EM Wave Propagation Research Articles

Red light, blue light, Feynman and a layer of glass: the causal propagator

A propagator–description approach of the propagation of EM waves is provided, in complex situations with underlying boundary conditions. To this end, the so-called Schwinger–Feynman causal propagator is explicitly derived, and spelled out, for the first time, for transmission of a photon through, and reflection off, a layer of glass of flat parallel surfaces. In a very general context, the corresponding transition amplitudes of a polarized or unpolarized photon are obtained, and the conservation of probabilities, and the underlying consistency conditions of the results, are established. Inspired by Feynman’s intuitive and well-publicized non-technical treatment of such a problem with red and blue light, one, in a quantum view-point, is interested in the probabilities of the events just described in determining the fate of a photon. This analysis provides an alternative way of looking at the problem in question, through propagation of photons, as a physically more appealing approach, in Feynman’s spirit, than by matching plane waves at boundaries as we often do. It also shows how a propagator may be derived, in more complex situations with specific boundary conditions, than just simply in infinite extended spaces. Finally, it is hoped that this work will be stimulating and of interest to practitioners with different emphases on EM wave propagation.

A Simple FDTD Algorithm for Simulating EM-Wave Propagation in General Dispersive Anisotropic Material

In this paper, an finite-difference time-domain (FDTD) algorithm for simulating propagation of EM waves in anisotropic material is presented. The algorithm is based on the auxiliary differential equation and the general polarization formulation. In anisotropic materials, electric fields are coupled and elements in the permittivity tensor are, in general, multiterm dispersive. The presented algorithm resolves the field coupling using a formulation based on electric polarizations. It also offers a simple procedure for the treatment of multiterm dispersion in the FDTD scheme. The algorithm is tested by simulating wave propagation in 1-D magnetized plasma showing excellent agreement with analytical solutions. Extension of the algorithm to multidimensional structures is straightforward. The presented algorithm is efficient and simple compared to other algorithms found in the literature.

Stady on a high efficient Denisov-type launcher for high-power gyrotron oscillators

In this paper, a high-efficiency Denisov-type launcher, a hardcore of quasi-optical mode converters in high-power gyrotron oscillators, is investigated. Based on integral expression of Bessel functions and geometric optics, the propagation of EM wave in circular waveguides, the syntheses of amplitude and phase of nine modes are analyzed in detail. A generalized method for designing the launcher with a dimpled waveguide wall operating in different modes is demonstrated. This method shows how to select a set of appropriate coupled modes to synthesize the Gaussian-like distribution on the inner wall of the launcher. A program is developed and its accuracy is confirmed by a high-power gyrotron at 140 GHz, in TE28,8 mode theoretically. Numerical calculations show a good agreement with reported results.

EM Wave Propagation Analysis and Channel Modeling in Aircraft Cabin with Finite Integration Technique

EM Wave Propagation Analysis and Channel Modeling in Aircraft Cabin with Finite Integration Technique

Study of EM Wave Propagation for Transformer PD Monitoring Using FDTD Method

Ultra high frequency (UHF) partial discharge (PD) detection technique is drawing attention to transformer insulation accident prevention. However, the configuration of a large oil-immersed transformer is very complicated, so the reflection, refraction and absorption phenomena between PD sources and UHF sensors need to be considered. The phenomena make it difficult to calibrate the magnitude and locate the source of a PD activity. Therefore, detailed investigation of EM wave propagation inside the tank is carried out to enhance the performance of UHF method. Numerical simulations are performed on the 3D models using finite difference time domain (FDTD) method. From the results, the effects of transformer oil, cores and the tanks are clarified.

