Showing papers on "Computational electromagnetics published in 1998"
TL;DR: In this paper, the authors consider absorbing layers that are extensions of the PML of Berenger (1994), which are constructed both for time problems and for Helmholtz-like equations.
338 citations
TL;DR: In this article, the authors provide a background and motivation for using model based parameter estimation (MBPE) in electromagnetics, focusing on the use of fitting models that are described by exponential and pole series.
Abstract: This article first provides a background and motivation for using model based parameter estimation (MBPE) in electromagnetics, focusing on the use of fitting models that are described by exponential and pole series. How data obtained from various kinds of sampling procedures can be used to quantify such models, i.e., to determine numerical values for their coefficients is also presented. The paper continues by illustrating applications of MBPE to various kinds of EM observables. It concludes by discussing how MBPE might be used to improve the efficiency of first-principles models based on frequency-domain integral equations.
177 citations
TL;DR: In this paper, the perfectly matched layer (PML) is adapted to computational acoustics, and its effectiveness as a nonreflecting boundary is examined. But the authors point out that the PML may not be an appropriate computational boundary if the analyst is only interested in the response of the radiator/scatterer and/or the acoustic field in the vicinity of the radiator/scatter.
114 citations
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01 Sep 1998
110 citations
Book•
01 Jan 1998
TL;DR: This paper presents a self-Adaptive Algorithm for the Finite Element Method and its application to Wave Guiding Problems and concludes that the method should be applied to open regions.
Abstract: Overview. The Finite Element Method. Application of the Finite Element Method to Wave Guiding Problems. Self-Adaptive Algorithm for the Finite Element Method. Introduction of an Adaptive Strategy for Terminating Finite Element Meshes for Open Regions. Conclusions. Appendices. Bibliography.
104 citations
TL;DR: An efficient algorithm of O(N) computational complexity is presented, enabling analysis of larger surfaces and revealing several interesting scattering and polarization characteristics of random rough surfaces.
Abstract: A new technique, the steepest descent-fast multipole method (SDFMM), is developed to efficiently analyze scattering from perfectly conducting random rough surfaces. Unlike other prevailing methods, this algorithm has linear computational complexity and memory requirements, making it a suitable candidate for analyzing scattering from large rough surfaces as well as for carrying out Monte Carlo simulations. The method exploits the quasiplanar nature of rough surfaces to efficiently evaluate the dyadic Green's function for multiple source and observation points. This is achieved through a combination of a Sommerfeld steepest descent integral and a multilevel fast multipole-like algorithm based on inhomogeneous plane wave expansions. The fast evaluation of the dyadic Green's function dramatically speeds up the iterative solution of the integral equation for rough surface scattering. Several numerical examples are presented to demonstrate the efficacy and accuracy of the method in analyzing scattering from extremely large finite rough surfaces.
97 citations
01 Jul 1998
TL;DR: The article discusses errors associated with truncating multipole expansions and methods for selecting an appropriate set of parameters for selecting the FMM degree and FMM cube size appropriately.
Abstract: The multilevel fast multipole method can provide fast, accurate solutions to electromagnetic scattering problems, provided its users select the FMM degree and FMM cube size appropriately. The article discusses errors associated with truncating multipole expansions and methods for selecting an appropriate set of parameters.
74 citations
TL;DR: Recent advances in forward modeling of the electromagnetic scattering properties of sea ice are presented and the general theory of scattering of electromagnetic waves from complex media as well as homogenization theory, which relates bulk properties of composite media to their microstructural characteristics are advanced.
Abstract: Recent advances in forward modeling of the electromagnetic scattering properties of sea ice are presented. In particular, the principal results include the following: (1) approximate calculations of electromagnetic scattering from multilayer random media with rough interfaces, based on the distorted Born approximation and radiative transfer (RT) theory; (2) comprehensive theory of the effective complex permittivity of sea ice based on rigorous bounds in the quasi-static case and strong fluctuation theory in the weakly scattering regime; (3) rigorous analysis of the Helmholtz equation and its solutions for idealized sea ice models, which has led in the one dimensional (1D) case to nonlinear generalizations of classical theorems in Fourier analysis. The forward models considered incorporate many detailed features of the sea ice system and compare well with experimental data. The results have advanced the general theory of scattering of electromagnetic waves from complex media as well as homogenization theory, which relates bulk properties of composite media to their microstructural characteristics. Furthermore, the results have direct application to microwave remote sensing and serve as the basis for inverse algorithms for reconstructing the physical properties of sea ice from scattering data.
