Showing papers on "Electromagnetic field published in 1995"

Handbook of radiation and scattering of waves

Abstract: Acoustic Waves in Fluids: Cartesian Tensors and Their Properties Integral-Transformation Methods Basic Equations of the Theory of Acoustic Waves in Fluids The Principle of Superposition and Its Application to Acoustic Wave Fields in Configurations with Geometrical Symmetry The Acoustic Wave Equations, Constitutive Relations, and Boundary Conditions in the Time Laplace-Transform Domain (Complex Frequency Domain) Acoustic Radiation from Sources in an Unbounded, Homogeneous, Isotropic Fluid Acoustic Reciprocity Theorems and Their Applications Plane-Wave Scattering by an Object in an Unbounded, Homogeneous, Isotropic, Lossless Embedding. Elastic Waves in Solids: Cartesian Tensors and Their Properties Integral-Transformation Methods Basic Equations of the Theory of Elastic Waves in Solids The Principle of Superposition and Its Application to Electromagnetic Fields in Configurations with Geometrical Symmetry The Elastic Wave Equations, Constitutive Relations, and Boundary Conditions in the Time Laplace-Transform Domain (Complex Frequency Domain) Elastodynamic Radiation from Sources in an Unbounded, Homogeneous, Isotropic Solid Plane Elastic Waves in Homogeneous Solids Elastodynamic Reciprocity Theorems and Their Applications Plane-Wave Scattering by an Object in an Unbounded, Homogeneous, Isotropic, Lossless Embedding. Electromagnetic Waves: Cartesian Tensors and Their Properties Integral-Transformation Methods The Electromagnetic Constitutive Relations The Electromagnetic Boundary Conditions Exchange of Energy in the Electromagnetic Field Vector Potentials, Point-Source Solutions, and Green's Function in the Theory of Electromagnetic Radiation from Sources The Principle of Superposition and Its Application to Electromagnetic Fields in Configuration with Geometrical Symmetry The Electromagnetic Field Equations, Constitutive Relations, and Boundary Conditions in the Time Laplace-Transform Domain (Complex Frequency Domain) Complex Frequency Domain Vector Potentials Point-Source Solutions and Green's Functions in the Theory of Electromagnetic Radiation from Sources Electromagnetic Radiation from Sources in an Unbounded, Homogeneous, Isotropic Medium Plane Electromagnetic Waves in Homogeneous Media Electromagnetic Reciprocity Theorems and Their Applications Plane-Wave Scattering by an Object in an Unbounded, Homogeneous, Isotropic, Lossless Embedding Interference and Shielding of Electromagnetic Systems Accessible via Low-Frequency Terminations Electromagnetic Compatibility (EMC).

Electromagnetic fields and dielectric response in empirical tight-binding theory.

Abstract: Relativistic and nonrelativistic empirical tight-binding theory is generalized to incorporate time-dependent electromagnetic fields in a gauge-invariant manner that does not introduce any extra adjustable parameters. Based on this approach, it is shown that explicit expressions can be derived for the effective mass tensor, the effective Land\'e g factor, the current, the frequency-dependent transverse dielectric function, and the wave-vector- and frequency-dependent longitudinal dielectric function. A finite basis analogue of the optical f-sum rule is derived and shown to impose a condition on tight-binding parameters.

Time profile of harmonics generated by a single atom in a strong electromagnetic field

Abstract: We show that the time profile of the harmonics emitted by a single atom exposed to a strong electromagnetic field may be obtained through a wavelet or a Gabor analysis of the acceleration of the atomic dipole. This analysis is extremely sensitive to the details of the dynamics and sheds some light on the competition between the atomic excitation or ionization processes and photon emission. For illustration we study the interaction of atomic hydrogen with an intense laser pulse.

Electromagnetic field quantization in absorbing dielectrics

Abstract: The electromagnetic field is quantized for normal transmission of incident waves through a parallel-sided dielectric slab. The dielectric material is dispersive and it acts as a linear amplifier over limited ranges of the frequency and as a linear attenuator at the remaining frequencies. The field operators derived for the three spatial regions within and on either side of the slab are shown to satisfy the canonical commutation relations. The noise fluxes emitted by the slab are evaluated and shown to satisfy the general requirements for the minimum noise associated with linear amplifiers and attenuators. The behavior of the amplifier gain profile on the approach to the lasing threshold of the slab is determined, but the results are restricted to the below-threshold state of the system. The spectra of the electric-field fluctuations are evaluated for the three spatial regions and for amplifying and attenuating frequencies.

