Magnetostatic Field Analysis Research Articles

An alternative method for field analysis in inhomogeneous domains

PurposeThis paper aims to solve inhomogeneous dielectric problems by matching boundary conditions at the interfaces among homogeneous subdomains. The capabilities of Hilbert transform computations are deeply investigated in the case of limited numbers of samples, and a refined model is presented by means of investigating accuracies in a case study with three subdomains.Design/methodology/approachThe accuracies, refined by Richardson extrapolation to zero error, are compared to finite element (FEM) and finite difference methods. The boundary matching procedures can be easily applied to the results of a previous Schwarz–Christoffel (SC) conformal mapping stage in SC + BC procedures, to cope with field singularities or with open boundary problems.FindingsThe proposed field computations are of general interest both for electrostatic and magnetostatic field analysis and optimization. They can be useful as comparison tools for FEM results or when severe field singularities can impair the accuracies of other methods.Research limitations/implicationsThis static field methodology, of course, can be used to analyse transverse electro magnetic (TEM) or quasi-TEM propagation modes. It is possible that, in some case, these may make a contribution to the analysis of axis symmetrical problems.Originality/valueThe most relevant result is the possible introduction of SC + BC computations as a standard tool for solving inhomogeneous dielectric field problems.

Observation of angle-dependent mode conversion and mode hopping in 2D annular antidot lattice

We report spin-wave excitations in annular antidot lattice fabricated from 15 nm-thin Ni80Fe20 film. The nanodots of 170 nm diameters are embedded in the 350 nm (diameter) antidot lattice to form the annular antidot lattice, which is arranged in a square lattice with edge-to-edge separation of 120 nm. A strong anisotropy in the spin-wave modes are observed with the change in orientation angle (ϕ) of the in-plane bias magnetic field by using Time-resolved Magneto-optic Kerr microscope. A flattened four-fold rotational symmetry, mode hopping and mode conversion leading to mode quenching for three prominent spin-wave modes are observed in this lattice with the variation of the bias field orientation. Micromagnetic simulations enable us to successfully reproduce the measured evolution of frequencies with the orientation of bias magnetic field, as well as to identify the spatial profiles of the modes. The magnetostatic field analysis, suggest the existence of magnetostatic coupling between the dot and antidot in annular antidot sample. Further local excitations of some selective spin-wave modes using numerical simulations showed the anisotropic spin-wave propagation through the lattice.

Design Strategy of Magnetizer for Post-Assembly Magnetization of Spoke-Type Ferrite Magnet Motor

Permanent magnets should receive external magnetic field energy for magnetization. It is a magnetizer that enables magnetization. The performance of magnets is determined by magnetization, and reaching 100% magnetization is very difficult. In this paper, a 3-times magnetizer was used for magnetization of a spoke-type ferrite magnet motor. The size of the permanent magnets and magnetizer winding must be designed appropriately to reach a high magnetization ratio. These parameters are determined using transient analysis, but this technique requires a significant amount of time. Magneto-static field analysis was used in this study with the goal of solving this problem. By using this method, the analysis time was reduced and a strategy for deriving a final model was proposed. The final model was designed using the proposed strategy and the model was manufactured. Finally, the performance of the 3-times magnetizer was confirmed by measuring the magnetization ratio of the magnets, and the proposed design strategy was verified through testing.

Physical insights about magnetic flux distribution and its effect on surface roughness in MR fluid based finishing process

A novel magnetorheological (MR) fluid based experimental system was designed to finish Ti–6Al–4V cylindrical rods. Here, the finishing action is achieved by rotating the rod to be finished which is in contact with MR fluid (mixed with silicon carbide loose abrasives) while applying a magnetic field across the finishing zone. Magneto-static field analysis was carried out using finite element method to design the magnetic circuit and predict the flux density around the finishing area. Practical results showed that the magnetic flux density of 0.2 T with a workpiece rotation of 3000 rpm provided the maximum change in average surface roughness. This paper focuses on studying the influence of magnetic flux distribution on the uniformity of the surface roughness along the axial length of the finished rods. The experiments revealed that the surface roughness significantly varied throughout the finishing rod length. The maximum change in surface roughness was seen at the lower part of the finished rod and progressively reduced towards the top of the rod. The magnetic flux distribution controls the mechanism of material removal and reveals its role to achieve close final surface roughness tolerance. With this understanding, a strategy is proposed to reduce the non-uniformity of surface roughness along the entire length of the cylindrical rod.

