In order to evaluate the electromagnetic environment of the 750 kV four-circuit transmission lines accurately, and design the optimal tower type and phase sequence of the four-circuit lines, the finite element method is used to analyze the distribution characteristics of power frequency electromagnetic field under the line. The excitation function method and the empirical formula method are used to calculate the radio interference and audible noise distribution under the line respectively. Electromagnetic environment parameters of various phase sequences of two tower types are analyzed to determine the optimal phase sequence of 750 kV four-circuit transmission lines. The results show that the electromagnetic environment of transmission lines is strongly influenced by different tower types and phase sequences. The magnetic flux density and radio interference of the various phase sequences of the two tower types reach the limit of code, and 43.52% and 64.81% phase sequences reach the audible noise limit conditions respectively. Electric field intensity is a main influence factor of electromagnetic environment. The optimal phase sequence layouts of the two tower types are 1661 and 1522, and the electric field intensities are 9.66 kV/m and 9.12 kV/m. The calculation method and results can be used for reference in practical engineering.
Matrix completion (MC) theory has attracted much attention for its capability of recovering a low-rank matrix through its partial entries. In this paper, we investigate the novel suppression methods of wind turbine clutter (WTC) and introduce the application of MC in WTC suppression for weather radar. First, the vectors of weather signals contaminated by WTC are sequentially constructed into a low-rank snapshot matrix satisfying random undersampling, and then, the weather data can be accurately recovered by minimizing the nuclear norm in the inexact augmented Lagrangian multiplier (IALM) method. The proposed algorithm can effectively suppress not only the wind turbine clutter but also the noise, greatly improving the signal-to-noise ratio of the echo. An experimental test validates the effectiveness of the proposed MC algorithm, and its performance is superior to the widely-used multiquadric interpolation algorithm with potential engineering applications.
In this paper, the double-walled carbon nanotube composite material (DWCNTs-composite) and bundle of DWCNT-composite material (CB-DWCNTs) for antenna applications at terahertz frequency range are presented and investigated. The mathematical modeling and analysis of DWCNTs-composite material is presented for the purpose of modelling and simulation approach. The bundle of DWCNTs-composite material is constructed and designed, based on this modeling approach. The DWCNT-composite material consists of double-walled carbon nanotube coated by a thin jacket of another different material. The dependency of the electrical conductivity of B-DWCNTs-composite on the different parameters is presented and investigated. The performance evaluation of B-DWCNTs-composite and CB-DWCNTs materials are presented based on their electromagnetic properties. For this purpose, the dipole antennas of these composite materials are designed and implemented using CST (MWS), where the cross sections of B-DWCNTs-composite and CB-DWCNT materials are circular geometry. Furthermore, comparative studies are performed to show the dependency of size and frequency of the DWCNT-composite material. The results obtained from the DWCNTs-composite and CB-DWCNTs dipole antennas are presented based on S11 parameters, resonant frequency, gain, bandwidth, and efficiency.
In order to reduce the underwater electric field generated by corrosion of ship, a boundary element method (BEM) combined with nonlinear polarization curve was employed to investigate the influence of output current of compensate anode in an electric field protection system on underwater electric field. Moreover, the BEM model was verified by physical scale modeling (PSM). The distribution characteristic of electric field and the variation trend of electric field with compensate current obtained by simulation are consistent with the experimental results. Moreover, the errors of peak-to-peak value of electric field obtained by experiment and simulation are within 20%. Compared with 0 mA compensation current, the peak-to-peak values of X component, Y component, Z component, and modulus are reduced by 52%, 70%, 72%, and 62% respectively when compensation current is 40 mA. The phenomenon of over-compensation will occur if compensation current is greater than 40 mA.