Foundations and Industrial Applications of Microwave and Radio Frequency Fields: Physical and Chemical Processes

Abstract: ELECTRICAL ASPECTS. Governing Electromagnetic and Thermal Field Relations. Radio Frequency and Microwave Transmission. Microwave and Radio Frequency Circuit Design. High Power Applicators and Loads. Instrumentation and Measurement Methods. MATERIAL ASPECTS. Introduction to the Macroscopic Theory of Dielectrics. Dynamic Aspects. Generalization of Dielectric Relaxation in Real Materials. PROCESSING ASPECTS. Theoretical Models and Experimental Methods in High Power Density Electromagnetic Fields. Electromagnetic Processing of Homogeneous Materials at High Power Density. Electromagnetic Processing of Heterogeneous Materials at High Power Density. Microwave-Enhanced Catalysis. Index.

Nonlinear ponderomotive scattering of relativistic electrons by an intense laser field at focus

Abstract: The relativistic dynamics of electrons subjected to the electromagnetic field of an intense, ultrashort laser pulse in vacuum is studied theoretically. The effects of both finite pulse duration and beam focusing are taken into account. It is found that when the quiver amplitude of the electrons driven by the laser field exceeds the focal spot radius of a Gaussian beam, the restoring force acting on the charge decays exponentially, and the electrons are scattered away from the focus. This physical process, known as ponderomotive scattering, effectively terminates the interaction within a laser wavelength, and the electrons can escape with very high energy, as the normalized laser field is of the order of or greater than unity. The relation between the scattering angle and the escape energy is derived analytically from the conservation of canonical momentum and energy in the photon field. For a linearly polarized laser field, the interaction produces two jets of high energy electrons. The theory is supplemented by detailed two-dimensional computer simulations.

Quantum-state mapping between multilevel atoms and cavity light fields

Abstract: A scheme for the preparation of Fock states and general superposition states of the electromagnetic field in a cavity is studied in detail. The scheme uses adiabatic passage in a strongly coupled atom-cavity system to "map" atomic ground-state Zeeman coherence onto the cavity-mode field. We model photon-counting and homodyne measurements of the field exiting the cavity and demonstrate the possibility of generating and detecting highly nonclassical states of the field parameter values close to currently realizable experimental values. The adiabatic passage process is also reversible, enabling cavity-mode fields to be mapped onto atomic ground-state Zeeman coherence. Application of this property to the measurement of cavity fields is discussed, with particular consideration given to a possible scheme for quantum measurements of the intracavity photon number.

Penetration characteristics of electromagnetic emissions from an underground seismic source into the atmosphere, ionosphere, and magnetosphere

Abstract: Theoretical calculations are made on electromagnetic fields in the frequency range 10−2 to 10−2; Hz on the ground surface and above the ionosphere induced by stochastic microcurrent activity inside the future seismic sources on the assumption of cylindrical symmetry of the effective current and three types of polarization. The inhomogeneity of the ground and atmosphere conductivity and anisotropy of the ionosphere are taken into consideration. The intensity of ULF magnetic and electric precursors observed on the ground, and their spatial distribution can be explained by using the results of the present computations. It is found that only the fields from a magnetic type source can penetrate into the magnetosphere and generate propagating Alfven waves. The expected values of magnetospheric electric and magnetic field are 1-10 μV m−1 Hz−1/2 and 1–10 pT Hz−1/2 respectively, and the horizontal scale of their distribution is about 100–200 km. Finally, these theoretical predictions are compared with the corresponding results of satellite observations.

Electromagnetic diffraction of light focused through a planar interface between materials of mismatched refractive indices: structure of the electromagnetic field. I

Abstract: We consider the electromagnetic diffraction occurring when light is focused by a lens without spherical aberration through a planar interface between materials of mismatched refractive indices, which focusing produces spherical aberration. By means of a rigorous vectorial electromagnetic treatment developed previously for this problem by Torok et al. [ J. Opt. Soc. Am. A12, 325 ( 1995)], the time-averaged electric energy density distributions in the region of the focused probe are numerically evaluated for air–glass and air–silicon interfaces as functions of lens numerical aperture and probe depth. Strehl intensity, lateral and axial sizes, and axial location of the probe are shown to be regular functions for low numerical apertures and probe depths but irregular functions for high numerical apertures and probe depths. An explanation to account for these occurrences is presented that also explains some previous experimental results of confocal microscopy.

