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To reduce the iron loss and noise of a three-phase reactor composed of grain-oriented (GO) steel plates, two types of core structures are proposed in this article. In the first type, the ordinary brick core model is improved to a hybrid one composed of GO and nonoriented steel plates, and in the second type, the T-joint part of the ordinary oblique-joint core model is improved to a straight joint. To show the effectiveness of the improved models, the iron loss and displacement distributions in the four core structures are evaluated using the 2-D magnetic field and mechanical analyses. In these analyses, the magnetic characteristics of the anisotropic cores are considered in detail. Namely, in the magnetic field analysis, the ${B}$ – ${H}$ curves in the arbitrary directions are considered. In the iron loss calculation, the rotational iron loss is calculated using the iron loss curves in the arbitrary directions. Moreover, the methods of calculating the displacements due to electromagnetism and magnetostriction considering the anisotropic ${B}$ – ${H}$ curves and magnetostriction in the arbitrary directions are proposed. It is shown that the iron losses and displacements of the two proposed core structures can be reduced compared with the ordinary ones. Moreover, the second proposed model is the most attractive one because both the iron loss and displacement are smaller than the other models.

Large fault direct current with fast rising speed has always been a significant threat to high voltage direct current systems. Fault current limiters (FCLs) are one of the most promising solutions. However, the biased permanent magnets (PM)s in traditional FCLs have large magnetic reluctance that causes FCLs to have small inductance changing ratios when a fault occurs. In this study, a novel three-limb topology of a saturated iron core-type fault current limiter (TSFCL) is proposed and a central PM bias limb is inserted to force flux flow through this limb. Therefore, the inductance changing ratio is greatly enhanced and the steep rising trend of fault current will be restrained effectively. The operating principles and characteristics of the TSFCL are analyzed to verify the deductions. Moreover, different lengths and cross-sectional areas of the inserted PM are tested and optimization study is carried out. The results show that the clipping inductance has a 55% increase compared with a traditional two-limb model. Moreover, compared with the existing smoothing reactor and traditional two-limb model, proposed topology can decrease the fault current by 45% and 16% within 5 ms, respectively. Finally, a typical HVDC system was built and the effectiveness of proposed TSFCL was verified.

Soft magnetic composites (SMCs) are composed of ferromagnetic particles surrounded by electrical insulation. To establish a homogenization technique for the magnetic field analysis of an electrical machine with an SMC core, we have already proposed a method to evaluate the effective permeability and iron loss of the SMC core using a cell model of one particle taking into account the nonlinear magnetic characteristics and eddy currents. However, the measured eddy current loss cannot be represented by using the proposed method. In this article, a 3-D eddy current analysis method modeling the anomalous eddy current loss due to the movement of domain walls in the cell model is developed based on the Pry and Bean magnetic domain model. The effect of the non-uniformity of the domain structure on the anomalous eddy current loss is investigated. It is shown that the measured eddy current loss can be almost represented by adding the anomalous eddy current loss to the classical one.

To reduce the iron loss of a three-phase reactor composed of grain-oriented (GO) silicon steel plates, we proposed two reactor models. One applies oblique joints between the legs and the yokes, and the other applies butt joints composed of non-oriented (NO) silicon steel plates at the L and T joint parts. The proposed models are aimed to relax the flux concentration inside the iron cores that occurs due to the anisotropic magnetic characteristics of GO silicon steel plates. The effectiveness of the proposed models are investigated through magnetic field and iron loss analyses considering the anisotropic magnetic characteristics of the iron cores. It is found that the flux concentration in the yoke can be relaxed in both proposed models. And iron loss of the proposed model with NO steel plates at the L- and T-shaped joints can be reduced about 12% compared with the ordinary one.

Local high iron loss may occur due to the deviation of magnetic flux from the rolling direction of electrical steel in the T-joint area of the transformer core. In this paper, to reduce the iron core loss in the T-joint region, a hybrid iron core model using nonoriented and grain-oriented magnetic materials is proposed. Three-dimensional magnetic field analysis considering the nonlinearity and laminated structure of the original and proposed iron core models is carried out by using the finite element analysis. The flux and iron loss distributions of the original and the hybrid cores are compared. The results show that approximately 2% iron loss reduction can be achieved by using the proposed hybrid structure.

