Showing papers on "Electromagnetic field published in 1979"
TL;DR: The well-known electromagnetic fields generated by infinitesimal dipoles in the presence of the earth are reviewed briefly with special reference to contributions by H. Bremmer as discussed by the authors.
Abstract: The well-known electromagnetic fields generated by infinitesimal dipoles in the presence of the earth are reviewed briefly with special reference to contributions by H. Bremmer. The fields due to currents in extended conductors can be expressed in terms of an integral over the occupied volume but its evaluation is possible only when the currents are known in their dependence on the properties of the earth. This is true of the horizontal-wire antenna quite close to the earth both when driven by a localized emf and when acting as a scatterer in an incident field. It is also true of horizontal antennas in the earth not too close to the surface. Expressions for the most useful component of the radiated or scattered field are formulated for an end-driven Beverage-type antenna, for the horizontal wire as a scatterer in the presence of the earth, and for the embedded insulated traveling-wave antenna.
466 citations
TL;DR: In this article, a variational finite-element algorithm was proposed to solve the problem of time-harmonic electromagnetic scattering by axisymmetric penetrable bodies having arbitrary cross-sectional profiles and continuous inhomogeneous consistency.
Abstract: This investigation is concerned with the numerical solution of time-harmonic electromagnetic scattering by axisymmetric penetrable bodies having arbitrary cross-sectional profiles and even continuously inhomogeneous consistency. The initiation of this effort involved the discovery and development of the coupled azimuthal potential (CAP) formulation, which is valid in generally lossy isotropic inhomogeneous rotationally symmetric media. Electromagnetic fields in such regions can be represented, using the CAP formulation, in terms of two continuous potentials which satisfy a self-adjoint system of partial differential equations or, equivalently, a variational criterion. Using an optimized variational finite-element algorithm in conjunction with a triregional unimoment method, a versatile computer program is described that provides scattering solutions for each of multiple incident fields impinging upon an arbitrarily shaped inhomogeneous penetrable body of revolution. An extensive evaluation of the accuracy and convergence of the algorithm is presented, which includes comparison of scattering computations and experimental measurements at X -band for several solid and hollow plexiglas bodies of revolution with maximum interior dimensions of over 4 wavelengths.
155 citations
CERN1
TL;DR: In this article, the charge operator and charged sectors in four-dimensional QED were investigated, both within a local, covarian (indefinite metric) and within a positive metric formulation of QED.
139 citations
TL;DR: The Weinberg-Salam theory was reformulated as a pure Yang-Mills theory in a six-dimensional space, the Higgs field being interpreted as gauge potentials in the additional dimensions as discussed by the authors.
Abstract: The Weinberg-Salam theory is reformulated as a pure Yang-Mills theory in a six-dimensional space, the Higgs field being interpreted as gauge potentials in the additional dimensions. Viewed in this way, the condition that the Higgs field transforms as a U(1) representation of charge one is equivalent to requiring a value of 30 degrees for the Weinberg angle. A second consistent determination comes form the idea borrowed from monopole theory that the electromagnetic field is the direction of the Higgs field.
136 citations
TL;DR: In this paper, the T-matrix equations describing boundary value problems of potential theory and electromagnetic scattering are obtained without recourse to the Huygens principle or physically fictitious fields.
Abstract: Employing a conserved‐flux concept, the T‐matrix equations describing boundary‐value problems of potential theory and electromagnetic scattering are obtained without recourse to the Huygens principle or physically fictitious fields. For scattering by dielectric objects, tangential electric and magnetic fields on the surface are both represented in a single expansion, cutting the computation in half. In the low‐frequency limit the dynamical equations are shown to reduce to the static case, and numerical computations then indicate that in comparison with other approaches, the present method can achieve as much as an order of magnitude reduction in the number of equations and unknowns needed for a given accuracy. New exact relations are found between the electrostatic and magnetostatic problems, and analytical results are also obtained from the equations, with and without truncation.
109 citations
TL;DR: In this paper, it was shown that nodal surfaces on which the tangential component of the electric field vector is zero can be regarded as defining mirror shapes for an open resonator supporting this Gaussian standing-wave pattern.
