

MATLAB-based Finite Element Programming in Electromagnetic Modeling

Abstract: This book is a self-contained, programming-oriented and learner-centered book on finite element method (FEM), with special emphasis given to developing MATLAB® programs for numerical modeling of electromagnetic boundary value problems It provides a deep understanding and intuition of FEM programming by means of step-by-step MATLAB® programs with detailed descriptions, and eventually enabling the readers to modify, adapt and apply the provided programs and formulations to develop FEM codes for similar problems through various exercises It starts with simple one-dimensional static and time-harmonic problems and extends the developed theory to more complex two- or three-dimensional problems It supplies sufficient theoretical background on the topic, and it thoroughly covers all phases (pre-processing, main body and post-processing) in FEM FEM formulations are obtained for boundary value problems governed by a partial differential equation that is expressed in terms of a generic unknown function, and then, these formulations are specialized to various electromagnetic applications together with a post-processing phase Since the method is mostly described in a general context, readers from other disciplines can also use this book and easily adapt the provided codes to their engineering problems After forming a solid background on the fundamentals of FEM by means of canonical problems, readers are guided to more advanced applications of FEM in electromagnetics through a survey chapter at the end of the book Offers a self-contained and easy-to-understand introduction to the theory and programming of finite element method Covers various applications in the field of static and time-harmonic electromagnetics Includes one-, two- and three-dimensional finite element codes in MATLAB® Enables readers to develop finite element programming skills through various MATLAB® codes and exercises Promotes self-directed learning skills and provides an effective instruction tool

How to Model Electromagnetic Problems Without Using Vector Calculus and Differential Equations

Abstract: Two important mathematical tools, namely, vector calculus and differential equations dominate the domain of computational electromagnetics. These two tools, though powerful, are not always needed f...

The Success of GPU Computing in Applied Electromagnetics

Abstract: In the field of electromagnetic modeling, whether it is the complex designs for engineered materials or devices and components integrated within their natural environments, there is a big drive for highly efficient numerical techniques to model the performance of complex structures. This often cannot be achieved by conventional computer systems, but rather through using the so-called high performance computing (HPC) systems that utilize hardware acceleration. We review recent General Purpose Graphics Processing Units (GPGPU) computing strategies introduced in four fields of computational electromagnetics: Finite-Difference Time-Domain (FDTD), Finite Elements Method (FEM), Method of Moments (MoM) and ElectroMagnetic Ray Tracing (EMRT).

Electromagnetic modeling of anisotropic ferrites—Application to microstrip Y-junction circulator design

Abstract: This paper presents a theoretical tool, which combines a generalized permeability tensor model, a homemade 3D magneto-static solver, and a commercial electromagnetic simulation software Ansys HFSS™ for accurate modeling of ferrite-based devices regardless of their state of magnetization. A magneto-static analysis is carried out to find the internal biasing fields in the ferrite sample. Permeability tensor components are computed using a generalized permeability tensor model. Real and imaginary parts of permeability tensor components are then integrated into the commercial 3D electromagnetic simulation software HFSS retaining the spatial variations of internal biasing fields in the ferrite sample. Frequency domain simulations are done using HFSS. This theoretical modeling approach is validated by comparing the theoretical simulation results with experimental ones in the case of a coaxial line loaded by a magnetized ferrite. Proposed approach is then applied to the design of a microstrip Y-junction circulator. Finally, a demonstration prototype is manufactured in the Low Temperature Co-fired Ceramics technology.

