Showing papers on "Computational electromagnetics published in 1980"
02 Jun 1980
TL;DR: In this paper, the time-domain transmission-line equations for uniform multiconductor transmission lines in a conductive, homogeneous medium excited by a transient, nonuniform electromagnetic (EM) field are derived from Maxwell's equations.
Abstract: The time-domain transmission-line equations for uniform multiconductor transmission lines in a conductive, homogeneous medium excited by a transient, nonuniform electromagnetic (EM) field, are derived from Maxwell's equations. Depending on how the line voltage is defined, two formulations are possible. One of these formulations is considerably more convenient to apply than the other. The assumptions made in the derivation of the transmission-line equations and the boundary conditions at the terminations are discussed. For numerical calculations, the transmission -line equations are represented by finite-difference techniques, and numerical examples are included.
209 citations
TL;DR: In this paper, the electromagnetic scattering resonances of a collection of macroscopic bodies with uniform electric properties are used to construct a spectral representation for the scattered field and their weights are found by solving for the eigenvalues and eigen states of a non-Hermitian, linear integral operator.
Abstract: The electromagnetic scattering resonances of a collection of macroscopic bodies with uniform electric properties are used to construct a spectral representation for the scattered field. The resonances and their weights are found by solving for the eigenvalues and eigenstates of a non-Hermitian, linear integral operator $\ensuremath{\Gamma}$. A scheme is developed for doing this by diagonalizing a matrix that represents $\ensuremath{\Gamma}$ by the set of individual grain eigenstates---the diagonal elements are individual grain eigenvalues while the off-diagonal elements are overlap integrals of eigenstates from two different grains. For a system of spherical scatterers, this scheme leads to a reasonable method of calculating numerically the scattered field in cases where the multiple scattering is important. As an example, the scattering by a pair of identical spheres is worked out analytically for a limiting case. Sum rules for the weights in the spectral representation are derived and discussed.
102 citations
TL;DR: In this paper, the propagation of a vector electromagnetic beam in a linear homogeneous dielectric half-space is considered using the Whittaker potentials for the electromagnetic fields.
Abstract: The propagation of a vector electromagnetic beam in a linear homogeneous dielectric half-space is considered using the Whittaker potentials for the electromagnetic fields. A relation between the Whittaker potentials and the vector and scalar potentials of the electromagnetic theory is obtained. The polarization properties of the beam are discussed in the paraxial approximation and beyond.
42 citations
TL;DR: In this article, a theoretical method for the analysis of the slot line employing the network analytical methods of electromagnetic fields and Galerkin's procedure is presented, and the propagation constants for the dominant and higher order mode as well as the effect of the metal-coating thickness on the propagation constant and the characteristic impedance are compared with other available data.
Abstract: A theoretical method is presented for the analysis of the slot line employing the network analytical methods of electromagnetic fields and Galerkin's procedure. The propagation constants for the dominant and higher order mode as well as the effect of the metal-coating thickness on the propagation constant and the characteristic impedance are obtained. The numerical results are compared with other available data.
30 citations
TL;DR: In this article, a method is presented whereby one can extract the singularity expansion method (SEM) description of an object's electromagnetic scattering response from spatially sampled transient surface currents.
Abstract: A method is presented whereby one can extract the singularity expansion method (SEM) description of an object's electromagnetic scattering response from spatially sampled transient surface currents. The currents are excited by a known excitation. The SEM data are recoverable to the degree that spatial coupling and (frequency) spectral intensity excite a given SEM mode. Results of a numerical study of the method using the transient response of a thin wire are reported. The data used in the study were computed using a time domain integral equation technique. The ultimate utility of the method lies in the recovery of SEM data from measured data, thus admitting complex-shaped objects into the realm of SEM description. The method is based on a Prony-type pole/residue extraction procedure.
14 citations
TL;DR: In this paper, the scattering of an axially incident plane electromagnetic wave by a perfectly conducting slender body of revolution is studied, where the scattered field is represented as the field due to a distribution of magnetic and electric dipoles distributed along a segment of the axis of the body and lying entirely inside the body.
