Showing papers on "Electromagnetic field published in 1981"
TL;DR: In this paper, highly absorbing boundary conditions for two-dimensional time-domain electromagnetic field equations are presented for both two-and three-dimensional configurations and numerical results are given that clearly exhibit the accuracy and limits of applicability of these boundary conditions.
Abstract: When time-domain electromagnetic-field equations are solved using finite-difference techniques in unbounded space, there must be a method limiting the domain in which the field is computed. This is achieved by truncating the mesh and using absorbing boundary conditions at its artificial boundaries to simulate the unbounded surroundings. This paper presents highly absorbing boundary conditions for electromagnetic-field equations that can be used for both two-and three-dimensional configurations. Numerical results are given that clearly exhibit the accuracy and limits of applicability of highly absorbing boundary conditions. A simplified, but equally accurate, absorbing condition is derived for two- dimensional time-domain electromagnetic-field problems.
2,553 citations
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, a compact approximate asymptotic solution for the field radiated by an antenna on a perfectly conducting smooth convex surface was developed for the GPDD field.
Abstract: A compact approximate asymptotic solution is developed for the field radiated by an antenna on a perfectly conducting smooth convex surface. This high-frequency solution employs the ray coordinates of the geometrical theory of diffraction (GTD). In the shadow region the field radiated by the source propagates along Keller's surface diffracted ray path, whereas in the lit region the incident field propagates along the geometrical optics ray path directly from the source to the field point. These ray fields are expressed in terms of Fock functions which reduce to the geometrical optics field in the deep lit region and remain uniformly valid across the shadow boundary transition region into the deep shadow region. Surface ray torsion, which affects the radiated field in both the shadow and transition regions, appears explicitly in the solution as a torsion factor. The radiation patterns of slots and monopoles on cylinders, cones, and spheroids calculated from this solution agree very well with measured patterns and with patterns calculated from exact solutions.
164 citations
TL;DR: In this article, an approximate asymptotic solution for the electromagnetic fields induced on an electrically large perfectly conducting smooth convex surface by an infinitesimal magnetic or electric current moment on the same surface is presented.
Abstract: An approximate asymptotic solution is presented for the electromagnetic fields which are induced on an electrically large perfectly conducting smooth convex surface by an infinitesimal magnetic or electric current moment on the same surface. This solution can be employed to calculate the mutual coupling between antennas on a convex surface in an efficient and accurate manner. In this solution, the surface fields propagate along Keller's surface ray paths, and their description remains uniformly valid within the shadow boundary transition region including the immediate vicinity of the source. Furthermore, the effect of surface ray torsion on the surface fields is indicated in the present solution, through a factor T/k , where T denotes the surface ray torsion and k is the surface curvature in the ray direction. This solution is deduced from the asymptotic solutions to simpler canonical problems. Numerical results for the mutual coupling between slots in cylinders and cones are presented, and are shown to compare very well with experiments.
163 citations
TL;DR: In this paper, a nonperturbative method was presented for studying molecular photodissociation processes in the presence of (weak or intense) electromagnetic fields, using only squareintegrable (L2) functions.
Abstract: A practical and nonperturbative method is presented for studying molecular photodissociation processes in the presence of (weak or intense) electromagnetic fields, using only square‐integrable (L2) functions. By means of the complex coordinate transformation and L2 discretization of the vibrational continua, the complex quasivibrational energies (QVE) of the Floquet Hamiltonian can be determined by standard non‐Hermitian eigenvalue analysis. The real parts of the QVE’s provide the ac Stark‐shifted vibronic energies, whereas the imaginary parts are related to the photodissociation transition rates. The theory is applied to the direct photodissociation of H+2(1sσg–2pσu) in both weak and strong fields.
125 citations
TL;DR: In this article, a quasi-linear theory of the interaction of relativistic electrons with a cyclotron resonant applied electromagnetic field described by geometric optics is developed, and the electron distribution function is written as the sum of a quasi−static part f0 and a high frequency part f1.
