Phase Velocity Of Electromagnetic Wave Research Articles

Efficient conversion from spoof surface plasmon polaritons to radiation mode.

A direct conversion from spoof surface plasmon polaritons (SSPPs) to radiation mode is proposed. A modified parallel two-wire SSPP transmission line is the key to the conversion, which is composed of traditional unit cells with slots among them. Taking advantages of the slots, the phase velocity of electromagnetic waves is larger than that of light, leading to the radiation. Both simulated and measured results show that the radiation occurs from 7.6 to 11 GHz, and the radiation angle keeps nearly stable in the whole operating frequency band, which can be predicted by theoretical calculation. The average gain and efficiency is 6.41 dBi and around 90%, respectively. The simple structure with flexibly tunable operating frequency makes the proposed design promising in planar integrated communication systems.

Research Status and Design Method of Slow Wave Transmission Lines

Abstract In this paper, the research status and implementation methods of slow wave transmission lines are analyzed. Slow wave transmission lines are distinguished from other planar artificial transmission lines by the positive and negative values of equivalent permittivity and permeability. On this basis, the realization method is summarized through the analysis of equivalent dielectric constant and permeability. The methods of multi-layer dielectrics, periodically loaded capacitors (inductors or branches), cascaded cells and defective ground structures are summarized to increase the value of e and μ, so as to reduce the phase velocity of electromagnetic wave and realize slow wave transmission line. It provides a reference for the design and application of slow wave transmission lines.

The Property of Phase Velocity in the Cloak Shell

According to classical EM field theory, the dispersion relation for anisotropic media in the 2-D cylinder cloak have been calculated in the KDB system(consisting of k vector and the DB plane ). Due to the special and variable Electromagnetic (EM) parameters, theoretical results indicate that the phase velocities of EM waves are non-uniform in the cloak shell. The numerical simulations show that the phase velocity is reduced, and less than that of light in vacuum in the front and rear of cloak shell. While in the upper and lower region of cloak shell, the phase velocities are larger than that of other regions, and exceed that of light in vacuum.

Birefringence induced by pp-wave modes in an electromagnetically active dynamic aether

In the framework of the Einstein–Maxwell-aether theory we study the birefringence effect, which can occur in the pp-wave symmetric dynamic aether. The dynamic aether is considered to be a latently birefringent quasi-medium, which displays this hidden property if and only if the aether motion is non-uniform, i.e., when the aether flow is characterized by the non-vanishing expansion, shear, vorticity or acceleration. In accordance with the dynamo-optical scheme of description of the interaction between electromagnetic waves and the dynamic aether, we shall model the susceptibility tensors by the terms linear in the covariant derivative of the aether velocity four-vector. When the pp-wave modes appear in the dynamic aether, we deal with a gravitationally induced degeneracy removal with respect to hidden susceptibility parameters. As a consequence, the phase velocities of electromagnetic waves possessing orthogonal polarizations do not coincide, thus displaying the birefringence effect. Two electromagnetic field configurations are studied in detail: longitudinal and transversal with respect to the aether pp-wave front. For both cases the solutions are found, which reveal anomalies in the electromagnetic response on the action of the pp-wave aether mode.

Demonstration of sub-luminal propagation of single-cycle terahertz pulses for particle acceleration

The sub-luminal phase velocity of electromagnetic waves in free space is generally unobtainable, being closely linked to forbidden faster than light group velocities. The requirement of sub-luminal phase-velocity in laser-driven particle acceleration schemes imposes a limit on the total acceleration achievable in free space, and necessitates the use of dispersive structures or waveguides for extending the field-particle interaction. We demonstrate a travelling source approach that overcomes the sub-luminal propagation limits. The approach exploits ultrafast optical sources with slow group velocity propagation, and a group-to-phase front conversion through nonlinear optical interaction. The concept is demonstrated with two terahertz generation processes, nonlinear optical rectification and current-surge rectification. We report measurements of longitudinally polarised single-cycle electric fields with phase and group velocity between 0.77c and 1.75c. The ability to scale to multi-megavolt-per-metre field strengths is demonstrated. Our approach paves the way towards the realisation of cheap and compact particle accelerators with femtosecond scale control of particles.

Formula for the phase velocity of electromagnetic waves

A new formula for the phase velocity of electromagnetic waves presented by Chen [Appl. Phys. Lett. 88, 121125 (2006)] is investigated and discussed here. The difference between the result obtained with the new formula and that obtained directly using the phase term is small for a fundament-mode Gaussian laser beam. However, this difference is qualitative in some high-order Gaussian-mode laser beams. Using the new formula for such beams, discontinuities arise in the distribution of the phase velocity. This distribution is not rotationally symmetric with respect to the optical axis, and an imaginary phase velocity may appear near these discontinuities.

