Transient Magnetic Field Research Articles

Design and Simulation of an Active Compensated Pulsed Alternator for the Flashlamp Load

This paper presents a nontraditional power supply system for lasers in which an active compensated pulsed alternator (ACPA) drives the flashlamp load directly instead of the capacitor groups. However, the delivered power and pulsed width of the ACPA are two pivotal machine output parameters, which are determined by the flashlamp load. In other words, the characteristics of the flashlamp load must be elaborately considered during the design process of ACPA. In this paper, the structure of a new single-phase iron-core nonsalient pole ACPA is proposed, which couples the flashlamp load. The theory and advantages of ACPA are also introduced. The characteristics of the transient magnetic field distributions are calculated by finite-element analysis to verify the electromagnetic programming design of ACPA. A circuit model of the power supply system is then established to simulate the performance. Some simulation waveforms are obtained and explained.

Finite element approximation of nonlinear transient magnetic problems involving periodic potential drop excitations

This paper deals with the computation of nonlinear 2D transient magnetic fields when the data concerning the electric current sources involve potential drop excitations. In the first part, a mathematical model is stated, which is solved by an implicit time discretization scheme combined with a finite element method for space approximation. The second part focuses on developing a numerical method to compute periodic solutions by determining a suitable initial current which avoids large simulations to reach the steady state. This numerical method leads to solve a nonlinear system of equations which requires to approximate several nonlinear and linear magnetostatic problems. The proposed methods are first validated with an axisymmetric example and sinusoidal source having an analytical solution. Then, we show the saving in computational effort that this methodology offers to approximate practical problems specially with pulse-width modulation (PWM) voltage supply.

Detecting neuronal currents with MRI: A human study

Recently developed neuronal current magnetic resonance imaging aims to directly detect neuronal currents associated with brain activity, but controversial results have been reported in different studies on human subjects. Although there is no dispute that local neuronal currents produce weak transient magnetic fields that would attenuate local MR signal intensity, there is not yet consensus as to whether this attenuation is detectable with present magnetic resonance imaging techniques. This study investigates the magnitude of neuronal current-induced signal attenuation in human visual cortex. A temporally well-controlled visual stimulation paradigm with a known neuronal firing pattern in monkey visual cortex provides a means of detecting and testing the magnitude of the neuronal current-induced attenuation in neuronal current magnetic resonance imaging. Placing a series of acquisition windows to fully cover the entire response duration enables a thorough detection of any detectable MR signal attenuation induced by the stimulus-evoked neuronal currents. No significant neuronal current-induced MR signal attenuation was observed in the putative V1 in any participated subjects. The present magnetic resonance imaging technique is not sensitive enough to detect neuronal current-induced MR signal attenuation, and the upper limit of this attenuation was found to be less than 0.07% under the study condition.

Singlet Exciton Fission in a Hexacene Derivative

Hexacene, an acene with six benzene rings, is notable for its exceptionally small triplet energy, around one third of the singlet energy. Herein, singlet fission, i.e., conversion of a singlet exciton into two triplets, is demonstrated in a thin film of hexacene derivative, employing both transient absorption spectroscopy and magnetic field effects on photocurrent.

Azimuthally fluctuating magnetic field and its impacts on observables in heavy-ion collisions

The heavy-ion collisions can produce extremely strong transient magnetic and electric fields. We study the azimuthal fluctuation of these fields and their correlations with the also fluctuating matter geometry (characterized by the participant plane harmonics) using event-by-event simulations. A sizable suppression of the angular correlations between the magnetic field and the 2nd and 4th harmonic participant planes is found in very central and very peripheral collisions, while the magnitudes of these correlations peak around impact parameter b∼8–10 fm for RHIC collisions. This can lead to notable impacts on a number of observables related to various magnetic field induced effects, and our finding suggests that the optimal event class for measuring them should be that corresponding to b∼8–10 fm.

A Characteristic Galerkin Method for Eddy-Current Field Analysis in High-Speed Rotating Solid Conductors

Standard Galerkin finite element method (FEM) performs poorly when simulating convection dominated problems using the Eulerian formulation. A numerical method for analyzing transient eddy-current magnetic field in high-speed rotating solid conductors using characteristic Galerkin finite element method (CGFEM) is presented. The convection-diffusion equation is discretized implicitly in time domain via the method of characteristics and in space via piecewise quadratic finite elements. An example with extremely large Peclet number is solved by using the CGFEM to validate its effectiveness. TEAM workshop problem 30 A which is a practical case with high-speed rotating conductors is studied to showcase the efficiency and accuracy of the proposed method.