50 citations
TL;DR: Inverse scattering algorithms for reconstructing the physical properties of sea ice from scattered electromagnetic field data are presented and have the potential to form the basis for a new generation of techniques for recovering sea ice properties, such as ice thickness, a parameter of geophysical and climatological importance.
Abstract: Inverse scattering algorithms for reconstructing the physical properties of sea ice from scattered electromagnetic field data are presented. The development of these algorithms has advanced the theory of remote sensing, particularly in the microwave region, and has the potential to form the basis for a new generation of techniques for recovering sea ice properties, such as ice thickness, a parameter of geophysical and climatological importance. Moreover, the analysis underlying the algorithms has led to significant advances in the mathematical theory of inverse problems. In particular, the principal results include the following. (1) Inverse algorithms for reconstructing the complex permittivity in the Helmholtz equation in one and higher dimensions, based on layer stripping and nonlinear optimization, have been obtained and successfully applied to a (lossless) laboratory system. In one dimension, causality has been imposed to obtain stability of the solution and layer thicknesses can be obtained from the recovered dielectric profile, or directly from the reflection data through a nonlinear generalization of the Paley-Wiener theorem in Fourier analysis. (2) When the wavelength is much larger than the microstructural scale, the above algorithms reconstruct a profile of the effective complex permittivity of the sea ice, a composite of pure ice with random brine and air inclusions. A theory of inverse homogenization has been developed, which in this quasistatic regime, further inverts the reconstructed permittivities for microstructural information beyond the resolution of the wave. Rigorous bounds on brine volume and inclusion separation for a given value of the effective complex permittivity have been obtained as well as an accurate algorithm for reconstructing the brine volume from a set of values. (3) Inverse algorithms designed to recover sea ice thickness have been developed. A coupled radiative transfer-thermodynamic sea ice inverse model has accurately reconstructed the growth of a thin, artificial sea ice sheet from time-series electromagnetic scattering data.
50 citations
TL;DR: In this article, a post-processing method is presented to approximate the correct field behavior at the interfaces by interpolating between the FDTD calculated values, splitting them into the components normal and tangential to the interfaces, and then enforcing the interface conditions for each of these components separately.
Abstract: In recent years, the finite-difference time-domain (FDTD) method has found numerous applications in the field of computational electromagnetics. One of the strengths of the method is the fact that no elaborate grid generation specifying the content of the problem is necessary-the medium is specified by assigning parameters to the regularly spaced cubes. However, this can be a weakness, especially when the interfaces between neighboring media are curved or "sloped" and do not exactly fit the cubic lattice. Since the E- and H-fields are only calculated at the regular intervals, sharp field discontinuities at the interfaces are often missed. Furthermore, the averaging of the material properties often leads to significant errors. In this paper, a post-processing method is presented, which approximates the correct field behavior at the interfaces by interpolating between the FDTD calculated values, splitting them into the components normal and tangential to the interfaces, and then enforcing the interface conditions for each of these components separately.
45 citations
TL;DR: The analysis of single and multiphase induction motors continues to represent a challenge to researchers in computational electromagnetics due to the presence of r/spl Omega//spl times/B electric fields.
Abstract: The analysis of single and multiphase induction motors continues to represent a challenge to researchers in computational electromagnetics due to the presence of r/spl Omega//spl times/B electric fields. This contribution cannot be inserted into the Green's function for boundary element codes; finite difference and finite element approaches are forced to hard code these effects, compensating at high speeds with upwinding techniques. The direct computation of these affects using transfer relations in a linear environment offers an analytical backdrop both for benchmark testing numerical codes and for design assessment criteria. In addition to torque-speed predictions, the terminal relations and total power dissipation in the rotor are computed for an exposed winding three-phase and single-phase machine.
21 Jun 1998
TL;DR: In this paper, an electromagnetic disturbance model is introduced for stability analysis and augmentation of any digitally implemented control law, composed of a Markovian exosystem supplying radiation events to a discrete-time jump linear system which models how the radiation interferes with the nominal operation of the closed-loop system.
Abstract: High intensity electromagnetic radiation has been demonstrated to be a source of computer upsets in commercially available digital flight control systems. In this paper we introduce an electromagnetic disturbance model which can be used for stability analysis and augmentation of any such digitally implemented control law. The model is composed of a Markovian exosystem supplying radiation events to a discrete-time jump linear system which models how the radiation interferes with the nominal operation of the closed-loop system. We discuss how this model can be used to characterize stability and how it can be parametrized and validated in an experimental setting.
