Showing papers on "Electromagnetic field published in 1977"

Photon Antibunching in Resonance Fluorescence

Abstract: The phenomenon of antibunching of photoelectric counts has been observed in resonance fluorescence experiments in which sodium atoms are continuously excited by a dye-laser beam. It is pointed out that, unlike photoelectric bunching, which can be given a semiclassical interpretation, antibunching is understandable only in terms of a quantized electromagnetic field. The measurement also provides rather direct evidence for an atom undergoing a quantum jump.

A surface formulation for characteristic modes of material bodies

Abstract: A theory of characteristic modes for material bodies is developed using equivalent surface currents. This is in contrast to the alternative approach using induced volume currents. The mode currents form a weighted orthogonal set over the material body surface, and the mode fields form an orthogonal set over the sphere at infinity. The characteristic modes of material bodies have most of the properties of those for perfectly conducting bodies. Formulas for the use of these modes in electromagnetic scattering problems are given. A procedure for computing the characteristic modes is developed, and applied to two-dimensional bodies. Illustrative examples of file computation of characteristic currents and scattering cross sections are given for cylinders of different material constants.

Magnetic Fields of a Dipole in Special Volume Conductor Shapes

Abstract: Expressions are presented for the magnetic fields produced by current dipoles in four basic volume conductor shapes. These shapes are the semi-infinite volume, the sphere, the prolate spheroid (egg-shape), and the oblate spheroid (discus-shape). The latter three shapes approximate the shape of the human head and can serve as a basis for understanding the measurements of the brain's magnetic fields. The semi-infinite volume is included in order to investigate the effect of the simplest boundary between a conductor and nonconductor. The expressions for the fields are presented in a form which separates the total field into two parts. One part is due to the dipole alone (the dipole field); the other is due to the current generated in the volume conductor by the dipole (the volume current field). Representative plots of the total field and the volume current field are presented for each shape. The results show that for these shapes the component of the total field normal to the surface of the volume conductor is produced completely or in large part by the dipole alone. Therefore, measurement and use of this component will greatly reduce the complexity of determining the sources of electrical activity inside a body from measurements outside the body by removing the necessity of dealing with the volume current field.

Quantum versus classical dynamics in the treatment of multiple photon excitation of the anharmonic oscillator

Abstract: The response of a one‐dimensional anharmonic Morse oscillator to an intense electromagnetic field has been investigated using both a quasiclassical and quantum mechanical description of the oscillator. The anharmonic nature of the Morse potential reduces the coherence of the quantum excitation process after only a few quanta have been absorbed. The classical and quantum behavior of averaged quantities such as the energy absorbed and the oscillator displacement as a function of time are in good agreement; however, the classical description cannot reproduce the multiphoton resonances. We are led to the conclusion that classical mechanics provides an adequate description of the response of a molecule in an intense laser field provided that multiphoton resonances do not individually play a fundamental role in the process.

The necessity of quantizing the gravitational field

Abstract: The assumption that a classical gravitational field interacts with a quantum system is shown to lead to violations of either momentum conservation or the uncertainty principle, or to result in transmission of signals faster thanc. A similar argument holds for the electromagnetic field.

Field intensification in radio frequency thermotherapy

Abstract: A technique in the treatment of tumors in humans utilizing radio frequency electromagnetic radiation to produce necrosis of the tumors by which intensification at the situs of the tumor of a radio frequency field applied across the portion of the body containing the tumor is obtained by positioning a small inductance element preferably in the form of a closed resonant circuit such that the inductance is in or adjacent to the tumor tissue and thus functions to concentrate the field at that location. Alternatively, rather than utilizing a resonant circuit, the inductance can be coupled to the output of the radio frequency generator utilized and applies the radio frequency electromagnetic field.

Electrodynamics of quasi-two-dimensional electrons

Abstract: For a system of electrons confined to a thin but finite layer, the nonlocal frequency-dependent dielectric tensor is constructed in the random-phase approximation and used in the Maxwell equations to study the electromagnetic properties. Retardation effects are negligible if the thickness of the electron layer is small compared with the wavelength of the electromagnetic wave.

