Showing papers on "Computational electromagnetics published in 2009"

CHIPIC: An Efficient Code for Electromagnetic PIC Modeling and Simulation

Abstract: Computer-aided highly efficient electromagnetic particle-in-cell (PIC) (CHIPIC) code, developed at the University of Electronic Science and Technology of China, is a fully computer-aided code which combines modeling, calculations, and analysis with an integrated environment. CHIPIC is specifically designed for efficient modeling and simulation. CHIPIC includes a computer-aided design (CAD) system and a physical kernel. The CAD system is designed based on the common flowchart of PIC simulation to provide efficient modeling and analysis, and the physical kernel is developed to provide fast and accurate calculations. The physical kernel can run on a single processor or in parallel mode. When it runs in parallel mode, the message-pass interface and open specifications for multiprocessing are adopted. The validity of this electromagnetic PIC code is proved by simulating a magnetically insulated transmission-line-oscillator tube.

Fast Full-Wave Surface Integral Equation Solver for Multiscale Structure Modeling

Abstract: We describe a full-wave solver to model large-scale and complex multiscale structures. It uses the augmented electric field integral equation (A-EFIE), which includes both the charge and the current as unknowns to avoid the imbalance between the vector potential and the scalar potential in the conventional EFIE. The formulation proves to be stable in the low-frequency regime with the appropriate frequency scaling and the enforcement of charge neutrality. To conquer large-scale and complex problems, we solve the equation using iterative methods, design an efficient constraint preconditioning, and employ the mixed-form fast multipole algorithm (FMA) to accelerate the matrix-vector product. Numerical tests on various examples show high accuracy and fast convergence. At last, complex interconnect and packaging problems with over one million integral equation unknowns can be solved without the help of a parallel computer.

Fractional integro-differential equations for electromagnetic waves in dielectric media

Abstract: We prove that the electromagnetic fields in dielectric media whose susceptibility follows a fractional power-law dependence in a wide frequency range can be described by differential equations with time derivatives of noninteger order. We obtain fractional integro-differential equations for electromagnetic waves in a dielectric. The electromagnetic fields in dielectrics demonstrate a fractional power-law relaxation. The fractional integro-differential equations for electromagnetic waves are common to a wide class of dielectric media regardless of the type of physical structure, the chemical composition, or the nature of the polarizing species (dipoles, electrons, or ions).

Bidirectional Analytic Ray Tracing for Fast Computation of Composite Scattering From Electric-Large Target Over a Randomly Rough Surface

Abstract: The bidirectional analytic ray tracing (BART) method is developed to rapidly calculate composite scattering from three-dimensional (3D) electrically large complex targets above a randomly rough surface. Ray tracing is carried out both along the incident (forward) direction and converse direction of scattering (backward) recording different orders of ray illumination on each facet or edge of the target and surface. Once a pair of forward and backward rays meet on a facet/edge, a scattering term is constructed using the diffused scattering/diffraction of this facet/edge and all reflections occurred on the tracing paths. The rough surface is modeled with ldquorough facetsrdquo including coherent scattering and diffused incoherent scattering, which can be directly calculated according to the IEM (integral equation method) of a randomly rough surface. Analytic tracing of polygon ray tubes is developed to precisely calculate the illumination and shadowing of facets, which exempt large patches of the target from any finer meshing. It significantly reduces the complexity relevant to the target electric-size. Higher orders of scattering and, in particular, interactions between the target and rough surface are then taken into account. The accuracy and performance of BART is validated and evaluated by comparing with exact computational electromagnetic methods for electrically small targets. Numerical examples of angularly composite scattering from a three-dimensional electrically large, e.g., a ship-like target over a randomly rough surface are presented and discussed.

A 3-D Radial Point Interpolation Method for Meshless Time-Domain Modeling

Abstract: In this paper, the radial point interpolation method, one of the meshless numerical techniques that has recently emerged in the area of computational electromagnetics, is extended to three dimensions for time-domain electromagnetic modeling. Its capabilities of conformal and multiscale modeling of arbitrary geometries over conventional grid-based numerical techniques are numerically validated and evaluated. A general approach to determining the numerical stability condition of the method is described. Consequently, this study presents another possible approach to automatic meshing of complex structures and an adaptive scheme for numerical solution refinements.