Abstract: Using the complex source-point method, we deduce simple approximate formulae for the six rectangular components of the electromagnetic field of a Gaussian beam. It is shown that in the standing-wave pattern formed by two oppositely directed Gaussian beams, nodal surfaces exist on which the tangential component of the electric field vector is zero. These surfaces can be regarded as defining mirror shapes for an open resonator supporting this Gaussian standing-wave pattern. These mirror shapes are nearly, but not exactly, spherical. The resonant frequencies for the fundamental transverse mode of such a resonator have been found as a function of the geometry and the axial mode number. Using a simple perturbation method the resonant frequency of an open resonator with spherical mirrors has been found. The result, though approximate is accurate to within ( kw 0 ) –6 in contrast to the commonly quoted result, which is only accurate to within ( kw 0 ) –4 , where k is the phase coefficient for TEM waves in free space and w 0 is the scale radius of the Gaussian beam at the beam waist.
95 citations
TL;DR: In this article, the authors considered a system comprised of identical two-level atoms interacting with the electromagnetic field in the dipole approximation and with an externally applied steady-state coherent driving field.
Abstract: The authors consider a system comprised of a collection of identical two-level atoms interacting with the electromagnetic field in the dipole approximation and with an externally applied steady-state coherent driving field. The atoms are considered to interact with each other only via the electromagnetic field and are assumed to be contained within a volume much smaller than a resonance wavelength. The system is treated as a quantum-statistical ensemble in the rotating frame, rotating at the carrier frequency of the externally applied coherent field. The Hamiltonian in this frame is explicitly time independent and the exact analog of a spin temperature is defined. The thermodynamic-Green's-function method is used to determine the thermodynamic equilibrium properties of the system in the rotating frame. This results in a nonlinear relation between the applied field and the field in the volume containing the atoms. The expression is a nonlinear function of the effective or "spin" temperature as well, and has the form of a first-order phase transition with the macroscopic atomic polarization as order parameter. In the low-"spin"-temperature limit, and for perfect tuning, the expression reduces to the exact form of the nonlinear relation for optical bistability derived by Bonifacio and Lugiato and relating the incident and transmitted fields for atoms in a ring cavity in the mean-field approximation. The results contain absorptive as well as dispersive contributions. These results predict essentially different behavior as a function of off tuning compared with behavior predicted by others using statistical steady-state models far from thermodynamic equilibrium. In the limit of zero value for the applied field amplitude, the results reduce to the conditions for the well-known second-order superradiant" phase transition. The condition for the existence of the second-order phase transition is shown to depend on the cavity tuning and the photon escape rate. The authors also show why, in light of the experiments in optical bistability, this second-order phase is difficult to observe.
89 citations
TL;DR: Particle-like static spherically symmetric solutions to massless scalar and electromagnetic field equations combined with gravitational field equations are considered in this paper, where two criteria for particle-like solutions are formulated: the strong one (solutions are required to be singularity free) and the weak one (singularities are admitted but the total energy and material field energy should be finite).
88 citations
01 Jan 1979
TL;DR: The characteristic value of the electromagnetic field intensity in quantum electrodynamics is studied and presented in this paper, where general remarks are given on processes in an intense electromagnetic field and their description is detailed.
Abstract: The characteristic value of the electromagnetic field intensity in quantum electrodynamics is studied and presented. General remarks are given on processes in an intense electromagnetic field and their description is detailed. Photon emission by electron in the field of an intense electromagnetic wave and pair production by a photon in the field of an intense electromagnetic wave are discussed. The authors examine shift and splitting of the atomic level by electromagnetic wave fields. Radiative corrections are presented.
82 citations
TL;DR: In this paper, the theory of lower-hybrid-drift instability is extended to include a finite value of the component of wave vector parallel to the ambient magnetic field so that the analysis bridges the usual lower hybrid-drifting instability of flute modes and the modified-two-stream instability.
Abstract: The theory of lower-hybrid-drift instability is extended to include a finite value of the component of wave vector parallel to the ambient magnetic field so that the analysis bridges the usual lower-hybrid-drift instability of flute modes and the modified-two-stream instability. The present theory also includes electromagnetic and ambient magnetic field-gradient effects. It is found that in the cold-electron limit the density and magnetic gradients can qualitatively modify the conclusion obtained in the early theory of the modified-two-stream instability. For example, even if the relative drift far exceeds the Alfven speed of the plasma, the instability may still persist. This result is in contrast to that established in the literature. When the electron temperature is finite, the problem is complicated. Numerical solutions are obtained for a number of cases.
