Electromagnetic Fields in a Bi-Isotropic Medium Inside and Outside a Metallic Sphere

The problem on an electromagnetic resonator that is a metallic (perfectly conducting) sphere filled with a bi-isotropic medium has been solved. Exact analytic solutions for monochromatic fields inside the sphere and a transcendent condition for the natural frequencies of the resonator have been found. The problem on the scattering of a plane, circularly polarized wave in a bi-isotropic medium at a metallic sphere has also been solved.     

An Exact Solution of the Problem on Dynamics of an Electromagnetic Field in a Cylindrical Resonator with Moving Boundaries

The dynamics of an electromagnetic field in an unsteady cylindrical resonator with perfectly conducting and impedance walls is considered. Exact solutions are found for fields as functions of time. Conservation of photon numbers during the compression is shown.     

Dielectric resonances and B(1) field inhomogeneity in UHFMRI: computational analysis and experimental findings

B(1) Field inhomogeneity and the relative effects of dielectric resonances are analyzed within the context of ultra high field MRI. This is accomplished by calculating the electromagnetic fields inside spherical phantoms and within a human head model in the presence and absence of an RF coil. These calculations are then compared to gradient echo and RARE images, respectively. For the spherical phantoms, plane incident wave analyses are initially presented followed by full wave finite difference time domain (FDTD) calculations. The FDTD methods are then utilized to examine the electromagnetic interactions between the TEM resonator and an anatomically detailed human head model. The results at 340 MHz reveal that dielectric resonances are most strongly excited in objects similar in size to the human head when the conducting medium has a high dielectric constant and a low conductivity. It is concluded that in clinical UFHMRI, the most important determinants of B(1) field homogeneity consist of 1) the RF coil design, 2) the interaction between the RF coil, the excitation source and the sample, and finally 3) the geometry and electrical properties of the sample.     

Non-inertial electromagnetic effects in matter. Gyromagnetic effect

Non-inertial electromagnetic effects in matter, i.e. electromagnetic fields created by a non-inertial motion of material bodies, are discussed within the Drude–Lorentz (plasma) model of matter polarization. It is shown that an oscillatory motion of a point-like body, or wavelike motion in an extended body gives rise to electromagnetic fields with the same frequency as the frequency of the original motion, while shock-like movements of a point-like body generate electromagnetic fields with the characteristic (atomic scale) frequency of the bodies. The polarization of a rigid body induced by rotations is discussed in various circumstances. A uniform rotation produces a static electric field in a dielectric and a stationary current (and a static magnetic field) in a conductor. The latter corresponds to the gyromagnetic effect (while the former may be called the gyroelectric effect). Both fields are computed for a sphere and the gyromagnetic coefficient is derived. A non-uniform rotation induces emission of electromagnetic fields. The equations of motion for the polarization are linearized for slight non-uniformities of the angular velocity and solved both for a dielectric and a conducting sphere. The electromagnetic field emitted by a dielectric spherically shaped body in (a slightly) non-uniform rotation has the characteristic (atomic scale) frequency of the body (slightly shifted by the uniform part of the angular frequency). In the same conditions, a conducting sphere emits an electromagnetic field whose frequency is double the uniform part of the angular frequency.     

Quantum Entropy of Spin Fields in the Schwarzschild-Anti-de Sitter Black Hole with a Global Monopole

The quantum entropies of gravitational, electromagnetic, neutrino and scalar fields in the static Schwarzschild-anti-de Sitter black hole with a global monopole are investigated by using the brick-wall model. The quantum entropy contain two parts: One is quadratically divergent term which takes a geometric character; the other is spin-dependent, logarithmically divergent terms. The whole expression of the entropy of a spin field does not take the form of the scalar field. PACS: 04.70. Dy, 97.60.Lf     

Electromagnetic wave generation in a cylindrical resonator by electrons orbiting in a radial electrostatic field

