Propagation Characteristics Of Electromagnetic Waves Research Articles

Electromagnetic propagation characteristics of one-dimensional photonic crystals with metal layers in quasi-parity-time (PT)-symmetric system

Abstract In this study, the propagation characteristics of electromagnetic waves in a parity-time (PT)-symmetrical 1D photonic crystal comprising dispersed silver layers are investigated. Based on the transmission matrix theory, the total reflection and transmission coefficients of the structure are obtained. It was found that, due to the PT-symmetrical structure, the reflections of the left and right incident waves are nonreciprocal. Numerical simulations indicated that the width of the band gap decreases with the increase in the gain and loss factor ρ in the PT medium, and the band gap ultimately disappears when ρ reaches a critical value, i. e., ρ P T ${\rho }_{PT}$ . With the increase in ρ > ρ P T $\rho { >}{\rho }_{PT}$ , anomalous transmittance and reflection occur within the original bang gap. As the gain and loss factor ρ continue to increase, the abnormal transmittance and reflectivity exhibit a trend of oscillatory decline, and perfect transmission can be achieved at larger values of ρ.

Experimental Investigation on Electromagnetic Waves Transmitting Through Exhaust Plume: From Propagation to Channel Characteristics

Exhaust-plume-induced plasma from solid rocket engines absorbs electromagnetic (EM) waves and may cause communication interruptions. Previous articles have proposed both physical phenomena and propagation models for this problem, but few articles have analyzed random fluctuations of EM waves propagating through plumes from a communications perspective. This article attempts to attach these fluctuations, which are caused by the plume-induced turbulent plasma spread medium, to the communications channel characteristics. A multi-parameter stochastic model is established to characterize the exhaust plume channel in which the first-order and the second-order statistical properties are presented. Accordingly, a ground firing test was conducted to validate the EM wave propagation characteristics and the channel characteristics. The experimental results are in good consistence with the theoretical results. The results indicated that the time-varying envelope of the transmitted EM waves obeys a log-normal distribution, whereas the time-varying phase shift obeys a normal distribution. Moreover, the time–frequency analysis method was applied to evaluate the EM–plume interactions in the time–frequency domain. These results are critical for designing the rocket communication systems and evaluating the systems performance.

Extraordinary propagation characteristics of electromagnetic waves in one-dimensional anti-PT-symmetric ring optical waveguide network**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674107, 61475049, 11775083, 61875057, 61774062, and 61771205), the Natural Science Foundation of Guangdong Province, China (Grant No. 2015A030313374), and the Special Funds for the Cultivation of Guangdong College Students’ Scientifific and Techonlogical Innovation, China (Grant No.

In this paper, we design a one-dimensional anti-PT-symmetric ring optical waveguide network (1D APTSPROWN). Using the three-material network equation and the generalized Floquet–Bloch theorem, we investigate its photonic mode distribution, and observe weak extremum spontaneous anti-PT-symmetric breaking points (WBPs) and strong extremum spontaneous anti-PT-symmetric breaking points (SBPs). Then the transmission spectrum is obtained by using the three-material network equation and the generalized eigenfunction method. The 1D APTSPROWN is found to generate ultra-strong transmission near SBPs and ultra-weak transmission near WBPs and SBPs, with the maximal and minimal transmissions being 4.08× 1012 and 7.08× 10−52, respectively. The maximal transmission has the same order of magnitude as the best-reported result. It is not only because the distribution of photonic modes generated by the 1D APTSROWN results in the coupling resonance and anti-resonance, but also because the 1D APTSROWN composed of materials whose real parts of refractive indices are positive and negative has two kinds of phase effects, which results in the resonance and anti-resonance effects in the same kind of photonic modes. This demonstrates that the anti-PT-symmetric and PT-symmetric optical waveguide networks are quite different, which leads to a more in-depth understanding of anti-PT-symmetric and PT-symmetric structures. This work has the potential for paving a new approach to designing single photon emitters, optical amplifiers, and high-efficiency optical energy saver devices.

