永磁卸载超导磁力轴承提供稳定的立轴旋转结构的实验研究

高温超导块材钇钡铜氧（ＹＢＣＯ）可用于超导磁力轴承。设计并制作了永磁轴承卸载、超导磁力轴承提供稳定的一个立轴旋转结构的模型。超导磁力轴承安装在转子的底部,提供轴向稳定力和径向恢复力。永磁轴承安装在转子的顶部,提供一个正刚度小于１Ｎ／ｍｍ的悬浮力。根据７个ＹＢＣＯ块材,设计了四种永磁结构。最小的径向刚度大于 ３Ｎ／ｍｍ。     

Merging formation and current amplification of field‐reversed configuration

The merging formation of the field‐reversed configuration (FRC) has been developed in the TS‐3 merging experiment, leading us to a new scenario of FRC slow formation, heating and current amplification. Two force‐free spheromaks with opposing toroidal fields were merged together in the axial direction to form a high‐β FRC with higher efficiency than the conventional field‐reversed theta‐pinch method. This unique relaxation from the force‐free (β ∼ 0.05 − 0.1) spheromaks to the high‐β (β ∼ 0.7 − 1) FRC is attributed to the conversion of toroidal magnetic energy into ion thermal energy through the reconnection outflow. A central ohmic heating (OH) coil worked successfully to amplify the FRC plasma current by a factor of 2. Toroidal mode analysis of magnetic structure indicated that the tilting stability of the oblate FRC was provided by an ion kinetic effect. This oblate FRC is also useful as an initial equilibrium to produce a high‐β_p spherical tokamak (ST) with diamagnetic toroidal magnetic field, suggesting the close relationship between FRCs and high‐β_p STs in the second stable region of the ballooning mode. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Suspension of soft magnetic materials using high Tc superconductors

This paper describes a novel suspension technique using high T_c superconductors and magnetic materials. It was found for a field-cooled superconductor and an adjacent magnetic material that the usual inverse relationship between the attractive magnetic force and gap distance reverts to a direct relationship for small gap length. Thus, stable, noncontact suspension is possible within a certain gap range. This phenomenon was found for even a soft magnetic material possessing minimal coercive force. Since remarkable reversals were observed for magnetic materials with diameters much smaller than that of the pinned area, it is considered that some of the pinned flux is subject to a gathering effect in the magnetic material. Stable, contactless suspension of a 180 g carbon steel weight under a high T_c superconductor was achieved using this technique.     

Eddy currents in a metallic disk and axial force on it due to suddenly applied magnetic field

Contents A method of calculation of the eddy currents and the axial force after applying a magnetic impulse to a metallic disk is presented. The distribution of the eddy currents in a disk as well as the axial force on that are examined. The results can be applied to the analysis of the forming process by magnetic impulses.

---

Wirbelströme in einer metallischen Kreisscheibe und die Kraftwirkung nach dem plötzlichen Einschalten eines magnetischen Feldes

Übersicht Es wird eine Methode zur Berechnung der Wirbelströme in einer metallischen Kreisscheibe nach dem Einschalten eines magnetischen Impulses angegeben. Weiterhin wird die Axialkraft auf die Scheibe bestimmt. Die Resultate können in der Analyse von Formungsprozessen mittels magnetischer Impulse angewendet werden.

---

List of Symbols a radius of disk - B magnetic flux density - e _z coordinate unit-vector - F force - g thickness of disk - H magnetic intensity - J current density - t time - conductivity - (t) Dirac delta function - ₀ permeability of vacuum - (l) unit step function     

Giant magnetoresistance and magnetic anisotropy of Co9Fe/Cu/Co9Fe multilayer thin films on an MgO(110) substrate

