Radiation of an Electric Dipole from a Small Plasma Spheroid

We obtain and analyze an analytical solution of the boundary-value problem of the field of an electric dipole located in a small spheroid filled with a cold isotropic plasma. The conditions of resonant amplification of the field in vacuum are studied for various shapes and curvatures of the plasma spheroid. It is shown that for a certain spheroid shape, the resonant amplification increases several times compared with the case of spherical plasma environment. The obtained results are compared with the resonant radiation of a dipole from a narrow elliptical plasma cylinder.     

Electromagnetic field created by a dipole oscillator in an anisotropic medium

General expressions in a covariant form for the fields created by arbitrary oriented electric and magnetic dipole oscillators in an anisotropic medium are obtained. As a simple application, a cold plasma is considered. The near zone and resonance cones are investigated as limit cases.     

Magnetic monopole-like response in metamaterials

In this paper, we explored magnetic monopole-like responses in metamaterials. We designed a sub-wavelength metamolecule that is composed of two dielectric-spaced split-ring resonators. In response to incident waves, the induced magnetic field in the metamolecule resembles that of a two-dimensional magnetic monopole. The magnetic monopole-like response is resulted from electric resonance of the metamolecule, so an electric dipole is always attached. By combining two mirror-symmetric metamolecules with inward and outward radial magnetic fields, magnetic dipole-like responses can be produced just as an electric dipole is formed by separating two opposite-signed electric charges.     

Analytic solutions to Maxwell–London equations and levitation force for a general magnetic source in the presence of a long type-II superconducting cylinder

The interaction between a general magnetic source and a long type-II superconducting cylinder in the Meissner or mixed state is studied within the London theory. We first study the Meissner state and solve the Maxwell–London equations when the source is a magnetic monopole located at an arbitrary position. Then the field and supercurrent for a more complicated magnetic charge distribution can be obtained by superposition. A magnetic point dipole with arbitrary direction is studied in detail. It turns out that the levitation force on the dipole contains in general an angular as well as a radial component. By integration we obtain the field and supercurrent when the source is a two-dimensional monopole (a magnetically charged long thread along the axial direction), from which the results for a two-dimensional point dipole easily follow. In the latter case the levitation force points in the radial direction regardless of the orientation of the dipole. The case for a current carrying long straight wire parallel to the cylindrical axis is solved separately. The limit of ideal Meissner state is discussed in most cases. The case of mixed state is discussed briefly. It turns out that vortex lines along the axial direction and vortex rings concentric with the cylinder have no effect outside the cylinder and the levitation forces remain the same as in the case of the Meissner state.     

Propagation of terahertz waves in nonuniform plasma slab under "electromagnetic window"

The application of magnetic fields, electric fields, and the increase of the electromagnetic wave frequency are up-and-coming solutions for the blackout problem. Therefore, this study considers the influence of the external magnetic field on the electron flow and the effect of the external electric field on the electron density distribution, and uses the scattering matrix method (SMM) to perform theoretical calculations and analyze the transmission behavior of terahertz waves under different electron densities, magnetic field distributions, and collision frequencies. The results show that the external magnetic field can improve the transmission of terahertz waves at the low-frequency end. Magnetizing the plasma from the direction perpendicular to the incident path can optimize the right-hand polarized wave transmission. The external electric field can increase the transmittance to some extent, and the increase of the collision frequency can suppress the right-hand polarized wave cyclotron resonance caused by the external magnetic field. By adjusting these parameters, it is expected to alleviate the blackout phenomenon to a certain extent.     

Selected aspects of the quantum dynamics and electronic structure of atoms in magnetic microtraps

We analyze the quantum properties of atoms in a magnetic quadrupole field. The quantum dynamics of ground state atoms in this field configuration is studied firstly. We formulate the Hamiltonian and perform a symmetry analysis. Due to the particular shape of the quadrupole field in general there exist no stable states. We provide resonance energies, lifetimes and calculate the density of states and investigate under what conditions quasi-bound states occur that possess long lifetimes. An effective scalar Schrödinger equation describing such states is derived. As a next step we explore the influence of a high gradient quadrupole field on the electronic structure of excited atoms. An effective one-body approach together with the fixed nucleus approximation is employed in order to derive the electronic Hamiltonian. We present the energy spectrum and discuss peculiar features such as non-trivial spin densities and magnetic field induced electric dipole moments.     

All-dielectric left-handed metamaterial based on dielectric resonator: design, simulation and experiment

Dipoles with Lorentz-type resonant electromagnetic responses can realise negative effective parameters in their negative resonant region. The electric dipole and magnetic dipole can realise, respectively, negative permittivity and negative permeability, so both the field distribution forms of electric and magnetic dipoles are fundamentals in designing left-handed metamaterial. Based on this principle, this paper studies the field distribution in high-permittivity dielectric materials. The field distributions at different resonant modes are analysed based on the dielectric resonator theory. The origination and influence factors of the electric and magnetic dipoles are confirmed. Numerical simulations indicate that by combining dielectric cubes with different sizes, the electric resonance frequency and magnetic resonance frequency can be superposed. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial composed by this means.     

