Propagation Characteristics Of Electromagnetic Waves Research Articles

Path-Loss Modeling for Wireless Sensor Networks: A review of models and comparative evaluations

Propagation models are used to abstract the actual propagation characteristics of electromagnetic waves utilized for conveying information in a compact form (i.e., a model with a small number of parameters). The correct modeling of propagation and path loss is of paramount importance in wireless sensor network (WSN) system design and analysis [1]. Most of the important performance metrics commonly employed for WSNs, such as energy dissipation, route optimization, reliability, and connectivity, are affected by the utilized propagation model. However, in many studies on WSNs, overly simplistic and unrealistic propagation models are used. One of the reasons for the utilization of such impractical propagation models is the lack of awareness of experimentally available WSN-specific propagation and path-loss models. In this article, necessary succint background information is given on general wireless propagation modeling, and salient WSN-specific constraints on path-loss modeling are summarized. Building upon the provided background, an overview of the experimentally verified propagation models for WSNs is presented, and quantitative comparisons of propagation models employed in WSN research under various scenarios and frequency bands are provided.

Frequency changes of electromagnetic waves in simple polar-molecule reactions

Characteristics of electromagnetic wave (EMW) propagation in microwave-assisted chemical reactions are critical to solve the problems of inhomogeneous heating and thermal runaway. By transforming the propagation equation of EMWs in simple polar-molecule reactions, the dispersive and time-varying characteristics of simple polar-molecule reactions are unfolded. Subsequently, we simulate the propagation of EMWs in simple polar-molecule reactions to disclose the effects of component concentration variation on frequency changes. Frequency changes can be neglected during the process of component concentration variation on the condition that the time scale of the variation is much greater than the wave period. If the time scale of the variation is comparable with or smaller than the wave period, frequency broadening or shift can be observed. Frequency changes are used to discuss the relationship between the time domain and frequency domain representation of the polarization in the reactions.

Electromagnetic waves propagation in hypersonic turbulence using fractal phase screen method

The experimental fractal measurements of hypersonic turbulence are used to calculate the scaling exponent, spectral index, and power spectrum of hypersonic turbulence. The characteristics of electromagnetic wave propagation through hypersonic turbulence are studied using the fractal phase screen method based on the Weierstrass fractal function. The effects of the fractal dimension, inner scale, outer scale, variance of the refractive index fluctuation, and the wavelength of incident electromagnetic wave on the diffracted average-intensity distribution by a fractal phase screen are analyzed. Results show that the variance of the refractive index fluctuation determines the ratio of coherent to incoherent intensity. The fractal dimension, Reynolds number, and outer scale of hype- rsonic turbulence determine the incoherent field distribution. As the variance of the refractive index decreases, the coherent portion of the diffracted average intensity becomes clearer. With the increasing fractal dimension, the maximum diffracted average intensity decreases and the incoherent intensity becomes more evident.

Modeling and simulations on the propagation characteristics of electromagnetic waves in sub-atmospheric pressure plasma slab

Sub-atmospheric pressure plasma slabs exhibit the feature of relatively high plasma number density and high collisional frequency between electrons and neutral gases, as well as similar thickness to the electromagnetic (EM) wavelength in communication bands. The propagation characteristics of EM waves in sub-atmospheric pressure plasma slabs are attracting much attention of the researchers due to their applications in the plasma antenna, the blackout effect during reentry, wave energy injection in the plasma, etc. In this paper, a numerical model with a one-dimensional assumption has been established and therefore, it is used for the investigations of the propagation characteristics of the EM waves in plasma slabs. In this model, the EM waves propagating in both sub-wavelength plasma slabs and plasmas with thicker slabs can be studied simultaneously, which is superior to the model with geometrical optics approximation. The influence of EM wave frequencies and collisional frequencies on the amplitude of the transmitted EM waves is discussed in typical plasma profiles. The results will be significant for deep understanding of the propagation behaviors of the EM waves in sub-atmospheric pressure nonuniform plasma slabs, as well as the applications of the interactions between EM waves and the sub-atmospheric pressure plasmas.

