宮城 大輔

The optimal design of a magnetic recording head is one important issue for high magnetic recording of 600-Gb/in(2) and beyond. In this paper, a three-dimensional topology optimization method (ON/OFF method) combined with a finite-element method is applied for the optimization of a cusp field single-pole-type head. In the ON/OFF method, the unknown variable is the reluctivity of magnetic material in the design domain and there is no special constraint. Therefore, the possibility of finding more optimal topology is increased compared with the conventional optimization method in which the design variables are specified. The optimal shape and dimension of a head is determined so that the flux density in a recording bit becomes the maximum and the leakage flux in the adjacent bit and adjacent track becomes the minimum. The recording field of 1.75 T and the field gradient of 0.038 T/nm (380 Oe/nm) are obtained for the head-soft underlayer distance of 25 nm.

The use of an iron core under dc-biased magnetization generates distorted asymmetrical hysteresis loop, and the iron loss is increased compared with that under sinusoidal excitation. Although the accurate measurement of magnetic properties under dc-biased magnetization is important for the estimation of iron loss of apparatuses, such as a reactor for an inverter which is operated under dc-biased condition, the reports of measurement of such magnetic properties are few. This is mainly because the measuring method of such magnetic properties and the method for accurate evaluation of dc-biased magnetization are not established yet. In this paper, a measuring system of magnetic properties of electrical steel sheet under dc-biased magnetization using an open-type single-sheet tester (SST) and a Helmholtz coil is developed. The newly developed system has an advantage that the interaction between ac and dc excitations is negligible, then the control is easy compared with the usual technique using a ring core or SST having both ac and dc exciting windings. It is shown that the increase of iron loss of 6.5% Si-Fe sheet due to the dc bias is larger than that of usual nonoriented silicon steel sheet.

3-D finite element analysis of current distribution taking account of the nonlinear E-J characteristic is carried out. In order to study the ac loss of multi-layered HTS power cable, the analysis region is considerably reduced by modeling spirally wound superconducting tapes as conductors having an anisotropic conductivity and using the periodic boundary condition. By using this model, the effect of the twist pitch on the current distribution of multi-layered HTS power cable with a shield layer is illustrated and the structure with low ac loss is discussed.

The eddy current is induced in silicon steel sheets of core block of power reactor due to the fringing flux, and this causes a local overheating. An exact and quick calculation using three-dimensional finite element method is important in order to design a reactor without such a local overheating. If each lamination of core is subdivided into a fine mesh, the number of unknown variables becomes huge and the calculation is difficult within an acceptable CPU time. Therefore, a practical modeling method of lamination of core should be investigated. In this paper, an exact and quick practical nonlinear analysis is performed by subdividing only the region near the surface of lamination into a fine mesh, and by modeling the inner part of lamination as a bulk core having anisotropic conductivity. A criterion how to determine the surface region of lamination which should be subdivided into a fine mesh is denoted. It is shown that the number of elements can be considerably reduced by classifying the analyzed region into two kinds of parts with fine mesh and coarse mesh. © 2006 IEEE.

In order to process a semiconductor device of high quality, uniform heating is necessary, but it is not easy to heat uniformly with conventional induction heating equipment. To solve this problem, zone control induction heating equipment has been jointly developed. In this paper, we examine the effect of dividing an induction heater into several small coil groups having different current and frequency, using the finite-element method. We describe the heating characteristics of the zone control coil groups and show that nearly uniform heating is possible by controlling both current and frequency.

Influence of ferromagnetism of the substrates on transport current losses in HoBaCuO-123 tape-shaped coated conductors with ferromagnetic Ni-alloy substrates was investigated by measuring the losses as a function of an external DC magnetic field. The losses were measured by electric and calorimetric methods simultaneously to prove the validity of the measured data. The experimental results showed significant influence of ferromagnetism of the substrates, when the substrates were not magnetically saturated by an external DC magnetic field. On the other hand, when the substrates were saturated, the loss characteristics were less influenced.

