Excitation Of Electromagnetic Waves Research Articles

The single-wall carbon nanotube waveguides and excitation of their σ+π plasmons by an electron beam

By using the linearized two-fluid quantum hydrodynamic model for σ and π orbitals, the dispersion relations of electromagnetic waves in the single-walled carbon nanotubes are investigated. By injection of a relativistic electron beam, the excitation of electromagnetic waves in this system is studied. The graphs of operating frequency with respect to the accelerating voltage and time growth rate with respect to the wave number for excitation of slow electric mode waves (transverse magnetic mode waves) are presented.

ELECTROMAGNETIC RADIATION FROM SOURCES EMBEDDED IN A CYLINDRICALLY STRATIFIED UNBOUNDED GYROTROPIC MEDIUM

A study is made of the excitation of electromagnetic waves by spatially bounded, arbitrary sources in the presence of a cylindrical guiding structure immersed in an infinitely extended, homogeneous gyrotropic medium whose permittivity and permeability are both describable by tensors with nonzero off-diagonal elements. The axis of symmetry of the considered cylindrical structure is assumed to coincide with the gyrotropic axis. The total field is sought in terms of vector modal solutions of the source-free Maxwell equations. We determine the content of the modal spectrum and obtain an eigenfunction expansion of the source-excited field in terms of discrete- and continuous-spectrum modes. The expansion coefficients of the modes are derived in explicit form. An expression for the total power radiated from sources is deduced and analyzed. It is shown that the

Excitation of s-polarized surface electromagnetic waves in inhomogeneous dielectric media

We consider a model of an inhomogeneous dielectric slab first studied by Shvartzburg, Petite and Auby [J. Opt. Soc. Am. B 16, 966 (1999)] and several variations of that model and study the excitation of s-polarized surface electromagnetic waves on the surface of inhomogeneous dielectric media. Using the invariant imbedding theory of wave propagation in stratified media, we calculate the reflectance and the absorptance of an s wave incident obliquely on a dielectric slab in the Otto configuration, as a function of incident angle and frequency. We also calculate the spatial distribution of the electric field intensity in the inhomogeneous region. We find that in all cases we have considered, s-polarized surface waves are excited at certain incident angles and frequencies. We discuss the physical mechanism of the surface wave generation and the possibility of experimental observations of these effects.

Whistler wave excitation by a loop antenna in a bounded collisional magnetoplasma

Excitation of electromagnetic waves by spatially bounded given electric currents in the presence of an axially magnetized cylindrical plasma column surrounded by free space is studied. A rigorous solution for the total field comprising both the discrete and continuous parts of the spatial spectrum of the excited waves is found. Using the obtained field representation, an expression for the impedance of a loop antenna is derived and the contributions of guided and unguided modes of the column to the antenna impedance are determined for the whistler frequency range. Conditions have been revealed under which the real part of the antenna impedance is dominated by the contribution of guided waves. It is shown that when allowance for relatively small collisional losses in the plasma results in division of the guided whistler waves into weakly and strongly damped modes with significantly different field structures, appreciable redistribution of the antenna-launched power among the excited modes takes place. The results obtained are useful for clarification of the power-absorption mechanisms of whistler-range waves in a cylindrical magnetoplasma.

Excitation and conversion of electromagnetic waves in pulsar magnetospheres

We demonstrate that nonlinear decay of obliquely propagating Langmuir waves into Langmuir and Alfvén waves (L --> L' + A) is possible in a one-dimensional, highly relativistic, streaming pair plasma. Such a plasma may be in the magnetospheres of pulsars. It is shown that the characteristic frequency of generated Alfvén waves is much less than the frequency of Langmuir waves and may be consistent with the observational data on the radio emission of pulsars.

A waveguide slit array antenna fabricated with subwavelength periodic grooves

This paper presents a waveguide slit array antenna with high gain and narrow beamwidth. This antenna is formed by subwavelength slits surrounded with periodic grooves. The far field radiation characteristics of the improved antenna are investigated. Simulation results show that the gain of the antenna with a designed working frequency is improved by 11dB and a strong beam can be obtained. The physical mechanism for the performance improvement is governed by the resonance excitation of surface electromagnetic waves and can be well described by the coherent superposition of power radiated from the grooves and central slits.

