Showing papers on "Electromagnetic field published in 1970"

Electromagnetic fields and waves

Abstract: Electromagnetic fields and waves , Electromagnetic fields and waves , کتابخانه دیجیتال جندی شاپور اهواز

Quantum Theory of the Electromagnetic Field in a Variable-Length One-Dimensional Cavity

Abstract: The quantum theory of linearly polarized light propagating in a 1‐dimensional cavity bounded by moving mirrors is formulated by utilizing the symplectic structure of the space of solutions of the wave equation satisfied by the Coulomb‐gauge vector potential. The theory possesses no Hamiltonian and no Schrodinger picture. Photons can be created by the exciting effect of the moving mirrors on the zero‐point field energy. A calculation indicates that the number of photons created is immeasurably small for nonrelativistic mirror trajectories and continuous mirror velocities. Automorphic transformations of the wave equation are used to calculate mode functions for the cavity, and adiabatic expansions for these transformations are derived. The electromagnetic field may be coupled to matter by means of a transformation from the interaction picture to the Heisenberg picture; this transformation is generated by an interaction Hamiltonian.

Nonlinear effects in quantum electrodynamics. photon propagation and photon splitting in an external field.

Abstract: The effective nonlinear Lagrangian derived by Heisenberg and Euler is used to describe the propagation of photons in slowly varying but otherwise arbitrary electromagnetic fields. The group and the phase velocities for both propagation modes are calculated, and it is shown that the propagation is always causal. The photon splitting processes are also studied, and it is shown that they do not play any significant role even in very strong magnetic fields surrounding neutron stars.

The propagation of electromagnetic energy through an absorbing dielectric

Abstract: The energy associated with an electromagnetic wave passing through a dielectric resides partly in the electromagnetic field and partly in the accompanying excitation of the dielectric. The theory of energy propagation through an absorbing classical dielectric having a single resonant frequency is presented in this paper. Simple expressions are derived for the velocity of energy transport associated with an electromagnetic wave, and for the finite energy relaxation time caused by the damping mechanism. The variations of these quantities, and of the absorption coefficient, with the relative values of the damping constant and dipole moment of the classical oscillator are investigated. This information is used to throw light on the basic mechanism of irreversible dissipation of energy by an electromagnetic wave in a dielectric. The similarities between the calculations of the dielectric constant by classical dispersion theory and by quantum mechanics are discussed.

Transmission through a Conducting Screen Perforated Periodically with Apertures

Abstract: A general solution to the problem of determining first the aperture field distribution and then the transmission and reflection coefficients of an infinite planar conducting sheet perforated periodically with apertures has been formulated. The excitation is considered to be a plane wave incident at any arbitrary angle. The aperture dimensions and array element spacings were assumed to be comparable with the wavelength of the incident electromagnetic field. The solution given can include the effect of a dielectric slab used to support the thin conducting sheet. The solution is obtained by matching the tangential field components at the surface of the screen. The resulting integral equation is solved by the method of moments which reduces the integral equation to a system of linear algebraic equations that can be solved with the use of a digital computer. Accurate results for both the magnitude and phase of the aperture field distribution and the transmission coefficients for the propagating modes are determined explicitly for a specific example of slots arranged in an equilateral triangular lattice. The balance of power flow between the reflected and the transmitted waves has been checked with satisfactory results. The solution can be applied to the problem of scattering from a conducting screen with periodic apertures and to the complementary problem of scattering from a set of conducting plates by the use of Babinet's principle.

Electromagnetic fields and life

Abstract: One Physical Principles and Experimental Methods of Investigation of the Biological Action of Electromagnetic Fields.- 1. Physical Characteristics of Electromagnetic Fields.- Chapter2. Natural and Artificial Sources of Electromagnetic Fields in the Habitats of Organisms.- 3. Electric Properties of the Tissues of Living Organisms.- 4. Physical Principles of the Interaction of Electromagnetic Fields with Biological Objects.- 5. Dosimetry of Electromagnetic Fields for the Assessment of Their Effects on Man and Animals.- Two Experimental Investigations of the Biological Action of Electromagnetic Fields.- 6. Irreversible and Permanent Effects of Electromagnetic Fields in Entire Organisms.- 7. Effect of Electromagnetic Fields on Neurohumoral Regulation in Entire Organism.- 8. Effect of Electromagnetic Fields on Reproduction and Development of Organisms.- 9. Effects of Electromagnetic Fields at the Cellular and Molecular Levels.- 10. Mechanisms of the Experimentally Observed Biological Effects of Electromagnetic Fields.- Three Role of Electromagnetic Fields in the Regulation of the Vital Activity of Organisms.- 11. Environmental Electromagnetic Fields and the Vital Activity of Organisms.- 12. Electromagnetic Fields within the Organism and Their Role in the Regulation of Vital Processes.- 13. Role of Electromagnetic Fields in Informational Interconnections between Organisms.- 14. Practical Applications.- Conclusion.- References.