Spiral Wave Law Is Involved in the Unification of Four Fundamental Forces and the Origin and the Evolution of the Universe

A long-term goal of theoretical physics is to develop a single simple theory or model that would unify the four known fundamental forces (or interactions) and give explanations for the origin and the evolution of the Universe. Here a “spiral wave law” has been proposed based on the previous studies that a consistent universe field presents various forms of spiral (helical) wave motions at the speed of light (c), and therefore, a mathematical equation for the relationship between the radius of a spiral wave motion (r) and its wave length (λ) is derived including a simplified formula ( or ), which could provide a novel explanation for the origin and the evolution of the Universe, and the space-time relationships. This model may give a new way for the unification of four fundamental forces and determine the moving properties of galaxies and basic particles, and the propagation characteristics of electromagnetic waves at the large or small scale.

Propagation characteristics of terahertz waves in temporally and spatially inhomogeneous plasma sheath

The plasma sheath is produced by high-temperature heating during the reentry of a hypersonic vehicle to the Earth atmosphere. Temperature around the vehicle rises rapidly because of severe friction with air. The vehicle temperature behind friction is high enough to excite various real gas effects including chemical reactions of air, which contains ablation particles of vehicle, free electrons, and ions. The plasma sheath greatly affects the transmission of electromagnetic waves and has very strong interference on the communication signals, which results in interrupt between the target and the ground station, namely, blackout. The electron density of plasma sheath surrounding the aircraft is inhomogeneous and varies with time. Temperature and pressure will also change at different altitudes. Therefore, it is meaningful to investigate the propagation characteristics of electromagnetic waves in temporally and spatially inhomogeneous plasma sheath. The temporally and spatially inhomogeneous plasma sheath model is introduced and the electron density data of the National Aeronautics and Space Administration (NASA) reentry vehicle is employed. The relationships among temperature, pressure, and collision frequency are obtained with the empirical formula of collision frequency. Then, the reflection coefficient and transmission coefficient of time-varying single layer plasma are calculated with the shift operator finite-difference time-domain (SO-FDTD) method. These results are compared to verify the correctness of the proposed method. Finally, the LTJEC-FDTD method is used to calculate the reflection coefficient, transmission coefficient and absorptivity at different relaxation time, temperature, and pressure in the terahertz (THz) band. The results show that the higher temperature and pressure will enable the electromagnetic wave to penetrate the plasma sheath at high relaxation time of electron density. If the incident wave frequency is lower than the cut-off frequency of plasma, the reflection of electromagnetic wave will be more obvious. However, when the incident wave frequency is in the THz band, the effects of temperature and pressure on the propagation of electromagnetic wave are obviously weakened. The absorption of electromagnetic wave by plasma will be more obvious when the relaxation time, temperature, and pressure decrease. If the relaxation time of electron density is shorter than or equal to the period of THz wave, more energy of electromagnetic wave will be absorbed by the plasma sheath. Contrarily, if the relaxation time of electron density is much longer than the period of THz wave, the absorption of electromagnetic energy will decrease. This study gives some insight into the temporally and spatially inhomogeneous plasma sheath, and provides a theoretical basis for solving the blackout problem.

電磁波伝搬特性解析による金属管内欠陥検出法

電磁波伝搬特性解析による金属管内欠陥検出法

Color Compensation of an Underwater Imaging System Using Electromagnetic Wave Propagation

Images can be obtained by collecting rays from objects. The characteristics of electromagnetic wave propagation depend on the medium. In particular, in an underwater imaging system, the interface between air and water must be considered. Further, reflection and transmission coefficients can be found by using electromagnetic theory. Because of the fact that the values of these coefficients differ according to the media, the recorded light intensities will change. A color image sensor has three different color channels. Therefore, the reflection and transmission coefficients have to be calculated individually. Thereafter, by using these coefficients, we can compensate for the color information of underwater objects. In this paper, we present a method to compensate for the color information of underwater objects by using electromagnetic wave propagation theory. To prove our method, we conducted optical experiments and evaluated the quality of the compensated image by a metric known as mean square error.

