Transverse Electromagnetic Waves Research Articles

Spectral singularities of a complex spherical barrier potential and their optical realization

The mathematical notion of a spectral singularity admits a physical interpretation as a zero-width resonance. It finds an optical realization as a certain type of lasing effect that occurs at the threshold gain. We explore spectral singularities of a complex spherical barrier potential and study their realization as transverse spherical electromagnetic waves emitted by a gain medium with a spherical geometry. In particular, for a typical dye laser material, we obtain a lower bound on the size of the gain medium for the occurrence of this kind of spectral singularities.

Transformation processes in a magnetized inhomogeneous plasma with a lower hybrid pump

By using the kinetic theory of fluctuations, the transformation of a Langmuir wave into a transverse electromagnetic wave in a magnetized inhomogeneous parametrically unstable plasma was studied. The transformation coefficient was obtained when the drift waves were excited by a lower hybrid pump wave. The intensity of transverse wave radiation from the turbulent plasma was calculated.

On the generation of electromagnetic waves in the terahertz frequency range

It is shown that a thin dielectric plate, which can act as an open dielectric waveguide, it is possible to produce amplification and generation of electromagnetic waves with frequencies in the terahertz range. For this purpose, we propose using a dielectric plate with a corrugated surface, in which case the electric field of the transverse electromagnetic wave in the waveguide has a periodic spatial structure in the local area near to the corrugation. Terahertz electromagnetic waves are excited by a beam of electrons moving in vacuum along the dielectric plate at a small distance from its corrugated surface. Corrugation period is chosen in order to ensure the most effective interaction of the electron beam with the first harmonic of the electric field induced by the corrugation. Amplification and generation of electromagnetic waves propagating in a dielectric waveguide is realized as a result of deceleration of the electron beam by a wave electric field induced by a corrugated dielectric surface in the zone near the corrugation. We discuss possible ways to create electron beams with the desired characteristics. We offer a way to stabilize the beam position above the plate, avoiding the bombardment of the plate by electrons. It is shown that it is possible to significantly increase the efficiency of the device through the recovery of energy that remains in the electrons after their interaction with the wave.

Stability and accuracy of the finite difference time domain (FDTD) method to determine transmission line traveling wave voltages and currents: The lightning pulse

The numerical solution of the transmission line wave equation is examined using the transmission line model of a lightning return stroke (LRS) taken as a case study. The LRS is represented by a transverse electromagnetic wave travelling at a velocity close to the velocity of light along a highly ionized lightning leader channel. The leader channel is modeled as a lossy transmission line. Attempts to model the lightning return stroke by an electric circuit in order to determine the currents and radiated electromagnetic fields is categorized as the distributed transmission line model (DTLM). The DTLM method in turn may be subdivided into two categories: Distributed inductance (L), capacitance (C) and resistance (R) model (DLCRM) and the lumped LCR model (LCRM). In this brief communication, we indicate some pitfalls to watch out for in solving for the transmission line wave equationusing numerical methods, and how these may be avoided. Furthermore, we propose tests that may be applied, including the analytical solution of diffusion waves, to ensure the stability and accuracy of the numerical solution DLCRM simulations. Key words: Finite difference time domain method, numerical solution of transmission line wave equation, lightning return stroke model, lightning radiated electromagnetic fields.

ACHIEVABLE TRANSVERSE CYLINDRICAL ELECTROMAGNETIC MODE

The system of Maxwell equations with an initial condition in a vacuum is solved in a cylindrical coordinate system. It derives the cylindrical transverse electromagnetic wave mode in which the electric fleld and magnetic fleld are not in phase. Such electromagnetic wave can generate and exist in actual application, and there is no violation of the law of conservation of energy during the electromagnetic fleld interchanges.

Particle heating by parametric decay of Alfvén-cyclotron and fast-magnetosonic waves

Nonlinear evolution of Alfvén-cyclotron and fast-magnetosonic waves accompanying ion and electron heating is investigated by means of a one-dimensional particle-in-cell simulation. The simulation is initiated with a spectrum of transverse electromagnetic waves with both left- and right-hand circular polarizations (i.e. Alfvén-cyclotron and fast-magnetosonic waves). It is shown that parametric decay processes lead to an inverse cascade of Alfvén-cyclotron waves and the generation of ion-acoustic waves by decay instability. It is found that the nonlinear decay processes accompany small perpendicular heating and parallel cooling of the protons, and a pronounced parallel heating of the electrons for a relatively low ion-to-electron mass ratio (mi/me = 16).