Bifurcation Analysis of Parametric Interaction of Magnetostatic and Electromagnetic Waves in Nonlinear 3-D Ferrite Film Structures

A rigorous mathematical model of nonlinear, parametric interactions of microwave magnetostatic dipole-dipole waves and electromagnetic waves in 3-D ferrite films in waveguiding structures is developed. The 3-D nonlinear diffraction boundary problem of the full nonlinear Maxwell's equations with electrodynamical boundary conditions, complemented by the Landau-Lifshitz equation (without the exchange term) is solved. The instability of parametric excitation process of magnetostatic waves in 3-D ferrite structures is simulated by the numerical method of bifurcation analysis of the nonlinear Maxwell's operator for the 3-D boundary problem. The results show discrete maxima in the magnitude of reflected electromagnetic waves for distinct ferrite thickness values in the 1 mum to 1 mm range. The mode profiles were obtained. The instability regions, depending on the bifurcation parameters, were determined, and shown to be more sensitive to the pumping power than the parametric excitation of electromagnetic waves alone

Excitation of backward Tamm states at an interface between a periodic photonic crystal and a left-handed metamaterial

We study the excitation of electromagnetic surface waves in a slab of a left-handed metamaterial separating a one-dimensional periodic photonic crystal and a homogeneous dielectric medium, the so-called surface Tamm states. We show that such a layered structure can exhibit a giant lateral Goos-H\anchen shift of the scattered beam accompanied by a splitting of the reflected and transmitted beams due to the resonant excitation of surface waves at the interfaces between the left-handed metamaterial and photonic crystal. The beam shift can be either positive or negative, depending on the type of the surface Tamm states excited by the incoming beam.

Excitation of surface and volume electromagnetic waves in left-handed media by an electron bunch

We study theoretically the Vavilov-Cerenkov radiation from a nonrelativistic electron bunch moving in free space over a left-handed medium. It is shown that in the frequency range in which the refractive index of the medium is negative, Vavilov-Cerenkov radiation leads to simultaneous excitation of volume and surface electromagnetic waves in the same frequency range. The wave vector of the surface wave in the plane of an interface of two media is greater in magnitude than the corresponding quantity for the volume wave. The energy fluxes of volume and surface waves in the left-handed medium are studied. The radiation pattern of the bunch is found.

The Excitation of the Low-Frequency Electromagnetic Wave in Dusty Plasma with Vortex Flows

The Excitation of Alfven wave in dusty plasma with vortex flows isinvestigated. The coupled equations for density and electromagneticpotential of dusty plasma with vortex-flow were obtained. Thestability and amplitude behavior were studied both analytically andnumerically. Using a non-modal method, it was found that thepresence of dust can suppress the growth of the instability whichcan also be affected by the vortexeccentricity.

Surface electromagnetic waves in a Fermi liquid

Surface electromagnetic waves propagating along a Fermi liquid-dielectric interface are investigated. A dispersion relation for the surface waves is obtained, and the frequency range of their existence is determined. The possibility of determining the contribution of a Fermi liquid to the dielectric permittivity of a metal from experiments on excitation of surface electromagnetic waves is shown.

Electron parallel-flow shear driven low-frequency electromagnetic modes in collisionless magnetoplasma

The free energy associated with shear in the equilibrium parallel electron velocity is shown to be responsible for the excitation of low-frequency electromagnetic waves in collisionless magnetoplasma. New dispersion relations are derived by using the hydrodynamic equations for the electron fluid, the magnetic-field-aligned (parallel) drift of which varies in one of the perpendicular directions, and by using a kinetic ion model, together with Ampère’s law and Poisson’s equation. The dispersion relations are analyzed both analytically and numerically for a set of parameters representative of a laboratory experiment. New filamentary instabilities are predicted.

Surface electromagnetic wave excitation and diffraction by subwavelength slit with periodically patterned metallic grooves

Based on the theoretical formalism derived from the diffraction theory and electromagnetic boundary condition [Phys. Rev. Lett. 167401 (2003)], we investigate numerically the diffraction behavior of light passing through a subwavelength metallic slit-grooves structure, slit surrounded symmetrically by a finite array of grooves at the output surface. The diffraction dependence with the geometrical parameters, groove depth, width and number is analyzed in detail. It is found that variant profile of angle spectra and beaming intensity can be obtained in the far field by tuning the geometrical parameters. Numerical analysis shows that these diffraction behaviors are associated with different excitation states of surface electromagnetic wave.

Excitation of electromagnetic waves by a current source in the inhomogeneous lossy magnetoplasma

The excitation of nonmonochromatic signals by source current and their longitudinal propagation in an inhomogeneous magnetoplasma is studied. Three types of excitation source current are considered for the study. The inhomogeneity of magneto-ionic medium is taken with respect to the variation in plasma density and strength of the magnetic field. The effect of interparticle collisions on the amplitude of the signal is studied. Properties of the excited signals are discussed in different frequency ranges in terms of charge per unit length of the excitation source and the distance of propagation of the signal.