A Novel Wideband FMM for Fast Integral Equation Solution of Multiscale Problems in Electromagnetics

Abstract: In this paper, we propose a novel scheme to accelerate integral equation solvers when applied to multiscale problems. These class of problems exhibit multiple length/frequency scales and arise when analyzing scattering/radiation from realistic structures where dense discretization is necessary to accurately capture geometric features. Solutions to the discretized integral equations due to these structures is challenging, due to their high computational cost and ill-conditioning of the resulting matrix system. The focus of this paper is on ameliorating the computational cost. Our approach will rely on exploiting the recently developed accelerated Cartesian expansion (ACE) algorithm to arrive at a method that is stable and efficient at low frequencies. These will then be integrated with the well known fast multipole method, thus forming a scheme that is wideband. Rigorous convergence estimates of this method are derived, and convergence and efficiency of the overall fast method is demonstrated. These are then integrated into an existing integral equation solver, whose efficiency is demonstrated for some practical problems.

A New Training Approach for Parametric Modeling of Microwave Passive Components Using Combined Neural Networks and Transfer Functions

Abstract: This paper presents a novel technique to develop combined neural network and transfer function models for parametric modeling of passive components. In this technique, the neural network is trained to map geometrical variables onto coefficients of transfer functions. A major advance is achieved in resolving the discontinuity problem of numerical solutions of the coefficients with respect to the geometrical variables. Minimum orders of transfer functions for different regions of geometrical parameter space are identified. Our investigations show that varied orders used for different regions result in the discontinuity of coefficients. The gaps between orders are bridged by a new order-changing module, which guarantees the continuity of coefficients and simultaneously maintains the modeling accuracy through a neural network optimization process. This technique is also expanded to include bilinear transfer functions. Once trained, the model provides accurate and fast prediction of the electromagnetic behavior of passive components with geometrical parameters as variables. Compared to conventional training methods, the proposed method allows better accuracy in challenging applications involving high-order transfer functions, wide frequency range, and large geometrical variations. Three examples including parametric modeling of slotted patch antennas, bandstop microstrip filters, and bandpass coupled-line filters are examined to demonstrate the validity of this technique.

Recursive Two-Way Parabolic Equation Approach for Modeling Terrain Effects in Tropospheric Propagation

Abstract: The Fourier split-step method is a one-way marching-type algorithm to efficiently solve the parabolic equation for modeling electromagnetic propagation in troposphere. The main drawback of this method is that it characterizes only forward-propagating waves, and neglects backward-propagating waves, which become important especially in the presence of irregular surfaces. Although ground reflecting boundaries are inherently incorporated into the split-step algorithm, irregular surfaces (such as sharp edges) introduce a formidable challenge. In this paper, a recursive two-way split-step algorithm is presented to model both forward and backward propagation in the presence of multiple knife-edges. The algorithm starts marching in the forward direction until the wave reaches a knife-edge. The wave arriving at the knife-edge is partially-reflected by imposing the boundary conditions at the edge, and is propagated in the backward direction by reversing the paraxial direction in the parabolic equation. In other words, the wave is split into two components, and the components travel in their corresponding directions. The reflected wave is added to the forward-wave in each range step to obtain the total wave. The wave-splitting is performed each time a wave is incident on one of the knife-edges. This procedure is repeated until convergence is achieved inside the entire domain.

Analysis of On-Body Transmission Mechanism and Characteristic Based on an Electromagnetic Field Approach

Abstract: In this study, an electromagnetic field approach is used to clarify the mechanism of on-body transmission. A homogeneous cylinder is used as an arm model, and the characteristic of electromagnetic field distribution around the cylinder is extracted based on surface wave approximation and numerical analysis, respectively. As a result, the surface wave approximation is found to be valid in the far-field region from the excitation source in the frequency range of 10-150 MHz. Moreover, in the near-field region of the excitation source, the attenuation along the cylinder surface is much smaller than that toward the outside. In addition, by using a numerical human body model, the path loss for on-body transmission is also formulated.

