Characteristics Of Electromagnetic Waves Research Articles

Дважды отрицательные среды на основе антиферромагнитных метаматериалов для терагерцевого диапазона частот

The paper presents the theoretical study results of the dispersion characteristics of electromagnet-ic waves existing in antiferromagnetic (AFM) metamaterial. The AFM metamaterial consists of a transversely magnetized antiferromagnet, inside of which a two-dimensional periodic structure of thin conducting wires surrounded by insulators is placed. It has been established that the AFM metamaterial has two frequency ranges, in which there are backward waves, and the material pa-rameters of the medium are twice negative. The indicated areas are located in the terahertz range.

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.

Krylov Subspace Methods for Regularized Models in Acoustic Temperature Reconstruction From Simulated and Real Measurements

In a microwave heating system, there is usually an anomaly like thermal runaway or local overheating due to the propagation characteristics of electromagnetic waves during the heating process. The anomalous situation can be coped with by analyzing the temperature information obtained from acoustic travel time tomography. The aim of the research is to investigate the possibility of applying the acoustic approach to microwave heating. When applying acoustic tomography, an ill-conditioned least-squares problem is formulated, and the problem is hard to solve for super bad condition numbers of the coefficient matrices. In computational mathematics, researchers make a lot of effort in developing Krylov subspace methods to solve ill-conditioned problems. Some existing methods show slow convergence for practical applications, which motivates us to improve one Krylov subspace method based on real cases. Our method can be treated as an application of heavy ball minimal residual (HBMR) method to regularized least-squares problems. Based on the data collected from a measurement platform that simulates the internal circumstance of the heating system, our method is compared with certain classical Krylov subspace methods from aspects of convergence rate, reconstruction accuracy, and anti-interference capacity. Numerical experiments demonstrate a significant improvement in convergence rate on our method for regularized ill-conditioned problems. In addition, we display how to select an optimal kernel function. Details of choosing the optimal parameter are shown as well.

Propagation of an electromagnetic wave based on a continuum model of kp-type in an almost circular bundle of packed metal nanotubes

A continuum model of kp-type for the approximate calculation of the characteristics of electromagnetic waves propagating in an almost circular (azimuthally symmetric), closely packed bundle of parallel, identical, and metal carbon nanotubes (CNTs) yields results in reasonably good agreement with the equivalent-multishell approach and with a many-body technique, for infinitely long bundles when the number of CNTs is moderately high. The slow-wave coefficients for azimuthally symmetric guided waves increase with the number of metallic CNTs in the bundle, tending for these bundles to unity, which is characteristic of macroscopic metallic wires. The existence of an azimuthally asymmetric guided wave at low frequencies in a bundle of a large number of finite-length CNTs stands in contrast to the characteristics of guided-wave propagation in a single CNT. A continuum model of kp-type yields the polarizability scalar and the antenna efficiency of a bundle of finite-length CNTs in the long-wavelength regime over a wide frequency range spanning the terahertz and the near-infrared regimes. Edge effects give rise to geometric resonances in such bundles. • The slow-wave coefficients for azimuthally symmetric directed waves. • The characteristics of electromagnetic waves propagating in an almost circular, bundle of carbon nanotubes (CNTs). • Contrast of characteristics of a guided-wave at low frequencies in a bundle of a large number of CNTs and in single CNT.

Real-Time Pattern-Recognition of GPR Images with YOLO v3 Implemented by Tensorflow.

Artificial intelligence (AI) is widely used in pattern recognition and positioning. In most of the geological exploration applications, it needs to locate and identify underground objects according to electromagnetic wave characteristics from the ground-penetrating radar (GPR) images. Currently, a few robust AI approach can detect targets by real-time with high precision or automation for GPR images recognition. This paper proposes an approach that can be used to identify parabolic targets with different sizes and underground soil or concrete structure voids based on you only look once (YOLO) v3. With the TensorFlow 1.13.0 developed by Google, we construct YOLO v3 neural network to realize real-time pattern recognition of GPR images. We propose the specific coding method for the GPR image samples in Yolo V3 to improve the prediction accuracy of bounding boxes. At the same time, K-means algorithm is also applied to select anchor boxes to improve the accuracy of positioning hyperbolic vertex. For some instances electromagnetic-vacillated signals may occur, which refers to multiple parabolic electromagnetic waves formed by strong conductive objects among soils or overlapping waveforms. This paper deals with the vacillating signal similarity intersection over union (IoU) (V-IoU) methods. Experimental result shows that the V-IoU combined with non-maximum suppression (NMS) can accurately frame targets in GPR image and reduce the misidentified boxes as well. Compared with the single shot multi-box detector (SSD), YOLO v2, and Faster-RCNN, the V-IoU YOLO v3 shows its superior performance even when implemented by CPU. It can meet the real-time output requirements by an average 12 fps detected speed. In summary, this paper proposes a simple and high-precision real-time pattern recognition method for GPR imagery, and promoted the application of artificial intelligence or deep learning in the field of the geophysical science.