Precise Magnetic Field Modeling Techniques of Rotary Machines Using Transient Finite-Element Method

A general and precise method to model rotary machines based on transient magnetic field computation using finite-element method (FEM) is presented. The merits of the proposed method are that the nonlinear iteration on the rotor position can be avoided. Formulas to predict the rotor position and speed of the machine are deduced based on Taylor's expansion. A curvilinear element is used on the two sides of the sliding surface to reduce the numerical noises arising from mesh rotation. The proposed methods for dealing with matching boundary conditions and periodic boundary conditions are very general, accurate and flexible. Typical numerical experiment shows that the numerical error of the local magnetic potentials on the motion sliding surface is only one twentieth of that of traditional interpolation method.

Calculation of Lorentz Forces on Coils for Transcranial Magnetic Stimulation During Magnetic Resonance Imaging

New applications for transcranial magnetic stimulation (TMS) are rapidly being developed for diagnostic and therapeutic purposes but are restricted by a number of technical limitations. The ability to reliably perform TMS concurrently with functional magnetic resonance imaging (fMRI) would be a valuable tool for researchers. However the forces experienced by TMS coils during normal operation due to large transient magnetic fields which are produced, are problematic. When operated within a large external field, such as in an fMRI scanner these forces can result in mechanical failure of the coils. This paper presents calculations of these forces to form a basis from which coil failure can be prevented.

Magneto–thermo–elastic fields caused by an unsteady longitudinal magnetic field in a conducting nanowire accounting for eddy-current loss

Nanowires are synthesized nanostructures with high levels of length-to-width ratio which are expected to have a wide range of applications in diverse fields of engineering and medicine; however, little is known about their dynamic response due to magnetic fields. Herein, magneto–thermo–elasto-dynamic analysis of a conducting nanowire is performed in the context of nonlocal continuum theory. A circular cylindrical solid nanowire subjected to an axisymmetric longitudinal transient magnetic field is considered. The equations of the magnetic, thermal, and elastic fields within the nanowire with their appropriate initial and boundary conditions are developed. The effect of eddy-current loss is also incorporated into the governing equations of the proposed model. The boundary value problem pertinent to each unknown field is solved analytically, and the nonlocal dynamic elastic fields within the nanowire are obtained. A comprehensive parametric study is conducted to determine the effects of the crucial factors on the maximum values of dynamic radial displacement as well as nonlocal stresses of the nanowire. The obtained results reveal that the eddy-current loss plays a crucial role in dynamic elastic fields within the nanowire, particularly for low initial duration of the applied magnetic field as well as low levels of the insulation of the nanowire's surface.

Workpiece Property Effect on Resistance Spot Welding

The weldability of resistance spot welding affected by different thermal, physical, and metallurgical properties is extensively investigated by realistically computing transient mass, momentum, energy, species, and magnetic field intensity transport in the alloy workpieces and electrodes. The properties considered are the thickness, radius, equilibrium partition coefficient of workpieces, electrode-to-workpiece electrical conductivity ratio, thermal conductivity ratio, and a joule heat-to-enthalpy change parameter. Resistance spot welding has been widely used in joining thin workpieces in various electronic packaging and manufacturing industries. Understanding of physical mechanisms for easily manipulating and controlling weld qualities in advance is important. This paper accounts for electromagnetic force, heat generations due to contact resistances at the electrode-workpiece interface and faying surface between workpieces, and temperature-dependent bulk resistance of the workpiece. The contact resistances are functions of hardness, temperature, electrode force, and surface condition. The computed results in general dimensionless expressions show that the welding is feasible or onset time is shortened by decreasing thickness, radius, equilibrium partition coefficient of the workpiece, and electrode-to-workpiece electrical conductivity and thermal conductivity ratios, and increasing the joule heat-to-enthalpy change parameter. The corresponding heat transfer and species patterns are also presented.

Reduction of a pre-formed radius in aluminium sheet using electromagnetic and conventional forming

Electromagnetic (EM) forming is a high-speed forming process that uses the forces induced on a conductive workpiece by a transient high frequency magnetic field to form the workpiece into a desired shape. This paper describes the results of a work undertaken to study the reduction of a 20mm radius to 5mm in 1mm AA 5754 sheet by conventional metal forming process and by electromagnetic forming. The combination of conventional and EM forming will be referred to as “hybrid forming”. The 20mm radius was pre-formed from flat sheet using a conventional die, punch and binder that allowed the material to draw in. The radius was then reduced to 5mm, with no draw-in allowed for either process. Sheets were studied in the as-received condition and were also pre-strained to 5%, 10% and 15% to simulate strain path effects in a multiple stage forming operation. The process was modelled numerically to gain insight into the stress, strain and strain rate histories. The research indicates that features that are not achievable using traditional stamping techniques can be obtained with the aid of EM forming.