TL;DR: In this paper, a 3D finite-difference time domain (FDTD) solution of Maxwell's equations is presented for modeling the near-field radiation of dipole antennas in ground-penetrating radar surveys.
Abstract: We present a 3-D finite-difference time domain (FDTD) solution of Maxwell's equations for modeling the near-field radiation of dipole antennas in ground-penetrating radar surveys The antenna is represented as a conducting wire with a narrow gap in the middle The electromagnetic field in the immediate vicinity of the wire is evaluated by numerical solution of an integral representation of Maxwell's equations Integration contours and surfaces are defined by the finite-difference cells surrounding the wire Everywhere else the electromagnetic wavefield is calculated using conventional FDTD approximations of Maxwell's equations The accuracy of the algorithm has been tested by comparing the simulated near-field radiation of a dipole antenna between two dielectric media with corresponding experimental observations
TL;DR: A nonuniform inverse fast Fourier transform (NU-IFFT) for non ununiformly sampled data is realised by combining the conjugate-gradient fast Fouriers transform (CG-FFT) method with the newly developed NUFFT algorithms.
Abstract: A nonuniform inverse fast Fourier transform (NU-IFFT) for nonuniformly sampled data is realised by combining the conjugate-gradient fast Fourier transform (CG-FFT) method with the newly developed nonuniform fast Fourier transform (NUFFT) algorithms. An example application of the algorithm in computational electromagnetics is presented.
TL;DR: In this article, a self-consistent system of equations describing wake-field generation in the weakly nonlinear limit is derived for short electromagnetic pulses in a magnetized plasma.
Abstract: We consider propagation of short electromagnetic pulses in a magnetized plasma. A self-consistent system of equations describing wake-field generation in the weakly nonlinear limit is derived. Due to the external magnetic field, the generated wake field becomes partially electromagnetic. The equations are applicable for arbitrary directions of propagation as compared to the external magnetic field. The conservation laws for the system are discussed in detail. The energy decrease rate and the frequency decrease rate of the short pulse are determined.
TL;DR: In this paper, two coupling models for analyzing dynamical behaviors of electromagnetic actuators are presented, one based on coupled finite element and parametrization methods and the other based on an iterative technique for the coupled electric, magnetic and mechanical phenomena.
Abstract: This paper presents two coupling models for analyzing dynamical behaviors of electromagnetic actuators. The first model is based on coupled finite element and parametrization methods. The second one is the transient coupling model, it makes use of an iterative technique for the coupled electric, magnetic and mechanical phenomena. A comparison of those models is given through the calculation of the dynamic behavior of a linear axisymmetrical actuator supplied by capacitor discharge voltage.
TL;DR: In this paper, the authors generalized the TE decomposition of electromagnetic fields with respect to four vectors (two six-vectors), which restrict the polarizations of the decomposed electromagnetic fields.
Abstract: TE/TM decomposition of electromagnetic fields, with respect to one special direction in space, is well known to be valid for fields in isotropic and uniaxially anisotropic media. The theory was recently generalized to bi-anisotropic media by defining the decomposition for linear combinations of electric and magnetic fields with respect to two vectors. In the present paper, the theory is further generalized by defining the decomposition with respect to four vectors (two six-vectors), which restrict the polarizations of the decomposed electromagnetic fields. It is shown that the class of bi-anisotropic media in which electromagnetic fields can be decomposed into two independent electromagnetic fields (a-field and b-field) is more general than in all previous decomposition theories. It is also shown that the decomposed a- and b-fields see the original bi-anisotropic medium as simpler equivalent ones (aand b-media) for which analytic Green dyadics were previously derived by these authors.
TL;DR: In this article, the authors introduce the concept of generalized differential matrix operators (GDMOs) that are useful for the formulation of electromagnetic boundary value problems in arbitrary orthogonal coordinate systems, e.g., Cartesian, cylindrical and spherical.