Fluctuations of polarization and magnetization in dielectric and magnetic media

Abstract: We consider thermal fluctuations of polarization, magnetization, and the associated electromagnetic fields in dielectric magnetic media which are allowed to be anisotropic and spatially nonhomogeneous. The theory is purely macroscopic and is based on an application of the fluctuation–dissipation theorem. It is shown that the correlation functions can be elegantly expressed in terms of the Green functions for Maxwell’s equations.

V Foundations of the Macroscopic Electromagnetic Theory of Dielectric Media

Abstract: Publisher Summary This chapter is concerned with the derivation of the macroscopic Maxwell equations and associated constitutive relations from the underlying microscopic equations describing the dynamics of the constituent particles and the electromagnetic fields created by these particles. In the most general context, these particles are assumed to be electrons and nuclei, bound together in stable groups. For fluid systems, the derivation of the Maxwell equations, but excluding the constitutive relations, has been achieved for an arbitrary state of motion of the atoms on the basis of classical statistical mechanics. The chapter also gives a brief outline of the structure and the equations of macroscopic electrodynamics to establish the notation and the necessary definitions.

A mathematical model of slag and metal flow in the ESR Process

Abstract: Through the statement of the turbulent Navier-Stokes equations and Maxwell’s equations a mathematical representation is developed for the electromagnetic force field and the velocity field in the slag phase and the metal pool of cylindrical ESR units. Computed results are presented for both industrial scale (0.5 m electrode diameter) and laboratory scale (0.05 m electrode diameter) units operating with direct currents. It was found that for industrial scale units, the computed slag velocities ranged from 5 to 10 cm/s, while the velocities in the metal pool were substantially lower, except at the slag-metal interface. At a given spatial position, the velocity was found to increase in an almost linear fashion with the current density. The flow was found to be predominately laminar in the laboratory scale units and for comparable current densities the melt velocities were very much smaller. Some 600 to 900 s were required on a CDC 6400 digital computer for the solution of each case involving turbulent flow.

Electromagnetic scattering by prolate spheroids for plane waves with arbitrary polarization and angle of incidence

Abstract: Using modal expansions of electromagnetic fields in terms of prolate spheroidal wave functions, an exact formulation is presented for the scattering by a conducting prolate spheroid of a plane electromagnetic wave of arbitrary polarization and incidence angle. In this formulation the column vector of the series coefficients of the scattered field is obtained from the column vector of the series coefficients of the incident field by means of a matrix transformation. The matrix depends only on the scatterer; hence the scattered field for a new direction of incidence is obtained without repeatedly solving a new set of simultaneous equations. The exact curves numerically obtained for the monostatic radar cross section and relative phase of the scattered field as a function of aspect angle (angle of incidence) for both principal polarizations are given for a variety of prolate spheroids in the resonance region.

Electromagnetic coupling through small apertures in a conducting screen

Abstract: The electromagnetic field coupling through small apertures illuminated by an arbitrary incident plane wave is discussed for general aperture shapes. A set of new integral equations in a form highly amenable to numerical solution techniques is derived. Based on the application of the Rayleigh series method, an analytical solution is obtained for the first few terms of the expansion of the aperture E - field of a circular aperture. Numerical results are also constructed for the aperture field and the diffracted field of small rectangular apertures and compared with those of the circular apertures.

Internal EM Field and Absorbed Power Density in Human Torsos Induced by 1-500-MHz EM Waves

Abstract: Numerical results on the internal electromagnetic (EM) field and absorbed power density inside a human torso induced by EM waves of frequencies ranging from 1 to 500 MHz and of both vertical and horizontal polarizations are presented. The induced fields inside the torso are shown to be dependent on the frequency and the torso geometry. Theoretical results are obtained based on the tensor integral equation method and some theoretical predictions are compared to existing experimental results.

Modal Theory of Spatially Periodic Media

Abstract: The modal theory is developed for a slab periodic medium bounded by different media on both sides. Dispersion analysis is carried out for the various cases. Wave amplitudes are determined from boundary conditions for electromagnetic field components. The results are compared and reduced to the well-known theories under simplified conditions. Analysis and calculations are aimed at applications to grating couplers, electrooptical modulators, and distributed feedback systems in integrated optics.

