Transverse Electromagnetic Waves Research Articles

Pulsed radiation from a coaxial line into an irregular waveguide

Pulses of transverse electromagnetic waves (TEM) propagating from coaxial lines, where they are formed, to irregular waveguides with simply connected sections are transformed into pulses with the structure of longitudinal waves (TM waves). These processes determine the operation efficiency of certain devices such as pulsed radiation antennas. The fast development of equipment for ultrawideband electromagnetic pulses [1, 2] has recently increased the interest in these processes. Nevertheless, they remain poorly studied due primarily to difficulties in the mathematical simulation of pulsed operation modes for irregular channels. These difficulties are aggravated by the presence of topologically discontinuous connections between transmission lines with doubly connected sections and waveguides with simply connected sections. As is shown in this study, the corresponding generalization of the model of connected strings for irregular waveguides with a conserved topology of sections [3, 4] makes it possible to perform such calculations with a high level of accuracy.

Nonlinear propagation of electromagnetic waves in a plasma by means of electromagnetically induced transparency

Magnetized plasma can be made transparent at the cyclotron frequency by addition of a helical undulator. The purpose of the undulator is to couple the transverse (propagating) and longitudinal (non-propagating) electromagnetic waves in the plasma. The coupling is particularly strong when the electron cyclotron and plasma frequencies are equal. It is demonstrated that this coupling gives rise to ultra-slow electromagnetic waves with group velocity vg ≪ c (where c is the speed of light in vacuum), resulting in the extreme energy compression in the plasma. A linear propagation equation for the electromagnetic wave envelope is derived, and its group velocity and group velocity dispersion are calculated. Relativistic corrections to the plasma electron motion are included to derive the nonlinear propagation equation. It is shown that, in comparison with unmagnetized plasma, an enhancement of non-linearities of order 1/v 2 g is expected. Implications for relativistic self-focusing in the plasma are discussed.

Banded frequency structure from linear mode conversion in inhomogeneous plasmas

Linear mode conversion of unmagnetized Langmuir waves into transverse electromagnetic waves in an inhomogeneous plasma is investigated numerically. It is shown that the presence of a tunneling region and density well near the mode conversion region can significantly influence the mode conversion efficiency. The density cavity acts as a resonator, such that the mode conversion efficiency shifts from zero to a local maximum (up to 100% efficiency) with variation of the cavity width on scales of order the Langmuir wavelength. In this way, Langmuir waves with a smooth (structureless) frequency dependence can be selectively mode converted to produce narrow frequency bands of electromagnetic radiation. Applications are discussed to banded frequency fine structure in electromagnetic emissions at the electron plasma frequency in Earth’s foreshock and the solar wind, type III solar radio bursts, and lower ionospheric auroral roar emissions.

Double-Continuum Mechanics of Dielectric Materials as the Basis of Electromagnetomechanics

A new concept is proposed for constructing the theory of coupled mechanical and electrodynamic processes in deformable media. It is based on the double-continuum mechanics of dielectric materials. The phenomenological and discrete-structural methods for deriving the equations of the theory are considered. These equations reduce to a system of connected equations for the displacements of neutral molecules and electric field intensity, satisfy the Galilean relativity principle, and describe longitudinal electric and transverse electromagnetic dispersive waves. Maxwell's equations follow from those equations as a particular case. The ether is modeled as a perfectly liquid dielectric. The theory is capable of explaining Fizeau's and Michelson's experiments and stellar aberration without invoking Einstein's postulates

Maxwell, Hertz, the Maxwellians, and the early history of electromagnetic waves

In 1864, Maxwell conjectured from his famous equations that light is a transverse electromagnetic wave. Maxwell's conjecture does not imply that he believed that light could be generated electromagnetically. In fact, he was silent about electromagnetic waves, and their generation and detection. It took almost a quarter of a century before Hertz discovered electromagnetic waves and his brilliant experiments confirmed Maxwell's theory. Maxwell's ideas and equations were expanded, modified, and made understandable by the efforts of Hertz, FitzGerald, Lodge, and Heaviside, the last three being referred to as the Maxwellians. The early history of electromagnetic waves, up to the death of Hertz in 1894, is briefly discussed. The work of Hertz and the Maxwellians is briefly reviewed in the context of electromagnetic waves. It is found that historical facts do not support the views proposed by some, in the past, that Hertz's epoch-making findings and contributions were significantly influenced by the Maxwellians..

