Electromagnetic Field Simulation Research Articles

Numerical study on action of HMF, PMF, DHMF, and DPMF on molten metal during electromagnetic casting

The effect of harmonic magnetic field (HMF), pulse magnetic field (PMF), differential phase harmonic magnetic field (DHMF), and differential phase pulse magnetic field (DPMF) on liquid and mushy zones of crystallizing metal was investigated by numerical simulation referring to electromagnetic DC (direct chill) casting process. Firstly, the experimental pulse current for electromagnetic casting was obtained by a digital oscilloscope. The physical and finite element models of Φ300-mm cylindrical crystallization for the electromagnetic field simulation were established. Then, the distribution of magnetic flux density (B) and electromagnetic forces (FMAG) generated by the four types of magnetic fields were obtained in a period (T). Actions of HMF, PMF, DHMF, and DPMF on molten melt were discussed based on radial and axial electromagnetic forces. Finally, the effects of electromagnetic parameters (current intensity, frequency, and duty cycle) on electromagnetic forces under PMF and DPMF were studied. The effect of electromagnetic forces on metal flow has been discussed. The results indicate that compared with harmonic current, the pulse current can generate a stronger magnetic field with the same conditions. Single-coil magnetic field can easily cause the molten metal radial vibration. The differential phase magnetic field can not only cause radial vibration but also produce axial convection, while the vibration effect is weaker. The electromagnetic forces increase with the increase of current intensity and duty cycle under PMF and DPMF. Moreover, the electromagnetic force has low sensitivity to frequency under DPMF.

Numerical Simulation Study on Electromagnetic Force Constrained Liquid Metal Deformation

In order to explore the mechanism of electromagnetic force restraining the deformation of liquid metal with non-uniform diameter, the coupling simulation of electromagnetic field and flow field was carried out to study the distribution of electromagnetic field and flow field in liquid metal. The simulation results show that the electromagnetic force at the convex position of the liquid metal is the largest, while the electromagnetic force at the concave position is smaller, and the diameter of the liquid metal with non-uniform diameter tends to be the same under the action of the pressure difference of the electromagnetic force.

Wireless coils based on resonant and nonresonant coupled-wire structure for small animal multinuclear imaging.

Earlier work on RF metasurfaces for preclinical MRI has targeted applications such as whole‐body imaging and dual‐frequency coils. In these studies, a nonresonant loop was used to induce currents into a metasurface that was operated as a passive inductively powered resonator. However, as we show in this study, the strategy of using a resonant metasurface reduces the impact of the loop on the global performance of the assembled coil. To mitigate this deficiency, we developed a new approach that relies on the combination of a commercial surface coil and a coupled‐wire structure operated away from its resonance. This strategy enables the extension of the sensitive volume of the surface coil while maintaining its local high sensitivity without any hardware modification. A wireless coil based on a two parallel coupled‐wire structure was designed and electromagnetic field simulations were carried out with different levels of matching and coupling between both components of the coil. For experimental characterization, a prototype was built and tested at two frequencies, 300 MHz for 1H and 282.6 MHz for 19F at 7 T. Phantom and in vivo MRI experiments were conducted in different configurations to study signal and noise figures of the structure. The results showed that the proposed strategy improves the overall sensitive volume while simultaneously maintaining a high signal‐to‐noise ratio (SNR). Metasurfaces based on coupled wires are therefore shown here as promising and versatile elements in the MRI RF chain, as they allow customized adjustment of the sensitive volume as a function of SNR yield. In addition, they can be easily adapted to different Larmor frequencies without loss of performance.

