Total Electric Field Research Articles

Inverse Scattering Analysis from Measurement Data of Total Electric and Magnetic Fields by Means of Cylindrical-Wave Expansion

Microwave tomography is an effective technique to estimate material distribution, where inverse scattering analysis is performed on the assumption that accurate information on the incident field is known for a measurement curve as well as in the target region. In reality, however, the information may often be unobtainable due to multiple scattering between the transmitting antenna and the target object, or existence of unwanted waves and obstacles. In this paper, a method to extract information on incident fields from measured total field data is proposed. The validity of the proposed method is verified on 2D TMz problems, where a cylindrical, a square, and an L-shape homogeneous object are employed as a target object. Furthermore, it is shown that the method is available even when there are unwanted obstacles outside the measurement curve.

Measurement and evaluation of occupational exposure to electromagnetic field in the vicinity of FM/TV broadcast radiation

This paper involves the measurement and evaluation of electromagnetic field exposure levels at Kamarkouh FM/TV transmitter station at Qom province with multiple-frequency sources. Electromagnetic radiation levels were measured at 34 points for 6 min by Strength Meter Probe which is a broadband meter. The measured electromagnetic radiation levels were then compared to the International Commission of Non-Ionizing Radiation Protection standard. In addition, the theoretical electric field strength values at these same 34 points as above were estimated based on a free-space modeling calculation. The measurement results show that the maximum electromagnetic radiation level was 13.45 V/m, and this is far below the International Commission of Non-Ionizing Radiation Protection limits. The analysis of the comparison between calculated and measured electromagnetic radiation levels showed that there were other sources that contributed to increases in the electric field intensity. The source contributions to the total electric field strength were measured in a practical way. It means that by switching of the transmitters, the electric field strength measured in each state. The results showed that FM frequency band sources provided the highest contributions to the overall electromagnetic radiation level.

Total Field Reconstruction in the Near Field Using Pseudo-Vector <inline-formula> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula>-Field Measurements

Exposure assessments in the frequency range above 10 GHz typically require knowledge of the power density very close to the radiator (at 2-mm distance), which can be obtained through the total electric and magnetic fields. However, phase measurements are often not feasible in this frequency range, in particular in the reactive near field. We developed a novel phase reconstruction approach based on plane-to-plane reconstruction algorithms. It uses $E$ -field polarization ellipse information, which can be obtained extremely close to the source with probes based on the pseudo-vector sensor design. The algorithm's robustness and accuracy were analyzed and optimized for distances of a fraction of the wavelength $\lambda$ , and a comprehensive set of realistic exposure conditions was simulated to evaluate the algorithm. For distances greater than $\lambda$ /5, the error of the spatially averaged peak incident power density is found to be below 0.5 dB. Measurements in four different antenna prototypes revealed that the simulated deviation of reconstructed averaged power density was consistently below 1.1 dB for distances as close as 2 mm, i.e., smaller than the estimated total experimental assessment uncertainty of 1.4 dB. This demonstrates that the power density can be reliably determined by measurements as close as $\lambda$ /5 from any transmitter.

Spatio-temporal evolution of electric field inside a microwave discharge plasma during initial phase of ignition and its effect on power coupling

During the initial phase of microwave (MW) power launch inside a MW discharge ion source (MDIS), plasma and the electric fields are evolved with time together in the plasma volume. The spatio-temporal evolution pattern in the cavity of a MDIS is reported here, highlighting the role of these electric fields on power coupling processes. Evolution of electric field and so power coupling processes are calculated using Finite Element Method (FEM). Unlike PIC/MCC or hybrid fluid, here FEM model uses time dependent Poisson solver through drift-diffusion approach. In presence of plasma gradient in the volume ambipolar electric field is generated which interacts with the MW electric field to form resultant total electric field which continuously vary during this evolution period. It is observed that main power coupling mechanism is electron cyclotron resonance (ECR) method, however with the evolution of plasma, the mode shifts from ECR to off-ECR type heating with time. Off-ECR heating in the form of upper-hybrid resonance (UHR) method, electro-static (ES) ion acoustic wave heating method are important heating mechanisms during the over-dense plasma condition, when density is above critical density for launched MW frequency, 2.45 GHz. An indirect verification of simulated temporal evolution of hot electron temperature and plasma density with the experiment, is done under similar configuration and operating environment. The experimental results are found to be agreed reasonably well with the simulation in the low power range.