Coherent states and transition probabilities in a time dependent electromagnetic field

Abstract: New time-dependent invariants for the $N$-dimensional nonstationary harmonic oscillator and for a charged particle in a varying axially symmetric classical electromagnetic field are found. For these quantum systems, coherent states are introduced, and the Green's functions are obtained in closed form. For a special type of electromagnetic field which is constant in the remote past and future, the transition amplitudes between both arbitrary coherent states and energy eigenstates are calculated and expressed in terms of classical polynomials. The adiabatic approximation and adiabatic invariants are discussed. In the special case of a particle with time-dependent mass, the solution of the Schr\"odinger equation is found. The symmetry of nonstationary Hamiltonians is discussed, and the noncompact group $U(N, 1)$ is shown to be the group of dynamical symmetry for the time-dependent $N$-dimensional oscillator.

Numerical Solution of Dielectric Loaded Waveguides: I-Finite-Element Analysis

Abstract: A variational expression of the electromagnetic fields in dielectric loaded waveguides is derived This expression is discretized using the finite-element method and an electromagnetic coupling matrix is derived and evaluated No restriction is placed on the shapes of the triangular elements or the order of the polynomial approximation A general finite-element computer program is described and dispersion curves and field plots of some dielectric loaded waveguides are presented

Spherically symmetric radiation of charge in Einstein-Maxwell theory

Abstract: We give solutions of the Einstein-Maxwell equations describing the emission of charged null fluid from a spherically symmetric body. The electromagnetic field is parallel to the direction of energy propagation, is of orderr −2 at infinity and is not null.

Theory of plasma simulation using finite-size particles.

Abstract: The elementary properties of a plasma, in which the small‐separation force is smoothed from the Coulomb force, are developed. The modification is considered as being produced by spreading out the charge distribution of a particle to make a particle of finite size R (cloud). These clouds move freely through one another and interact through normal electromagnetic fields. A method to adapt point‐particle results for plasma oscillations, shielding, fluctuations, and collisions, is shown, and the modifications to these plasma properties discussed in detail. The relevance of these considerations to computer simulation of plasmas (in which some smoothing is a consequence of the numerical methods used and additional smoothing is sometimes added) is discussed. It is found that smoothing the short wavelength interaction can be used without destroying the desired physics, while suppressing collisional effects and noise at wavelengths < R which are exaggerated in simulation due to the use of far fewer particles than in a real plasma.

Group-theoretical analysis of elementary particles in an external electromagnetic field II.—The nonrelativistic particle in a constant and uniform field

Abstract: Two subgroups of the Galilei group are shown to play a particular role in the case of charged systems in an external electro-magnetic field which is constant and uniform. Projective representations of these subgroups involve the electric charge and mass as generators of phase factors. Additivity and superselection rules for charge and mass appear as direct consequences. A comparison is made with the relativistic case investigated in the first part of this article.

Field-correlation effects in multiphoton absorption processes.

Abstract: The dependence of the multiphoton absorption probability for an atomic system on the statistical properties of the incident light is investigated. It is shown, by means of nth-order time-dependent perturbation theory, that the multiphoton absorption probability depends on the (n, n)th normally ordered correlation functions of the electromagnetic field. For stationary fields, the transition probability per unit time is constant and is directly related to the reduced cross-spectral correlation function of the electromagnetic field. This expression for the transition probability is then analyzed under various conditions of coherence. Explicit calculations are carried out for thermal light and for laser light, and the transition rates are compared when each has a Lorentzian spectrum. In particular, when the width of the final atomic level is much larger than the bandwidth of the field, the transition rate for thermal light is n! times higher than with laser light of the same mean intensity. The other extreme case, i.e., when the width of the final atomic level is much smaller than the bandwidth of the field, is also considered in detail. An equation for the density operator of the field is derived; this equation governs the change in the statistical properties of the photon system in n-photon absorption processes. On the basis of this equation, the time-dependent properties of the photon system are then studied and some physical consequences of these equations are discussed. Some numerical solutions relating to the time dependence of the factorial moments in two-photon absorption processes are presented.

