Electromagnetic Wave Transmission Characteristics Research Articles

Analysis of the Electromagnetic Wave Transmission Characteristics in Inhomogeneous Plasma Based on an Equivalent Circuit Model

Analysis of the Electromagnetic Wave Transmission Characteristics in Inhomogeneous Plasma Based on an Equivalent Circuit Model

Analysis of electromagnetic waves reflected by re-entry plasma sheath based on CSO-FDTD

A transmission model of terahertz waves in the plasma sheath is established based on a cascaded finite time domain difference method and analyzed the transmission characteristics of electromagnetic waves under the action of an external magnetic field and collision frequency. The flow field around the hypersonic aircraft is simulated and the characteristics of the flow field as the altitude changes of the aircraft are analyzed based on the flow field distribution of the RAM-C (Rapid Attenuation Measurement) vehicle. The results show the transmission characteristics of terahertz waves in plasma that will be affected by flight height, plasma parameters, external magnetic field, and collision frequency. In addition, under the action of an external magnetic field and the different collision frequency, the transmission characteristics of the left-handed terahertz wave will be improved. The application of the magnetic field will introduce an absorption peak in the right-handed terahertz wave, and it will move to the high frequency direction with the increase of the magnetic induction intensity.

Study on weak signal enhancement method in wireless communication under electromagnetic interference environment

In order to overcome the problems of high bit error rate and high signal enhancement time in weak signal enhancement methods, this paper proposes a weak signal enhancement method in wireless communication under electromagnetic interference environment. Firstly, the transmission characteristics of electromagnetic wave are analysed and the attenuation results of electromagnetic wave signal transmission are determined. Then, the bandwidth of weak signal is determined by band-pass sampling theorem, and the key characteristics of weak signal are determined by time-domain characteristic analysis. Finally, the amplitude modulation coefficient is used to adjust the frequency offset and initial phase through a low-pass filter to enhance the weak signal in wireless communication. The experimental results show that the lowest bit error rate of this method is about 1%, the weak signal enhancement time is no more than 2.6 s, and the weak signal enhancement effect is good.

Manipulating electromagnetic waves in a cavity-waveguide system with nontrivial and trivial modes.

The coupled cavity-waveguide approach provides a flexible platform to design integrated photonic devices that are widely applied in optical communications and information processing. Topological photonic crystals that can excite the nontrivial edge state (ES) and corner state (CS) have an unprecedented capability to manipulate electromagnetic (EM) waves, leading to a variety of unusual functionalities that are impossible to achieve with conventional cavity-waveguide systems. In this Letter, two-dimensional photonic crystals consisting of an ES waveguide, a CS cavity, and a trivial cavity are proposed as a means to robustly control the transmission characteristics of electromagnetic waves. As a proof-of-principle example, the analog of electromagnetically induced transparency (EIT) that is tolerated in disorders due to the robustness of the CS is numerically demonstrated. In addition, the analog of multi-EIT is also verified by introducing a trivial cavity with two degenerate orthogonal modes. This unique approach for robustly manipulating EM waves may open an avenue to the design of high-performance filters, modulators, and on-chip processors.

Mie–Debye–Monte Carlo Method to Analyze the Transmission Characteristics of Electromagnetic Waves in Dusty Plasma

Dusty plasma environments, such as aircraft sheaths and rocket exhaust plumes, significantly affect the propagation of electromagnetic (EM) waves. In this study, the Mie theory and the dyadic Green method were used to calculate the Mie scattering cross section, Debye scattering cross section of the surrounding Debye cloud, and Mie–Debye coherence cross section formed by the two scattering fields. We propose that the Mie–Debye model should be regarded as a whole particle, and the dusty plasma can be simplified by assuming that it is composed of Mie–Debye spherical models of different densities. These assumptions were combined with the scattering characteristics of the microscopic Mie–Debye model and Monte Carlo method to analyze the propagation characteristics of EM waves in dusty plasma.

Electromagnetic wave forward modeling of coal-gangue mixed model in top coal caving mining face

The automatic control of top coal caving is of great significance to realize intelligent coal mining. In the process of top coal caving, a coal-gangue mixed area containing coal, gangue, and air is formed at the tail beam of the hydraulic support, which has different electromagnetic parameters, different volumes, and different shapes. To explore the transmission characteristics of electromagnetic wave in coal-gangue mixed model and the influence of different gangue ratios on electromagnetic wave propagation, the coal-gangue mixed model is established based on the random medium theory. Some electromagnetic forward modeling is carried out with different coal-gangue granularities, electromagnetic parameters, and gangue ratios based on finite-difference time-domain (FDTD) and finite-integration time-domain (FITD) methods. The results show that different granularities of coal and gangue will affect the amplitude of electromagnetic wave time-domain waveform. Under the same particle size, the equivalent electromagnetic parameters in the coal-gangue mixed medium will be larger with higher gangue ratio. Furthermore, the difference of transmitted wave signals between different gangue ratios will be larger with higher electromagnetic parameters difference of the coal and gangue. For higher refractive index, the propagation velocity of electromagnetic wave in the medium and the transmitted wave amplitude will be smaller. In addition, the comparison results illustrate that the rules of electromagnetic wave propagation obtained by FDTD and FITD methods are basically the same, which verifies the correctness of the simulations in this paper. The simulation results can lay a theoretical foundation for identifying the coal-gangue mixed degree in the process of top coal caving.