TL;DR: By using several biophysical approximations and considering man as free space model limiting order-of-magnitude values for external electric and magnetic field strengths which may be hazardous for human beings were calculated, a “lower boundary-line” was estimated.
Abstract: By using several biophysical approximations and considering man as free space model limiting order-of-magnitude values for external electric and magnetic field strengths which may be hazardous for human beings were calculated. Danger may occur by excitation processes below 30 kHz for field strengths exceeding these limiting values; for frequencies larger than 60 kHz, thermal effects are predominant before excitation occurs. The external electric field strength necessary for causing action potentials in the central nervous system exceeds by far the corona forming level. But excitation is possible by strong alternating magnetic fields. Furthermore, by comparing the electrically and magnetically induced currents with the naturally flowing currents in man caused by the brain's and heart's electrical activity, a "lower boundary-line" was estimated. Regarding electric or magnetic field strengths undercutting this boundary-line, direct effects on the central nervous system may be excluded. Other mechanisms should be responsible for demonstrated biological effects.
TL;DR: In this paper, a general formulation to the problem of the radiation of arbitrary distribution of buried sources within a horizontally stratified anisotropic medium is presented, where the fields are obtained in terms of appropriately defined electric and magnetic types of dyadic Green's functions which are dual to each other.
Abstract: A general formulation to the problem of the radiation of arbitrary distribution of buried sources within a horizontally stratified anisotropic medium is presented. The fields are obtained in terms of appropriately defined electric and magnetic types of dyadic Green's functions which are dual to each other. The formulation is considerably simplified by the resolution of these dyadic Green's functions into transverse electric (TE) and transverse magnetic (TM) waves and by the existing duality between them. A systematic procedure for deriving the fields in an arbitrary layer in terms of the primary source excitation and appropriately defined wave amplitude matrices is described.
TL;DR: An exact solution for the canonical model equations describing the electromagnetic fields on a free-electron-laser amplifier comprised of a high-quality relativistic electron beam propagating along the axis of a helical pump magnetic field is given in this paper.
Abstract: An exact solution is given for the canonical model equations describing the electromagnetic fields on a free-electron-laser amplifier comprised of a high-quality relativistic electron beam propagating along the axis of a helical pump magnetic field. The case of a cold beam is analyzed in detail and it is shown that, depending upon the parameters, one can have gain when the system is stable, owing to constructive spatial interference of modes, or exponential gain when it is unstable. Gain curves, line shapes, and linewidths are presented for conditions of reported and planned experiments. Reasonable agreement is found with the reported experiments.
TL;DR: In this paper, the gravitationally induced self-interaction force at a large distance from a Schwarzschild black hole is calculated at the horizon of the black hole, and it is shown that the self-force has the same magnitude but opposite direction.
Abstract: The gravitationally induced self-interaction force is calculated at a large distance from a Schwarzschild black hole. If, instead of the electromagnetic field, the particle is coupled to a vector-meson field of vanishingly small, but nonzero, mass, then it is shown that the self-force has the same magnitude but opposite direction. A sharp difference between massive and massless vector fields is a result of different boundary conditions at the horizon surface.
TL;DR: In this article, a method for calculating the electric and magnetic fields from dipoles embedded in anisotropic stratified media is presented. But the method is based on decomposing the fields into transverse electric (TE) and transverse magnetic (TM) modes, which is more computationally efficient than using the Hertz potential.
Abstract: A method is presented for calculating the electric and magnetic fields from dipoles embedded in anisotropic stratified media. By decomposing the fields into transverse electric (TE) and transverse magnetic (TM) modes, the results are obtained more directly and are more computationally efficient than methods using the Hertz potential. The electromagnetic fields are obtained for four types of dipole sources: horizontal electric, horizontal magnetic, vertical electric, and vertical magnetic. The source is embedded within one of several anistropic layers, which are further sandwiched between two semi-infinite media.