Losses at corner bends in dielectric waveguides

Abstract: An approximate technique based on a sum rule is used to treat mode conversion at corner bends in dielectric waveguides. Matrix elements which describe the mode coupling are expressed as spatial integrals over electromagnetic field distributions for the guided modes. These matrix elements provide information on the magnitude, average propagation constant, and coherence of power propagating in radiation modes. Numerical results are obtained for single mode and multimode slab waveguides, and implications for the design of low-loss interconnections and mode converters for integrated optics are discussed.

Electrogravitational conversion cross sections in static electromagnetic fields

Abstract: We use Feynman perturbation techniques to analyze a classical process: the conversion of gravitational waves into electromagnetic waves (and vice versa) under the "catalytic" action of a static electromagnetic background field. Closed-form differential cross sections are presented for conversion in the Coulomb field of a point charge, electric and magnetic dipole fields, and uniform electrostatic and magnetostatic fields. Using the model calculation of conversion in a Coulomb field, we discuss the problems we must face when calculating non-gauge-invariant quantities, as is frequently done in literature. The cross sections are extremely small, but may lead to observable effects if allowed to act on astrophysical distance and time scales. The calculations also provide additional insight into the physics of electromagnetic detectors of gravitational waves.

H-Field, E-Field, and Combined Field Solutions for Bodies of Revolution

Abstract: : H-field, E-field, and combined field solutions are developed for the electric surface current and far scattered fields of a perfectly conducting body of revolution excited by an incident plane wave. These solutions are obtained by applying the method of moments to the H-field, E-field, and combined field integral equations, respectively. The H-field integral equation is obtained by requiring the tangential magnetic field to be zero just inside the surface S of the body of revolution. The E-field integral equation is obtained by requiring the tangential electric field to be zero on S. The combined field integral equation is a linear combination of the H-field and E-field integral equations. Computations show that both the H-field and the E-field solutions deteriorate near internal resonances of the conducting surface S, but that the combined field solution does not. The computer program subroutines used to perform these computations will appear in a forthcoming report.

Coupled azimuthal potentials for electromagnetic field problems in inhomogeneous axially symmetric media

Abstract: Classical electromagnetic potential formulations are, with the exceptions of a few special cases of one-dimensional stratification, restricted to use in uniform media. A recently developed potential formulation that provides a flexible basis for numerical computation of time-harmonic field problems involving continuously and discretely inhomogeneous axially symmetric media is the topic of this paper. The formulation manifests itself in both a differential equation system and, alternately, a variational criterion. Typical numerical applications include solutions of scattering by arbitrarily shaped material bodies of revolution and radiation from inhomogeneously loaded rotationally symmetric antenna structures. Current numerical investigations by the authors, using Mei's unimoment method in conjunction with both finite-difference and finite-element techniques, have shown the formulation to be highly feasible for computation of field problems having dimensions as large as several wavelengths.

Mechanical forces in a dielectric due to electromagnetic fields

Abstract: Experimental evidence is obtained indicating a mechanical force in a dielectric subjected to crossed electric and magnetic fields consistent with the predictions of the Abraham energy momentum tensor. In the course of the experiment a most unusual force was observed, which appeared as a surface drag on a thin metal coating applied to the dielectric. It is suggested that the force was due to the action of a tangential electric field component acting on the induced surface charge of the metal coating.

Method and apparatus for producing uniform electromagnetic fields in an article detection system

Abstract: An electromagnetic article detection system of the type wherein a target having frequency selective electrical characteristics produces predetermined electromagnetic effects in response to an alternating electromagnetic field. A large resonant electric circuit is placed across an interrogation zone from an interrogation antenna and is inductively coupled to the interrogation antenna to generate secondary electromagnetic waves which cooperate with the primary electromagnetic waves from the interrogation antenna to provide improved distribution of electromagnetic field strength in the interrogation zone.

Quantum mechanical theory of molecular collisions in a laser field

Abstract: The effect of a radiation field on (ion)atom–(di)atom collision systems is considered. A detailed derivation is presented for the modified coupled equations that result from adding the field to the coupled channel formalism for nonreactive collisions. A discussion of the coherent state in this context concludes that the number state representation of the field offers a more convenient basis for defining probability channels in the combined system, but that further research on the applicability of the coherent state in more approximate treatments of the system should be carried out. An example of the general formalism is worked out for collinear Br+H2 collisions in the presence of the field, and calculated results are presented. Comparison is made with the results obtained from a vibronic (resonance) model.