Abstract: The formal theory of the interaction of mildly relativistic electrons with a cyclotron resonant applied electromagnetic field described by geometric optics is developed. The electron distribution function is written as the sum of a quasi‐static part f0 and a high frequency part f1. A quasi‐linear theory is employed to describe these. The resulting transport equation f0 is written to lowest significant order jointly in the reciprocal of the gyration frequency and the bounce frequency. It includes a relativistic collision term and a drag term associated with synchrotron emission. The linearized equations for f1 are solved, and an expression for the high‐frequency current is derived.
111 citations
DOI•
01 Aug 1981TL;DR: In this article, a narrow slot in the broad wall of a rectangular waveguide is analyzed using a moment method which takes account of both the wave guide wall thickness, and the influence of side walls.
Abstract: A narrow slot in the broad wall of a rectangular waveguide is analysed using a moment method which takes account of both the wave guide wall thickness, and the influence of side walls. In essence, the method of moments is used to solve a pair of coupled-integral equations, derived from the electromagnetic boundary conditions using Green's function techniques, to find the tangential electric fields on the upper and lower surfaces of the slot. These fields are represented by a sinusoidal Fourier set of basis functions, and it is shown that only a few terms are required to cause the series to converge. The necessity of inverting large, full matrices, which can be a disadvantage of this method, is thus avoided. Theoretical results are presented for the scattering parameters of slots and these are compared with experiment. A computed curve showing the functional form of the tangential electric field in the slot is also included and is compared with some earlier calculated and trial slot-field distribution.
109 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: An analysis is given of the interaction between extremely low-frequency (ELF) electric fields and animals of arbitrary body shape based on three approximations which are valid in the ELF range.
Abstract: An analysis is given of the interaction between extremely low-frequency (ELF) electric fields and animals of arbitrary body shape. This analysis is based on three approximations which are valid in the ELF range: In living tissues, capacitive (displacement) currents are negligible compared to conduction currents; effects resulting from the finite velocity of propagation of electromagnetic fields are negligible; skin effect in living tissues is negligible. Major conclusions of the analysis are: (a) The electric field outside the body, the induced charge on the surface of the body, and the total current crossing any section through the body (eg, through the neck or limbs) are completely determined by the characteristics of the applied ELF electric field, the shape of the body, its location relative to ground and other conductors, and any conduction currents from the body to ground or other conductors. (b) All of the quantities in (a) can be measured using conducting animal models. (c) The magnitudes of the electric field outside the body and the induced charge density on the surface of the body are independent of frequency, in the ELF range, when the body is either insulated from or shorted to ground (and any other conductors in the system). (d) The only quantities affected by the electrical properties of the tissues comprising the body are the current density and electric field inside the body. (e) The electric field outside and inside a body will be unchanged by a scaled change in its size.
84 citations
TL;DR: The existence of unguided TM and TE Gaussian beams is derived in a simple way from the wave equation for the vector potential, and the field configurations are discussed.
Abstract: The existence of unguided TM and TE Gaussian beams is derived in a simple way from the wave equation for the vector potential, and the field configurations are discussed. We point out the possibility of a new type of free-electron laser.
82 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.
TL;DR: In this article, a model is analyzed to study the electromagnetic acceleration of projectiles using a device known as the rail gun, where current is conducted between the rails by a plasma arc which drives the projectile.
Abstract: A model is analyzed to study the electromagnetic acceleration of projectiles using a device known as the rail gun. Current is conducted between the rails by a plasma arc which drives the projectile. The analysis includes determining the electromagnetic fields within the gun and solving the fluid‐mechanical equations of the plasma under the assumption that the flow parameters are steady in a frame that accelerates with the arc. Specifically, a set of coupled equations is derived which, when solved, yields the properties of the arc and the acceleration of the projectile. A limiting‐case analytic solution to the equations is found, and an iterative technique is employed to solve the equations numerically in the more general case. The results of the calculation are applied to analyze the arc in an experiment recently carried out by Rashleigh and Marshall. Some approximate scaling relations, which indicate how the properties of the arc vary with the dimensions of the rail gun, the mass of the projectile, the mass of the arc, and the accelerating current, are then derived. The results of the calculation are compared with those of others and some suggestions for future investigations are given.