Atom-field interactions and dressed atoms

Abstract: Preface 1. Classical electromagnetic field in the absence of sources 2. Quantum electromagnetic field in the absence of sources 3. The quantum matter field 4. Electrodynamics in the presence of sources 5. Atoms dressed by a real electromagnetic field 6. Dressing by zero-point fluctuations 7. Energy density around dressed atoms 8. Further considerations on the nature of dressed states Appendices.

Electromagnetic field coupling to a line of finite length: theory and fast iterative solutions in frequency and time domains

Abstract: A system of integral-differential equations for evaluating currents and voltages induced by external electromagnetic fields on a finite-length horizontal wire above a perfectly conducting ground is derived under the thin wire approximation. Based on perturbation theory, an iterative procedure is proposed to solve the derived coupling equations, where the zeroth iteration term is determined by using the transmission line (TL) approximation. The method can be applied both in the frequency and in the time domains. The proposed iterative procedure converges rapidly to the exact analytical solution for the case of an infinite line, and to the NEC solution for a line of finite length. Moreover, with only one iteration, an excellent approximation to the exact solution can be obtained. The method is applied to assess the validity of the TL approximation for plane wave coupling to an overhead line of finite length. It is shown that the resulting errors for the early-time response are generally higher than those corresponding to infinite lines.

The influence of electromagnetic fields on human brain activity.

Abstract: Possible effects of electromagnetic fields on human brain activity were studied In a single-blind, cross-over-designed and placebo-controlled study 36 volunteers were exposed firstly to an electromagnetic field originating form a MediLine "MEGA-WAVE 150/1" therapy instrument and secondly to a field originating from a mobile, digital tetlephone as used for wireless telecommunication All volunteers also underwent a control experiment with no field exposure Application of the MEGA-WAVE instrument caused an increase in EEG power in the frequency bands Alpha2, Beta1 and Beta2 during and after field exposure Operation of the mobile telephone caused an increase in the same frequency bands with a delay of approximately 15 minutes after exposure

On the relaxation of a two-level system driven by a strong electromagnetic field

Abstract: A detailed and unified account of the theory of the generalized Bloch equations is presented. The equations apply to a two‐level system weakly coupled to a heat bath and subject to a monochromatic rotating field of arbitrary intensity. The relaxation tensor obtained is explicitly field‐dependent. The derivation is valid for general coupling to a quantum heat bath. The generalized Bloch equations are shown to be thermodynamically consistent, as opposed to the standard Bloch equations. Different limits of the generalized Bloch equations are examined and related to previous studies. The potential use of the generalized Bloch equations as a probe of the bath spectral density is demonstrated for the case of a two‐level system embedded in a Debye solid.

Electromagnetic Fields: Biological Interactions and Mechanisms

Abstract: Biological Effects of Environmental Electromagnetic Fields: An Overview Spectrum and Intensity of Environmental Electromagnetic Fields from Natural and Man-Made Sources Typical Electric and Magnetic Field Exposures at Power-Line Frequencies and Their Coupling to Biological Systems Bioelectromagnetic Dosimetry Issues Relating to Causality of Bioelectromagnetic Effects Comparison of Endogenous Currents in and Around Cells with Those Induced by Exogenous Extremely Low Frequency Magnetic Fields Endogenous Electric Fields Measured in Developing Embryos Streaming and Piezoelectric Potentials in Connective Tissues Electric Stimulation of Protein Synthesis in Muscle Epidemiologic Studies and Their Role in Identifying Potential Risks from Exposure to Electromagnetic Fields Magnetic Field Exposure Assessment Electromagnetic Fields and Cancer: Laboratory Studies Electric and Magnetic Field Mitigation Strategies Bioelectromagnetics in the Service of Medicine Therapeutic Aspects of Electromagnetic Fields for Soft-Tissue Healing Electromagnetic Heating for Cancer Treatment Tissue Electroporation for Localized Drug Delivery The Role of Coherence in Electromagnetic Field-Induced Bioeffects: The Signal-to-Noise Dilemma Electric and Magnetic Field Signal Transduction in the Membrane Na]+/K]+ -adenosinetriphosphatase The Role of Cell and Tissue Calcium in Transducing the Effects of Exposure to Low-Frequency Electromagnetic Fields Magnetoreception and Electromagnetic Field Effects: Sensory Perception of the Geomagnetic Field in Animals and Humans Magnetokinetic Effects on Radical Pairs: A Paradigm for Magnetic Field Interactions with Biological Systems at Lower Than Thermal Energy Biosynthetic Stress Response in Cells Exposed to Electromagnetic Fields Membrane Signal-Transduction Mechanisms and Biological Effects of Low-Energy Electromagnetic Fields Melatonin Suppression by Time-Varying and Time-Invariant Electromagnetic Fields Effects of Radio-Frequency Radiation on Mammalian Cells and Biomolecules In Vitro