Abstract: Scattering of an axially incident plane electromagnetic wave by a perfectly conducting slender body of revolution is studied. The scattered field is represented as the field due to a distribution of magnetic and electric dipoles distributed along a segment of the axis of the body and lying entirely inside the body. The boundary conditions on the body lead to a pair of coupled linear integral equations for the (unknown) dipole densities. The first few terms in the asymptotic expansion of the dipole densities, as well as the extent of the distributions, are found in terms of the slenderness ratio of the body. The far field behavior of the scattered fields, the induced dipole moments, and the scattering cross section are computed. The special case of a prolate spheroid is treated to illustrate the general theory, and the general results are found to agree with the exact solution in this case.
13 citations
12 citations
TL;DR: In this article, a synthesis technique is presented which produces the backscatter impulse response of a conducting ellipsoid, for arbitrary direction of incidence and polarization, for which the basic features of the response waveform are determined by using the laws of physical optics and the time domain interpretation of the creeping wave mechanism.
Abstract: A synthesis technique is presented which produces the backscatter impulse response of a conducting ellipsoid, for arbitrary direction of incidence and polarization. The basic features of the response waveform are determined by using the laws of physical optics and the time domain interpretation of the creeping wave mechanism. The above waveform is further refined by forcing it to satisfy five (namely zeroth- to fourth-order) moment conditions through the use of nonlinear optimization. Numerical results and their verification are presented.
12 citations
TL;DR: In this article, the electromagnetic scattering behavior of a perfectly conducting, infinitesimally thin, spherical shell with a circular aperture is studied, where a time-harmonic plane wave is symmetrically incident upon the aperture.
Abstract: The electromagnetic scattering behavior of a perfectly conducting, infinitesimally thin, spherical shell with a circular aperture is studied. A time-harmonic plane wave is symmetrically incident upon the aperture. The problem is formulated in terms of the E -field integral equation. This produces two coupled integral equations for the tangential components of the currents on the scatterer surface. The equations are cast into matrix form by application of the method of moments, and expressions for the matrix elements are derived. Calculated values of the surface currents and radar cross sections, not previously available in the open literature, are presented and discussed for several cases of interest.
11 citations
TL;DR: In this paper, the singularity expansion method (SEM) parameters from transient thin-wire data are computed using a computer code to generate response data, and the parameters are computed from these data.
Abstract: The problem of determining the singularity expansion method (SEM) parameters from transient thin-wire data is examined. A computer code is used to generate response data. The SEM parameters are computed from these data. For noisy data, it is shown that the parameter values can be improved by averaging.
10 citations
TL;DR: In this article, the authors analyzed the scattering of electromagnetic waves by planar arrays of perfectly conducting strips by a simple method based on physical optics and showed that the induced current as determined by physical optics is used in simple hand computation to obtain the amplitudes of various propagating space harmonics.
Abstract: The scattering of electromagnetic waves by planar arrays of perfectly conducting strips is analyzed by a simple method based on physical optics. The induced current as determined by physical optics is used in simple hand computation to obtain the amplitudes of various propagating space harmonics. Results are compared against some exact results available in the literature to show the accuracy of the proposed approximate method.
TL;DR: In this paper, the use of symmetry groups in reducing the size of a matrix arising in the discretization of an integral equation describing electromagnetic fields induced in penetrable obstacles is discussed.
Abstract: An analysis is given of the use of symmetry groups in reducing the cost of some electromagnetic field calculations. The savings is obtained by reducing the size of a matrix arising in the discretization of an integral equation describing electromagnetic fields induced in penetrable obstacles.
TL;DR: In this paper, the number of natural modes which can be extracted from a complex scatterer was shown to be three to six for an aircraft, five for a "fat" cylinder and thin wire.
Abstract: Practical limitations arising from limited signal-to-noise ratios in actual transient electromagnetic measurements limits the number of natural modes which can be extracted from such measurements. This number is shown here to be three to six for a complex scatterer, in this case an aircraft, five for a "fat" cylinder and thin wire. This is for double exponential waveform excitation of the aircraft and step function excitation of the fat cylinder and thin wire. A few more modes can be resolved if the excitation is altered so as to provide more high frequency energy, as can be accomplished by changing the step excitation to a delta function excitation, or by signal conditioning, for example making a derivative measurement that emphasizes the high frequency response. Even so, far fewer modes can be resolved experimentally than can be predicted. Experimental electromagnetic transient response measurements should therefore be made with these practical limitations in mind.
