Showing papers on "Electromagnetic field published in 1993"

Measurement of the Wigner distribution and the density matrix of a light mode using optical homodyne tomography: Application to squeezed states and the vacuum.

Abstract: We have measured probability distributions of quadrature-field amplitude for both vacuum and quadrature-squeezed states of a mode of the electromagnetic field. From these measurements we demonstrate the technique of optical homodyne tomography to determine the Wigner distribution and the density matrix of the mode. This provides a complete quantum mechanical characterization of the measured mode.

Polarized light. Fundamentals and applications

Abstract: Part 1 The classical optical field: the wave equation in classical optics the polarization ellipse the Stokes polarization parameters the Mueller matrices for polarizing components methods for measuring the Stokes polarization parameters the measurement of the characteristics of polarizing elements Mueller matrices for reflection and transmission the Mueller matrices for dielectric plates the Jones matrix calculus the Poincare sphere the interface laws of Fresnel and Arago Part 2 The classical and quantum theory of radiation by accelerating charges: Maxwell's equations for the electromagnetic field the classical radiation field radiation from accelerating charges the radiation of an accelerating change in the electromagnetic field the classical Zeeman effect further applications of the classical radiation theory the Stokes parameters and the Mueller matrices for optical and Fararaday rotation the Stokes parameters for quantum systems Part 3 Applications: crystal optics optics of metals ellipsometry

Quantum theory of field-quadrature measurements.

Abstract: The quantum effects on a cavity mode of the electromagnetic field caused by measuring one of its quadrature components is analyzed. We consider three measurement schemes: an intracavity quantum-nondemolition coupling to another mode, simple homodyne detection, and balanced homodyne detection. It is shown that, for suitable initial conditions, the first scheme has an effect which approaches that of a projective collapse of the state vector for long measurement times. However, the two homodyne schemes (which are shown to be equivalent for large local-oscillator amplitudes) do not approximate a projective measurement in any limit. In particular, it is shown that homodyne measurement cannot produce a squeezed state from a classical initial state. All three schemes are analyzed in terms of ‘‘quantum trajectories’’ which link measurement theory with stochastic quantum-jump processes.

Simulation of three-dimensional optical waveguides by a full-vector beam propagation method

Abstract: Simulations of optical guided waves in three-dimensional waveguide structures by a full vector beam propagation method are described. Two sets of coupled equations governing the propagation of the transverse electric and magnetic fields are derived systematically. Polarization dependence and coupling due to the vectorial nature of the electromagnetic fields are considered in the formulations. The governing equations are solved subsequently by finite-difference schemes. The vector BPM is first assessed for a step-index circular fiber by comparing the numerical results with the exact analytical solutions. The guided modes of a rib waveguide are then investigated in detail. Comparisons among the scalar, semi-vector and full-vector simulations of the rib waveguide are made. Finally polarization rotation of a periodically loaded rib waveguide operated fully based on the vector nature of the electromagnetic waves is modeled and simulated. >

A finite-difference, time-domain solution for three-dimensional electromagnetic modeling

Abstract: We have developed a finite-difference solution for three-dimensional (3-D) transient electromagnetic problems. The solution steps Maxwell's equations in time using a staggered-grid technique. The time-stepping uses a modified version of the Du Fort-Frankel method which is explicit and always stable. Both conductivity and magnetic permeability can be functions of space, and the model geometry can be arbitrarily complicated. The solution provides both electric and magnetic field responses throughout the earth. Because it solves the coupled, first-order Maxwell's equations, the solution avoids approximating spatial derivatives of physical properties, and thus overcomes many related numerical difficulties. Moreover, since the divergence-free condition for the magnetic field is incorporated explicitly, the solution provides accurate results for the magnetic field at late times.An inhomogeneous Dirichlet boundary condition is imposed at the surface of the earth, while a homogeneous Dirichlet condition is employed along the subsurface boundaries. Numerical dispersion is alleviated by using an adaptive algorithm that uses a fourth-order difference method at early times and a second-order method at other times. Numerical checks against analytical, integral-equation, and spectral differential-difference solutions show that the solution provides accurate results.Execution time for a typical model is about 3.5 hours on an IBM 3090/600S computer for computing the field to 10 ms. That model contains 100 X 100 X 50 grid points representing about three million unknowns and possesses one vertical plane of symmetry, with the smallest grid spacing at 10 m and the highest resistivity at 100 Omega . m. The execution time indicates that the solution is computer intensive, but it is valuable in providing much-needed insight about TEM responses in complicated 3-D situations.