MAGNETOSTATIC FIELD ANALYSIS OF DC COMMUTATOR MOTORS WITH GEAR-TEETH ON THE ROTOR

This paper presents the open-circuit magnetostatic field analysis of a DC commutator motor by applying 1-D and 2-D equivalent magnetic circuit methods. For the 1-D and 2-D equivalent magnetic circuit method, the average air-gap flux density of a DC commutator motor and magnetic flux in every node are derived respectively, and the validity is verified by the finite-element analysis. The Carter’s coefficient is applied to model the permeance of the slot and gear-teeth space. The differences of the air-gap flux density are 3.21% and 3.06% for 1-D and 2-D methods, respectively. The flux linkages, back-EMF constants, cogging torques, electromagnetic torques, and torque ripples of the two gear profiles with feasible number of teeth integrated on the rotor are analyzed to verify the effects of gear profiles. The result shows that the gear-teeth integrated on the motor act as dummy slots, which reduce the cogging torque and torque ripple by 92.02% and 50.14 %, respectively.

境界積分方程式を用いた静磁界解析における多重連結処理手法に関する一考察

境界積分方程式を用いた静磁界解析における多重連結処理手法に関する一考察

Finite-Element Analysis of the Magnetostatic Field of a Coaxial Magnetic Gear Device

This paper presents the magnetostatic field analysis of a coaxial magnetic gear device proposed by Atallah and Howe. The structural configuration and speed reduction ratio of this magnetic gear device are introduced. The 2-dimensional finite-element analysis (2-D FEA), conducted by applying commercial FEA software Ansoft/Maxwell, is performed to evaluate the magnetostatic field distribution, especially for the magnetic flux densities within the outer air-gap. Once the number of steel pole-pieces equals the sum of the pole-pair numbers of the high-speed rotor and the low-speed rotor, the coaxial magnetic gear device possesses higher magnetic flux densities, thereby generating greater transmitted torque.

Characteristic analysis and design of a novel lorentz force driving actuator for a molded case circuit breaker

Recently, the demand for a remote controllable actuator for a circuit breaker (CB) has increased because of the trend towards the automation and information technology (IT) of the power system. However, the conventional molded case CB (MCCB) - of which demand is high among CBs - is not only manually controlled, but also liable to breakdown and difficult to find broken components because of the use of the mechanical spring type actuator. To address these problems, a novel Lorentz force driving actuator (LA) is proposed in this research. The LA is suitable for both low- and high-power CBs because of its high power density and the unaffectedness of performance by the stroke. The MCCB equipped with the LA is the first remote controllable low-power CB and low in maintenance cost. The correct and rapid analysis and design method using a two-dimensional magneto-static field analysis and a dynamic analysis is proposed for the small size actuator as LA in this research.

Finite-Element Analysis of Electrical Machines for Sensorless Drives With High-Frequency Signal Injection

A challenge during the design process of an electrical machine is the characterization of the various parameters in a computational time as short as possible. Frequently it is required the computation of the electrical machine parameters that are necessary for the tuning of the drive control algorithm. This paper deals with a strategy to compute the high-frequency signal injection response of a sensorless controlled electrical machine. It allows to determine the self-sensing capability of the machine directly during the design process. Such capability can be defined in any given operating point, for example, along the maximum-torque-per-amps trajectory. Then, also the high-frequency machine parameters can be computed. In addition, the strategy proposed here requires a very short computational time to get such data. After a magnetostatic field analysis, carried out so as to get the torque for a given current, the flux density distribution is stored, and the differential reluctivity tensor is evaluated in each element of the mesh. Then, a time-harmonic analysis is carried out in a linearized structure so as to compute the d - q parameters at the injection frequency. In order to validate the proposed procedure, experimental results on different machine type are included in this paper. This allows to prove the reliability of the procedure as a valued tool for the characterization of the machine.