In this paper, an excess loss modeling method of the laminated iron core is proposed. The 1-D single sheet silicon steel plate analysis is combined with the 3-D solid-core analysis to model the laminated structure. The modeling is improved by including the domain wall bowing due to pinning effect, which is considered as the main cause of excess loss. The domain wall bowing due to pinning is considered in the 1-D steel plate analysis because the excess loss generated by the flux density in the parallel direction of the stack is dominant compared with that in the perpendicular direction. In the 1-D analysis, an initial bowing flux distribution along the thickness direction of one lamination is introduced. The results of iron losses show that the hysteresis and eddy current losses vary with the flux and eddy current distribution in the laminated iron cores. Finally, the 1-D–3-D combined method is applied to a single-phase reactor; the magnetic flux and eddy current distribution are analyzed in detail. The eddy currents generated by the parallel flux are increased, hence, the skin effect of flux in the parallel direction of laminations is enhanced; thus, the hysteresis and eddy current losses are increased and the iron loss is increased by 8%.

Soft magnetic composite (SMC) is composed of ferromagnetic particles surrounded by electrical insulation. SMC has advantages such as isotropic magnetic characteristics, low eddy current loss, and easy to be manufactured into complex shapes compared with electrical steel sheets. In this paper, to establish the homogenization technique for the magnetic field analysis of an electrical machine using SMC, a method to evaluate the effective permeability and iron loss taking account of nonlinear magnetic characteristics and eddy currents is proposed by using a cell model composed of one particle of SMC. Then, the effects of the frequency and particle size on the effective permeability and iron loss are investigated numerically. Finally, the effective permeability and iron losses of an actual SMC are calculated, and they are compared with measured results to verify the proposed method. It is shown that theoretically proper results are obtained by using the proposed method. The calculated iron losses coincide well with the measured ones below 10 kHz, whereas the calculated effective permeability is smaller than the measured one due to different effective gap lengths.

It is necessary for companies supplying reclaimed oil to analyze polychlorinated biphenyls (PCBs), because there is a possibility of the presence of contaminants due to trace-level PCBs in the reclaimed oil. However, common analysis methods of PCBs are time-consuming and complicated. Fast-GC triple stage quadrupole mass spectrometer with the 13-component quantitation method is an official method for analyzing PCBs in insulating oil in Japan. This method is extremely fast and simplified. The purpose of this study involves an investigation of the aforementioned fast and simple method for potential use in the analysis of reclaimed oil. Furthermore, it was attempted to combine the method with sample preparation involving only hexane dilution. The effect of sample dilutions corresponding to 100, 300, and 500 times was evaluated for reducing the matrix effect. The matrix effect was suppressed at a dilution ratio equal to or exceeding 300 times. Calibration curves of four points, namely 0.01, 0.05, 0.1, and 0.5 ng/mL, (ignored origin) by using an internal standard method were prepared for the 13 components. The square of regression coefficient (R2) values of all calibration curves exceeded 0.997. This method was adopted for the analysis of reclaimed oil containing 0.5 μg/mL PCBs, which corresponds to the judgment criteria, and accurate quantitation (accuracy value, 94.0–102%) and good repeatability (%RSD, 3.6%) were obtained. Furthermore, the required sensitivity was maintained even when 800 samples were analyzed without a cleaning ion source and an exchanging analysis column.

The saturated-core fault current limiter (SFCL) is an effective device for limiting fault current. This paper proposes and analyzes a novel bridge-type SFCL (BSFCL) that uses a permanent magnet (PM) to reduce dc bias while improving the stability of the PM. The bridge structure in the BSFCL consists of four coils and a fault-limiting reactor which is used to limit fault current. The ac and the dc share coils to help reduce energy loss. The iron core uses air-gap branches to offer paths for ac flux, which reduces eddy current in the PMs and enhances their stability. The operating principle and characteristics of the BSFCL were analyzed using the electromagnetic coupling method. To investigate the effects of parameters on the performance of the BSFCL, various finite-element analysis simulations were performed by Maxwell. Experimental results of a 220 V prototype verify the effectiveness of the BSFCL.