TL;DR: In this article, a kinetic theory of ponderomotive effects and magnetic field generation is presented, where the main source of the magnetic field is the off-diagonal terms of the particle pressure tensor.
Abstract: A kinetic theory of ponderomotive effects and magnetic field generation is presented. For a comparison with standard fluid theories, explicit equations for momentum and energy conservations are established. As an example, it is shown that collisions do not lead to the usual resistive drag. In the important case of magnetic field generation via resonant absorption, three regimes with different behavior are found. In the collision‐dominated regime of the parameters, the main source of the magnetic field is the off‐diagonal terms of the particle pressure tensor. An intermediate regime appears when the nonlinear effects are collisionless and the amplitude of electromagnetic field due to the resonance absorption mechanism is limited by the plasma resistivity. In the collisionless regime, the validity of published results is extended by a self‐consistent nonlinear calculation. As a result, the distribution function of electrons may include suprathermal tails, and the magnetic field generated does not appear explicitly in the formula.
TL;DR: In this article, the development of the electromagnetic field in the magnetosphere-ionosphere system is examined under the condition that a constant current generator supplies current to the system after t = 0.
Abstract: Development of the electromagnetic field in the magnetosphere-ionosphere system is examined under the condition that a constant current generator supplies current to the system after t=0. It is shown that at high altitudes there are intervals when the electric field is transiently directed opposite to the direction of the supplied current. Namely, transient dusk-to-dawn electric field can be generated from ionospheric channeling of the dawn-to-dusk tail current during an early stage of the development of the tail-ionosphere current system. Electric field with the opposite polarity is produced during intervals when the field reflected from the ionosphere dominates over the incident field.
TL;DR: In this paper, an asymptotic expression for the mass correction of order alpha to the electron propagator in an intense electromagnetic field is presented, which is used for the calculation of radiation corrections to electron and photon elastic scattering amplitudes.
Abstract: A derivation of an asymptotic expression for the mass correction of order ..cap alpha.. to the electron propagator in an intense electromagnetic field is presented. It is used for the calculation of radiation corrections to the electron and photon elastic scattering amplitudes in the ..cap alpha../sup 3/ approximation. All proper diagrams contributing to the amplitudes and containing the above-mentioned correction to the propagator were considered, but not those which include vertex corrections. It is shown that the expansion parameter of the perturbation theory of quantum electrodynamics in intense fields grows not more slowly than ..cap alpha..chi/sup 1/3/ at least for the electron amplitude, where chi = ((eF/sub ..mu nu../p/sub ..nu../)/sup 2/)/sup 12//m/sup 3/, p is a momentum of the electron, and F is the electromagnetic field tensor.
TL;DR: In this paper, a Lagrangian L for non-minimally coupled gravitational and electromagnetic fields will usually lead to higher-order field equations, in the sense that the functional derivatives of L with respect to the gravitational potential gij and the electromagnetic potential phi i will involve at least the third derivatives of these quantities.
Abstract: An arbitrarily chosen Lagrangian L for non-minimally coupled gravitational and electromagnetic fields will usually lead to higher-order field equations, in the sense that the functional derivatives of L with respect to the gravitational potential gij and the electromagnetic potential phi i will involve at least the third, instead of merely the second, derivatives of these quantities. By temporarily contemplating a five-dimensional formalism this paper uncovers an exceptional case in which one is led to second-order equations. The result obtained is in agreement with the conclusions reached by Horndeski (1976) by quite different means.
TL;DR: In this paper, the authors investigated all type D solutions of the Einstein-Maxwell equations with cosmological constant such that the Debever-Penrose vectors are aligned along the two eigenvectors of the electromagnetic field, in the special case when a direct generalization of the Goldberg-Sachs theorem is not possible.
Abstract: We investigate all type D solutions of the Einstein–Maxwell equations (with cosmological constant) such that the Debever–Penrose vectors are aligned along the two eigenvectors of the electromagnetic field, in the special case when a direct generalization of the Goldberg–Sachs theorem is not possible. A solution is found which admits no Killing vectors. We also present an extension of the Golberg–Sachs theorem valid for type D metrics.
