Transient Electromagnetic Field Research Articles

Investigations of lightning accidents on automobiles

Many kinds of electronic equipment have been used in recent automobiles. Eco-friendly automobiles such as electric, fuel-cell and hybrid vehicles have spread rapidly. Those automobiles are usually sensitive to electromagnetic disturbance caused by lightning and so on. When an automobile is struck by lightning, lightning current usually flows into the earth through the vehicle body. The corresponding transient electromagnetic fields appearing inside the vehicle and shunt lightning current through electronics systems are considered sources of malfunctions. From an automobile safety and equipment protection viewpoints, investigations of protective measures are imperative. Before lightning protection methodologies are proposed, existing lightning damages to automobiles must be clarified. The statistical data on automobile lightning damage reports by conducting field surveys and web-based researches had been gathered. In this paper, the result of statistical data has been introduced. Right in the middle of the field surveys of lightning protection for automobiles, the outstanding fire accident of an automobile in Kanto district in Japan occurred. Right after hearing the news, interviews against the fire fighters about their field survey had been conducted; the scene of the accident and burned automobile had also been investigated. In this paper, the results of the interview and investigation have also been discussed.

自己相似性に基づく植物生体電位の過渡電磁界応答解析

This paper presents a self-similarity-based-analysis of effects of transient electromagnetic fields on bioelectric potentials of plants. In our experiment, a single transient electromagnetic field was applied to aloe and pachira. As a result, we found that the Hurst exponent of bioelectric potential was increased by the application of a transient electromagnetic field.

Implementation of a measurement system on field uniformity of transient electromagnetic field

Electromagnetic pulse and transient electromagnetic field have received a large concern. To guarantee the validity of the test results in transient field facilities, field uniformity is addressed and required in many international standards. This paper focuses on the implementation of such a measuring system according to the field uniformity requirements of MIL-STD-461F. Also the specific requirements are highlighted and the field sensor calibration is detailed. The measurement uncertainty budget of the field uniformity measuring system is briefly given.

JOR Iterative Method for the Modeling of MTLs Excited by EMP

In recent years, the distributed analytical representation and iterative technique (DARIT) based on the Jacobi iteration method (Jacobi-DARIT-field) and the Gauss-Seidel iteration method (Seidel-DARIT-field) were proposed to handle the transient electromagnetic field or the electromagnetic pulse (EMP) radiated field coupling to multiconductor transmission lines (MTLs). Compared to the Seidel-DARIT-field method, the Jacobi-DARIT-field method has a higher computational efficiency but a lower convergence rate. In order to improve its convergence rate, this letter extended the Jacobi-DARIT-field method with the Jacobi over relaxation (JOR) iteration algorithm and proposed a JOR-DARIT-field method. The performances of the JOR-DARIT-field method and the Jacobi-DARIT-field method were compared through the MTL modeling examples. It could be concluded that both methods have a high computational efficiency when computing the EMP coupling to MTLs. However, the JOR-DARIT-field method has a higher convergence rate than the Jacobi-DARIT-field method with a proper relaxation factor (RF).

Transient Electromagnetic Field Coupling to Buried Thin Wire Configurations: Antenna Model versus Transmission Line Approach in the Time Domain

The paper examines the antenna model for the transient analysis of electromagnetic field coupling to straight wire configurations buried in a lossy half-space. The wire antenna theory (AT) model is implemented directly in the time domain and it is based on the corresponding space-time Pocklington integrodifferential equation. The solution of the Pocklington equation is carried out analytically. The obtained results are compared against the results calculated via the transmission line (TL) approach. The TL approach is based on the telegrapher’s equations, which are solved using the modified transmission line method (MTLM) and Finite Difference Time Domain (FDTD) technique, respectively. Some illustrative computational examples for buried straight wire scatterer and horizontal grounding electrode are given throughout this work.

CIP法による雷電磁界・サージ解析

The constrained interpolation profile (CIP) method, which is one sort of the finite-difference methods, has been recently applied to transient electromagnetic field simulations. Differently from the finite-difference time-domain (FDTD) method, the CIP method considers not only electric- and magnetic-field values at grid points but also their spatial derivative values there. In principle, therefore, it could suppress numerical dispersion and instability even when a relatively coarse grid is used. In this technical note, fundamentals of the CIP method and its formulations for computing electromagnetic fields in the 3D Cartesian coordinate system and in the 2D cylindrical coordinate system are briefly explained. Representative applications are also shown.