The saturated core fault current limiter (SFCL) is one of the most effective methods for limiting fault current. A permanent magnet (PM)-biased SFCL (PFCL) can reduce dc bias current and additional energy consumption. However, the thermal stability of NdFeB PMs in PFCL poses a major challenge. This paper proposes a novel hybrid-type SFCL (HSFCL) topology that can reduce this risk. In the HSFCL, a hybrid PM/dc coil is designed to saturate the core, and a fault-limiting reactor is used to guarantee fault-clipping performance. The new structure provides air-gap branches for the time-varying magnetic field produced by alternating current, which reduces the eddy current in the PMs and enhances their stability. Electromagnetic coupling is used to analyze the operating principles and characteristics of HSFCL. Finite-element analysis simulations were performed using Maxwell and compared with verification experiments, proving that HSFCL is efficient in fault clipping and PM reliability enhancement.

Compared with grain-oriented SiFe sheets, the domain structure of nonoriented (NO) SiFe sheets is very different, and the magnetization processes of NO SiFe sheets are much less investigated. Thus, the excess loss of NO SiFe sheets is less well-known. In this paper, we propose a numerical method to estimate the excess loss in NO SiFe sheets, considering the pinning and skin effects. We apply an initial magnetic field distribution that reflects the pinning effect in our nonlinear eddy current finite element analysis model, which reflects the skin effect of the magnetic flux. Thus, the pinning effect can be coupled with the skin effect in the proposed numerical method. The hysteresis loss and eddy current loss calculated from the flux and eddy current distributions are directly obtained from the proposed analysis method. Thus, excess loss is included in both the hysteresis and the eddy current loss calculations. We first apply the proposed method to two different grades of NO SiFe sheets. The calculated iron losses in one sheet are compared at various frequencies with the measured losses from catalogue data, and less than 2% deviation can be achieved. Finally, we apply the proposed method to the loss calculation for the iron core of a reactor.

A method of 3-D finite element magnetomechanical analysis is developed to investigate the effect of magnetostriction (MS) and stress on the core loss and vibration of motors. Shrink-fit stress calculation is carried out using static structural analysis and equivalent thermal force calculated by a novel method using the thermal stress tensor. A method of core loss calculation is proposed to take account of the 3-D stress in the core loss calculation. The methods are applied to the core loss and the vibration analysis of a permanent magnet motor. Numerical results show that the stator core loss increases significantly due to the shrink-fit stress. However, the radial velocity of the housing surface slightly decreases due to the MS and further decreases due to the shrink-fit stress because the MS increases under compressive stress.

Grain-oriented (GO) materials are widely used in the iron cores of power transformers and reactors, as they provide a high permeable path within low iron losses. However, magnetic properties of GO materials exhibit strong anisotropy, and this intensifies the flux concentration inside the iron core. Furthermore, in a three-phase transformer, rotational magnetic field is generated at the T-joint part. Therefore, the magnetic flux path is not parallel to the rolling direction of the steel plate in the T-joint area, thus results in higher iron loss at the T-joint area. To overcome the foregoing problems, we proposed two kinds of hybrid iron core models applying different grades of silicon steel plates and their effectiveness is investigated by using magnetic field analysis and iron loss analysis with finite element method.

To reduce the iron loss of a three-phase reactor composed of Grain-oriented silicon steel plates, we proposed two reactor models: applying oblique joints between the legs and yokes, and applying isotropic brick iron cores at the L and T shaped joints. The effectiveness of the proposed models are investigated through magnetic field and iron loss analyses considering the anisotropic magnetic characteristics. It is found that the iron loss of the proposed model with isotropic butt joints can be about 12 % reduced compared with the ordinary one.

The saturable magnetically controlled reactor (MCR) applying dc control currents has been widely used in the voltage regulation and reactive power compensation in the electric power system [1].

In the magnetic field analysis of magnetic devices using a ferrite core, such as a pulse transformer, the frequency-domain analysis is often carried out using the measured complex permeability under different frequency range. However, the nonlinear magnetic characteristics cannot be considered in the frequency-domain analysis because of the harmonics caused by it cannot be represented. The nonlinear magnetic characteristics can be considered in the time-domain analysis, but suitable constant conductivity and permittivity taking account of the microstructure of ferrite core, which can represent the measured complex permeability under different frequencies, needs to be investigated for the time-domain analysis. In this paper, the effective permeability of a toroidal ferrite core is tried to be demonstrated by using the linear ac steady state magnetic field analysis taking account eddy currents and displacement currents. It is shown that the measured permeability can be realized roughly by using the modified constant conductivity and permittivity. The nonlinear time-domain magnetic field analysis can be carried out using the modified constant conductivity and permittivity obtained from this paper.