Substorm‐like magnetospheric response to a discontinuity in the Bx component of interplanetary magnetic field

We examined the magnetospheric magnetic field and plasma responses to an encounter of a discontinuity in the Bx component of interplanetary magnetic field (IMF). The striking variations of simultaneous solar wind dynamic pressure and IMF‐Bz were not observed. Furthermore, we found that this IMF‐Bx discontinuity was a heliospheric current sheet, separating two high‐speed solar wind streams with different velocity and magnetic polarity. In this study, the magnetic field and plasma data were obtained from Time History of Events and Macroscale Interactions during Substorms (THEMIS), Cluster, and GOES to investigate the magnetospheric responses, and those were taken from ACE and Geotail to monitor the solar wind conditions. Simultaneous geomagnetic field variations from the ground observatories and aurora activity from Polar were also examined. When the discontinuity encountered the magnetosphere, THEMIS‐D, ‐E, and THEMIS‐A observed abrupt and transient magnetic field and plasma variations in the dawnside near‐Earth magnetotail and tail‐flank magnetopause. Significant magnetic field perturbations were not observed by Cluster as located in the duskside magnetotail at this time interval. Although simultaneous dipolarization and negative bay variations with Pi2 waves were observed by GOES and the ground observatories, global auroral activities were not found. Around the dawnside tail‐flank magnetopause, THEMIS‐C and ‐A experienced the magnetopause crossings due to the magnetopause surface waves induced by Kelvin‐Helmholtz instability. These results suggest that the magnetic field and plasma variations in the near‐Earth magnetotail and tail‐flank magnetopause were caused by moderate substorm‐like phenomena and magnetopause surface waves. They also indicate that clear magnetospheric disturbances can be brought even without significant variations in the solar wind.

Comparison Study of Finite Element Methods to Deal With Floating Conductors in Electric Field

In transient magnetic field computation, it is highly desirable if the stray capacitances among all conductors can be computed and their effects addressed conveniently. Because of the existence of floating conductors, the general finite element (FE) solver of Poisson's equation, which is a commonly used magnetic field solver, cannot be used to extract the capacitance matrix directly. In this paper, methods to deal with floating conductors in the electrostatic field for field solution, and capacitance matrix extraction using finite element method (FEM) are compared; their merits and shortcomings are discussed. A method to compute the electric field and extract the capacitance matrix to include the effect of floating conductors inside the solution domain is put forward. The merit of the proposed algorithm is that the general FE solver can be used without the need for any special program modification. A FE formulation to automatically include the capacitances in transient magnetic field is presented. By using the proposed method, users only need to input the information as how the conductors are connected. All the stray capacitances among conductors are automatically included in the solution of transient magnetic field with the proposed algorithm.

A Sensitivity Analysis Method for Equivalent Parameter Extraction of Transient Magnetic Field With Internal Circuits

A sensitivity analysis method for the equivalent parameter extraction of transient magnetic field problems with internally coupled circuits is presented. In contrast to conventional methods using physical meaning and physical relationships for parameter extraction, this method is based on a collection of mathematical system equations which include transient magnetic field equations and internal circuit equations. The extracted parameters include the collective effects of eddy currents, internal circuits, and mechanical motion. Compared with previous sensitivity analysis methods which extract only the equivalent inductance, the proposed algorithm extracts also the equivalent resistance. A laminated transformer with internal circuit is reported to validate and showcase the proposed method.

Application of Multi-Stage Diagonally-Implicit Runge-Kutta Algorithm to Transient Magnetic Field Computation Using Finite Element Method

A multi-stage diagonally-implicit Runge-Kutta (DIRK) algorithm is applied to discretize the time variable in transient magnetic field computation using finite element method (FEM). A formulation, which has the same format as the backward Euler (BE) algorithm for both linear and nonlinear problems, is deduced for simple and ready numerical implementation. The DIRK algorithm is compared with the BE algorithm which is an effective and popular algorithm in FEM. The merits and disadvantages of these two algorithms are highlighted. An ingeniously combined algorithm exploiting the merits of both BE and DIRK is presented and a numerical experiment shows that it can significantly improve the accuracy with no additional computing burden. For nonlinear problems, a DIRK nonlinear iteration strategy is presented and it can be shown that the total computing time of one integration time step can be shortened by about 36% without any accuracy loss in the solutions.