CustEM: Customizable finite-element simulation of complex controlled-source electromagnetic data

We have developed the open-source toolbox custEM (customizable electromagnetic modeling) for the simulation of complex 3D controlled-source electromagnetic (CSEM) problems. It is based on the open-source finite-element library FEniCS, which supports tetrahedral meshes, multiprocessing, higher order polynomials, and anisotropy. We use multiple finite-element approaches to solve the time-harmonic Maxwell equations, which are based on total or secondary electric field and gauged potential formulations. In addition, we develop a secondary magnetic field formulation, showing superior performance if only magnetic fields are required. Using Nédélec basis functions, we robustly incorporate the current density on the edges of the mesh for the total field formulations. The latter enable modeling of CSEM problems taking topography into account. We evaluate semianalytical 1D layered-earth solutions with the pyhed library, supporting arbitrary configurations of dipole or loop sources for secondary field calculations. All system matrices have been modified to be symmetric and solved in parallel with the direct solver MUMPS. Aside from the finite-element kernel, mesh generation, interpolation, and visualization modules have been implemented to simplify and automate the modeling workflow. We prove the capability of custEM, including validation against analytic-solutions, crossvalidation of all implemented approaches, and results for a model with 3D topography with four examples. The object-oriented implementation allows for customizable modifications and additions or to use only submodules designed for special tasks, such as mesh generation or matrix assembly. Therefore, the toolbox is suitable for crossvalidation with other codes and as the basis for developing 3D inversion routines.

Standing wave approach in the theory of X-ray magnetic reflectivity.

An extension of the exact X-ray resonant magnetic reflectivity theory has been developed, taking into account the small value of the magnetic terms in the X-ray susceptibility tensor. It is shown that squared standing waves (fourth power of the total electric field) determine the output of the magnetic addition to the total reflectivity from a magnetic multilayer. The obtained generalized kinematical approach essentially speeds up the calculation of the asymmetry ratio in the magnetic reflectivity. The developed approach easily explains the peculiarities of the angular dependence of the reflectivity with the rotated polarization (such as the peak at the critical angle of the total external reflection). The revealed dependence of the magnetic part of the total reflectivity on the squared standing waves means that the selection of the reflectivity with the rotated polarization ensures higher sensitivity to the depth profiles of magnetization than the secondary radiation at the specular reflection condition.

The dc power observed on the half of asymmetric superconducting ring in which current flows against electric field

The observations the dc voltage on asymmetric superconducting ring testify that one of the ring segments is a dc power source. The persistent current flows against the total electric field in this segment. This paradoxical phenomenon is observed when the ring or its segments are switched between superconducting and normal state by non-equilibrium noises. We demonstrate that the dc voltage and the power increase with the number of the identical rings connected in series. Large voltage and power sufficient for practical application can be obtained in a system with a sufficiently large number of the rings. We point to the possibility of using such a system for the observation of the dc voltage in the normal state of superconducting rings and in the asymmetric rings made of normal metal.

The effect of a saturated kink on the dynamics of tungsten impurities in the plasma core

We studied the effect of saturated kink-like instabilities on the redistribution of W impurities. A numerical code that follows the exact trajectories of the impurity ions in the total fields and includes collisions was employed. The code is written in CUDA C and runs in graphical processing units, allowing simulations with a large number of particles with modest resources. The total electric and magnetic fields are calculated as the sum of a simple analytical equilibrium (large aspect ratio, circular cross section) plus the fields of the kink mode. Our simulations show that when the W ions have a thermal velocity distribution, with zero mean velocity, the kink has no effect on the W density. However, when we include the plasma rotation and the drag on the impurities, the kink can affect the W density. When the average passing frequency of the W ions is similar to the frequency of the kink mode, the expulsion of W ions from the plasma core is maximized and the W density profile shows a hollow structure. This could have implications for the mitigation of W accumulation.

3D CSAMT modelling in anisotropic media using edge-based finite-element method

ABSTRACTControlled-source audio-frequency magnetotellurics (CSAMT) is an important geophysical technique. Numerous studies have shown that the electrical anisotropy in the Earth cannot be ignored because it would probably lead to misinterpretations of electromagnetic data. It is necessary and meaningful to study CSAMT responses in three-dimensional (3D) electrical anisotropic media; therefore, we have developed an edge-based finite element method for 3D CSAMT forward modelling in generalised anisotropic media. The total electric field in this approach is decomposed into a primary electric field and a secondary electric field, and the Galerkin weighted residuals method is adopted to obtain the variational equation. The accuracy of this algorithm was initially validated by comparing solutions with those obtained in previous work on a 3D arbitrary anisotropic model. We then studied the responses of an oblique source as well as equatorial and axial configurations and the tensor source for anomalies with different Euler’s angles. Several meaningful conclusions can be derived from this work and a synthetic model is developed; the results also confirm the validity of previous conclusions. This study shows that a tensor source is necessary for a CSAMT survey in 3D anisotropic media, and the anisotropic parameters of anomalies have complex and significant influences on CSAMT responses.