Feasibility study of a double resonant (1H/23Na) abdominal RF setup at 3 T

Sodium magnetic resonance imaging (MRI) of the human abdomen is of increasing clinical interest for e.g. kidney, intervertebral disks, prostate and tumor monitoring examinations in the abdomen. To overcome the low MR sensitivity of sodium, optimal radio frequency (RF) structures should be used. A common approach is to combine a volumetric transmit coil for homogeneous excitation with an array of sensitive receive coils adapted to the human shape.Additionally, proton imaging is required to match the physiological sodium images to the morphological proton images. In this work, we demonstrated the feasibility of a double resonant proton/sodium RF setup for abdominal MRI at 3T, providing a high sodium sensitivity. After extensive simulations, a 16-channel sodium receive array was built and used in combination with a volumetric sodium transmit coil. Additionally, a local proton coil was included in the setup for anatomical localizations. The setup was investigated using electromagnetic field simulations, phantom measurements and final in-vivo measurements of a healthy volunteer. A 3 to 6-fold sensitivity improvement of the sodium receive array compared to the volumetric sodium coil was achieved using the phantom simulations and measurements. Safety assessments of the local proton transmit/receive coil were performed using specific absorption rate simulations.Finally, the feasibility of such a setup was proven by in-vivo measurements.

Experiment study on a spiral-cup shaped TMF contact

In this paper, combined with the characteristics of spiral-shaped transverse magnetic field (TMF) contacts and cup-shaped TMF contacts, a new structure of spiral-cup shaped contacts was designed. Firstly, experiments were carried out on two kinds of TMF contacts – the traditional cup shaped contacts and the new spiral-cup shaped contacts. Arc behaviors were recorded and the arc motion were studied. The experimental results indicated that the arc motion between new contacts was better than that between the traditional cup-shaped contacts. Here, we paid particular attention to the arc characteristics between spiral-cup shaped TMF contacts. The duration and threshold current of different stages with different tested currents were discussed, and the arc characteristics during arc motion stage was analyzed. Moreover, electromagnetic field simulation was conducted on above two kinds of TMF contacts, and the distributions of magnetic field and the electromagnetic forces acted on arc were compared. According to the simulation results, some experimental phenomena were explained theoretically. In addition, the spiral-cup shaped structure proposed here makes it possible to research on arc movement mechanism without considering the complex mechanism of arc stepping over slots.

Numerical simulation and experimental verification of electromagnetic field of continuous casting copper crucible

The electromagnetic field of continuous casting square copper crucible was simulated by numerical simulation using Ansoft Maxwell in order to clarify the influence of current frequency and intensity on the distribution of magnetic flux density in the crucible. The simulation results showed that as the current frequency increases or current intensity decreases, the distribution of the magnetic flux density in each vertical position of the crucible hardly changed, but the value of the magnetic flux density was gradually reduced, and the magnitude of the decrease was decremented from the maximum position of the magnetic flux density to the upper and lower ends. The maximum value of the magnetic flux density in different axial directions was proportional to the current intensity. In the radial direction, the magnetic flux density of the surface of the crucible was large, and gradually decreased toward the inner layer. The magnetic field at the slit was higher than the middle portion of the ridge due to the reinforcing effect at the slit. The small coil method was used to measure the actual electromagnetic field distribution in the crucible. It can be found that the magnetic flux density in the crucible decreased from the crucible wall to the crucible center, which is consistent with the results of the numerical simulation.

Численное моделирование электромагнитных полей: мультифизические задачи, инструментарий и обучение

Численное моделирование электромагнитных полей: мультифизические задачи, инструментарий и обучение

Optimized sleeve monopole antenna for detection of electrostatic discharge radiation of spacecraft solar array.

The spacecraft operating on a geosynchronous orbit (GEO) is affected by the plasma environment and is prone to electrostatic discharges (ESD) that affect the safe operation of the spacecraft, especially solar array, radiating electromagnetic (EM) signals of a few MHz to tens of MHz. The capture of radiated EM signals helps to better study the characteristics and suppress the occurrence of ESD. In this paper, based on the frequency band characteristics of the EM wave signal radiated by ESD in space, a novel optimized compact sleeve monopole antenna is designed by using three-dimensional EM field simulation software High Frequency Structure Simulator. The length of the proposed antenna is only about 52 mm and its center frequency is 30 MHz. The frequency band of the voltage standing wave ratio (VSWR) less than 2 is 28.8-31.1 MHz and that of less than 5 is 26.8 MHz-33.2 MHz, and the bandwidth is 21.3%. The sample preparation and VSWR test by using the vector network analyzer were carried out. Finally, the sensitivity test was carried out in an EM shielding room by the piezoelectric ceramic ESD simulation experiment. The test results show that the designed antenna can receive the EM wave signal radiated by the ESD stably and can be used for spacecraft discharge detection.

