Characteristics Of Electromagnetic Waves Research Articles

Design and application of flat spiral phase plate

Phase is an important characteristic of electromagnetic waves. It is well known that a beam with a helical wave front characterized by a phase of <inline-formula><tex-math id="M1">\begin{document}$\exp({\rm{i}}l\theta )$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181677_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181677_M1.png"/></alternatives></inline-formula> (which depends on azimuthal angle <inline-formula><tex-math id="M2">\begin{document}$\theta$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181677_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="5-20181677_M2.png"/></alternatives></inline-formula> and topological charge <i>l</i>), has a momentum component along the azimuthal direction, resulting in an orbital angular momentum of per photon along the beam axis. Owing to its fascinating properties, the beam has received a great deal of attention and has provided novel applications in manipulation of particles or atoms, optical communication, optical data storage. In order to meet the needs of various applications, techniques for efficiently generating optical beams carrying orbital angular momentum are always required. Current schemes for generating the beams carrying orbital angular momentum include computer-generated holograms, spiral phase plates, spatial light modulators, and silicon integrated optical vortex emitters. Among the usual methods to produce helical beams, the traditional spiral phase plate is an optical device that utilizes the progressive increasing of height of a dielectric material along an azimuthal direction to produce a vortex beam for beam phase modulation with a high conversion efficiency. However, it is difficult to regulate the topological charge <i>l</i> of the outgoing beam through the superposition of the phase plates due to the special geometric feature. In this paper, the flat spiral phase plate is designed by compressing the height of traditional spiral phase plate, and inducing the refractive index to increase in the azimuthal direction based on coordinate transformation. By means of theoretical analysis and numerical simulation, it is found that the flat spiral phase plate can produce high quality vortex beams just as the traditional spiral phase plate can do. Particularly, the height of the flat spiral phase plate and the topological charge <i>l</i> carried by the vortex beams can be arbitrarily adjusted according to the refractive index selection of the dielectric material. In order to meet the needs of practical applications, the vortex beams with different topological charges can be obtained by stacking multiple layers of flat spiral phase plates. The flat spiral phase plate has broad potential applications in the fields of optical transmission and optical communication.

Features of electromagnetic wave propagation in two- and three-layer cylindrical dielectric waveguides

Various characteristics of electromagnetic waves propagating in two- and three-layer open-dielectric waveguide structures of cylindrical shape are studied. Parameters of wave components in separate areas of the waveguide are considered. Electrodynamic characteristics and frequency dependencies for several values of layer dielectric permittivity obtained during the study are analyzed. The corresponding graphs of dependencies are presented. The dependencies of the power flux density of transverse magnetic (TM) waves in two- and three-layer waveguide structures in the absence of field dependence on azimuthal angle are considered.

Study on the propagation properties of TM electromagnetic wave in Lossy left‐handed material based on CUDA‐implemented parallel

By using the method of Finite Difference Time Domain (FDTD) and the technology of Compute Unified Device Architecture (CUDA), the propagation characteristics of electromagnetic waves in Left-Handed Materials (LHM) have been studied in this paper. The LHM slab was matched with the free space and the secondary focusing phenomenon of LHM was simulated. Compared with the serial FDTD program, our work showed that this method had a high accuracy. The phase compensation effect and the inverse Snell effect of LHM were also discussed by using the parallel FDTD method based on CUDA, which further proved that our results were consistent with the theoretical study. By comparing the calculation time of traditional FDTD program with that of the CUDA based parallel FDTD program, we conclude that the latter is more efficient than the former. This parallel method can be used as a more efficient way to study LHM.

Dispersion properties of one-dimensional magnetized ferrite photonic crystals in transverse magnetization configuration for transverse magnetic modes

The dispersion characteristics of electromagnetic wave in one-dimensional magnetized ferrite photonic crystals containing yttrium iron garnets and nickel ferrite in a unit cell is investigated for transverse magnetic mode when external magnetic field is perpendicular to the plane of wave propagation. The dispersion relation is derived using transfer matrix method based on the continuity conditions of tangential electric and magnetic field components. It is observed that dispersion properties and phase index are strongly dependent on the normalized parallel wave vector and the filling factor. At the Brewster angle, width of photonic band gap shrinks to zero. Also, the considered structure indicates its dielectric behavior for electromagnetic wave propagation.