A study on the discrete image method for calculation of transient electromagnetic fields in geological media

We conducted a study on the numerical calculation and response analysis of a transient electromagnetic field generated by a ground source in geological media. One solution method, the traditional discrete image method, involves complex operation, and its digital filtering algorithm requires a large number of calculations. To solve these problems, we proposed an improved discrete image method, where the following are realized: the real number of the electromagnetic field solution based on the Gaver–Stehfest algorithm for approximate inversion, the exponential approximation of the objective kernel function using the Prony method, the transient electromagnetic field according to discrete image theory, and closed-form solution of the approximate coefficients. To verify the method, we tentatively calculated the transient electromagnetic field in a homogeneous model and compared it with the results obtained from the Hankel transform digital filtering method. The results show that the method has considerable accuracy and good applicability. We then used this method to calculate the transient electromagnetic field generated by a ground magnetic dipole source in a typical geoelectric model and analyzed the horizontal component response of the induced magnetic field obtained from the “ground excitation–stratum measurement” method. We reached the conclusion that the horizontal component response of a transient field is related to the geoelectric structure, observation time, spatial location, and others. The horizontal component response of the induced magnetic field reflects the eddy current field distribution and its vertical gradient variation. During the detection of abnormal objects, positions with a zero or comparatively large offset were selected for the drillhole measurements or a comparatively long observation delay was adopted to reduce the influence of the ambient field on the survey results. The discrete image method and forward calculation results in this paper can be used as references for relevant research.

Finite-Element Calculation of 3-D Transient Electromagnetic Field in End Region and Eddy-Current Loss Decrease in Stator End Clamping Plate of Large Hydrogenerator

The stator clamping plate is an important component of hydrogenerators used to fasten the stator end core. Due to the complex leakage electromagnetic field in the end region, eddy-current loss in the stator clamping plate is usually very large, which will lead to partial overheat. Evaluation of eddy-current losses in stator clamping plates and reasonable structure design are the premise of ensuring the safe and stable operation of a large hydrogenerator. A 278-MVA hydrogenerator is taken as an example in this paper, and the calculation model of 3-D transient electromagnetic field of end region is established and validated by temperature test value. Then, a new arch-shaped clamping plate structure is presented. The transient electromagnetic field and eddy-current losses of end regions with traditional fan-shaped and new arch-shaped stator clamping plate structures are calculated by time-stepping finite-element method and are compared. Calculation results indicate that the new arch-shaped clamping plate structure can effectively reduce the eddy-current loss of stator clamping plate.

PCB Near-Field Transient Emission Time-Domain Model

This study is aimed at the time-domain (TD) electromagnetic compatibility (EMC) modeling of a planar near-field (NF) emission. The radiated EMC model is built, consisting of elementary dipole array, capable of accurate reproduction of NFs emitted by electronic circuits with transient excitations of nanoseconds duration. The details of the modeling approach are explained. The determination method of dipole parameters from the given time-dependent scanned 3-D electromagnetic (EM) field is developed. The proposed TD model was validated first with ideal sources excited by electrostatic discharge standard surge currents. Then, it was validated with the experimental scanned magnetic NF radiated by a microstrip circuit excited by a pulse RF signal. The magnetic field predictions confirmed the modeling procedure correctness. Modeling errors in reproducing the scanned transient 3-D EM field were better than 0.1%. Errors in NF to NF transformation of the transient EM field were in the range of 2%. The suggested model is particularly useful for the EMC NF emission investigation of modern multifunctional electronic systems with a mixture of analogue and digital blocks generating transient and impulse disturbances.

The development of high-speed actuator and its modeling

Nowadays, an increasing demand for high-speed actuators appears in mechanical switches, motors, and automotive devices, which mainly benefits from massive forces that are produced in extremely short time to drive the mechanism to a very high speed. During the action of actuators, various physical processes including the hydrodynamics, mechanical motion, electromagnetic, and circuit may couple with each other, which altogether determine the dynamic characteristics of actuators. However, the key factors that limit the actuator performance still exist. On one hand, enormous impact will be created during the high-speed actuation, which results in the structure strength and buffer of actuator not satisfying the requirement of engineering application. On the other hand, the computational models to solve the dynamic mechanical characteristics of actuator are not perfect. This indicates that the assessment of actuator dynamic performance and its structure optimization become more and more difficult. The objective and focus of this Special Issue are to present the achievement and innovation in the high-speed actuation technology. New principles of high-speed actuation technology are reviewed. Lots of improvements are proposed for conventional highspeed actuators, particularly the novel buffer schemes for actuators. At the same time, a number of numerical models to analyze the dynamic mechanical characteristics of actuator are discussed, in which the multi-physics equations that may reflect the flow field, transient electromagnetic field, electric circuit, and mechanical motion are coupled. These calculation methods can well reveal the interaction mechanism among various physical fields during the actuation, analyze the operational characteristics, and optimize the structure.