Quantitative observation of attenuation coefficient of electromagnetic wave propagation in haze incorporating charged aerosol

Haze incorporating abundant charged aerosol has become a main air problem in various metropolitan cities worldwide. Studying the propagation characteristics of electromagnetic wave (EMW) in charged haze aerosol is conducive to calibrate instruments designed based on energy attenuation of EMW and is critical to providing guidance for deployment of network base stations. Here, we simulated haze conditions by quantitatively controlling the concentration, water content, and charge quantity of aerosols in laboratory and first found that attenuation coefficient of EMW changes linearly with these factors. In addition, we proposed a method to determine the complex dielectric constant of haze aerosols. Upon this, a new model, which combines the surface conductivity of a single particle at micro level with the charge density of the aerosol at macro level, was developed to quantitatively evaluate the contributions of aerosol concentration, water content and charges on the attenuation of EMW. The results show that when EMW propagates in charged haze aerosol, its attenuation coefficient can be quantitatively characterized by mass concentration, particle moisture and charge-to-mass ratio of aerosol. And the simulated results are in good agreement with the experiments.

Research on RCS Simulation Characteristics of Fixed Low-Grazing-Angle FOD Radar

Fixed low-grazing-angel foreign object debris (FOD) radar, which is erected at a designated height beside the airport and scans the runway at a low-grazing angle, is used to detect foreign object debris on airport runways. In operation, it is found that the power of reflected electromagnetic wave decreases significantly when the radar is erected at some height, as a result of which the radar detection rate reduces. In this paper, the electromagnetic reflection and polarization modes of fixed low-grazing-angle radar are analyzed based on some concepts of refraction characteristics of electromagnetic wave, such as Fresnel’s Law and Brewster’s Angle. Then the paper explains the theoretical reasons for this problem. Meanwhile, the GO & MLFMM algorithm is used to simulate the relationship between radar height and radar reflected power, and finally the theoretical results are verified.

Analysis and optimization of electromagnetic scattering characteristics of two-dimensional metal airfoil covered with metamaterial

Airfoil is one of the strong scattering sources of aircraft, so it is of great significance to study the stealth characteristics of airfoil for the reduction of the radar cross section of the whole aircraft. As is known, the airfoil of aircraft is the main component that generates lift. Shaping the airfoil will reduce the aerodynamic performance of the aircraft. However, the emergence of metamaterials allows aircraft designers to achieve a good balance between stealth and aerodynamics. Considering the high cost of stealth test, numerical simulation is proposed to guide the design of metamaterial stealth. Then, the bistatic radar cross section (RCS) of airfoil covered with metamaterial is researched in this paper. We employ the 2-D auxiliary differential equation finite-difference time-domain (ADE-FDTD) to simulate the airfoil’s stealth characteristics. The two-dimensional situation can be regarded as a special approximate when electromagnetic waves are perpendicularly incident on the three-dimensional infinitely long airfoil. The tuning parameters including coating thickness, Drude frequency and collision frequency are considered on the airfoil’s bistatic RCS. The calculation program verified its correctness by simulating the perfect lens characteristics of electromagnetic waves propagating in the metamaterial plate. The numerical experiments show that the meta-material Drude frequency and collision frequency mechanism are more complicated than the coating thickness. The dual-station RCS increases at some angles and decreases at other angles than metal airfoils. But by choosing appropriate metamaterial parameters, airfoils with excellent stealth effect can be obtained.