Electromagnetic Waveform Identification of Electric Spark Based on BP Neural Network

Electromagnetic wave of electrical spark is a potential cause to eletrical equipment failure. This research focused on identificating and comparative analyzing the different types of electromagnetic waveform generated by eletrical equipment failure based on BP neural networks. After analyzing and extracting the features the electromagnetic waveform, BP neural network was chosen to build and train model because of fewer actual samples. The collected standard electromagnetic waveforms were used as the input of the train model, so that the nonlinear mapping between the input electromagnetic wave characteristics and the output electromagnetic wave types of the network can be maximally simulated. The model accuracy was improved by adjusting training parameters after analyzing the results. Then adjusted models were used to identificate the types of electromagnetic waveforms. The result shows that the identification of electrical spark electromagnetic waveform based on BP neural network is effective and feasible.

Propagation characteristics of electromagnetic wave on multiple tissue interfaces in wireless deep implant communication

The use of wireless networked miniaturised medical implants is promising a significant leap forward in health monitoring and medical treatment. In contrast to conventional wireless communication which takes place over the air, implant communication through the body poses unique challenges. Considering there is less literature available on out-to-in and in-to-out propagation mechanisms on the different tissue interfaces for deep implant communication, in this study, the multi-layered planar model and the mathematical equations of multiple incidence are proposed to calculate and analyse some key transmission characteristics of body channel. The authors take human arm as the research object, and compute four cases of electromagnetic wave normal incidence on multi-layer human body tissues with different positions of the deep implant at the frequency of 10 Hz-100 GHz. They also establish a simulation model of normal incidence on three-layer human body tissues at a frequency of 2.45 GHz based on the finite-element method in COMSOL Multiphysics. The relative differences in simulation results are all <;3.14%, which show a good agreement with the theoretical calculation results.

Scattering characteristics of electromagnetic waves in time and space inhomogeneous weakly ionized dusty plasma sheath

The dielectric coefficient of a weakly ionised dusty plasma is used to establish a three-dimensional time and space inhomogeneous dusty plasma sheath. The effects of scattering on electromagnetic (EM) waves in this dusty plasma sheath are investigated using the auxiliary differential equation finite-difference time-domain method. Backward radar cross-sectional values of various parameters, including the dust particle radius, charging frequency of dust particles, dust particle concentration, effective collision frequency, rate of the electron density variation with time, angle of EM wave incidence, and plasma frequency, are analysed within the time and space inhomogeneous plasma sheath. The results show the noticeable effects of dusty plasma parameters on EM waves.

Temporal Analysis of S-Band Microwave Backscattering From an Inland Reservoir Surface

This letter presents an analysis of the temporal characteristics of electromagnetic waves scattered from a time-varying reservoir surface at low grazing angles. The data collection campaigns were conducted using a polarimetric S-band radar at Wachusett Reservoir in MA, USA, and VV and HH polarized radar returns were simultaneously captured. The temporal behavior of the backscattering from the reservoir surface was analyzed for 180 distinct radar geometries, focusing in particular on the impact of polarization, radar geometry, and wind condition. To understand the shape of the Doppler spectrum, the power spectral density is estimated by a periodogram. In addition, decorrelation time, Doppler centroid, and variance are estimated and compared with the associated Doppler spectral width and peak Doppler frequency. Results show that Doppler spectral width, decorrelation time, and the standard deviation of Doppler spectra are correlated. In addition, the Doppler frequency shift induced by the motion of the water surface is analyzed by peak Doppler frequency and Doppler centroid, which show dependence on radar geometry and wind direction.