Cherenkov radiation by an electron bunch that moves in a vacuum above a left-handed material

Cherenkov radiation by a nonrelativistic electron bunch that moves above an interface of a vacuum-left-handed material has been investigated theoretically. The electron density of the bunch is described by a Gauss distribution. Cherenkov radiation for the frequency range where the refractive index is negative is shown to lead to simultaneous excitation of both bulk and surface electromagnetic waves over one and the same frequency range. In this case the wave vector magnitude in the plane of the interface of surface electromagnetic waves is larger than the corresponding wave vector magnitude of bulk electromagnetic waves. The energy flows in a left-handed material have been calculated. The spectral density and the radiation pattern have been investigated.

Dynamic resistivity of a two-dimensional electron gas with electric modulation

We explore anomalies in the ac transport or produced by electromagnetic wave radiation on the quantum magnetotransport (QMT) coefficients of a two-dimensional electron system (2DES) with electrostatic modulation. An applied magnetic field is perpendicular to the 2DES. The QMT coefficients are determined by the scattering produced by the electrostatic modulation potential, the sub-Landau level eigenstates arising from the formation of new magnetic Brillouin zones, and the ratio of the frequency $\ensuremath{\omega}$ of the electromagnetic radiation to the cyclotron frequency. For strong modulation, it is found that the Hall resistivity ${\ensuremath{\rho}}_{\mathrm{xy}}(\ensuremath{\omega})$ is quenched and becomes negative for low magnetic fields. The magnetic field range over which ${\ensuremath{\rho}}_{\mathrm{xy}}(\ensuremath{\omega})$ is quenched and negative increases as the frequency is increased. The longitudinal resistivity ${\ensuremath{\rho}}_{\mathrm{xx}}(\ensuremath{\omega})$ has been observed experimentally to have a double peak structure (commensurability of the orbits with the lattice) for strong modulation when $\ensuremath{\omega}=0$. In the presence of electromagnetic wave excitation, we find that the double peaks are shifted to a higher magnetic field and the resistivity is reduced.

Electromagnetic Wave Excitation by a Modulated Electron Beam Injected from Spacecraft into the Ionosphere

Electromagnetic wave excitation can be excited by injecting a modulated electron beam into ionosphere, with varied mechanisms under different experimental conditions. This article presents calculation of the radioemission of a semi-restricted thin modulated electron beam injected from the spacecraft into the ionosphere plasma along the geomagnetic field. The result shows that the radiation pattern for the whistlers' frequency range has a sharp peak that corresponds to the Cerenkov resonance condition. In addition, the radiated power increases with the length of relaxation characteristic. This shows that the intensity of electromagnetic wave can be strengthened by electron beam modulation.

AC driven zero-resistance states and oscillatory magnetoresistance in GaAs/AlGaAs devices

Novel zero resistance states are induced by electromagnetic wave excitation in ultra high modility GaAs/AlGaAs heterostructure devices at low magnetic fields. Zero-resistance states occur about B=(4/5)Bf and B=(4/9)Bf, where Bf=2πfm*/e, m* is an electron effective mass, e is electron charge, and f is the radiation frequency. Surprisingly, the absence of backscattering appears to be associated with an ordinary Hall effect here, unlike the typical quantum Hall situation.

Surface properties and electromagnetic excitation of a piezoelectric gallium phosphate biosensor

The surface properties of GaPO4 have been studied by secondary ion mass spectrometry, X-ray photoelectron spectroscopy and electromagnetic acoustic wave excitation in order to explore the potential of this relatively new piezoelectric material as a biosensor. The X-ray photoelectron spectrum of the substrate shows a Ga-rich surface (Ga:P = 1.4), while the negative secondary ion mass spectrum is similar to that of other phosphates, with PO3- and PO2- being the main fragments derived from the substrate. Surface analysis reveals that the linker protein for biotinylated moieties, neutravidin, is both readily chemisorbed to bare gallium phosphate at pH 7.5 and attached to p-hydroxy benzaldehyde-treated devices, establishing the possibility to exploit the surface chemistry of the phosphate for the fabrication of an electrode-free acoustic wave biosensor. Preliminary results regarding the detection of the adsorption of neutravidin with an electromagnetic field-excited GaPO4 device incorporated in a FIA configuration showed comparable results with those obtained with a quartz-sensor equivalent. The frequency shift for the adsorbed protein layer at the device fundamental frequency was 200 Hz and the noise was routinely around 13 Hz. The possibility to use the electrodeless acoustic GaPO4 device at higher harmonics in the liquid phase has also been confirmed.

Excitation of electromagnetic surface waves by an annular electron beam in a plasma waveguide with a dielectric rod and a magnetized plasma column

The dispersion relation for symmetrical TM electromagnetic surface waves propagating in a plasma waveguide with a strongly magnetized plasma column and a dielectric rod is investigated. The growth rate for excitation of these waves is obtained and its dependence on the radius of the annular beam, current intensity and accelerating voltage are investigated.