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渦電流による電磁制動力を測定している．金属板に磁極を近づけるあるいは金属板から遠ざけた時，両者には力が作用する．磁石の移動速度と力の関係を調べるためにミシンを改造した実験器を試作している．測定した結果，磁石の移動速度に対して発生する力が比例することを明らかにしている．誘導される電流が磁石の移動速度に密接に関係していることを再確認している．The measuring instrument of the electromagnetic braking force by eddy current is produced experimentally. The force occurs both when a magnetic pole is close to a metal plate and when, it was kept away. Experiment vessel which remodeled the sewing machine in order to examine the relationship between magnetic mobile speed and force, is produced experimentally. The experimental results show that there is the force which arises is proportional to the speed of the mobile magnet. They also confirmed that the induced current is closely related to the speed of the mobile magnetic pole.

The time-periodic FEM (TP-FEM) that can directly derive a steady state solution in the time domain has been proposed. A linear equation obtained by TP-FEM is composed of linear equations derived from all time steps so that the convergence characteristic of nonlinear analysis by the Newton-Raphson (NR) method tends to deteriorates. To improve convergence characteristic of nonlinear analysis based on NR method, effective line-search is proposed in which the step size is evaluated by higher order approximation of the derivative of functional with respect to step size. In this paper, the performance of the proposed line-search on TP-FEM. To achieve further speed-up, subspace correction method that can accelerate convergence of linear solver is also demonstrated.

現在，わが国における消費エネルギーのうち，50 %以上が電気エネルギーを占めており，その内の50 %はモータや変圧器を駆動するために消費されている．これらの電気機器の損失には，鉄芯中の鉄損と巻線内部のJoule 損に起因する銅損がある．これら損失の低減と電気機器利用効率の改善は，温室効果ガスの排出量の削減，環境汚染や地球温暖化の防止に寄与する．こうした目的のための電気機器の高効率化に伴い，それぞれの素子の小型化が図られている．そのために，近年電気機器の駆動周波数が高くなる傾向にある．高周波化が進むと，体積は小さくなるものの，界磁巻線における銅損が顕著となる．銅損には電源からの電流による表皮効果と，素線に印加される近接効果から発生する渦電流損がある．例えば，近接効果損失低減のためには，銅線を薄い磁性体で被覆した磁性被覆線が有効である．磁性被覆線においては，外部磁束は磁性体に集中し，銅線と鎖交する磁束が低減するため，近接効果を抑制することが可能である．別の方策として，占積率を向上するために，素線の平角線化が注目されている．平角線を用いると，表皮効果を抑制でき，占積率が90 %程度にまで改善できる．一方で，鉄損の低減のために，現在圧粉磁芯を用いた磁性体コアを用いることが検討されている．この磁性体コアは，フェライト等とは異なり，透磁率がやや低いものの，磁気飽和と渦電流損を抑制できる．また，磁性粉体は3 次元形状を生成しやすく，製造に向いているという利点も有している．上記のような電気機器の構造を変化させることによる銅損，鉄損の損失の低減に加えて，外部漏洩磁界の低減も重要になる．そのためには，電気機器の一部を電磁シールドで覆うことが必要になる．現在は，数μm の厚さの電磁シールドが用いられている．これらを考慮した電気機器の設計には，多数のパラメータがあり，実験ベースでは試作・製造コストが膨大である．そこで，電磁界有限要素解析により電気機器の最適化を行うことが重要となる．しかし，磁性被覆線や電磁シールドを含む系はいずれも微細な構造を有しており，直接的な有限要素解析が難しい．本博士論文においては，これらの渦電流特性を考慮した解析を行うための均質化有限要素法，インピーダンス境界条件の導入を行い，電気機器の損失を精度よく評価するための方法を提案する．, (主査) 教授 五十嵐 一, 教授 小笠原 悟司, 教授 北 裕幸, 准教授 野口 聡, 情報科学研究科（システム情報科学専攻）

本研究では，金属管の中空および金属板における誘導起電力を測定している．金属管の中空および金属板の表面を磁石が通過する．試料と通過する磁石の位置，およびその位置と誘導起電力の関係を調べる．既存のミシンを分解・改造した自作器で測定を行っている．種々の試料を用いて実験・測定を行い，良好な結果を得ている．, In this study, induced electromotive force in the metal wall of a hollow metal pipe is measured. The magnet passes through the hollow metal pipe. The relationship between position of the magnet that passes through the sample and the position and induced electromotive force is examined. The measurement is carried out by the self-making vessel that decomposed and remodeled existing sewing machine. Experiment and measurement are carried out using various samples with good results.