A New Thomson Coil Actuator: Principle and Analysis

A new design of Thomson coil (TC) actuator based on pressure buffer for high-speed switch (HSS) is proposed, in which the pressure buffer is realized by utilizing the internal flow field variation caused by the fast moving of metal plate in the enclosed actuator. The dynamic characteristics of the actuator have been investigated by using a new model with multiphysics field effects of flow field, transient electromagnetic field, electric circuit, and mechanical motion coupled in the calculation. Compared with the traditional simulation models, such a model well considers the influence of flow field on the motion of a metal plate. To show the validity and usefulness of this proposed model, a prototype of HSS based on TC actuator is successfully developed, which shows sufficient dynamic performance with satisfying pressure buffer. In contrast to laminar, the turbulence model predicts a closer result to the measurements with stronger pressure buffer and is more suitable to calculate the dynamic characteristics of the actuator. Finally, the influences of metal components in the actuator on the opening process and different design parameters on pressure buffer are analyzed in detail.

Modeling of electrodynamic‐mechanical coupling phenomena in smart magnetoelectroelastic materials

AbstractThe coupling of electric, magnetic and mechanical phenomena may have various reasons. The famous Maxwell equations of electrodynamics describe the interaction of transient magnetic and electric fields. On the constitutive level of dielectric materials, coupling mechanisms are manyfold comprising piezoelectric, magnetostrictive or magnetoelectric effects. Electromagnetically induced specific forces acting at the boundary and within the domain of a dielectric body are, within a continuum mechanics framework, commonly denoted as Maxwell stresses. In transient electromagnetic fields, the Poynting vector gives another contribution to mechanical stresses. First, a system of transient partial differential equations is presented. Introducing scalar and vector potentials for the electromagnetic fields and representing the mechanical strain by displacement fields, seven coupled differential equations govern the boundary value problem, accounting for linear constitutive equations of magnetoelectroelasticity. To reduce the effort of numerical solution, the system of equations is partly decoupled applying generalized forms of Coulomb and Lorenz gauge transformations [1,2]. A weak formulation is given to establish a basis for a finite element solution. The influence of constitutive magnetoelectric coupling on electromagnetic wave propagation is finally demonstrated with a simple one‐dimensional example. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A new model for Thomson-type actuator including the pressure buffer

The motion characteristics and flow field variation of Thomson-type actuator have been investigated in this article, in which a two-dimensional axisymmetric cylindrical coordinate model is constructed and described by a set of multi-physical equations reflecting the flow field, transient electromagnetic field, electric circuit, and mechanical motion. The motion performance of the actuator and the pressure drag caused by the high-speed movement of metal plate are analyzed under different opening speeds. It shows that the pressure drag has a strong buffer effect on the actuator. The influence of the laminar and standard [Formula: see text] models on the pressure distribution, velocity distribution, and motion characteristics is focused on. In comparison with the laminar model, the pressure drag of the turbulence model is much higher than the laminar model and is more beneficial for the buffer design of the mechanism.

CHEBYSHEV FILTER APPLIED TO AN INVERSION TECHNIQUE FOR BREAST TUMOUR DETECTION

Microwave imaging has been extensively studied in the past several years as a new technique for early stage breast cancer detection. The rationale of microwave imaging for breast tumour detection is significant contrast in the dielectric properties of normal tissue and malignant tumours. However, in practice noise present from the environments during screening/examination degrades the quality of the image. Inaccurate reconstructed image caused false/misleading interpretation of the image which leads to inappropriate diagnose or treatment to the patient. In the simulation works, noise is added to imitate the actual environment scenario. The two-dimensional (2D) object that identical to breast model is developed using numerical simulation to imitate the breast model. A filter is integrated with an iterative inversion technique for breast tumour detection to eliminate the noise. To assess the effectiveness of this approach, we consider the reconstruction of the electrical parameter profiles of 2D objects from measurements of the transient total electromagnetic field data contaminated with noise. Additive white Gaussian noise is utilized to mimic the effect of random processes that occur in the nature. This paper presents the filter settings and characteristics that affect the reconstruction of the image in order to obtain the most reliable and closer to the actual image. Selection of filter settings or design is important in order to achieve desired signal, most accurate image and provide reliable information of the object. Chebyshev low pass filter is applied in the Forward-Backward Time-Stepping (FBTS) algorithm to filter the noisy data and to improve the quality of reconstructed image.