A frequency continuous reconfigurable microstrip patch antenna with operation band covering S-band and C-band is introduced. The antenna consists of a central rectangular patch and four parasitic patches with a symmetrical structure, connected by four varactor diodes in the middle position of the edge of each patch. With help of HFSS microwave studio simulation, results have shown that, by altering the bias voltage on varactor diodes, the operated frequencies vary continuously within a wide range from 3.29 to 4.01 GHz and 5.35 to 7.00 GHz, which cover S-band and C-band. Further measurement, which verifies the simulation by reasonable agreement, has been carried out. Besides, this frequency reconfigurable antenna maintains broadside radiation and stable radiation pattern. Specifically, the gain is basically maintained at around 4.5 dBi with the working frequency increasing from 3.60 to 7.00 GHz. Compared with other frequency-reconfigurable antennas available in previous literature, the proposed antenna has advantages of a wide frequency tuning range, high frequency selectivity, simple and stable structure, low cost, and miniaturization, which make it a promising candidate as cognitive radio and future wireless communication systems.
In this paper we are concerned with a microwave imaging problem for a non-magnetic two-layered background medium, where objects are buried in the lower half-space, and the scattered field is collected in the upper one according to a multi-monostatic configuration. In particular, we are interested in estimating the achievable transverse resolution. As well known, range resolution mainly depends on the working frequency band whereas transverse resolution depends on the geometrical parameters of the configuration and is usually computed in correspondence to the highest (or even the average) adopted frequency. Determining transverse resolution is much more difficult, and closed form estimations have been actually found only for the case of unbounded observation domain. However, in real scattering scenarios measurements have to be necessarily collected under an aspect limited setup. Therefore, in order to fill such a theoretical gap, here the focus is on the estimation of transverse resolution for bounded observation domains. To this end, we consider a single-frequency 2D scalar prototype configuration where the buried scattering object domain is represented by a strip parallel to the half-space interface. More in detail, we succeed in finding an analytical estimation of the transverse resolution which highlights the role of the configuration parameters as well as the dielectric permittivity of the lower half-space.
The presence of the ground affects the propagation on overhead lines through a magnetically induced earth return current. Numerous researches have been conducted to study this influence by considering a homogeneous earth. In the current paper, the transient response of Multi-conductor transmission Lines (MTL) considering a lossy stratified earth is presented. Based on the finite difference time-domain (FDTD) and an improvement of the convolution integral arising from time-domain modeling of frequency-dependent conductors' parameters through the Vector Fitting (VF) algorithm, a novel numerical procedure for solution of a system of telegraph equations is presented. Many simulations are introduced to highlight the effect of soil stratification on the response of the line for a given excitation. The efficiency of an equivalent model, using an equivalent single-conductor, of a multiple conductor system is also established in this work.
This paper considers the class of Iterative Shrinkage Threshold Algorithm (ISTA) to solve the linear inverse problem that occurs in magnetic resonance (MR) image recovery. The ISTA algorithm adheres to the principle of minimizing the L1 norm. This method can be considered as an extension of the classical gradient algorithm. However, it is known that the ISTA algorithm converges slowly, and the accuracy of the algorithm is not sufficient. In many MR image recovery problems, using non-convex log-sum norm minimization can often obtain better results than the l1-norm minimization. In this paper, we firstly transform the MR image recovery into a non-convex optimization problem with log-sum norm regularization and combine it with a faster global convergence method. Then a Log-sum generalized iterated shrinkage threshold algorithm (LISTA) for solving the MR image recovery problem is proposed. Finally, numerical experiments are conducted to show the superiority of our algorithm.
Degree of the electric field (EF) amplification at the tips of thin and long conductive rods array has been calculated. It is shown that such amplification depends on the rods height (H) and radius (R), as well as on distance between separate rods in the array. For simulation, an approach to numerical calculation of the EF near conductive rods with a large ratio of height to radius: H/R>102-104 has been proposed. Rods with such parameters may represent carbon nanotubes, channels of breakdowns in insulation, lightning leader channels, lightning rods, etc. The proposed approach is based on the finite integration technique. It uses also the analytical law of decrease of the EF strength and potential of a conductive ellipsoid under potential in the directions perpendicular to the ellipsoid axis and above its tip. As a result, numerical calculations of the EF distribution in systems with such rods were carried out applying calculation grids with steps proportional to the rods length, not their diameters. It permits substantial decrease of the required computational resources such as memory and time.