Effect of structure parameters on performance of N-polar GaN/InAlN high electron mobility transistor

Based on the drift-diffusion transport model, Fermi-Dirac statistics and Shockley-Read-Hall recombination model, the effect of the structure parameters on the performance of N-polar GaN/InAlN high electron mobility transistor is investigated by self-consistently solving the Schrodinger equation, Poisson equation and carrier continuity equation. The results indicate that the saturation current density of the device increases and the threshold voltage shifts negatively with GaN channel thickness increasing from 5 nm to 15 nm and InAlN back barrier thickness increasing from 10 nm to 40 nm. The maximum transconductance decreases with GaN channel thickness increasing or InAlN back barrier thickness decreasing. The change trends of the various performance parameters become slow gradually with the increase of the thickness of the GaN channel layer and InAlN back barrier layer. When the GaN channel thickness is beyond 15 nm or the InAlN back barrier thickness is more than 40 nm, the saturation current, the threshold voltage and the maximum transconductance tend to be stable. The influence of the structure parameter on the device performance can be mainly attributed to the dependence of the built-in electric field, energy band structure and the two-dimensional electron gas (2DEG) on the thickness of the GaN channel layer and InAlN back barrier layer. The main physical mechanism is explained as follows. As the GaN channel thickness increases from 5 nm to 15 nm, the bending of the energy band in the GaN channel layer is mitigated, which means that the total built-in electric field in this layer decreases. However, the potential energy drop across this GaN channel layer increases, resulting in the fact that the quantum well at the GaN/InAlN interface becomes deeper. So the 2DEG density increases with GaN channel thickness increasing. Furthermore, the saturation current density of the device increases and the threshold voltage shifts negatively. Moreover, due to the larger distance between the gate and the 2DEG channel, the capability of the gate control of the high electron mobility transistor decreases. Similarly, the depth of the GaN/InAlN quantum well increases with InAlN back barrier thickness increasing from 10 nm to 40 nm, which results in the increase of the 2DEG concentration. Meanwhile, the electron confinement in the quantum well is enhanced. Therefore the device saturation current and the maximum transconductance increase with InAlN back barrier thickness increasing.

Simulations of Secondary Farley‐Buneman Instability Driven by a Kilometer‐Scale Primary Wave: Anomalous Transport and Formation of Flat‐Topped Electric Fields

AbstractSince the 1950s, high frequency and very high frequency radars near the magnetic equator have frequently detected strong echoes caused ultimately by the Farley‐Buneman instability (FBI) and the gradient drift instability (GDI). In the 1980s, coordinated rocket and radar campaigns made the astonishing observation of flat‐topped electric fields coincident with both meter‐scale irregularities and the passage of kilometer‐scale waves. The GDI in the daytime E region produces kilometer‐scale primary waves with polarization electric fields large enough to drive meter‐scale secondary FBI waves. The meter‐scale waves propagate nearly vertically along the large‐scale troughs and crests and act as VHF tracers for the large‐scale dynamics. This work presents a set of hybrid numerical simulations of secondary FBIs, driven by a primary kilometer‐scale GDI‐like wave. Meter‐scale density irregularities develop in the crest and trough of the kilometer‐scale wave, where the total electric field exceeds the FBI threshold, and propagate at an angle near the direction of total Hall drift determined by the combined electric fields. The meter‐scale irregularities transport plasma across the magnetic field, producing flat‐topped electric fields similar to those observed in rocket data and reducing the large‐scale wave electric field to just above the FBI threshold value. The self‐consistent reduction in driving electric field helps explain why echoes from the FBI propagate near the plasma acoustic speed.

Theoretical Research on Properties of Spatial Harmonics in Corrugated Waveguide

This paper investigates the dependence of the properties of the spatial harmonics on the overmoded ratio of the corrugated waveguide operating in TM01 at 30 GHz with the consideration of the effects of the ripple shape. It is found that as the overmoded ratio grows, the electric fields concentrate towards the ripple surface, which weakens the enhancement of the power handling capacity caused by augmentation of the overmoded ratio. As the overmoded ratio grows, the ratio between the field amplitudes of the -1st spatial harmonic and the fundamental harmonic increases monotonically. Therefore, the total electric fields composed of the spatial harmonics become the spatial beating-wave with the single frequency, whose amplitudes vary along z-axis with the spatial period determined mainly by the -1st spatial harmonic and the fundamental harmonic. Researches on coupling impedances show that with the same overmoded ratio, the corrugated waveguide consisting of the improved rectangular ripples provides better synchronous coupling for the wave-beam interaction than that of the sinusoidal ripples does. Moreover, it is better to choose the fundamental harmonic close to the light line as the synchronous wave for the wave-beam interaction in the low magnetic field. In that case, even if the electron beam keeps far away from the ripple surface, the synchronous wave still provides strong enough coupling for the electron beam.

