Showing papers on "Computational electromagnetics published in 1981"
TL;DR: Many of the popular methods for the solution of large matrix equations are surveyed in this paper with the hope of finding an efficient method suitable for both electromagnetic scattering and radiation problems and system identification problems.
Abstract: Many of the popular methods for the solution of large matrix equations are surveyed with the hope of finding an efficient method suitable for both electromagnetic scattering and radiation problems and system identification problems.
188 citations
TL;DR: In this paper, reference beam addition, apodization and the use of multiple intensity distributions have been proposed for phase retrieval in a one-dimensional field, where the phase ambiguity arises as the result of the possibilities of conjugating the zeros of F(z), z = x + jy.
Abstract: The phase retrieval problem arises in applications of electromagnetic theory in which wave phase is apparently lost or impractical to measure and only intensity data are available. The mathematics of the problem provides unusual insights into the nature of electromagnetic fields. The theory is reviewed and illustrated. The basic issue of the phase retrieval problem, stated for a one-dimensional field, is that although a unique Fourier transform relation exists between the field F(x) in the Fraunhofer plane and the field u(x') in the object plane, the infinite fold phase ambiguity which appears as the result of the possibilities of conjugating the zeros of F(z), z = x + jy implies that additional information or processing of the object wave must be available to obtain the phase. Among the possible solutions which are described are reference beam addition, apodization and the use of multiple intensity distributions, permitting the use of iterative computational procedures in some applications.
107 citations
TL;DR: In this paper, the variational formulations of magnetostatic scalar and vector potentials are reviewed and an original energy functional for non linear anisotropic vector potential with a proof of uniqueness of solution is proposed.
Abstract: 3D modeling becomes necessary for analysis of special electromagnetic systems and also for testing the consistency of two dimensional models In this paper, the variational formulations of magnetostatic scalar and vector potentials are reviewed An original energy functional for non linear anisotropic vector potential with a proof of uniqueness of solution is proposed The biggest problems remain data input and results reduction; these two problems are analysed and solutions are given with some illustrated examples
95 citations
TL;DR: In this article, a method for calculating the electromagnetic scattering properties of a cluster of spheres of arbitrary radii and (possibly complex) refractive indexes is proposed, taking proper account of multiple scattering effects and does not require any approximation except for the truncation of the multipolar expansions describing the scattered field.
Abstract: A method for calculating the electromagnetic scattering properties of a cluster of spheres of arbitrary radii and (possibly complex) refractive indexes is proposed. The approach takes proper account of multiple scattering effects and does not require any approximation except for the truncation of the multipolar expansions describing the scattered field. The convergence of the expansions is tested through the application to the simple but significant system of two spheres with varying interparticle separation.
92 citations
TL;DR: In this article, a numerical method is presented to compute one unknown constitutive parameter of an inhomogeoeous lossy dielectric slab from the reflected field in the time domain.
Abstract: A numerical method is presented to compute one unknown constitutive parameter of an inhomogeoeous lossy dielectric slab from the reflected field in the time domain. The method is based upon a space-time discretization of the integral equation for the reflected field. In the inversion, especially those space-time points where the numerical computation of the electric-field strength in the slab is most accurate are taken into account. This is achieved by computing the unknown parameter iteratively. Alternately solving equations for an approximate direct-scattering problem and an approximate inverse-scattering problem yields successive approximations for the electric field in the slab and the unknown constitutive coefficient. Both problems lead to an infinite system of linear equations from which a finite subsystem is selected. General criteria for this selection are presented. Various profiles have been reconstructed numerically from the reflected field due to a sine-squared incident pulse.
89 citations
TL;DR: In this article, it was shown that failure to take these singularities into account leads to large errors in the finite-difference solution of the time-domain electromagnetic field equations.
Abstract: When the electromagnetic-field equations are solved in a region with a corner, singularities in the field or in its spatial derivatives will be present at these corners. These singularities cause the load truncation error in a finite-difference approximation of the field equations to be unbounded. In this paper it is shown that failing to take these singularities into account leads to large errors in the finite-difference solution of the time-domain electromagnetic-field equations. A simple method is described to account for these singularities while retaining the simplicity of the finite-difference formulation. Numerical results are given that demonstrate the accuracy obtained when our technique is used.