Magnetoresistive effects have been investigated using Co₉Fe/Cu/Co₉Fe that were deposited on an MgO(110) substrate by ion beam sputtering with a 21-A-thick CU layer and with various thicknesses of the Co₉Fe films. The influence of a 50-A-thick Fe buffer layer has also been investigated. In addition to a cubic symmetry anisotropy (K₁), an in-plane uniaxial magnetic anisotropy (K_u) was induced, which easy axis is parallel to the (110) plane of the MgO substrate and the (001) plane with and without the 50-A-thick Fe buffer layer, respectively. The magnetoresistance (MR) ratio decreased monotonically with increasing thickness of the Co₉Fe films from 25 A to 70 A. A maximum MR ratio of 11.5 percent was obtained at room temperature. With increasing magnetic field, the MR ratio reached a plateau gradually after a steep drop at small magnetic fields without the Fe buffer layer. It reached a plateau rapidly at small magnetic fields with the Fe buffer layer. By considering both K_u and K₁, these behaviors can be accounted for by the magnetization processes involved.     

Measurement of dynamic magnetic loss parameter in ferrites

The measurement of the iron loss in ferrites is important for developing high‐efficiency switching power supplies. The authors have proposed the dynamic magnetic loss parameter, λ_f, for evaluating the iron loss in ferrites. In previous studies, the parameter was assumed to be a constant value for an individual ferrite material and defined for one period of a small B–H loop. In this paper, assuming that λ_f is a function of the time derivative of the magnetic flux density, dB/dt, a novel measurement method of λ_f of a Ni‐Zn ferrite is proposed using rectangular wave voltage excitation and the Fourier expansion of the exciting current. In order to realize an iron loss measurement system with the rectangular wave voltage excitation, a high‐frequency FET inverter has been developed. The results of measuring λ_f show that it is uniquely determined by dB/dt regardless of the B–H loop size. The measured dB/dt characteristics of λ_f are applied to practical examples for switching power supplies and sinusoidal wave voltage excitations. Their experimental and computational results coincide and it is clarified that the measured dB/dt characteristics are effective and useful. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(1): 1–6, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20101     

Extension of Mathematical Models Taking Temperature Variation in Permanent Magnet Synchronous Motors into Consideration

We have developed novel mathematical models of d‐axis and q‐axis magnetic fluxes ?_d and ?_q for permanent magnet synchronous motors (PMSMs). The models can be used to approximate magnetic characteristics using simple fractional equations with i_d and i_q as variables. They include eight constants, and some of them represent the degree of magnetic saturation and cross‐coupling. However, the magnetic characteristics are varied with the temperature rise in PMSMs, which are dependent on the load torque and motor speed. In this paper, the characteristics of the eight constants that vary with the motor temperature and the residual flux density B_r are shown. Further, we propose to extend the mathematical models by considering the temperature and B_r variation.     

永磁式磁轴承的电磁力及刚度的工程化算法

在综述当前磁轴承刚度计算方法的基础上，提出了一种适合本研究对象的刚度的工程计算方法，即通过对磁轴承的磁路分割，求出极间气隙磁导，从而推出一种计算径向不平衡刚度和轴向恢复刚度的比较简便的工程化计算方法。     

Development of a high‐pressure air‐insulated 72/84‐kV disconnecting switch corresponding to bus‐transfer current switching

SF₆ gas has excellent dielectric strength and current interruption performance. For these reasons, it has been widely used for gas‐insulated switchgear (GIS). Today, such global environmental problems as global warming are important issues of concern. SF₆ gas is known as a greenhouse gas with a long atmospheric lifetime, and has global warming potential of 23,900. SF₆‐free 72‐kV GIS was recently developed by using high‐pressure air and a gas/solid hybrid structure. But an alternating current disconnecting switch (DS) has yet to be developed thus making this type of SF₆‐free 72‐kV GIS unsuitable for double bus‐bar application. Consequently, the development of a high‐pressure air‐insulated DS corresponding to bus‐transfer current switching has been expected. The bus‐transfer current is the highest among all current interruption requirements for the DS. To develop an alternating current DS, efforts must be made to reduce arcing damage to the electrode. This paper describes the fundamental characteristics of current interruption in the plain break type and the magnetic field driven type. Then, average arcing time of the magnetic field driven type was estimated by magnetic flux density. Finally, two types of DS, which were a high‐speed plain break and a low‐speed magnetic field driven, were confirmed to comply with bus‐transfer current switching requirements on JEC standard. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 48–55, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20595     

