Showing papers on "Electromagnetic field published in 1992"

Wave-function approach to dissipative processes in quantum optics.

Abstract: A novel treatment of dissipation of energy from a ``small'' quantum system to a reservoir is presented. We replace the usual master equation for the small-system density matrix by a wave-function evolution including a stochastic element. This wave-function approach provides new insight and it allows calculations on problems which would otherwise be exceedingly complicated. The approach is applied here to a two- or three-level atom coupled to a laser field and to the vacuum modes of the quantized electromagnetic field.

Quantization of the electromagnetic field in dielectrics.

Abstract: We present a fully canonical quantization scheme for the electromagnetic field in dispersive and lossy linear dielectrics. This scheme is based on a microscopic model, in which the medium is represented by a collection of interacting matter fields. We calculate the exact eigenoperators for the coupled system and express the electromagnetic field operators in terms of them. The dielectric constant of the medium is explicitly derived and is shown to satisfy the Kramers-Kronig relations. We apply these results to treat the propagation of light in dielectrics and obtain simple expressions for the electromagnetic field in the medium in terms of space-dependent creation and annihilation operators. These operators satisfy a set of equal-space commutation relations and obey spatial Langevin equations of evolution. This justifies the use of such operators in phenomenological models in quantum optics. We also obtain two interesting relationships between the group and the phase velocity in dielectrics.

Uniform magnetic fields and double-wrapped coil systems: Improved techniques for the design of bioelectromagnetic experiments

Abstract: A common mistake in biomagnetic experimentation is the assumption that Helmholtz coils provide uniform magnetic fields; this is true only for a limited volume at their center. Substantial improvements on this design have been made during the past 140 years with systems of three, four, and five coils. Numerical comparisons of the field uniformity generated by these designs are made here, along with a table of construction details and recommendations for their use in experiments in which large volumes of uniform intensity magnetic exposures are needed. Double-wrapping, or systems of bifilar windings, can also help control for the non-magnetic effects of the electric coils used in many experiments. In this design, each coil is wrapped in parallel with two separate, adjacent strands of copper wire, rather than the single strand used normally. If currents are flowing in antiparallel directions, the magnetic fields generated by each strand will cancel and yield virtually no external magnetic field, whereas parallel currents will yield an external field. Both cases will produce similar non-magnetic effects of ohmic heating, and simple measures can reduce the small vibration and electric field differences. Control experiments can then be designed such that the only major difference between treated and untreated groups is the presence or absence of the magnetic field. Double-wrapped coils also facilitate the use of truly double-blind protocol, as the same apparatus can be used either for experimental or control groups.

Electromagnetic pulses from high-energy showers: Implications for neutrino detection.

Abstract: We review the properties of electromagnetic showers in dense media and calculate in detail the associated electromagnetic pulses generated by shower electrons. We perform real-time simulations recording the charge, trajectory, and time of each cascade particle and compute the associated electromagnetic wave. Our results are relevant to experiments detecting radio pulses from showers initiated by cosmic particles interacting with the Earth.

Numerical dosimetry at power-line frequencies using anatomically based models.

Abstract: We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function ofmore » height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively. 34 refs.« less

Horizontal fields generated by return strokes

Abstract: Horizontal fields generated by return strokes play an important role in the interaction of lightning-generated electromagnetic fields with overhead power lines. In many of the recent investigations on the interaction of lightning electromagnetic fields with power lines, the horizontal field was calculated by employing the expression for the tilt of the electric field of a plane wave propagating over the finitely conducting Earth. In this paper we show that the horizontal field generated by return strokes over the finitely conducting ground can be obtained to a high accuracy by using the expression for the surface impedance of the finitely conducting Earth. The method is suitable to calculate horizontal fields generated by return strokes at distances as close as 200 m. At these close ranges the use of the wave tilt expression can cause large errors.

Mechanisms of electromagnetic interaction with cellular systems.

Abstract: The question of how electromagnetic fields - static or low to high frequency - interact with biological systems is of great interest. The current discussion among biologists, chemists, and physicists emphasizes aspects of experimental verification and of defining microscopic and macroscopic mechanisms. Both aspects are reviewed here. We emphasize that in certain situationsnonthermal interactions of electromagnetic fields occur with cellular systems.