Transmission characteristics of microwave in a glow-discharge dusty plasma

In this study, the propagation characteristics of electromagnetic wave in a glow discharge plasma with dust particles are experimentally investigated. A helium alternating current glow discharge plasmas have been successfully generated. Measurements of the plasma parameters using Langmuir probes, in the absence of dust particles, provide plasma densities (ne) of 1017 m−3 and electron temperatures (Te) ranging from 2 to 4 eV. Dusty plasmas are made by adding 30 nm radius aluminum oxide (Al2O3) particles into the helium plasma. The density of the dust particle (nd) in the device is about 1011–1012 m−3. The propagation characteristics of electromagnetic waves are determined by a vector network analyzer with 4–6 GHz antennas. An apparent attenuation by the dust is observed, and the measured attenuation data are approximately in accordance with the theoretical calculations. The effects of gas pressure and input power on the propagation are also investigated. Results show that the transmission attenuation increases with the gas pressure and input power, the charged dust particles play a significant role in the microwave attenuation.

Investigation of Propagation Characteristics of UHF Electromagnetic Wave Due to PD in Switchgear

Investigation of Propagation Characteristics of UHF Electromagnetic Wave Due to PD in Switchgear

Study on the electromagnetic waves propagation characteristics in partially ionized plasma slabs

Propagation characteristics of electromagnetic (EM) waves in partially ionized plasma slabs are studied in this paper. Such features are significant to applications in plasma antennas, blackout of re-entry flying vehicles, wave energy injection to plasmas, and etc. We in this paper developed a theoretical model of EM wave propagation perpendicular to a plasma slab with a one-dimensional density inhomogeneity along propagation direction to investigate essential characteristics of EM wave propagation in nonuniform plasmas. Particularly, the EM wave propagation in sub-wavelength plasma slabs, where the geometric optics approximation fails, is studied and in comparison with thicker slabs where the geometric optics approximation applies. The influences of both plasma and collisional frequencies, as well as the width of the plasma slab, on the EM wave propagation characteristics are discussed. The results can help the further understanding of propagation behaviours of EM waves in nonuniform plasma, and applications of the interactions between EM waves and plasmas.

Electromagnetic wave propagation characteristics in unimolecular reactions

Microwave-assisted chemical reactions have attracted interests because of their benefits for enhancement of reaction rates. However, the problems, such as hot spots and thermal runaway, limit the application of microwaves in the chemical industry. To study the characteristics of electromagnetic wave propagation in a chemical reaction is critical to solve the problems. The research on the characteristics of electromagnetic wave propagation in the unimolecular reaction that is a simple model reaction, can be generalized to the research in a chemical reaction. The approximate expressions of the attenuation and dispersion characteristics of electromagnetic wave propagation in the unimolecular reaction are derived by the nonlinear propagation theory. Specially, when the reaction rate is zero, the derived approximate expressions can be reduced to the formulas in low-loss dispersive media. Moreover, a 1D mold is used to validate the feasibility of the approximate expressions. The influences of the reaction rate and initial reactant concentration on the characteristics are obtained.

電磁波伝搬特性を用いた金属管内の欠陥検出法

Serious defects may occur in metallic tubes used in factories and power plants owing to long-term usage. Until now, various non-destructive inspection (NDI) methods have been proposed to prevent accidents caused by deformation. However, these conventional methods require longer detection times for very long tubes. Therefore, to overcome this limitation, we propose a new detection method using electromagnetic wave propagation characteristics. In the proposed method, metallic tubes are regarded as waveguides, and we can detect defects based on the propagating electromagnetic waves. To verify this method, we conducted experiments using a vector network analyzer. As a result, we found that the proposed method is effective for detecting defects such as foreign matter and cracks, and for estimating the location and direction of the cracks. Furthermore, the proposed method is effective even if there is a bend or a branch in the metallic tubes.

