Showing papers on "Electromagnetics published in 1988"
TL;DR: The basis and applications of the finite-difference time -domain (FD-TD) numerical modeling approach for Maxwell's equations are reviewed, providing highly accurate modeling predictions for a wide variety of electromagnetic wave interaction problems.
312 citations
TL;DR: In this paper, the concept of combining the finite element method with the boundary element method for electromagnetic problems is introduced, and the general equations are derived, and examples are given for a number of two-and three-dimensional cases.
Abstract: The concept of combining the finite-element method with the boundary-element method for electromagnetic problems is introduced. The general equations are derived, and examples are given for a number of two- and three-dimensional cases. These include both static and time-varying problems. >
87 citations
06 Jun 1988
TL;DR: In this article, the authors define hard and soft surfaces in terms of an anisotropic surface impedance, and propose to refer to such surfaces and their relatives by the common name "soft" surfaces.
Abstract: Transversely corrugated surfaces are widely used in the design of hybrid-mode horn antennas. The authors propose referring to such surfaces and their relatives by the common name 'soft' surfaces. The reasons for this are that (1) these surfaces have the same characteristics relative to electromagnetic waves as the so-called acoustically soft surfaces have relative to acoustic waves, i.e., that the density-of-power flux along the surface is zero at the surface, and that (2) there also exists so-called artificially hard surfaces in electromagnetics, along which the power flux has a maximum for any polarization of the electric field. The authors define hard and soft surfaces in terms of an anisotropic surface impedance. Characteristics and possible applications of soft and hard surface are described. >
63 citations
01 Mar 1988
TL;DR: In this article, a hybrid technique for solving electromagnetic radiation and scattering problems by combining the method of moments (MM) with a special Green's function is presented, referred to as an MM/Green's function solution, which combines the ability of MM solutions to treat geometrically complex bodies with the accuracy and computational efficiency of Green's functions.
Abstract: An overview is presented of a hybrid technique for solving electromagnetic radiation and scattering problems by combining the method of moments (MM) with a special Green's function. The method, referred to as an MM/Green's function solution, combines the ability of MM solutions to treat geometrically complex bodies with the accuracy and computational efficiency of Green's function solutions. Compared to a standard MM solution, the MM/Green's function solution reduces the number of unknowns and thus the computer storage requirements. In most cases the CPU time for the MM/Green's function solution is considerably less than that for a standard MM solution. An example problem of TM scattering by a semicircular strip in the presence of a circular cylinder is solved by the MM, and by the MM/Green's function technique with a matrix, exact eigenfunction, and high-frequency Green's function. >
60 citations
TL;DR: A method for modeling 3D voltage forced coils is described in this paper, where the magnetic vector potential A is used within the coil with an additional equation to ensure EMF balance at the terminals.
Abstract: A method for modeling 3D voltage forced coils is described The magnetic vector potential A is used within the coil with an additional equation to ensure EMF balance at the terminals This approach is useful for nonlinear or transient problems when the terminal voltage is specified The coil model has been incorporated into the general 3D electromagnetics program MEGA A simple voltage-forced coil has been simulated on the computer and compared with experimental results >
45 citations
01 Aug 1988
TL;DR: The wire grid geometry modeling approach has been sucessfully used where primarily far field quantities such as RCS or radiation patterns are of interest as discussed by the authors, but it often proves unsatisfactory where near field quantities, such as surface currents or input impedance are desired.
Abstract: : In recent years, researchers in electromagnetics have expended considerable effort capitalizing on computational advances made possible by new developments in computer technology. These advances have made it easier to develop highly efficient, specialized computer codes for many scattering or radiation problems. However, because of the high cost of developing a code for each specialized geometry, it has increasingly become more cost effective to use possibly less efficient, but more general purpose codes which apply to a broader class of problems. Most general purpose codes employ an integral equation formulation which is solved by the method of moments. Under this type of formulation, the structure geometry is usually modeled either as a wire mesh or as a surface subdivided into discrete planar patches. The wire grid geometry modeling approach has been sucessfully used where primarily far field quantities such as RCS or radiation patterns are of interest. Principal advantages of the wire grid approach are the geometry is easily specified for computer input, and only one-dimensional integrals need to be numerically evaluated in the method of moments. The wire grid modeling approach, however, often proves unsatisfactory where near field quantities such as surface currents or input impedance are desired. One obvious difficulty is in interpreting computed wire currents as equivalent surface currents.
38 citations
TL;DR: In this article, the authors summarize their three-year experience with a computer-methods course for electromagnetics, introduced as an elective for senior undergraduates, including the inclusion of the finite-difference method of solving engineering problems formulated in terms of partial differential equations.
