Electromagnetic Field Computation Research Articles

Necessity of self-consistent calculations for the electromagnetic field in probing the nuclear symmetry energy using pion observables in heavy-ion collisions

Within an isospin- and momentum-dependent transport model, we investigate the necessity of selfconsistent calculations for the electromagnetic field in probing the nuclear symmetry energy using pion observables in heavy-ion collisions at intermediate energies. To this end, we perform the $^{96}$Ru + $^{96}$Ru collisions at 400 MeV/nucleon with two calculations scenarios for the electromagnetic field including the selfconsistent calculation and the most used Li\'{e}nard-Wiechert formula, while the latter is a simplified one of the complete Li\'{e}nard-Wiechert formula by neglecting the radiation field for practical calculations in heavy-ion collisions at intermediate and/or relativistic energies. As a comparison, we also consider the static Coulomb field formula for calculations of the electromagnetic field in heavy-ion collisions. It is shown that the most used simplified Li\'{e}nard-Wiechert formula is not enough for the electromagnetic field calculation because the absent radiation field in this formula also affects significantly the charged pions as well as their $\pi^{-}/\pi^{+}$ ratio. Moreover, we also examine effects of the electromagnetic field in these scenarios on the double $\pi^{-}/\pi^{+}$ ratio of two isobar reaction systems of $^{96}$Ru + $^{96}$Ru and $^{96}$Zr + $^{96}$Zr at 400 MeV/nucleon. It is shown that the double $\pi^{-}/\pi^{+}$ ratio of two reactions tends to be less affected by the electromagnetic field calculation scenario and thus can still be an effective probe of the nuclear symmetry energy in heavy-ion collisions. Therefore, according to these findings, it is suggested that the selfconsistent calculation for the electromagnetic field should be carefully taken into account when using the pion observables to probe the nuclear symmetry energy in heavy-ion collisions.

Three-Dimensional Electromagnetic Field Calculation for Microwave Holography

Three-Dimensional Electromagnetic Field Calculation for Microwave Holography

GSvit — An open source FDTD solver for realistic nanoscale optics simulations

Surface and volume imperfections can significantly affect the performance of nanoscale or microscale devices used in photonics, optoelectronics or scientific instrumentation. In this article we present an open source software package for Finite-Difference Time-Domain electromagnetic field calculations suitable for calculations on graphics cards. Its special features include handling realistic models of imperfect nanoscale objects, such as treatment of arbitrary geometries including addition of random roughness to any geometrical object. The method is compared to conventional optical approach represented by Rayleigh-Rice theory. Practical applicability is demonstrated using a calculation of variation of field enhancement at proximity of a rough nanoscale antenna and rough particle scattering. It is shown that such approach can be namely useful in the areas where many repeated calculations are necessary, e.g. when studying how the optical response of nanoscale objects can vary when they are rough. Program summaryProgram Title: GSvitCPC Library link to program files:https://doi.org/10.17632/k424zbsxnk.1Licensing provisions: GPLv2Programming language: CNature of problem: If we want to analyse impact of random imperfections, in particular surface roughness, on optical response of nanoscale and microscale objects, we need to run many calculations with different random realisations. GSvit is a general electromagnetic field solver optimized for running such calculations, via fast computing on graphics cards and algorithms for loading of arbitrary data and modification of their geometry to construct randomly rough surfaces and interfaces.Solution method: Finite-Difference Time-Domain method implemented on computer processor and on graphics card, with advanced pre-processing in order to add realistic roughness to 3D objects.Additional comments including restrictions and unusual features: The current version of software, including the documentation and downloadable examples can be found on http://gsvit.net/.

Field‐Line‐Circuit Coupling Based Method for Predicting Radiated Electromagnetic Emission of IGBT‐PMSM Drive System

Electric drive system with Insulated gate bipolar transistor (IGBT) power device is widely used in Electric vehicle (EV), which consists of inverter, cables and Permanent magnet synchronous motor (PMSM). Due to the fast switching in di/dt and dv/dt of IGBT device, the system produces serious radiated Electromagnetic interference (EMI) through the interconnection cables. Thus, modeling of EMI source, propagation path and load PMSM is the key to accurately evaluate the system's radiation level. In addition, the system's radiated EMI involves the integrated calculation of circuit, cable and electromagnetic field, which cannot be solved by using a single circuit or electromagnetic calculation method. Therefore, this paper develops an effective field-linecircuit coupling based method to investigate the radiated EMI problems for IGBT-PMSM drive system, which is validated by experimental measurement. Besides, the impact of power cable parameters on radiated EMI is discussed. The proposed approach has guiding significance for electromagnetic compatibility design of EV.