Prediction of pathological tumor volume in clinically localized prostate cancer: value of endorectal coil magnetic resonance imaging

The purpose of this study was to determine whether endorectal coil magnetic resonance imaging (MRI) enables accurate assessment of pathologic tumor volume in patients with clinically localized prostate carcinoma. Twenty-four patients with biopsy-proved prostate carcinoma underwent MRI at 0.5 T before radical prostatectomy. Tumor volumes were determined independently on axial fast-spin-echo (SE) T₂-weighted MR images and whole-mount pathology slides of the surgical specimens. At pathology, tumor volumes ranged from 0.17 to 9.42 cm³ (mean±SD, 3.11±2.99 cm³). A strong correlation (r=.944) was found between measurements of tumor volume based on MR images and pathological specimens. The error was less than 0.5 cm³ in 14 cases, in the range of 0.5–1 cm³ in 7 cases, and more than 1 cm³ in 3 cases. By using an MR tumor volume of 2 cm³ as cutoff value, extracapsular tumor spread could be predicted with a sensitivity of 81.2%, a specificity of 100%, and an accuracy of 87.5%. Tumor volume determinations based on MR images seem to be accurate enough to be helpful in clinical decision-making.     

Energy model based loss‐minimized speed control of induction motor with a full‐order observer

In this paper, a loss‐minimization algorithm is developed to achieve maximum efficiency in terms of slip frequency. The optimal value of slip frequency can be obtained by minimizing all controllable losses of the induction motor (IM). The ratio of magnetic energy converted to torque (W_T) to magnetic energy stored in the rotating field (W_q) is defined in terms of slip frequency to obtain an error function that is used to design a controller to achieve the desired speed. Since the energy model of the IM can be expressed by the multi‐input and multi‐output (MIMO) system, an MIMO optimal regulator is proposed to achieve the desired speed with maximum efficiency. To design an optimal regulator, it is necessary to measure all state quantities. But W_T and W_q cannot be measured directly. Therefore, a full‐order observer is proposed to estimate these state quantities. The gains of the observer system are calculated by using the pole placement technique. Consequently, the observer system becomes stable. The performance of the proposed controller and observer system are verified by using simulation. With regard to the simulation results, it can be concluded that the desired speed can be achieved by using the proposed controller and the unknown state quantities can be estimated properly by using the proposed observer system. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Complex permeability of polycrystalline Mn-Zn and Ni-Zn ferrites

The complex permeability of ferrites is frequency dependent. The real part of the complex permeability deteriorates in a high frequency range and the imaginary part has a peak after starting the deterioration. This paper examines the possibility that the frequency characteristics for some ferrites can be approximately derived from a first-order linear differential equation for the magnetic field intensity and magnetic flux density. The first-order differential equation is expressed by the reciprocal of the complex permeability and provides first-order magnetic and electric circuits for ferrite cores. In contrast with the commonly used series R_s-L_s, circuit for the cores, obtained from B = (μ′ − jμ′)H, the first-order electric circuit derived consists of an inductance (L) and resistance connected in parallel. In this paper, it is demonstrated that the inductance L remains constant, whereas Ls decrease with the increase in frequency. In other words, the real part of the reciprocal of the complex permeability remains constant for an increase in frequency. In addition, it is found that the imaginary part of the reciprocal of the complex permeability is approximately proportional to the frequency. © 1998 Scripta Technica, Electr Eng Jpn, 123(2): 1–7, 1998     

Development of anisotropic phantoms using wood and fiber materials for diffusion tensor imaging and diffusion kurtosis imaging

Objective

Several studies have demonstrated that anisotropic phantoms can be utilized for diffusion magnetic resonance imaging. The purpose of our study was to examine whether wood is suitable as an anisotropic phantom material from the viewpoints of affordability and availability. In the current study, wood was used for restricted diffusion, and fibers were used for hindered diffusion.