To reduce the iron loss of a reactor stacked with non-oriented steel plates, we have proposed the method of loss reduction improving the iron core configuration using the magnetic field analysis taking account of the laminated structure by the homogenization technique. In this paper, the iron loss reduction method is expanded to a reactor stacked with grain-oriented steel plates. The magnetic field analysis taking account of the laminated structure and steel plate anisotropy using homogenization technique is developed. The flux concentration due to the laminated structure, steel plate anisotropy, and joint between the leg and yoke of the reactor is analyzed and relaxed by the improvement of the core and joint configurations. It is shown that the iron loss can be about 36% reduced by the improvements.

A homogenization technique of a laminated core taking account of the eddy currents in the steel plates by combining a three-dimensional (3-D) solid core model with a one-dimensional (1-D) steel plate model has already been proposed. In this paper, to apply the proposed technique to a motor core, in which flux rotates, the 1-D eddy current analysis of the steel plate is expanded to a 3-D analysis. The proposed method is applied to a simple laminated core model under the rotational flux in the linear analysis. Then, the eddy current loss obtained from the developed method is compared with those obtained by the homogeneous solid core model with 1-D steel plate model and the real laminated core model. It is shown that error occurs by neglecting the edge of the model but the accuracy is much improved in the eddy current loss calculated by using the proposed method.

In the ordinary saturable magnetically controlled reactors inserted in the legs with magnetic valves of smaller cross-sectional areas (VMCR), the flux concentrates in the legs due to the valves so the iron loss and noise are increased. In this paper, to reduce the iron loss and noise of VMCR, the structure of the valves is improved by using 3D nonlinear magnetostatic field analysis taking account of the laminated structure and the anisotropy of iron cores. It is shown that the iron losses can be reduced by about 30% improving the valve structure.

In this paper, a simple structure of L and T shaped butt joints composed of anisotropic and isotropic block cores is proposed. The iron loss of a three-phase reactor having the proposed joints is compared with that having ordinary joints composed of anisotropic block cores only. It is shown that the iron loss can be reduced by applying the proposed joints because the flux distribution becomes more uniform.

To calculate the iron loss in an electric machine accurately, the anomalous eddy current loss generated by domain wall motion should be considered. A simple numeric modeling of anomalous eddy current loss by modifying the conductivity of steel plates is sometimes used. However, investigation on this method in detail has not been carried out. In this paper, this method is investigated in two iron-loss models neglecting and including the skin effect and then applied to the loss calculation of various kinds of nonoriented and oriented silicon steel plates. Then, the dependence of the modified conductivity on the amplitude and frequency of the induction magnetic field for each material is obtained and the appropriate iron-loss model and method for modifying the conductivity are proposed for the nonoriented and oriented silicon steel plates. The calculated iron losses using the appropriate iron-loss model with modified conductivity are compared with the measured data. It is clarified that for nonoriented materials, the iron-loss model including the skin effect with constant modified conductivity shows good agreement. And for oriented materials, the model neglecting the skin effect with the modified conductivity depending on frequency is better.

To reduce the noise of a reactor connected to an inverter power supply, we have already proposed an improved one-phase reactor, in which the hard materials are chosen as the insulators inserted in the gaps between the cores, and gaps are added in the yokes, using a three-dimensional (3-D) coupled magnetic field and vibration analyses taking account of both the electromagnetism and magnetostriction. The effectiveness was shown by experiment. In this paper, the design method is improved and applied to a three-phase reactor. First, the method of determining the optimal hardness of insulators inserted in gaps, so that both the displacements by electromagnetism and magnetostriction are canceled with each other, is proposed. In this method, the optimal hardness of gaps can be represented using a simple equation involving the lengths of the iron cores and the gaps, and a parameter concerned with magnetostriction. Moreover, the method of adding gaps in the yokes without changing the balance and reluctance of a three-phase reactor is also proposed. It is shown that the displacements of the reactor improved by using the proposed methods can be reduced to be 1/25 of the ordinary reactor in the 3-D coupled magnetic field and mechanical analyses taking account of both the electromagnetism and magnetostriction and laminated structure of the iron cores.