80 citations
TL;DR: In this paper, an efficient numerical method for computing electromagnetic scattering of arbitrary 3-D local inhomogeneities buried in a uniform or two-layered earth is presented, where the inhomogeneity is enclosed by a volume whose conductivity is discretized by a finite-element mesh and whose boundary is only a slight distance away from the inhomeogeneity.
Abstract: We present an efficient numerical method for computing electromagnetic (EM) scattering of arbitrary three‐dimensional (3-D) local inhomogeneities buried in a uniform or two‐layered earth. In this scheme the inhomogeneity is enclosed by a volume whose conductivity is discretized by a finite‐element mesh and whose boundary is only a slight distance away from the inhomogeneity. The scheme uses two sets of independent equations. The first is a set of finite‐element equations derived from a variational integral, and the second is a mathematical expression for the fields at the boundany in terms of electric fields inside the boundary. The Green’s function is used to derive the second set of equations. An iterative algorithm has been developed to solve these two sets of equations. The solutions are the electric fields at nodes inside the finite‐element mesh. The scattered fields anywhere may then be obtained by performing volume integrations over the inhomogeneous region. The scheme is used for modeling 3-D inho...
67 citations
TL;DR: In this article, the authors introduced the concept of polarization utilization in practice for the radar case and generalizations to other electromagnetic inverse problems are presented in the conclusions of the analysis. But the main objective of this analysis is to show that because of the vector nature of electromagnetic inverse scattering, theories, if applicable in practice, require incorporation of complete polarization information into their formulation.
Abstract: The complete description of electromagnetic scattering processes implies polarization and since an electromagnetic scatterer acts like a polarization transformer we require measurements for the complete description of the target scattering matrices so that the descriptive parameters of a scatterer can be uniquely recovered from the measured field data. For the purpose of introducing the concept of polarization utilization in practice, the radar case is chosen and generalizations to other electromagnetic inverse problems are presented in the conclusions. For example, in radar target discrimination, identification and imaging use of measurement data available over the entire spatial frequency domain of the radar cross section must be made leading to various approximate frequency domain related approaches. Mainly for historical reasons of having had amplitude data available only, in most cases the approximations had been simplified to purely scalar nature; i.e., polarization-dependent properties were discarded, and the resulting theories are no longer valid or unique. It is the main objective of this analysis to show that because of the vector nature of electromagnetic inverse scattering, theories, if applicable in practice, require incorporation of complete polarization information into their formulation. By applying this approach to existing theories, it is shown that remarkable improvements in fidelity and quality of the reconstructed images are obtained and that indeed there is ample justification for continuing efforts in developing methods and theories of inverse scattering applicable to all those fields of physical sciences where information on the characteristic parameters of a scattering process is to be drawn from remote measurements, be it the electromagnetic vector case or the even more complicated seismic case of s and p wave interactions in elastic media.
45 citations
TL;DR: In this article, the authors apply the Fourier-Radon transform to the case of far field inverse scattering and show that the Bojarski and the Kennaugh identities constitute a Fourier Radon transform pair.
Abstract: In a wide variety of electromagnetic profile reconstruction or shape imaging techniques, a need often arises to deduce the three-, two-, or one-dimensional distribution of different physical quantities from their projections, e.g., in radio-astronomy, structural biology, roentgenology, geophysics, and also in electromagnetic imaging. Investigation of such problems in various specialized areas resulted in the establishment of the new interdisciplinary subject known as "reconstruction from projections." The underlying theory, which was first rigorously formulated by Radon, will become of increasing importance to radar target mapping, wave-imaging, and related electromagnetic inverse problems; therefore, a tutorial exposition is timely and well suited for this issue. Major emphasis will be placed on showing how Ludwig's theorems on support, determinacy, and self-consistency can be used favorably to analyze the data-limited reconstruction cases. The derived theorems will be applied to the specific case of physical optics far field inverse scattering, clearly proving that the Bojarski and the Kennaugh identities constitute a Fourier-Radon transform pair.