Double-layer woven lattice truss sandwich composite for multifunctional application: Design, manufacture and characterization

Woven lattice truss sandwich (WLTS) structures have excellent debonding resistance with integral textile construction. As the WLTS has limited thickness, a double-layer WLTS (DWLTS) composite was designed and fabricated to improve the blast resistance of the sandwich panel, as well as keep its electromagnetic (EM) wave transmission properties. The panel was placed by two layers of WLTSs and plain fabrics, and co-cured using vacuum bag molding process to ensure the interfacial shear resistance. In-field explosion experiments reveal that the DWLTS has excellent blast-resistance and EM wave transmission characteristics. The transmission exceeds 80% in 4.5–8.5 GHz and 16–17.2 GHz, and the maximum transmittance is 98.27% at 4.9 GHz. The panel has little damage until the scaled distance is smaller than 1.026 kg/m1/3 with standoff distance of 0.6 m and TNT mass of 0.2 kg. No debonding was observed.

Phase Function of Seawater Polluted by Oil Emulsion

Oil droplets suspended in the seawater will seriously affect the transmission characteristics of electromagnetic wave from ultraviolet and visible light to infrared. The scattering phase function can show the laser transmission characteristics in seawater polluted by oil. Water with oil emulsion has a phase function significantly different from that of natural ocean water. The accurate calculation of phase function can lay the foundation for laser propagation in the oil spill seawater, and is of great significance for protection of marine environment. This paper presents the modeling of phase function of seawater polluted by dispersed oil based on Mie scattering theory. Numerical calculation of scattering phase function of dispersed oil droplets in various times and at different wavelengths is conducted, and the numerical results of Henyey-Greenstein phase function and the modified Henyey-Greenstein phase function is given. The results show that the shapes of Mie scattering phase function of water with oil emulsion depend on wavelength and the oil emulsion ageing. The forward scattering attenuates with the time of oil emulsion ageing and the increase of incident wavelength, and the scattering gradually becomes homogeneously. Compared with Henyey-Greenstein the modified Henyey-Greenstein phase function can describe the scattering property of oil emulsion in the seawater better. But the fitting effects of both Henyey-Greenstein phase function and the modified Henyey-Greenstein phase function are undesirable for long time oil droplets, long wavelength and strong absorption ultraviolet light.

3D printing of metasurface-based dual-linear polarization converter

Three-dimensional printing using digital light processing (DLP) technology has been studied in various fields because of its ability to create complex shapes through a simple process. In this study, DLP 3D printing was employed in the implementation of the metasurface-based dual-linear polarization converter (DLPC). The unit cell of the metasurface-based DLPC for linear polarization conversion was designed consisting of the upper and lower dipole-pair antennas connected through vias and a shielding layer that electrically shields the antennas from each other, and its fabrication was based on the characterization results of the dielectric properties of the photocurable substrate materials and electrical properties of the conductive materials used for synthesizing the metasurface. The printability evaluation of dipole pairs, vias, and a shielding layer was carried out to implement the detailed structures of the DLPC in 3D printing. The electromagnetic wave transmission characteristics of the 3D-printed 8 8 array DLPC demonstrated an orthogonal polarization conversion, as predicted by the simulation results. This study confirmed that the DLP-based 3D printing technology can go beyond the existing functions of manufacturing objects and can be applied to the implementation of various electronics based on different meta-structures.

The Influence of Dusty Size Distribution Model on Propagation of Electromagnetic Waves in Inhomogeneous Plasma Sheath

In this paper, a linear distribution model, a double exponential distribution model and a hyperbolic number distribution model are developed, and the effect of dust particle size distribution on its attenuation coefficient is considered. On this basis, the transmission characteristics of electromagnetic waves in dusty plasma under different electron density distribution models are investigated. The attenuation coefficients of electromagnetic waves are derived in detail using analytical methods, and the effects of electromagnetic wave frequency, particle collision frequency and dust particle density on the transmission characteristics of electromagnetic waves are discussed. The results show that the choice of terahertz wave as the carrier wave and the appropriate change of particle collision frequency can improve the attenuation of electromagnetic waves. In summary, the relevant research can provide some theoretical references for propagation science.