To investigate the noise reduction for an electrical machine, coupled magnetic field and mechanical analyses should be carried out. In this paper, the method of modeling the laminated core using a homogeneous core model with equivalent anisotropic parameters considering the laminated structure in the coupled magnetic field and mechanical analyses is proposed and the effect of the laminated structure on the coupled analysis is investigated. The distributions of the flux densities, nodal forces by electromagnetism and magnetostriction, and displacements corresponding to these forces of the real laminated iron core model, the solid core model neglecting the laminated structure and the homogeneous core model considering the laminated structure are obtained and compared. It is shown that the laminated structure cannot be neglected in both the magnetic field and mechanical analyses and the displacement distribution obtained from the homogeneous model is in good agreement with the real model.

In order to increase amenity for hospital patients, we introduce an open-type magnetically shielded room (MSR) in tight space composed of magnetic and conductive cylinders for a magnetic resonance imaging (MRI). This paper presents a design for the MSR opening part for an actual 3T MRI that combines magnetic cylinders with magnetic mullions to decrease the leakage flux density to less than 0.5 mT, taking magnetic saturation into account. The design utilizes the homogenization technique to model the opening part which reduces the number of elements. Moreover, a newly optimized design approach is proposed for the design of openings. First, the opening part is designed while treating the magnetic property in linear analysis to obtain an ideal flux distribution without magnetic saturation. Then, the thickness of the magnetic cylinders is determined for magnetic cylinders to stay unsaturated. Finally, the open-type MSR presented in this paper is built in a hospital, and the design method is verified.

We have developed an open-type magnetically shielded room composed of magnetic square cylinders that has been used for an actual MRI in a hospital. To improve shielding performance, we propose here a method to control the path of the magnetic flux in the wall composed of the magnetic square cylinders by changing the magnetic permeability in each direction of the square cylinders spatially. First, we discuss a method to control the magnetic permeability in each direction of the square cylinders independently by inserting slits without changing the outside dimensions of the square cylinders, by using 3-D magnetic field analysis. Then, the effectiveness of the design of controlling the flux pass was shown by magnetic field analysis and experiments.

For non-destructive and non-invasive inspection of water content and chloride concentration of concrete, a new electric method, by measuring the impedance between two rectangular metallic electrodes setting on the surface of the sample using the impedance meter with an AC voltage at frequencies of 10 Hz to 100 kHz was proposed. This paper describes the basic research of this easy, cheap, onsite, and non-invasive inspection system. First, the effects of water content and chloride concentration on the measured impedance dependence of frequency of small concrete samples were investigated. Secondly, the phase shift dependence of frequency was measured to estimate water content and chloride concentration individually by the peak of the phase shift and its frequency. Finally, the equivalent circuit of concrete that reproduces the curve of measured phase shift dependence of frequency by fitting the curves obtained from the equivalent circuit and measurement was proposed. It was shown that there is a possibility to estimate the water content and chloride concentration of concrete.

When the magnetic field analyses of the architectural components, in which magnetic materials are distributed complicatedly, are carried out, great efforts toward the modellings and high computational costs are required. To overcome these problems, the homogenization technique seems to be attractive. In this paper, from the standpoint of a practical use, the effectiveness of the homogenization technique is investigated in the analyses of the magnetic disturbance due to a building and the shielding performance of an open-type magnetically shielded room with a wall made up of magnetic cylinders. First, the effect of the region, where the homogenization technique is applied, on the accuracy of the flux distribution is investigated. Then, to examine the possibility that the homogenization technique can be applied to a practical design, the accuracy of the homogenization technique to a real model is investigated. Moreover, the reproduction of the flux distribution of the real model using that obtained from the homogenization technique is also tried. It is shown that the homogenization technique should be applied to not only the region of the magnetic materials but also the air region surrounding them. Moreover, the accuracy of the flux distribution obtained from the homogenization technique is satisfactory for a practical design.

To reduce the noise of a reactor under inverter power supply, the cause of noise should be investigated. For this purpose, we have already proposed a 3-D vibration analysis considering electromagnetism and magnetostriction, and the proposed method was applied to one phase of a reactor. It was found that the displacements in the yoke of the reactor are large and the hardness of insulators inserted in the gaps between cores affects the displacements. However, the optimal design to reduce the noise is not carried out. In this paper, first the better hardness of the gaps are determined by using the static structure analysis and a new design is proposed to reduce the noise. Moreover, the effectiveness of the improved hardness of gaps and the proposed new design of reactor is investigated by using the vibration analysis and the experiment.