Collapse of a Magnetized Star to a Black Hole

We study of the collapse of a magnetized spherical star to a black hole in general relativity theory. The matter and gravitational fields are described by the exact Oppenheimer-Snyder solution for the collapse of a spherical, homogeneous dust ball. We adopt a ``dynamical Cowling approximation'' whereby the matter and the geometry (metric), while highly dynamical, are unaffected by the electromagnetic fields. The matter is assumed to be perfectly conducting and threaded by a dipole magnetic field at the onset of collapse. We determine the subsequent evolution of the magnetic and electric fields without approximation; the fields are determined analytically in the matter interior and numerically in the vacuum exterior. We apply junction conditions to match the electromagnetic fields across the stellar surface. We use this model to experiment with several coordinate gauge choices for handling spacetime evolution characterized by the formation of a black hole and the associated appearance of singularities. These choices range from ``singularity avoiding'' time coordinates to ``horizon penetrating'' time coordinates accompanied by black hole excision. The later choice enables us to integrate the electromagnetic fields arbitrarily far into the future. At late times the longitudinal magnetic field in the exterior has been transformed into a transverse electromagnetic wave; part of the electromagnetic radiation is captured by the hole and the rest propagates outward to large distances. The solution we present for our simple scenario can be used to test codes designed to treat more general evolutions of relativistic MHD fluids flowing in strong gravitational fields in dynamical spacetimes.

Nonlinear propagation of electromagnetic waves in a plasma by means of electromagnetically induced transparency

Abstract Magnetized plasma can be made transparent at the cyclotron frequency by addition of a helical undulator. The purpose of the undulator is to couple the transverse (propagating) and longitudinal (non-propagating) electromagnetic waves in the plasma. The coupling is particularly strong when the electron cyclotron and plasma frequencies are equal. It is demonstrated that this coupling gives rise to ultra-slow electromagnetic waves with group velocity vg ≪ c (where c is the speed of light in vacuum), resulting in the extreme energy compression in the plasma. A linear propagation equation for the electromagnetic wave envelope is derived, and its group velocity and group velocity dispersion are calculated. Relativistic corrections to the plasma electron motion are included to derive the nonlinear propagation equation. It is shown that, in comparison with unmagnetized plasma, an enhancement of non-linearities of order 1/v 2 g is expected. Implications for relativistic self-focusing in the plasma are discussed.

Magnetoinductive waves in one, two, and three dimensions

The propagation of waves supported by capacitively loaded loops is investigated using a circuit model in which each loop is coupled magnetically to a number of other loops. Since the coupling is due to induced voltages the waves are referred to as magnetoinductive (MI) waves. The mathematical formulations are mostly analytical thanks to long standing previous work on the magnetic and electric fields generated by currents flowing in loops. Retardation is neglected, i.e., dimensions of the structure are assumed to be small relative to the free space wavelength. The dispersion relations, derived in the most general case for a tetragonal three-dimensional structure, exhibit both forward and backward waves within a pass band. It is shown that for reproducing the salient features of the waves it is sufficient to take nearest neighbor coupling into account but coupling between loops further away must also be considered if higher accuracy is required. The investigations include that of resonances, conditions for the existence of traveling waves, tolerances, and streamlines of the Poynting vector. Waveguide components, like bends, power dividers and couplers are considered due to the potential applications of the MI waves as magnetic guides. Generality of the results, their possible implications for transverse electromagnetic wave propagation, previous work on similar waves, including the possibility of phase conjugation, are discussed in a separate section.

Evidence for Langmuir wave tunneling in the inhomogeneous solar wind

Spacecraft observations of beat‐like Langmuir waveforms on two orthogonal antennas in Earth's foreshock and the solar wind have been interpreted as beating associated with large‐angle reflection of Langmuir waves from density inhomogeneities or nonlinear decay processes. However, the waveforms are often irregular, with uncorrelated waveform envelopes on orthogonal antennas. One interpretation is that irregular waveforms are a manifestation of the electromagnetic nature of Langmuir waves scattered to low wave numbers in the inhomogeneous solar wind. An alternative interpretation, investigated here, is that the shape of the waveform envelopes on orthogonal antennas becomes substantially different as Langmuir waves tunnel through evanescent regions, where the local plasma frequency in the inhomogeneous plasma exceeds the Langmuir wave frequency. We demonstrate that observations of uncorrelated waveform envelopes on orthogonal antennas are consistent with theoretical predictions for Langmuir wave tunneling in evanescent regions in the inhomogeneous solar wind. Incident Langmuir waves which are nearly aligned with the density gradient are also partially converted to transverse electromagnetic waves at the plasma frequency. The characteristic dual‐antenna waveform signature of mode conversion is difficult to detect for typical solar wind parameters.