Research on Electric Field Simulation of GTEM Cell Based on UHF Sensor Calibration

In this paper, the GTEM cell electric field using to UHF sensor calibration is simulated by HFSS software. According to the simulation results, the field uniformity of the total electric field strength in the “1/3 area” of the GTEM cell can meet the requirements before being placed in the UHF sensor. However, the field uniformity of the total electric field strength has been greatly changed after the UHF sensor is placed. In addition, the maximum amplitude of the field strength change in the UHF sensor test area exceeds 10 dB compared to that before the UHF sensor is placed. It has a great influence on the calibration accuracy of UHF sensors. Through the simulation study of the electric field of GTEM cell, it provides a reference for further improving the calibration accuracy of UHF sensor.

Simplified calculation of maximum ground‐level electric field when two HVDC transmission lines run across at any intersection angle

When two HVDC transmission lines run across, because of the interaction between the two lines, the maximum ground-level total electric field is not a simple superposition of the maximum ground-level total electric field generated when the two lines exist alone. This paper presents an approximate method to use the maximum ground-level total electric field when only the lower line exists as the maximum ground-level total electric field when two lines run across. Here, the 3D method of characteristics has been improved to make it suitable for structure of two lines intersected at an angle using a method of coordinate transformation. The 3D method of characteristics is used to calculate the theoretical maximum electric field when the two lines run across. The 2D FEM is used to calculate the approximate maximum electric field when only the lower line exists. The approximate results and theoretical results are compared for line structures of ±800 kV line runs across ±800 kV line, ±660 kV line, and ±500 kV line at any intersection angle. The approximate errors are < ±10%, which can meet the engineering requirement.

Calculation and Analysis of Electromagnetic Environment Indexes and Influence Factors of ±1100 kV UHVDC Transmission Lines

In order to study the influence of electromagnetic environment of ±1100 kV Changji-Guquan the UHVDC lines, the ground total electric field and ion current density of the HVDC line is studied in this paper by using the charge simulation method and Deutsch’s hypothesis-based analytical method. And the correctness of the method is verified by the measured results. The EPRI formula and CISPR formula are applied to study the audible noise and radio interference. At last, the influence of UHVDC transmission line parameters on the electromagnetic environment is analyzed, and the influence factors that restrict the construction of the UHVDC transmission lines are also studied. The results show that the minimum height of the pole is limited by the total electric field strength, and the influence of the roughness coefficient should also be taken into account when calculating the minimum height of the wire, while the selection of the diameter of the wire is constrained by both the ground total electric field and the audible noise.

Study on the Effect of Altitude on the Corona Inception Field and the Ground-Level Total Electric Field Under HVdc Lines Using Bipolar Test Lines

With the growing public awareness of environmental protection, the dc ground-level total electric field (TEF) is attracting increasing attention. Especially in high-altitude areas, it has become a key technical factor in deciding conductor types and the height of the transmission line. To determine the altitude effect and correction of the ground-level TEF for HVdc transmission lines, four short bipolar test lines with bundle conductors with the same parameters were built in China at altitudes of 50, 1700, 3400, and 4300 m. Using the test facilities, the dc ground-level TEF was measured over a long period of time, from Jan. 2010 to Nov. 2015. Through a statistical analysis of a large amount of data, the ground-level TEF characteristics of short bipolar test lines at different altitudes were obtained. By comparing the statistical results from different altitudes, it is determined that the dc ground-level TEF and corona inception field strength are linearly dependent on the altitude. Finally, the ground-level TEF and corona inception field strength altitude correction formulas of HVdc transmission lines are proposed.