Microwave breakdown in an overmoded relativistic backward wave oscillator operating at low magnetic field

Microwave breakdown has always been a huge challenge to the development of high-power microwave (HPM) sources. Some unique breakdown phenomena in a novel and powerful overmoded relativistic backward wave oscillator (RBWO) operating at low magnetic field are demonstrated. Three different breakdown mechanisms are utilized to explain these phenomena through detailed electromagnetic field calculation and particle-in-cell demonstration and effective methods are applied or suggested to mitigate the breakdown. The breakdown in the slow wave structure (SWS) mainly results from bombardment by the main electron beam under the intense radial electric field. Increasing the span between the main electron beam and the SWS or applying a coaxial extraction structure operating at coaxial TM01 mode might decrease the radial electric field and lessen the bombardment. The breakdown in the internal reflector originates with the field-induced emission in the inner ring under the intense axial electric field of the TM01 and TM02 mode and the subsequent electron-triggered emission in the outer ring. Removing the central part or constructing a complex reflector surface can suppress the emission. The breakdown in the slot retained for the Rogowski coil results from low pressure gas discharge initiated by microwave leakage from the RBWO into the diode region. Pasting microwave absorbing material into the coaxial diode region helps to obtain normal beam current waveforms measured by the Rogowski coil.

Coupled plasma transport and electromagnetic wave simulation of an ECR thruster

An electron-cyclotron resonance thruster (ECRT) prototype is simulated numerically, using two coupled models: a hybrid particle-in-cell/fluid model for the integration of the plasma transport and a frequency-domain full-wave finite-element model for the computation of the fast electromagnetic (EM) fields. The quasi-stationary plasma response, fast EM fields, power deposition, particle and energy fluxes to the walls, and thruster performance figures at the nominal operating point are discussed, showing good agreement with the available experimental data. The ECRT plasma discharge contains multiple EM field propagation/evanescence regimes that depend on the plasma density and applied magnetic field that determine the flow and absorption of power in the device. The power absorption is found to be mainly driven by radial fast electric fields at the electron-cyclotron resonance region, and specifically close to the inner rod. Large cross-field electron temperature gradients are observed, with maxima close to the inner rod. This, in turn, results in large localized particle and energy fluxes to this component.

Microwave Bragg structures in a half-open coaxial line

Bragg microwave structures in a coaxial line have found application as converting elements in devices for dielectric control of liquid and bulk medias. A feature of the measuring conversion of the complex dielectric constant in coaxial structures is the introduction of the substance under study into the inner space of the line. The latter circumstance imposes certain restrictions on the design of the external conductor for express control. In this regard, the consideration of half-open coaxial lines based on an external conductor in the form of longitudinal conducting rods is an urgent problem. The article proposes a method for calculating the wave impedance of a half-open coaxial line using a numerical calculation of electromagnetic fields. Based on the results of modeling Bragg microwave structures in a half-open coaxial line, recommendations are made for the construction of conversion elements based on them.

Fast Computation of Multi-Parametric Electromagnetic Fields in Synchronous Machines by Using PGD-Based Fully Separated Representations

A novel Model Order Reduction (MOR) technique is developed to compute high-dimensional parametric solutions for electromagnetic fields in synchronous machines. Specifically, the intrusive version of the Proper Generalized Decomposition (PGD) is employed to simulate a Permanent-Magnet Synchronous Motor (PMSM). The result is a virtual chart allowing real-time evaluation of the magnetic vector potential as a function of the operation point of the motor, or even as a function of constructive parameters, such as the remanent flux in permanent magnets. Currently, these solutions are highly demanded by the industry, especially with the recent developments in the Electric Vehicle (EV). In this framework, standard discretization techniques require highly time-consuming simulations when analyzing, for instance, the noise and vibration in electric motors. The proposed approach is able to construct a virtual chart within a few minutes of off-line simulation, thanks to the use of a fully separated representation in which the solution is written from a series of functions of the space and parameters coordinates, with full space separation made possible by the use of an adapted geometrical mapping. Finally, excellent performances are reported when comparing the reduced-order model with the more standard and computationally costly Finite Element solutions.