The adhesive-coated nonoriented electromagnetic steel sheet is well known to be effective in realizing high-efficiency, high-power motors with compact size, low noise, and low vibration, as shown in Kaido et al. The authors developed newly adhesive-coated grain-oriented electromagnetic steel sheets. We developed the gapped iron-core-type reactor having a new iron-core structure using this material. By adapting the adhesive-coated grain-oriented electromagnetic steel sheets to the leg of the reactor, the fastening studs of the laminated electromagnetic steel sheets, which are required in a conventional, reactor, and the through hole for the fastening studs could be omitted. This enabled us to simplify the structure and reduce the core diameter. On the other hand, we examined the magnetic flux distributions and local loss distributions in the yoke by a detailed magnetic-field analysis to use the oriented electromagnetic steel sheet with boltless construction, and realized the reduction of dimensions and weights due to the increase of magnetic flux density. The reactor developed has such features as smaller size, lighter weight, lower noise level, and low loss.

Analytical formulas derived by Norris [J. Phys. D 3 (1970) 489] and Brandt et al. [Phys. Rev. B 48 (1993) 12893] are often used to calculate the AC transport current and magnetization losses in HTS strip conductors. In those formulas, homogeneous distribution of critical sheet current density ac in the strip is assumed. However, it is considered that sigma(c) in actual HTS strips are distributed inhomogeneously and that deviations of the measured AC loss data of actual HTS strips from those formulas are due to the inhomogeneous sigma(c) distributions. We derived a semi-analytical method to calculate the transport current and magnetization losses in an HTS strip with inhomogeneous sigma(c) distribution. The validity of the semi-analytical method is shown by comparing the experimental and analytical data. (c) 2005 Elsevier B.V. All rights reserved.

AC transport current losses in HoBaCuO-123 tape-shaped coated conductors with ferro-magnetic Ni-alloy substrates were measured as a function of an external DC magnetic field. Influence of ferromagnetism of the substrates on transport current losses in the conductors was investigated. The experimental results were compared with theoretical models given by the Norris equations, and showed significant influence of ferromagnetism of the substrates, when the substrates were not magnetically saturated by an external DC magnetic field. However, when the substrates were saturated, the loss characteristics were similar to those of coated conductors with non-magnetic substrates. The experiments also showed that the influence of the ferromagnetism was strongly dependent of the direction of the external DC magnetic field to the wide face of the tape. (c) 2005 Elsevier B.V. All rights reserved.

We measured AC transport current losses in three kinds of thin-film YBCO-coated conductors made by different processes. The results showed that the loss characteristics were different and that some of the conductors did not follow the Norris strip model which is generally believed to well explain the loss characteristics of YBCO conductors. In the paper, an analytical model in which distribution of critical current density and n value of the conductor are taken into consideration is proposed to describe the AC transport current loss characteristics more generally than the Norris strip and elliptical models. It is shown that the analytical model explains well the measured loss characteristics of the three kinds of conductors. (c) 2005 Wiley Periodicals, Inc.

NdFeB sintered magnets are widely used in rotating electrical machines. In order to develop an efficient rotating machine, it is important to estimate ac loss of the permanent magnet of rotor precisely. In this paper, the ac losses of the permanent magnet of IEEJ model (surface permanent-magnet motor model) are examined by using the three-dimensional finite-element method taking into account the newly measured hysteresis losses of permanent magnet. The result shows that we should consider not only the eddy-current loss but also the hysteresis loss, when the frequency of ac field due to a slot ripple is of the order of several hundred hertz.

Air-gapped iron-cores are widely used for power reactors. Eddy currents are induced in silicon steel sheets due to fringing flux, and this causes local overheating. In order to avoid local heating and to design reactors with high efficiency, the analysis and experiments for evaluating local losses in the core block of the reactor are necessary. In this paper, the modeling of laminated core for practical and accurate analysis is investigated. The number of elements can be reduced by classifying the analyzed region in terms of the amount of fringing flux penetration. The eddy-current losses due to fringing flux are examined using three-dimensional finite-element method and experiments. New concepts for optimal designing of slits are shown.