Inductively coupled passive responder and interrogator unit having multidimension electromagnetic field capabilities

Abstract: An interrogator-responder system wherein the responder is a passive responder receiving an inductively coupled electromagnetic power field from an interrogator unit and generating an unique predetermined electromagnetic coded information field in response to the presence of the electromagnetic power field The interrogator unit has multidimensional recognition capabilities for detecting the electromagnetic coded information field independent of the orientation of the responder for two dimensional or three dimensional capabilities

Quantum electrodynamics of spinless particles between conducting plates

Abstract: The energy of any system containing charged particles arises partly from its coupling to the quantized electromagnetic field; it changes on inserting the system between conducting plates, because these alter the normal modes of the field relative to free space. We calculate to order e2 such energy shifts for a free electron and for a hydrogen atom, neglecting spin, but allowing in full for electrostatic and retardation corrections as well as for changes in the Lamb shift proper. The potential between a particle and a single plate follows as a limiting case. An appendix details the distinction between classical and quantum effects.

H. A. Lorentz and the Electromagnetic View of Nature

Abstract: AN ELECTROMAGNETIC VIEW OF NATURE was announced at the beginning of the twentieth century. It drew influential followers from among younger physicists, those in Germany especially, and for a time it was widely regarded as the most promising projection of the future of physical theory. It was advocated as a replacement for the mechanical view of nature that had ably guided physical research for more than two centuries. The mechanical view asserted that the ultimate constituents of physical reality are discrete or, sometimes, continuous inertial masses, and that they move according to the laws of mechanics under the influence of distance or contact forces. The electromagnetic view of nature asserted that the only physical realities are the electromagnetic ether and electric particles and that all laws of nature are reducible to properties of the ether, properties which are defined by the electromagnetic field equations. The simplest version of the electromagnetic view held that electric particles are merely structures in the ether and that therefore the ether is the sole reality. The Lorentz electron theory together with the empirical confirmation of the electron and the evolution of techniques for directly testing electron dynamics led to the anticipation of a purely electromagnetic understanding of physical reality. The electromagnetic view expressed a programmatic intent in physics: it called for a concentration of effort on problems whose solution promised to secure a universal physics based solely on electromagnetic laws and concepts. The feasibility of the program depended critically on the successful reduction of mechanical concepts and laws to electromagnetic analogues. Problems concerning the stability and deformability of the electron and its dynamic relation to the electromagnetic field acquired an enhanced importance and priority by being intimately related to the larger reduction problem.

Electromagnetic fields about a loop source of current

Abstract: Integral expressions for the electromagnetic field components produced by a horizontal loop, carrying a current Ieiωt and placed on or above the surface of an n‐layered half‐space, are deduced in a form such that numerical integration can be performed easily. The expressions are free of approximations and completely general for all frequencies. They are constrained only to the uniformity of current around the transmitting loop. The resulting computed electromagnetic fields are valid for arbitrary values of the electrical parameters σ, μ, and e. The quasi‐static approximation for the region above the half‐space, wherein the wave equation is replaced by the Laplace equation, can be avoided. Measurements outside the loop constitute induction depth sounding. Induction depth sounding curves of field components and magnetic polarization parameters show good resolution of subsurface layering. In particular, it is suggested that the measurements of tilt angle and/or ellipticity of the magnetic polarization ellips...

Conversion of photons into gravitons and vice versa in a static electromagnetic field

Abstract: Production of gravitational waves by photons incident on a static electromagnetic field as well as the production of photons by gravitational waves incident on a static electromagnetic field are studied. The possibility of using these results for the detection of gravitational waves is also examined.

The two-dimensional inverse scattering problem

Abstract: It is demonstrated that the knowledge of the incident field and the scattered far fields at one frequency may be employed to determine the size, shape, and location of a perfectly conducting scatterer. The reconstruction of the scattering body is accomplished via an analytic continuation procedure that generates the fields in the neighborhood of the scatter from the specified far-field distribution. The geometry of the body is then determined by locating a closed surface for which the total tangential electric field, i.e., the sum of the tangential components of the incident and scattered field, is zero. Whereas exact knowledge of the entire far field is sufficient to determine the scatterer, a technique is also given for size and shape determination when only part of the far field is available. Numerical examples of several different geometries are given for ranges of ka (a the largest dimension of the body) from 0.2 to 10. Geometries considered were elliptic and circular cylinders, conducting strips, and two cylinders. Plots of the fields reconstructed from the far-field data are compared to the known solutions, and the accuracy of the procedure is demonstrated. The effects of noise in the far-field pattern is also considered, and it is shown that even with noise levels of -20 dB the scattering geometry can be recovered.