Frequency effects of spatial dispersion in semiclassical model of conductivity

Effect of significant retardation of an electromagnetic wave in microstrip microwave systems, where the phase velocity becomes less than the Fermi velocity, opens a novel experimental approach to investigations of properties and pairing mechanisms of carriers in superconductors by measurements of spatial dispersion effects at low temperatures. In this study, we present for the first time the semiclassical model of the current carrier dynamics depending on the frequency and phase velocity of electromagnetic wave, which accounts the unlocal spatial dispersion effects. These equations make it possible to perform a comparative analysis of the spatial effects observed in high-temperature superconductors, conventional superconductors, and normal metals.

Blandford-Znajek Mechanism versus Penrose Process

During the three decades since its theoretical discovery the Blandford-Znajek process of extracting the rotational energy of black holes has become one of the foundation stones in the building of modern relativistic astrophysics. However, it is also true that for a long time its physics was not well understood, as evidenced by the controversy that surrounded it since 1990s. Thanks to the efforts of many theorists during the last decade the state of affairs is gradually improving. In this lecture I attempt to explain the key ingredients of this process in more or less systematic, rigorous, and at the same time relatively simple fashion. A particular attention is paid to the similarities and differences between the Blandford-Znajek and Penrose processes. To this purpose I formulate the notion of energy counter flow. The concept of horizon membrane is replaced with the concept of vacuum as an electromagnetically active medium. The effect of negative phase velocity of electromagnetic waves in the black hole ergosphere is also discussed.

Integration of interdigital-gated plasma wave device for proximity communication system application

Interdigital-gated AlGaAs/GaAs high-electron-mobility transistor (HEMT) structure was used to investigate the interaction between the drifting carrier plasma waves and electromagnetic (EM) waves. It was shown theoretically that the interaction in the range from microwave to terahertz (THz) at room temperature should produce negative conductance characteristics when the carrier drift velocity slightly exceeds the phase velocity of EM waves. S-parameter reflection measurements were carried out at room temperature for a frequency range from 1 to 20GHz and a drastic change in conductance was observed at 5 and 10GHz with the increase of drain–source voltage. Large conductance change over 1000mS/mm was obtained and it showed a peak at a certain frequency. The peak position could be controlled by changing the pitch size of the interdigital gates. These characteristics can be used for high-frequency applications such as high-speed switching devices although a feature size of our interdigital-gated HEMT device is much larger than conventional HEMT device.

Transition radiation: scientific implications and applications in high-energy physics

In their pioneering work on transition radiation, Ginzburg and Frank showed for the first time that a charge may radiate electromagnetic waves not only because of its accelerated motion but also because of time variation of the phase velocity of electromagnetic waves in the ambient medium. This result is of very general importance for physics. For example, a charge at rest can radiate in a nonstationary medium. Transition radiation is widely used in high-energy particle detectors, mainly for identification of ultrarelativistic electrons in accelerator and collider experiments.

Propagation of microwaves in dielectric waveguide surrounded by plasma

Microwave interferometer is a useful device in plasma diagnostics. An important advantage of this device is that it does not disturb the plasma. However, in classical arrangement, microwave interferometer measurement yields a line integrated plasma density. Localized measurement of plasma density may be carried out using microwave interferometer with dielectric rod antennae. Electromagnetic wave propagating along such a dielectric rod is, in general, influenced by dielectric properties of outer medium i. e., the plasma. Phase velocity of electromagnetic wave propagating along a dielectric waveguide surrounded by plasma is computed and the results concerning microwave interferometry diagnostics are discussed.

Measurements of accelerator beam spectrum through dependence of Cherenkov radiation intensity on phase velocity of electromagnetic waves in optical and microwave ranges

The use of Cherenkov radiation in the optical and microwave ranges for measuring the accelerator beam energy and the energy spectrum is described. Suggested methods are based on a dependence of the radiation intensity on the phase velocity of electromagnetic waves in the Cherenkov radiator medium. Mathematical procedure of extraction of the energy spectrum from the measured intensity is given in detail.

Negative phase velocity of electromagnetic waves and the cosmological constant

Examining the propagation of electromagnetic plane waves with the wavevector directed in opposition to the time-averaged Poynting vector in cosmological spacetime with piecewise uniform metric, we show that such negative-phase-velocity (NPV) propagation is possible in certain de Sitter spacetimes but not in anti-de Sitter spacetimes. This difference suggests the possibility of an optical/electromagnetic experiment to discern the cosmological constant of a four-dimensional universe stemming from a five-dimensional brane universe.