The electromagnetic plane wave diffraction by the half-plane with fractional boundary conditions is considered in this article. The theoretical part is given based on that the near field, pointing vector and energy density distribution are calculated for different values of the fractional order. The results are compared with classical cases for marginal values of the fractional order. Interesting results are obtained for fractional orders between marginal values. Results are analyzed.
This paper presents a technique to design a very small planar antenna for ultra-wideband (UWB) communication applications. To cover UWB frequency range by a small-size antenna, the ground plane influence on the antenna impedance bandwidth is suppressed at middle and higher frequencies. To accomplish this purpose, a rectangular and several stepped slots are etched on the conventional radiator. Also, a tuning stub is printed in the rectangular slot, and its length is optimized. This technique decreases current distribution on the ground plane at higher frequencies, and the impedance matching of the antenna is significantly influenced by the radiating patch. The antenna has a compact size of 25 × 25 × 1.6 mm3. It can provide a wide impedance bandwidth from 2.8 to 15.4 GHz (|S11| < -10 dB) which covers the entire UWB spectrum (3.1-10.6 GHz). Two prototypes of the antenna were fabricated and measured. The impedance matching, group delay, fidelity factor, and the antenna radiation characteristics, including co- and cross-polarized far-field patterns and realized gain were analyzed with numerical simulation and experimental measurement. Measured data are in good agreement with the simulated ones. Based on the obtained frequency- and time-domain characteristics, the designed antenna is an excellent candidate for UWB wireless devices.
Millimetre-wave thermography is used to image through the soles of shoes as proof of principle study into the application of such an approach for security inspection. Current airport security screening practice necessitates the removal of shoes prior to x-ray screening for potential threats or other concealments, for example explosive or explosive precursor materials; narcotic substances or small weapons. The authors demonstrate that thermography at ~250 GHz is able to reveal a variety of objects concealed within the soles of typical shoes, and that such an approach might be applied to rapidly screen passengers without necessitating the removal of their footwear.
The design, analysis, and manufacturing of an oversized circular metallic corrugated waveguide with rectangular and square grooves for transmitting power from gyrotron to tokamak or dummy load have been carried out. To carry high power at millimeter wave with lower transmission loss, a corrugated waveguide is preferred. A corrugated waveguide with HE11 mode gives lower attenuation than a smooth circular waveguide with TE11 mode. The theory behind the depth and width selection of corrugations required to carry the linearly polarized (HE11) mode is explained in this paper. The proposed structures are designed and simulated in CST microwave studio software. Rectangular and square groove circular corrugated waveguides each having a length of 500\,mm were fabricated and tested using ZVA50 vector network analyzer. Based on the performance results, it is derived that the square groove corrugated waveguide gives lower insertion loss of 0.08 dB/meter than rectangular groove corrugated waveguide which gives insertion loss of 0.11 dB/meter.
After reaffirming that the macroscopic dipolar electromagnetic equations, which today are commonly referred to as Maxwell's equations, are found in Maxwell's Treatise, we explain from his Treatise that Maxwell defined his displacement vector D as the electric polarization and did not introduce in his Treatise or papers the concept of electric polarization P or the associated electric-polarization volume and surface charge densities, -n.P and n.P, respectively. With this realization, we show that Maxwell's discussion of surface charge density between volume elements of dielectrics and between dielectrics and conductors becomes understandable and valid within the context of his definition of electric polarization as displacement D. Apparently, this identification of D with electric polarization in Maxwell's work has not been previously pointed out or documented except very briefly in .
In this paper, a numerical algorithm for computation of electric and magnetic fields inside a multilayer cylindrical structure with an arbitrary number of homogeneous layers is presented. Each layer can have arbitrary value of electrical conductivity, permeability and permittivity. Theoretical background of the model is based on Maxwell equations where modified Bessel functions have been chosen for solution formulas. Modified Bessel functions are also scaled to avoid underflow/overflow issues. This results in a numerically robust and highly accurate numerical algorithm for computation of electric and magnetic fields inside a multilayer conductor. Using the derived expression for electric field on the surface of the conductor, the formula for per-unit-length internal impedance of the general multilayer cylindrical conductor is also obtained.