Three-dimensional magnetotelluric modeling using difference equations­ Theory and comparisons to integral equation solutions

Abstract: We have developed an algorithm for computing the magnetotelluric response of three‐dimensional (3-D) earth models. It is a difference equation algorithm that is based on the integral forms of Maxwell’s equations rather than the differential forms. This formulation does not require approximating derivatives of earth properties or electromagnetic fields, as happens when using the second‐order vector diffusion equation. Rather, one must determine how averages are to be computed. Side boundary values for the H fields are obtained from putting two‐dimensional (2-D) slices of the model into a larger‐scale 2-D model and solving for the fields at the 3-D boundary positions. To solve the 3-D system of equations, we propagate an impedance matrix, which relates all the horizontal E fields in a layer to all the horizontal H fields in that same layer, up through the earth model. Applying a plane‐wave source condition and the side boundary H field values allows us to solve for the unknown fields within the model. The r...

Formulation of the field-to-transmission line coupling equations in terms of magnetic excitation field

Abstract: Different formulations of the field-to-transmission-line coupling equations are reviewed and discussed. An equivalent formulation is derived in which the source terms (or forcing functions) are expressed in terms of the magnetic excitation field. This formulation is particularly useful for evaluating field-to-transmission-line coupling when the exciting field is determined experimentally, since only the measurement of the electric field-generally easier to measure than the electric field-is necessary. >

Standard probes for electromagnetic field measurements

Abstract: Discusses various standard antennas for measuring radio-frequency electric and magnetic fields. A theoretical analysis of each antenna's receiving characteristics is summarized and referenced. The standard probes described are an electrically short dipole, a resistively-loaded dipole, a half-wave dipole, an electrically small loop, and a resistively-loaded loop. A single-turn loop designed for simultaneous measurement of the electric and magnetic components of near-fields and other complex electromagnetic environments is also described. Each type of antenna demonstrates a different compromise between broadband frequency response and sensitivity. >

Breaking of conformal invariance and electromagnetic field generation in the Universe.

Abstract: It is shown that the breaking of conformal invariance in quantum electrodynamics due to the trace anomaly results in the generation of long-wave electromagnetic fields during the inflationary stage of the evolution of the Universe. If the coefficient of the logarithmic charge renormalization is large (due to a large number of charged particles species), these primordial electromagnetic fields can be strong enough to create the observed galactic magnetic fields.

Pulsed-DC position and orientation measurement system

Abstract: A remote object position and orientation determining system employs electromagnetic coupling to sense the position and orientation of a remote object. A plurality of electromagnetic fields are generated having steady state components by applying time-division multiplexed pulsed DC signals to a plurality of field generating elements having spatially independent components defining a source reference coordinate frame. In this manner, the fields are distinguishable from one another. The generated electromagnetic fields are sensed with a remote sensor having a plurality of passive field-sensing elements having spatially independent elements in order to detect the rate-of-change of each of the generated electromagnetic fields. The output of the remote sensors are integrated in order to establish the steady state components of the generated electromagnetic fields. The steady state components are resolved into remote object position and orientation relative to the source reference coordinate frame.