Usage of T-Resonator Method at Determination of Dielectric Constant of Fabric Materials for Wearable Antenna Designs

Abstract In this study, determination of dielectric constants of fabric materials accurately by using T resonator method is aimed. Dielectric constant is one of the most important parameters that have a large effect on micro strip antenna performance. Small shifting at dielectric constant can cause huge alterations on electrical parameters of the antenna, especially at high frequencies. For this reason, a T resonator is designed on the wool felt fabric as the lower layer material at constant frequencies and the resonator dimensions are calculated. Using these calculated values, the finite element method is simulated with a High Frequency Electromagnetic Field Simulation (HFSS) as a resonator. After some size optimizations, the dielectric constant of the fabric was obtained correctly from the simulations. In order to validate the accuracy of the study and the values obtained, T resonator design on woolen felt material is manufactured and measurements of the resonator is realized with a vector network analyzer. Measurements of this resonator are compared with results from simulations and calculations. As a result, it has been shown that the dielectric constant of any fabric can be accurately determined using an easy, fast and inexpensive method and can be used in wearable micro strip antenna designs

Damping performance analysis of magnetorheological damper with serial-type flow channels

In order to obtain a larger damping force with the limited axial size of the vehicle suspension system, a new magnetorheological damper with serial-type flow channels was developed. The piston head was equipped with two piston end covers, three piston non-magnetic sleeves, and four piston magnetic sleeves, which were sequentially combined into three serial-type flow channels to form three groups of effective damping gaps. The structure and principle of the proposed magnetorheological damper were described in detail, and the model for calculating damping force was deduced too. Simulation and analysis for the proposed magnetorheological damper was implemented using electromagnetic field simulation software. The damping performance was tested and analyzed on the test rig under different applied current, amplitude, and frequency excitation. The experimental results show that the damping force is 6838 N under the load excitation with frequency of 1 Hz, amplitude of 7.5 mm, and current of 1.5 A, which is 1.6 times than the expected damping force. The equivalent damping coefficient is attained to 290 kN/s m−1, which shows that the developed magnetorheological damper has high vibration control ability and good mechanical properties.

Sensitivity analysis of neurodynamic and electromagnetic simulation parameters for robust prediction of peripheral nerve stimulation

Peripheral nerve stimulation (PNS) has become an important limitation for fast MR imaging using the latest gradient hardware. We have recently developed a simulation framework to predict PNS thresholds and stimulation locations in the body for arbitrary coil geometries to inform the gradient coil optimization process. Our approach couples electromagnetic field simulations in realistic body models to a neurodynamic model of peripheral nerve fibers. In this work, we systematically analyze the impact of key parameters on the predicted PNS thresholds to assess the robustness of the simulation results. We analyze the sensitivity of the simulated thresholds to variations of the most important simulation parameters, including parameters of the electromagnetic field simulations (dielectric tissue properties, body model size, position, spatial resolution, and coil model discretization) and parameters of the neurodynamic simulation (length of the simulated nerves, position of the nerve model relative to the extracellular potential, temporal resolution of the nerve membrane dynamics). We found that for the investigated setup, the subject-dependent parameters (e.g. tissue properties or body size) can affect PNS prediction by up to ~26% when varied in a natural range. This is in accordance with the standard deviation of ~30% reported in human subject studies. Parameters related to numerical aspects can cause significant simulation errors (>30%), if not chosen cautiously. However, these perturbations can be controlled to yield errors below 5% for all investigated parameters without an excessive increase in computation time. Our sensitivity analysis shows that patient-specific parameter fluctuations yield PNS threshold variations similar to the variations observed in experimental PNS studies. This may become useful to estimate population-average PNS thresholds and understand their standard deviation. Our analysis indicates that the simulated PNS thresholds are numerically robust, which is important for ranking different MRI gradient coil designs or assessing different PNS mitigation strategies.