In this article we theoretically investigate the visible extinction efficiency that can be obtained using a two dimensional particle. We show that extinction efficiencies up to the upper limit can be obtained from two dimensional particles (thin circular disks or flakes) compared with one dimensional (fibers) and three dimensional particles (spheres). Features of the theory of electromagnetic extinction by thin circular disks are thoroughly investigated for wide size and material contents parameters in the visible. The results of this article are of importance for the search of efficient aerosol attenuative candidates in the visible spectral region.
Tunneling of microwave radiation through a symmetrical trilayer ENG-ferrite-ENG is considered, where ENG refers to a medium of negative permittivity. Such trilayer is an example of a magnetically controlled structure that under certain conditions allows a complete (or perfect) tunneling of the incident radiation. In this paper, the general conditions of the perfect tunneling are analyzed, and the transmissive properties of the structure are studied numerically. It is demonstrated that a broad passband, in which the structure is almost completely transparent, may be obtained both above and below the frequency of the ferromagnetic resonance. The bandwidth can be effectively controlled by an external field that is magnetizing the ferrite layer.
In this paper 8000 rpm generators with the magnetic cores made of amorphous low-coercivity material and electrotechnical steel were designed. The sizes of the magnetic cores of generators were calculated analytically. Computer simulations of the generators under study were carried out to obtain a complete pattern of the magnetic field distribution in the magnetic cores and to estimate the generator losses. Experimental models of the generators were also made, which were studied at no load and with load. A special bench with a torque sensor was used for experimental studies.
Regarding the increasing application of terahertz technology, the interest in using two-wire waveguides is getting more and more popular due to their favorable propagation properties. Therefore, a more accurate analysis of these structures is very important. In this paper, a simple analysis of the guided waves in a two-wire waveguide based on Bipolar Coordinate System (BCS) has been investigated. The structure under study is two infinite perfect electric conductor (PEC) cylinders in z direction, whose axes are positioned at a distance d from each other. The solution of TE and TM modes is sought by the aid of electromagnetic formulation, and an analytical expression is proposed for electromagnetic fields and cutoff wave numbers, which have not been present in any of the previous studies. In this study, for the first time a BCS has been used to formulate two-wire waveguide problem, and the validity range of the answer is discussed. The values of the cutoff wave numbers are calculated for the first few modes of TE and TM, using both the proposed method and Finite Difference Method (FDM). The precise correspondence of the obtained values with the proposed method with those of FDM, along with the high speed and simplicity in implementation, introduces the present method as an appropriate candidate for analyzing transmission lines using parallel cylinders.
Development of Compartment Syndrome (CS) could affect blood flow to muscles, nerves, and as a result could causes permanent damage to tissues and nerves with risk of amputations and even death. The lack of non-invasive clinical diagnosis of compartment syndrome has led to thousands of permanent nerve and tissue damages. This paper aims to present a novel method, design concept, and numerical realization of non-invasive Radio Frequency (RF) based detection of compartment syndrome. The proposed method uses electromagnetic waves, produced by a small printed antenna at frequency of 300 MHz for identifying compartment syndrome. The effects of compartment syndrome and changes on tissue electrical properties are taken into account, since the ways in which electrical properties differences between normal and injured tissue should aid diagnosis on injured area by RF-wave radiation. We used a numerical leg model to identify inter-compartmental edema size of the lower leg, the most commonly effected area for patients. Because the antenna can be made very small, RF-based detection of compartment syndrome applications can be extended to small-scale devices. Numerical studies show that compartment syndrome as small as 5 ml can be detected with this method. We hope that our novel method will improve both diagnosis and overall patient care for compartment syndrome. Moreover, this detection system is intended to provide a safe, economical, and less distressing method to monitor compartment syndrome.