Showing papers on "Electromagnetic field published in 1989"

Advanced engineering electromagnetics

Abstract: Time--Varying and Time--Harmonic Electromagnetic Fields. Electrical Properties of Matter. Wave Equation and Its Solutions. Wave Propagation and Polarization. Reflection and Transmission. Auxiliary Vector Potentials, Contruction of Solutions, and Radiation and Scattering Equations. Electromagnetic Theorems and Principles. Rectangular Cross--Section Waveguides and Cavities. Circular Cross--Section Waveguides and Cavities. Spherical Transmission Lines and Cavities. Scattering. Integral Equations and the Moment Method. Geometrical Theory of Diffraction. Greena s Functions. Appendices. Index.

Phase properties of the quantized single-mode electromagnetic field.

Abstract: The usual mathematical model of the single-mode electromagnetic field is the harmonic oscillator with an infinite-dimensional state space, which unfortunately cannot accommodate the existence of a Hermitian phase operator. Recently we indicated that this difficulty may be circumvented by using an alternative, and physically indistinguishable, mathematical model of the single-mode field involving a finite but arbitrarily large state space, the dimension of which is allowed to tend to infinity after physically measurable results, such as expectation values, are calculated. In this paper we investigate the properties of a Hermitian phase operator which follows directly and uniquely from the form of the phase states in this space and find them to be well behaved. The phase-number commutator is not subject to the difficulties inherent in Dirac's original commutator, but still preserves the commutator--Poisson-bracket correspondence for physical field states. In the quantum regime of small field strengths, the phase operator predicts phase properties substantially different from those obtained using the conventional Susskind-Glogower operators. In particular, our results are consistent with the vacuum being a state of random phase and the phases of two vacuum fields being uncorrelated. For higher-intensity fields, the quantum phase properties agree with those previously obtained by phenomenological and semiclassical approaches, where such approximations are valid. We illustrate the properties of the phase with a discussion of partial phase states. The Hermitian phase operator also allows us to construct a unitary number-shift operator and phase-moment generating functions. We conclude that the alternative mathematical description of the single-mode field presented here provides a valid, and potentially useful, quantum-mechanical approach for calculating the phase properties of the electromagnetic field.

Fifth-order corrected electromagnetic field components for a fundamental Gaussian beam

Abstract: Fifth‐order corrected expressions for the electromagnetic field components of a monochromatic fundamental Gaussian beam (i.e., a focused TEM00 mode laser beam) propagating within a homogeneous dielectric media are derived and presented. Calculations of relative error indicate that the fifth‐order Gaussian beam description provides a significantly improved solution to Maxwell’s equations in comparison with commonly used paraxial (zeroth‐order) and first‐order Gaussian beam descriptions.

Time-Harmonic Electromagnetic Fields in Chiral Media

Abstract: This book deals with the fundamental aspects of electromagnetic field theory in chiral media in the frequency domain. All such aspects are covered: field equations, constitutive equations, integral equations and representations, Green's functions, radiation, reciprocity relations, and equivalence and duality relations. Scattering of waves by chiral spheres and cylinders are covered, and layered chiral media are examined. This book is timely both for theorists and experimentalists. Theorists can build upon the work to discover and predict new phenomena, while experimentalists may use it to design clever experiments and construct artificially chiral materials.

On the possibility of transistor action based on quantum interference phenomena

Abstract: A theoretical study of quantum interference phenomena in a T‐shaped semiconductor structure is presented. Transmission and reflection coefficients are computed by use of a tight‐binding Green function technique. As expected, the results resemble the well‐known solutions for the electromagnetic field in waveguides with the main difference that the penetration of the wave function of the electrons can be controlled by external voltages. We conclude that transistor action based on quantum interference should be observable in such structures, and we present general results for the functional dependences of the transmission coefficient which corresponds to a transconductance.