Comparison of hourly variations of radio refractivity for quiet and disturbed days during dry and rainy seasons at Minna

In principle, the EM wave propagation characteristics during quiet or disturbed air conditions are straightforwardly determined by the state of atmospheric refractivity. Nevertheless, atmospheric refractivity varies in time and space more or less randomly. Therefore the statistics of atmospheric refractivity and related propagation effects are of main interest. This work clearly investigates the major difference between radio refractivity changes for quiet and disturbed days during dry and rainy season for Minna. Radio refractivity values were calculated from measured meteorological parameters (relative humidity, temperature and pressure) at Minna, in 2008. The result showed that, there is a sharp decrease in radio refractivity at the early hour of the day (6:00hr) during dry season, while during rainy season, the sharp decrease occurred at the noon time (13:00hr). The result equally showed that radio refractivity has higher values ~388N-units during rainy season than during dry season with the highest value of ~318N-units. This is due to decrease in relative humidity during dry season than during rainy season.

Effect of environment on the propagation of electromagnetic waves in GRC 408E digital radiorelay devices

Effect of environment on the propagation of electromagnetic waves in GRC 408E digital radiorelay devices

General Solution of EM Wave Propagation in Anisotropic Media

When anisotropy is involved, the wave equation becomes simultaneous partial dierential equations that are not easily solved. Moreover, when the anisotropy occurs due to both permittivity and permeability, these equations are insolvable without a numerical or an approximate method. The problem is essentially due to the fact neither nor µ can be extracted from the curl term, when they are in it. The terms r ◊ E (or H) and r ◊ E (or µH) are practically independent variables, and E and H are coupled to each other. However, if Maxwell’s equations are manipulated in a dierent way, new wave equations are obtained. The obtained equations can be applied in anisotropic, as well as isotropic, cases. In addition, E and H are decoupled in the new equations, so the equations can be solved analytically by using tensor Green’s functions.

Subwavelength waveguiding and imaging with a one-dimensional array of metallic H-fractals

We demonstrate, both experimentally and theoretically, subwavelength waveguiding and imaging through a one-dimensional (1D) array of 3D metallic H-fractals. The waveguide formed by the fractal array is subwavelength in all cross-sectional dimensions, thereby allowing compact designs for guided propagation of long-wavelength EM waves. The underlying physics is governed by the fractal metallic wire structure that allows subwavelength resonances. The measured results indicate that such waveguides can provide low-loss propagation of EM waves with a decay length in the range 10–40 m, achieved through coupling of resonant dipoles/multipoles between neighboring H-fractals along the wave propagation direction. By treating the waveguide as a 1D photonic crystal, the calculated bandstructure shows that in the neighborhood of peak transmission frequencies the dispersion relations are relatively flat as a function of the wave vector, implying low group velocities. This is experimentally verified. Owing to the increased spatial information carried at such transmission frequencies, imaging becomes possible and this was observed by placing an obstacle at the inlet and scanning the local field intensity at the other end of the waveguide.

An EM Absorber and Frequency Selective Shielding by Use of Metal Fiber Array Composites

The construction of EM absorber and frequency selective shielding has been investigated by using two dimensional metal fiber array (MFA) composites. The MFA composite shows a resonant type frequency dispersion in the complex relative permittivity spectra (er = e'r - je ''r) having a negative e'r region. The frequency characteristics of the conventional ferrite-rubber EM absorber can be improved by combining with the negative permittivity property of the MFA composite. A frequency selective shielding can be achieved by the evanescent EM wave propagation in the layered MFA composite structure.

Three-Dimensional Urban EM Wave Propagation Model for Radio Network Planning and Optimization Over Large Areas

A new 3D urban electromagnetic wave propagation model is presented. It provides fast 3D deterministic predictions in urban radio configurations and over large areas. The various techniques to make it suitable to the network planning and optimization of large wireless networks are described. The resulting radio propagation maps exhibit seamless coverage between the various environments (dense urban, urban, and suburban). The model efficiently addresses all types of outdoor transmitter configurations (macrocells, minicells, microcells, and picocells) and all types of receiver locations (at ground level, over the rooftop, and at high building floors). It predicts the field strength as well as the dominant specular contributions of the impulse responses to build ray spectra (including delays and angles). Thus, the model may also be used to estimate the performances of new radio systems [diversity and multiple-input-multiple-output (MIMO)]. The narrowband power prediction of the model is evaluated by comparison with microcell measurements. The evaluation stresses the advantage of 3D modeling compared with the vertical-plane approach or 2D ray tracing. Finally, the ability of the model to simulate radio wideband characteristics in a complex environment is demonstrated by comparing delay-spread estimates to measurements collected from a high-macrocell transmitter in a hilly city and to arrival angles collected in a suburban macrocell area.