Increasing flux density by HTS shielding pellet in superconducting synchronous machine based on flux concentration

In this paper, we propose a solution which enhances the performance of the inductor in high-power superconducting synchronous machines based on the flux concentration while keeping the same topology and using a high temperature superconducting shielding pellet located between the two coils of the inductor. This pellet permits to recover the magnetic field which vanishes in the medium region due to the opposite direction of the coils. A method for 3D magnetostatic field analysis using the control volume method with unstructured grid is proposed. With this topology, we have obtained a maximum efficiency of about 8 % in the flux density.

Conditions of Exciting Coils Used in Evaluation of Shielding Factor of Magnetically Shielded Rooms for Uniform Magnetic Field

To shield the environmental magnetic noises, magnetically shielded rooms (MSRs) are used for biomagnetic measurements, etc. The sources of environmental noises are far away from the MSR, in such a way that almost uniform magnetic field is applied to the MSR. To evaluate the shielding factor SF <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</i> for the uniform magnetic field in a construction site, the magnetic noises are applied by coils. However, SFs depend on the size and position of the coils, so a standardization of the method for accurately evaluating SF <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</i> using coils is being discussed in the Japan Electronics and Information Technology Industries Association (JEITA). In JEITA, we have already proposed and verified the method of estimating SF <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</i> 's by smaller coils placed near MSRs in the low frequency region without eddy current effect. In this paper, the suitable size and position of coils, such that the errors of the SF <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</i> 's estimated and directly evaluated are within 10%, on various shapes of MSRs are obtained using 3-D linear magnetostatic field analysis. Moreover, to correct SFs when the magnetic noises are applied to MSRs through a reinforced concrete wall, etc., the effect of wall on the applied magnetic field is also obtained from the experiment. Finally, the suitable coil conditions and the correction method are verified by the experiment using an actual double-layered MSR.

Shape Design of the Surface Mounted Permanent Magnet in a Synchronous Machine

This paper deals with how to obtain the optimal shape of a permanent magnet of surface mounted permanent magnet brushless synchronous machine using the level set based topology optimization method. Two types of the flux linkage calculation method are formulated; one is a modified method based on traditional flux linkage calculation through transient analysis and the other is the mono-tooth method newly introduced in this study. The mono-tooth method makes it possible to avoid time-consuming transient analysis because it requires only magnetostatic field analysis and may deal with infinite design points. The level set based topology optimization method is combined with both types of flux linkage calculation method. The optimization problem for shape design of a surface mounted permanent magnet synchronous machine is defined focused on the permanent magnet shape design and optimization results by two different approaches are compared. The performance of the optimal model is also compared with that of a conventional magnet shape model.

Magnetostatic Field Analysis and Diagnosis of Mixed Eccentricity Fault in Switched Reluctance Motor

In this article, a novel view of airgap magnetic field analysis of a switched reluctance motor under mixed eccentricity to provide a precise fault diagnosis based on the three-dimensional finite element method is presented. The analytical nature of this method makes it possible to simulate a reliable and precise model by considering the end effects and axial fringing effects. The results of the three-dimensional finite element analysis of a 6/4 switched reluctance motor, such as flux linkages, terminal inductance per phase, and static torque for various eccentric motor conditions, are obtained, evaluated, and discussed. The diagnostic evaluation is based on monitoring these parameter variations and analyzing the shape of the self-inductance in the stator windings via the multiple signal classification pseudo-spectrum. Fault analysis and detection in a switched reluctance motor demonstrate that the presented scheme can assure the detection reliability and sensitivity of an eccentricity fault in a switched reluctance motor. To the best knowledge of the authors, such an analysis has not been carried out previously.

The Suction Characteristics Simulation of Electromagnet Based on Maxwell

This paper makes the analysis to magnetostatic field and transient of electromagnet by using Maxwell. The magnetic-flux density of electromagnet and the distribution map of magnetic induction intensity are obtained and it has been verified that the electromagnet can meet the first pilot valve's open and close completely under the essential security power equipment's condition by the magnetostatic field analysis. Dynamic characteristic of the electromagnet is obtained under the constant load, and has further confirmed the reliability of electromagnet by the transient analysis.