Satellite launch vehicle effect on the Earth’s lower ionosphere: A case study

The effect of the rocket exhaust products on the D-region of the ionosphere is investigated with the help of Very low frequency (VLF) electromagnetic wave propagation characteristics within the Earth-ionosphere waveguide. The changes in the electron density profile are computed from the observed VLF signal amplitude perturbations about 3 dB during the rocket launch. We find a localized electron depletion in the lower ionosphere at an altitude of around 58 km, that is thought to be originated by the attachment of ionospheric ion and molecular hydrogen along with water molecule in the exhaust product of first stage burn of Geosynchronous Launch Vehicle (GSLV) rocket at the time of GSLV launched from Sriharikota, India, on 27 August 2015 at 11:22 UT (16:52 IST). The ionospheric depletion perturbed the navigational VLF signal (VTX = 17 kHz) 134 s after the launch of the GSLV rocket.

Numerical Simulation of the Plane Electromagnetic Wave Transient Propagation in Lossy Medium

In the field of geophysical exploration, it is of great value to study the transient propagation characteristics of electromagnetic waves in lossy medium. The equations of electric field and magnetic field are derived. The absorbing boundary conditions and numerical stability conditions are analyzed. The two-layer medium model is established to simulate the propagation characteristics of plane waves. The simulation results show that the transient analysis of electromagnetic wave propagation can reflect the time fluctuation characteristics of electromagnetic field in multilayer media, and provide the indication of the boundary position.

The study of spatial dispersion effect on electromagnetic waves propagation in the warm non-uniform re-entry plasma sheath

“Communication blackout” is such a consequence that the attenuation of electro-magnetic (EM) waves becomes drastic when the frequency of EM waves is near or below the oscillation frequency of plasmas. Deep comprehension on the propagation characteristics of EM waves in the plasma sheath plays an important role in solving this issue. However, relevant works in the literature are almost based on the cold plasma sheath model, neglecting the temperature of the plasmas as well as the spatial dispersion effect. We apply COMSOL Multiphysics software to simulate and study the spatial dispersion effect in the warm plasma sheath in this paper. The mode conversion between EM waves and Langmuir waves in the warm plasmas is observed. The characteristics of field distributions in the warm plasma sheath are different from the cold plasma sheath distinctly, when the resonance between EM waves and the plasmas happens. The reflection and absorption coefficients are also influenced accordingly. The research in this paper gives an insight into EM waves propagation in the warm re-entry plasma sheath and supplies a better comprehension on the interaction between EM waves and the plasma sheath.

Incorporating electromagnetic measurements into drilling systems with a relay station

Electromagnetic measurement while drilling (EM-MWD) systems transmit downhole data by emitting electromagnetic waves into the formation, thereby carrying the emitted data to a surface antenna; however, these electromagnetic waves are attenuated when transmitted into the formation. To further extend depth capabilities, Extended-Range EM-MWD systems have been developed. Expanding on this approach, this paper introduces an EM-MWD system that incorporates a relay station within ultra-deep wells; our proposed system consists of a downhole instrument assembly, a relay station and a ground receiver assembly. After decoding a received signal, the relay station amplifies, filters and recodes the signal; then, the relay station emits the augmented signal. Through numerical simulations, as presented in this paper, propagation characteristics of electromagnetic waves in heterogeneous and stratified strata show that when the resistivity of the upper formation and the lower formation is kept constant, the voltage of the ground receiving signal first increases and then decreases with the increased resistivity of the interlayer. Similarly, when the resistivity of the upper stratum and interlayer is kept constant, the voltage of the ground receiving signal first increases and then decreases with the increased resistivity of the lower stratum. This paper also presents the design schemes, the technology used to process the insulation gap, and the power-saving technology to increase the lifetime of the downhole instruments. Furthermore, the working principle of the relay station is described. Moreover, by analysing the electric and magnetic excitation methods, under the same conditions, signal attenuation is fast and the signal strength obtained on the ground is low when magnetic excitation is used. Therefore, an electric excitation method is adopted for implementing the relay station. To conclude, suggestions as to reasonable locations of the relay station and reception and decoding of the ground signal are provided.