Abstract: The authors summarize their three-year experience with a computer-methods course for electromagnetics, introduced as an elective for senior undergraduates. The main features of the course include: (1) the inclusion of the finite-difference method of solving engineering problems formulated in terms of partial differential equations; (2) the use of the finite-difference method to solve engineering problems such as the design of microstrip transmission lines and eigenvalue problems including the propagation characteristics in waveguides of arbitrary cross sections; and (3) the use of the method of moments to solve dynamic field problems including radiation from linear antennas and scattering from two-dimensional inhomogeneous dielectric objects. Key steps in developing the course are noted and results from the various computer programs written by the students are presented. >
29 citations
TL;DR: The first century of experiments into microwaves, which he considers began with the experiments of Heinrich Hertz, between 1886 and 1889, using what are now called microwave circuits and techniques as mentioned in this paper.
Abstract: The author reviews the first century of experiments into microwaves, which he considers began with the experiments of Heinrich Hertz, between 1886 and 1889, using what are now called microwave circuits and techniques. Hertz's thorough investigations validated the Faraday-Maxwell theory of electromagnetism, opened up the electromagnetic spectrum between DC and light for scientific and practical uses, and opened up a new line of investigation in the ultraviolet. The author's work is in two parts. Two of the objectives of the first part are to identify, and establish a uniform nomenclature for, the apparatus used by Hertz in his experiments, and to serve as a guide to the understanding of the work of Hertz in electromagnetics, especially his experiments. After briefly reviewing Maxwell's contributions, Hertz's career is discussed with emphasis on the work in understanding and using Maxwell's work (the Berlin Prize Problem). The discovery by Hertz of a method to generate and detect electromagnetic waves is then detailed. The second part outlines his succeeding work to the early 1940s. Examples of some of the ensuring advances described are drawn from a search of historical records and from personal correspondence and interviews with some pioneers in microwave devices and applications. >
29 citations
25 citations
TL;DR: In this article, the authors derived the spin magnetic moment of an electron at a distance z from a perfect plane reflector of light (a perfect mirror) in terms of relative order delta, provided β 0z ⪡ 1.
24 citations
TL;DR: In this paper, the authors discuss the free-space electric dyadic Green's function for layered dielectrics and show that using the Sommerfeld-integral representation of the Green's functions leads to an innate choice for the depolarizing dyad.
Abstract: The authors discuss the electric dyadic Green's function for layered dielectrics. It is known that for the free-space electric dyadic Green's function, evaluation of the electric field at observation points within the source region requires specification of a principal volume along with the corresponding depolarizing dyad. Special considerations are invoked for layered background media which are appropriate for the electromagnetics of integrated electronics. It is shown that use of the Sommerfeld-integral representation of the electric dyadic Green's function leads to an innate choice for the depolarizing dyad. A corresponding principal volume is subsequently identified; it is demonstrated that there exists an alternative choice for this excluding region which leads to the same depolarizing dyad. >
TL;DR: In this paper, a thin-slot formalism for finite-difference time-domain (FDTD) electromagnetics codes has been evaluated in both two and three dimensions.
Abstract: A thin-slot formalism proposed by Gilbert and Holland (1981) for use with finite-difference time-domain (FDTD) electromagnetics codes has been evaluated in both two and three dimensions. This formalism allows narrow slots to be modeled in the wall of a scatterer without reducing the spatial grid size to the slot width. In two dimensions, the evaluation involves the calculation of the total fields near two infinitesimally thin coplanar strips separated by a gap. A method-of-moments (MoM) solution of the same problem serves as a benchmark for comparison. Results in two dimensions show that up to 10 percent error can be expected in total electric and magnetic fields both near ( lambda /40) and far (1 lambda ) from the gap. In three dimensions, the evaluation is similar. The finite-length slot is placed in a finite plate and an MoM surface patch solution is used for the benchmark. These data show that slightly larger errors can be expected. >
TL;DR: Sufficiency conditions for the intersection of different cuts show that when several cuts are required it may not be possible to avoid intersections, which clarifies the question of what data must necessarily be given in order for an algorithm to work.
Abstract: Kotiuga [J. Appl. Phys. 61, 3916 (1987)] showed that the integral (co)homology groups of a region Ω in R3 are torsion free and that cuts for magnetic scalar potentials can be realized by embedded orientable submanifolds which represent generators of the homology group H2(Ω,∂Ω;Z). The present paper makes these formal results intuitive by appealing to concepts familiar from electromagnetics and clarifies several issues relating to an algorithm for finite element meshes. Sufficiency conditions for the intersection of different cuts show that when several cuts are required it may not be possible to avoid intersections. This in turn clarifies the question of what data must necessarily be given in order for an algorithm to work.
TL;DR: In this paper, the generalized Haskell matrix/layer Eigenstate Propagator method is introduced to solve the problem of nonseparable field equations in borehole electromagnetics, where both cylindrical and planar interfaces are present.