Electromagnetic and absorption properties of some microwave absorbers

Electromagnetic properties of a thermoplastic natural rubber (TPNR), a lithium–nickel–zinc (Li–Ni–Zn) ferrite and a TPNR–ferrite composite subjected to transverse electromagnetic (TEM) wave propagation were investigated. The incorporation of the ferrite into the matrix of the TPNR was found to reduce the dielectric loss but the magnetic loss increased. The absorption characteristics of all the samples subjected to a normal incidence of TEM wave were investigated based on a model of a single-layered plane wave absorber backed by a perfect conductor. It is evident from a computer simulation that the ferrite is a narrowband absorber, whereas the polymeric samples show broadband absorption characteristics. Minimal reflection of the microwave power or matching condition occurs when the thickness of the absorbers approximates an odd number multiple of a quarter of the propagating wavelength. This is discussed as due to cancellation of the incident and reflected waves at the surface of the absorbers. The Li–Ni–Zn ferrite exhibits another matching condition at low frequency when the magnitude of the complex relative dielectric permittivity (εr*) equals that of the complex relative magnetic permeability (μr*). The specular absorber method provides a simple theoretical graphic aid for determining the absorption characteristics and the location of the matching conditions in the frequency domain. The result for the ferrite sample was tested and confirmed directly from terminated one-port measurements.

Scattering of electromagnetic waves in a magnetized plasma with an HF pump

The scattering of transverse electromagnetic waves by turbulent density fluctuations in a magnetized plasma in the presence of external pump fields is investigated. The case where a lower-hybrid pump wave decays into daughter and ion-cyclotron waves in a plasma with ion-temperature anisotropy is considered. The situation where an upper-hybrid pump wave parametrically excites modified convective cells and electron drift waves is also analyzed. The differential scattering cross-sections in the region above the parametric instability thresholds for these three cases are calculated.

Electromagnetically induced transparency for two intense waves in plasma

The coupled propagation of two electromagnetic waves in plasma is studied in order to find the conditions for induced transparency. This means unattenuated propagation of the waves through plasma which is overdense, and thus opaque, for one (or both) of them. This is made possible by a modulation of the refractive properties of the plasma, due to a relativistic increase in the electron mass, or to a variation in electron density caused by longitudinal plasma oscillations driven by the ponderomotive potential associated with the beat of the waves. Starting from a relativistic fluid description, we make an Ansatz containing two transverse monochromatic electromagnetic plane waves, and longitudinal plasma oscillations at the sum and difference of their frequencies. For weakly relativistic intensities we derive coupled dispersion relations, which take into account the polarization of the waves and the nonlinearities with respect to both their amplitudes. This serves to explore the conditions for induced transparency and the modes of propagation.

Unipolarized Generalized Inhomogeneous TEM Plane Waves in Differential Geometric Lens Synthesis

Previous results have shown that one can have a generalized Transverse Electromagnetic (TEM) plane wave propagating in the u3 direction in u1, u2, u3 orthogonal curvilinary coordinates. The formal fields are functions of u1 and u2 only and have components in both these directions. The medium is inhomogeneous but isotropic, with formal propagation speed (with respect to the u3 coordinate) a function of only u3. In this case the u3 surfaces can only be planes or spheres. The case of constant φ surfaces for u3 gave a class of TEM waves propagating in the φ

Application of adaptive basis functions for a diagonal moment‐matrix solution of two‐dimensional field problems—TE case

AbstractIn this work, we present the application of specially constructed adaptive basis functions to generate a diagonal matrix in the method‐of‐moments solution procedure for the calculation of a scattered electromagnetic field from arbitrarily shaped two‐dimensional cylinders excited by a transverse electric incident electromagnetic wave. Several numerical examples are also presented to validate the new method. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 270–273, 2001.

Calibrated electro-optic E-field sensors for hyperthermiaapplications

E-field measurements are an important task for the investigation of newlydeveloped hyperthermia applicators as well as for online control ofhyperthermia treatments. Compact and non-perturbing integrated opticalE-field sensors based on LiNbO3 as well as optical E-field sensorsbased on infrared emitting diodes and light bulbs are suitable for nearfieldmeasurements of hyperthermia antennas. In order to investigate theirproperties a calibration cell with transverse electromagnetic (TEM) waves hasbeen constructed. By using this cell, calibration curves and directionalpatterns for all sensors have been measured. Due to the threshold behaviour ofthe IRED and light bulb sensor, only the LiNbO3 sensor is capable ofmeasuring weak fields inside an applicator or a homogeneous phantom.

