Search

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.

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.

To investigate the noise reduction of an electrical machine, the deformation and vibration of the cores are evaluated by using the coupled magnetic and mechanical analyses [1]. In these analyses, the local force calculated by using the flux distribution obtained from the magnetic field analysis is required in the mechanical analysis. In the local force calculation [2], the Maxwell stress tensor is usually used. The Maxwell stress tensors are often represented by the Minkowski and Chu models with linear and nonlinear energy expressions, respectively. In the nonlinear magnetic field analysis, the volume forces, which move the magnetic bodies, obtained from both models coincide with each other, whereas their local forces, which deform the magnetic bodies, are different. Therefore, more investigation is required to clarify the suitable expression of the Maxwell stress tensor. In this paper, to clarify the proper expression of the Maxwell stress tensor for the local force calculation of a nonlinear magnetic body, the Maxwell stress tensors are derived from the Fleming’s left hand rule because the volume current density can be used to determine the magnetization in the nonlinear magnetic body. As a result, a new Maxwell stress tensor is derived. The surface force obtained from the new Maxwell stress tensor is compared with those obtained from the ordinary Minkowski and Chu models, and the equivalent magnetizing current method [3] to show the effectiveness and validity of the proposed Maxwell stress tensor.

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.

When a magnetically shielded room (MSR) to shield leakage fluxes of electric machines is designed by using magnetic field analysis, it is difficult to represent the leakage magnetic field of an electric machine accurately. In this paper, a method of modeling it using a simple solid model with multiple magnetization vectors is proposed. In this method, the magnetization vectors are determined by an inverse technique to represent a real leakage flux distribution. First, the proposed method is explained and verified using a simple 2-D linear magnetostatic one-phase transformer model. Then, the method is applied to a 3-D model and the effect of selected measured surface on representation of leakage flux is investigated. Finally, an experimental verification is carried out. It is shown that the proposed method can represent the leakage magnetic field with small number of magnetizations. The leakage flux only in the region behind the measured surface can be represented, and it is verified by experiment. Moreover, the shielding performance of MSR can be evaluated by using the proposed solid model with suitable permeability.

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.

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 standard of Japan Electronics and Information Technology Industries Association EM-4502, in which the shielding factor (SFo) of magnetically shielded rooms (MSRs) for the uniform magnetic field can be estimated using coils within 10% error for the extremely low-frequency region of

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.

To develop further higher efficiency induction motors, the reduction of the stray load losses, which are the increase of loss in the load condition relative to that in no-load test condition, should be investigated by using the magnetic field analysis. However, the calculation of the stray load losses using the magnetic field analysis requires high computation cost due to consideration of the slot harmonics in the flux densities, and the large time constant. In this paper, to evaluate the stray load losses in the cores and the secondary conductors of induction motors using the two-dimensional (2-D) magnetic field analysis within practical computation cost, some useful techniques, to mention a few, the nonconforming technique and the simplified time-periodic explicit error correction method, are introduced. Then, the stray load loss of an actual induction motor without skew is evaluated by the developed 2-D magnetic field analysis. It is shown that the calculated no-load losses are almost the same with the measured one, and the stray load losses in the stator core and secondary conductors due to the harmonic components in the secondary current are large.

In this paper, the play model and the free energy model are applied to represent the hysteretic properties of non-oriented steel plates and compared. The ac symmetric B-H loops and PWM minor loops are represented by both methods and the results are compared with the measured ones. Small minor loops representation is found not complete with both methods. However, in play model, it can be easily improved by increasing the number of hysterons. In the spring model, the way to improve the minor loop representation accuracy is under discussion, whereas its identification is simpler than play model as less parameters are required.