Very fast transients in GIS

Abstract: Different types of very fast transients (VFTs) are classified and their characteristic parameters are summarized based on measurements in a 800 kV SF/sub 6/ gas-insulated pilot installation and 420 kV GIS (gas-insulated switchgear) in service. The electromagnetic field between the enclosure and earth results in a transient enclosure voltage of up to some 10 kV and at the same time in a radiated electromagnetic field from the enclosure with amplitude of some 10 kV/m. The electromagnetic wave guided by the overhead line results in an overvoltage with a multifrequent oscillation of some 10 to 100 kHz, depending on the parameters of the overhead line and the adjacent equipment, e.g. the transformer. The transient enclosure voltage and measures to reduce it are analyzed. >

Two-dimensional electromagnetic field effects in induction plasma modelling

Abstract: Based on the electromagnetic vector potential representation, a two-dimensional, axisymmetric model is proposed for the calculation of the electromageetic fields in an inductively coupled, radiofrequency (r.f.) plasma. A comparative analysis made between the flow, temperature, and electromagnetic fields obtained using this model and those given by our earlier one-dimensional electromagnetic fields model show relatively little difference between the temperature fields predicted by the two models. Significant differences are observed, however, between the corresponding flow and electromagnetic fields. The new model offers an effective means of accounting for variations in the coil geometry on the flow and temperature fields in the discharge and for achieving a better representation of the electromagnetic fields under higher frequency conditions (f>10 MHz).

A topological theory of the electromagnetic field

Abstract: It is shown that Maxwell equations in vacuum derive from an underlying topological structure given by a scalar field ϕ which represents a map S3×R→S2 and determines the electromagnetic field through a certain transformation, which also linearizes the highly nonlinear field equations to the Maxwell equations. As a consequence, Maxwell equations in vacuum have topological solutions, characterized by a Hopf index equal to the linking number of any pair of magnetic lines. This allows the classification of the electromagnetic fields into homotopy classes, labeled by the value of the helicity. Although the model makes use of only c-number fields, the helicity always verifies ∫ A·Bd3r=nα, n being an integer and α an action constant, which necessarily appears in the theory, because of reasons of dimensionality.

Methods for calculating the electromagnetic fields from a known source distribution: application to lightning

Abstract: Two different techniques (monopole and dipole) for calculating the electric and magnetic fields from a distribution of currents and charges are discussed. Both techniques have been used for calculating the fields from lightning. A simple lightning return stroke current model, consisting of a square current pulse traveling up a vertical antenna above a ground plane, is used to compare the two techniques. Analytical expressions are obtained for the fields using each technique. These expressions are shown to be numerically equivalent, but the authors are unable to prove their equivalence analytically. It is concluded that the monopole and the dipole techniques can both be derived from Maxwell's equations and hence that both are correct. In attempting to dispel the apparent confusion that has existed regarding the validity of the monopole technique, the authors show that the monopole approach, as discussed in the literature, is applicable only to upward-traveling current waves and hence is not particularly useful in the realistic modeling of lightning return strokes. >

A time-domain differential solver for electromagnetic scattering problems

Abstract: The authors' objective is to extend computational fluid dynamics (CFD) based upwind schemes to solve numerically the Maxwell equations for scattering from objects with layered non-metallic sections. After a discussion on the character of the Maxwell equations it is shown that they represent a linearly degenerate set of hyperbolic equations. To show the feasibility of applying CFD-based algorithms, first the transverse magnetic (TM) and the transverse electric (TE) waveforms of the Maxwell equations are considered. A finite-volume scheme is developed with appropriate representations for the electric and magnetic fluxes at a cell interface, accounting for variations in material properties in both space and time. This process involves a characteristic subpath integration known as the 'Riemann solver'. An explicit-Lax-Wendroff upwind scheme, which is second-order accurate in both space and time, is employed to solve the TM and TE equations. A body-fitted coordinate transformation is introduced to treat arbitrary cross-sectioned bodies with computational grids generated using an elliptic grid solver procedure. For treatment of layered media, a multizonal representation is employed satisfying appropriate zonal boundary conditions in terms of flux conservation. The computational solution extending from the object to a far-field boundary located a few wavelengths away constitutes the near-field solution. A Green's function based near-field-to-far-field transformation is employed to obtain the bistatic radar cross section (RCS) information. >