Abstract: In this paper, the authors introduce the concept of generalized differential matrix operators (GDMOs) that are useful for the formulation of electromagnetic boundary value problems in arbitrary orthogonal coordinate systems, e.g., Cartesian, cylindrical and spherical. The most significant attribute of the GDMO approach is that their use helps to simplify the complicated manipulation of vector differential equations, especially in problems dealing with an anisotropic media. They show that the use of the GDMOs enable one to replace, for most problems in electromagnetics, the complicated vector differential operations with manipulation of 3/spl times/3 matrices. In addition, they demonstrate GDMOs are convenient for deriving many differentiation identities and integral theorems which find extensive applications in electromagnetics.
TL;DR: The authors describe how methods for constructing one-dimensional electrical conductivity models of the Earth from surface electromagnetic measurements can be modified to incorporate what is known in computer vision as the line process (LP) decoupling technique, which has the ability to include discontinuities in the models.
Abstract: This paper presents a new method for constructing one-dimensional (1D) electrical conductivity models of the Earth from surface electromagnetic measurements. The construction of these models is a nonlinear inverse problem that can be approached by linearization techniques combined with iterative methods and Tikhonov's regularization. The standard application of these techniques usually leads to smooth models that represent a continuous variation of conductivity with depth. In this work, the authors describe how these methods can be modified to incorporate what is known in computer vision as the line process (LP) decoupling technique, which has the ability to include discontinuities in the models. This results in piecewise smooth models that are often more adequate for representing stratified media. They have implemented a relaxation technique to construct these types of models and present numerical experiments as well as an application to field data. These examples illustrate the performance of the combined LP and Tikhonov's regularization method.
TL;DR: In this paper, a hybridization of time-domain integral equation methods with time domain physical optics (PO) is presented, where an isoparametric curvilinear treatment is adopted.
Abstract: Full-field solutions for scattering and similar problems become prohibitively expensive for electrically large bodies. Fortunately, broadly "optical" methods become accurate as larger bodies are considered. Often, however, large bodies have significant features that are not electrically large and here hybrid approaches are appropriate. We present a novel hybridization of time-domain integral equation methods with time-domain physical optics (PO). For both methods, an isoparametric curvilinear treatment is adopted. The application of the approach is demonstrated by investigating the convergence of the solution for a pulse incident on a large target with a small feature (a 16-pulsewidth plate with a /spl sim/1/3-pulsewidth sphere placed centrally just in front of it). It is demonstrated that a full-field solution for the sphere and a fairly small region around the sphere, coupled with the PO solution of the remainder of the plate, produces a converged prediction of the time-dependent fields.
TL;DR: In this article, the authors presented two approaches to extract the broadband multimode parameters of guided wave structures from a single-pass finite-difference time-domain (FDTD) simulation, including a two-dimensional Fourier transform (FT) algorithm and a super-resolution estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm.
Abstract: We present two approaches to extract the broadband multimode parameters of guided wave structures from a single-pass finite-difference time-domain (FDTD) simulation. They include a two-dimensional (2-D) Fourier transform (FT) algorithm and a super-resolution estimation of signal parameters via rotational invariance technique (ESPRIT) algorithm. Comparison is made to show the superiority of the super-resolution approach. As a typical application, a three-line coupled microstrip structure is studied. After a single-pass FDTD simulation, broadband multimode parameters such as propagation constants, modal-field templates, and modal impedances are extracted and verified against published data obtained by the spectral-domain method. The main feature of this parameter-extraction methodology is that it decouples the computational electromagnetics engine (in this case, the FDTD simulator) from the post-processing parameter-extraction algorithm, thus providing more flexibility and connectivity among the various simulation tools.
TL;DR: In this article, a generalized technique is developed to truncate the computational domain without reflection, which transforms the unbounded space Maxwell's equations to a set of auxiliary equations in a closed domain.
Abstract: A generalized technique is developed to truncate the computational domain without reflection. It transforms the unbounded-space Maxwell's equations to a set of auxiliary equations in a closed domain. A reflection-free amplitude-reduction scheme applied over the entire computational domain reduces the auxiliary field components outwardly and makes them equal to zero at the closed boundary. No additional absorbing region surrounding the domain of interest is needed with this technique because the relationship between the physical fields and their auxiliary counterparts is explicitly known and the former can be found from the latter within the computational domain.
07 Jun 1998
TL;DR: A state variable implementation of harmonic balance circuit analysis for spatially distributed systems is developed and it is compatible with port-based network descriptions which occur with electromagnetic modeling.