This paper proposes a model order reduction (MOR) technique based on the proper orthogonal decomposition method, to speed up nonlinear magnetostatic analysis of inverter-driven electrical machines. In this method, a set of solutions of the original problem is obtained at relatively large intervals, covering the whole cycle. The solutions, known as snapshots, are then used for the linearization as well as the order reduction of the matrices at the intervals. The reduced linearized matrices are then interpolated for time instance within the strides, supplemented with initial guess obtained by interpolating the snapshots. The method enormously reduces the number of matrix projections. Furthermore, it limits the number of the Newton-Raphson iteration to one. The results of applying the method on the magnetostatic analysis of interior permanent magnet motor shows that the method is several time faster than the conventional MOR with almost the same accuracy.

Excess loss evaluation in SiFe electrical steel sheets is important for accurate iron loss prediction of electrical machines, especially under high frequencies. In this paper, a numerical excess loss estimation method of SiFe sheets considering the domain wall bowing caused by pinning sites is proposed. An equivalent magnetic field representing the pinning effect is implemented into a general nonlinear eddy current finite element analysis. The hysteresis and eddy current losses are calculated using the flux and eddy current distributions obtained from the proposed analysis directly. The proposed method is applied to two different grades SiFe sheets first. The calculated iron losses under various frequencies in one sheet are compared with catalogue data and less than 2% deviation can be achieved.

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

To establish a large-scale magnetic field analysis, the magnetic field analysis with the voxel modeling is investigated. To reduce the number of elements, the nonconforming technique is introduced. The accuracy of flux densities, eddy current densities, and forces obtained from the nonconforming voxel modeling is verified by comparing with those obtained from the ordinary voxel modeling in a simple 2-D model. Moreover, the proposed method is applied to a 3-D eddy current model as well as to a 2-D nonlinear IPM motor model. It is shown that the results obtained from the proposed method sometimes converge to true values slowly, whereas it provides acceptable results.

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.

To shield environmental magnetic noise, magnetically shielded rooms (MSRs) made of ferromagnetic materials are used for biomagnetic measurements. The shielding performances of MSRs are usually represented by the shielding factor, SF. The source of environmental noise is far away from the MSR, so that almost uniform magnetic field is applied to the MSR. Therefore, the shielding factor SF0 for uniform magnetic field needs to be evaluated. To evaluate SF at a construction site, magnetic noise is applied to the MSR by coils. However, the magnetic noise generated by coils is not uniform, and SFs depend on the sizes and positions of the coils and are not unique for the same MSR. Therefore, standardization of a method to evaluate SF0 accurately using coils is being discussed by the Japan Electronics and Information Technology Industries Association (JEITA). We discuss here a method for estimating the SF0s of MSRs by placing a smaller coil near the MSR under the condition with very low frequency, in which the eddy current effect can be neglected, using both 3D linear and nonlinear magnetostatic field analyses and measurements. A method to estimate SF0s by extrapolation using simple numerical expressions representing the relation between the SF and the size and the position of the coil is proposed in the 3D linear magnetostatic analysis. The proposed method is applied to an experiment with a single-layered MSR under ideal conditions. Namely, MSR is placed in a spacious building so that the experiment is not affected by the steel frames and the reinforcing bars of the building. Moreover, the door of MSR does not affect its SFs. In these conditions, we were able to accurately estimate SF0s in the experiment.

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.

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 shield the environmental magnetic noises, magnetically shielded rooms (MSRs) are used for biomagnetic measurements, etc. The sources of environmental noises are placed far away from the MSR, in such way that almost uniform magnetic fluxes are applied to the MSR. Therefore, to specify the shielding performance of MSR, the shielding factor SF? for the uniform magnetic flux density should be evaluated. To evaluate SF?, in a construction site, the magnetic noise is applied by coils. However, SF's depend on the size and position of the coil. Therefore, to accomplish a standardization of the method for evaluating SF?, accurately, by coils, the method for estimating SF?'s by smaller coil placed near MSR is being investigated in JEITA (Japan Electronics and Information Technology Industries Association). In JEITA, we have already proposed the method of estimating SF?'s by the extrapolation using simple numerical expressions representing the relations between the SF and the size, position of coil. The proposed method was verified by the actual single-layered MSR using coils placed on double sides. In this paper, the method of estimating SF? of the double-layered MSR, using coils placed only on one side of MSR and taking account of door effect, is investigated using 3D nonlinear magnetic field analysis and measurements. By using the analysis, it is shown that the single coil should be set in front of the door. Moreover, SF?'s estimated by using the measured data with the optimal coil setting can almost represent the tendencies of the true SF?.