Transverse Electromagnetic Standing Waves: A New Length Scale in Superconducting Thin Films

The resonance condition for transverse standing waves in superconducting thin films is derived and shown to relate the film's thickness (d) to its material parameters. Surface reactance (Xs) data are shown to be important in interpreting the surface resistance (Rs) data: their relative magnitude bears on the detectability of these standing wave resonances. The periodicity of these resonant thicknesses of otherwise identical films (Δ d) is a new length scale in superconductors and is given by \(\Delta d = {{ - \pi \left| {\tilde \lambda } \right|^2 } \mathord{\left/ {\vphantom {{ - \pi \left| {\tilde \lambda } \right|^2 } {\Im \left( {\tilde \lambda } \right)}}} \right. \kern-\nulldelimiterspace} {\Im \left( {\tilde \lambda } \right)}}\), where \({\tilde \lambda }\) is the complex electromagnetic penetration depth of the superconducting thin film. Many signatures of these standing waves, including an oscillatory transition temperature (Tc) vs. d and an anticorrelation between Tc and the normal state resistance—as a function of the film thickness—collaborate with data reported in the literature. It is important to delineate the contribution of this length scale in superconducting thin-film data that has been known for more than 30 years as, inter alia, the quantum-size effect, the Wyatt–Dayem effect, nonequilibrium superconductivity, and the Carlson–Goldman mode. This is the first report to suggest these standing waves are a possible origin to these phenomena. To further test if noted experimental data are consistent with the standing waves discussed herein, Xs experiments to compliment Rs experiments are proposed.

Mode Conversion and Reflection of Langmuir Waves in an Inhomogeneous Solar Wind

AbstractBeam-driven Langmuir waves in the solar wind are generated just above the electron plasma frequency, which fluctuates in the inhomogeneous solar wind plasma. Consequently, propagating Langmuir waves encounter regions in which the wave frequency is less than the local plasma frequency, where they can be reflected, mode converted to transverse electromagnetic waves, and trapped in density wells. The aim here is to investigate Langmuir wave reflection and mode conversion at a linear density gradient for typical solar wind parameters. It is shown that higher mode conversion efficiencies are possible than previously calculated, but that mode conversion occurs in a smaller region of parameter space. In addition, the possibility of detecting mode conversion with in situ spacecraft Langmuir wave observations is discussed.

Dynamical conductivity of type-I semiconductor superlattices

We calculated longitudinal and transverse macroscopic as well as microscopic dynamical conductivity for a modulation-doped type-I superlattice. Our computed long wavelength macroscopic conductivity significantly differs from Drude conductivity in the low-frequency regime (microwave and infrared radiations). Macroscopic conductivity shows oscillatory behaviour along the direction of growth of the superlattice. Propagation of transverse electromagnetic waves in a superlattice has been studied for all possible values of frequency and wavevector. It is found that microscopic transverse conductivity exhibits poles along both real and imaginary axes of frequency. Depending on the values of wavevector components, along and perpendicular to the direction of the superlattice, both poles can lie on real or imaginary axes of frequency. We also find that there can be more than one penetration depth for a superlattice and one of them decreases with frequency for frequencies below the microwave regime.

Particle acceleration by a fast ordinary mode in an electron–positron plasma

The possibility of nonresonant particle acceleration in an electron–positron plasma of a pulsar magnetosphere is investigated. A mechanism is proposed in which modulations of a fast superluminal (with phase velocity exceeding the speed of light) longitudinal ordinary mode (caused by a beat wave of two transverse electromagnetic waves propagating along the magnetic field) stimulate nonresonant quasilinear diffusion leading to a redistribution of plasma particles in pitch angle. The resulting perpendicular momenta of the particles lead to synchrotron radiation which is in the γ-ray range.

Swihart waves and surface plasmons in a parallel-plate superconducting transmission line

The electromagnetic waves propagating inside a parallel-plate transmission line are investigated. In the case of a finite penetration depth of the electromagnetic field into the metal, a longitudinal electric E wave propagates in the the line instead of a transverse electromagnetic wave. At small thicknesses of the dielectric this wave goes over to a Swihart wave, and at large thicknesses of the dielectric it is converted into a surface wave (plasmon). It is shown that there exists an optimum thickness of the superconducting film coating the parallel-plate transmission line, for which the electromagnetic wave experiences the maximum slowing down. Using waveguides for surface waves, one can construct surface-wave microwave resonators. These resonators have a highly uniform microwave current distribution and, have a high concentration of microwave current in the superconducting film, and they are simple to fabricate.