The adhesive coated non-oriented electromagnetic steel sheet is well known to be effective in realizing high efficiency, high power motors with compact size and low noise. The authors developed newly adhesive coated grain oriented electromagnetic steel sheets. Then, a gapped iron-core type reactor having a new iron-core structure is developed using the adhesive coated steel sheets. By adopting the adhesive coated grain oriented electromagnetic steel sheets to the leg of the reactor, the fastening studs of the laminated electromagnetic steel sheets, which are required in conventional reactor, and the through hole for the fastening studs could be omitted. This enabled us to simplify the structure and reduce the core diameter. On the other hand, we examined the magnetic flux distributions and local loss distributions in the yoke by the detailed magnetic field analysis to utilize the grain oriented electromagnetic steel sheet with bolt-less construction, and realized the reduction of dimensions and weights due to the increase of magnetic flux density. The reactor developed has such features of smaller size, lighter weight and lower noise level. © 2005, The Institute of Electrical Engineers of Japan. All rights reserved.

If the magnetic field in a magnetic device which is operated at high temperature, for example 100 °C, is analyzed using magnetic characteristics at a room temperature (RT), there occur some errors. Although the measurement method using a single sheet tester (SST) has advantages that the material characteristics can be measured precisely, the research about the correlation between the temperature and the magnetic characteristics using SST is few. In this paper, firstly, the temperature characteristics of magnetic properties of silicon steel sheet were measured using SST, then, the temperature characteristics of the iron loss of the permanent magnet motor were estimated by using the finite element method (FEM). It is shown that the permeability is increased at low flux density, and decreased at high flux density when the temperature is increased. The iron loss is decreased similarly in almost all range of Bm. The change of iron loss is remarkable in the low grade steel (50A1300). The iron loss of SPM motor at 100 °C is decreased by about 10–20% compared with that at RT. © 2005, The Institute of Electrical Engineers of Japan. All rights reserved.

Purpose - In this paper, a new method for estimating iron loss under a distorted elliptical rotating flux is proposed. Design/methodology/approach - In order to precisely analyze the iron loss of rotating machines, the iron loss under distorted rotating flux should be taken into account. However, reports of precise analysis considering measured iron loss data under rotating flux are few. Findings - The iron loss of surface permanent magnet (SPM) motor model proposed by the investigation committee of IEE of Japan is estimated using the proposed method. The experimental examination is carried out by measuring the iron loss of the motor using a torque meter. Originality/value - Examines an estimation method of iron loss of motors.

A method for analysing the current distribution in high-T-c superconducting (HTS) power cable is examined by the aid of the novel use of anisotropic conductivity and 3-D finite element method considering E-J power law characteristic. The detailed current distribution in the cable is illustrated and the shielding effect of HTS shield layer with intervals is also examined. It is shown that AC losses in shield layer with intervals are increased when the interval between wires becomes large.

We have fabricated cable-in-conduit conductors (CICCs) with two kinds of nonmetallic conduit materials. Difference of frictional coefficients on surfaces of the materials vary by factors of two or three, and void ratios of the conductors are from 14% to 42%. We wound these CICCs on same-shaped bobbins, and measured the AC losses of the CICC coils. In spite of the fact that the coil shape, the superconducting wire, and background magnetic fields were the same, the measured losses were not, and depended on conduit materials and void ratios. According to the experimental results, in order to decrease the losses, a conduit material with high frictional coefficient is desirable. It is also shown that the losses decrease with the decrease of the void ratios in the CICCs.

A method for analyzing the current distribution in higli-T-c superconducting (HTS) power cable is examined by the aid of the novel use of anisotropic conductivity and three-dimensional finite element method in consideration of the E-J power law characteristic. The detailed current, distribution in the cable is illustrated and the shielding effect of HTS shield is also examined.

We measured AC transport current losses in three kinds of thin film YBCO coated conductors made by different processes. The results showed that the loss characteristics were different and that some of the conductors did not follow the Norris strip model which was generally considered to well explain the loss characteristics of YBCO conductors. In the paper, an analytical model in which distribution of critical current density and n value of the conductor are taken into consideration is proposed to describe the AC transport current loss characteristics more generally than the Norris strip and elliptical models. It is shown that the analytical model well explain the measured loss characteristics of the three kinds of the conductors. © 2004, The Institute of Electrical Engineers of Japan. All rights reserved.