01 Feb 1979
TL;DR: In this article, the authors considered the case of a Fabry-Perot resonator with plane-parallel mirrors and derived the time evolution of the polarization parameters of both modes in a two-mode operating gas laser.
Abstract: Starting from a theory in which laser operation is described as the excitation of the natural modes of an open-resonator system, the case of a Fabry-Perot resonator with plane-parallel mirrors is treated. It is shown that, in the case of weakly anisotropic mirrors, the natural modes can be grouped in pairs, such that each pair corresponds to one scalar longitudinal mode. In that case, laser operation can and will be described in terms of these longitudinal modes, which then possess a vectorial field amplitude, in agreement with the usual formalism. The polarization preference in a single-mode gas laser operating on a transition between a singlet and a triplet state is investigated, taking into account differences in the relaxation constants for the various expectation values of atomic variables. A calculation of the effect on the relaxation constants due to interatomic collisions leads to the conclusion that theory and experiment are in good agreement with each other. Equations describing the time evolution of the polarization parameters of both modes in a two-mode operating gas laser are derived. It is found as a general rule that mode-mode interaction results in modes whose polarizations are mutually orthogonal. An exception to this rule is found in the case in which the single-mode preference is for circular polarization. The influence of two specific mirror anisotropies is discussed. The polarization behaviour of a single-mode gas laser in the presence of (partly) applied, transverse magnetic fields is extensively dealt with. It appears to be essential to distinguish between the case in which the magnetic field is applied only to a fraction of the active medium and the case in which the magnetic field is uniform in the entire medium. This distinction is shown to lead to a satisfactory theoretical description of a certain class of experiments. In the case of two other experiments, good agreement with the theory is obtained, by assuming the presence of mirror anisotropies of acceptable kind and size. Finally, the influence of small anisotropies on the degree of polarization of a single-mode gas laser is theoretically investigated, when the latter is polarized by means of a strong transverse magnetic field.
TL;DR: In this paper, the interaction of magnetized monoenergetic ions (a ring in velocity space) with a homogeneous Maxwellian target plasma is studied numerically using linear Vlasov theory.
Abstract: The interaction of magnetized monoenergetic ions (a ring in velocity space) with a homogeneous Maxwellian target plasma is studied numerically using linear Vlasov theory. The ring may be produced when an energetic beam is injected perpendicular to a uniform magnetic field. In addition to yielding the previously known results, the present study classifies this flute‐like instability into three distinct regimes based on the beam density relative to the plasma density, where many features such as physical mechanisms, dispersion diagrams, and maximum growth rates are quite different. The effects of electron dynamics, plasma or ring thermal spread, the ratio of ωp/ωc for plasma ions, and electromagnetic modifications are also considered.
TL;DR: In this article, the basic physics underlying the operation of a device of this type and describe the plane wave procedure discussed by these authors for relating the phase shift and attenuation measurements made by such a device to the formation dielectric properties.
Abstract: The composite dielectric constants of earth formations at microwave frequencies are strongly dependent on formation water saturations and relatively independent of water salinities. Therefore, microwave frequency dielectric constant logging offers an attractive new electromagnetic (EM) method of formation evaluation. The EM wave propagation method of dielectric constant logging attempts to deduce the dielectric properties of earth formations from phase shift and attenuation measurements of EM field, which have been propagated in the formation. A device which utilizes this method of well logging has been proposed by Calvert (1974) and Rau (1976) in two recent U.S. patents. We discuss the basic physics underlying the operation of a device of this type and describe the plane wave procedure discussed by these authors for relating the phase shift and attenuation measurements made by such a device to the formation dielectric properties. This procedure is suspect, since it is based on an unrealistic plane wave m...
TL;DR: In this article, the pulsed electromagnetic radiation from a two-dimensional line source in a lossless two-media configuration is investigated theoretically and closed-form expressions for the electromagnetic field components anywhere in the configuration are derived.
Abstract: The pulsed electromagnetic radiation from a two-dimensional line source in a lossless two-media configuration is investigated theoretically. The author's modification of Cagniard's technique is used to derive closed-form expressions for the electromagnetic field components anywhere in the configuration. Numerical results are presented pertaining to the incident, the reflected, and the transmitted wave for different positions of the source and the observer, as well as for different contrasts of the two media. Also, the corresponding total-field plots are shown. In an appendix, the modified Cagniard contours pertaining to a lossless N-media configuration are discussed and some two-media modified Cagniard contours are shown.