Control of collisionless and collisional processes by nonresonant laser fields

Abstract: The presence of coherent radiation fields can modify various atomic, ionic, and molecular processes. Cases were examined where the changes can be effected without actual absorption or emission of photons. The radiation fields cause optical Stark shifts of the energies and dress the nonadiabatic couplings between states. Rates of processes such as dissociation, predissociation, atomic and molecular collisions can be radiatively controlled. Formation of new avoided crossings due to radiative interaction gives rise to new phenomena. B exact numerical results from which the influences of the radiation field on arbitrary configurations can be calculated, and simple but accurate analytic results, from which these effects can be conveniently assessed are given. It is shown that the inelastic transition probability is decreased at a true crossing and is increased at an avoided crossing as a result of the presence of the nonresonant radiation field. Furthermore, for two parallel levels with constant nonadiabatic coupling, it is shown that the amplitudes of the nonadiabatic transition are invariant, but its flopping frequency is reduced by the field. Depending on the kinds of final measurements with the field on or off, general behaviors of the inelastic transition probability as a function of the field parameters andmore » the charge-system parameters are predicted and the possibility of inversion (from a field-free value of less than 1/2 to a value greater than 1/2) is demonstrated. Experimental investigation with iodine molecules is suggested. Comparison of nonperturbative results with those of stationary perturbation theory shows that the latter is inadequate in an important parameter region where the field modification of processes is greater than 1%.« less

Cosmic ray kinetics in space

Abstract: This work gives a systematic description of the statistical theory of the propagation of cosmic ray charged particles through random electromagnetic fields in space. A kinetic equation is derived for the cosmic ray distribution function averaged over the statistical ensemble corresponding to a random field. Transition to the diffusion approximation is considered, and the problems of the scattering and acceleration of charged particles are analyzed. The theory of fluctuation effects in cosmic rays is briefly discussed.

Electromagnetic field near the focus of wide-angular lens and mirror systems

Abstract: The time-averaged electric energy density near the focus of a parabolic mirror of wide-angular aperture is calculated and compared with that of an aplanatic lens system. The distributions exhibit great differences, the mirror showing a greater departure from circular symmetry, a more complicated structure and increased sidelobes. The vectorial integral representation of Wolf is derived from the Stratton-Chu formula.

Unified Approach to the Derivation of Variational Expression for Electromagnetic Fields

Abstract: A unified procedure to derive the variational expressions for electromagnetic field problems is presented. It is shown that the variational expressions for a variety of electromagnetic parameters such as, for instance, a resonant frequency, a propagation constant, and an impedance matrix, can be formulated systematically all from "the principle of least action" point of view. It is pointed out that the Maxwell's equations themselves can also be derived from the least action principle.

Electromagnetic fields of dipoles in stratified media

Abstract: A general theory for the electromagnetic fields of dipoles in stratified isotropic media is outlined. The stratified model consists of a stack of layers sandwiched between two semi-infinite media. Either an electric or a magnetic dipole can be placed at any position in the stack, or in the upper or lower half-space. Dipoles can be electric or magnetic and can be oriented horizontally or vertically. The fields in the layer containing the source are given in terms of reflection coefficients, impedance and admittance terms, and wavenumber ratios. Recursion relations are developed to propagate the Hankel-domain field coefficients to other layers or to the half spaces. This allows the observation point to be placed anywhere except at the source. Numerical checks show that the derived algebra is at least self-consistent.

Analytical method of calculating the electromagnetic field and power losses in ferromagnetic halfspace, taking into account saturation and hysteresis

Abstract: The steady-state solution of electromagnetic-field problems in ferromagnetic materials is given. The effects of magnetic saturation and hysteresis are included. The solution is based on the differential diffusion equation assuming variable complex magnetic permeability. A precise formula is given to calculate the total power losses due to eddy currents and hysteresis. Computed curves, together with measured curves, are given for active and reactive losses in mild steel. Good agreement is obtained between measured and computed values.