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 design a new model to reduce the noise of a reactor under inverter power supply, the cause of noise should be investigated. We carry out vibration analysis of a single phase of a reactor while considering electromagnetism and magnetostriction to clarify the mechanism of noise generation in the reactor. In this analysis, magnetostriction is modeled three-dimensionally with equivalent nodal forces. First, the nodal forces in the cores of reactor due to the electromagetism and magnetostriction are calculated using the flux distribution obtained from magnetic field analysis. To determine the dominant cause of noise, the spatial distributions of displacements generated by both nodal forces are then obtained by static structure analysis and they are compared in detail. Moreover, the actual movements of the cores are calculated by vibration analysis. Finally, the effect of the hardness of the cores on noise generation is calculated and measured. It is shown that the hardness of the insulator inserted in gaps between cores affects the vibration and it seems to have an optimal value. Moreover, the analyzed results are proved by measurement.

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.

To evaluate eddy current losses of permanent magnets (PMs) in motors driven by inverter power supplies in less computation time, we propose the coupled 2-D analysis of the motor and 3-D eddy current analysis of only the PM. In the proposed method, we carry out 2-D nonlinear magnetostatic analysis of the PM motor by rotating the rotor. We then perform 3-D eddy current analysis of only the PM using the temporally varying flux distributions in the PM obtained from the 2-D analysis. For 3-D eddy current analysis, we investigate methods that do and do not consider the compensation field generated by eddy currents. Moreover, for the case in which the compensation field is considered, we demonstrate the method of considering the reluctance of the motor core by the equivalent gap. Finally, we verify the proposed method by comparing results obtained using the proposed method and results obtained by full 3-D analysis for an interior PM motor. We show that the eddy current loss can be estimated in 1/15 of the computation time required for full 3-D analysis when the proposed method takes both the compensation field and the reluctance of motor core into account.

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.

Exposure to man-made electromagnetic fields has increased over the past century. As a result of exposure to these fields, concerns have been raised regarding the relationship between electromagnetic fields and human health. Interest in the biological and health effects of intermediate frequency (IF) magnetic fields has grown recently because of the increase in public concern. In order to investigate whether IF magnetic fields have biological effects, we have developed a 20 kHz (IF) magnetic field exposure system for in vivo studies. The exposure facility was designed to study the biological effects of IF magnetic field on laboratory animals. The facility consists of a 9 m × 9 m × 5 m high room containing seven separate rooms including a 5.3 m × 4.5 m × 3 m high specific-pathogen free exposure room. The dimensions of the exposure system are 1.6 m × 1.6 m × 1.616 m high located inside this exposure room. The system is designed to provide magnetic fields up to 200 µT at 20 kHz with the uniformity within ±5% over the space occupied by animals. After constructing the facility, performance tests were carried out. As a result, it was confirmed that our facility met requirements for evaluation of the biological effects of IF magnetic field on small animal experiments. In this paper, the design, construction, and results of evaluation of an animal exposure facility for the in vivo biological effects of an IF magnetic field are described. Bioelectromagnetics 30:36–44, 2009. © 2008 Wiley-Liss, Inc.

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.