Analysis of Electromagnetic Environment and Influencing Factors of Yihua DC Transmission Lines

The electromagnetic environment of transmission lines is one of the major constraints to the design and construction of HVDC transmission lines. In this paper, the charge simulation method and the analytic method based on the Deutsch hypothesis are used to calculate the total electric field strength and ion current density of the 500 kV Yihua DC transmission lines, and the correctness of the calculation is verified by the actual measurement results. Then the EPRI formula and CISPR formula are applied to analyse the audible noise and radio interference of HVDC transmission lines. At last, the influence of factors such as the pole spacing of HVDC lines, the conductor height to the ground, the splitting spacing and the roughness coefficient on the electromagnetic environment of HVDC transmission lines are analysed. Among them, the height of conductor has effective impact on the total electric field strength, while the control of polar spacing is limited. The height of the conductor and the distance between the poles affect the level of audible noise and radio interference mostly, but the control effect of the two is opposite.

Surface NMR Responses of Typical 3-D Water-Bearing Structures Evaluated by a Vector Finite-Element Method

Surface nuclear magnetic resonance (SNMR) technique has been widely applied to noninvasive groundwater exploration and aquifer quantitative characterization. Furthermore, it has the potential for studying and detecting hydrocarbon contaminants and for water resource management. To increase the tomography resolution of groundwater and expand the application range of SNMR, we first implemented its 3-D forward modeling using a vector finite-element (FE) method based on the total electric field. The key of SNMR forward modeling is the calculation of excitation magnetic field, and the total-field algorithm is an alternative scheme to numerically simulate the electromagnetic field. In this paper, we viewed the circular loop source as the combination of a certain number of horizontal electric dipoles. The unstructured tetrahedral mesh and local refinement technology were combined to precisely delineate the distribution of circular loop source, which effectively reduces the adverse effects of field source singularity. Then, the vector FE solver based on the total electric field was used to calculate the magnetic field distribution. The accuracy of the calculated results was validated by the analytical solutions for a circular loop laid on the surface of a homogeneous half-space. After calculating the excitation field, SNMR responses of three typical synthetic 3-D groundwater models were obtained with the basic signal response formula. Finally, we studied the effects of some important factors which have significant influences on SNMR signal responses and have practical importance in groundwater issues.

The influence of polarity reversal time on interface charges in oil-impregnated pressboard insulation under non-uniform electric field

The polarity reversal test is one of the routine tests for the evaluation of electric insulation in converter transformers. The polarity reversal time (PRT) has significant effect on the accumulation of interface charges in oil-impregnated pressboard insulation. IEC standard recommends that polarity reversal should be performed within 2 min so as to match with the dispersion rate of interface charges in uniform filed, but not necessarily in the non-uniform field. In order to investigate the influence of PRT on the dissipation rate of interface charges in non-uniform electric field, the density of interface charges was measured by an electrostatic capacitance probe in the needle-plate non-uniform field at the PRT of 2 ms, 4 ms and 2 min respectively. The results showed that the polarity of interface charges did not change with the applied voltage jump at the PRT of 2 ms and 4 ms, while the polarity of interface charges almost synchronously changed with the polarity reversal of applied voltage at the PRT of 2 min. For the PRT of 2 ms and 4 ms, the electric field nearby the needle electrode would be enhanced with applied electric field of the same direction, whilst the total electric field of insulation system would be weakened at the PRT of 2 min. It was inferred that polarity of interface charge might have not enough time to change in polarity reversal test within the PRT of 4 ms under non-uniform electric field, which was more close to the severe condition of covert transformer. The paper suggest that the value of PRT be reconsidered when the polarity reversal test is performed in non-uniform electric field.

A Modeling Study of Narrow Electric Field Signatures Produced by Lightning Strikes to Tall Towers

AbstractThe lumped voltage source model proposed by Baba and Rakov (2005b, https://doi.org/10.1029/2004JD005202) for studying the interaction of lightning with tall objects was used to examine the origin of earlier zero crossings observed in electric field signatures produced by lightning strikes to towers. Different return stroke models of transmission line type were used, and model parameters were varied in wide ranges. Lightning channel was assumed to be straight and vertical. It was found that the observed narrow field signatures cannot be reproduced by traditional models and require a narrower input current waveform or/and its faster decay with height. Contribution to the total electric field peak from a tower whose height exceeds 100 m or so is greater than that from the lightning channel. At distances of 2 to 50 km, the electric field signature due to the tower current was found to be bipolar, while that due to the lightning channel current was unipolar. The narrow bipolar electric field waveforms produced by lightning striking the 257‐m tower in Florida were reproduced using two approaches. In the first one, we employed as input a typical channel base current waveform and the transmission line with exponential current decay with height model with a very small decay height constant. In the second approach, we used a narrow pulse followed by a steady‐level tail as the input current waveform and the transmission line with linear current decay with height model. In both approaches, the computed electric field waveforms matched well the corresponding measured waveforms, at least for the initial half‐cycle and opposite polarity overshoot.