Abstract: In borehole electromagnetics, both cylindrical and planar interfaces are present, leading to nonseparable field equations. The problem is two‐dimensional (2-D), and the finite‐element method is usually employed for solution. In this paper, the Generalized Haskell Matrix/Layer Eigenstate Propagator method is introduced to this class of problems. In the method, the solution problem is decomposed into a set of one‐dimensional (1-D) problems, and then the 1-D solutions are combined to form the final solution. The method employs no approximation, other than discretization of a continuous system as in all computer methods. Induction logs are calculated for the 6FF40 tool and a number of models. Results agree well with those of the finite‐element method. An important case in induction‐log interpretation is studied; namely, a three‐layer formation traversed by a borehole, the center layer being an oil‐bearing (resistive) layer sandwiched between two conductive shoulder layers. Simulation shows that conventional c...
TL;DR: In this article, three simple examples of the use of the method of moments in electromagnetics, i.e., analysis of the input impedance of a short dipole, and plane-wave scattering from both a short and two coupled short dipoles, are presented.
Abstract: Three simple examples of the use of the method of moments in electromagnetics, i.e. analysis of the input impedance of a short dipole, and plane-wave scattering from both a short dipole and two coupled short dipoles, are presented. The relative simplicity of the examples is a direct result of obtaining simple expressions for the elements in the method-of-moments impedance matrix. >
TL;DR: In this paper, a general approach to TLM through transmission-line graphs is presented, and how the theory is applied to electromagnetics through a brief review of methods and applications.
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22 Mar 1988
TL;DR: In this paper, a self-contained treatment of the fundamentals of microwave circuits and passive devices is presented, including the basic electromagnetics required for the understanding of field theory, as well as design and performance considerations of microwave components.
Abstract: This self-contained treatment of the fundamentals of microwave circuits and passive devices, provides coverage on transmission lines, guided waves, resonators, reciprocal and non-reciprocal devices, slow-wave structures and filters. It considers the basic electromagnetics required for the understanding of field theory, as well as design and performance considerations of microwave components. Also incorporated into the text are diagrams and solved problems for reinforcing key concepts, together with end-of-chapter bibliographies.
TL;DR: Two- and three-dimensional electromagnetic resonance calculations have been performed on rising-sun magnetron structures using the transmission-line matrix method andylindrical coordinates have been used in order to facilitate modelling of the essentially cylindrical device.
Abstract: Two- and three-dimensional electromagnetic resonance calculations have been performed on rising-sun magnetron structures. These calculations have been made using the transmission-line matrix method. Cylindrical coordinates have been used in order to facilitate modelling of the essentially cylindrical device. Recent improvements to the TLM technique, such as the development of the symmetric condensed node for electromagnetics, have been fully exploited. The numerical procedure is described, the modelling process is discussed, and the results obtained are evaluated in comparisons with corresponding empirical data.
TL;DR: In this paper, the advantages and difficulties associated with the use of the Coulomb gauge in solving source-excited boundary value problems of electromagnetics have been examined, and the correct dyadic Green's function for Coulomb vector potential in a rectangular waveguide is derived.
Abstract: The advantages and difficulties associated with the use of the Coulomb gauge in solving source-excited boundary value problems of electromagnetics are examined. The correct dyadic Green's function for the Coulomb vector potential in a rectangular waveguide is derived to elucidate the discussion. The attractive feature of the Coulomb gauge is the explicit separation of the electric field into its lamellar and solenoidal constituents. A flaw in the usage of the Coulomb gauge in W.R. Smythe's text Static and Dynamic Electricity (1968) is noted and corrected. >
01 Feb 1988
TL;DR: In this paper, the principal characteristics of gyromagnetic materials that are useful for microwave applications are reviewed, and both the large signal and small signal models that govern wave propagation at microwave frequencies are given.
Abstract: The principal characteristics of gyromagnetic materials that are useful for microwave applications are reviewed, and both the large-signal and small-signal models that govern wave propagation at microwave frequencies are given. Uniform and nonuniform plane waves in an unbounded ferrite medium are considered from the complementary viewpoints of electromagnetics and mechanics. Both electromagnetic and quantum-mechanical exchange channels of power exist in such materials, which can be ascribed to either waves or quasiparticles. Regimes of wave propagation that are magnetostatic in character are shown to exist, as well as the relationships between the Walker modes of a small spheroid and the magnetostatic wave propagation in thin films. When the power densities within these waves or modes exceed certain thresholds, the linear model breaks down and parametric instabilities can create a form of magnetic turbulence. The thresholds for both first-order and second-order processes that involve the uniform precession mode and parallel-pumping process that do not are reviewed. >
TL;DR: The rationale for teaching undergraduate electromagnetics partly through the finite element method, is put forward and helps to replace large portions of syllabi devoted to special solution methods, with problems of industrial magnitude and character.