37 citations
TL;DR: The integral equation for the electromagnetic response of a sphere in a layered medium may be solved as follows: the unknown time harmonic electric field in the sphere is expanded in spherical vector waves as mentioned in this paper.
Abstract: The integral equation for the electromagnetic response of a sphere in a layered medium may be solved as follows. First, the unknown time harmonic electric field in the sphere is expanded in spherical vector waves. Secondly, the coefficients for these wave functions are found by a set of equations. The equations are found by multiplying the integral equation throughout by each wave function and integrating over the spherical conductor. Once the unknown coefficients have been determined, then the transient response may be found by taking the inverse Fourier transform. In carrying out the Fourier transform one learns that for most of the time range used in prospecting, only the lowest order vector wave function is significant. A study of the singularities of the spectrum of the transient shows that, for the time range considered, only a single branch cut is significant. There are no pole type responses. That is, the field does not decay exponentially. Previous studies of a sphere in free space reported only pole type responses. That is, at the later stages, the field decays exponentially. This study shows that, in order to model satisfactorily the effect of the host rock on transient electromagnetic fields, the sphere must be placed in layered ground.
23 citations
Book•
01 Jan 1981
TL;DR: In this article, the authors reviewed diverse current applications of electromagnetic wave theory, particularly those of interest in aerospace and defense research, and used the topic of random media to model the ionosphere and the earth terrain with applications to pulse distortion and microwave remote sensing.
Abstract: Reviews diverse current applications of electromagnetic wave theory, particularly those of interest in aerospace and defense research. Uses the topic of random media to model the ionosphere and the earth terrain with applications to pulse distortion and microwave remote sensing. Studies inhomogeneous plasmas and magnetized ferrites for the propagation, reflection, and transmission of electromagnetic waves with a variational formulism and a coordinate invariant method, and from the point of view of linear mode conversion. Treats result sensing based on microwave radiometer for earth terrain and line-of-sight method for atmosphere parameters. Examines the interaction of electromagnetic fields with biological bodies. In the antenna field, coverage encompasses the topics of broadband antenna arrays, dipole radiation in stratified media, insulated linear antennas, and offset fuel reflector antennas.
TL;DR: In this article, a frequency domain system identification program has been interfaced to the Electromagnetic Transients Program at BPA for constructing detailed dynamic models of transmission lines and cables, including a duplication of transposition point reflections produced in a double-circuit line during energization of one circuit with the other grounded at the sending end.
Abstract: A frequency domain system identification program has been interfaced to the Electromagnetic Transients Program at BPA for constructing detailed dynamic models of transmission lines and cables. This paper develops the modeling strategies involved, and presents initial benchmark comparisons with field tests. These include a duplication of transposition-point reflections produced in a double-circuit line during energization of one circuit with the other grounded at the sending end.
TL;DR: In this article, the authors apply the many scanning procedures of the author's unified theory of near field analysis and measurement to the determination of complex bistatic scattering patterns of scalar and electromagnetic systems, both with and without correction for the patterns of the probes.
Abstract: The many scanning procedures of the author's unified theory of near-field analysis and measurement are applied to the determination of complex bistatic scattering patterns of scalar and electromagnetic systems, both with and without correction for the patterns of the probes, one of which may be a compact range. For high accuracy, both the incident and scattered fields are expressed as linear combinations of exact solutions of the differential equations involved (Maxwell's in the electromagnetic cases). For high efficiency, natural orthogonalities with respect to summation are used to decouple the simultaneous equations expressing the measurements in terms of the desired pattern coefficients, implemented by the highly efficient fast Fourier transform as an approximation-free symmetry decomposition. The scanning procedures include spherical, a new, more accurate, more efficient type of plane polar, and many types of plane rectangular, plane radial, and circular cylindrical. All these results are expressed with a single notation and generally applicable equations, based upon symmetry analysis and relativistic invariances. The full apparatus of group representations is applied to reducing the measurement and computational effort, determining symmetries from scattering patterns, and determining Garbacz and singularity expansion method (SEM) modes. Further, Snell's laws, Fresnel's law, and conservation of momenta (e.g., propagation constants) are explained in terms of relativistic invariances.