TL;DR: The theory of cyclotron plasma sources of coherent microwave radiation excited by intense electron beams is reviewed systematically in this article, where the linear approximation of the theory yields the output frequency spectra, the wave growth rates, and the threshold electron beam currents required for exciting these sources.
Abstract: The theory of Cherenkov and cyclotron plasma sources of coherent microwave radiation excited by intense electron beams is reviewed systematically. The linear approximation of the theory yields the output frequency spectra, the wave growth rates, and the threshold electron beam currents required for exciting these sources. The general theory is illustrated for some particular devices: the forward-wave plasma Cherenkov source, foward-and backward-wave cyclotron-resonance masers, and foward-and backward-wave Cherenkov sources in a slightly corrugated slow-wave structure. The nonlinear theory of plasma microwave sources leans heavily on a numerical solution of the dynamic equations of the electromagnetic field and the charged particles in the system. The nonlinear operation of a forward-wave plasma Cherenkov source is analyzed. Under optimum conditions, the efficiency of this device can reach 30–35%. The efficiencies of other high-current plasma sources are comparable in magnitude. Experimental progress toward the development of high-power pulsed microwave sources of the Cherenkov and cyclotron types using intense relativistic electron beams is reviewed briefly.
TL;DR: In this article, a method for the calculation of the electromagnetic torque in electric machines is proposed based on an analytical field calculation in the air-gap combined with finite element field calculations in the saturated rotor and stator iron.
Abstract: In many engineering applications the calculation of forces and torques is subject of great importance [7] , [8]. A method for the calculation of the electromagnetic torque in electric machines is proposed in the paper. This method is based on an analytical field calculation in the air-gap combined with finite element field calculations in the saturated rotor and stator iron. The results of field calculation obtained using such a method are more precise than those calculated by the classical finite element method; thus the accuracy of the calculated torque will be better. An application for the case of synchronous machine is given at the end of the paper.
Patent•
12 Feb 1981TL;DR: In this paper, an electromagnetic system for determining the orientation including position of a helmet worn by a pilot is described, which is based on the rotation matrix determined by a previous solution for the orientation of the helmet.
Abstract: An electromagnetic system for determining the orientation including position of a helmet worn by a pilot is disclosed having a transmitting antenna for transmitting electromagnetic field vectors, a receiving antenna for sensing the electromagnetic field vectors generated by the transmitting antenna, and a control apparatus responsive to the sensed electromagnetic field vectors and the transmitted electromagnetic field vectors for determining the compensated orientation of the helmet, the compensated orientation relying upon the rotation matrix determined by a previous solution for the orientation of the helmet.
TL;DR: In this paper, a cosmological solution of the source-free Einstein-Maxwell equations with stiff matter and an electromagnetic null field is presented, which is a locally rotationally symmetric tilted Bianchi type-V universe.
Abstract: We present a cosmological solution of the source-free Einstein-Maxwell equations with “stiff” matter and an electromagnetic null field, which is a locally rotationally symmetric tilted Bianchi type-V universe.
TL;DR: The results show that, unlike the symmetric dielectric sphere, the relative position of the spheroid with respect to the orientation of the impressed electric field is an extremely important parameter which considerably affects the electric field coupling.
Abstract: The extremely low frequency (ELF) electric field coupling to dielectric spheroidal models of biological objects is studied. Simple expressions are obtained to determine the internal electric field strength induced inside two nonspherical spheroids; a prolate dielectric spheroid and an oblate dielectric spheroid. Certain numerical results are graphically presented for various geometric shapes of the spheroid. The results show that, unlike the symmetric dielectric sphere, the relative position of the spheroid with respect to the orientation of the impressed electric field is an extremely important parameter which considerably affects the electric field coupling.
TL;DR: In this paper, the Dirac equation of a relativistic free charged particle interacting with one quantised mode of the electromagnetic field is solved exactly, and the corresponding eigenvalues of the spectrum are obtained in closed analytical form for linear and circular polarisation.