Electromagnetics and calculation of fields

Abstract: This introduction to electromagnetics emphasizes the computation of electromagnetic fields and the development of theoretical relations. Beginning with the idea that Maxwell's equations are primary, the authors avoid the lengthy discussions of electro - and magneto - statics that are customary in texts on electromagnetism. After a chapter, therefore, on the basics of vector calculus, the discussion begins with the electromagnetic field and Maxwell's equations; the two following chapters then present the special cases of electrostatic and magnetostatic phenomena. Dynamics is introduced in chapter 5, and electromagnetic induction in chapter 6. The discussion of wave propagation and high-frequency fields emphasizes such practical matters as propagation in lossy dielectrics, waveguides, and resonators. The remaining four chapters discuss computational techniques; the finite element method, Galerkin's residual approach, software implementation, and recent developments in computer techniques.

Direct Time Integration of Maxwell's Equations in Nonlinear Dispersive Media for Propagation and Scattering of Femtosecond Electromagnetic Solitons

Abstract: The initial results for femtosecond electromagnetic soliton propagation and collision obtained from first principles, i.e., by a direct time integration of Maxwell's equations are reported. The time integration efficiently implements linear and nonlinear convolutions for the electric polarization and can take into account such quantum effects as Kerr and Raman interactions. The present approach is robust and should permit the modeling of 2D and 3D optical soliton propagation, scattering, and switching from the full-vector Maxwell's equations.

Electromagnetic Fields And Waves

Abstract: Presents comprehensive coverage of the fundamentals of electromagnetic theory and applications. Basic laws and physical phenomena are illustrated by numerous examples.

Magnetic reconnection in electron magnetohydrodynamics

Abstract: The magnetic field dynamics and reconnection processes in a highly conducting plasma are investigated in the regimes where Ohm’s law is dominated by the Hall term, using a single (electron) fluid description (electron magnetohydrodynamics). In these regimes, which correspond to the frequency range of the so‐called whistler (helicon) mode, the electromagnetic field is nearly force free: (j×B)/c+eneE=0. The evolution of the magnetic field in the vicinity of an X line is discussed in the linear and nonlinear regimes. The propagation of whistler waves results in the steepening of their wave front and in the increase of the electric current density in the neighborhood of the magnetic separatrix surfaces. Small‐scale magnetic reconnection occurs near surfaces where k⋅B=0, with k the mode wave number, and tearing‐type modes can be unstable due to the effect of electron inertia. A class of exact self‐similar solutions is obtained. These describe, within the scope of a local approximation, the nonlinear time devel...

Computational modeling of femtosecond optical solitons from Maxwell's equations

Abstract: An algorithm is developed that permits the direct time integration of full-vector nonlinear Maxwell's equations. This capability permits the modeling of both linear and nonlinear instantaneous and dispersive effects in the electric polarization in material media. The modeling of the optical carrier is retained. The fundamental innovation is to notice that it is possible to treat the linear and nonlinear convolution integrals, which describe the dispersion, as new dependent variables. A coupled system of nonlinear second-order ordinary differential equations can then be derived for the linear and nonlinear convolution integrals, by differentiating them in the time domain. These equations, together with Maxwell's equations, are solved to determine the electromagnetic fields in nonlinear dispersive media. Results are presented of calculations in one dimension of the propagation and collision of femtosecond electromagnetic solitons that retain the optical carrier, taking into account the Kerr and Raman interactions. >

Chapter 1 – The Nonlinear Optical Susceptibility

Abstract: Publisher Summary Nonlinear optics is the study of phenomena that occur as a consequence of the modification of the optical properties of a material system by the presence of light. Nonlinear optical phenomena are “nonlinear” in the sense that they occur when the response of a material system to an applied optical field depends in a nonlinear manner upon the strength of the optical field. Two additional symmetries of the nonlinear susceptibility tensor occur for the case of a lossless nonlinear medium. The condition that the nonlinear susceptibility must possess full permutation symmetry for a lossless medium can be deduced from a consideration of the form of the electromagnetic field energy within a nonlinear medium. It is also possible to describe optical nonlinearities directly in the time domain by considering the polarization P (t) that is produced by some arbitrary applied field E(t). These two methods of description are entirely equivalent; description in the time domain is more convenient for certain types of problems, such as those involving applied fields in the form of short pulses, whereas description in the frequency domain is more convenient when each input field is nearly monochromatic.