Maximum Rain-Rate Evaluations in Aegean Archipelagos Hellas for Rain Attenuation Modeling at Microwave Frequencies

By utilizing meteorological data such as relative humidity, temperature, pressure, rain rate and precipitation duration at eight (8) stations in Aegean Archipelagos from six recent years (2007 – 2012), the effect of the weather on electromagnetic (EM) wave propagation is studied. The EM wave propagation characteristics depend on atmospheric refractivity and consequently on Rain-Rate which vary in time and space randomly. Therefore the statistics of radio refractivity, Rain-Rate and related propagation effects are of main interest. This work investigates the maximum value of rain rate in monthly rainfall records, for a 5 min interval comparing it with different values of integration time as well as different percentages of time. The main goal is to determine the attenuation level for microwave links based on local rainfall data for various sites in Greece (L-zone), namely Aegean Archipelagos, with a view on improved accuracy as compared with more generic zone data available. A measurement of rain attenuation for a link in the S-band has been carried out and the data compared with prediction based on the standard ITU-R method.

The propagation characteristics of electromagnetic waves through plasma in the near-field region of low-frequency loop antenna

A high-speed vehicle flying through the atmosphere between 100 and 20 km may suffer from a “communication blackout.” In this paper, a low frequency system with an on-board loop antenna to receive signals is presented as a potential blackout mitigation method. Because the plasma sheath is in the near-field region of the loop antenna, the traditional scattering matrix method that is developed for the far-field region may overestimate the electromagnetic (EM) wave's attenuation. To estimate the EM wave's attenuation in the near-field region, EM interference (EMI) shielding theory is introduced. Experiments are conducted, and the results verify the EMI shielding theory's effectiveness. Simulations are also conducted with different plasma parameters, and the results obtained show that the EM wave's attenuation in the near-field region is far below than that in the far-field region. The EM wave's attenuation increases with the increase in electron density and decreases with the increase in collision frequency. The higher the frequency, the larger is the EM wave's attenuation. During the entire re-entry phase of a RAM-C module, the EM wave's attenuations are below 10 dB for EM waves with a frequency of 1 MHz and below 1 dB for EM waves with a frequency of 100 kHz. Therefore, the low frequency systems (e.g., Loran-C) may provide a way to transmit some key information to high-speed vehicles even during the communication “blackout” period.

Electromagnetic field radiated in air from a horizontal/vertical magnetic dipole in sea

The propagation characteristics of electromagnetic (EM) waves across the seawater–air interface influence seawater to air communication. The type of underwater antenna determines EM wave propagation performance. However, studies rarely compared the performance of horizontal and vertical magnetic dipoles (HMD and VMD). In this study, the EM fields in air due to HMD/VMD immersed in sea were derived to provide a basis for selecting a suitable underwater antenna for EM wave propagation in undersea–air communication. Analytic results were obtained from the model of a three-layered conducting media. Associated expressions in air were numerically calculated using the fast Fourier Transform algorithm to present the propagation curves and the distribution patterns of the EM fields. A proof of concept measurement system was constructed, and sea experiments were conducted and compared with theoretical studies. The maximum transmitting–receiving distance in the experiment was achieved by the HMD. The theoretical and experimental results indicate that the HMD antenna is superior to the VMD antenna and that the suggested band of EM wave is feasible for transmission across the seawater–air interface.

The Force-Gradient Symplectic Finite-Difference Time-Domain Scheme for Maxwell's Equations

In this paper, a novel force-gradient explicit symplectic finite-difference time-domain (SFDTD) algorithm based on the T + V type Hamiltonian decomposition is derived to investigate the propagation characteristics of electromagnetic waves, in which Maxwell's equations are numerically integrated by third-order symplectic map combined with force gradient in the time direction. The numerical stability and dispersion analyses are presented. The numerical results effectively confirm that the force-gradient SFDTD (F-SFDTD) method is reliable for electromagnetic wave computation; its accuracy is superior to the non-force-gradient SFDTD method and the traditional FDTD method. The implementation of F-SFDTD method is easily applied to compute the back scattered radar cross sections (RCS) using 2-D TM mode for a perfectly conducting cylinder.