TL;DR: In this article, a vector integral equation for the calculation of the elements of Green's tensor function is presented for solving the problem of the electromagnetic induction by means of vector integral equations, where the boundary condition requiring the vertical component of the electric current to be zero at the Earth's surface is made.
Abstract: The calculation of the elements of Green's tensor function is presented for solving the problem of the electromagnetic induction by means of a vector integral equation. A two-layered Earth is considered as the medium, the surface layer including a three-dimensional conductivity inhomogeneity. Use is made of the boundary condition requiring the vertical component of the electric current to be zero at the Earth's surface which partly simplifies the theoretical computation. Long-period asymptotics of the individual complicated functions, occurring in Green's tensor function as well as in the tensor function required to calculate the components of the anomalous magnetic field at the surface of the halfspace, were effected. With the aid of these asymptotics one can obtain estimates of the functions occurring in the theoretical analysis of the problem.
TL;DR: In this paper, the problem of electromagnetic pulse propagation over a dissipative earth surface, excited by a vertical electric dipole located on the earth surface is investigated, and it is shown that the scattering contribution of the earth, which is formally expressed in terms of several double infinite integrals, can be efficiently computed from some single finite integrals and is amenable to physical interpretation.
Abstract: The problem of electromagnetic pulse propagation over a dissipative earth surface, excited by a vertical electric dipole located on the earth surface, is investigated. By deforming related integrals in the complex frequency domain it is shown that the scattering contribution of the earth, which is formally expressed in terms of several double infinite integrals, can be efficiently computed from some single finite integrals and is amenable to physical interpretation. Dispersion of electromagnetic waves eminating from an impulse current is presented as a function of both the observation distance and the earth conductivity.
16 Jun 1981
16 Jun 1981
01 Aug 1981
TL;DR: In this paper, when a transmission line is illuminated by an external electromagnetic wave, the line equations are deduced by making use of the principle of superposition, and the equivalent circuit is derived from the solutions, and some interesting characters of induced currents are found for the line terminated by loads at the both ends.
Abstract: When a transmission line is illuminated by an external electromagnetic wave, the line equations are deduced by making use of the principle of superposition. The equivalent circuit is derived from the solutions, and some interesting characters of induced currents are found for the line terminated by loads at the both ends. The results of experiment are proved to be in very good agreement with the theories.
TL;DR: In this paper, the absorption of electromagnetic energy by matter distributed in a predefined loading domain of finite extent is investigated in its general aspects, and it is shown that under variation of the medium properties in the loading domain, the electromagnetic energy absorbed by the load can, at least in principle, be maximized.
Abstract: The absorption of electromagnetic energy by matter distributed in a predefined loading domain of finite extent is investigated in its general aspects. It is shown that under variation of the medium properties in the loading domain, the electromagnetic energy absorbed by the load can, at least in principle, be maximized. The maximization condition serves as constitutive relation, in a nonstandard form, for the relevant medium. The condition is a configurational property and is independent of the distribution of the sources that generate the exciting electromagnetic field.
TL;DR: In this article, the connections between invariant electromagnetic fields and four-potentials are examined through minimal couplings and wave equations, and the subsymmetrics associated with the four-potsentials entering into these minimal coupling are discussed.
Abstract: Connections betweeninvariant electromagnetic fields and four-potentials are examined through minimal couplings and wave equations. The subsymmetrics associated with the four-potentials entering into these minimal couplings are discussed.
TL;DR: In this article, a rigorous theoretical solution for the problem of scattering by a perfectly conducting inclined half-plane buried in a uniform conductive half-space has been obtained for plane wave excitation.
Abstract: FollowingDmitriev (1960) a rigorous theoretical solution for the problem of scattering by a perfectly conducting inclined half-plane buried in a uniform conductive half-space has been obtained for plane wave excitation. The resultant integral equation for the Laplace transform of scattering current in the half-plane is solved numerically by the method of successive approximation. The scattered fields at the surface of the half-space are found by integrating the half-space Green's function over the transform of the scattering current.