Materials and methods

Wood and fiber phantoms were made. Diffusion kurtosis images were acquired with three magnetic resonance scanners. Fractional anisotropy, radial diffusivity, axial diffusivity, radial kurtosis and axial kurtosis values were measured. The wood phantom was imaged, and its durability was confirmed. The phantoms were imaged in varying orientations within the magnetic field. The wood was observed using an optical microscope.

Results

Ten kinds of wood and the fiber had a diffusion metrics. The wood diffusion metrics suggested low variation over a period of 9 months. Changing the orientation of the phantoms within the magnetic field resulted in changes in diffusion metrics. Observation of wood vessels and fibers was conducted.

Discussion

Wood and fibers have anisotropy and are promising as phantom materials. The development of anisotropic phantoms that anyone can use is useful for diffusion magnetic resonance imaging research and clinical applications.

     

Fundamental performance of superconducting fault current limiter with two air core coils

In this paper, we theoretically compared the fundamental characteristics of fault current limiter (FCL) with high‐Tc superconductor (HTS) and two coaxial air‐core coils based on steady‐state analysis. Two types of FCL are possible. One is parallel type and the other is transformer type. The parallel type can be divided into two types according to the combination of the winding direction of coils. That is, there are two cases that the coils are wound so that the magnetic fluxes induced by coils reduce and increase each other. In this paper, we called them parallel type 1 and 2, respectively. There is no significant difference in the HTS volume required to satisfy both the specified limiting impedance Z_FCL and initial current I_ini in limiting operation among those three FCLs although the HTS in each type of FCL has different length and cross‐sectional area. In the cases of those FCLs, we can improve the current limiting performance by arranging the HTS in the coils and applying the magnetic flux to the HTS in the limiting operation. The magnitudes of the magnetic flux density are almost the same. From the viewpoint of the FCL impedance in normal operation, parallel type 1 has the most desirable structure. On the other hand, transformer type is the best to eliminate the magnetic flux applied to the HTS in the normal operation. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(3): 29–36, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20477     

Magnetic instability of ac multifilamentary superconductors in spatially distributed magnetic field

Alternating current (ac) superconducting machines such as superconducting generators, transformers, or resistive current limiters need large‐current‐capacity conductors. These conductors are generally fabricated as multistrand cables stacked with multifilamentary NbTi superconductors whose current capacity is a few tens of amperes. ac quench current degradation has often been observed in ac use of such multistrand cables. Several reasons for this degradation have been pointed out: nonuniformity of each strand current, mechanical disturbances, thermomagnetic instability, and ac losses. However, it has not as yet been overcome. Since the angle between the strand axis and the cable axis changes along the cable axis in multistrand cables, the strands are exposed to a spatially (axially) distributed magnetic field, which has longitudinal and transverse components changing periodically due to multiple cabling. This paper mainly discusses the thermomagnetic instability due to the distributed transverse magnetic field, which was compared with the self‐field instability and the longitudinal field instability experimentally and theoretically. It was confirmed that the ac quench current degradation due to the distributed transverse field could be induced by the following: nonlinear E–j characteristic, strong dependence of E–j characteristic on magnetic field in low field region, uniformity of the axial current profile inside the superconductor with the high resistive matrix, and the poor thermal diffusion of CuNi/NbTi composites. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 45–55, 2000     

Relaxivity of liposomal paramagnetic MRI contrast agents

Paramagnetic liposomes, spherical particles formed by a lipid bilayer, are able to accommodate a high payload of Gd-containing lipid and therefore can serve as a highly potent magnetic resonance imaging contrast agent. In this paper the relaxation properties of paramagnetic liposomes were studied as a function of composition, temperature and magnetic field strength. The pegylated liposomes with a diameter of approximately 100 nm were designed for favorable pharmacokinetic properties in vivo. The proton relaxivity, i.e. the T₁ relaxation rate per mmol of Gd(III) ions, of liposomes with unsaturated DOPC phospholipids was higher than those with saturated DSPC lipids. Addition of cholesterol was essential to obtain monodisperse liposomes and led to a further, although smaller, increase of the relaxivity. Nuclear magnetic relaxation dispersion measurements showed that the relaxivity was limited by water exchange. These results show that these paramagnetic liposomes are very effective contrast agents, making them excellent candidates for many applications in magnetic resonance imaging.     