Electromagnetic field perturbation by an internal void in a conducting cylinder excited by a wire loop

A thin prolate spheroidal void in an infinite conducting circular cylinder is used to model an internal flaw in a wire rope. The rope is excited by an electric ring current which is a model for a thin solenoid or multi-turn wire loop. The anomalous external fields are computed from the induced electric and magnetic dipole moments of the void. For this type of excitation, the induced axial magnetic dipole moment is the dominant contributor to the scattered field. The results have application to nondestructive testing of wire ropes.     

DC column plasma kinetics in a longitudinal magnetic field

The cylindrical column plasma of a neon dc glow discharge under the influence of a weak longitudinal magnetic field is studied. An extended, fully self-consistent model of the column plasma has been used to determine the kinetic quantities of electrons, ions and excited atoms, the radial space charge field, and the axial electric field for given discharge conditions. The model includes a nonlocal kinetic treatment of the electrons by solving their spatially inhomogeneous kinetic equation, taking into account the radial space charge field and the axial magnetic field. The treatment is based on the two-term expansion of the velocity distribution and comprises the determination of its isotropic and anisotropic components in the axial, radial, and azimuthal direction. A transition from a distinctly nonlocal kinetic behavior of the electrons in the magnetic-field-free case to an almost local kinetic behavior has been found by increasing the magnetic field. The establishment of the electron cyclotron motion around the column axis increasingly restricts the radial electron energy transport and reduces the radial ambipolar current. The complex interaction of these transport phenomena with the alterations in the charge carrier production leads finally to a specific variation of the electric field components. The axial field increases by applying weak magnetic fields, however, decreases with increasingly higher magnetic fields. At higher magnetic fields, the radial space-charge field is considerably reduced     

Effective medium representation and complex modes in 3D periodic metamaterials made of cubic resonators with large permittivity at mid-infrared frequencies

We review some of the techniques that lead to the effective medium representation of a three-dimensional (3D) periodic metamaterial. We consider a 3D lattice of lead telluride cubic resonators at mid-infrared (MIR) frequencies. Each cubic resonator is modeled with both an electric and a magnetic dipole, through a method called the dual dipole approximation. The electric and magnetic polarizabilities of a cubic resonator are computed via full-wave simulations by mapping the resonator's scattered field under electric/magnetic excitation only to the field radiated by an equivalent electric/magnetic dipole. We then analyze the allowed modes in the lattice, with transverse polarization and complex wavenumber, highlighting the attenuation that each mode experiences after one free space wavelength. We observe the presence of two modes with low attenuation constant, dominant in different frequency ranges, able to propagate inside the lattice: this allows the treatment of the metamaterial as a homogeneous material with effective parameters, evaluated by using various techniques. We then show that the metamaterial under analysis allows for the generation of artificial magnetism (i.e., relative effective permeability different than unity, including negative permeability with low losses) at MIR frequencies.     

电偶极子在磁各向异性介质中的辐射功率

在经典电动力学框架下对磁各向异性介质中的电磁辐射问题进行研究, 得到了电偶极子在磁各向异性介质中的辐射功率表达式. 当介质为磁各向同性时其结果与文献报道的结果相符合, 验证了推导结果的正确性. 利用本文结果可对电偶极子在磁各向异性介质中的辐射效果做出判断, 而且对于进一步研究磁各向异性介质的电磁特性、更有效地开发利用磁各向异性介质具有实际意义.     

Computation of far radiation field of an arbitrarily oriented dipole above layered anisotropic half space

Based on the reciprocity theorem, the far field formulation of an arbitrarily oriented electric dipole located at the interface of layered anisotropic half space is deduced. Then, considering the optical path difference of the direct wave and reflected wave, the formulation of the electric dipole located above the interface of layered anisotropic half space is discussed, and the transmission matrix method for computing the reflection coefficients of anisotropic layered half space is introduced in detail. Finally, numerical examples of the field produced by an electric dipole located above layered anisotropic half space are given. The numerical results show that this method can be used in the fast computation of far radiation field of an arbitrarily oriented dipole above layered anisotropic half space.     

Efficiency of the structure analysis of complex molecules in the gas phase by their optical rotation

It was shown in the dipole approximation of optical rotation that in the general case only in orientationally anisotropic vapors is the rotational force dependent on the intramolecular orientation of both the electric and magnetic dipole moments. Expressions relating the optical rotational force to the intramolecular orientation of these moments, the orientational distribution in an anisotropic ensemble, and the configuration of a measurement have been obtained. Calculated dependences of the rotational force on the intramolecular orientation of the magnetic moment at a fixed electric moment and “rotational force excitation spectra” obtained for different types of rigid asymmetric top molecules and rotational contours are presented. It is proposed to measure the intramolecular orientation of the electric and magnetic dipole moments with the use of the rotational force normalized to that detected in the case of observation at a “magic” angle to the direction of the exciting light electric vector. Institute of Molecular and Atomic Physics of the Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 6, pp. 843–849, November–December, 1998.     