01 Jun 1981
TL;DR: In this paper, the authors present a simple and straightforward approach to the analysis of near-field scattering problems using the plane wave spectrum (PWS) scattering matrix, which is a 2D integration performed over the set of incident plane waves.
Abstract: Recently, due to the ability of a computer to perform two-dimensional (2D) Fourier transformations via the Fast Fourier Transformation (FFT) algorithm and its capability to perform numerical integrations, Plane Wave Spectrum (PWS) Scattering techniques have become practical. The PWS scattering analysis represents a radiating source by a twodimensional spectrum of plane waves and characterizes a scatterer by its PWS scattering matrix. The scattered field is then obtained by calculating the integral of the inner product of the incident PWS and the scattering matrix. This calculation is, in effect, a 2D integration performed over the set of incident plane waves. It is the objective of this article to demonstrate that this analysis is, in fact, simple and straightforward. Several examples will be presented wherein simple scattering models, such as Physical Optics, have been used to describe the PWS scattering matrix and thus calculate the scattered field with good results. Also, the technique is both straightforward and powerful for the analysis of antenna coupling in the presence of obstacles. These examples demonstrate that the PWS Scattering Matrix method is a practical and cost effective approach to the analysis of many near-field scattering problems.
TL;DR: The characteristic manifolds of the systems of equations for the free gravitational and electromagnetic fields are considered in this paper, and it is shown that these equations are compatible with the existence of wave fronts whose velocity may differ from c.
Abstract: The characteristic manifolds of the systems of equations for the free gravitational and electromagnetic fields are considered. It is shown that these equations are compatible with the existence of wave fronts whose velocity may differ from c.
TL;DR: In this paper, a class of solution of Maxwell equations which implies the solution of arbitrary holomorphic hypercomplex functional with brief discussion of their physical meaning is given. But the authors do not discuss the physical properties of these solutions.
Abstract: This article gives a class of solution of Maxwell equations which implies the solution of arbitrary holomorphic hypercomplex functional with brief discussion of their physical meaning. It exhibites some wider nature than classical electromagnetic theory:
This article also makes an inference and a description about the example of the above-mentioned strange electromagnetic field. It relates to some hard-to-explain phenomena through different physical models.
TL;DR: In this paper, the authors derived solutions of the electromagnetic wave equation in systems containing spherical interfaces when the source field is that of a magnetic or electric point dipole, and the solutions were obtained in terms of scalar and vector spherical harmonics.
Abstract: Solutions of the electromagnetic wave equation are derived in systems containing spherical interfaces when the source field is that of a magnetic or electric point dipole. Piecewise constant electromagnetic parameters are assumed, but their values as well as the frequency of the source field are arbitrary. The solutions are obtained in terms of scalar and vector spherical harmonics. A sphere embedded in full space with a radial or transverse source dipole is considered explicitly.
16 Jun 1981
01 Dec 1981
TL;DR: In this article, the free space interaction of the near zone electromagnetic fields external to a leaky coaxial cable and a moving dipole is investigated using the equivalence principle and the method of moments.
Abstract: : The free space interaction of the near zone electromagnetic fields external to a leaky coaxial cable and a moving dipole is investigated The method of moments and the equivalence principle are used to find the currents on the dipole and the electromagnetic fields scattered from the dipole Finally, the overall interaction between these two fields is determined by superposition The theoretically derived results are then compared with experimental measurements The findings of this report indicate that exact results are not obtained with a free space analysis; therefore, further work involving electronic intruder detection analysis should include the effects of the earth-air interface (Author)
TL;DR: In this article, the Boundary Integral Equation (BIE) method was used to analyze a single-sided linear induction pump with respect to the electromagnetic field and force analysis.
Abstract: This paper utilizes the Boundary Integral Equation Method to analyse the single sided linear induction pump. The advantage offered by the method is that transverse edge effects are not neglected. The equations necessary for the electromagnetic field and force analysis of the pump are developed and the numerical solution of the equations is described. Particular attention is given to means of calculating the electromagnetic fields within the molten metal secondary. Typical field and force distributions are presented.