Finite element modelling of transient electromagnetic fields near steel-cased wells

Finite element modelling of transient electromagnetic fields near steel-cased wells

Исследование влияния выбора начального приближения на сходимость решения конечно-элементной СЛАУ при моделировании процесса становления поля

Исследование влияния выбора начального приближения на сходимость решения конечно-элементной СЛАУ при моделировании процесса становления поля

A Comparison of Different-Mode Fields Generated from Grounded-Wire Source Based on the 1D Model

Traditional TEM study mainly focuses on the generation and application of the TE field using a loop or grounded-wire source; but in recent decades, lots of efforts have been made for implementation of the TM field and even the integration of the TE field with the TM one into anomaly detection in the subsurface. However, no applicable principles have been proposed for selecting the optimal electromagnetic field for various subsurface targets. The transient electromagnetic (TEM) fields generated from grounded-wire source consist of the TE-mode response (current-carrying wire), the TE–TM mode response (grounding ends) and the combined TEM-mode response (current-carrying wire and grounding ends). This study performs a comparison of TE/TE–TM/TEM fields by generating them from grounded-wire source and testing their distribution characteristics, detection depth, and sensitivity to anomalies, using both synthetic 1D model and two field surveys in China. The comparisons demonstrate that, the detection depth of the TE–TM field is smaller than those of both the TE and combined TEM fields. Meanwhile, for electric field, the TE–TM response provides a better detection than the TEM one, but with an uneven distribution. Therefore, the TE–TM electric field requires well-designed arrangements of receiving positions when applied to real projects. For the magnetic field, the TEM response has the best detection capability compared to the TE and TE–TM ones, but is least sensitive to layer thickness and resistivity, especially for an embedded layer with low resistivity.

Numerical Simulation of Electromagnetic Field and Flow Pattern in a Continuous Slab Caster with In-roll Type Strand Electromagnetic Stirring

The electromagnetic field and flow analysis model were developed to simulate the electromagnetic field and the flow pattern in a vertical curved continuous slab caster with the in-roll type strand electromagnetic stirring. The transient electromagnetic field distribution and the induced electromagnetic force were numerically described. The effects of stirring current, stirring frequency, and different stirrer configurations on the electromagnetically driven flow field in the strand were investigated and the optimization of the stirring parameters was discussed by performing a relative comparison of numerical results. Results show that the in-roller type strand electromagnetic stirrer (SEMS) pair generates the fluctuating magnetic fields, penetrating through the cast slab and periodically parallel shifting along the slab wide face with time evolution. The transient induced electromagnetic forces travels toward the magnetic flux shifting direction. Different stirring parameters (i. e. current and frequency) and stirrer configurations affect the stirring strength and the flow recirculation pattern in the strand, which are closely related to metallurgical performances of the stirrers. There is an optimum frequency to obtain the maximum stirring. The present model provides a relatively theoretical insight into the in-roll type strand electromagnetic stirring system for best operating.

Inverse transformation algorithm of transient electromagnetic field and its high-resolution continuous imaging interpretation method

We introduce a new and potentially useful method for wave field inverse transformation and its application in transient electromagnetic method (TEM) 3D interpretation. The diffusive EM field is known to have a unique integral representation in terms of a fictitious wave field that satisfies a wave equation. The continuous imaging of TEM can be accomplished using the imaging methods in seismic interpretation after the diffusion equation is transformed into a fictitious wave equation. The interpretation method based on the imaging of a fictitious wave field could be used as a fast 3D inversion method. Moreover, the fictitious wave field possesses some wave field features making it possible for the application of a wave field interpretation method in TEM to improve the prospecting resolution.Wave field transformation is a key issue in the migration imaging of a fictitious wave field. The equation in the wave field transformation belongs to the first class Fredholm integration equation, which is a typical ill-posed equation. Additionally, TEM has a large dynamic time range, which also facilitates the weakness of this ill-posed problem. The wave field transformation is implemented by using pre-conditioned regularized conjugate gradient method. The continuous imaging of a fictitious wave field is implemented by using Kirchhoff integration. A synthetic aperture and deconvolution algorithm is also introduced to improve the interpretation resolution. We interpreted field data by the method proposed in this paper, and obtained a satisfying interpretation result.

Time‐domain vector potential technique for the meshless radial point interpolation method

SummaryA time‐domain meshless algorithm based on vector potentials is introduced for the analysis of transient electromagnetic fields. The proposed numerical algorithm is a modification of the radial point interpolation method, where radial basis functions are used for local interpolation of the vector potentials and their derivatives. In the proposed implementation, solving the second‐order vector potential wave equation intrinsically enforces the divergence‐free property of the electric and magnetic fields. Furthermore, the computational effort associated with the generation of a dual node distribution (as required for solving the first‐order Maxwell's equations) is avoided. The proposed method is validated with several examples of 2D waveguides and filters, and the convergence is empirically demonstrated in terms of node density or size of local support domains. It is further shown that inhomogeneous node distributions can provide increased convergence rates, that is, the same accuracy with smaller number of nodes compared with a solution for homogeneous node distribution. A comparison of the magnetic vector potential technique with conventional radial point interpolation method is performed, highlighting the superiority of the divergence‐free formulation. Copyright © 2015 John Wiley & Sons, Ltd.