Broadband Characterization of Bulk and Thin Magnetic Composites Using Stripline Structures

We present two broadband characterization techniques to extract the RF (50 MHz-4.5 GHz) permeability of bulk and thin magnetic composite materials. Both techniques are based on broadband stripline structures with the permeability determined from -parameter measurements. For bulk samples, a tapered stripline fixture, supporting transverse electromagnetic (TEM) waves, is employed. As this approach is not suitable for thin material samples (thickness t <; 1 mm), a microstrip line fixture is proposed along with a new permeability de-embedding technique. Compared with conventional microstrip line methods, this approach is found to be accurate for thin samples with small surface areas (less than 1 × cm × 1 cm). The validity of the techniques is demonstrated by measuring a bulk ferrite slab and a thin patterned ferrite composite with in-plane anisotropy.

Fabrication techniques for three-dimensional metamaterials in the midinfrared

The authors have developed two versions of a flexible fabrication technique known as membrane projection lithography that can produce nearly arbitrary patterns in “212 D” and fully three-dimensional (3D) structures. The authors have applied this new technique to the fabrication of split ring resonator-based metamaterials in the midinfrared. The technique utilizes electron beam lithography for resolution, pattern design flexibility, and alignment. The resulting structures are nearly three orders of magnitude smaller than equivalent microwave structures that were first used to demonstrate a negative index material. The fully 3D structures are highly isotropic and exhibit both electrically and magnetically excited resonances for incident transverse electromagnetic waves.

Beam forming transition based upon a zero-phase-shift metamaterial

A sector-shaped transmission line along with a zero-phase-shift metamaterial lens has been demonstrated to optimise the coupling between a narrow transmission line connected to the apex of the sector, and a wide transmission line connected to one face of the lens. Throughout the zero-phase-shift metamaterial lens, the phase is constant. One face of the zero-phase-shift lens is connected to, and conforms to, the circular end of the sectoral transmission line, the other face of the zero-phase-shift lens is flat and connects to the wide transmission line. The sectoral transmission line performs impedance transformation, whereas the zero-phase-shift metamaterial lens is a beam former transforming cylindrical waves to plane waves. The flare angle can be large thereby reducing the length of the transition, and the device can be used in compact multiway power dividers. Both spatial and frequency response calculations of a transition with a 90° flare angle, and operating at 1 GHz, show that a pure transverse electromagnetic (TEM) wave is excited in the wide transmission line with negligible transverse variation in both amplitude and phase, compared to considerable transverse variation without the lens. At 1 GHz the input reflection coefficient was −8.7 dB compared to −6.9 dB without the lens, and −2.5 dB using a slab of the zero-phase-shift metamaterial in place of the lens.

Instabilities and generation of a quasistationary magnetic field by the interaction of relativistically intense electromagnetic wave with a plasma

It is shown that the interaction of the superstrong laser radiation with an isotropic plasma leads to the generation of low frequency electromagnetic (EM) waves and in particular a quasistationary magnetic field. When the relativistic circularly polarized transverse EM wave propagates along z-axis, it creates a ponderomotive force, which affects the motion of particles along the direction of its propagation. On the other hand, motion of the particles across the direction of propagation is defined by the ponderomotive potential. The dispersion relation for the transverse EM wave using a special distribution function, which has an anisotropic form, is derived. The dispersion relation is subsequently investigated for a number of special cases. In general, it is shown that the growth rate of the EM wave strongly depends upon its intensity.

Non-relativistic quantum theory of stimulated Cherenkov radiation and Compton scattering in plasma

The stimulated processes in electron plasma, i.e., Cherenkov radiation by a nonrelativistic electron beam of longitudinal oscillations and Compton scattering of a transverse electromagnetic wave in plasma with quantum mode excitation (de Broglie wave), are considered in the three-wave approximation. The possibility of the occurrence of quantum oscillations is discussed.

Terahertz photomixers based on ultra-wideband horn antennas

Abstract We review recent advances in the development of new terahertz photomixers based on the integration of an ultrafast photodetector with an ultra-wideband transverse electromagnetic wave horn antenna. We expose first a simplified theory of this antenna, the choice of the dimensions and the results of electromagnetic modeling. We expose then the technological process of the antenna and its integration with ultrafast photodetectors. In the last part we present a photomixing experiment and radiation patterns measurements.

Geometrical control of transverse electromagnetic wave propagation in nonuniform microwave superconducting transmission lines

It is well known that photonic structures with subwavelength features can be homogenized and thus be accurately approximated by homogeneous yet spatially dispersive structures. This idea is here applied to nonuniform superconducting transmission lines with subwavelength nonuniformities, i.e. subcentimeter features in the microwave regime. A closed form expression is found for the equivalent characteristic impedance and propagation constant of a uniform transmission line that can accurately model the transverse electromagnetic (TEM) propagation within nonuniform superconducting transmission lines with subwavelength inhomogeneities. It is shown that electromagnetic wave propagation, in particular the group velocity of propagating TEM waves, can be well controlled by introduction of subwavelength (subcentimeter) geometrical variations within the line. This ability is of great importance in design of matching stages. In our numerical examples, quasi-TEM superconducting microstrip lines with a superconductive strip of varying width are considered and the group velocity of the quasi-TEM modes is controlled by duly varying the line width. The obtained results are validated by being compared against the well-known technique of stair-case approximation whereby the considered nonuniform line is sliced into several sections each being small enough to be considered uniform.