Induction heating is widely used in the industry due to high efficiency, precise control, rapid heating and low pollution properties. To process a semiconductor of high quality, uniform heating is necessary, but it is not easy to heat uniformly by using the conventional induction heating equipment For this purpose, the zone control induction heating equipment is jointly developed with Mitsui Engineering Shipbuilding Co., Ltd. In this paper, the optimization of current in each cad is carried out using the finite element method and the optimization method in order to obtain a uniform eddy current loss distribution on graphite.

When alternating current superconducting coils having cable-in-conduit conductors are fabricated, non-metallic conduit materials are necessary to avoid eddy current losses in the conduits. Using two kinds of non-metallic tapes made of glass fiber reinforced plastics (GFRPs) and Dyneema fiber reinforced plastics (DFRPs), we made the conductors with the GFRP conduits and DFRP conduits, and experimentally studied the total losses of the conductors. The measured results showed that the total loss of the conductor with the GFRP conduit was smaller than that with the DFRP conduit at the same value of the void ratio, the transport current, the external magnetic field, and so on. When the void ratios become high, the superconducting bundle cable can easily move in the conduit. Hence the measured total losses increased with the void ratios of the conductors. (C) 2003 Published by Elsevier B.V.

We measured the AC transport current losses in Bi2223/Ag sheathed tapes stacked laterally with gaps between the tapes, wide faces of a tape facing to those of the other tapes. The data were compared with the AC transport current losses in isolated Bi2223/Ag tapes and also with those in Bi2223/Ag tapes arranged in a single flat layer with the wide faces of the tapes on a flat plane. The experimental results showed that the AC transport current losses in the tapes laterally stacked were higher than those in the isolated tapes and those in the tapes arranged in a single flat layer. Reason for those results is studied by considering that the current distribution in the tapes is affected by the magnetic fields produced by the neighboring tapes. (C) 2002 Elsevier Science B.V. All rights reserved.

Round-shaped Bi2223/Ag sheathed wires were developed to apply to AC superconducting apparatuses. Round high temperature superconductor wires are convenient to assemble into a twisted cable conductor to obtain homogeneous current distribution in the wires. We measured AC transport current losses in a round wire itself and a (6+1) assembled cable conductor. The experimental results showed that the AC transport current loss per one wire in the assembled conductor was larger than that in an isolated wire. Reason for this difference of the AC losses is discussed. (C) 2002 Published by Elsevier Science B.V.

We measured AC transport current losses in two kinds of thin film YBCO coated conductors with different critical current densities. The results show that the loss characteristics do not follow the Norris strip model. The loss in one of the samples follows the Norris elliptical model and the loss data of the other sample fall in between the elliptical and strips models. It is considered that the loss in a YBCO conductor of high quality, that is, high critical current density, follows the strip model. However, the measured losses of even high critical current density conductor (J(c) approximate to 10(6) A/cm(2)) does not follow the strip models. In the paper, an analytical model is presented to describe the AC transport current loss characteristics more generally than the Norris models and the model can well describe the experimental results.

To study a mechanism of AC transport current losses in HTS wires, we measured the AC transport current losses of two kinds of MTS wires subject to DC background magnetic field by changing frequency of currents. The tested wires are a multifilamentary Bi2223/Ag sheathed tape and YBCO thin film conductors. The measurement results show that the losses in the Bi/Ag sheathed tape and YBCO conductors deviate from the Norris model in different ways and are only weakly dependent on frequencies of transport currents. In this paper, measured results are presented and the loss characteristics are explained based on a numerical model which we made in a previous work to analyze the AC transport current losses.

We measured AC transport current loss of a high current density YBCO tape conductor. The tape conductor was made by depositing YBCO thin layer of similar to 1 mu m thick on a LaAlO3 single crystal substrate and its critical current was around 100A at 0T and 77K, The loss data deviated from the Norris curves for the elliptical and strip models. We made an analytical model to numerically calculate the AC transport current loss. In the model, critical current density (J(c)) distribution in the wire cross section is taken into consideration. It is shown by the analysis based on the model that the deviation of the measured AC loss from the Norris equations is due to inhomogeneous J(c) distribution in the cross section of the tape. The J(c) distribution was investigated by subdividing the YBCO layer along the longitudinal direction. The results of the investigation are compared with the J(c) distribution deduced from the analysis. The loss data showed frequency dependency, which can be explained by assuming that the loss has hysteretic and eddy-current-like loss components.