A Novel Numerical Model for Simulating Three Dimensional MIMO Channels With Complex Antenna Arrays

We develop a novel three-dimensional (3D) numerical model for rigorously simulating mutual coupling effects on the channel capacity of the multiple input multiple output (MIMO) systems. In this model, the efficient integral equation method mutlilevel Green's function interpolation method (MLGFIM) is for the first time employed to calculate the input admittances and radiation patterns of the transmit and receive antennas of MIMOs. Comparing with the method of moments whose complexity is O(N2) , MLGFIM has an efficiency of O(NlogN) and is suitable for efficiently solving antenna arrays problems. To accurately model the EM wave propagation, we (1) use the ray tracing method to obtain the multi-paths and (2) rigorously obtain the dyadic path loss factor model from which a novel stochastic path loss model that is flexible for both the environments with PEC walls and that with infinite thick lossless dielectric walls is devised. Using the proposed model, we successfully analyze mutual coupling effects on the 3D correlation of a 2-by-2 monopole array and the indoor channel capacity of a 20-by-20 planar array and a 20-by-20 icosahedron array. The numerical examples in this paper demonstrate the efficiency of our model for simulating the MIMO system with complex radiators.

Propagation characteristics of electromagnetic waves in three-phase-type tank from viewpoint of partial discharge diagnosis on gas insulated switchgear

The authors have been examining the diagnosis method for partial discharge (PD) occurring inside gas insulated switchgear (GIS) using the UHF method with a focus on electromagnetic (EM) wave mode conversions at L-shaped, T-shaped pipes, and components existing in actual GIS. Based on these conversion characteristics, an on-site, high-accuracy PD diagnosis algorithm was constructed for use on high-order mode EM-waves. All the researches so far were targeted at an isolated-phase-type (singlephase- type) tank. The present study was targeted at a straight-pipe three-phase structure, the most basic form, in order to apply the evaluation method to a three-phase-common-type tank (three-phase-type tank). Through the implementation of EM-wave propagation experiments and the EM-field analysis, the presence of TEM, TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> , and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> modes was verified also in the three-phase-type tank. Next, the EM-field analysis was conducted on models equivalent to actual apparatuses of 72 to 550 kV classes. Then, formulas for simplified calculation of cutoff frequencies in TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> and TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> in a three-phase-type tank were proposed. Furthermore, the basic concept of the PD diagnosis method was examined and the work flow was presented.

Antenna design for the propagation of EM waves in seawater

Antenna design for the propagation of EM waves in seawater

Examination of Electromagnetic Mode Propagation Characteristics in Straight and L-Section GIS Model Using FD-TD Analysis

It is an effective method of insulation accident prevention for gas-insulated switchgear (GIS) to detect a partial discharge (PD) that occurs as a preceding phenomenon for an insulation accident. Among various methods, a PD detection method based on the detection of electromagnetic emission through measurement of the UHF band (300 MHz to 3 GHz), which is relatively free of influences from external noises, is drawing attention as an effective method in terms of extensive and highly sensitive detection. This paper describes conducting EM-wave propagation analysis on GISs with L-sections using the finite difference-time domain (FD-TD) method and examining the influences of the Insertions on the propagation characteristics of EM-wave modes with comparison of straight GIS part. As a result, this study identified that, even on a straight GIS, the velocity dispersion characteristic of high-order modes resulted in a decrease in the crest value even if there is no reflection or conductor loss in the discontinuities. And that mode conversions and reflections in L-sections also resulted in a decrease in the crest value.