TL;DR: In this paper, the theory of free-carrier absorption in nondegenerate semiconductors is extended to take into account quantizing magnetic fields in the presence of a magnetic field.
Abstract: The theory of free-carrier absorption in nondegenerate semiconductors is extended to take into account quantizing magnetic fields In the presence of a magnetic field, the behavior of the free-carrier absorption depends not only upon the magnitude of the magnetic field but also upon the polarization of the electromagnetic field relative to the magnetic field direction For electromagnetic radiation polarized transverse to the magnetic field, the phenomenon of free-carrier absorption merges into that of cyclotron resonance, which has been extensively reported in the literature However, when the radiation is polarized parallel to the magnetic field, the absorption depends critically on the mechanisms by which the carriers are scattered in the semiconductor When acoustic phonon scattering is dominant, we find that the free-carrier absorption is an oscillatory function of the magnetic field which increases in magnitude with the magnetic field The oscillations only occur when the photon frequency $\ensuremath{\Omega}$ is greater than the cyclotron frequency of the carriers When $\ensuremath{\Omega}l{\ensuremath{\omega}}_{c}$ the free-carrier absorption is predicted to increase linearly with the magnetic field The magnetic-field dependence of the free-carrier absorption is explained in terms of phonon-assisted transitions between the various Landau levels of the carriers
TL;DR: In this article, a method for the analysis of measurements of n components of a random electromagnetic wave field (n ⩽6) is developed for describing statistically the distribution of wave energy with respect to the variables frequency and wave-normal direction.
Abstract: A method is developed for the analysis of measurements of n components of a random electromagnetic wave field (n ⩽6). This field observed at a fixed point in a magnetoplasma is described statistically by the distribution of wave energy with respect to the variables frequency and wave-normal direction. The frequency is supposed to be fixed. The distribution function considered as the most reasonable one maximizes the entropy and satisfies the values of the n × n elements of the spectral matrix of the n components. This solution obeys the nonnegativity constraint on the wave distribution function. Its properties are discussed in terms of stability and predictive power. Applications are proposed to simulated data and to satellite data.
Patent•
13 Apr 1979TL;DR: In this article, a resonant circuit sensor of physical properties of objects that monitors measurable properties of resonant circuits affected by interactions of the objects with the polarized, resonant oscillations of the circuits is presented.
Abstract: The invention is a resonant circuit sensor of physical properties of objects that monitors measurable properties of resonant circuits affected by interactions of the objects with the polarized, resonant oscillations of the circuits. The circuits can be passive with excitation by an external energy source or active with a source included as an integral part. Simultaneous or sequential sensing of more than one physical property of objects is obtained by detecting resonant oscillation characteristics such as amplitude, frequency, phase or polarization and by detecting quantities influenced by such characteristics for one or more orientations of the objects relative to the polarization of the oscillations. These resonant oscillations can be in the form of electromagnetic fields, electric fields, magnetic fields, or acoustic waves. For electromagnetic fields in the microwave frequency range, device structures, such as Gunn device flanges, that have current and voltage properties that depend on microwave signal properties can provide versatile output signals for the sensor. The sensing can be relative and detect differences in object properties and it can be absolute and measure values for object properties.
TL;DR: In this paper, an analysis of the electromagnetic field excited by a toroidal cofl that is coaxial with a circular metal rod located in a conducting medium is presented, and the integral representation for the induced axial current on the rod is cast in a form that is suitable for numerical evaluation.
Abstract: We present an analysis of the electromagnetic fields excited by a toroidal cofl that is coaxial with a circular metal rod located in a conducting medium. The integral representation for the induced axial current on the rod is cast in a form that is suitable for numerical evaluation. Some results for the electric current distribution on the infinitely long configuration are given for a fixed magnetic current source. Good agreement is obtained with an asymptotic estimate for this quantity. The effects of truncating the bottom end of the rod and terminating the top in an ideal ground plane are treated by an approximate method. Numerical results for this confilguration are also given.