In order to detect steel bars and power cables inside pliable plastic conduit tubes buried in concrete walls and slabs during the renovation of old buildings, we have developed a new nondestructive inspection (NDI) system. This system, which enables high precision detection and easy handling at low cost, works by measuring the impedance due to the inductance change of a solenoid coil which exposes the test material to a magnetic field. In this system, the solenoid coil is connected to a compensating capacitor with a series-resonant circuit to reduce the impedance and multiply the impedance change by increasing the quality factor, Q, i.e., the ratio of the inductive reactance, ?L, to the coil resistance, R, which contributes to improving the signal-to-noise ratio for detection. This paper describes the validity of the design method of this NDI system. Firstly, the fractional deviation of inductance, ?, the inductance changes between with and without a steel bar and power cables were analyzed. The deviations due to the eddy currents and magnetization induced in the steel bars and power cables were computed through 3-D magnetic field analysis taking eddy currents at 5, 40 and 800 kHz into account. Secondly, the rates of change of impedance (RCIs) and phase angles were measured with the impedance meter of the newly developed NDI system. This system was designed so that the value of became roughly 200 and the resonance frequencies became about 5, 40 and 800 kHz. For steel bars, the predicted RCIs, which were calculated from the computed s multiplied by the designed Q factor, roughly matched those measured. In case of power cables, the tendency of predicted RCIs were roughly in accord with those measured. The validity of the design method's detecting system was verified. In addition, the analysis and measurement proved that this NDI system can distinguish steel bars from power cables by the polarity of the phase angle.

In order to protect high voltage direct current (HVDC) system from destructive consequences caused by fault current, a novel concept of HVDC system fault current limiter (DCSFCL) was proposed previously. Since DCSFCL is based on saturable core reactor theory, iron core becomes the key to the final performance of it. Therefore, three typical kinds of soft magnetic materials were chosen to find out their impact on performances of DCSFCL. Different characteristics of materials were compared and their theoretical deductions were carried out, too. In the meanwhile, 3D models applying those three materials were built separately and finite element analysis simulations were performed to compare these results and further verify the assumptions. It turns out that materials with large saturation flux density value Bs like silicon steel and short demagnetization time like ferrite might be the best choice for DCSFCL, which can be a future research direction of magnetic materials.

Metallic implants composed of paramagnetic materials, such as stainless steel (SUS), Ti, Co-Cr-Mo alloy, etc., are widely used as artificial hip joints or aneurysm clips. When the metallic implant is placed in a uniform magnetic field of a magnetic resonance scanner, a magnetic disturbance is created due to its magnetization. This magnetic disturbance distorts the image of the metallic implant and body tissues in the magnetic resonance imaging (MRI). In order to overcome this problem, a method of coating the metallic implant with diamagnetic material has been proposed as the magnetic disturbance created by the metallic implant can be removed by the cancellation of the respective magnetizations of the paramagnetic and diamagnetic materials. But the optimal thickness of the diamagnetic coating has been obtained only for a sphere model by mathematical modeling. In this paper, the effects of a straight cylindrical hip joint model and an aneurysm clip model on the magnetic disturbance are investigated by using the magnetic field analysis of the finite element method (FEM). First, the magnetic disturbances generated by the two models made of paramagnetic material are calculated and compared with measured results. Moreover, the associations of susceptibilities chipar and chidia of the paramagnetic and diamagnetic materials and the optimal thicknesses of the diamagnetic coating when the magnetic disturbances can be reduced for the two models are shown.

To shield the leakage flux densities of 3 T magnetic resonance imaging (MRI) higher than 1.5 T MRI and to reduce the degradation of magnetic properties during construction, the design of an open-type magnetically shielded room (MSR) combined with square cylinders made of magnetic and conductive materials should be improved. This paper reports on an optimal design for magnetic cylinders to improve the shielding effect, while also considering ease of construction with a view to practical use. Firstly, the structure of the magnetic cylinders, such as their opening width and the slit width were optimized using a 3D linear magnetic-field analysis. Using optimal magnetic cylinders, when the relative permeability (μ_r) of the magnetic material is larger than 10 000, the reluctance of gaps between the cylinders is the main contributor to the leakage flux. So, the required (μ_r) of the magnetic material is 10 000 and oriented silicon steel is adopted instead of the non-oriented type. Secondly, as an optimal construction method, it was determined by experiment that oriented silicon steel sheets, annealed after bending, should be laminated so that the effect of gaps on butt joints between steel sheets on the magnetic property of the cylinder becomes smaller. This enables the relative permeability of 10 000 when the maximum flux density of the material in the cylinder is less than 1.7 T. Finally, the minimum thickness of oriented silicon steel sheet of cylinders depending on the distance from a 3 T MRI is obtained using linear magnetic analysis under the condition that the maximum flux density of the material of the cylinder is less than 1.7 T. In the case of the thickness of 3.8 mm, the leakage flux density of 3 T MRI is decreased to less than a guideline (0.5 mT) when the distance between the cylinders and the center of MRI is larger than 2 750 mm. This indicates that the optimal design and construction method of an open-type MSR for 3 T MRI composed of magnetic square cylinders are realized.