Eddy current testing (ECT) is one of the most representative nondestructive testing methods for metallic materials, parts, structures and so on. Operating principle of ECT is based on two major properties of the magnetic field. One is that alternating magnetic field induces eddy current in conducting materials. Thereby, an input impedance of the magnetic field source, i.e., electric source, depends on the eddy current path. Second is that the magnetic field distribution depends not only on the exciting but also on the reactive magnetic fields caused by the eddy currents in targets. Former and latter are the impedance sensing and magnetic flux sensing types, respectively.This paper concerns with an optimization of a new magnetic flux sensing type sensor named “∞ coil”. Exciting and sensing coils are composed of ∞ shape coil and a finite length solenoid coil wound on ferrite bar, respectively. Development of this ∞ coil fully depends on the 2D and 3D finite elements method modeling. According to the simulation results, we have worked out two types of ∞ coils. Practical experiments reflect the validity of both simulation and design aims, quite well. Thus, we have succeeded in developing ∞ coil having a higher sensibility compared with that of conventional one.

Cam-shafts used for internal-combustion engines need to be chilled at the foundry stage to increase the cam hardness, however, unexpected chilled structures may occur on the sensor plate surface. Chilled structures on the sensor plate may break a grinding tool during the grinding process and may also hinder the fabrication of a specified shape due to resistance arising from the hyper-hardness of the chilled structure. For this reason, developing an inspection technique and a device for detecting unnecessary chilled structures before the grinding process of cam-shafts is needed to determine the rejection and removal of a sample with chilled structures. This paper reports on a recently developed non-destructive method employing the Eddy Current method to detect chilled structures on a cam-shaft sensor plate accurately.

Eddy current testing (ECT) is one of the most representative nondestructive testing methods for metallic materials, parts, structures and so on. Operating principle of ECT is based on the two major properties of magnetic field. One is that alternating magnetic field induces eddy current in all of the conducting materials. Thereby, an input impedance of the magnetic field source, i.e., electric source, depends on the eddy current path. Second is that the magnetic field distribution depends only on the exciting but also the reactive magnetic fields caused by the eddy currents in targets. Former and latter are the impedance sensing and magnetic flux sensing types, respectively. This paper concerns with an optimization of a new magnetic flux sensing type sensor named "∞ coil" whose exciting and sensing coils are composed of the ∞ shape and finite length solenoid coil wound ferrite bar, respectively. Optimization of this ∞ coil fully depends on the 3D finite elements methods. According to the 3D finite element simulation results, we have successfully carried out the optimum size of two exciting coils and a sensing coil.

An eddy current sensors have various uses, for example metal detection and determination, nondestructive inspection, and position detection. However, there are few studies which show the influence of a conductor on the impedance of a detector coil using a theoretical formula. This paper shows the simplified calculation method on impedance of a planar coil that can be found from an equivalent circuit by considering that a conductor plate is one turn of coil which form changes according to displacement. The impedance corresponding to the overlap length of a conductor plate was calculated about the planar rectangular coil and the planar triangular coil. The calculated value was compared with the measured value and the calculated value of finite element method. The calculated value of impedance of rectangular coil and triangular coil agreed with the measured value within an error of ± 5.98%. Mutual inductance between the planar coil and conductor plate was calculated from the area ratio of planar coil and overlap., Article, 日本AEM学会誌. 21(2):234-239 (2013)

On designing and developing products, the finite element analysis of three dimensional eddy current-thermal problems is very useful. This paper shows effectiveness of a large scale eddy current-thermal analysis for a transformer tank using the domain decomposition method.

Induction electric field by center solenoid coil plays a roll to produce initial plasma. According to Townsend avalanche theory, minimum electric field for plasma breakdown depends on neutral gas pressure and connection length. On QUEST spherical tokamak, a connection length is evaluated as 966m on null point neighborhood with coil current ratio IPF26/ICS=0.1, and induction electric field considering eddy current of vacuum vessel is evaluated as about 0.1V/m on null point neighborhood. With Townsend avalanche theory, there values manage to produce initial plasma on QUEST.

第58回宇宙科学技術連合講演会（2014年11月12日-14日. 長崎ブリックホール), 長崎市, 長崎県, The infrared space telescope SPICA (Space Infrared Telescope for Cosmology and Astrophysics) is a next-generation astronomical mission in JAXA, which has a 3m-class and 6K cryogenically-cooled space telescope. The connecting part between the mission module and the bus module has low thermal conductivity to reduce heat penetration to the telescope module and low vibration transmissibility to reduce the micro-vibration transferred to the telescope module. As the stiffness of the connecting part is quite low, some kind of damping mechanism are demanded to suppress natural frequency of the connecting part, but dampers utilizes viscoelastic material or oil are not applicable as the operating temperature of the connecting part is supposed to be around 30 K. In this paper, we studied applicability of eddy current damper for the connecting part of SPICA., 資料番号: AC1500025000, レポート番号: JSASS-2014-4143