Abstract: A state variable implementation of harmonic balance circuit analysis for spatially distributed systems is developed. The equations are formulated with the minimum number of unknowns and error functions starting from the modified nodal admittance matrix of the linear part of the circuit. The program uses advanced numerical techniques, such as automatic differentiation to calculate the Jacobian of the system and it is compatible with port-based network descriptions which occur with electromagnetic modeling.
21 Jun 1998
TL;DR: The major features and some preliminary results from the parallel fast multipole library, ScaleME (scalable multipole engine), are presented.
Abstract: In this paper, we have presented the major features and some preliminary results from the parallel fast multipole library, ScaleME (scalable multipole engine). We have briefly outlined the major features of the library and its applications.
TL;DR: In this paper, the authors examined the scattering from cylindrically periodic engine-like structures using integral-equation methods, where the periodic scatterer is enclosed in a cylindrical waveguide, and the primary goal was to show that this type of geometry affords substantial computational reductions by exploiting the periodicity of the blade structure and characteristics of the modal scattering matrix.
Abstract: We examine the scattering from cylindrically periodic engine-like structures using integral-equation methods. The periodic scatterer is enclosed in a cylindrical waveguide, and the primary goal of this paper is to show that this type of geometry affords substantial computational reductions by exploiting the periodicity of the blade structure and characteristics of the modal scattering matrix of the engine-like termination. Also, as a result of the periodic waveguide termination, a limited number of modes are excited by a given incoming mode, and this is exploited for a further reduction of the storage requirements of the modal scattering matrix.
TL;DR: In this paper, the authors present the impedance matrix compression (IMC) method for a more effective integration of wavelet-based transforms into existing numerical solvers by using a digital filtering approach.
Abstract: The use of wavelet expansions in numerical solutions of electromagnetic frequency-domain integral equation formulations is steadily growing. In this paper we review the recently suggested impedance matrix compression (IMC) method for a more effective integration of wavelet-based transforms into existing numerical solvers. The difference between the IMC method and the previous approaches to applying wavelets in computational electromagnetics is twofold. Firstly, the transformation is effected by means of a digital filtering approach. This approach renders the transform algorithm adaptive and facilitates the derivation of a basis which best suits the problem at hand. Secondly, the conventional thresholding procedure applied to the impedance matrix is substituted for by a compression process in which only the significant terms in the expansion of the (yet-unknown) current are retained and hence a substantially smaller number of coefficients has to be determined. A few numerical results are included to demonstrate the advantages of the presented method over the currently used ones. The feasibility of ensuring a slow growth in the number of unknowns even when there is a rapid increase in the problem complexity is shown by an illustrative example. © 1998 John Wiley & Sons, Ltd.
01 Jan 1998
TL;DR: FDTD Computational Electromagnetics Modeling of Microcavity Lasers and Resonant Optical Structures (FDTD-EMMS) as mentioned in this paper ) is a model for the model of MicroCavity Lenses.
Abstract: FDTD Computational Electromagnetics Modeling of Microcavity Lasers and Resonant Optical Structures
24 Aug 1998
TL;DR: In this paper, the authors derived a new approximation for the case of an electromagnetic wave interacting with a long (compared to a wavelength) transmission line, which does not make additional assumptions made by previous authors, allowing for reradiation of electromagnetic radiation.
Abstract: The authors have derived a new approximation for the case of an electromagnetic wave interacting with a long (compared to a wavelength) transmission line. This treatment does not make additional assumptions made by previous authors, allowing for reradiation of electromagnetic radiation. They show that this approximation reduces to previous results in the appropriate limiting cases. They also introduce a new approximation that removes some of the previous assumptions.
01 May 1998
TL;DR: A systematic approach to analyze complex power/ ground structures and simulate their effects on digital systems is developed and effects related to power/ground networks, such as simultaneous switching noises, crosstalk, and ground discontinuity are analyzed for realistic designs.
Abstract: The electromagnetic modeling and parameter extraction of digital packages and PCB boards for system signal integrity applications are presented. A systematic approach to analyze complex power/ground structures and simulate their effects on digital systems is developed. First, an integral equation boundary element algorithm is applied to the electromagnetic modeling of the PCB structures. Then, equivalent circuits of the power/ground networks are extracted from the EM solution. In an integrated simulation scheme, the equivalent circuits are combined with signal nets, package models, device circuits, and other external circuitry for system level signal integrity analysis and simulation. This methodology has been implemented as software tools and applied to practical design problems. Effects related to power/ground networks, such as simultaneous switching noises, crosstalk, and ground discontinuity are analyzed for realistic designs.