Showing papers on "Electromagnetic field published in 1976"

Conservation of charge and the Einstein–Maxwell field equations

Abstract: In a space of four dimensions I determine all possible second‐order vector–tensor field equations which are derivable from a variational principle, compatible with the notion of charge conservation and in agreement with Maxwell’sequations in a flat space. The general solution to this problem contains the Einstein–Maxwell field equations (with cosmological term) as a special case.

Transient Electromagnetic Fields

Abstract: Propagation and diffraction of transient fields in non-dispersive and dispersive media.- Integral equation methods for transient scattering.- The singularity expansion method.- Radiation and reception of transients by linear antennas.- A pulsed dipole in the earth.

Dirac's Monopole Without Strings: Classical Lagrangian Theory

Abstract: The non-quantum-mechanical interaction of a Dirac magnetic monopole and a point charge through the electromagnetic field is studied. A classical action integral which is multiple-valued is found. Stability of this action integral against variations of the world lines of the point charge and the monopole, and against variations of the electromagnetic potentials, yields the correct Lorentz equations of motion of the particles and the Maxwell equations for the field. No strings are introduced in the formalism. (AIP)

Electromagnetic fields in the presence of rotating bodies

Abstract: Field calculations in the presence of rotating bodies with symmetry of revolution can be performed in the (inertial) laboratory frame of reference. Specific results are presented for a rotating circular cylinder immersed in a plane wave of the E or H type. Particular emphasis is put on the low-frequency limit, but some numerical data are also given for a typical frequency in the "resonance" region. The analysis becomes more complicated in the absence of symmetry of revolution. It is then necessary to solve the problem in a rotating system of coordinates. Maxwell's equations are written in these coordinates, together with the relevant constitutive equations and boundary conditions. The general formalism is applied to a typical two-dimensional configuration, viz., a cylinder immersed in an incident E wave. Considerable simplification obtains if all material velocities are negligible with respect to c, a condition which is always met in practice. Even simpler results are obtained if the cross-sectional dimensions of the cylinder are small with respect to λ. Some numerical results are presented, at low frequencies, for a dielectric cylinder of rectangular cross section.

Frequency Response of Multiconductor Transmission Lines Illuminated by an Electromagnetic Field

Abstract: A well-known result [1], [2] for the response of a two-wire transmission line illuminated by a nonuniform electromagnetic field is extended to multiconductor lines. A simple matrix equation for the currents induced in arbitrary termination networks is obtained. Air Development Center.

Maxwell equations in material form

Abstract: The Maxwell electromagnetic equations are obtained expressed in the material coordinate system of elasticity theory for a moving, deforming body. They are shown to be form-invariant to the deformation transformation. The transformation laws for the electric field, the electric displacement, the magnetic induction, the magnetic intensity, the charge density, the current density, the vector and scalar potentials, the polarization, and the magentization are found. The boundary conditions on the fields are derived in the material coordinate system and the simplicity of the derivation for moving, deforming bodies is emphasized. The boundary conditions are then transformed to the familiar spatial coordinate system. A Lagrangian density capable of giving the Lorentz form of the electromagnetic equations in the material coordinate system is found. The Lorentz form of the equations is shown not to be form-invariant to the deformation transformation.

A new formulation of classical electrodynamics

Abstract: A new mathematical formulation of classical electrodynamics is presented. In the theory, the nature of Minkowski space, Lorentz transformations and Maxwell's equations is reduced to those of biquaternions and their functions, the theory of functions of a biquaternion variable. Maxwell's equations in vacuum become equivalent to the «regularity condition» for functions of a «real biquaternion» variable in the sense that Cauchy-Riemann equations are the regularity condition for functions of a complex variable. Several applications of the theory are given.

New theory of radiative energy transfer in free electromagnetic fields

Abstract: A new theory of radiative energy transfer in free, statistically stationary electromagnetic fields is presented. It provides a model for energy transport that is rigorous within the framework of the stochastic theory of the classical field as well as within the framework of the theory of the quantized field. Unlike the usual phenomenological model of radiative energy transfer that centers around a single scalar quantity (the specific intensity of radiation), our theory brings into evidence the need for characterizing the energy transport by means of two (related) quantities: a scalar and a vector that may be identified, in a well-defined sense, with "angular components" of the average electromagnetic energy density and of the average Poynting vector, respectively. Both of them are defined in terms of invariants of certain new electromagnetic correlation tensors. In the special case when the field is statistically homogeneous our model reduces to the usual one and our angular component of the average electromagnetic energy density, when multiplied by the vacuum speed of light, then acquires all the properties of the specific intensity of radiation. When the field is not statistically homogeneous our model reduces in good approximation to the usual phenomenological one, provided that the angular correlations between plane wave modes of the field extend over a sufficiently small solid angle of directions about the direction of propagation of each mode. It is tentatively suggested that, when suitably normalized, our angular component of the average electromagnetic energy density may be interpreted as a quasiprobability (general quantum-mechanical phase-space distribution function, such as Wigner's) for the position and the momentum of a photon.