Limiting configurations allowed by the energy conditions

Abstract: The energy conditions of general relativity are satisfied by all experimentally detected fields. We discuss their interpretation and application to charged spheres. It is found that they prevent the existence of naked singularities, and demand that the effective gravitational mass be everywhere non-negative. We focus on the emergence of limiting configurations-sources of the Reissner-Nordstrom field that have vanishing effective mass everywhere within the sphere. These configurations have a number of interesting features. Among them we find that, near the center, the limiting form of the equation of state isρ+3p=0. Notably this is the only equation of state consistent with the existence of zero-point electromagnetic field, and it has been considered in different contexts, in discussions of cosmic strings and in derivations of (3+1) properties of matter from (4+1) geometry. The consistency of these configurations with the Einstein-Maxwell equations is shown by means of explicit examples. These configurations can be interpreted as due to selfinteracting gravitational effects of the zero-point electromagnetic field.

Near-dipole-dipole effects in dense media: Generalized Maxwell-Bloch equations.

Abstract: A self-consistent generalization of the Maxwell-Bloch formulation is presented here for a nonlinear system of saturable two-level atoms interacting with the electromagnetic field, under the condition that the atomic density is such that there are, on the average, many atoms within a cubic resonance wavelength such that near--dipole-dipole interactions, which lead to local-field corrections, cannot be neglected.

Electromagnetic fields in a radio-frequency induction plasma

Abstract: The electromagnetic fields which drive a radio‐frequency induction plasma are both modeled and measured. The plasma source consists of a planar, square coil separated from a low pressure plasma chamber by a 2.54‐cm‐thick quartz window. A small loop antenna, which is sealed in a pyrex tube, is immersed in the discharge to determine the magnitude and direction of the rf magnetic field. The measured B field is primarily radial and axial. Typical rf field strengths vary from 2 to 7 G for rf powers of 0.1–1 kW. The radial B field decays exponentially in the axial direction. The skin depth of the electromagnetic field is 1.6–3.6 cm which is consistent with Langmuir probe measured ion densities (typically 3×1011 cm−3) in argon. Invoking Maxwell’s equations to deduce the rf electric field from the measured B field, we find the E field to be primarily azimuthal. Peak field strengths increase from 100 V/m at 100 W to 200 V/m at 600 W where they saturate for higher powers. Finally, we present a 3D finite element solution for the fields produced by this plasma source which employs a cold, collisionless plasma model to relate the relative plasma permittivity er to the electron plasma frequency, ωpe, using er=1−(ωpe/ω)2. The measured fields support this numerical solution.

Electromagnetic induction by a finite electric dipole source over a 2-D earth

Abstract: A numerical solution for the frequency domain electromagnetic response of a two-dimensional (2-D) conductivity structure to excitation by a three-dimensional (3-D) current source has been developed. The fields are Fourier transformed in the invariant conductivity direction and then expressed in a variational form. At each of a set of discrete spatial wavenumbers a finite-element method is used to obtain a solution for the secondary electromagnetic fields. The finite element uses exponential elements to efficiently model the fields in the far-field. In combination with an iterative solution for the along-strike electromagnetic fields, this produces a considerable reduction in computation costs. The numerical solutions for a horizontal electric dipole are computed and shown to agree with closed form expressions and to converge with respect to the parameterization. Finally some simple examples of the electromagnetic fields produced by horizontal electric dipole sources at both the seafloor and air-earth interface are presented to illustrate the usefulness of the code.

Electromagnetic effect on the toroidal ion temperature gradient mode

Abstract: A systematic study of the electromagnetic effects on the toroidal ion temperature gradient mode is presented using the local and nonlocal theories with the full kinetic terms. For the nonlocal study, a numerical code is developed to solve the electromagnetic gyrokinetic equation in the ballooning space. The electromagnetic coupling to the shear Alfven mode is shown to give a stabilization of the toroidal temperature gradient mode at almost the same plasma pressure as that at which the kinetically modified magnetohydrodynamic (MHD) ballooning mode becomes destabilized. The transitional β value is shown to be lower in the full kinetic description than in the fluid theory. Possible correlations of these stability results with experimental observations are discussed.