Electromagnetic wave scattering by Schwarzschild black holes.

Abstract: We analyze the scattering of a planar monochromatic electromagnetic wave incident upon a Schwarzschild black hole. We obtain accurate numerical results from the partial wave method for the electromagnetic scattering cross section and show that they are in excellent agreement with analytical approximations. The scattering of electromagnetic waves is compared with the scattering of scalar, spinor, and gravitational waves. We present a unified picture of the scattering of all massless fields for the first time.

Higher Order Hybrid FEM-MoM Technique for Analysis of Antennas and Scatterers

Abstract: A novel higher order large-domain hybrid computational electromagnetic technique based on the finite element method (FEM) and method of moments (MoM) is proposed for three-dimensional analysis of antennas and scatterers in the frequency domain. The geometry of the structure is modeled using generalized curved parametric hexahedral and quadrilateral elements of arbitrary geometrical orders. The fields and currents on elements are modeled using curl- and divergence-conforming hierarchical polynomial vector basis functions of arbitrary approximation orders, and the Galerkin method is used for testing. The elements can be as large as about two wavelengths in each dimension. As multiple MoM objects are possible in a global exterior region, the MoM part provides much greater modeling versatility and potential for applications, especially in antenna problems, than just as a boundary-integral closure to the FEM part. The examples demonstrate excellent accuracy, convergence, efficiency, and versatility of the new FEM-MoM technique, and very effective large-domain meshes that consist of a very small number of large flat and curved FEM and MoM elements, with p-refined field and current distributions of high approximation orders. The reduction in the number of unknowns is by two orders of magnitude when compared to available data for low-order FEM-MoM modeling.

Understanding and manipulating the RF fields at high field MRI.

Abstract: This paper presents a complete overview of the electromagnetics (radiofrequency aspect) of MRI at low and high fields. Using analytical formulations, numerical modeling (computational electromagnetics), and ultrahigh field imaging experiments, the physics that impacts the electromagnetic quantities associated with MRI, namely (1) the transmit field, (2) receive field, and (3) total electromagnetic power absorption, is analyzed. The physical interpretation of the above-mentioned quantities is investigated by electromagnetic theory, to understand 'What happens, in terms of electromagnetics, when operating at different static field strengths?' Using experimental studies and numerical simulations, this paper also examines the physical and technological feasibilities by which all or any of these specified electromagnetic quantities can be manipulated through techniques such as B(1) shimming (phased array excitation) and signal combination using a receive array in order to advance MRI at high field strengths. Pertinent to this subject and with highly coupled coils operating at 7 T, this paper also presents the first phantom work on B(1) shimming without B(1) measurements.

Surface Integral Equation Solutions by Hierarchical Vector Basis Functions and Spherical Harmonics Based Multilevel Fast Multipole Method

Abstract: The method of moments solution of electromagnetic surface integral equation formulations for perfect electric conductors or impedance boundary objects is obtained using hierarchical vector basis functions. The singular and hypersingular integrals involved in the near field coupling matrix are computed fully numerically using adaptive singularity cancellation technique. Multilevel fast multipole method with spherical harmonics expansion of the k-space representations of the basis vectors and the incoming waves at the finest level is utilized for its memory and computation time efficient implementation. Improved performance of the proposed techniques in terms of accuracy, computational time, and memory requirements is demonstrated by comparing various results with some of the existing implementations available in the literature.

A Radially-Dependent Dispersive Finite-Difference Time-Domain Method for the Evaluation of Electromagnetic Cloaks

Abstract: A radially-dependent dispersive finite-difference time-domain (FDTD) method is proposed to simulate electromagnetic cloaking devices. The Drude dispersion model is applied to model the electromagnetic characteristics of the cloaking medium. Both lossless and lossy cloaking materials are examined and their operating bandwidth investigated. It is demonstrated that the perfect ldquoinvisibilityrdquo of electromagnetic cloaks is only available for lossless metamaterials and within an extremely narrow frequency band.