02 Jun 1980
TL;DR: In this paper, a study of the electromagnetic cavity mode structure of a cylindrical tank consisting of a damper membrane was made. And the authors considered the problem of solving a single transcendental equation written in terms of the Bessel function of the first and second kind for some representative damped cavities.
Abstract: A study is made of the electromagnetic cavity mode structure of a cylindrical tank containing a cylindrical damper membrane. Maxwell's equations for the most general mode of a cylindrical tank is considered and reduced to the problem of solving a single transcendental equation written in terms of the Bessel function of the first and second kind. This equation is solved numerically for some representative damped cavities yielding modal frequencies and damping rates.
01 Jan 1980
TL;DR: In this article, the authors measured surface roughness using scattering of electromagnetic waves in the Ka and X microwave frequency bands and analyzed the dependence of the normalized moments of the returned scatter on distance from the rough surface to the receiving antenna.
Abstract: This was a study to measure surface roughness using scattering of electromagnetic waves in the Ka and X microwave frequency bands. The detected fluctuations of the reflected field intensity is a measure of surface roughness. The reflected field intensity depends on the wavelength, the angle of incidence and the electrical properties of the media. Since the surface presents irregularities with randomly distributed facets, the characteristics of the roughsurface reflected wave can only be described by the statistical properties of the field intensity. The dependence of the normalized moments of the returned scatter on distance from the rough surface to the receiving antenna was analyzed as a function of surface roughness distribution at two different frequency-bands.
TL;DR: In this paper, the volume and surface integral equation formulations relevant to the scattering and absorption of electromagnetic waves by thin, finite and lossy dielectric cylinders are investigated and interpreted, and computational data are presented, describing the effective current distributions and the scattered and absorbed power for widely varying electromagnetic and geometrical parameters.
Abstract: This work investigates and interprets the volume and surface integral equation formulations relevant to the scattering and absorption of electromagnetic waves by thin, finite and lossy dielectric cylinders. Computational data are presented, describing the effective current distributions and the scattered and absorbed power for widely varying electromagnetic and geometrical parameters.
TL;DR: The electromagnetic interaction between a resonator and a lossy dielectric body is examined by means of a simple model suitable for computer simulation which allows a simple numerical evaluation of the variation in the resonant frequency caused by the interaction.
Abstract: In this paper the electromagnetic interaction between a resonator and a lossy dielectric body is examined by means of a simple model suitable for computer simulation; the body was assumed to have a revolution form and the resonator was electromagnetic coupled to the body by its inductive element constituted by a planar circular or spiral coil. On the basis of the model a computer program was derived which allows a simple numerical evaluation of the variation in the resonant frequency caused by the interaction mentioned above.
TL;DR: In this paper, a new divergenceless tensor Green's function was given for cylindrical symmetry, and in terms of it, new scattering integral equations with Hilbert-Schmidt kernels were presented.
Abstract: The scattering of electromagnetic waves by an infinite dielectric cylinder with variable dielectric permeability presents, in general, certain mathematical difficulties regarding the construction of rigorous solutions. We give a new divergenceless tensorGreen’s function, specially appropriate for cylindrical symmetry, and, in terms of it, present new scattering integral equations. We prove that the series for med by all successive iterations of those scattering integral equations converge under certain conditions. Suitable transformations lead to new integral equations with Hilbert–Schmidt kernels, which imply further rigorous results.
01 Dec 1980
TL;DR: In this paper, the authors present a comprehensive text on electromagnetic scattering for graduate students, which is a laudable aim but for the reasons given above and because of the absence of any exercises I do not think that this book meets the objective.