The mechanisms leading to the generation of microwaves by electrons orbiting in a radial electrostatic field produced by a positively charged filament on the axis of a cylindrical resonator are investigated theoretically. The dispersion relations describing the interaction of the waves with the electrons are obtained. It is shown that the generation of electromagnetic fields is possible on account of both Cherenkov and plasma resonances. The frequencies and growth rates of waves under Cherenkov resonance conditions and also plasma resonance conditions in uniform and nonuniform electron layers are found. The advantages and disadvantages of different generation mechanisms are determined. Zh. Tekh. Fiz. 68, 91–94 (August 1998)     

Plasmonic nanostructures for local field enhancement in the UV region

In this work we describe an ultraviolet subwavelength focusing in plasmonic nanostructures. A system which provides a 20–25 times local field enhancement at a wavelength of 350 nm is proposed. This system represents a metalized V-shaped groove in a surface of a dielectric medium. Subwavelength focusing is achieved by a plasmon wave propagation along the surface of metal film and by the transfer of electromagnetic field through the dielectric medium. The influence of system parameters on a local field enhancement is investigated. A simplified model that allows for determining the geometric parameters of an optimized resonator is proposed.     

Distribution of the electric field and current in a turbulent conducting fluid for small magnetic Reynolds numbers

Various aspects of the influence of an external magnetic field on turbulent flow of a conducting fluid are investigated. The distributions of electric variables are determined for weak magnetic fields (both the electric field and the current have nonzero values in this case). For very strong magnetic fields it is shown that turbulent motion acquires a two-dimensional character. The emergence of an electric current component perpendicular to the flow and to the magnetic field is described in the case of a temperature-stratified medium in the presence of turbulent heat flux. Zh. éksp. Teor. Fiz. 111, 528–535 (February 1997)     

Equations of electrodynamics in a rotating solid dielectric

The equations of electrodynamics in a rotating isotropic homogeneous dielectric are obtained in a covariant form in coordinates of a reference frame that accompanies the rotation of the dielectric. It is found from these equations, which have variable coefficients, that the medium of the rotating dielectric is anisotropic and inhomogeneous. To derive tensors of the electromagnetic field in a rotating reference frame (RRF), the fields and inductions of a virtual inertial reference frame (IRF) that instantaneously accompanies the motion of one of the points of the dielectric are used twice. Initially, using instantaneous local relations, they are expressed in terms of real fields and inductions of the rotating medium, and then they are transformed into fields and inductions of a stationary IRF, in which they are used as components of the tensors of the electromagnetic field. Thus, the electromagnetic field tensors in the IRF are determined taking into account a priori unknown real inhomogeneous permittivity \(\bar \varepsilon \) and permeability \(\bar \varepsilon \) of the rotating medium. At the final stage, the tensors in the RRF are obtained by transformation rules for covariant and contravariant tensor components in accordance with known analytical relationships of fixed and rotating coordinates. The properties of modes of a rotating ring resonator in the form of homogeneous TE waves that travel along and against the direction of rotation and, in particular, their normal frequencies are examined. The contribution of inhomogeneous properties of the medium of a rotating dielectric to the difference between the normal frequencies of the counterpropagating waves (to the Sagnac effect) is determined. In a solid material with known elastic and striction characteristics, its density and dielectric permittivity depend on the radial coordinate. These dependences are caused by the action of the centrifugal force and changes in the polarization and magnetization of the medium because of the rotational motion of charged particles. The coordinate dependences of permittivity \(\bar \varepsilon \) and permeability \(\bar \varepsilon \) make additional contributions to the inhomogeneous properties of the medium of the rotating dielectric and to the Sagnac effect.     