Errata:. Strong and Weak Forms of the Method of Moments and the Coupled Dipole Method for Scattering of Time-Harmonic Electromagnetic Fields

Abstract: Algorithms based on the method of moments (MOM) and the coupled dipole method (CDM) are commonly used to solve electromagnetic scattering problems. In this paper, the strong and the weak forms of both numerical techniques are derived for bianisotropic scatterers. The two techniques are shown to be fully equivalent to each other, thereby defusing claims of superiority often made for the charms of one technique over the other. In the final section, reductions of the algorithms for isotropic dielectric scatterers are explicitly given.

Development and analysis of electric field sensor using LiNbO/sub 3/ optical modulator

Abstract: The sensitivity of an electromagnetic field sensor which uses a LiNbO/sub 3/ electrooptical crystal and an optical-fiber link is improved by using a Mach-Zehnder interferometer, whose half-wave voltage is about 4 V at 1.3- mu m wavelength, and a YAG laser pumped by a laser diode whose output power is 25 mW. The resulting frequency response is about flat from 100 Hz to 300 MHz, and the minimum detectable electric field strengths are 0.22 mV/m at 50 MHz and 0.079 mV/m at 750 MHz. The variation of the sensitivity with the frequency and element length are analyzed using the moment method, and the calculated results agree with the measured results. The measurement of the cross-polarization of the sensor indicates that this property is similar to that of a dipole antenna. The improved sensor can measure an electromagnetic impulse whose peak value is larger than 10 V/m and whose width is wider than 5 ns. >

Three-dimensional Gross-Neveu model at nonzero temperature and in the presence of an external electromagnetic field

Abstract: The phase structure of the (2+1)-dimensional Gross-Neveu model is considered at a nonzero temperatureT and in the presence of an external electromagnetic field. The major results are as follows: 1. AtT=0,H≠0 (a magnetic field), the original symmetry of the model breaks for anyH values. 2. AtT=0,E≠0 (an electric field) anEc is shown to exist, such that forE Ec the vacuum of the model is symmetric. 3. AtT≠0,H≠0, and at a fixedT value such anHc(T) is shown to exist that forH>Hc(T) the chiral invariance of the model is spontancously broken. For any fixedH value there exists such anTc(H) that forT>Tc(H) the symmetry restores. The phase portrait of the model is drawn.

Coherent phenomena in multilevel systems with closed interaction contour

Abstract: The work presented considers a new coherent phenomenon, i.e. the influence of the phases of electromagnetic fields interacting with a multilevel system on the character of excitation of this system. On the basis of analysing the equation for an N-level quantum system density matrix, it was established that in multilevel systems containing a closed contour of transitions, resonantly interacting with the field, stationary populations always depend on the total interaction contour phase Phi . For the simplest multilevel systems, i.e. three-level, the authors have obtained analytical expressions, connecting populations with the relative field phase in such systems. Thus, for a Lambda system, interacting with three resonant electromagnetic fields, it is discovered that, depending on the total phase value of the transition contour, both destruction and successive restoration of a coherent trapping state can take place. The work provides qualitative explanations of phase effects and suggests some possibilities for their application.

Interaction of electromagnetic waves with general bianisotropic slabs

Abstract: An efficient, elegant, and systematic formulation technique which, combining Fourier transform with matrix analysis methods, is suitable for problems related to radiation by dipole or other sources in the presence of an arbitrarily general stratified anisotropic medium has been recently developed. This technique is adapted further extended to allow the presence of general bianisotropic media described by four tensors with no limitations on their elements. Two specific applications pertaining to some canonical problems of fundamental importance are included to exemplify the method and demonstrate its usefulness: radiation by an arbitrarily oriented elementary electric dipole source located in the vicinity of a general bianisotropic slab, either grounded or ungrounded, leading to the expressions of the dyadic Green's function of the structure, and reflection and transmission of an arbitrarily polarized plane wave incident upon such a slab, leading to closed-form concise expressions for the reflection and transmission coefficient matrices. >

Finite element analysis in electromagnetic systems-accounting for electric circuits

Abstract: Two approaches for the numerical simulation of electromagnetic systems, accounting for electric circuit equations, are presented. First, the indirect coupled model, which permits the simulation of synchronous machines fed by controlled inverters with moderate calculation time is considered. Second, a direct coupled model where the magnetic and electric circuit equations (2-D or 3-D) are solved simultaneously is developed. This approach takes more calculation time but gives more precision. Applications concerning several electromagnetic systems are treated, and numerical results are compared with experimental ones to verify the validity of the models. >

Chaos sensing arc detection

Abstract: An arc detection method and apparatus is provided for an electric circuit having an electrified conductor (46) connecting a voltage source (26) to a load (30). The arc detector includes a field sensor (62) sensing an electromagnetic field established about the conductor by the occurrence of an electrical arc in the electric circuit, and generating a field responsive signal in response thereto. Arc discrimination circuitry responds to the field sensor and generates an arc indicative signal in response to a random chaotic pattern of the field responsive signal.