Forward recursion approach of electromagnetic wave propagation characteristics in a slab of inhomogeneous magnetoplasma

Propagation characteristics of electromagnetic radiation incident on an inhomogeneous magnetoplasma slab near a good conducting metallic surface is investigated. The inhomogeneous plasma slab is divided into thin layers (sub-cells) in order to allow for treating each plasma sub-cell as a homogeneous medium. A global matrix is formed upon matching the fields at all interfaces, which allows for the analytical determination of the reflection, absorption and transmission coefficients. For matching the tangential fields at the metallic surface, an impedance (Leontovich) boundary condition has been used. Propagation characteristics are calculated numerically for a set of parameters that may be suitable for many applications including stealth plasma. Numerical results show resonant absorption peaks near the electron cyclotron frequency that increase by increasing the equilibrium plasma density. They also show absorption enhancement by increasing the plasma slab width.

Propagation characteristics of electromagnetic waves in mine roadways

The environment of an underground roadway following a mine disaster affects multimedia communication during mine rescue. The propagation characteristics of electromagnetic waves in a wireless mesh network were studied by means of theoretical analysis, experiments, and simulations. The roadway shape factor, dust in the roadway, and its surface roughness are the main factors affecting signal attenuation. When the roadway shape factor tended to 2, signal attenuation was minimal; as the dust concentration in the roadway increased, signal attenuation increased. When operating frequencies of 600, 900, 1800, and 2400 MHz were evaluated in a curved roadway, it was found that attenuation of the 900 MHz signal was smallest and that of 2400 MHz was largest. Signal attenuation increased with increase in the incident angle of the electromagnetic waves and the undulation height of the roadway; variation of the incident angle exerted the greater influence.

Measurement of Water Holdup in Oil-Water Two-Phase Flows Using Coplanar Microstrip Transmission Lines Sensor

This paper presents the research of water holdup detection in oil-water two-phase flows and sensor design based on coplanar microstrip transmission line (also known as coplanar waveguide, CPW). The relationship between the CPW structure/material parameters and electromagnetic wave propagation characteristics was analyzed using conformal transformation method. Adopting double-sided and S-shaped wiring sheet structure, the dynamic range of detection is improved while the structure of the sensor is miniaturized. Therefore, multiple sensors can be arranged on the cross-section of the oil well to form a detection array, which can provide differential information of water holdup on the cross-section of horizontal wells or highly deviated wells and improve the spatial resolution of the measurement. Numerical simulations and experimental results show that the phase shifts of the signal detected by sensors are approximately linearly proportional to the water holdup of the measured fluid, the resolution is up to 3% in the whole range of water holdup from 0% to 100%. This method makes up for the disadvantages of capacitance method and conductance method, which are only effective for low water holdup and high holdup scenarios respectively.

Equivalent Circuit Model for One-Dimensional Plasma Photonic Crystals

Plasma photonic crystals (PPCs) is promising metamaterial for electromagnetic wave transmission, due to its superior performance and broad application prospects. However, the design of plasma photonic crystals with adjustable structural parameters is one of the main issues limiting its commercial application. We propose a new method to use the equivalent circuit model to quickly analyze the electromagnetic wave propagation characteristics of 1D PPC. The 1D PPCs structure was constructed with vacuum discharge tube, and we found that the experiment is consistent with the simulation. The research results provide theoretical guidance for the design and optimization of microwave segment multi-channel filters and dynamic microwave devices.

Matlab Simulation of Electromagnetic Waves Propagation Characteristics

Military technology has developed rapidly in recent years and used widely in marine communications, maritime aviation, and underwater exploration. With the rapid development of signal processing and antenna technologies, underwater electromagnetic communication has received much attention. Since water is a conductive medium, characteristics exhibited by electromagnetic waves in water are fundamentally different from those in oil. In order to better study the propagation characteristics of electromagnetic waves within the medium, the simulation of the electromagnetic wave propagation in water and oil were conducted using MATLAB, and variation of the electric field and magnetic field vector with time were obtained. Moreover, the three-dimensional real-time graphics of electromagnetic wave propagation can also be simulated in MATLAB; different patterns of electromagnetic waves propagating in oil and water were generated.

Study of the electromagnetic wave propagation in realistic plasma

AbstractA self‐consistent calculation model combining flow field and electromagnetic wave propagation is presented. The hypersonic flow field around the RAMC‐II vehicle at different reentry heights is numerically solved using a computational fluid dynamics technique with a two‐dimensional model, and then perform self‐consistent calculations in conjunction with electromagnetic wave propagation models. The dependence of wave frequency, polarization mode, incident angle, and plasma collision frequency on the wave propagation is presented. Electromagnetic wave propagation characteristics have been investigated experimentally with shock tube, and the experimental results are consistent with the simulation results. Conclusions in this article can be the foundation to study the interactions between the electromagnetic wave and the realistic reentry plasma sheath.