微谐振环结构体内太赫兹增强效应

基于严格电磁场理论,给出了微型谐振环形和Fishnet结构体内太赫兹波的严格表达式,并利用电磁场的边界条件分析了太赫兹波在微型谐振环形和Fishnet结构体内空间分布的增强效应。数值模拟结果表明:谐振环金属条附近的电场大于磁场,金属条附近的电场相对其他区域明显要强得多,开口处表现更为突出,太赫兹波在Fishnet结构体内电磁场的峰位处电场和磁场分布关于x对称;电场的极值出现在大十字架的上下四个角,而磁场的极值则出现在小十字架的上下两端点。同时用电磁场传输线理论对该现象作出一定的物理解释。收稿日期:; 修订日期:     

Whispering gallery modes in a hemispherical isotropic dielectric resonator with a perfectly conducting planar surface

The eigenmodes of a hemispherical dielectric resonator placed on a perfectly conducting planar surface are studied. The resonator is shown to support independent E-and H-type oscillations. For E and H oscillations, the sums n + m of the polar and azimuthal indices are, respectively, even and odd. Accordingly, E and H oscillations exhibit, respectively, n-and (n + 1)-fold frequency degeneracy in azimuthal index m. The distributions of the whispering gallery mode fields on the surface of the hemisphere and on the external conducting plane are obtained. The energy distribution among the eigenmodes with polar index n=36 is studied. The polar angle that corresponds to the maximum of the whispering gallery mode field and the width of the energy localization region in terms of the polar angle are calculated. The number of field variations in the spherical coordinates are correlated with the indices of the resonator’s eigenmodes. The eigenfrequencies and Q factors of the resonator are plotted versus the permittivity of the isotropic environment in the 8-mm wavelength range.     

Homogenization of a set of parallel fibres

Abstract

Rigorous results concerning the possibility of homogenizing a set of parallel fibres are given from the viewpoint of electromagnetic scattering. We deal with the classical time-harmonic Maxwell problem and distinguish the two cases of polarization, i.e. electric field parallel to the fibres (E∥) and magnetic field parallel to the fibres (H∥). Assuming a low density of fibres, we obtain, in the E∥ case, an effective medium with a possibly negative permittivity, whereas in the H∥ case the fibres disappear completely. On the other hand, for a high density of fibres, the E∥ case leads to a perfectly conducting medium and the H∥ case to a dielectric medium with a surface current on its boundary.     

Generation of electromagnetic waves by a rotating plasma

Generation of electromagnetic waves by an annular shell of plasma rotating in crossed radial electrostatic and axial magnetic fields in a cylindrical resonator is investigated theoretically. Dispersion relations are obtained describing the interaction of the waves with the plasma. It is shown that generation of waves by a narrow plasma shell is possible due to a cyclotron resonance, Čerenkov resonance, or plasma resonance. Here we consider a Čerenkov resonance, where the velocities of the plasma components and the phase velocities of the waves are perpendicular to the constant magnetic field. The frequencies and growth rates of the waves are found under conditions of the above-mentioned resonances in a uniform and in a nonuniform plasma shell. Advantages and disadvantages of wave generation under various conditions are noted. Zh. Tekh. Fiz. 69, 16–21 (February 1999)     

Studying surface vortices and potential fields in a conducting cylinder

The surface electromagnetic waves in a conducting cylinder are studied with allowance for the different polarization properties of a medium with respect to potential and vortex electromagnetic fields.     

Generation of electromagnetic waves by relativistic electrons in a cavity with crossed radial electrostatic and axial magnetic fields under plasma resonance conditions

A theoretical analysis is made of the conditions for generation of electromagnetic waves by a thin cylindrical layer of relativistic electrons rotating in crossed axial magnetic and radial electrostatic fields in a cylindrical cavity. A dispersion equation is obtained to describe the interaction between waves and electrons under plasma resonance conditions. The dependence of the growth rates on the relativistic factor and the magnetic field are studied. Zh. Tekh. Fiz. 69, 112–114 (June 1999)     