Finite-difference time-domain modeling of nonperfectly conducting metallic thin-film gratings

Abstract: A simulation tool based on the finite-difference time-domain (FDTD) technique is developed to model the electromagnetic interaction of a focused optical Gaussian beam in two dimensions incident on a simple model of a corrugated dielectric surface plated with a thin film of realistic metal The technique is a hybrid approach that combines an intensive numerical method near the surface of the grating, which takes into account the optical properties of metals, with a free-space transform to obtain the radiated fields A description of this technique is presented along with numerical examples comparing gratings made with realistic and perfect conductors In particular, a demonstration is given of an obliquely incident beam focused on a uniform grating and a normally incident beam focused on a nonuniform grating The gratings in these two cases are coated with a negative-permittivity thin film, and the scattered radiation patterns for these structures are studied Both TE and TM polarizations are investigated Using this hybrid FDTD technique results in a complete and accurate simulation of the total electromagnetic field in the near field as well as in the far field of the grating It is shown that there are significant differences in the performances of the realistic metal and the perfect metal gratings

Electromagnetically triggered, responsive gel based drug delivery device

Abstract: A system for remotely inducing a phase transition in a gel is provided. The system includes a gel capable of volume change in response to an environmental stimulus, a seed material in contact with the gel, and generating a time-varying magnetic or a time-varying electric or electromagnetic field in the proximity of the gel to produce the environmental stimulus. In a preferred embodiment, the environmental stimulus is temperature.

A proposed dielectric-loaded resonant laser accelerator.

Abstract: A laser-pumped accelerator utilizing a resonant, periodic, dielectric structure is proposed. The electromagnetic fields due to a side-injected laser beam impinging on this structure are calculated in a two-dimensional standing-wave approximation, leading to an estimated accelerating field in excess of 1 GV/m for accessible experimental parameters. The longitudinal dynamics of injected electrons in the device are discussed, as are the first- and second-order transverse focusing effects inherent to this structure. Similarities and differences between this scheme and conventional and other advanced accelerators are examined.

Field Quantization and Radiative Processes in Dispersive Dielectric Media

Abstract: The electromagnetic field in a dispersive dielectric medium is quantized in a straightforward manner based on the classical expression for the field energy away from absorption resonances. Results for spontaneous and stimulated radiative rates, and absorption and gain coefficients, are obtained and compared with other expressions in the literature. Local field corrections, when they exist, are included. A level shift for an atom in a host dielectric medium is obtained and interpreted as the van der Waals interaction between that atom and its neighbours in the host medium.

Local field effects and electric and magnetic dipole transitions in dielectrics.

Abstract: We report measurements of the refractive index dependence of the spontaneous emission rate of electric and magnetic dipole transitions in dielectrics. Local field effects are clearly observed in the electric dipole results and discrimination between different theoretical descriptions is made. The magnetic dipole results are well described by quantum electrodynamical considerations without local field effects.

Method for solution of Maxwell's equations in non-uniform media

Abstract: SUMMARY It is shown that the L2 norm of electric currents induced in a dissipative medium can never exceed the norm of the external currents. This allows the construction of a simple iteration method to soIve the Maxwell's equations. The method produces a series converging to the solution for an arbitrary conductivity distribution and arbitrary frequency of field variations. The convergence is slow if the lateral contrast of the conductivity distribution is about lo4 or higher. A modification significantly improving the convergence is described in this paper. As an example, electromagnetic fields induced in the model (including the western part of the Northern American continent and the adjacent part of the Pacific Ocean) are calculated.