A new approach to modeling the electromagnetic response of conductive media

Abstract: We introduce a new and potentially useful method for computing electromagnetic (EM) responses of arbitrary conductivity distributions in the earth. The diffusive EM field is known to have a unique integral representation in terms of a fictitious wave field that satisfies a wave equation. We show that this integral transform can be extended to include vector fields. Our algorithm takes advantage of this relationship between the wave field and the actual EM field. Specifically, numerical computation is carried out for the wave field, and the result is transformed back to the EM field in the time domain. The proposed approach has been successfully demonstrated using two‐dimensional (2‐D) models. The appropriate TE‐mode diffusion equation in the time domain for the electric field is initially transformed into a scalar wave equation in an imaginary q domain, where q is a time‐like variable. The corresponding scalar wave field is computed numerically using an explicit q‐stepping technique. Standard finite‐diffe...

Internal fields of a spherical particle illuminated by a tightly focused laser beam: Focal point positioning effects at resonance

Abstract: The spherical particle/arbitrary beam interaction theory developed in an earlier paper is used to investigate the dependence of structural resonance behavior on focal point positioning for a spherical particle illuminated by a tightly focused (beam diameter less than sphere diameter), linearly polarized, Gaussian‐profiled laser beam. Calculations of absorption efficiency and distributions of normalized source function (electric field magnitude) are presented as a function of focal point positioning for a particle with a complex relative index of refraction of n=1.33+5.0×10−6i and a size parameter of α≊29.5 at both nonresonance and resonance conditions. The results of the calculations indicate that structural resonances are not excited during the on‐center focal point positioning of such a tightly focused beam but structural resonances can be excited by proper on‐edge focal point positioning. Electric wave resonances were found to be excited by moving the focal point from on‐center towards the edge of the sphere parallel to the direction of the incident beam electric field polarization. Magnetic wave resonances were found to be excited by moving the focal point from on‐center towards the edge of the sphere perpendicular to the direction of the incident beam electric field polarization.

Source of vacuum electromagnetic zero-point energy

Abstract: Nature provides us with two alternatives for the origin of electromagnetic zero-point energy (ZPE): existence by fiat as part of the boundary conditions of the universe, or generation by the (quantum-fluctuation) motion of charged particles that constitute matter. A straightforward calculation of the latter possibility has been carried out in which it is assumed that the ZPE spectrum (field distribution) drives particle motion, and that the particle motion in turn generates the ZPE spectrum, in the form of a self-regenerating cosmological feedback cycle. The result is the appropriate frequency-cubed spectral distribution of the correct order of magnitude, thus indicating a dynamic-generation process for the ZPE fields.

Introduction to Engineering Electromagnetic Fields

Abstract: This is a textbook designed to provide analytical background material in the area of Engineering Electromagnetic Fields for the senior level undergraduate and preparatory level graduate electrical engineering students. It is also an excellent reference book for researchers in the field of computational electromagnetic fields. The textbook covers — Static Electric and Magnetic Fields: The basic laws governing the Electrostatics, Magnetostatics with engineering examples are presented which are enough to understand the fields and the electric current and charge sources. Dynamic Electromagnetic Fields: The Maxwell's equations in Time-Domain and solutions, the Maxwell's equations in Frequency-Domain and solutions. Extensive approaches are presented to solve partial differential equations satisfying electromagnetic boundary value problems. Foundation to electromagnetic field radiation, guided wave propagation is discussed to expose at the undergraduate level application of the Maxwell's equations to practical engineering problems.