Microstrip line Antenna Fabrication Material

This paper presents an extensive survey of electromagnetic materials used for antenna fabrication, which find application in Civilian life as well as defense life. When a densely packed microwave integrated circuit is designed, it requires protection from higher power transient because of specific polarization and frequency response. To meet specification of such kind of microwave circuits it is desired to exploit properties of fabricating materials, which are not found in nature but can be prepared with specific proportion of chemical element combination. This study provides in-depth responses of materials toward electromagnetic wave's characteristics such as dielectric, flexible electronics, electrical and thermal properties, which have vast potential in communication engineering.

Research on the scattering characteristics of electromagnetic waves in time‐varying and weakly collisional and fully ionized dusty in plasma

In this study, a three-dimensional (3D) time-varying dusty plasma iterative finite-difference time-domain (FDTD) algorithm is deduced by combining the relative permittivity of fully ionised dusty plasma and the shift-operator FDTD method. Then, a 3D time-varying dusty plasma model is established. The scattering characteristics of electromagnetic (EM) waves are analysed by calculating the backward radar cross-sections (RCSs) of different parameters in time-varying dusty plasma. The results show that the RCS will increase when the dust particles are considered in plasma. The values of RCS increase with the dust radius dust concentration relaxation time of charge and electron density increasing. In dusty plasma, the electron temperature has a different effect on the incident wave frequency bands. Finally, the effects of dust to electron density ratio on RCS are analysed and as the increase of the incident frequency, the absorption of dusty plasma on EM wave will reduce.

Effect of cell morphology on electrical properties and electromagnetic interference shielding of graphene-poly(methyl methacrylate) microcellular foams

Nowadays, polymer-based foams have gained much attention for absorption of electromagnetic wave due to their desirable properties such as wide absorption band, low reflection and also light weight. However, the impact of the foam morphology including shape, cell size and its structure as open and close cell, on the electromagnetic wave has been rarely investigated. In this study, the operational conditions for manufacturing various structured foams based on poly(methyl methacrylate)/graphene nanoparticle sheets have been optimized for investigating the effect of cellular structure on the characteristics of electromagnetic wave as well as electrical properties. Hence, a foaming system with great controllability and repeatability has been employed. It should be noted that this system is capable of stabilizing the cellular structure with millisecond accuracy during and after the pressure drop. The close cell structured foam showed a decrement in the electrical and electromagnetic properties with increasing the cell size and shifting from spherical to polygonal shape. Moreover, the results related to the prepared open cell structured foams with similar cell size and density to close cell ones, have demonstrated higher absorption characteristics for microcellular open cell foams while shielding was better in close cell counterparts.

Propagation characteristics of electromagnetic waves in dusty plasma with full ionization

This study investigates the propagation characteristics of electromagnetic (EM) waves in fully ionized dusty plasmas. The propagation characteristics of fully ionized plasma with and without dust under the Fokker–Planck–Landau (FPL) and Bhatnagar–Gross–Krook (BGK) models are compared to those of weakly ionized plasmas by using the propagation matrix method. It is shown that the FPL model is suitable for the analysis of the propagation characteristics of weakly collisional and fully ionized dusty plasmas, as is the BGK model. The influence of varying the dust parameters on the propagation properties of EM waves in the fully ionized dusty plasma was analyzed using the FPL model. The simulation results indicated that the densities and average radii of dust grains influence the reflection and transmission coefficients of fully ionized dusty plasma slabs. These results may be utilized to analyze the effects of interaction between EM waves and dusty plasmas, such as those associated with hypersonic vehicles.

Wave Absorption and Thermal Stability of Nickel Coated Al2O3 Core-shell Composite Powder

As a composite cermet material, the nickel coating on the surface of alumina particles has important application value because of its good electromagnetic wave absorption performance. In this study, nickel was deposited on the surface of alumina nanopowders by hydrothermal method and sintering method. The results show that the XRD results of nickel alumina show that Ni-Al2O3 nanoparticles has FCC face-centered cubic structure. The grain size is about 50 nm. The absorption characteristics of electromagnetic waves were measured at 2-18 GHz by HP 8722 es microwave network analyzer. The results show that Ni-Al2O3 nanoparticles has certain wave-absorbing properties.