A method of magnetic field analysis which takes eddy currents into account in laminated steel core is extended into loss calculation to investigate the loss reduction of reactor connected to inverter power supply. In the proposed method, the iron loss in the laminated core can be calculated considering the flux and eddy current distributions in steel plate affected by harmonic components. The proposed method is applied to a single-phase model of reactor connected to inverter power supply and the loss distributions are demonstrated in detail. Moreover, in order to reduce the loss, the shape configurations of core and plate are improved. Finally, the experiments using three-phase reactors are carried out to verify the calculation and investigate the effectiveness of the proposed shape configuration.

To reduce the iron losses of reactors under inverter power supply, the loss was calculated by using magnetic field analysis, which models a laminated core by combining a 3D solid-core model with a 1D steel plate model, using the finite element method (FEM). In this method, the structure of the laminations and the eddy currents in the steel plates can be taken into account. However, for reactors driven by inverter power supply, the calculated iron losses are much smaller than the measured results, because the anomalous eddy current loss induced by domain wall motion in the steel plates is neglected in the loss calculation. Therefore, this paper investigates a simple numeric modelling method that takes account of the anomalous eddy current loss by modifying the conductivity of the steel plates. First, the method is verified by comparing the calculated iron loss of one sheet of steel plate with the measured data. The method is then applied to the loss calculation of reactors under inverter power supply. The differences between the calculated and measured results become smaller when the anomalous eddy current loss in the steel plates is taken into account.

To improve the comfort of hospital patients, we have developed a new open-type magnetically shielded room (MSR) for magnetic resonance imaging (MRI), constructed by stacking square cylinders composed of magnetic material on the inside and a conductive material on the outside. The magnetic cylinder shields against leakage of the magnetic field from the MRI, while the conductive outer cylinder prevents intrusion of the electromagnetic field from outside by waveguide attenuation. First, the optimal design of the magnetic cylinder was determined, using 3-D magnetic field analysis with a simple cubic MSR. Second, the validity of the analysis and the practical realization of the designed MSR were investigated using a small experimental model. Finally, from a design perspective and the standpoint of saving space, the optimal combination of electromagnetically shielded glass and conductive cylinders made of aluminum was studied by measuring the electromagnetic shielding effect. As the optimal design of an open-type MSR for an MRI, we have adopted a combination of single-layered electromagnetically shielded glass together with stacked cylinders. These cylinders are made of a square cylinder, 144 x 144 mm and 300 mm long, made of silicon steel (thickness t =1 mm) and divided into three parts along the axial direction, placed inside a second square cylinder made of aluminum, 150 x 150 mm and 300 mm long (t = 3 mm). This MSR construction technique creates an open, spacious feeling inside the facility and can be easily fabricated at low cost.

In order to investigate the magnetic property of material for scaled-down experiments on electric machines, numerical modeling on the power and loss densities of scaled-down laminated cores is studied in this paper. To reduce computational cost, the laminated core is modeled combining a 3D solid core analysis with a 1D steel plate analysis The hysteresis loss, eddy current loss, iron loss and power density of the laminated core are calculated using the electromagnetic field distribution result from the finite element analysis. The relationship between the increment of the power density and iron loss density versus the coil current density and frequency are investigated. The proposed method can be used to design and optimize the scaled-down electromagnetic devices with laminated cores.

Numerical modeling of iron loss considering the pinning and skin effect in silicon steel sheets is approached in this work. The pinning and skin effect are considered as the main factors of anomalous eddy current loss in silicon steel plates. The pinning is considered by implementing an initial flux distribution in the nonlinear eddy current finite element analysis, which includes the skin effect of flux. Thus the mutual coherence between pinning and skin effect can be achieved in the proposed numerical method. The hysteresis loss and eddy current loss are calculated using the obtained flux and eddy current distribution, while anomalous eddy current loss is spontaneously included in the calculation. The proposed method is applied to different grade non-oriented materials, and the calculated iron losses are compared with the measured data under various frequency.