Electromagnetic (EM) wave characteristics in GIS and measuring the EM wave leakage at the spacer aperture for partial discharge diagnosis

For the insulation diagnosis of gas-insulated switchgears, the UHF method, which detects electromagnetic wave (EM-wave) in the UHF band (300 MHz to several GHz) with little noise influence, has rapidly developed in recent years. The study in this paper has proposed the evaluation of the location of adhering metallic particles based on the theory of EM-wave propagation by only using the time-waveform information of the EM-wave emitted due to partial discharge, and also analyzed and studied the validity using the FD-TD method. As a result, the duration of the time-waveform differed with respect to the location of the adhering metallic particle, and this difference was caused by the difference in the relative electric field intensity at the tip of the metallic particle among EM-wave modes and the difference was more when the tank diameter was larger. Based on this result, the method for evaluating the location of metallic particle according the time-waveform was studied. In addition, the characteristics of the leakage EM-wave at the spacer aperture were analyzed, and based on the result obtained, two types of antennas, patch and waveguide slot antennas, achieving compactness and a high sensitivity were proposed

Absorption of ultra-short laser pulses and particle transport in dense targets

A new version of the numerical code KALOS has been developed to solve the Vlasov-Fokker-Planck equation for electrons as well as EM wave propagation. KALOS represents the electron distribution function in momentum space by an expansion in spherical harmonics. Its unique features make possible simultaneous investigations of fast electron generation and transport and the collisional evolution of thermal particles, including the return current of cold electrons. We report here on results obtained in one spatial dimension. Absorption of 100fs, 1015W/cm2laser pulses has been studied at normal incidence in sharp-edged dense plasmas. We have studied the effect on absorption of energy transport into the target as well as the deviation of the electron distribution function from Maxwellian. It is shown that it is necessary to take into account collisional heat transport into the target in order to correctly model the absorption rate at the front surface.

Architectural Features and Urban Propagation

Radiocoverage measurements in urban environments often unveil unexpected power distribution patterns. Architectural features seem to be the cause of this behavior, as demonstrated in this paper. We demonstrate that the elements of a typical building facade, such as windows, exterior doors, balconies and railings, should be considered as significant "sources" of EM radiation in several current wireless communication systems. We propose a method for modeling the influence of those scatterers in EM wave propagation. In our model, the major structural elements are represented by two sets of orthogonally arranged wedges. The uniform geometrical theory of diffraction is employed to calculate the scattering field. The simulation results show that such "urban" scatterers may create a dominant propagation mode in an urban canyon. Our predictions are additionally verified by experimental measurements, performed at two different sites. Finally, the influence of roadside foliage is investigated and conclusions are drawn on the resultant field

Optimization of optical transmittance of a layered metamaterial on active pairs of nanowires

Optical metamaterials with a negative value of the refractive index can be fabricated by means of patterning techniques developed for microelectronics. One of those is a layered metamaterial, where the electric and magnetic response comes from coupled parallel subwavelength size wires. We simulate propagation of EM waves through such a metamaterial. Its properties depend on the density of pairs of nanowires oriented in parallel in one layer. There is a tradeoff between high transmittance and large negative refractive index value n. The smaller is the density of nanowires; 1 masculine - the narrower the range of frequencies, where n is negative; 2 masculine - the less negative is n; 3 masculine - the higher is the transmission.

Electromagnetic wave propagation in an active medium and the equivalent Schrödinger equation with an energy-dependent complex potential

We study the massless limit of the Klein-Gordon (K-G) equation in 1+1 dimensions with static complex potentials as an attempt to give an alternative, but equivalent, representation of plane electromagnetic (em) wave propagation in active medium. In the case of dispersionless em medium, the analogy dictates that the potential in the K-G equation is complex and energy-dependent. In the non-relativistic domain we study an analogous inertial system by considering wave packet propagation through a complex potential barrier and solve the time-independent Schrodinger equation with a potential that has the same energy dependence as that of the K-G equation. The behavior of these solutions is compared with those found elsewhere in the literature for the propagation of electromagnetic plane waves in a uniform active medium with complex dielectric constant. Our study concluded that the discrepancy between the time dependent and stationary results is due to the energy poles crossing the real axis in the complex energy plane. It was demonstrated unambiguously that there is a frequency (energy) and size dependent gain threshold above which the stationary results become unstable. This threshold corresponds to the value of the gain at which the pole crosses the real axis.