Transmission characteristics of terahertz wave in high temperature plasma

In the hypersonic flight, the air surrounding an aircraft under the effect of high temperature will be ionized. The ionized gas is called plasma. Because of the influence of interaction between electromagnetic wave, in some cases the communication will be interrupted. High temperature effect is an important characteristic of the plasma. Therefore, the study of terahertz wave propagation in high temperature plasma is of great significance. In this paper, the transmission of terahertz wave in a high temperature plasma slab is studied. Generally, high temperature plasma is an anisotropic medium. The electromagnetic wave propagates in anisotropic high-temperature plasma and forms left-hand circular polarization mode or right-hand circular polarization (RCP) mode. It is found that the RCP wave can exhibit some novel characteristics, such as the forbidden band transmission characteristics, which is discovered in this paper. The transmission characteristics of terahertz wave in high temperature plasma are studied analytically. The results show that when the frequency of terahertz wave is lower than plasma frequency, the wave cannot be propagated in high temperature plasma, and it shows a stopband characteristic. When the frequency is higher, it can be transmitted through the plasma, and it presents a passband characteristic. These are consistent with the propagation characteristics of electromagnetic waves in cold plasma. However, some characteristics in high temperature plasma are different from those in the cold plasma. In high temperature plasma, the transmission characteristics are influenced by the electron temperature and external magnetic field. When the two parameters are chosen appropriately, a sharp transmission peak will be produced in the stopband. This phenomenon has never been found in cold plasma models before. And the paper will discuss this problem by the two influencing factors. It is also found that the frequency of the transmission peak is affected by magnetic field, and the peak amplitude is influenced by electron temperature. The electron temperatures at high transmittance (transmittance is about 1) under different applied magnetic fields are calculated. In order to study the law embodied in the data, the method of data fitting is adopted. And the formula of transmission peak frequency is obtained by curve fitting. The fitting results show that the transmission peak frequency is proportional to the external magnetic field. The relationship between peak electron temperature and external magnetic field is exponential. Finally, the fitting formula is verified by the finite-difference time-domain method. The numerical results are in good agreement with the analytical solution results, which proves the correctness of the work.

Experimental study of electromagnetic wave transmission characteristics in S-Ka band in plasma

When hypersonic vehicle flies in the atmosphere at a high altitude with a high speed, plasma sheath is generated around the vehicle, and thus attenuating the electromagnetic wave signals and even interrupting the communication. Therefore the control, guidance, and navigation of hypersonic vehicle can be affected seriously by the plasma sheath. It is necessary to study this problem in reasonable ground experiment. The inductively coupled plasma (ICP) wind tunnel is an ideal equipment for studying electromagnetic transmission characteristics in plasma because it can produce uncontaminated plasma and the electrode cannot be ablated in the process of plasma production. We carry out the experiment in ICP wind tunnel. A thin slice of plasma jet is generated by a rectangular nozzle with an outlet size of m 50 mm250 mm. Plasma jets with different parameters are obtained by adjusting the operating power and inlet flow of the wind tunnel. Four kinds of states are provided with the electron densities of 7.01010, 5.01011, 3.51012 and 1.01013/cm3, and the collision frequencies of 1.5109, 1.6109, 2.0109 and 9.0109 Hz, respectively. The amplitude attenuations and phase changes of the electromagnetic waves are measured with microwave diagnostics system consisting of a vector network analyzer and high gain antennas. And electron density and collision frequency of plasma are obtained according to the transmission characteristics of electromagnetic waves in plasma. The attenuations of the electromagnetic wave in plasmas of different states are measured via microwave transmission system which is composed of a vector network analyzer and pairs of horn antennas covering a frequency range of 2.6-40 GHz. The results show that both the amplitude attenuation and attenuation band increase with the increase of electron density. The classical theory and thin layer theory are used to simulate the transmission attenuation. The results are compared with the experimental ones. The results in this paper provide basic data for further theoretical and numerical study of electromagnetic wave transmission characteristics in plasma.