Simulation of Partial Discharge Induced EM Waves Using FDTD Method—A Parametric Study

This paper reports the results of a parametric study on the characteristics of electromagnetic (EM) waves propagated due to surface- and cavity-type partial discharges (PD) in materials using the finite-difference time domain (FDTD) method. First, the EM waves emitted by such discharges in material samples were measured using a broadband aperture antenna. The measurements showed that the frequency range of the measured signals lay within the ultra-high frequency (UHF) range, suggesting that by carefully choosing the UHF antenna characteristics and its location it might be possible to apply this method to characterize the PD-emitted waves; and hence, to potentially use it to detect and monitor PD defects. In this context, the FDTD simulations were used here to simulate the experimental set-up and examine the propagation characteristics of EM waves emitted by such discharges under uniform and non-uniform test electrode configurations. Using an approximation of the exciting PD current pulses, the electromagnetic field components and the voltage signals captured on a simulated monopole sensor were computed in the time domain at various locations. To explore the limits of the application of the UHF method for detecting these PD types, a parametric study was carried out to clarify how the captured signals are influenced by the PD intensity, the frequency content of the exciting PD pulse, the type of insulation material, the dimensions and the position of the UHF antenna. One of the challenges that needs further investigation is the accurate simulation of the actual PD current pulse produced by such discharges, and hence its frequency content, as there is limited or no measured data available. The results showed that while the amplitude of the captured EM signals increase with the PD intensity, no appreciable signal is detected when the PD pulse width is higher than about 4ns, which may not occur often in unbounded air insulated systems. Equally important is the location and orientation of the UHF sensor—the results showed improved sensitivity when the sensor is vertically polarized and placed in close proximity in the lateral direction with reference to the discharge path.

Study and improvement in the radio communication quality for rotating electrical machine

The wireless communication for rotating electrical machines is beneficial for diagnosis purposes as well as real-time monitoring. The electromagnetic waves propagation characteristics inside electrical machine is rather delicate. So it will be interesting to find a dynamic tool adapted to our problem. The idea is to validate these propagation concepts with real signatures. The tool must then analyze the signatures of the received signal strength indication. These experiments have shown that the antenna rotation is a disturbance-causing factor of the signal transmission. Thus, in this paper, our aim is to analyze the electromagnetic wave propagation characteristics in rotating environments in order to obtain the optimum parameters and providing a strong theoretical support for radio monitoring system performance improvement. Therefore, our work will process the important parameter which is the path loss variation in rotating environments.

The electromagnetic waves propagation characteristics of inhomogeneous dusty plasma

In this paper, the double exponential and hyperbolic electron number density distribution models are firstly established for dusty plasma. And then, the power transmission coefficient and reflection coefficient of those two models are respectively derived based on analytic method. In further, the numerical analysis is used to analyze the propagation characteristics of electromagnetic waves in inhomogeneous dusty plasma, taking rocket exhaust as a typical example. Finally, the comparison between the dusty plasma and common plasma is realized. In a word, the simulation results reveal that the transmission coefficient of dusty plasma is smaller than that of common plasma, and it increases with the increase of incident wave frequency.

EM Waves Propagation Characteristics Based on Modified Dielectric Constant Model in Nonuniform Weakly Ionized Dusty Plasma

The influence of weakly ionized dusty plasma on electromagnetic (EM) wave propagation was investigated to understand blackouts in communications during the reentry of hypersonic vehicles. Adopting the Bhatnagar–Gross–Krook (BGK) collision model and charging theory, the total complex dielectric constant of weakly ionized dusty plasma is derived considering solely: 1) a nonzero minimum velocity of the electron; 2) a contribution of the second term of the collision cross-section; and finally, 3) both 1) and 2) considered. Using the propagation matrix method, we analyzed the dielectric constant and propagation properties from our modified models and those of the traditional model for weakly ionized plasma with and without dust. The results show that, regarding EM waves, the dust-free weakly ionized plasma has a larger coefficient of reflection than weakly ionized dusty plasma. Simultaneous considering nonzero velocity and contribution of the second term of the collision cross-section significantly changed the dielectric constant and propagation properties, indicating the nonnegligible role of these two factors. Furthermore, the influence of dust size and concentration on the propagation properties of the EM wave was discussed with considering the two factors. The simulated results show that the coefficient of absorption increases and the coefficient of transmission decreases with increase in size and concentration of dust particles.