In order to calculate the eddy current losses in the thin surface layer of a laminated core, in which the insulation between steel sheets is broken by a process of a polish, the leaf element is expanded into the edge finite element method. Several treatments for the leaf element are illustrated and the effectiveness is investigated by using a simple model. Then, the effect of the surface layer on the iron losses is discussed in an actual magnetic bearing system

In order to investigate an effective method for removing the residual magnetization in the steel structure of a building by a demagnetizing coil, a method for estimating the distribution of residual magnetization by means of a three-dimensional nonlinear eddy-current analysis was proposed. The tendency of the result obtained from the proposed method was in good agreement with the experimental result. Moreover, it was found that the demagnetizing coil should be set perpendicular to the steel structure.

In this paper, the method for modeling laminated core by a solid one is investigated. The method for taking into account eddy current in each steel plate used for laminating, which has already been developed in linear analysis, is expanded to nonlinear analysis by using one-dimensional finite-element analysis and the step-by-step method instead of the analytical solution and the phasor method, respectively. The effectiveness of the proposed method is shown by using a simple model.

Although the method of optimal design of magnetically shielded rooms (MSRs) for dc magnetic noise seems to be well established, that for ac magnetic noise at a frequency range from 0.01 to 1 Hz is also required for measurements of extremely weak magnetic fields such as biomagnetic measurements. However, such a method cannot easily be established due to eddy current effects. In order to establish an optimal design method of an MSR for low frequency ac magnetic noise, we have investigated an optimal structure of the magnetic and conductive layers using three-dimensional (3-D) linear magnetic field analysis taking into account eddy currents. We show why a structure which sandwiches the conductive layer between double magnetic layers gives high shielding effect. Moreover, we found that the spacing between the layers does not affect the shielding effect for ac magnetic noise. This is useful knowledge from the standpoint of MSR production

Low-cycle fatigue tests were carried out on spring steels at room temperature under a triangular strain wave form to obtain basic information about low-cycle fatigue behavior of springs.The results obtained are summarized as follows:(1) Cyclic softening behavior was observed under cyclic straining with plastic strain component.(2) Fatigue life properties and cyclic deformation properties of spring steel are the same as those which obtained by extrapolating properties of tempered steels for machine structural use to higher level of hardness.(3) Estimation method of low-cycle fatigue lives from tensile properties is proposed by modifying Manson's Universal Slope Method.(4) Total damage under incremental step tests becomes 1 to 1.8 at failure. Miner's cumulative rule is applicable to fatigue life estimation under straining of randon amplitudes.(5) Total damage is very small compared with 1 at failure, when stress controlled fatigue tests are carried out after a part of strain controlled test with plastic strain component. Cyclic softening by strain cycling promotes fatigue damage due to stress cycling.

To improve amenity for patients in hospitals, we have proposed an open-type magnetically shielded room (MSR) composed of magnetic and conductive cylinders for a magnetic resonance imaging (MRI). The design method of the opening part, that enables the leakage flux densities outside to be less than 0.5mT, is discussed taking account of magnetic saturation. First, the homogenization technique is applied to the design method of the opening part to reduce the number of elements for cylinders. Moreover, the magnetic characteristic of the opening part is assumed to be linear to obtain the ideal flux distribution. Next, the thickness of the magnetic cylinders is determined using the flux distribution in the real model reproduced from that in the homogeneous model so that the magnetic cylinders are not saturated. Finally, the design method is verified using the realized open-type MSR.

The method of coating the metallic implant made of paramagnetic materials with diamagnetic materials has been proposed to reduce the magnetic disturbance of metallic implants which causes artifact in magnetic resonance imaging. The optimal thicknesses of the diamagnetic coatings have been obtained for a straight cylindrical hip joint and an aneurysm clip by using the magnetic field analysis of the finite element method (FEM). Whereas in the manufacturing, with respect to the mechanical force of the diamagnetic material, etc., the new structure of dual-material model with diamagnetic material inside and paramagnetic material outside is considered better. In this paper, first the effectiveness of the structure of the dual-material model with actual diamagnetic material inside and paramagnetic material outside is investigated by using the FEM. Then optimal thicknesses of paramagnetic coating of two models are obtained. Finally the effectiveness of the dual-material model is verified by the experiment.