Numerical Solutions of the Response of a Two-Dimensional Earth to AN Oscillating Magnetic Dipole Source

Abstract: A finite difference formulation is developed for computing the frequency domain electromagnetic fields due to a point source in the presence of two‐dimensional conductivity structures. Computing costs are minimized by reducing the full three‐dimensional problem to a series of two‐dimensional problems. This is accomplished by Fourier transforming the problem into the x-wavenumber (kx) domain; here the x-direction is parallel to the structural strike. In the kx domain, two coupled partial differential equations for H⁁x(kx,y,z) and E⁁x(kx,y,z) are obtained. These equations resemble those of two coupled transmission sheets. For a requisite number of kx values these equations are solved by the finite difference method on a rectangular grid on the y-z plane. Application of the inverse Fourier transform to the solutions thus obtained gives the electric and magnetic fields in the space domain. The formulation is general; complex two‐dimensional structures containing either magnetic or electric dipole sources can ...

Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models

Abstract: When the body of man, small compared to a wavelength, is exposed to high frequency (HF) electromagnetic (EM) fields, the absorbed power density patterns and total absorbed power may be approximated by the simple superposition of the internal electric fields obtained from the quasistatic coupling characteristics of the electric and magnetic field components determined independently. These characteristics were obtained for full scale man by thermographic studies of power absorption in scale models of man exposed to fields at frequencies scaled up inversely proportional to the model size. A VHF resonant cavity was used to provide the necessary field strengths for producing measurable power absorption patterns under simulated HF exposure conditions. The results indicate that peak power absorption densities as high as 5.63 W/kg can be produced in man exposed to 10 mW/cm 2 31 MHz radiation fields. The results show that the absorption decreases as the square of the frequency as predicted by theory for frequencies below 31 MHz.

Transmission line fields

Abstract: Calculated and measured transmission line electrostatic and electromagnetic fields are presented. The 30 line rotating E and B vectors are presented as vector loci and the phasor space potentials are presented as mappings. Lateral profiles of ground level electrostatic and electromagnetic fields are calculated and compared to measured values.

Radiation of electromagnetic fields in uniaxially anisotropic media

Abstract: The angular spectrum of plane-waves representation is obtained for the electromagnetic field radiated by a localized current source in a biaxially anisotropic medium. The linear medium is homogeneous throughout all space. It may be absorbing and temporally dispersive but is not spatially dispersive. The conductivity and the permeability are scalar constants. The time behavior of the current is arbitrary except that its magnitude is always bounded and it is zero prior to a fixed finite time. The representation of monochromatic fields radiated by time-harmonic sources is included also in the results. The radiated field is expressed as a superposition of monochromatic extraordinary plane waves propagating in various directions. The spectral amplitudes of the plane waves are determined explicitly in terms of the source. The guide axis of the representation coincides with one of the principal axes of the medium. The form of the solution is particularly appropriate for the study of diffraction, reflection, and refraction at plane boundaries normal to one of the principal axes of the medium.

Time-dependent perturbation of a two-state quantum system by a sinusoidal field

Abstract: Different methods for solving the 'two-level problem' are discussed, namely, the problem of what happens to a material system having only two nondegenerate energy levels when it is perturbed by an electromagnetic field that varies with time in a monochromatic sinusoidal fashion. The various methods discussed include: (1) the Sen Gupta technique using nondegenerate Rayleigh-Schroedinger perturbation theory, (2) the Salwen-Winter-Shirley partitioning perturbation technique, (3) the Shirley and series degenerate Rayleigh-Schroedinger expansion, (4) the degenerate Rayleigh-Schroedinger technique for considering high frequency fields, and (5) the singular perturbation expansion technique.

Electromagnetic Field Penetration into a Cylindrical Cavity

Abstract: For an E-polarized plane wave incident on a perfectly conducting cylindrical shell having a longitudinal slit aperture, the fields inside the cavity are determined by a numerical solution of the E-field integral equation. Selected data are presented and the first few complex frequency (SEM) singularities are determined for a variety of aperture sizes.

Field measurements and calculations of electrostatic effects of overhead transmission lines

Abstract: The results of an electrostatic measurements program held in conjunction with the IEEE Working Group on E/S and E/M Effects of Transmission Lines and attended by representatives of several organizations are presented. Measurements were made at ground level under an energized 525-kV line of electric field intensity, of induced currents and voltages on objects, and of perception and annoyance levels of men, women, and children for steady state and transient shocks. Three types of field strength meter were employed. They gave consistent readings in agreement with predicted field strength. Analytical estimates of short circuit current for various objects are in agreement with measured values.