Analysis of wireless power transfer based on metamaterial using equivalent circuit

The metamaterial (MA) has been proved to enhance the efficiency of the wireless power transfer (WPT) system considerably in many studies. This study presents an equivalent circuit model using a qualitative and even quantitative simple explanation for the behaviour of MA in WPT. For this purpose, the electromagnetic field simulation of WPT system with MA is carried out by the high-frequency structure simulation three-dimensional electromagnetic simulator. Also, the authors propose the circuit structure of the WPT system based on MA and explore its characteristics by numerical calculation and advanced design system simulation. The transmission efficiency of the simulator is characterised by reflection coefficient here. Although some methods, such as interference theory, transmission line circuit model, and effective medium theory, have been put forward to explain the physics mechanism of WPT system with MA, some of reactive parameters and the basic physical interpretation have not been expounded clearly so far. Differ from the existing theoretical model, the proposed approach focuses on the effect of the system parameters of MA and transfer coils on the transfer characteristics and is beneficial to the analysis of the complicated system.

Waveform relaxation: a convergence criterion for differential-algebraic equations

While waveform relaxation (also known as dynamic iteration or co-simulation) methods are known to converge for coupled systems of ordinary differential equations (ODEs), they may suffer from instabilities for coupled differential-algebraic equations (DAEs). Several convergence criteria have been developed for index-1 DAEs. We present here a convergence criterion for a coupled system of an index-2 DAE with an ODE. The analysis is motivated by the wish to combine electromagnetic field simulation with circuit simulation in a stable manner. The spatially discretized Maxwell equations in vector potential formulation with Lorenz gauging represent an ODE system. A lumped circuit model via the established modified nodal analysis is known to be a DAE system of index ≤ 2. Finally, we present sufficient network topological criteria to the coupling that are easy to check and that guarantee convergence.

A novel meander line integrated E-shaped rectenna for energy harvesting applications

In this article, design of a novel meander integrated E-shaped rectenna is presented. The designed rectenna operates at ISM frequency range from 2.2 to 2.5 GHz with acceptable reflection coefficients, gain and VSWR values. The designed rectenna is simulated using HFSS 15 (High Frequency Electromagnetic Field Simulation) and FR4 epoxy material is used in rectenna design for low cost having dielectric constant of 4.4 and thickness of 1.6 mm. In the rectifying stage full wave voltage doubler circuit is designed for DC power generation with SMS7630 Schottky diode and lumped circuit elements. The impedance matching circuit between the antenna and the rectifier is designed and simulated using advanced design system (ADS) software for efficient power transmission from the antenna to the load. The simulation and measurement results with different load and input power levels prove that the designed and implemented system can be used for low power energy harvesting applications in order to feed electronic components and battery free sensor networks.

A Mobile System for Integrated Characterization of Electromagnetic Radiation Danger

To monitor the electromagnetic situation in different spheres of domestic service and industry under the conditions of uncertainty of frequency ranges and behavior of spatial distribution of electromagnetic field, an approach based a map showing the admissible time of in which a human being can remain in various zones of the studied space has been suggested. The map is on the basis of the results of a limited number of measurements and electromagnetic field simulations taking into account the simultaneous effect and amplification of the resulting action of several electromagnetic radiation sources. The principles of the creation of point and cylindrical pictures of electromagnetic radiation danger using the transformation of distributions of electric field, magnetic field, and energy flux density parameters have been considered. The transformation is on the basis of the systematization of approaches to determine the admissible stay time in different zones of the space under study. The structure and performance of a basic modification of integrated characterization of electromagnetic radiation danger (i.e., a technological module) have been presented. A technique that implements the suggested approach to characterization of the electromagnetic situation using the technological module has been given taking into account the possibility of a simultaneous effect of different components of the electromagnetic field.

Unconditionally Stable Multiple One-Dimensional ADI-FDTD Method for Coupled Transmission Lines

The unconditionally stable multiple one-dimensional alternating direction implicit finite-difference time-domain (M1-D ADI-FDTD) method for coupled transmission lines is presented. The differential equations for coupled transmission lines are formulated in compact matrix form. Proper $4 \times 4$ split matrices are introduced, which feature unconditional stability for the ADI procedures. These matrices also lead to update equations with the left-hand sides involving tridiagonal matrices that can be solved efficiently. The update equations of the M1-D ADI-FDTD method are given, which comprise one implicit and three explicit updates in each procedure. The analytical proof of unconditional stability is also provided based on the von Neumann method. The M1-D ADI-FDTD method allows quick simulation and visualization of electromagnetic fields everywhere along the coupled transmission lines. To demonstrate the usefulness of the M1-D ADI-FDTD method, various coupled line structures for filter and filtering antenna are analyzed using the method.