Electromagnetic fields of energized conductors

Abstract: The electric field due to single-frequency current distribution in a buried horizontal rod with current leakage along its length and at its ends is computed for observation points at the soil-surface for low and high frequencies. The computation results are based on a general formulation which permits observation points in air or soil for an arbitrary network of energized conductors. The contribution of in-air and in-soil thin-wire conductors to electromagnetic fields is represented by path integrals. >

Equations of Motion for Spinning Particles in External\\Electromagnetic and Gravitational Fields

Abstract: The equations of motion for the position and spin of a classical particle coupled to an external electromagnetic and gravitational potential are derived from an action principle. The constraints ensuring a correct number of independent spin components are automatically satisfied. In general the spin is not Fermi-Walker transported nor does the position follow a geodesic, although the deviations are small for most situations.

Quantum phenomena in resonators with moving walls

Abstract: New solutions for the mode functions of the electromagnetic field in ideal cavity which boundary oscillates at a resonance frequency are obtained in the long‐time limit. The rate of photons creation from initial vacuum state is shown to be time independent and proportional to the amplitude of oscillations and the resonance frequency. Temperature corrections are evaluated. The squeezing coefficients for the quantum states of the field generated are calculated, as well as the backward reaction of the field on the vibrating wall.

Classical Electromagnetic Theory

Abstract: Static Electric and Magnetic Fields in Vacuum.- Charge and Current Distributions.- Slowly Varying Fields in Vacuum.- Energy and Momentum.- Static Potentials in Vacuum - Laplace's Equation.- Static Potentials with Sources-Poisson's Equation.- Static Electromagnetic Fields in Matter.- Time-Dependent Electromagnetic Fields in Matter.- Waveguide Propagation-Bounded Waves.- Electromagnetic Radiation.- The Covariant Formulation.- Radiation Reaction-Electrodynamics.

Direct time integration of Maxwell's equations in two-dimensional dielectric waveguides for propagation and scattering of femtosecond electromagnetic solitons

Abstract: We present what are to our knowledge first-time calculations from vector nonlinear Maxwell's equations of femtosecond soliton propagation and scattering, including carrier waves, in two-dimensional dielectric waveguides. The time integration efficiently implements linear and nonlinear convolutions for the electric polarization, and the nonlinear convolution accounts for two quantum effects, the Kerr and Raman interactions. By retaining the optical carrier, the new method solves for fundamental quantities - optical electric and magnetic fields in space and time - rather than a nonphysical envelope function. It has the potential to provide an unprecedented two- and three-dimensional modeling capability for millimeter-scale integrated-optical circuits with submicrometer engineered inhomogeneities.

Casimir-Polder potential as an interaction between induced dipoles.

Abstract: The retarded van der Waals forces between neutral molecules in their ground states is obtained by a conceptually simple route. Vacuum fluctuations of the electromagnetic field induce a dipole moment in each molecule and these induced moments interact via the retarded potential that is appropriate for resonant coupling. The dispersion potential is the sum over the field modes of the product of this potential and the second-order spatial correlation function of the electromagnetic field. This gives the familiar Casimir-Polder potential an an integral over imaginary frequencies. An extension to obtain the interaction energy between one molecule in its ground state and another in an excited state is outlined.

Essays on the formal aspects of electromagnetic theory

Abstract: Scalar potential formulations for magnetic field problems, I.R. Ciric inhomogeneous waves and Maxwell's equations, P. Cornille calculation of the effective electromagnetic properties of granular materials, C.A. Grimes atomic theory and radiative transfer, on the basis of nonlinear, classical electrodynamics, D.M. Grimes drifting ions, J.E Jones the Maxwell-Dirac isomorphism, H.H. Sallhofer the gauge invariance, radiation and toroid order parameters in electromagnetic theory, V.M. Dubovik and S.V. Shabanov electromagnetic phenomena not explained by Maxwell's equations, T.W. Barrett transverse electromagnetic waves with E II B, H.A. Zaghloul and H.A Buckmaster universal boundary conditions and Cauchy data for the electromagnetic, M. Idemen and others.