Transmission characteristics of electromagnetic waves in 2D tunable plasma photonic crystals

The transmission characteristics of electromagnetic waves in a 2D plasma photonic crystal (PPC) in the frequency range of 1–12 GHz are investigated by experiments and numerical simulations. For PPC composed of discharge plasma tubes, the transmission characteristics of electromagnetic waves in PPC can be adjusted by changing the discharge current. The transmission characteristics of PPC in different array arrangements and working modes are obtained experimentally; the finite difference time domain (FDTD) method is used to obtain the band structure of PPC in different array arrangements and working modes. The results show the following: the simulation results of the layered model are close to the experimental results; whether the discharge plasma tube is working or not has an important influence on the transmission characteristics of PPC; and Bragg scattering and the localized surface plasmons (LSPs) are the main reasons for the generation of the bandgap. The increase in electron density causes the bandgap to move to higher frequencies and increases the number of bandgaps. The research results can be used as a reference for the evaluation of electromagnetic properties of 2D PPCs and the design of new devices such as plasma antennas.

Transmission characteristics of electromagnetic waves in a semicircular plasma filament layer generated by a femtosecond laser

AbstractThe transmission characteristics of electromagnetic (EM) waves in a semicircular plasma filament layer generated by a femtosecond laser were studied in a wide frequency band including radar waves. We have focussed on the influence of plasma parameters and filament arrangement based on the diffraction and superposition theory of EM waves on the transmittance. A numerical simulation model using the current density convolution finite‐difference time‐domain method was constructed in a semicircular multilayer filament structure, and the transmission characteristics of spherical EM waves were examined. The simulation results showed that in this semicircular structure, the transmittance was periodically changed at a frequency interval corresponding to the thickness of the filament channel. This phenomenon was more pronounced as the number of the filament layers increased. In the lower band (<30 GHz), there was little change in the transmittance according to layer‐to‐layer distance, but in the higher band (>30 GHz), it changed irregularly. On the contrary, for the electron number density, it changed regularly in the lower frequency and hardly changed in the higher frequency. When the number of layers was 3 or more, the transmittance became 0 at the centre of the channel, and a discontinuous interference pattern appeared more clearly as the frequency increased.

Transmission enhancement effect of electromagnetic wave in non-uniform collisional plasma

The effect of plasma on the transmission properties of electromagnetic waves and its application have always been one of the key research directions of electromagnetic theory and technology and plasma physics. The enhancement effect of collisional plasma on electromagnetic waves is a classic subject of the interaction between electromagnetic waves and plasma. Based on the transmission characteristics of electromagnetic waves in medium, this paper takes plasma as a special medium, and carries out experimental, theoretical and simulation studies on the transmission characteristics of high power microwave (HPM) atmospheric plasma and a certain range of electromagnetic waves under certain experimental conditions. The study found that the plasma formed by the S-band HPM under a vacuum of 50 Pa has a great influence on the electromagnetic wave transmission characteristics of different frequencies, and the electromagnetic wave transmission signal enhancement effect occurs regularly within a certain frequency range. A series of transmission waveforms of continuous electromagnetic waves of different frequencies passing through the HPM plasma area were obtained, and the waveforms were normalized. At 32.4 GHz, the transmission coefficient of continuous electromagnetic waves passing through the plasma area with plasma is about twice as high as that through the area without plasma. A simulation model was established, and the transmission coefficient distribution curve in the range of 31.5−32.5 GHz was obtained. The electromagnetic wave passing through the plasma showed a transmission enhancement effect, and at some frequency points, there was a transmission enhancement of about 1.9 times. The research results provides important technical support for the application of plasma in stealth, emergency communications, and black barrier communications.

Transmission Characteristics of Electromagnetic Waves in Plasma with External Orthogonal Electromagnetic Fields

在基于磁流体动力学和电磁波传播理论的基础上，针对航天飞行器再入过程中的黑障问题，提出了一种物理模型.利用数值分析方法，研究电磁窗周围的电子密度在不同的飞行器轴向距离下，随着飞行器法向距离增加呈现出的变化趋势；改变外加电场和磁场的交叉角度，分析不同角度下电磁窗周围电子密度的变化趋势；研究有外加正交电磁场的电子密度与无外加电磁场电子密度比值的变化趋势和电磁波衰减的变化趋势.结果表明：当外加正交电磁场时，接收天线周围的电子密度随飞行器法向距离的增加而不断减小，其与无外加电磁场时电子密度之比呈现不断下降的趋势；电磁波的衰减在不同飞行高度和外加磁场强度下，随着电磁波频率的增加而不断减小.这为减缓“黑障”问题提供了一种新的方法.