Electrostatic potential calculation by application of walk-on-spheres method

The paper is devoted to mixed boundary-value problem solving for Laplace equation with the use of walk-on-spheres algorithm. The problem under study is reduced to finding a solution of integral equation with the kernel nonzero only at some sphere in the domain considered. Ulam-Neumann scheme is applied for integral equation solving; the appropriate Markov chain is introduced. The required solution value at a certain point of the domain is approximated by the expected value of special statistics defined on Markov paths. The algorithm presented guarantees the average Markov trajectory length to be finite and allows one to take into account boundary conditions on required solution derivative and to avoid Markov paths ending in the neighborhood of the boundaries where solution values are not given. The method is applied for calculation of electric potential in the injector of linear accelerator. The purpose of the work is to verify the applicability and effectiveness of walk-on-spheres method for mixed boundary-value problem solving with complicated boundary form and thus to demonstrate the suitability of Monte Carlo methods for electromagnetic fields simulation in beam forming systems. The numerical experiments performed confirm the simplicity and convenience of this method application for the problem considered.

Modeling and simulation of Electromagnetic Fields on a Floating Aluminium

The electromagnetic field calculation for a floating aluminum disc is difficult to calculate since the equation involved does not produce a closed solution. The numerical, analytical, semi-analytical techniques that are already developed to find these magnetic fields have no proper mathematical formulation when the disc is disturbed from its coaxial position. The stabilization of disc is going to be effected when the disc moves away from its coaxial position due to a change in inductance between the disc and coils, due to change in magnetic flux linkage, etc. In this paper, a 2D FEM model is developed to determine the magnetic fields on a floatingaluminum disc when it is moved away from its coaxial position. The 3D FEM model developed is simulated in both COMSOL-Multiphysics and ANSYS-Electronics. The results obtained by simulation are compared, for accuracy, with the numerical solution developed earlier using Finite Difference method (FDM) and also discussed.

Numerical Simulation of Electromagnetic Field in Round Bloom Continuous Casting with Final Electromagnetic Stirring

A 3D mathematical model was developed to simulate the electromagnetic field in Φ600 mm round bloom continuous casting with final electromagnetic stirring (F-EMS), and the model was verified using measured data for the magnetic flux density in the stirrer centre. The distribution of electromagnetic force and the influence of current intensity and frequency were investigated. The results show that the Joule heat generated by F-EMS is very small and its influence on secondary cooling heat transfer in the stirring zone can be ignored. With an increase in current frequency, the electromagnetic force density at R/2 and R/3 of the Φ600 mm round bloom first increases and then decreases, reaching a maximum at 10 Hz.

A Fast Electromagnetic Field and Radio Frequency Circuit Co-Simulation Approach for Strongly Coupled Coil Array in Magnetic Resonance Imaging

Electromagnetic (EM) coupling between radio frequency (RF) coils is a common cause of coil performance degradation and must be sufficiently reduced in the design of RF coils. The EM field simulation is a primary tool in analyzing the coupling condition and optimizing the decoupling method. A theoretical analysis of co-simulation under the conditions of strongly coupled RF coils is proposed in this paper. The proposed co-simulation method is evaluated through the comparison with the conventional simulation methods in terms of the efficiency and of the EM fields and specific absorption rate (SAR) of a two-channel strongly coupled coil array. The results demonstrate that the proposed co-simulation method saves approximately 94.5% of the total simulation time for strongly coupled coil arrays while the EM field and SAR variation is less than 4%. As a method demonstration, the proposed co-simulation method was used to analyze the capacitance decoupling of adjacent coils with the scattering matrix and saves about 95.78% of the total simulation time for the optimization of decoupling capacitors.