To shield magnetic noise, magnetically shielded rooms (MSR) are used for biomagnetic measurements, etc. To evaluate the shielding factor SF (SF=B n / B s , B n and B s are the flux densities at the center of the room without and with MSR, respectively), the magnetic noise is applied by coils. However, SF depends on the size and position of the coils, so the standard of JEITA (Japan Electronics and Information Technology Industries Association) EM-4502, in which the shielding factor (SF o ) of MSR for the uniform magnetic field in the extremely low-frequency region of less than 1 Hz without eddy current effect is estimated using coils within 10% error [1-2], has been already published [3]. Currently, a standard method for the low-frequency region, e.g. 50 Hz, with eddy current effect is being discussed. In a previous work [4], it was shown that the coil should be placed in front of the door of MSR and a much larger estimation error than 10% should be permitted for practical use in the standard to estimate SF o for the low-frequency region.

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.

A method for analyzing three-dimensional (3-D) magnetic field in a model including moving parts, such as linear actuator, was developed by using a nonconforming mesh with edge elements. In this method, the meshes for moving and nonmoving parts are generated individually, and they are overlapped together at an arbitrary position. Then, the magnetic field analysis is carried out by using the nonconforming technique with interpolation. It is shown that the proposed method is useful for a dynamic analysis of a 3-D actuator model.

A highly practical method for evaluating magnetic disturbance due to adjacent buildings for the design of a magnetic testing site with nearly zero magnetic field was proposed. A modeling technique for complicatedly distributed magnetic materials in buildings was verified by the measurement using an actually constructed building. Moreover, a convenient formula was conceived, in which a building is replaced simply into a brick magnetic body and the flux distribution due to its magnetization is calculated analytically. It was shown that the proposed formula is useful for investigating the effect of the positions of buildings for additional construction on the magnetic disturbance.

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.

Methods of analyzing three-dimensional magnetic fields using nonconforming mesh with edge elements are investigated. Two kinds of interpolation techniques at the nonconforming surface, of which the tangential components of the potential are discontinuous and continuous, are proposed. Both methods are compared with each other using a simple model from a viewpoint of the accuracy. It is shown that the tangential components of the potential should be continuous at the nonconforming surface.

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

In order to improve the design efficiency of multilayer-type magnetically shielded rooms (MSRs), the magnetic property of mu-metal in low magnetic fields was investigated. The shielding effects (SEs) of multilayered cylinders composed of mu-metal were measured by using a superconducting quantum interference device (SQUID) magnetometer. Then, the incremental permeability of mu-metal was estimated by numerical analysis. It is shown that the incremental permeability becomes constant against the biasing flux density, and is a function of only the magnetic fluctuations, when the biasing flux density is under 0.1 T, which is less than that of the typical MSR set in the geomagnetism.

In the magnetic field analysis with the voxel modelling, to reduce the error due to the rough shape approximation, the nonconforming mesh is introduced. The flux density and the force obtained from the voxel modelling with nonconforming mesh are compared with those obtained from the ordinary voxel modelling in a simple 2D model. It is shown that the nonconforming mesh is effective because the number of elements can be greatly reduced compared with that for the conforming mesh with the same accuracy.

At the Japan Aerospace Exploration Agency, a zero magnetic field is required to test the magnetic characteristics of spacecrafts, satellites and to calibrate magnetometers. This zero-magnetic field is realized by means of a three-axis coil system which can cancel the uniform earth's magnetic field, but cannot cancel magnetic disturbance because of no magnetically shielded room. Therefore, the magnetic disturbance within and in the vicinity of the zero-magnetic field of a Spacecraft Magnetic Test Site (SMTS) is investigated by comparing the results of three-dimensional (3-D) finite-element analysis with measurements. Distributions of the magnetic disturbance due to three hemispherical objects-the roof, the foundation made of concrete, and the hole in the ground for the SMTS building-are analyzed and compared with those measured by a proton magnetometer. Consequently, it is shown that the hemispherical hole in the ground for the SMTS building, which has weak magnetism and is a little higher than that of concrete, generates a weak magnetic disturbance in the zero-magnetic field of the SMTS

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.