Transformation of electromagnetic waves in turbulent magnetized plasmas

In the present paper, on the basis of kinetic theory fluctuations the transformation of transverse electromagnetic waves into longitudinal Langmuir oscillations in turbulent magnetized plasma subjected to the influence of a lower hybrid pump wave is investigated. We consider the case when the decay of the pump into daughter and ion-acoustic waves occurs. The transformation cross section of electromagnetic waves by turbulent density fluctuations in the region above the parametric instability threshold is calculated. The comparative preference of transformation and scattering processes is discussed.

Extremely low frequency electromagnetic energy in the air

The present paper reveals that the air contains electromagnetic energy of extremely low frequency, low amplitude as well as of a low phase speed. The energy is of great interest because of its impact on certain biological processes. It is created by the interaction of two well-known phenomena. The rotation of the earth generates 24 h periods currents in the magnetosphere, known as the Birkeland currents. The currents generate transverse electromagnetic waves (EM waves) propagating parallel to the geomagnetic field lines. Furthermore, the air and the earth crust contain electrons caused by the global electric circuit. The electric field vectors of the EM waves exert a force on these electrons, causing them to oscillate and thus generate currents of extremely low frequency both in the air and in the earth crust. A theoretical model of the system is presented and measurement techniques are described. Measurements have been performed during a six year period. The results of the performed measurements verified the theoretical model. Impact on biological processes is discussed.

Transverse wave propagation in relativistic two-fluid plasmas around Reissner–Nordström–de Sitter black hole

The transverse electromagnetic waves propagating in a relativistic two-fluid plasma influenced by the gravitational field of the Reissner-Nordstr\"{o}m-de Sitter black hole has been investigated exploiting 3+1 split of spacetime. Reformulating the two-fluid equations, the set of simultaneous linear equations for the perturbations have been derived. Using a local approximation, the one-dimensional radial propagation of Alfv\'{e}n and high frequency electromagnetic waves are investigated. The dispersion relation for these waves is obtained and solved numerically for the wave number.

Quantum theory of stimulated Cerenkov radiation of transverse electromagnetic waves by a low-density electron beam in a medium

The quantum theory of stimulated Cerenkov radiation of transverse electromagnetic waves by an electron beam in an anisotropic medium is presented. Relativistic quantum nonlinear equations of the Cerenkov beam instability are obtained. In the linear approximation, the quantum dispersion equation is derived and the instability growth increments are determined. The nonlinear problem of the saturation of the quantum Cerenkov beam instability is solved.

Relative local density of states for homogeneous lossy materials

We derive the appropriate form of the relative local density of states (RLDOS) for the two-dimensional Helmholtz equation in a homogeneous lossy medium, and give the corresponding result for the three-dimensional equation. The RLDOS enables the calculation of the enhancement or suppression of the energy radiated in the form of transverse electromagnetic waves by a localized source in the medium, and so would be useful in studies of either electromagnetic communication from inside a cloaking system or detection of the cloaking system by radiation from thermally excited atoms within it.

Transverse wave propagation in relativistic two-fluid plasmas in de Sitter space

We investigate transverse electromagnetic waves propagating in a plasma near the horizon of the de Sitter space. Using the 3+1 formalism we derive the relativistic two-fluid equations to take account of the effects due to the horizon and describe the set of simultaneous linear equations for the perturbations. We use a local approximation to investigate the one-dimensional radial propagation of Alfvén and high frequency electromagnetic waves and solve the dispersion relation for these waves numerically.

An Optically Coupled System for Quantitative Monitoring of MRI-Induced RF Currents Into Long Conductors

The currents induced in long conductors such as guidewires by the radio-frequency (RF) field in magnetic resonance imaging (MRI) are responsible for potentially dangerous heating of surrounding media, such as tissue. This paper presents an optically coupled system with the potential to quantitatively measure the RF currents induced on these conductors. The system uses a self shielded toroid transducer and active circuitry to modulate a high speed light-emitting-diode transmitter. Plastic fiber guides the light to a photodiode receiver and transimpedance amplifier. System validation included a series of experiments with bare wires that compared wire tip heating by fluoroptic thermometers with the RF current sensor response. Validations were performed on a custom whole body 64 MHz birdcage test platform and on a 1.5 T MRI scanner. With this system, a variety of phenomena were demonstrated including cable trap current attenuation, lossy dielectric Q-spoiling and even transverse electromagnetic wave node patterns. This system should find applications in studies of MRI RF safety for interventional devices such as pacemaker leads, and guidewires. In particular, variations of this device could potentially act as a realtime safety monitor during MRI guided interventions.