Design of linear phase shift transformer and analytical calculation of no-load electromagnetic field

Linear phase-shift transformer is a new type of transformer, which can be used in multi-rectifier and multi-inverter system. Taking the design of a linear phase-shifting transformer for multiple superimposed inverters as an example, a layered magnetic field analysis model of the linear phase-shifting transformer is established. Firstly, the primary side slot is treated as a smooth structure, then the model is layered and the current density of primary side is calculated by the single Fourier method Taking into account the boundary conditions of the transformer, the distribution expressions of the vector magnetic potential and the magnetic flux density in the solution region are derived, the relative permeability function of the air gap is established and the influence of the slot effect on the air gap electromagnetic field is calculated. In this paper, the distribution of electromagnetic field without load is calculated. Finally, the feasibility of the method is verified by simulation, which provides basis for the following engineering calculation and optimization design of linear transformer.

Integration of Energetic Model for Ferromagnetic Hysteresis in Finite Volume Method for Electromagnetic Field Calculation

In this article, a coupled algorithm between the control volume method and the hysteresis dynamic energetic model for ferromagnetic hysteresis is presented. To illustrate the dynamic behavior of ferromagnetic materials, the quasi-static model is extended by adding two components to the applied magnetic field “Hedd”, and “Hexc”. The added fields are related to the excess losses and classical eddy losses. Thus, two new supplementary coefficients are added to the model parameters. The determination of those coefficients is attained by measuring the energy density for two distinct frequencies. This model introducing the magnetic induction as an independent variable is presented in order to be directly used in time-stepping finite volume calculations applied to the magnetic vector potential formulation. The calculated results are validated by experiences performed in an Epstein’s frame. To check the effectiveness of this model combined with the control volume method in the time domain, the obtained results are compared with experiments.

Numerical Computation and Analysis of Electromagnetic Field in Magnetic Suspension and Balance System

The magnetic suspension wind tunnel balance (MSBS) is an entirely new device for aerodynamic measurement, and it makes the best of the electromagnetic force to suspend the aircraft model in the wind tunnel without contact. Compared with conventional wind tunnel balance, it absolutely abandons the model support and airflow interference. Therefore, the aerodynamic measurement environment is more authentic and the aerodynamic measurement results are more accurate. The electromagnetic field in MSBS plays a major role in bearing the force of wind. The numerical computation and finite element numerical analysis are performed to investigate key factors of electromagnetic force under different conditions. The calculation results based on finite element method (FEM) have revealed that the diameter and the spacing of of the axial coil, the number of segments and the pitch angle of the suspension model are key factors of electromagnetic force. Based on the above key factors, the structure of the magnetic suspension balance is optimized to maximize the electromagnetic force under multiple constraints.

Influential factors of inclined fracture induction logging based on numerical simulation and physical experiment

When the fracture normal forms an angle relative to the borehole axis, the induction logging response to the fractured formation consists of two contributions: one is the volume contribution caused by the eddy current, and the other is the charge contribution caused by the cumulative charges on the upper and lower boundaries of the fracture; both contributions are nonlinear. Researching the distribution of surface charges and eddy current in inclined fractured formations is of great significance for logging analysts and geologists to fully understand induction logging laws in such setting. However, there is insufficient research on this aspect. In this work, first, an electromagnetic field calculation method under the condition of existing cumulative charges at the interfaces was developed. Second, an induction logging numerical simulation model of inclined fractures based on the three-dimensional (3D) finite element method (FEM) was established, and the distribution laws of cumulative charges and eddy current in fractures under different dip angles were summarised. Third, we used the annular conductive region in the fracture as the object of our research, and analysed the influence law of different conductive regions distribution on induction logging. Finally, we carried out physical experiments to verify the numerical results and achieved good agreement between the two results. Hence, it proves the validity of the methods and conclusions.