Electromagnetic Design of Microwave Cavities for Side-Coupled Linear Accelerators: A Hybrid Numerical/Analytical Approach

Abstract: A homemade computer code for designing the coupled microwave cavities of a linear accelerator (linac) has been developed. A hybrid approach, based on both analytical investigation and numerical calculation, is exploited. A finite-element method (FEM) based on 2-D/3-D electromagnetic simulation software is used to find the eigenmodes and eigenfrequencies of the accelerator cavities as well as design typical figures of merit. The FEM investigation is integrated with a multiobjective particle swarm optimization approach in order to automatically optimize the geometry of the accelerating tanks. This approach seems very promising and general, allowing the optimization of a wide class of side-coupled resonant structures. The computer code is validated via measurements on a 27-MeV 3-GHz standing-wave side-coupled linac tank of five cavities closed with suitable end cells. The agreement between simulation and experiment is excellent; the displacement between the maxima of the simulated and measured longitudinal electric field modulus is close to 0.2%.

Ray tracing using shooting-bouncing technique to model mine tunnels: Theory and verification for a PEC waveguide

Abstract: We present a shooting-bouncing approach to ray-tracing as applied to signal propagation modeling in electrically large waveguides, such as underground mine tunnels at wireless communication frequencies. The method is verified for a dominant-mode rectangular metallic waveguide excited by a dipole antenna.

Three-Dimensional Modeling of Permanents Magnets Synchronous Machines Using a 3D Reluctance Network

Abstract: For electromagnetic actuators whose magnetic fields are three-dimensional, the use of the 3D finite element (FE) method is required. On the other hand, 3D FE analysis is expensive in computation time, especially for high power machines involving potentially high numbers of nodes. In this paper, a 3D reluctance network (RN) modeling approach is proposed for the pre-design of permanents magnets synchronous machines (PMSM). The RN model developed is used to model three types of electrical machines (linear machine, radial field rotating machine and axial field rotating machine). Our goal is to establish lightweight models for the pre-design of electrical machines. The performances (local and global quantities) of these machines are evaluated using this 3D RN modeling. The results obtained from this approach are validated by comparison with results issued from the 3D FE analyses.

High-Order Integral Equation Methods for Quasi-Magnetostatic and Corrosion-Related Field Analysis with Maritime Applications

Abstract: OF DISSERTATION HIGH-ORDER INTEGRAL EQUATION METHODS FOR QUASI-MAGNETOSTATIC AND CORROSION-RELATED FIELD ANALYSIS WITH MARITIME APPLICATIONS This dissertation presents techniques for high-order simulation of electromagnetic fields, particularly for problems involving ships with ferromagnetic hulls and active corrosion-protection systems. A set of numerically constrained hexahedral basis functions for volume integral equation discretization is presented in a method-of-moments context. Test simulations demonstrate the accuracy achievable with these functions as well as the improvement brought about in system conditioning when compared to other basis sets. A general method for converting between a locally-corrected Nyström discretization of an integral equation and a method-of-moments discretization is presented next. Several problems involving conducting and magnetic-conducting materials are solved to verify the accuracy of the method and to illustrate both the reduction in number of unknowns and the effect of the numerically constrained bases on the conditioning of the converted matrix. Finally, a surface integral equation derived from Laplace’s equation is discretized using the locally-corrected Nyström method in order to calculate the electric fields created by impressed-current corrosion protection systems. An iterative technique is presented for handling nonlinear boundary conditions. In addition we examine different approaches for calculating the magnetic field radiated by the corrosion protection system. Numerical tests show the accuracy achievable by higher-order discretizations, validate the iterative technique presented. Various methods for magnetic field calculation are also applied to basic test cases.

Adjoint methods for uncertainty quantification in applied computational electromagnetics: FEM scattering examples

Abstract: We present methods for quantifying uncertainty and discretization error of numerical electromagnetics solvers based on adjoint operators and duality. We briefly introduce the concept of the adjoint operator and describe applications of adjoint solutions for predicting and analyzing numerical error and approximating sensitivity of a given quantity of interest to a given parameter. Forward solutions are based on the higher order finite element method (FEM).

Comparison of Three Sampling Methods for Shooting-Bouncing Ray Tracing Using a simple Waveguide Model

Abstract: This paper addresses shooting-bouncing rays (SBR) ray-tracing techniques and their applications in computational electromagnetics. It specifically discusses uniform random, low-discrepancy deterministic, and uniform sampling techniques for the standard SBR formulation and compares their effects for a simple waveguide model.