First-principles density-functional calculations on HCr3O8: An exercise to better understand the ACr3O8(A = alkali metal) family

Accurate ab initio density-functional calculations are performed to understand structural stability, electronic structure, and magnetic properties of the ACr₃O₈(A = H, Li, Na, K, Rb, Cs) series. The ground-state structures for the compounds with A = Li−Rb take the same KCr₃O₈-type atomic arrangement (space group C2/m), whereas CsCr₃O₈adopts a modified atomic architecture (prototype; space group Pnma), in agreement with available experimental findings. The hypothetical compound HCr₃O₈is found to stabilize in an LiV₃O₈-type structure (space group P2₁/m), with an unexpectedly large equilibrium volume. The electronic structures of the ACr₃O₈compounds are analyzed using density-of-states, charge-density, and electron-localization-function plots, and all are found to exhibit semiconducting (insulating at 0 K) properties with very narrow band gaps. The Cr atoms occur in two different valence states and all compounds (except NaCr₃O₈) are found to exhibit antiferromagnetic ordering of magnetic moments at 0 K.     

Effect of CaO and SiO2 addition on magnetic properties of anisotropic Ba-Zn system W-type hexagonal ferrite magnets

An experiment was carried out to investigate the effect of CaO and SiO₂ addition on the magnetic and physical properties of anisotropic Ba-Zn W-type hexagonal ferrite magnets. It was found that magnetic properties of BaO.2ZnO.8Fe₂O₃ compounds added with CaO and SiO₂ were improved. The optimum conditions of typical specimens are as follows: chemical analysis composition-Ba_0.857 Zn_1.643 Ca_0.150 Si_0.266 Fe²⁺_0.030 Fe³⁺_15.857 O₂₇; semisintering condition-1275°C × 1.0 h in air; sintering condition- 1250°C × in air, magnetic and physical properties are J_m = 0.436 T, J_r = 0.393 T. H_cj = 64.4 kA/m, H_cB = 64.1 kA/m, (BH)_max = 16.1 kJ/m³, T_c = 357°C, H_A = 971 kA/m, K_A = 2.03 × 10⁵ J/m³ and n_B = 33.2 μ_B.     

Preparation of Multi-walled Carbon Nanotube/Polyaniline/Fe3O4 Composites

A method to prepare multi-walled carbon nanotube/polyaniline/Fe₃O₄ nanocomposites was developed. Acid-treated multi-walled carbon nanotubes (MWCNTs) were first encapsulated with polyaniline (PANI) by an in-situ micro-emulsion polymerization and then reacted with Fe₃O₄ modified with aniline dimer (ADM-Fe₃O₄). Fourier transform infrared spectrometry demonstrated that there existed chemical linkages between the MWCNTs and the PANI as well as between the MWCNTs and the ADM-Fe₃O₄ nanoparticles. The morphology of the nanocomposites was examined using transmission electron microscopy. The bulk structure of the nanocomposites was investigated with X-ray diffraction. The resulting products could be separated from the deionized water under an external magnetic field within about several seconds.     

Magnetic noise caused by output waveform harmonics of voltage-source inverters

Harmonic components included in the output waveforms of inverter circuits cause magnetic noise, that is, audio noise, from the output transformers or load motors. To estimate the magnetic noise due to the harmonic components, we have already proposed the equivalent noise voltage E_s and current I_s. In this paper, by applying the aforementioned E_s, we compare quantitatively the magnetic noise in the various ordinary voltage-source inverters, both PWM inverters with multipulse waveforms and PAM inverters with multistep waveforms. Then, to reduce the magnetic noise, the output waveforms of the PWM inverters are improved by applying E_s into the idea of harmonic elimination. Moreover, by employing PAM system as voltage regulation in the aforementioned method, the more improved output waveforms can be obtained with lower noise and also lower distortion.