3-D FDTD Method for Fast Calculation of Geomagnetic Storm Electromagnetic Fields

In this article, a 3-D finite-difference time-domain (FDTD) method is proposed for rigorous modeling and fast calculation of ultralow frequency geomagnetic storm electromagnetic fields (GS-EMFs). The proposed FDTD approach enables modeling of large-scale and complex 3-D earth structure (e.g., multilayer ground and earth curvature). Unlike conventional FDTD methods, the proposed FDTD method does not require extensive computational resources when dealing with ultralow frequency problems. In this article, the ground surface GS-EMFs produced by an electrojet (line current and sheet current sources) are compared with those obtained using the classical 1-D approaches for case of uniform and horizontally stratified ground. The effect of horizontally vertically multilayer ground and earth curvature on the GS-EMFs is evaluated by the proposed FDTD method. The presented results fully support the adequacy and efficiency of the proposed FDTD method for modeling of large-scale and complex 3-D earth structures for calculation of GS-EMFs.

Thermal Modeling and Experimental Validation in the Rotor Region of Hydrogenerator With Different Rotor Structures

Thermal management is often considered a bottleneck in the pursuit of the next generation hydrogenerator in the electric power system. Overheating of the complex rotor parts has become one of the main problems affecting safe and stable hydrogenerator operation. In this paper, a 250 MW hydrogenerator is analyzed. The transient electromagnetic field of the hydrogenerator is calculated and the losses of the rotor parts are obtained. The rotation of the hydrogenerator rotor is considered. Three-dimensional fluid and thermal mathematic and physical models of the hydrogenerator are established. The loss values from electromagnetic field calculations are applied to the rotor parts as heat sources in the temperature field. After solving the fluid and thermal equations of fluid-solid conjugated heat transfer, influence of the structures of rotor support plate, rotor pole body insulation, and rotor excitation winding on the fluid flow and temperature distribution in the rotor region of hydrogenerator is studied using the finite volume method. The calculated temperature result of rotor excitation winding is compared with the measured value. The calculated temperature result agrees well with the measured value. It provides an important reference for optimizing the rotor structure of the larger hydrogenerator.

Calculation of the pulsed electromagnetic field of a plane annular magnetic current

The work calculates the radiation fields of a plane ring magnetic current in the time domain. Two functions are considered that describe the dependence of the magnetic current on time: the delta function and the unit drop. All calculations are performed in the time domain without using the Fourier transform. First, the time-dependent vector potential is calculated. When writing expressions for the vector potential, the annular magnetic current is represented by the difference between two circular magnetic currents. Then, the magnetic field created by the ring magnetic current is found through the vector potential. Only one φ-th component of the magnetic field is nonzero. Further, from Maxwell's equations through the magnetic field, the components of the electric field of the annular magnetic current are calculated. On the basis of the formulas obtained, various special cases showing the dependence of the emitted field on time and spatial coordinates are considered. The time dependence of the electric field on the ring axis is calculated. It is shown that the Fourier transform of this field leads to a formula known from the literature in the frequency domain for calculating the field on the axis of the ring. The graphs are given showing that near the wave front, the transverse components of the electric and magnetic fields differ only by a factor equal to the wave resistance of the medium (120π for the air medium). The images of the electric field at different times are shown. In the given pictures of the fields, one can observe the movement of the radiation field near the wave front and the formation of a static field in the vicinity of the ring. The analytical expressions obtained in this work can be used to calculate antennas and other structures excited by a coaxial line. They can be used to solve integral equations in the time domain.

Multi-Physical Coupling Field of a Permanent Magnet Linear Synchronous Generator for Wave Energy Conversion

Permanent Magnet Linear Synchronous Generators (PMLSG) has high power density and high efficiency, which is always employed in industrial application field. However, as temperature increases, it is easy to cause demagnetization of the permanent magnet, and the applications of PMLSG is limited. In this paper, a PMLSG is optimized which is used in a low speed power generation system. Firstly, a multi-physical coupling field system is described, and introduced the main factors which affecting the design of the PMLSM. Secondly, a multi-physics optimization method based on Genetic Algorithm (GA) is to improve the power density and efficiency. At the same time reduce the material cost of the generator. The thermal model is established and analysis the losses of PMLSG. The conductive heat transfer coefficient is calculated. Then, a Finite Element Analysis (FEA) model is established, and the electromagnetic properties of PMLSG were analyzed. The results of the electromagnetic field calculation are imported into the transient thermal analysis model by FEA, and the temperature of each part for PMLSG are calculated. Finally, an experimental test platform is built for verifying the correctness of the analysis.