Features of control of characteristics of radio engineering devices in the multi-wave mode of operation

In multi-wave elements of radio devices at frequencies, 1,2,..., 10 times the operating frequency, conditions arise for the propagation of several types of waves. This leads to the dependence of the characteristics of electronic devices and, consequently, the parameters of frequency selectivity on the spatial structure (spatial spectrum, mode composition) of the electromagnetic signal at the input of the element under study. The presence of such” spatial selectivity” requires taking into account the features of the multi-wave mode in solving various problems of electromagnetic compatibility. The article is devoted to the actual problemthe development of new methods of experimental research and control of the characteristics of electromagnetic waves of radio devices operating in multi-wave mode. The solution of the problem of studying the impact of a plane electromagnetic wave on the emitters of the radio-thnical system is carried out. The analytical calculation of the electrodynamics effects in the multi-wave mode is carried out.

Collision effects on propagation characteristics of electromagnetic waves in a sub-wavelength plasma slab of partially ionized dense plasmas

Intensive collisions between electrons and neutral particles in partially ionized plasmas generated in atmospheric/sub-atmospheric pressure environments can sufficiently affect the propagation characteristics of electromagnetic waves, particularly in the sub-wavelength regime. To investigate the collisional effect in such plasmas, we introduce a simplified plasma slab model with a thickness on the order of the wavelength of the incident electromagnetic wave. The scattering matrix method (SMM) is applied to solve the wave equation in the plasma slab with significant nonuniformity. Results show that the collisions between the electrons and the neutral particles, as well as the incident angle and the plasma thickness, can disturb the transmission and reduce reflection significantly.

High-efficiency broadband polarization converter based on Ω-shaped metasurface

The polarization state, which cannot be directly detected by human eyes, forms an important characteristic of electromagnetic waves. Control of polarization states has long been pursued for various applications. Conventional polarization converters can hardly meet the requirements in lab-on-chip systems, due to the involvement of bulk materials. Here, we propose the design and realization of a linear to circular polarization converter based on metasurfaces. The metasurface is deliberately designed using achiral two-fold mirror symmetry Ω-shaped antennas. The converter integrates a ground metal plane, a spacer dielectric layer and an antenna array, leading to a high conversion efficiency and broad operating bandwidth in the near infrared regime. The calculated Stokes parameters indicate an excellent conversion of linear to circular polarization for the reflected light. The tunability of the bandwidth by oblique incidence and by modulating the thickness of the dielectric layer is also introduced and demonstrated, which shows great flexibilities for such metasurface converters. The proposed metasurface may open up intriguing possibilities towards the realization of ultrathin nanophotonic devices for polarization manipulation and wavefront engineering.

On the Feasibility of Gap Detection of Power Transformer Partial Discharge UHF Signals: Gap Propagation Characteristics of Electromagnetic Waves

This study analyzed the transformer electromagnetic gap propagation characteristics. The influence of gap size is also analyzed, and the results experimentally verified. The obtained results indicated that the gap propagation characteristics of electromagnetic wave signals radiated by the partial discharge (PD) source in different directions are substantially different. The intensity of the electromagnetic wave in the gap reaches a maximum at a gap height of 1 cm; and inside the gap, the intensity of the electromagnetic wave depicted an increasing trend at the tail area of the gap. Finally, from the obtained results, some suggestions on where to install sensors in practical systems for ultra high frequency (UHF) PD signal detection in the transformer gap are provided. The obtained results confirmed the feasibility of using this approach. These results can be seen as a benchmark and a challenge for further research in this field.

A comparative study on the propagation characteristics of electromagnetic waves in inhomogeneous plasma sheath

A plasma sheath is formed on the surface of high speed spacecrafts when they return to atmosphere, which leads to electromagnetic waves be reflected, absorbed, and finally the intensity decreases. In this paper, the hyperbolic electron number density distribution model is established firstly. Then, the power reflection coefficient, power absorption coefficient and the power transmission coefficient of this model is derived by the analytic method. Finally, this study mainly focuses on the comparison of the analytic method and Wentzel-Kramer-Brillouin (WKB) method about their applicability and limitations, by discussing the electromagnetic wave power transmission coefficient of one-dimensional case. In short, the related research can provide a theoretical reference for the spacecraft to overcome the “blackout” effect of communication.