Novel wireless channels characterization model for underground mines

The propagation characteristics of electromagnetic waves in underground mines are different from those in free space because of the harsh underground environment. Physical phenomena like severe reflection, scattering, and diffraction along the mines’ rough walls will affect the propagation of electromagnetic waves. Channel predictions are crucial for reliable and optimal wireless communication in an underground environment. Although there are several channel prediction techniques, most of them are very difficult and time consuming. This work presents a new approach in wireless channel modeling in underground mines. The model is generated by adopting a performance-based approach rather than classical coverage-based approach. This new model, called “Mine Segmenting Wireless Channel Model”, divides the mine area into three main segments: (1) Line-of-Sight (LOS), (2) Partial-Line-Of-Sight (PLOS) and (3) Non-Line-Of-Sight (NLOS). We examine the impact of topology on performance of 802.11b system with Rician/Rayleigh fading.The model is statistically verified using simulations and is applied to fading wireless local area networks channel for IEEE 802.11 applications. Finally, the communication performance of a realistic IEEE 802.11b signal is evaluated in a real underground mine gallery (NORCAT Mine, Sudbury, Ontario, Canada). The results of the actual experiment were very similar to that of the model simulation.

Propagation Characteristics of Circularly and Linearly Polarized Electromagnetic Waves in Urban Macrocell Scenario

Linear polarization (LP) has been the traditional transmission strategy employed in current mobile wireless communication systems. Recently, circular polarization (CP) has regained much interest as CP proves to be a potential candidate to maximize the polarization efficiency component of the link budget. In this paper, the essential concepts of CP are first reinforced by a tutorial description in terms of mathematical insight, propagation characteristics, as well as related applications. Most reported works on CP chiefly focus on the theoretical description of its propagation benefits, such as significant amplitude fade and delay spread (DS) reduction, without simultaneously providing convincing proofs. In other words, CP propagation has not been investigated in sufficient depth. Therefore, we then propose a method for synthesizing CP that is implementation friendly to practical antennas. The engineering validity is subsequently verified by a series of chamber measurements. Intuitively, the polarization trajectory of a synthetical circularly polarized electromagnetic wave is illustrated to further prove the point. Finally, by conducting channel measurement campaigns in a typical urban macrocell scenario, radio propagation characteristics with a dipole as the receive apparatus are analytically extracted for both LP and CP. To facilitate fair competition, the radiation field patterns of two relevant transmitting antennas are intentionally designed to be identical. Numerical results quantitatively demonstrate that, compared with LP, CP can significantly alleviate branch power imbalance between vertical and horizontal polarizations and decrease DS. These advantages are in line with theoretical anticipation and can be fully exploited to upgrade the performance limits of current mobile wireless communication systems.

Investigation on broadband propagation characteristic of terahertz electromagnetic wave in anisotropic magnetized plasma in frequency and time domain

In this paper, we investigate the propagation of terahertz (THz) electromagnetic wave in an anisotropic magnetized plasma by JE convolution-finite difference time domain method. The anisotropic characteristic of the plasma, which leads to right-hand circularly polarized (RCP) and right-hand circularly polarized (LCP) waves, has been taken into account. The interaction between electromagnetic waves and magnetized plasma is illustrated by reflection and transmission coefficients for both RCP and LCP THz waves. The effects of both the magnetized plasma thickness and the external magnetized field are analyzed and numerical results demonstrate that the two factors could influence the THz wave greatly. It is worthy to note that besides the reflection and transmission coefficients in the frequency domain, the waveform of the electric field in the time domain varying with thicknesses and external magnetic fields for different polarized direction has been studied.