Abstract: For pt.I see ibid., vol.14, no.6, p.1469-82 (1981). The Dirac equation of a relativistic free charged particle interacting with one quantised mode of the electromagnetic field is solved exactly. Stationary eigenstates and the corresponding eigenvalues (the spectrum) are obtained in closed analytical form for linear and circular polarisation. The states are parametrised by two quantum numbers, one of which, corresponding to the four-momentum, is continuous and the other, roughly corresponding to the photon content, discrete. Based on these results, the cross section of nonlinear Compton scattering is calculated. It is shown explicitly that the results reduce to the semiclassical one in the limit of high intensity and small depletion, while in the large (complete) depletion limit they contain a depletion factor which ensures convergence of the highly nonlinear processes.
TL;DR: In this article, the authors describe the spin degree of freedom in terms of Grassmann variables, and study the quantization problem of nonrelativistic and relativistic spinning particles interacting with crossed electric and magnetic fields by using the path integral method.
Abstract: Describing the spin degree of freedom in terms of Grassmann variables, we study the quantization problem of nonrelativistic and relativistic spinning particles interacting with crossed electric and magnetic fields by using the path integral method. The problem presents some difficulties due to the odd-dimensional nature of the phase space for the spin variables. We show how to deal with these difficulties by bringing back all the problems to the study of the quantum mechanics of a single Grassmann variable. Then it is straightforward to perform the path integrals in all the cases considered here, simply by solving the classical equations of motion.
TL;DR: In this article, the authors derived formulas on eddy current losses in non-magnetic (?s=1) and magnetic (? s>1) pipes from electromagnetic field theory and gave precise and approximate solutions for both cases where conductors are placed inside and outside the pipe in any configuration.
Abstract: Formulas on eddy current losses in non-magnetic (?s=1) and magnetic (?s>1) pipes are derived from electromagnetic field theory. These formulas are given in the forms of precise and approximate solutions for both cases where conductors are placed inside and outside the pipe in any configuration.
TL;DR: In this paper, four methods of electromagnetic probing of an inhomogeneous plane stratified medium are presented, which differ by the nature of the incident wave used in the diagnostic, i.e., the medium is considered as a structure propagating guided modes, and permittivity profiles are determined from the knowledge of one of the guided modes.
Abstract: Four methods of electromagnetic probing of an inhomogeneous plane stratified medium are presented. They differ by the nature of the incident wave used in the diagnostic. In the first method, the medium is considered as a structure propagating guided modes, and permittivity profiles are determined from the knowledge of one of the guided modes. In the next three, the medium is considered as a scatterer illuminated by a plane wave. Two of them are devoted to reconstruction of conductivity or permittivity profiles from time domain analysis of the reflected field. The last one allows one to obtain permittivity profiles from spectral domain analysis of the reflection coefficient. In spite of their apparent diversity, all these methods are issued from integral representations of the electromagnetic fields. These representations provides the simulated experimental data for the inverse problems. The behavior of these processes has been examined when parameters of practical interest are varied.
TL;DR: In this paper, the existence of a unique solution to Maxwell's equations defined in an exterior domain with impedance boundary condition is established for all frequencies, by reducing this problem to that of solving a system of singular integral equations and then regularizing this system such that the Riesz theory is applicable.
Abstract: The existence of a unique solution to Maxwell's equations defined in an exterior domain with impedance boundary condition is established for all frequencies. This is accomplished by reducing this problem to that of solving a system of singular integral equations and then regularizing this system such that the Riesz theory is applicable. We also consider the inverse problem in which it is desired to determine the impedance from a knowledge of the far field pattern. By restricting the impedance to lie a priori in a compact set results are obtained on the existence, uniqueness, and stability of the solution to this inverse scattering problem.
TL;DR: In this article, the position of a free charged particle subject to the zero-point electromagnetic field with Lorentz-invariant spectral density proportional to π/(omega/sup 3/ ) is obtained.
Abstract: The ''elementary propagator'' for the position of a free charged particle subject to the zero-point electromagnetic field with Lorentz-invariant spectral density proportional..omega../sup 3/ is obtained. The nonstationary process for the position is solved by the stationary process for the acceleration. The dispersion of the position elementary propagator is compared with that of quantum electrodynamics. Finally, the evolution of the probability density is obtained starting from an initial distribution confined in a small volume and with a Gaussian distribution in the velocities. The resulting probability density for the position turns out to be equal, to within radiative corrections, to psipsi* where psi is the Kennard wave packet. If the radiative corrections are retained, the present result is new since the corresponding expression in quantum electrodynamics has not yet been found. Besides preceding quantum electrodynamics for this problem, no renormalization is required in stochastic electrodynamics.