Structured Methods for Improving Flow Measurement Accuracy in Pipelines

The issue of the development and creation of intelligent flow rate sensors of free-flowing and fluid substances carried on pipelines is considered timely during this era of digital conversion of production processes in industry and science. With this objective, this article presents new approaches to improving the measurement precision of microwave flow rate measuring units. Taking into account the characteristics of electromagnetic waves propagating along the pipeline, analysis was conducted of a wave scattered by the inhomogeneities of the medium being monitored. The features of the transformation of a polarized scattered wave, the limiting geometrical sizes of the pipeline, and optimization of the values of the true scattered signal, are revealed. The feasibility of picking up an information signal with orthogonal polarization of the scattered wave, and via a directional coupler, is substantiated. A methodology was developed to estimate measurement precision with an association to the signal-to-noise ratio at input to a processing unit. It has been shown that the results of the studies can be used in the cryogenic engineering industry to measure the volume and mass flow rates of liquid cryoproducts.

Attenuation characteristics of electromagnetic waves in plasma generated by coating radionuclide on surface structures

Stealth technology plays an important role in modern military conflicts, especially when used in fighter jets. Since airfoil structures have a leading edge, inlet, and surface bulge that are easily detected by radar, it is necessary to study the stealth of these structures. In this study, we investigate structures coated with radionuclides to generate plasma. Using simulation and calculation methods, the attenuation of 0.1–10 GHz electromagnetic waves propagating in plasma was studied. The results showed that the attenuation of low-frequency electromagnetic waves is greater than that of high-frequency electromagnetic waves. The attenuation of 0.1–1 GHz electromagnetic waves is found to be less than − 2.7 dB, − 3.0 dB, and − 15.6 dB at the airfoil leading edge, inlet, and surface bulge structures, respectively. We also found that the attenuation of electromagnetic waves with 0°-incidence is greater than that of waves with 10°, 20°, and 30° incidence angles. Additionally, the attenuation of electromagnetic waves decreases gradually as the incident angle increases.

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.

Multifunctional composites for elastic and electromagnetic wave propagation

Composites are ideally suited to achieve desirable multifunctional effective properties since the best properties of different materials can be judiciously combined with designed microstructures. Here, we establish cross-property relations for two-phase composite media that link effective elastic and electromagnetic wave characteristics to one another, including the respective effective wave speeds and attenuation coefficients, which facilitate multifunctional material design. This is achieved by deriving accurate formulas for the effective electromagnetic and elastodynamic properties that depend on the wavelengths of the incident waves and the microstructure via the spectral density. Our formulas enable us to explore the wave characteristics of a broad class of disordered microstructures because they apply, unlike conventional formulas, to a wide range of incident wavelengths (i.e., well beyond the long-wavelength regime). This capability enables us to study the dynamic properties of exotic disordered "hyperuniform" composites that can have advantages over crystalline ones, such as nearly optimal, direction-independent properties and robustness against defects. We specifically show that disordered "stealthy" hyperuniform microstructures exhibit novel wave characteristics (e.g., low-pass filters that transmit waves "isotropically" up to a finite wavenumber). Our cross-property relations for the effective wave characteristics can be applied to design multifunctional composites via inverse techniques. Design examples include structural components that require high stiffness and electromagnetic absorption; heat sinks for central processing units and sound-absorbing housings for motors that have to efficiently emit thermal radiation and suppress mechanical vibrations; and nondestructive evaluation of the elastic moduli of materials from the effective dielectric response.

Laws of reflection and refraction of TE and TM polarization waves on the border of rhombic crystals