Experimental apparatus for investigating the propagation characteristics of the low-frequency electromagnetic waves in hypersonic plasma fluid generated by shock tube.

The shock tube generates a near real hypersonic plasma sheath environment with high temperature and high pressure for investigating the propagation characteristics of the electromagnetic (EM) waves in a hypersonic plasma fluid. With existing methods, it is difficult to measure the propagation characteristics from the transmitted component of low-frequency (LF) EM waves due to large-size LF focusing antennas and LF shielding structure. In this paper, a novel experimental apparatus is proposed to measure the propagation characteristics of the LF EM waves in a shock-tube-generated hypersonic plasma fluid. The tested plasma is utilized as a dynamic fluid EM shield of a receiver during the experiment. This individual receiver is placed in the center of the experimental segment tube of the shock tube so that it is enveloped completely by the hypersonic plasma fluid during the shock, thereby only allows the transmitted component of the LF EM waves to reach the receiver. The proposed method guarantees good measurement accuracy without requiring large LF focusing antennas, and the complex LF shielding structure extends to the shock tube. Both experiments and simulations were performed to evaluate its performance. The results indicated that the propagation characteristics of the transmitted magnetic field component meet that of the numerical simulations faithfully, where the shock wave velocity reached approximately 5 km/s, the plasma layer thickness was 80 mm, the electron density was 1012-1013/cm3, and the collision frequency was approximately 36 GHz. The proposed experimental apparatus is also suitable in studying the EM wave propagation, testing communication system performances, and testing the properties of transmitting and receiving antennas in the hypersonic plasma fluid.

Propagation characteristics of THz waves in space-time inhomogeneous and fully ionized dusty plasma sheath

When a hypersonic vehicle flies in near-space, the electron density of the plasma surrounding the aircraft is inhomogeneous and varies with time. Ablation occurs around the vehicle as the temperature rises. Therefore, investigating the propagation characteristics of electromagnetic (EM) waves in a space/time inhomogeneous and fully ionised dusty plasma sheath is important. In this article, a space/time inhomogeneous dusty plasma sheath model is first established. The expression of the dielectric coefficients of weakly collisional and fully ionised dusty plasma sheath is adopted. The shift-operator finite difference time-domain method is used to calculate the reflection and transmission coefficients of different dusty particle concentrations and radii, changes in electron density with time, electron temperatures and ion charges in the terahertz (THz) band. Finally, the propagation characteristics of THz waves with different electron density distributions at eight re-entry heights are analysed. Results show that increasing the incident wave frequency can effectively improve the effects of dusty particle concentration and radius, electron temperature and ion charge on the transmission of the EM wave. Different electron density change forms and electron density distributions significantly influence the propagation properties of THz waves.

Parabolic Equation Modeling of Electromagnetic Wave Propagation over Rough Sea Surfaces.

The parabolic equation is an efficient numerical solution for electromagnetic wave propagation. In order to address the difficulties in predicting electromagnetic wave propagation in the maritime environment caused by atmospheric dust and rough sea surfaces, and the shortcomings of the existing research that cannot fully reflect the rough characteristics of sea surfaces, the authors have modelled electromagnetic wave propagation in the maritime environment, including in the presence of atmospheric dust. In this study the authors present a parabolic equation modeling method for calculating the electromagnetic wave propagation over rough sea surfaces. Firstly, the rough sea surface is generated by building a double summation model of three-dimensional random sea surface. Then, combined with the piecewise linear shift transformation method of the parabolic equation model, the parabolic equation random sea surface model is constructed, and the electromagnetic wave propagation characteristics in a rough sea environment are analyzed. Finally, a large number of results are compared with the Miler-Brown model and shadow effect model in rough sea environments, which verifies that the random sea surface model can better characterize the influence of rough sea surfaces on electromagnetic wave propagation. The model can be used to improve the reliability of marine microwave communication links and the detection performance of ship-borne radar.