Improving the MFIE's accuracy by using a mixed discretization

Abstract: The scattering of time-harmonic electromagnetic waves by perfect electrical conductors (PECs) can be modelled by several boundary integral equations, the magnetic and electric field integral equations (MFIE and EFIE) being the most prominent ones[1]. These equations can be discretized by expanding current distributions in terms of Rao-Wilton-Glisson (RWG) functions defined on a triangular mesh approximating the scatterer's surface and by testing the equations using the same RWG functions [2].

Efficient Generation of Method of Moments Matrices Using Equivalent Dipole-Moment Method

Abstract: In this letter, the equivalent dipole-moment (EDM) method is applied to compute the matrix elements of the method of moments (MoM) via solving the volume-surface integral equation (VSIE). Besides the advantage of reducing the calculation time significantly, this extended method is unnecessary to treat the boundary condition on the surface of dielectric body and easily constructed by using a simple procedure. The proposed approach can be applied if the distance between the source and the testing basis functions is beyond a threshold distance. Numerical results validate the efficiency and accuracy of the generated matrix elements, and the radar cross-section (RCS) has been verified.

A Numerical Scheme for the Solution of the Vector Parabolic Equation Governing the Radio Wave Propagation in Straight and Curved Rectangular Tunnels

Abstract: A high-frequency field prediction model, useful to evaluate the radio wave propagation in realistic tunnels having rectangular cross-section, is presented. The model is based on a hybrid implicit/explicit finite-difference numerical scheme adopted to solve the vector parabolic equation (VPE) governing the electromagnetic field propagation in straight and curved tunnels. To model the materials forming the tunnel walls, mixed Dirichlet-Von Neumann boundary conditions are employed. In this way, all the relevant field propagation processes are properly taken into account. To show the feasibility of the proposed numerical method, results concerning the spatial distribution of the electromagnetic field and the power flux in straight and curved rectangular tunnels are provided. An analysis concerning the convergence properties of the proposed numerical scheme is also reported.

A high order hybrid finite element method applied to the solution of electromagnetic wave scattering problems in the time domain

Abstract: The development of a hybrid high order time domain finite element solution procedure for the simulation of two dimensional problems in computational electromagnetics is considered. The chosen application area is that of electromagnetic scattering. The spatial approximation adopted incorporates both a continuous Galerkin spectral element method and a high order discontinuous Galerkin method. Temporal discretisation is achieved by means of a fourth order Runge–Kutta procedure. An exact analytical solution is employed initially to validate the procedure and the numerical performance is then demonstrated for a number of more challenging examples.

Evaluation of Lightning-Induced Voltages Over a Lossy Ground by the Hybrid Electromagnetic Model

Abstract: In this paper, the hybrid electromagnetic model is applied to calculate lightning-induced voltages over a lossy ground. Results provided by this model are compared with experimental data obtained from a reduced-scale model and with results simulated by the numerical electromagnetics code. Good agreement is achieved in all cases.

Contactless Microwave Technique Based on a Spread-Loss Model for Dielectric Materials Characterization

Abstract: A free-space method without any focusing mechanisms for determining the complex permittivity of dielectric materials is demonstrated. A model based on geometrical optics is developed for the propagation of a spherical electromagnetic wave through a material. The proposed method implemented using a four-port reflectometer associated to a pyramidal horn antenna is validated through an application related to the moisture measurement of a sample of cellular concrete.

High-Fidelity Magnetic Equivalent Circuit Model for an Axisymmetric Electromagnetic Actuator

Abstract: A computationally inexpensive magnetic equivalent circuit (MEC) improves axisymmetric electromagnet design and modeling tools by accurately capturing fringing and leakage effects. Lumped parameter MEC models are typically less accurate for modeling electromagnetic devices than distributed parameter finite-element models (FEMs). However, MEC models require significantly less computational time to solve than FEMs and therefore lend themselves to applications where solution time is critical, such as in optimization routines, dynamic simulation, or preliminary design. This paper describes how fringing permeances in axisymmetric electromagnetic devices can be derived and then included in a MEC model. Including fringing field effects significantly decreases error in the MEC model, creating a more accurate, or high fidelity, magnetic equivalent circuit (HFMEC). Eighty-nine electromagnets with unique geometries, coil currents, and materials were modeled with MEC, HFMEC, and FEM methods. The axisymmetric HFMEC developed in this work had 67% less average force error and 88% less average flux error compared to traditional MEC results while still being computationally inexpensive to solve.