The article analytically solves the problem of reflection and refraction of electromagnetic plane waves of different polarization at the boundary of anisotropic half-spaces of rhombic symmetry. Based on the matrix method, the angles of refraction of electromagnetic waves of different polarization, the amplitudes of the reflected and refracted waves, the angles that determine the direction of the group velocities and vectors of the flow of electromagnetic energy, the magnitudes of the flows of electromagnetic energy and their components depending on the direction of the wave vector of the incident wave are determined. The determination of the angles of total internal reflection and the refractive index of electromagnetic waves of different polarization is considered. A significantly different dependence of the kinematic and energy characteristics of electromagnetic waves of different polarization on the anisotropy of the magnetic and dielectric tensors is shown. For electromagnetic waves, the polarization of which is determined by the component of the electric tension vector perpendicular to the wave propagation plane (TE wave), the characteristics of the reflected and refracted waves, the velocity indicatrix, the propagation angles, etc. determined primarily by the components of the magnetic permeability tensor. In the case of electromagnetic waves, when the polarization is determined by the component of the magnetic field (TM wave), perpendicular to the plane of wave propagation, all characteristics depend mainly on the components of the dielectric constant. The validity of the Fresnel formulas for determining the coefficients of reflected and refracted waves at the boundary of anisotropic media of rhombic symmetry is shown. However, in this case, the components of the wave vectors included in the Fresnel formulas are determined by their indicatrices. In addition, it is necessary to take into account the dependence of these components on the angle of refraction in the second medium.

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.

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.

A new BGK model to compute the scattering characteristics of electromagnetic waves by weakly ionized dusty plasma shroud

The dynamics theory of dust charging in the Bhatnagar–Gross–Krook (BGK) model is changed, and the updated expression of the complex permittivity for weakly ionized dusty plasma is derived. Then, by using the physical optics method, the radar-cross section (RCS) of electrically large blunt cones covered by dusty plasma with weak ionization is calculated under the new complex permittivity and compared with the traditional results. The numerical results indicate that the new values of the RCS are significantly smaller than their traditional values. In addition, the influence of dust plasma parameters on the scattering characteristics of EM waves is discussed under the new BGK model. The results enriched the physical mechanisms of the scattering characteristics of weakly ionized dusty plasma shroud and provide a theoretical basis for future studies.

Strong Dispersive Propagation of Terahertz Wave: Time‐Domain Self‐Consistent Modeling of Metallic Wall Losses

AbstractThe dispersion characteristics of electromagnetic waves have led to a wide range of applications, such as pulse compression, superluminal propagation, wave tunneling effect, and electron–wave interaction. The near‐cutoff wave inside a guiding system is strong dispersive. When the wave frequency reaches the terahertz band, this strong dispersive property is extremely sensitive to the losses induced by the limited conductivity of the component. This phenomenon is traditionally investigated through perturbation of boundary conditions in the frequency domain, which does not deal well with broad‐spectrum signals. Two simple and efficient time‐domain schemes to study the strong dispersive propagation of terahertz waves are proposed. One is based on relatively concise principles, called the constant frequency method. The second is the recursive convolution method, which is suitable for dealing with a wave with wider spectrum range. The reliability of both approaches is verified by the comparison of the dispersion curves. Using the proposed methods, the pulse compression of terahertz wave inside a strong dispersive waveguide is verified in principle.

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.

Effect of Plasma Sheath Velocity on Propagation of Electromagnetic Waves

Hypersonic velocities can theoretically affect the propagation of electromagnetic waves in a plasma sheath covering a vehicle. This article is the continuation of our previous study and, for the first time, investigates the reflection characteristics of electromagnetic waves by a moving bounded plasma slab and examines five typical plasma parameters in detail when the plasma moves parallel to the interface. The results show that the motion of the plasma slab significantly affects electromagnetic propagation, and the reflection coefficient oscillates with the velocity of the plasma sheath. In addition, different physical parameters cause different oscillation characteristics. Various interesting features of the reflection coefficient are obtained, which are very important for researching the propagation of electromagnetic waves in this extreme physical environment or providing reference for researching “blackouts” in the future.

Structured methods for improving flow measurement accuracy in pipelines

In the age of digital transformation of production processes in industry and science the development and design of intelligent flow sensors for granular and liquid substances transferring through pipelines becomes more important. With this in view new approaches for improving the accuracy of microwave flowmeters are proposed. Taking into account the characteristics ofelectromagnetic waves propagating through a pipeline, a wave scattered by inhomogeneities of the controlled medium is analyzed. Features of the transformation of the polarized scattered wave limiting the geometric dimensions of the pipeline and optimizing the values of the useful scattered signal are revealed. Expediency of collection of the information signal with orthogonal polarization of the scattered wave and through a directional coupler is substantiated. The method of estimating the measurement accuracy with reference to the signal-to-noise ratio at the input of the processing device is given. The research results can be used in cryogenic machine engineering to measure volume and mass flows of liquid cryogenic products.