Mixed-potential integral expression formulation of the electric field in a stratified dielectric medium-application to the case of a probe current source

Abstract: The well-known procedure for determining the electric field in a structure consisting of an arbitrary number of planar dielectric layers is modified in order to obtain a form specially suited for the analysis of multiprobe multipath configurations. In general, the field is generated by arbitrary currents in the layers and arbitrary sheet currents in the transitions between the layers. The currents may be electric as well as magnetic, and the dielectric layers are isotropic, homogeneous, and lossy. The procedure results in Green's functions especially suited for the analysis of multiprobe multipatch configurations. They can be used in an efficient mixed-potential integral expression formulation. The theoretical procedure is applied in the case of a probe current source situated in one of the dielectric layers of the structure. For this probe current a highly efficient attachment current distribution is derived. Comparison of measured and calculated results for example structures proves the accuracy of both the approach and the attachment mode. >

Decoherence in quantum electrodynamics and quantum gravity.

Abstract: We treat the interaction of a semiclassical electromagnetic field with a complex scalar field as a continuous measurement process through which certain interference terms between electromagnetic field states may become suppressed---they decohere.'' The formal framework is the functional Schroedinger picture for scalar QED. The reduced density matrix for the electromagnetic field is discussed in detail. We calculate the remaining coherence width for realistic laboratory field strengths. The back reaction of the scalar field on the electromagnetic state is discussed with the help of the Wigner function and is explicitly calculated. We compare our results with the corresponding case in quantum gravity where the radius of the Universe is measured'' by inhomogeneous scalar field modes. We propose to render the decoherence factor finite by summing over a set of rescaled field modes.

The fall of charged particles under gravity: A study of experimental problems

Abstract: There are currently proposals to test the weak equivalence principle for antimatter by studying the motion of antiprotons, negative hydrogen ions, positrons, and electrons under gravity. The motions of such charged particles are affected by residual gas, radiation, and electric and magnetic fields, as well as gravity. The electric fields are particularly sensitive to the state of the "shielding" container. This paper reviews, and extends where necessary, the physics of these extraneous influences on the motion of charged particles under gravity. The effects considered include residual gas scattering; wall potentials due to patches, stress, thermal gradients, and contamination states; and image-charge-induced dissipation.

Quantized electromagnetic field on a manifold

Abstract: We develop the quantization of the electromagnetic field on an arbitrary globally hyperbolic Lorentzian manifold with a compact Cauchy surface.

The split-cavity oscillator: a high-power E-beam modulator and microwave source

Abstract: A compact device, called a split-cavity oscillator, whose self-excited oscillating electromagnetic field converts a large-area steady electron beam into one that is highly density modulated, is described. It does this in a short beam travel length, easing both space-charge and pinching limitations. Thus, high currents are possible without requiring a magnetic guide field. Methods for converting the modulated output beam into high-power microwaves are discussed, as are ways to phase-lock several oscillators together. Analytic theory, numerical simulations, and experiments describing the device are presented. >

A general purpose method for electric and magnetic combined problems for 2D, axisymmetric and transient systems

Abstract: The non-linear analysis of electrical devices is often limited by the complexity of the power supply. In effect, in the case of solid conductors, the voltage is required, while in the case of stranded conductors the current must be known. These restrictions are due to the nature of the field equations. A new formulation is proposed which allows the possibility to choose the power supply and choose any kind of connection between components. Two types of 'magnetic conductors' are considered: solid conductors, in which eddy current be induced and stranded conductors without eddy current. An equation combining the magnetic potential, the current and the voltage is established for each conductor. This equation is introduced into a conventional circuit analysis method. The magnetic field and circuit equations can be solved simultaneously in the resulting system. An implicit method is used to dicretize the equations in time. A Newson-Raphson linearization algorithm is used to handle problems that include materials with non-linear properties. This formulation is used in the commercial program FLUX2D. To illustrate one of the many applications, an A.C. electromagnet is studied.