Cosmic-ray particle transport in weakly turbulent plasmas. Part 1. Theory

Abstract: We consider a quasi-linear theory for the acceleration rates and propagation parameters of charged test particles in weakly turbulent electromagnetic plasmas. The similarity between two recent approaches to modelling of therandom electromagnetic field is demonstrated. It is shown that both the concept of dynamical magnetic turbulence and the concept of superposition of individual plasma modes lead to particle Fokker—Planck coefficients in which the sharp delta functions describing the resonant interaction of the particles have to be replaced by Breit—Wigner-type resonance functions, which are controlled by the dynamical turbulence decay time and the wave-damping time respectively. The resulting resonance broadening will significantly change the evaluation of cosmic-ray transport parameters.

A calculation method and some features of transient field under polarity reversal voltage in HVDC insulation

Abstract: Mathematical equations are derived for the transient electric field in insulation media with permittivity and resistivity during boundary excitation due to changing from one steady state to another, such as a polarity reversal voltage imposed on the insulation of HVDC apparatus. The equations are solved by the finite element method, and a program for calculating the transient field is developed. Calculated results of some illustrative examples, including a typical bushing barrier system of power converter transformers, verify the method. Some distinguishing features of the transient field are discussed. >

Planar electromagnetic transducer

Abstract: An electromagnetic transducer diaphragm (110) having an electrical conductor layer (221), with a conductor pattern, positioned between two insulating layers (220, 222) of a flexible, electrically insulating material bonded together to protect the diaphragm. An electrical current can flow through the conductors to produce magnetic and electrostatic fields around said conductors which interact with an electromagnetic field to produce mechanical displacement of the diaphragm which is turn produces an audio signal. Non-ferrous supports can be used to support the diaphragm. A magnet or magnets may be used to create the electromagnetic field. The magnets can be bonded to the cross arms of the non-ferrous support.

Analytic methods and free‐space dyadic Green's functions

Abstract: A number of mathematical techniques are presented which have proven successful in obtaining analytic solutions to the differential equations for the dyadic Green's functions of electromagnetic theory. The emphasis is on infinite-medium (or free-space) time-harmonic solutions throughout, thus putting the focus on the physical medium in which the electromagnetic process takes place. The medium's properties enter Maxwell's equations through the constitutive relations, and a comprehensive listing of dyadic Green's functions for which closed-form solutions exist, is given. Presently, the list of media contains (achiral) isotropic, biisotropic (including chiral), generally uniaxial, electrically (or magnetically) gyrotropic, diffusive and moving media as well as certain plasmas. A critical evaluation of the achievements, successes, limits, and failures of the analytic techniques is provided, and a prognosis is put forward about the future place of analytic methods within the general context of the search for solutions to electromagnetic field problems.

Electromagnetic field generated by an off-axis source in a cylindrically layered medium with an arbitrary number of horizontal discontinuities

Abstract: We investigate the propagation of electromagnetic waves in a cylindrically layered medium with an arbitrary number of horizontal discontinuities. The dielectric constant, conductivity, and magnetic permeability of the medium are functions of ρ and z only (i.e., independent of the azimuthal angle ϕ), but the field generated by an off‐axis source in this medium is in general a function of ρ, ϕ, and z. This two and a half‐dimensional (2.5-D) problem is often encountered in electromagnetic well logging, as well as in other areas such as optical fiber communications and integrated optics. We show that a coupling exists between the transverse electric (TE) and transverse magnetic (TM) components of the field even in the absence of the horizontal discontinuities, which makes it difficult to solve for the field. We apply an efficient numerical mode‐matching (NMM) algorithm to tackle this 2.5-D problem. This algorithm uses the local reflection and transmission operators developed in the recent work on the diffract...