Electromagnetic analysis of cylindrical invisibility cloaks and the mirage effect

We present a finite-element analysis of a diffraction problem involving a coated cylinder enabling the electromagnetic cloaking of a lossy object with sharp wedges located within its core. The coating consists of a heterogeneous anisotropic material deduced from a geometrical transformation as first proposed by Pendry [Science 312, 1780 (2006)]. We analyze the electromagnetic response of the cloak in the presence of an electric line source in p polarization and a loop of magnetic current in s polarization. We find that the electromagnetic field radiated by such a source located a fraction of a wavelength from the cloak is perturbed by less than 1%. When the source lies in the coating, it seems to radiate from a shifted location.     

Tailoring magnetic and electric resonances with dielectric nanocubes for broadband and high-efficiency unidirectional scattering

The interference of optically induced electric and magnetic resonances in high-refractive-index dielectric nanoparticles provides a new approach to control and shape the scattering patterns of light in the field of nanophotonics. In this Letter, we spectrally tune the electric and magnetic resonances by varying the geometry of a single isolated lead telluride(Pb Te) dielectric nanocube. Then, we overlap the electric dipole resonance and magnetic dipole resonance to suppress backward scattering and enhance forward scattering in the resonance region.Furthermore, a broadband unidirectional scattering is achieved by structuring the dielectric nanocuboids as a trimer antenna.     

Paraelectricity in magnetized massless QED

We show that the chiral-symmetry-broken phase of massless QED in the presence of a magnetic field exhibits strong paraelectricity. A large anisotropic electric susceptibility develops in the infrared region, where most of the fermions are confined to their lowest Landau level, and dynamical mass and anomalous magnetic moment are generated via the magnetic catalysis mechanism. The nonperturbative nature of this effect is reflected in the dependence of the electric susceptibility on the fine-structure constant. The strong paraelectricity is linked to the electric dipole moments of the particle-antiparticle pairs that form the chiral condensate. The significant electric susceptibility can be used as a probe to detect the realization of the magnetic catalysis of chiral symmetry breaking in physical systems.     

Effective material parameter retrieval for thin sheets: Theory and application to graphene,thin silver films,and single-layer metamaterials

An important tool in the field of metamaterials is the extraction of effective material parameters from simulated or measured scattering parameters of a sample. Here we discuss a retrieval method for thin-film structures that can be approximated by a two-dimensional scattering sheet. We determine the effective sheet conductivity from the scattering parameters and we point out the importance of the magnetic sheet current to avoid an overdetermined inversion problem. Subsequently, we present two applications of the sheet retrieval method. First, we determine the effective sheet conductivity of thin silver films and we compare the resulting conductivities with the sheet conductivity of graphene. Second, we apply the method to a cut-wire metamaterial with an electric dipole resonance. The method is valid for thin-film structures such as two-dimensional metamaterials and frequency-selective surfaces and can be easily generalized for anisotropic or chiral media.     

Anisotropic behaviour of the faraday rotation in erbium iron garnet

Faraday rotation (FR) measurements performed on single crystals Erbium Iron Garnet (ErIG) at 1.15 μm wavelength are presented in a magnetic field up to 20 kOe applied along the three main crystallographic directions. Spontaneous FR and FR susceptibilities are found to be anisotropic. The results are discussed in terms of electric and magnetic dipole transitions and compared to the magnetic anisotropy. A strong anisotropy of the first order electric dipole coefficient of the Er³⁺ ion is evidenced at low temperature (below 30 K).     

Field of an Electric Dipole Surrounded by a Small Plasma Spheroid with a Cavity

We obtain and analyze a solution of the boundary-value problem for the field of an electric dipole centered in a vacuum cavity inside a small plasma spheroid. The influence of the cavity size on the field enhancement in an outer vacuum region is analyzed as a function of the curvature of the plasma-spheroid surface. The results are compared with the case of a sphere with similar cavity.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 2, pp. 142–151, February 2005     

Magnetic-field-induced insulator-conductor transition in SU(2) quenched lattice gauge theory

We study the correlator of two vector currents in quenched SU(2) lattice gauge theory with a chirally invariant lattice Dirac operator with a constant external magnetic field. It is found that in the confinement phase the correlator of the components of the current parallel to the magnetic field decays much slower than in the absence of a magnetic field, while for other components the correlation length slightly decreases. We apply the maximal entropy method to extract the corresponding spectral function. In the limit of zero frequency this spectral function yields the electric conductivity of quenched theory. We find that in the confinement phase the external magnetic field induces nonzero electric conductivity along the direction of the field, transforming the system from an insulator into an anisotropic conductor. In the deconfinement phase the conductivity does not exhibit any sizable dependence on the magnetic field.