Abstract: The rationale for teaching undergraduate electromagnetics partly through the finite element method, is put forward. Properly presented, the finite element method, easily within the ken of the engin...
TL;DR: In this article, the structural integrity of the first wall of a fusion reactor after a plasma disruption is evaluated. And the authors focus on the following issues: (1) electromagnetics, (2) heat conduction with melting, (3) structural mechanics when material melts and resolidifies, (4) magnetohydrodynamics of liquid metal with free surface, (5) simple evaluation of coupled problem, (6) lifetime evaluation of first wall and (7) a new concept of thermal-stress-free.
TL;DR: In this article, the authors traced the development of electrostatics and magnetostatics through the end of the 18th century, climaxed by the work of Coulomb and Poisson and showed how Maxwell's prediction of the existence of electromagnetic waves set the stage for the epochal experiments of Hertz.
Abstract: Highlights of the separate developments of the sciences of electrostatics and magnetostatics are traced through the end of the 18th century, climaxed by the work of Coulomb and Poisson. The linkage of these two sciences due to the discoveries of Oersted, Ampere, Biot and Savart, and Faraday are described, followed by the theoretical culmination embodied in the work of Maxwell. It is shown how Maxwell's prediction of the existence of electromagnetic waves set the stage for the epochal experiments of Hertz. >
TL;DR: In this paper, the importance of an improved knowledge of electromagnetics has been discussed, and some of the many developments in computer aids to electromagnetic design has been described, as well as the technologies which have contributed to the developments.
Abstract: Electrical machines play an important part in the lives of all of us: in power generation, in transport, in industry and in our homes They are very much taken for granted, yet there have been many interesting developments and innovations, which have led, for example, to great increases in power per unit volume, reduced cost, improved efficiency and reliability and greater controllability This article discusses some examples, draws attention to the technologies which have contributed to the developments, and shows the importance of an improved knowledge of electromagnetics In addition, some of the many developments in computer aids to electromagnetic design will be described
TL;DR: In this paper, the antenna test range at the US Naval Ocean Systems Center (NOSC) provides solutions to some formidable electromagnetics problems on ships, such as power lines, buildings, and even mountains.
Abstract: The authors discuss the antenna test range at the US Naval Ocean Systems Center, which provides solutions to some formidable electromagnetics problems on ships. They describe the measurement approach; the pattern range, a 160 ft diameter ground plane constructed of prestressed concrete covered with a very thin coating of lead; the impedance range, which has a subterranean instrument room that houses the measurement equipment and personnel during the test; and the time-domain measurement range. The authors then examine computer modelling of antennas and analysis of the EMC (electromagnetic compatibility) problem. The modelling approach as presented is not limited to ships; it can work for power lines, buildings, and even mountains. >
TL;DR: A finite element program for use in the instruction of electromagnetic field theory and the unity among the various disciplines of physics through the Poisson equation is exploited to make the same program solve problems from many areas.
Abstract: A finite element program for use in the instruction of electromagnetic field theory is described. The unity among the various disciplines of physics through the Poisson equation is exploited to mak...
TL;DR: In this paper, the authors pointed out that since the Prony method has not been eclipsed by many other methods and has been commonly used as the standard benchmark, the authors feel that the comparison in question was not unfairly selective.
Abstract: The commenters take issue with the comparisons presented by A.J. Mackay and A. McCowan (ibid., vol.AP-35, no.4, p.435-41, Apr. 1987). Specifically, it is claimed that the authors neglect the large body of results in electromagnetic system identification that have appeared since the early adaptations of Prony's method to electromagnetics. In a reply, the authors state that since the Prony method has not been eclipsed by many other methods and has been commonly used as the standard benchmark, the authors feel that the comparison in question was not unfairly selective. >
02 Aug 1988
TL;DR: The Mini Electromagneticnetics Code (MININEC) as mentioned in this paper is a method-of-moments computer program for the analysis of thin-wire antennas, which can be used to determine antenna-to-antenna coupling.
Abstract: The Mini Electromagnetics Code, or MININEC, is a method-of-moments computer program for the analysis of thin-wire antennas. A Galerkin procedure is applied to an electric-field integral equation to solve for the wire currents. This formulation results in an unusually short computer program suitable for implementation on a microcomputer. Hence, MININEC is written in BASIC, which is compatible with many popular microcomputers. MININEC capabilities include determination of impedance and currents, calculation of near and far fields, and calculation of radiation patterns. The solution includes all electromagnetic interactions between conductors, so the code can be used to determine antenna-to-antenna coupling, a necessary requirement for the electromagnetic compatibility (EMC) assessment of a cosite antenna environment. The development of MININEC from its conception is described. The capabilities are described and illustrated with examples. Future developments are included. >