Spinor Relativity

Spinor relativity is a unified field theory, which derives gravitational and electromagnetic fields as well as a spinor field from the geometry of an eight-dimensional complex and ‘chiral’ manifold. The structure of the theory is analogous to that of general relativity: it is based on a metric with invariance group GL(ℂ²), which combines the Lorentz group with electromagnetic U(1), and the dynamics is determined by an action, which is an integral of a curvature scalar and does not contain coupling constants. The theory is related to physics on spacetime by the assumption of a symmetry-breaking ground state such that a four-dimensional submanifold with classical properties arises. In the vicinity of the ground state, the scale of which is of Planck order, the equation system of spinor relativity reduces to the usual Einstein and Maxwell equations describing gravitational and electromagnetic fields coupled to a Dirac spinor field, which satisfies a non-linear equation; an additional equation relates the electromagnetic field to the polarization of the ground state condensate.     

Superconducting resonator in strong microwave fields: Thermal domain, nonlinear thermal effects

The thermal nonlinearity of superconducting films in an electromagnetic field is investigated theoretically. It is shown that the transition of the superconductor from the superconducting to the normal state as a result of Joule heating exhibits hysteresis, corresponding to the onset of a bistable state in the film. It is shown that as a result of the nonuniformity of the amplitude of the electromagnetic field along the surface of the superconducting film, above some threshold a normal-phase domain forms in the superconductor. It is ascertained that the temporal evolution of the domain walls exhibits the character of thermal autowaves of heating or cooling. The nonlinear radio-frequency characteristics (reflection and transmission coefficients and frequency responses) of a stripline resonator under conditions of thermal nonlinearity are calculated. Zh. Tekh. Fiz. 67, 81–89 (October 1997)     

Effect of background plasma on electromagnetic properties of coaxial gyrotron cavity

We analyze the effect of the background plasma on the electromagnetic properties of coaxial resonators with a smooth and a corrugated inner conductors used in high-power gyrotrons. It is shown that the plasma produces different effects on the modes with different signs of the azimuthal index, leading to a decrease or an increase in the resonance frequencies. A modification of the distributions of electromagnetic fields and the electromagnetic energy density by the background plasma occurs in such a way that Ohmic losses decrease both on the inner and on the outer conductors. In the case of a smooth inner conductor, this is due to a decrease in the field strengths on the surface of the conductors. If the inner conductor is corrugated, the background plasma leads to an increase in the field strengths on its surface. Nevertheless, the relative Ohmic loss power decreases due to an increase in the energy density in the resonator (which is also caused by the background plasma). Calculations were mainly performed for a coaxial resonator of a gyrotron operating on the TE34.19 mode (Karlsruhe, Germany).     

Effect of the spectral profile of a deriving field on the bistability of a dissipative medium

 Through the differential equation describing the behavior of the nonlinear polarization of a medium with respect to an incident field, the Maxwell field equations and the boundary conditions of the field inside a resonator, the relationship between the output and the incident fields is obtained, describing a bistability phenomena. The effect of the spectral profile of the incident field and its spectral halfwidth on the bistability phenomena is studied.     

Amplification of light during the scattering of a relativistic electron by a nucleus in a moderately strong field of a circularly polarized light wave

The amplification (attenuation) factor of an electromagnetic wave during the scattering of a relativistic electron by a nucleus in a moderately strong field of a circularly polarized electromagnetic wave is studied theoretically. The effect of amplification of an electromagnetic field is discovered in a certain interval of polar angles of the incident electron; this interval of angles essentially depends on the electron energy and the field intensity. It is shown that the amplification of a field attains its maximum for nonrelativistic electrons in the range of medium fields. As the electron energy increases, the amplification decreases and vanishes for ultrarelativistic electrons. An increase in the field intensity for a given electron energy also leads to a slow decrease in the amplification of a field. At high intensities of the wave, the effect of amplification vanishes. It is shown that, in the range of optical frequencies for medium fields (F ～ 10⁶V/cm), the amplification factor of laser light may amount to about μ ～ 10^?1 cm^?1 for sufficiently high-power electron beams.