A Fast Volume Integral Equation Solver With Linear Basis Functions for the Accurate Computation of EM Fields in MRI

A stable volume integral equation (VIE) solver based on polarization/magnetization currents is presented, for the accurate and efficient computation of the electromagnetic (EM) scattering from highly inhomogeneous and high contrast objects. We employ the Galerkin method of moments to discretize the formulation with discontinuous piecewise linear basis functions on uniform voxelized grids, allowing for the acceleration of the associated matrix-vector products in an iterative solver, with the help of FFT. Numerical results illustrate the superior accuracy and more stable convergence properties of the proposed framework, when compared against standard low-order (piecewise constant) discretization schemes and a more conventional VIE formulation based on electric flux densities. Finally, the developed solver is applied to analyze complex geometries, including realistic human body models, typically used in modeling the interactions between EM waves and biological tissue.

Nonlinear Digital Simulation Models of Switched Reluctance Motor Drive

The paper deals with nonlinear simulation models of a drive consisting of the four-phase 8/6 doubly salient switched reluctance motor (SRM), the four-phase dissymmetric bridge power converter and the closed-cycle rotor speed control strategy carried out by the pulse width modulation (PWM) with variable angle and combined control scheme with the PI algorithm. All presented considerations are based on a MATLAB-SIMULINK platform. The nonlinear mathematical model of the analyzed SRM drive was obtained as a combination of the two dimensional (2D) finite element model (FEM) of the motor and the nonlinear model of the electrical network of the power supply circuit. The main model and its seven sub-modules, such as the controller module, one phase simulation module, rotor position angle transformation module, power system module, phase current operation module, “subsystem” module, and electromagnetic torque of one phase operation module, are described. MATLAB functions store the magnetization curves data of the motor obtained by the 2D FEM electromagnetic field calculations, as well as the data of magnetic co-energy curves of the motor calculated from the magnetization curves. The 2D specimen insert method is adopted in MATLAB functions for operating the flux linkage and the magnetic co-energy at the given phase current and rotor position. The phase current waveforms obtained during simulations match with the tested experimentally phases current waveforms at the same rotor speed and the same load basically. The simulated rotor speed curves also agree with the experimental rotor speed curves. This means that the method of suggested nonlinear simulation models of the analyzed SRM drive is correct, and the model is accurate.

Some peculiarities of the polarization structure of the electromagnetic field at high frequencies in geological sections: mathematical solutions and experiments

The effects of induced polarization (IP) in the ore bodies and host rocks in the frequencies above 1 000 000 Hz were considered. The phase response of the complex resistivity (CR) system equipment Geozond have been explored instrumentally. The reliability of high-frequency IP measurements was confirmed by independent verification by mining activities. The results confirm the presence of IP effects in the ore bodies and host rocks. They suggest the necessity to account for IP effects in the interpretation of electromagnetic data, in particular, in induction logging data. The purpose of mathematical computer modeling in this work was to study the propagation of a high frequency electromagnetic field from a linear current source in a material medium by solving Maxwell's equations using finite-difference approximations (iterations) in the time domain. The measurement results were processed according to a well-known scheme, using the method of iterative selection in automatic mode. This allows to use this method for end-to-end calculation of electromagnetic fields in complex three-dimensional inhomogeneous structures.

Simulation research on magnetoacoustic B-scan imaging of magnetic nanoparticles

As drug carriers, magnetic nanoparticles can specifically bind to tumors and have the potential for targeted therapy. It is of great significance to explore non-invasive imaging methods that can detect the distribution of magnetic nanoparticles. Based on the mechanism that magnetic nanoparticles can generate ultrasonic waves through the pulsed magnetic field excitation, the sound pressure wave equation containing the concentration information of magnetic nanoparticles was derived. Using the finite element method and the analytical solution, the consistent transient pulsed magnetic field was obtained. A three-dimensional simulation model was constructed for the coupling calculation of electromagnetic field and sound field. The simulation results verified that the sound pressure waveform at the detection point reflected the position of magnetic nanoparticles in biological tissue. Using the sound pressure data detected by the ultrasonic transducer, the B-scan imaging of the magnetic nanoparticles was achieved. The maximum error of the target area position was 1.56%, and the magnetic nanoparticles regions with different concentrations were distinguished by comparing the amplitude of the boundary signals in the image. Studies in this paper indicate that B-scan imaging can quickly and accurately obtain the dimensional and positional information of the target region and is expected to be used for the detection of magnetic nanoparticles in targeted therapy.