Mode tracking for parametrized eigenvalue problems in computational electromagnetics

Abstract: An algorithm to perform a mode tracking for parameter dependent eigenvalue problems is presented. By computing the eigenvalue and eigenvector derivatives a Taylor expansion can be used to efficiently calculate the Brillouin diagram for periodic structures. Furthermore, the derivatives allow distinguishing intersection and touching points in the diagram. The discrete model with periodic boundaries is described using the Finite Integration Technique.

Advanced Parabolic Equation-Based Propagation Modeling for Train Communication Systems

Abstract: Advanced Parabolic Equation-Based Propagation Modeling for Train Communication Systems Xingqi Zhang Doctor of Philosophy Graduate Department of Electrical and Computer Engineering University of Toronto 2018 With the continuing expansion of metropolitan areas, the demand for e cient mass transportation systems is increasing accordingly. An emerging wireless technology for rail signaling, which can significantly improve the e ciency of light rail, subway, and high-speed train transit systems, is communication-based train control (CBTC). In CBTC systems, trains communicate wirelessly with wayside access points, which are connected to a central control station. A prerequisite for the deployment of such systems is the existence of a suitable propagation model, which can provide accurate path-loss predictions of corresponding wireless channels. This is of particular importance due to the safety-critical nature of rail signaling and the rapid, cost-e↵ective nature of system deployment. This thesis presents an advanced propagation modeling tool, based on parabolic equation methods, to characterize radio wave propagation in realistic, complex railway environments. Concrete guidelines are provided on how to extract input models from point cloud data and what level of detail is necessary and su cient to obtain results agreeing with measured data. Moreover, enhanced techniques dealing with geometrical variations of guideways and practical antenna patterns are presented. The accuracy and e ciency of the developed propagation model are demonstrated in various practical scenarios. Furthermore, a robust approach on extracting surrogate models from arbitrary tunnel geometries is proposed. The extracted surrogate models can lead to significant computational savings, especially in optimization studies where repetitive calls of the propagation model are required. The thesis also presents two hybrid propagation modeling techniques, aimed at achieving a better trade-o↵ between accuracy, e ciency, and generality, via using the advantages of one method to compensate for the limitations of another and vice versa. Moreover, e↵ects of uncertainty in the environment and experimental setup on the variability of predicted signal strength are investigated. A new approach that can incorporate wall roughness into the model is introduced. It can be applied to tunnels with arbitrary cross-section geometries and large-scale surface roughness. Finally, a physics-based optimization strategy is presented to optimize the placement of access points for train communication systems. The validity and usefulness of the proposed methodology are demonstrated in an actual deployment site of CBTC systems.

Reduction of Electromagnetic Reflections in 3D Airborne Transient Electromagnetic Modeling: Application of the CFS-PML in Source-Free Media

Abstract: To solve the problem of electromagnetic reflections caused by the termination of finite-difference time-domain (FDTD) grids, we apply the complex frequency-shifted perfectly matched layer (CFS-PML) to airborne transient electromagnetic (ATEM) modeling in a source-free medium To implement the CFS-PML, two important aspects are improved First, our method adopts the source-free Maxwell’s equations as the governing equations and introduces the divergence condition, consequently, the discrete form of Maxwell’s third equation is derived with regard to the CFS-PML form Second, because our method adopts an inhomogeneous time-step, a recursive formula composed of convolution items based on a nonuniform time-step is proposed The proposed approach is verified via a calculation of the electromagnetic response using homogeneous half-space models with different conductivities The results show that the CFS-PML can reduce a 60 dB relative errors in late times Moreover, this approach is also applied to 3D anomalous models; the results indicate that the proposed method can reduce reflections and substantially improve the identification of anomalous bodies Consequently, the CFS-PML has good implications for ATEM modeling in a source-free medium