RCS of two-dimensional structures consisting of both dielectrics and conductors of arbitrary cross section

Abstract: The problem of determining the electromagnetic field scattered by two-dimensional structures consisting of both dielectric and conducting cylinders of arbitrary cross section is considered. The conductors may be in the form of strips and the dielectrics may be in the form of shells. The conductors may be partially or fully covered by dielectric layers, while the dielectrics may be partially covered by conductors. Only homogeneous dielectrics are studied. Both the transverse electric (TE) and the transverse magnetic (TM) cases are considered. The problem is formulated in terms of a set of coupled integral equations involving equivalent electric and magnetic surface currents radiating in unbounded media. The method of moments is used to solve the integral equations. Simple expansion and testing procedures are used. Numerical results for scattering cross sections are given for various structures. >

Electromagnetic energy transmission and detection apparatus

Abstract: An electromagnetic transmission and detection apparatus comprising a transmission coil (20) for producing a high intensity electromagnetic field including one or more conductive windings (24) circumscribing a substantially polygonal volume of space having a central axis, and first and second receiver coils (22) disposed within the polygonal volume of space for receiving a low-intensity electromagnetic field transmitted from an external source. The receiver coils (22) are co-planar with the transmitter coil (20) and are disposed within the polygonal volume of the transmitter coil at positions which are polygonally, diametrical opposed to one another. The receiver coils (22) are electrically connected to each other in a differential circuit relationship such that the magnitude of electrical signals induced in the receiver coils (22) by uniform electromagnetic energy are substantially equal and opposite to one another. The differential circuit is operative to substract the electrical signals induced in the receiver coils and output a differential output signal, which is at a minimum when the two receiver coils receive approximately equal quantities of energy and is at a maximum when one of the receiver coils receives more electromagnetic energy from the external source than the other receiver coil. A display device (19) receives the differential output signal and displays a measure of the identification signal when the differential output signal is at a maximum.

Frequency shifts of spectral lines generated by scattering from space-time fluctuations.

Abstract: The scattering of a class of partially coherent electromagnetic fields by a model medium whose dielectric susceptibility fluctuates in space and in time is considered within the accuracy of the first-order Born approximation. It is shown that if the incident field is a linearly polarized, polychromatic plane wave whose spectrum is a line of Gaussian profile, the spectrum of the scattered light is, in some cases, approximately Gaussian and is shifted towards the shorter or the longer wavelengths, depending upon the angle of scattering.

Electromagnetic fields of elementary dipole antennas embedded in stratified general gyrotropic media

Abstract: Using matrix methods in conjunction with Fourier transformation techniques, the field excited by arbitrarily oriented elementary electric or magnetic dipole sources in the presence of a uniaxial or biaxial stratified gyrotropic medium is obtained in the form of a full dyadic Green's function. Both the permittivity and permeability tensors, being completely unrestricted, assume their most general forms in each layer separately. The singular behavior of the solution in the close vicinity of the source-point is properly taken into account by separate, suitably selected dyadic delta function terms. Using suitably selected upward or downward wave amplitude matrices, the field inside any of the layers is determined. >

Analysis of the power coupling from a waveguide hyperthermia applicator into a three-layered tissue model

Abstract: The power deposition from a rectangular-aperture flanged waveguide into a three-layered stratified tissue medium is analyzed theoretically. The fields inside the tissue layers are expressed in terms of Fourier integrals satisfying the corresponding wave equations, while the fields inside the waveguide are expanded in terms of the guided and evanescent normal modes. An integral equation is derived on the aperture plane of the flanged waveguide by applying the continuity of the tangential electric and magnetic fields. This integral equation is solved by expressing the unknown electric field in terms of the waveguide mode fields and by applying a Galerkin procedure. The electromagnetic fields inside the tissue medium are then determined and patterns of the deposited power at frequencies of 432 MHz and 144 MHz for apertures of 5.6*2.8 cm/sup 2/ and 16.5*8.3 cm/sup 2/, respectively, are computed and presented. >

Electromagnetic radiation from an AT‐cut quartz plate under lateral‐field excitation

Abstract: Equations of linear piezoelectricity (with the quasistatic approximation) for the quartz plate and Maxwell’s equations for the electromagnetic field in the surrounding vacuum are solved for the thickness‐shear vibrations of rotated Y cut of quartz plate. For an AT‐cut plate vibrating near the thickness‐shear resonance excited by a uniform, lateral electric field of magnitude 1 V/m, the electromagnetic energy radiated from each face is about 0.13 μW/cm2. The radiated power is about 0.1 μW/cm2 if the plate is excited by a shearing face traction which produces a strain of 10−5. Present solution is compared in detail with Mindlin’s [Int. J. Solids Struct. 9, 697 (1972)] solution of equations of piezoelectromagnetism (without the quasistatic approximation) for the thickness‐shear vibrations excited by shearing face traction. It is found that the percent difference in radiated powers computed from these two solutions, due to the quasistatic approximation, is in the order of β2(=v2/c2), where v is the velocit...