Mathematical theory of nonrelativistic matter and radiation

Abstract: We consider a system of finitely many nonrelativistic electrons bound in an atom or molecule which are coupled to the electromagnetic field via minimal coupling or the dipole approximation Among a variety or results, we give sufficient conditions for the existence of a ground state (an eigenvalue at the bottom of the spectrum) and resonances (eigenvalues of a complex dilated Hamiltonian) of such a system We give a brief outline of the proofs of these statements which will appear at full length in a later work

On the contribution of the electromagnetic field components in field-to-transmission line interaction

Abstract: Based on the transmission line approximation, three different equivalent formulations have been proposed for evaluating the interaction between an external electromagnetic field and a transmission line, The difference among these "coupling" formulations, which are summarized for the case of a lossless line, lies essentially in the representation of the source terms as a function of the external electromagnetic field components. The authors show that the contribution of a given electromagnetic field component is different depending on the particular adopted formulation, To show that, the three formulations are employed to calculate the voltages induced on an overhead line by a nearby lightning strike, and the contribution to the induced voltage of the various electromagnetic field components explicitly appearing in each formulation is emphasized. The authors conclude that it is misleading to speak about the contribution of a given electromagnetic field component to the total induced voltages without first specifying the coupling formulation one is using.

Internal and near-surface electromagnetic fields for an absorbing spheroidal particle with arbitrary illumination

Abstract: A theoretical procedure in which a spheroidal coordinate separation-of-variables solution is used is developed for the determination of the internal and the near-surface electromagnetic fields for an arbitrary monochromatic field that is incident upon a homogeneous spheroidal particle. Calculations are presented for both the prolate and the oblate geometries, demonstrating the effects of particle size, particle axis ratio, and the orientation and character (plane-wave and focused Gaussian beam) of the incident field on the resultant internal and near-surface electromagnetic-field distributions.

The electromagnetic field of elementary time-dependent toroidal sources

Abstract: The radiation field of toroidal-like time-dependent current configurations is investigated. The infinitesimal time-dependent configurations are found outside which the electromagnetic strengths disappear but the potentials survive. For a number of time dependences, their finite radiationless counterparts can be found. In these cases topologically non-trivial (unremovable by a gauge transformation) electromagnetic potentials exist outside sources. The well-defined rule obtained for constructing time-dependent infinitesimal sources suggests the existence of finite non-trivial radiationless sources with an arbitrary time dependence. The latter can be used to carry out time-dependent Aharonov-Bohm-like experiments and to transfer the information. Using the Neumann-Helmholtz parametrization of the current density we represent the time-dependent electromagnetic field in a form convenient for applications.

Mass transport in ionic crystals induced by the ponderomotive action of a high-frequency electric field

Abstract: A possible explanation of the experimentally observed enhancement of mass transport processes in ionic crystalline solids under the action of high-frequency (HF) electromagnetic fields is suggested. It is based on the ponderomotive effects that occur due to the nonlinear interaction of the HF electric field with the space charge induced by it within the crystal near its surface. Due to the action of the tangential component of the field in the near-surface amorphized layer, where the vacancy mobility is greater than in the bulk, the ponderomotive effects are found to be of sufficient strength to manifest themselves in the experimental conditions.

Method for detecting, distinguishing and counting objects

Abstract: A method and apparatus for detecting, distinguishing and counting marked objects and particularly marked surgical objects having a marker made of a selected nonmagnetostrictive, soft magnetic material which will emit known specific selected high harmonic frequencies when exposed to an alternating electromagnetic field. That emission will cause a change in the alternating electromagnetic field which can be correlated to the presence of only the selected nonmagnetostrictive, soft magnetic material.

Exponentially convergent and numerically efficient solution of Maxwell’s equations for lamellar gratings

Abstract: A new numerical mathematical method is presented for stack of lamellar gratings. It is based on expansion of the electromagnetic field in terms of the eigenfunctions of the Helmholtz equation. These eigenfunctions are in turn expanded in terms of sets of polynomial basis functions. It is shown that, for arbitrary polarization and for both dielectrics and lossy metals, the eigenvalues and the eigenvectors and, consequently, the spectral location of resonances converge at an exponential rate with increasing dimension of the polynomial basis. For the solution of the boundary-value problem physical arguments are used to derive a new algorithm that is of high numerical accuracy and is inherently stable. Single-precision arithmetic is sufficient, even for the calculation of strong resonances.