04 Aug 1981
TL;DR: A finite amplitude linearly polarized electromagnetic wave propagating in a relativistic plasma, was found to generate the longitudinal d.c. as well as the oscillating electric field at the second harmonic as discussed by the authors.
Abstract: A finite amplitude linearly polarized electromagnetic wave propagating in a relativistic plasma, is found to generate the longitudinal d.c. as well as the oscillating electric field at the second harmonic. In a plasma consisting of only electrons and positrons, these fields cannot be generated.
TL;DR: In this article, single propagation models are investigated for analyzing VLF electromagnetic wave fields observed in magnetosphere, and two models are selected according to the values of the eigenvalues of the spectral matrices of the three magnetic field components.
Abstract: Single propagation models are investigated for analyzing VLF electromagnetic wave fields observed in magnetosphere. They are selected according to the values of the eigenvalues of the spectral matrices of the three magnetic field components. If there is one single nonzero eigenvalue, a one-direction model is considered, while if there are two nonzero eigenvalues, a two-direction model is chosen. A likelihood ratio test is performed in the doubtful cases. The two models are used to analyze VLF chorus and hiss observed onboard the Geos 1 satellite. The two-direction model is generally the most likely, suggesting that waves are simultaneously generated at all wave normal directions.
TL;DR: In this article, the electromagnetic and gravitational fluctuations about the classical gravitational field of a rotating black hole are quantized by imposing commutation relations on the Newman-Penrose quantities phi/sub 0/ and psi/sub 1/.
Abstract: The electromagnetic and gravitational fluctuations about the classical gravitational field of a rotating black hole are quantized by imposing commutation relations on the Newman-Penrose quantities phi/sub 0/ and psi/sub 0/. Two examples which illustrate the utility of the formalism concern the vacuum expectation value of the stress-energy tensor for the electromagnetic field in the Boulware vacuum and the response of an Unruh box coupled to fluctuations of the gravitational field. These quantities are computed in the vicinity of the horizon.
TL;DR: In this article, a thirty-six day recording of the natural electric and magnetic field variations obtained on the deep ocean floor north-east of Hawaii was analyzed using singular value decomposition (SVD) to remove uncorrelated noise.
Abstract: Summary. We have analysed a thirty-six day recording of the natural electric and magnetic field variations obtained on the deep ocean floor north-east of Hawaii. The electromagnetic fields are dominated by tides which have an appreciable oceanic component, especially in the east electric and north magnetic components. The techniques of data analysis included singular value decomposition (SVD) to remove uncorrelated noise. There are three degrees of freedom in the data set for periods longer than five hours, indicating a correlation of the vertical magnetic field and the horizontal components, suggesting source field inhomogeneity. Tensor response functions were calculated using spectral band averaging with both SVD and least squares techniques and rotated to the principal direction. One diagonal component, determined mainly by the north electric and east magnetic fields, is not interpretable as a one-dimensional induction phenomenon. The other diagonal term of the response function indicates a rapid rise in conductivity to 0.05 mho m−1 near 160 km. No decrease in conductivity below this depth is resolvable. Polarization analysis of the magnetic field indicates moving source fields with a wavelength near 5000 km. Model studies suggest that the two dimensionality in the response function may be caused by motion in the ionospheric current system.
TL;DR: In this article, it was observed that with a sufficiently large incident extraordinary wave amplitude, the electrostatic upper hybrid wave resulting from the mode conversion process at the resonant layer can scatter off the lower hybrid wave and penetrate through its original cutoff to a distance proportional to the product of the scale length and the square root of the mass ratio.
Abstract: It is observed that with a sufficiently large incident extraordinary wave amplitude, the electrostatic upper hybrid wave resulting from the mode conversion process at the resonant layer can scatter off the lower hybrid wave and penetrate through its original cutoff to a distance proportional to the product of the scale length and the square root of the mass ratio. A substantial number of energetic ions also appear in the resonant region which is well inside the plasma slab as a result of lower hybrid wave excitation.