THEORETICAL ASPECTS OF WAVE PROPAGATION IN RANDOM MEDIA BASED ON QUANTY AND STATISTICAL FIELD THEORY

In this work, we summarize the existing theoretical methods based on statistical and quanty theory and give some non-standard mathematical approaches based on such theories to explain the principal scalar and vector electrodynamic problems for future applications to acoustic, radio and optical wave propagation in homogeneous, isotropic, anisotropic and inhomogeneous media. We show of how the statistical description of wave equations can be evaluated based on quantum field theory with presentation of Feynman's diagrams by a limited-to-zero finite set of expanded Green functions according to perturbation theory for single, double, triple, etc, scattering phenomenon. It is shown that at very short wavelengths, the Green's function is damped over a few wavelengths if the refractive index fluctuations in the medium are strong; at long wavelengths the effective phase velocity of electromagnetic waves may be increased. It is shown, that the coupling between different wave modes and the energy transfer between different wave modes, may be important, even for week random fluctuations of parameters of the medium, but it takes a very long time.

An improved masking method for absorbing boundaries in electromagnetic particle simulations

We have developed a new scheme to mask electromagnetic fields for absorbing boundaries used in electromagnetic particle codes. The conventional masking method can suppress reflection of various plasma waves by assigning large damping regions for absorbing boundaries. It requires substantial computer memory and processing time. We introduce two new parameters to control absorption of outgoing electromagnetic waves. The first parameter is a damping parameter to change the effective length of damping regions. The second parameter is a retarding parameter to change phase velocities of electromagnetic waves in the damping regions. As a new masking method, we apply both damping and retarding factors. We also found that the best absorption of outgoing waves is realized with a combination of a smaller damping factor and a larger retarding factor. The new method allows us to reduce the size of damping regions substantially.

Influence of the idle region on the dynamic properties of window Josephson tunnel junctions

The processes developed in the last years for the fabrication of high quality, reliable all-refractory Josephson tunnel junctions open a window in an insulating region, called the idle region, which provides the passivation of the base electrode all around the junction itself. We report experimental data showing that the phase velocity of electromagnetic waves in the junction barrier can be considerably modified by the presence of the insulating region surrounding the window Josephson tunnel junctions. We have investigated this phenomenon in unidimensional junctions, measuring the asymptotic voltage of the Fiske resonances in the presence of an externally applied magnetic field. We have considered the effect of an idle region: (i) along the long junction dimension and (ii) at the extremities of the junction. When comparing the behavior to that of a bare junction, in the first case the phase velocity has been found to increase and to be affected by dispersion, while in the latter case it decreased and was frequency independent. In order to interpret the main features of the phenomena observed experimentally in terms of basic mechanisms, we propose two simple models for the two different geometrical configurations.

Effective Propagation Constant of Fibrous Media Containing Parallel Fibers in the Dependent Scattering Regime

The radiative properties of a particulate medium are strongly influenced by the particle concentration and wavelength of the incident radiation. Independent scattering prevails at very low particle concentration, such that the spacing between the particles is much larger than the particle size and incident wavelength. As the particle spacing decreases, near-field multiple scattering and far-field interference of the scattered waves become increasingly pronounced. These dependent scattering effects cause the extinction efficiency and the phase velocity of electromagnetic waves, which are related to the effective propagation constant of the medium, to deviate from those in the independent scattering regime. This paper presents the theoretical formulation of the effective propagation constant of a nondissipative medium containing closely spaced parallel fibers. The dispersion relations for oblique incidence are derived for a transverse magnetic and a transverse electric mode incident wave. Numerical results for Rayleigh limit fibers are presented to illustrate the effect of fiber volume fraction on the propagation constant and extinction efficiency of the medium.

Polarisation of atmospheric bremsstrahlung

THE terrestrial atmosphere is bombarded continuously by energetic charged particles of extraterrestrial origin. When a charged particle penetrates deep into the atmosphere, either its direction changes or its speed varies with respect to the local phase velocity of electromagnetic waves. These changes, caused by the dense atmosphere at altitudes of about 90–100 km, generate bremsstrahlung X rays. The flux of atmospheric bremsstrahlung X rays has been measured using balloons1–3, rockets and satellites4,5. Measurement of the atmospheric X-ray flux has become routine in the study of electron flux precipitation into the lower ionosphere6,7. The degree of polarisation of emitted radiation changes rather drastically with the changing energy of precipitating electrons and with the height of precipitation. But no effort has yet been made to measure the polarisation of atmospheric bremsstrahlung. We here show the potential importance of bremsstrahlung X-ray polarisation and its probable role in atmospheric diagnostics.

Phase and group velocity in a drifting magnetoplasma

Relationship between group and phase velocities of electromagnetic waves in a drifting uniaxial plasma is discussed. When determining whether propagation between two points is possible, the allowed direction of the group velocity vector and not that of the phase velocity vector is important.

Equivalent electromagnetic constants of moving media

It is shown that if the velocity of a medium is small compared to the phase velocity of electromagnetic waves in it, then the electromagnetic field in the moving medium is identical with the field in a stationary medium with modified constants.