Influence of discharge parameters on electromagnetic scattering

Setting the thickness and pressure for an absorbing plasma is difficult in plasma stealth engineering. In this study we established a numerical model of electromagnetic wave propagation in radiofrequency plasma using a z-transformed, finite-difference, time-domain method. We studied the effects of thickness and pressure on the reflectance, transmittance and attenuation of the plasma under three typical electron density distributions: uniform, axially symmetric and monotonic. The results show that the electron density distribution has a significant influence on the electromagnetic wave transmission characteristics. The attenuation effect reaches a maximum when the electron density is increased monotonically along the wave propagation direction. An increase in thickness can significantly increase the attenuation rate of the incident wave and reduce the transmittance, but has little effect on the reflectance. An increase in air pressure reduces the reflectance of the incident wave and increases the transmittance and the attenuation rate. However, once the air pressure exceeds a certain threshold, any further increase in air pressure will no longer enhance the attenuation rate.

A study of frequency selection characteristics of negative conductivity in high temperature plasma

Abstract The transmission characteristics of electromagnetic wave in a high temperature plasma slab are investigated by using transfer matrix method in this paper. The phenomenon of negative conductivity that emerged from high temperature plasma is investigated. The absorption of high temperature plasma is negative in the corresponding frequency band where the negative conductivity appears. According to the law of energy conservation, the sum of the reflection and transmission of electromagnetic waves in this frequency band will be greater than 1. That is, there should be an anomalous transmission phenomenon. According to the research, anomalous transmission is found in right-handed circular polarizations (RCP), while left-handed circular polarizations (LCP) do not occurred the similar phenomenon. In our study, it shows that the anomalous transmission is affected by external magnetic field, and different external magnetic field corresponding to different transmission frequencies. In the same time, the transmission frequencies move towards high band with the increasing of the magnetic field. Therefore, the negative conductivity and anomalous transmission can be artificial controllable. So, it can be used as a gain medium at a specific frequency or as an effective way to transmit information by frequency selection.

Study on the velocity band gap characteristics of photonic crystal under the relativistic conditions

The periodic dielectric slabs are investigated. The reflection and transmission characteristics of electromagnetic wave are researched when photonic crystals are moved at a uniform velocity close to the light speed under the relativistic conditions. When the motion direction of photonic crystal is perpendicular to the propagation direction of electromagnetic wave, the electromagnetic band gap is formed alternately by the reflection spectrum of photonic crystal changed with velocity. The gap is different from the traditional electromagnetic band gap, which is not a function of the spectrum but corresponding to the velocity. The peculiar phenomenon generated by electromagnetic wave at different velocity band is called velocity band gap. The velocity band gap is affected by the frequency of electromagnetic wave, period of photonic crystal, permittivity and other parameters. It varies periodically in the whole velocity range and decreases with the increasing velocity. The velocity band gap is expanded and moved to the low velocity interval with the period of photonic crystal increasing. When the difference in permittivity of the two adjacent dielectric slabs becomes higher and the frequency of electromagnetic wave increases, the velocity band gap is changed accordingly. The change is similar to the state in which a spring fixed at one end is stretched, but the change in velocity band gap is not uniform.

Engineering Electromagnetic Wave Propagation in Periodically Layered Gyromagnetic Metamaterials with an External Magnetic Field

Tunable transmission characteristics of electromagnetic waves in periodically layered metamaterials (PLMMs), constructed by alternating dielectric layer and gyromagnetic layer such as yttrium-iron-garnet (YIG), are investigated through an external magnetic field. Based on transfer matrix method (TMM) and effective medium theory (EMT), we compare the dispersion curves of TE waves propagating in the PLMMs, and obtain the effective permeability and permittivity tensors of the homogenized gyromagnetic PLMMs by expanding the exact dispersion relation in long-wavelength limit. Then, we calculate some propagating parameters when TE waves incident on the PLMMs by EMT in detail. Numerical results show that the refraction state of TE waves in the PLMMs can be dynamically changed between positive refraction state and cutoff state by controlling the external magnetic field. These exotic properties of gyromagnetic PLMMs may have wide potential applications in many fields such as sub-wavelength all-optical switches and wave cutoff devices.

Regulating Detectable Optical Domain in Sensing Technology Using Metal Mesh Devices and Detection of Submicron-size Particles.

A metal mesh device has a structure in which through-holes of the same shape are periodically placed on a thin metal film, and the selection of such a structure makes it possible to sense objects of various sizes. In this study, we showed the structure of the metal mesh device and the relationship between the detectable optical domain and the size of the objects to be measured. In addition, from measurement of changes in electromagnetic wave transmission characteristics of the metal mesh device due to specific adsorption of particles with a mean diameter of 100 nm with surface modification with Streptavidin to a metal mesh device fixed with biotin, we showed that even large particles can be sensed. Based on these examinations, we showed that, by using a metal mesh device with detectable optical domain corresponding to the size of objects, even objects that are larger than protein can be sensed.

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.