Multi-frequency and multi-layer frequency selective surface analysis using modal decomposition equivalent circuit method

Abstract: A new modal decomposition equivalent circuit method has been proposed for an analysis of multi-frequency and multi-layer frequency selective structure (FSS). The present paper is an extension of the previously published work where it has been shown that the method is valid for ‘thin’ and ‘thick’ FSS both for angles of incidence up to 60° and for any lattices and potentially allows the synthesis of FSS by the optimisation of circuit parameters. Further investigation has shown the methods validity for the analysis of complex FSS geometries. The method has been successfully applied for the analysis of double-ring slot FSS, ‘A-sandwich’ structures and so on. A very good agreement in comparison with the computational electromagnetic software and rigorous methods such as a periodic method of moments has been obtained.

$S$ -Parameter Sensitivities for Electromagnetic Optimization Based on Volume Field Solutions

Abstract: We propose a sensitivity analysis method that computes the S-parameter Jacobian from the volume E-field solutions in the frequency domain. The field solutions may be provided by any valid electromagnetic analysis. The computation is a post-process, which is independent from the simulator's grid, system equations, and discretization method. The sensitivity solver uses its own finite-difference grid and a sensitivity formula based on the finite-difference frequency-domain vector Helmholtz equation for the electric field. Its computational overhead is negligible in comparison with the simulation. We use the sensitivity solver in the gradient-based optimization of microwave structures. Significant reduction of the time required by the overall optimization process is achieved. In all design examples, the sensitivities are computed from the field solutions provided by a commercial finite-element simulator.

A Multiresolution Curvilinear Rao–Wilton–Glisson Basis Function for Fast Analysis of Electromagnetic Scattering

Abstract: A new set of multiresolution curvilinear Rao-Wilton-Glisson (MR-CRWG) basis functions is proposed for the method of moments (MoM) solution of integral equations for three-dimensional (3-D) electromagnetic (EM) problems The MR-CRWG basis functions are constructed as linear combinations of curvilinear Rao-Wilton-Glisson (CRWG) basis functions which are defined over curvilinear triangular patches, thus allowing direct application on the existing MoM codes that using CRWG basis The multiresolution property of the MR-CRWG basis can lead to the fast convergence of iterative solvers merely by a simple diagonal preconditioning to the corresponding MoM matrices Moreover, the convergence of iterative solvers can be further improved by introducing a perturbation from the principle value term of the magnetic field integral equation (MFIE) operator to construct diagonal preconditioners for efficient iterative solution of the electric field integral equation (EFIE) Another important property of the MR-CRWG basis is that the MoM matrices using the MR-CRWG basis can be highly sparsified without loss of accuracy The MR-CRWG basis has been applied to the 3-D electromagnetic scattering problems and the numerical results indicate that the MR-CRWG basis performs much better than the CRWG basis

Accelerating the Multilevel Fast Multipole Algorithm with the Sparse-Approximate-Inverse (SAI) Preconditioning

Abstract: With the help of the multilevel fast multipole algorithm, integral-equation methods can be used to solve real-life electromagnetics problems both accurately and efficiently. Increasing problem dimensions, on the other hand, necessitate effective parallel preconditioners with low setup costs. In this paper, we consider sparse approximate inverses generated from the sparse near-field part of the dense coefficient matrix. In particular, we analyze pattern selection strategies that can make efficient use of the block structure of the near-field matrix, and we propose a load-balancing method to obtain high scalability during the setup. We also present some implementation details, which reduce the computational cost of the setup phase. In conclusion, for the open-surface problems that are modeled by the electric-field integral equation, we have been able to solve ill-conditioned linear systems involving millions of unknowns with moderate computational requirements. For closed-surface problems that can be modeled by the combined-field integral equation, we reduce the solution times significantly compared to the commonly used block-diagonal preconditioner.