Optimization of Magnetization Directions in a 3-D Magnetic Structure

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study introduces a design method for determining the optimized magnetization directions in 3-D magnetic systems. Based on a modified topology optimization method, discrete magnetizations are investigated in six directions <formula formulatype="inline"><tex Notation="TeX">$(\pm{x},\pm{y},\pm{z})$</tex></formula>. The finite-element method is used for the 3-D magnetostatic field analysis. The proposed method is applied to the design of a magnet pattern having “one-sided flux” and the design results show that the optimized magnet pattern appears as one or two Halbach arrays according to the shape of the design domain. The optimization process is accomplished by using sequential linear programming and the adjoint variable method. </para>

Proposal for a benchmark model of a laminated iron core and a large‐scale and highly accurate magnetic analysis

AbstractThis paper describes a benchmark model proposed for the clarification of the characteristic of various methods for modeling the laminated iron core. In order to obtain a reference solution of the benchmark model, a large‐scale nonlinear magnetostatic field analysis with a mesh fine enough to represent the microscopic structure of the laminated iron core is carried out by using the hybrid finite element–boundary element (FE‐BE) method combined with the fast multipole method (FMM) based on diagonal forms for translation operators. The computational costs and accuracy of two kinds of homogenization methods are discussed, comparing them with the reference solution. As a consequence, it is verified that the homogenization methods can analyze magnetic fields in laminated iron core within acceptable computational costs. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(1): 26–35, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20809

New multigrid method including elimination algorithm based on high‐order vector finite elements in three‐dimensional magnetostatic field analysis

AbstractA new multigrid method based on high‐order vector finite elements is proposed in this paper. Low‐level discretizations in this method are obtained by using low‐order vector finite elements for the same mesh. The Gauss–Seidel method is used as a smoother, and a linear equation of lowest level is solved by the ICCG method. But it is often found that multigrid solutions do not converge into ICCG solutions. An elimination algorithm of constant term using a null space of the coefficient matrix is also described. In three‐dimensional magnetostatic field analysis, convergence time and number of iteration of this multigrid method are discussed with the conventional ICCG method. © 2009 Wiley Periodicals, Inc. Electron Comm Jpn, 92(1): 39–45, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecj.10228

Large-Scale Magnetic Field Analysis of Laminated Core by Using the Hybrid Finite Element and Boundary Element Method Combined with the Fast Multipole Method

This paper shows a large-scale and highly accurate nonlinear magnetostatic field analysis of laminated iron core by using the hybrid finite element and boundary element (FE-BE) method. The hybrid FE-BE method is fairly effective to directly deal with the microstructure because no mesh division is required for the free space. In order to obtain the drastic reduction of the computational costs and stabilize the convergence characteristic of the Newton-Raphson method, the fast multipole method and the line search are introduced. Some numerical results that verify the effectiveness of the developed method are also presented

Large-Scale and Fast Nonlinear Magnetostatic Field Analysis by the Magnetic Moment Method With the Adaptive Cross Approximation

This paper describes large-scale and fast nonlinear magnetostatic field analyses by the magnetic moment method (MMM) with the adaptive cross approximation. In order to stabilize the convergence characteristic of the Newton-Raphson method, we apply a line search technique to the MMM. Some numerical results that demonstrate the validity of the developed method are also presented

積層鉄芯ベンチマークモデルの提案とその高精度磁界解析

This paper describes a benchmark model proposed for the clarification of the characteristic of various methods for modeling the laminated iron core. In order to obtain a reference solution of the benchmark model, a large-scale nonlinear magnetostatic field analysis with a fine mesh enough to represent the microscopic structure of the laminated iron core is carried out by using the hybrid finite element-boundary element (FE-BE) method combined with the fast multipole method (FMM) based on diagonal forms for translation operators. The computational costs and accuracy of two kinds of the homogenization methods are discussed comparing the reference solution. As a consequence, it is verified that the homogenization methods can analyze magnetic fields in laminated iron core within acceptable computational costs.