ELF Coupling to Spherical Models of Man and Animals

Abstract: The induced fields, currents, and power absorbed by spherical models of humans or animals when exposed to extremely low frequency (ELF) electromagnetic fields are calculated. Spherical models can be expected to provide values of the right order of magnitude. The induced fields are a sum of the quasistatic solutions for a sphere irradiated by a uniform electric and magnetic field. Calculations are provided for ELF fields emanating from the proposed Navy's Sanguine antenna and extra high voltage (EHV)/ultra high voltage (UHV) transmission lines proposed by the utility industry. The question of biological hazards from exposure to fields of these systems is also considered.

Method for excitation and reception of ultrasonic plate waves in workpieces and devices for realizing same

Abstract: A method and apparatus for excitation and reception of ultrasonic plate waves in a workpiece in which the surface of the workpiece is acted upon by a high-frequency electromagnetic field excited by a system of flat radiators forming a comb-shaped structure and positioned discretely in the direction of radiation with a pitch divisible by the wave length. A magnetizing field, whose vector is parallel to the surface of the workpiece under test, is introduced into the workpiece in the area of the high-frequency electromagnetic field and the vector of the magnetizing field is arranged at an angle relative to the radiation direction with respect to the flat radiator array to excite transverse normal waves.

Experimental and Theoretical Studies on Electromagnetic Fields Induced Inside Finite Biological Bodies

Abstract: The total electric field inside some simulated biological bodies induced by an electromagnetic wave has been quantified by the recently developed tensor integral equation method and measured by an insulated probe. In general, the induced electric field inside a biological body was found to be quite complicated. An excellent agreement was obtained between theory and experiment.

Electromagnetic wave propagation well logging utilizing multiple phase shift measurement

Abstract: The invention disclosed herein includes methods and apparatus for determining true formation resistivity, flushed zone resistivity and invasion diameter of the earth formation in the vicinity of a well borehole. A radio frequency electromagnetic field in the frequency range from 800 kilohertz to 4 megahertz is generated in a borehole and the electromagnetic field is detected at a plurality of longitudinally spaced locations. Measurements of the attenuation and propagation velocity of the electromagnetic wave at the longitudinally spaced receivers may then be interpreted according to predetermined relationships in terms of the formation resistivity, flushed zone resistivity and invasion diameter surrounding the borehole.

The electromagnetic theory of three-dimensional inhomogeneous lenses

Abstract: The characteristics of some inhomogeneous lenses are investigated. The lenses covered are the Luneburg, the Eaton-Lippmann, and the Eaton. Radiation patterns and the bistatic scattering cross sections for the small-diameter lenses as well as the directivity and the distribution of the energy around the geometrical focus of the Luneburg lenses are numerically computed and examined in detail.

Quantum frequency shifts near a plasma surface

Abstract: The electromagnetic field coupled to a model of a semi-infinite plasma is quantized. A technical difficulty, related to the choice of gauge in the presence of the plasma surface, is resolved by appeal to the Power-Zienau transformation, far enough to allow level shifts to be calculated for nearby overall-neutral atoms or molecules outside the plasma. Charged systems are not covered. The level shifts, functions of plasma frequency and distance, are displayed as Laplace transforms, simple asymptotic forms being given for small and for large distances. Special treatment is needed for excited states. The results are compared to a recently proposed classical model; and to expressions based on Lifshitz's theory, which appears to be neither designed nor adequate to deal with excited states.

Remarks on forces and the energy-momentum tensor in macroscopic electrodynamics

Abstract: The conservation laws which follow from the field equations and their relation to the energy and momentum conservation laws are discussed. On the basis of the electrodynamics of slowly moving bodies, an expression is derived for the density of the force which acts on an isotropic inhomogeneous medium in an electromagnetic field. Attention is concentrated on elucidating the difference between the energymomentum tensors of Minkowski and Abraham. It is emphasized either of these can be used in practice to consider the exchange of energy and momentum between an emitter and a medium in which the emitter is placed. However, to analyze the processes in the medium itself, Abraham's should be used because it takes into account Abraham's volume force, which acts even on a homogeneous medium (whereas according to Minkowski no force acts at all on a transparent, homogeneous medium with density-independent permittivity in an electromagnetic field).

Ball lightning as electromagnetic energy

Abstract: NONE of the theories1–8 proposed to explain ball lightning seems able to account satisfactorily for the experimental evidence9–14. Jennison15 has suggested that ball lightning is a spherical stable standing wave of electromagnetic radiation. The proposal that ball lightning in effect consists of electromagnetic field energy trapped in an evacuated cavity of approximately spherical shape, with an ionised sheath separating it from the atmosphere, merits further examination.