Electromagnetic wave radiated from an insulating spacer in gas insulated switchgear with partial discharge detection

Abstract: As a means of diagnosing partial discharge (PD) signals propagate inside a gas insulated switchgear (GIS), a study for the leakage of electromagnetic waves (EM-waves) emitted from the insulating spacer was implemented. The EM-waves leaking out from the solid insulator have the resonance frequencies depend on the spacing between adjacent bolts in the direction of the flange circumference, because the leakage portion is the equivalent of a slot antenna. In this paper, using an electromagnetic analysis model which has a simulated spacer on a concentrically-shaped GIS tank, the output characteristics of the EM-waves that leaked out from the slit were analyzed under various conditions such as the spacing between adjacent bolts, the width of the spacer, the dielectric constant of the spacer and the form of the flange. Also the actual measurement by the experimental equipment used to simulate the model was implemented for comparison with the analytical results. Consequently, the optimal specifications of the sensor and the measurement method used to achieve highly-sensitive detection for practical use were summarized and proposed as well as evaluating the effectiveness of the electromagnetic analysis model adopted in this paper.

The Method of Weighted Residuals: A General Approach to Deriving Time- and Frequency-Domain Numerical Methods

Abstract: The method of the weighted residuals (MWR), sometimes known as the method of moments (MoM), has traditionally been applied in the frequency domain and has been shown to be effective and efficient, especially in computing open electromagnetic structure problems. Although it has been extended to the time domain in various forms, it is generally employed to solve integral formulations derived from Maxwell's equations. Therefore, it is often considered to be one type of numerical method that is different from other numerical methods, such as finite-difference methods. However, in this paper we will show that the MWR, or MoM, is not just a method per se: it can in fact be a general framework for or approach to unifying or deriving most of the numerical methods developed so far, either in the frequency domain or in the time domain. As a result, all numerical methods can be quite easily understood and can be categorized in one general method, although their conventional derivations may still have their respective advantages. One potential application is that the hybridization of different numerical methods can now be done within a uniform framework. The paper is intended for both beginners and experienced practitioners in the area of numerical electromagnetic modeling.

The Concept of Scale-Changing Network in Global Electromagnetic Simulation of Complex Structures

Abstract: The concept of Scale-Changing Network is reported for the electromagnetic modeling of complex planar structures composed of a collection of metallic patterns printed on a dielectric surface and whose size covers a large range of scale. Examples of such multi-scale structures are provided by multi-band frequency-selective surfaces, flnite-size arrays of non-identical cells and fractal planar objects. Scale-Changing Networks model the electromagnetic coupling between various scale levels in the studied structure and are computed separately. The cascade of Scale-Changing Networks bridges the gap between the smallest and the highest scale levels and allows forming a monolithic (unique) electromagnetic formulation for the global electromagnetic simulation of complex planar structures. Derivation of these networks is presented and key advantages of the electromagnetic approach are reported.

Overview of Electromagnetic Modeling Software

Abstract: Computational electromagnetic modeling (CEM) software is widely used to model antennas, microwave circuits, circuit boards, components, shielded enclosures, cables, motors, sensors, actuators and a wide variety of electrical and electronic devices. The general features, capabilities and costs vary greatly among different codes and new codes are introduced on a regular basis. This paper provides an overview of currently available CEM codes grouped by type, cost and the specific numerical techniques they employ.

Multi-Objective Optimization in High Frequency Electromagnetics—An Effective Technique for Smart Mobile Terminal Antenna (SMTA) Design

Abstract: This paper describes several major optimization techniques, such as FDTD-simulated annealing (SA), FEM-Genetic algorithms (GA), and FD-TD-particle swarm optimization (PSO) and frequency domain FEM-PSO used for high-frequency electromagnetics and their applications in smart mobile terminal antenna (SMTA) design. Two SMTAs, a dielectric embedded electronically switched multi-beam (DE-ESMB) antenna and a dielectric embedded electronically steerable passive array radiator (DE-ESPAR) antenna, were successfully developed by using these multi-objective optimization techniques. The design considerations and rules based on computational electromagnetics and optimization techniques are explored for the practical application of dielectric embedded SMTAs.