Charge-dependent azimuthal correlations in relativistic heavy-ion collisions and electromagnetic effects

We propose a scenario where the pattern of the recently observed charge-dependent azimuthal correlations can be understood qualitatively. This is based on the cluster picture and the assumption that the charged hadrons that flow outward from the surface of the overlapping region of the colliding nuclei move primarily parallel to the reaction plane. We also point out the there is a strong electric field induced by the transient magnetic field during the parton production in the initial phase of the relativistic heavy-ion collision and discuss its possible relevance to the scenario.

Transient Magnetic Fields and Current Distributions in an Electric Vehicle Caused by a Lightning Stroke

Summary An electric vehicle has more electronic parts than a gasoline-powered vehicle. Not only the control circuits but also the driving circuits of electric vehicles are electrical, in contrast to those of gasoline-powered vehicles. This means that there is a higher possibility of malfunctions in an electric vehicle due to electromagnetic disturbances caused by a lightning stroke. Therefore, it is important to establish lightning protection methodologies for electric vehicles. To clear up with the mechanisms whereby the lightning current following through the vehicle body and some other parts causes the malfunctions, it is important to clarify the transient magnetic fields and current distributions in electric vehicles. In this paper, the transient magnetic fields and the current distributions in an electric vehicle are simulated by the FDTD method, and the probability of lightning damage is discussed.

On the possibility to determine the electrical conductivity of 67P/CG from ROSETTA magnetic field observations

The ROSETTA mission to comet 67P/Churyumov-Gerasimenko presents us for the first time the opportunity to study the interior of a cometary nucleus. Information about the electrical conductivity and its distribution inside the nucleus can be derived by measuring the magnetic fields induced in the nucleus by variations of the interplanetary magnetic field. Due to the relatively small size of the nucleus, this task is not trivial and requires very precise magnetic field measurements.Here we analyze the response of a conductive nucleus to transient step-like magnetic field changes as well as the response in frequency domain to electromagnetic waves. For the nucleus we use a spherical model with either uniform conductivity or consisting of a core and an outer layer with different conductivities. The space outside of the nucleus is modeled either by highly conductive solar wind plasma or by zero conductivity void.Various combinations of conductivities, radii of the nucleus and of the core, and properties of the space outside the nucleus result in different inductive responses. Several such combinations which could be encountered by ROSETTA are studied in detail in order to estimate which conductivity ranges and core radii can be determined using the ROSETTA instruments and which mission operations would facilitate such measurements.

Firstg-factor measurements of the21+and the41+states of radioactive100Pd

The $g$ factors of the first ${2}^{+}$ and ${4}^{+}$ states of the radioactive ${}^{100}$Pd nucleus have been investigated for the first time, using an $\ensuremath{\alpha}$-particle transfer reaction from ${}^{12}$C to ${}^{96}$Ru. The transient magnetic field technique in inverse kinematics was used. The ${}_{\phantom{\rule{0.28em}{0ex}}\phantom{\rule{0.16em}{0ex}}46}^{100}$Pd${}_{54}$ nucleus is a suitable candidate for studying single-particle proton and neutron effects in the nuclear wave functions near the $N=Z=50$ shell closures. The results are discussed within the frameworks of both large-scale shell-model calculations and collective-model predictions.

Left-inversion soft-sensor of synchronous generator

SUMMARY The online measurement of some crucial variables in synchronous generator (such as the power angle, the d-axis and q-axis transient electric and magnetic fields, and the d-axis and q-axis stator circuit currents) is very important in many applications, but they are difficult to be measured by ordinary sensors. In the paper, these variables are estimated (soft-sensed) on the basis of the online directly measurable variables of generator (such as the active and reactive powers and the amplitude of current). First, a new model of synchronous generator is proposed, which fully includes the online measurable variables of synchronous generator and is suitable for designing soft-sensors. Second, aiming at the specialty of the proposed model (a typical kind of nonlinear differential-algebraic subsystem), the original left-inversion soft-sensing algorithm proposed in a previous paper is expanded. Then a left-inversion soft-sensor is designed while the fourth-order transient practical model of synchronous generator is considered, and all of the to-be-estimated variables are soft-sensed. Finally, the simulation is performed on the basis of MATLAB/SimPowerSystems (MathWorks, Natick, MA, USA), in which the sixth-order subtransient practical model of generator is used to simulate the real generator, and the results demonstrate the validity of the proposed method. Copyright © 2011 John Wiley & Sons, Ltd.