Homogeneous Electromagnetic and Massive Vector Meson Fields in Bianchi Cosmologies

Abstract: Maxwell equations and equations of massive-vector- meson fields in spatially homogeneous Bianchi cosmologies, obtaining formula for homogeneous EM field

Electromagnetic Fields in a Dissipative Half‐Space: A Numerical Approach

Abstract: The electromagnetic fields of a source in a dissipative half‐space are evaluated by a numerical technique. This report illustrates the application of the method to the case of the submerged horizontal electric dipole, but the method is applicable to horizontal or vertical dipoles located in either medium. The major advantage of this method is that it provides solutions for media and frequencies which were previously unavailable. In addition, this numerical solution can independently verify previously obtained asymptotic solutions and their regions of validity. Comparisons are included between numerical results and experimental measurements performed in the Atlantic Ocean.

Response to Double Irradiation of a Nuclear Spin System: General Treatment and New Multiple Quantum Transitions

Abstract: A general theory has been developed to calculate the response, in NMR conditions, of a spin system irradiated by two nearly resonant waves having different frequencies and intense enough to produce an appreciable saturation. The absorption signal has been calculated employing the statistical operator technique, treating the electromagnetic field by the second quantization formalism. Two kinds of transitions are expected: The first one arises from processes in which n photons of one wave are emitted and n photons of the other wave are absorbed, the second one arises from processes involving the emission of n photons of one wave and the absorption of n ± 1 photons of the other. In the first case all the transitions coalesce in a single dispersionlike signal, which occurs when the frequencies of the two waves are nearly the same; in the second case a many‐line spectrum occurs in which emission and absorption lines are present. The experimental results here reported strictly agree with theoretical previsions.

Evaluation of the measurement of induced electrical polarization with an inductive system

Abstract: The induced polarization (IP) technique is based on the observation that variations of earth conductivity with frequency may be indicative of buried metallic mineralization. Conventional IP involves the use of grounded electrodes, the installation of which can be quite time consuming. However, the electromagnetic fields about an oscillating magnetic dipole also depend on ground conductivity. Thus, it is conceivable that we might be able to detect IP anomalies with an inductive system, thereby eliminating the need for grounded electrodes. An airborne induced polarization method is a theoretical possibility.Theoretical calculations based on a conductivity model determined experimentally at frequencies less than 30 hz suggest that the effect of polarizable material on electromagnetic response is quite small.In order to check the theory and to determine experimentally whether inductive IP is feasible, field tests were conducted in two areas in Nevada which exhibit strong conventional IP anomalies. The field tests consisted of measurements of the amplitudes of the electric and magnetic fields about a horizontal loop of wire carrying current at frequencies ranging from 15 hz to 1500 hz. The presence of the polarizable material is not evident in the inductive data; in fact, the observations can be fitted to theoretical curves for nonpolarizable models.Hence, on the basis of both theory and field tests, it is concluded that inductive IP based on amplitude measurements is not a practical exploration tool for environments such as that of the southwestern United States.

Penetration of an electromagnetic wave into a hot plasma slab.

Abstract: The penetration of a small‐amplitude high‐frequency electromagnetic wave into a plasma slab is calculated making allowance for the thermal motion of electrons. For low collision rates the electromagnetic field distribution in the plasma is strongly dependent on the ratio of the wave period to the transit time of electrons crossing the slab.

Variation of the Luminescence Lifetime of a Molecule near an Interface between Differently Polarizable Dielectrics

Abstract: IN a recent paper1 the energy transfer from an excited molecule S to an acceptor A was considered as a retardation effect. In classical terms, the field of S induces A to oscillate and the induced field of A, arriving at S, slows down this oscillator. This effect may be studied, too, without A being an absorber, but simply a polarizable molecule, oscillating in phase with the radiation field of S at the location of A. Then the field which is produced by A and acting at S accelerates or slows down this oscillator depending on the phase relation to its motion; thus the decay time of the luminescence of S will be prolonged or shortened. This phase relation depends on the time needed for the propagation of the electromagnetic field from S to A and from A to S.