Abstract: The number 17 is a prime whose only factor apart from itself is unity and the 17 chapters of this book have one factor in commonthe persons writing them are all experts. But there is little else which connects them. There is no consistency of notation. The depth of treatment and clarity of exposition vary considerably from chapter to chapter. Some chapters assume that the reader has a highly sophisticated background and proceed at a rapid pace while others s t a r t from hrst principles and travel more leisurely. While it is well know that it is difficult to get experts to agree, more persuasion in this direction is necessary when producing a book which is alleged to be suitable for graduate students. To create a comprehensive text on electromagnetic scattering for graduate students is a laudable aim but for the reasons given above and because of the absence of any exercises I do not think that this book meets the objective. A graduate student would need to be well supervised to draw proper benefit from i t Yet for the professional scientist this is an admirable book to have around. He will not be disturbed by the features mentioned already nor by the uneven distribution of material which results in the last six chapters occupying nearly half the book. He will find every chapter rewarding reading and knows that if he wishes to concentrate on the particular chapter he does not need to consult any other to understand it. Most chapters review their topic in a length which enables the reader to cover it as the bath water cools down and at the end supply a very valuable list of references for further reading. This is just the sort of thing which the professional wants and the book can be highly recommended to him, especially since it contains much that is not readily available elsewhele. The first chapter deals with low frequency radiation and its approximation via potential problems but does not give any application. The next three chapters are concerned with high frequencies. Complex and evanescent rays are treated as well as their relevance to waveguides, optical resonators and scattering at concave surfaces. There is a good description of uniform asymptotic theory which brinp out the main points of the procedure which has to be followed in practice, including specific formulae for edges on thin screens and wedges. The uniform theory of diffraction is discussed in connection with the half-plane and two staggered screens ending with the suggestion that the best approach may be through a plane wave spectral representation and
01 Jan 1980
TL;DR: In this article, the authors investigated time harmonic modal electromagnetic fields in two-medium half spaces, where the primary sources of the modal fields are chosen to be the spherical multipoles, and the potential vectors are z-directed.
Abstract: : Time harmonic modal electromagnetic fields in two-medium half spaces are investigated. For practical and numerical considerations, the primary sources of the modal fields are chosen to be the spherical multipoles, and the potential vectors are z-directed. It is shown that modal fields of such combination are not able to represent a conventional spherical modal field. The horizontal rotating potentials are added to ensure proper representation and fast convergence. The recurrence relations which transform the spherical Hankel-Lengendre functions into the Fourier-Bessel integrals are derived. The secondary fields of the Sommerfield's type are obtained for all spherical multipole sources, and the added horizontally rotating potentials. The combination of the modal fields are capable of representing arbitrary electromagnetic fields resulting from radiation and scattering problems. (Author)
TL;DR: In this paper, a study is made of numerical techniques used to simulate electromagnetic penetration through small apertures in cavities, and the theory of these processes is reviewed and applied to a rectangular box model system, where agreement between theory and calculations are good for the modal amplitudes (usually within a factor of two) as long as the aperture is not too large to avoid reemerging electromagnetic fields and care is taken to assure local symmetry in the electromagnetic structure of the aperture.
Abstract: A study is made of numerical techniques used to simulate electromagnetic penetration through small apertures in cavities. The theory of these processes is reviewed and applied to a rectangular box model system. Agreement between theory and calculations are good for the modal amplitudes (usually within a factor of two) as long as the aperture is not too large to avoid re-emerging electromagnetic fields and care is taken to assure local symmetry in the electromagnetic structure of the aperture.
TL;DR: In this article, the authors studied the scattering of electromagnetic radiation by linearized gravitational fields to second order in a perturbation expansion and found that all electromagnetic multipole radiation is scattered by gravitational monopole and time-varying dipole fields.
Abstract: The scattering of electromagnetic radiation by linearized gravitational fields is studied to second order in a perturbation expansion. The incoming electromagnetic radiation can be of arbitrary multipole structure, and the gravitational fields are also taken to be advanced fields of arbitrary multipole structure. All electromagnetic multipole radiation is found to be scattered by gravitational monopole and time-varying dipole fields. No case has been found, however, in which any electromagnetic multipole radiation is scattered by gravitational fields of quadrupole or higher-order multipole structure. This lack of scattering is established for infinite classes of special cases, and is conjectured to hold in general. The results of the scattering analysis are applied to the case of electromagnetic radiation scattered by a moving mass. It is shown how the mass and velocity may be determined by a knowledge of the incident and scattered radiation.