Reflection of light from a moving mirror and related problems

Abstract: The Maxwell equations, the Minkowski material equations, and the conditions which must be obeyed by fields on moving interfaces are used to obtain expressions for the frequencies and wave vectors of all the waves that appear on reflection and refraction by moving interfaces, by a tangential discontinuity of velocities of two media, and by a moving mirror. The main reported investigations of these topics are discussed. Calculations are made of a large frequency shift, of a considerable increase in the amplitudes, and of a change in the direction of propagation of waves reflected by a rapidly moving mirror or by the front of a parameter traveling in a medium at rest. Allowance is made for the Fresnel transmission of waves across such an interface and for the finite thickness of the transition layer. The change in the parameters of the reflected wave packets is considered together with the problem of the exchange of energy and momentum between an electromagnetic field and a moving mirror. In the case of a tangential discontinuity the rotation of the plane of polarization of reflected and refracted waves is dealt with, as well as the amplification of these waves on reflection from a medium moving faster than light.

Three-dimensional field expansion in the most general rotationally symmetric anisotropic material: application to scattering by a sphere

Abstract: A field expansion is described for the solution of three-dimensional electromagnetic problems in material regions characterized by the most general rotationally symmetric anisotropy. The analysis (in spherical coordinates) reveals that the angular dependence is dictated by spherical harmonics, whereas the radial functions satisfy a set of coupled second-order ordinary differential equations. Due to birefringence, four sets of radial functions (each set representing mode coupling), which are described in detail, are obtained. The expansion is applied to the problem of scattering by an anisotropic sphere, where the numerical calculations confirm the existence of integrable field singularities at the origin of coordinates. >

Question of the nonlocality of the Aharonov-Casher effect

Abstract: The Aharanov-Casher effect is manifested in a (2+1)-dimensional model that screens the electromagnetic fields, in order to demonstrate that the effect is essentially nonlocal in its nature. The question of nonlocality is discussed by means of a nonrelativistic model for a superconductor. It is demonstrated that although the superconductor screens the electric field generated by an external charge it does not screen the modular electric field which is a constant of motion of the system. Consequently, a magnetic fluxon will accumulate the same phase as if the electric field were unscreened and the Aharonov-Casher effect will exist even in a force-free region.

Atoms in molecules in external fields

Abstract: The theory of atoms in molecules is extended to the case where the molecule is in the presence of an electromagnetic field. This theory is based upon a generalization of quantum mechanics to an open system, as obtained through a corresponding extension of Schwinger’s principle of stationary action. The extension of this principle is possible only if the open system satisfies a particular boundary condition, one which is expressed as a constraint on the variation of the action integral. This is the condition that it be bounded by a surface of zero flux in the gradient vector field of the charge density, the definition of an atom in a molecule. It is shown that this boundary constraint again suffices to define an atom as a quantum subsystem when the molecule is in the presence of an electromagnetic field. The mechanics of an open system and its properties are determined by the fluxes in corresponding vector current densities through its surface. As in the fieldfree case, the obtainment of these currents from the variation of the action integral is a direct result of the variation of the atomic surface and of the imposition of the variational constraint on its boundary. The currents in this case consist of a paramagnetic and a diamagnetic contribution, currents whose presence are a necessary requirement for the description of the properties of a system in the presence of external fields. The variational statement of the Heisenberg equation of motion obtained from the principle of stationary action is used to derive the Ehrenfest force and virial theorems for an atom in a molecule in the presence of external electric and magnetic fields. In this case, there are forces acting on the interior of the atom which arise from the magnetic pressures acting on its surface. It is shown that the molecular electric polarizability and magnetic susceptibility, like other properties, are rigorously expressible as a sum of atomic contributions.