本論文では電子機器近傍の電磁界分布を可視化する一方法を提案する。まず最初に、局所的に測定された磁界から磁界源分布を逆問題的手法で推定する。次に、推定された磁界源から電子機器近傍の磁界分布を計算し可視化する。最後に3次元ウェーブレット変換を用いて主要な磁界分布を抽出する。, This paper proposes a methodology for visualizing the electromagnetic field distributions vicinity of the electronic devices. At first, we solve an inverse source problem in order to identify the magnetic field sources from the locally measured magnetic fields. Second, we calculate the magnetic field distributions from the estimated magnetic field sources. Third, we calculate the eddy current induced on a sheet of iron. Finally, we extract the most dominant magnetic field distributions using the 3D wavelet transform.In the present paper, basic principle and initial experiments to verify our approach are described. As a result, it is revealed that the magnetic field distributions near the electronic devices can be visualized from the locally measured magnetic fields. Further, we have succeeded in extracting the major magnetic field vectors as well as their sources by the multi-dimensional wavelet transform.

To visualize the electromagnetic fields, we have previously proposed a semi-analytical method, which has made it possible to simulate the complex electromagnetic field distributions not obtain by the conventional numerical schemes, such as finite elements and boundary elements means. Distinguished superior point of our semi-analytical method is that our semi-analytical method is only one way solving for the electromagnetic field, conducting and displacement currents simultaneously.In this paper, we propose a new semi-analytical approach to visualize the eddy current distribution in a two-dimensional plate, Successful result of this computation promises that eddy current testing may be carried out taking into account the displacement current, i.e., capacitive, effects.

application/pdf, Braking effect by electromagnetic induction is one of physical phenomena of magnetic field. Due to easiness of observation this phenomenon is used to exemplification experiments in physics education. Authors measured time and falling velocity of a neodymium magnet in an aluminum pipe, and modeling of the motion and simple formulation by the approximation in the falling were examined. In an aluminum pipe, time for the falling of the magnet was longer than in an ordinary environment. In addition, falling velocity in the pipe was almost fixed, and time for the falling was almost proportional to the square of the central magnetic flux density of the magnets.

In the preceding related paper, the authors discussed a plate-type magnetic damper with alternative magnetic poles. The paper presented the analytical expressions of eddy currents in the conductor and the damping coefficients for the single row of alternative poles. The damping effects of the damper having alternative poles of a number of rows and columns are different from those of the previous model. The present article discusses the damping increasing mechanisms for the plate-type damper with alternative magnetic poles of a number of rows and columns. The analytical expression for finding the eddy current patterns and the damping coefficient are obtained. Numerical calculations are carried out for some important examples. Since the present article gives the analytical expression and the numerical data of dimensionless damping coefficients, the results may be used directly in the practical design of such devices as vibration absorbers.

A magnetic damper in which opposite poles are arranged by turns has great deal of damping effects as compared with a normal magnetic damper. However the reason of it has not been clarified, and the analysis has not been reported. To clarify the mechanisms of increasing dampings for the damper, this paper presents an analytical results for the eddy current, and the damping coefficient. Numerical calculations are carried out for some important examples, and the results are compared with those of the normal magnetic damper.

In the preceding related paper (Part 1), the authors presented expressions for finding the eddy current, braking force and damping coefficient on the rotary magnetic damper, consisting of one sector magnet and a circular conductor, and investigated the validity of the constant flux assumption for the magnet. This paper extends the analysis of the authors' previous report to the problem of the rotary magnetic damper, consisting of several sector magnets and a circular conductor with a circular cavity. Numerical calculations have been carried out for the dimensionless damping coefficients with variations of factors, such as the flux range, the radius of the circular cavity of a circular conductor, the position and the number of the magnets. The characteristics of the rotary magnetic damper have been investigated in detail ; especially the optimal values of the damping coefficient have been clarified.

This paper is concerned with a method for analyzing a rotary magnetic damper (eddy current brake) consisting of a sector magnet (sector magnetic flux) and a circular conductor. Since the magnetic flux density is a function of the position in the radial direction, the analytical solution for obtaining the eddy current, braking force and damping coefficient is arrived at by dividing the magnetic flux into the narrow sector bonds, and applying the unit step function to solve the differential equation of the electromagnetic fields. Numerical calculations have been carried out for the dimensionless damping coefficients versus the flux range, the position and the distribution of the magnetic flux in the radial direction. Experimental tests are also carried out to verify the present theoretical results. The theoretical results are in good agreement with the experimental ones, and the characteristics of the rotary magnetic damper have been investigated in detail, with the optimal values of the damping coefficient having been clarified.