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This paper presents the newly proposed heating method named “secondary current heating method” to reduce the iron loss on laminated electrical steel sheet cores for high-efficiency electrical motors. It is well known that the magnetic properties of electrical steel sheets, which are used for electrical motor cores, are deteriorated by the residual stress during manufacturing of the electrical motors, and then the iron loss of the laminated electrical steel sheet cores of the electrical motors increases inevitably. The newly proposed secondary current heating method can improve the magnetic properties on laminated electrical steel sheet cores and reduce the iron loss of them in the very short time in comparison with conventional methods. In this paper, the electromagnetic and heating characteristics of the specimens by the proposed method were confirmed, and then it was applied into the laminated cores to reduce iron loss.

This paper discusses mathematical properties of preconditioned finite-element matrices based on vector potential formulation (A method) and vector and scalar potential formulation (A-V method) for eddy-current problems. Numerical results show that A-V method with preconditioning is stable at all frequencies in contrast to A method. In this paper, this property is mathematically discussed by considering the diagonal scaling which is one of the simple preconditioning methods. In addition, regularization of A method is discussed.

Plastic deformation and fatigue damage, as the typical micro-damage caused by external loads such as earthquake and long-term process of liquid flow/stress, may seriously affect the material electromagnetic properties and shorten the structural lifespan. In this paper, first, the correlation between the material electromagnetic properties and the plastic deformation is investigated for a 304 austenitic stainless steel, and the mechanism is discussed based on the microstructure analysis. It is indicated that the increasing of plastic deformation leads to the material conductivity decrease which is considered to relate to the micro-defects including slip and twins, while the increasing of plastic deformation leads to the material magnetic property increase that has a close relationship with the martensitic transformation. Moreover, the influence of fatigue damage on the material electromagnetic properties and the microstructure analysis (slips, twins, and martensitic transformation) are also confirmed. Finally, the combined effect of plastic deformation and fatigue damage is also investigated through experiment. Besides, the difference of microstructures of three kinds of damage specimens is observed and analyzed.

金沢大学環日本海域環境研究センター生体機能計測研究部門, This paper describes the detection of conductive microbeads (PbSn) based on eddy-current testing (ECT) technique. High-frequency magnetic field applied to the conductive microbeads enables spin-valve giant magnetoresis-tance (SV-GMR) sensor to detect the magnetic fields occurred from eddy currents flowing in the conductive microbeads. In this paper, analysis of these magnetic fields by an analytical method is discussed and compared with experimental results. © 2005 IEEE.

金沢大学環日本海域環境研究センター生体機能計測研究部門, This paper proposes an eddy-current testing (ECT) probe composed of a spin-valve giant magnetoresistance (SV-GMR) sensor and a meander coil for the inspection of bare printed circuit board. The SV-GMR sensor serves as a magnetic sensor for the ECT probe to sense the variation of the magnetic field distribution occurred on the printed circuit board. The SV-GMR sensor is used specifically to detect the changing magnetic field distribution occurred at the defect point. The characteristics of the proposed probe are discussed in this paper. The comparisons of signal-to-noise ratios obtained from ECT probe with SV-GMR sensor and with solenoid coil verify that the applying of SV-GMR sensor to the ECT probe can improve the PCB inspection results.

金沢大学環日本海域環境研究センター生体機能計測研究部門, Various applications of a single-axis controlled repulsive-type magnetic bearing have been proposed earlier. However, most conventional systems are equipped with a set of passive magnetic bearings and an active magnetic bearing. In this paper a new repulsive-type conveyor system with many passive magnetic bearing pairs is proposed. This system enables an easy rotation with negligible friction and soft conveyance by radial stiffness between the rotor and the stator permanent magnets. This paper also reports a conveyance test using ellipse motion of each shaft.

This paper proposes a topology optimization method for a dielectric optical cloak that provides results that are perfectly free from intermediate materials, based on a level set boundary expression and the Finite Element Method. The finite element mesh is re-generated to fit the iso-surface of the level set function at every iterative step, to remove intermediate materials, so that the obtained optimal structure consists of only two materials, the dielectric material and air. First, the level set-based topology optimization is formulated and a topology optimization algorithm is proposed for the exact level set approach. Next, design requirements for the dielectric optimal cloak device are clarified and an objective functional for the design is formulated. The proposed method is then applied to a simple numerical problem to illustrate its effectiveness.

Electric city commuters are vehicles used for commuting from suburbs to inner cities and for movement within cities. Because of the short distances that they cover and their small battery size, such vehicles are beginning to attract attention. Generally, a high-performance permanent magnet (PM) composed of rare earth elements, such as neodymium and dysprosium, is used in the in-wheel PM synchronous motor (PMSM) of an electric city commuter. However, rising prices of rare earth elements and export restrictions on them are serious problems. Development of an in-wheel PMSM that does not utilize rare earth PMs is therefore highly desirable for electric city commuter vehicles. Accordingly, our research group has focused on a surface PM type axial gap structure that can achieve a high torque density and a short motor length in the axial direction. The designed motor structure with ferrite PMs replacing the rare earth PMs and the results of a three-dimensional finite element analysis are introduced in detail in this paper. Moreover, to examine the fundamental characteristics of the designed motor, a prototype is produced and tested.

This paper reports novel design method of waveguide slot array antenna with dielectric lenses by using the evolutionary optimization. We adopt the micro-genetic algorithm (MGA) with the real-coded gene as the optimization method and the finite-difference time-domain (FDTD) method to evaluate the objective function. The purpose of this study is to establish the design method of the above antenna by optimizing slot length and offset parameters. In the optimization of the antenna aperture distribution, it is shown that the optimized aperture field becomes sufficiently uniform, and the side-lobe levels (SLL) are improved in comparison with those of conventional antennas. Another optimization in which the objective function is evaluated by the array factor controls directly the side-lobe levels, to design low side-lobe antennas. By using the proposed method, the target antenna is optimized to satisfy the given SLL. It is confirmed that the proposed design method is a promising tool for designing the antennas loaded with dielectric materials.

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.

This paper describes topology optimization of electromagnetic systems using the multi-grid method. The present topology optimization employs uniform rectangular finite elements, in which the multi-grid method effectively works as a fast linear solver. Moreover, the present method uses a new optimization algorithm, based on the artificial immune systems paradigm, in which multi-level search is carried out

This paper discusses convergence of the incomplete Cholesky conjugate gradient method (ICCG) which solves edge-based finite-element equations for quasi-static electromagnetic fields. It has been observed in numerical computations that convergence of ICCG for the A-V method is faster than that for the A method. This phenomenon is found to be explained by the fact that, in the A-V method, the preconditioning eliminates the small singular values which deteriorate the condition number while they remain after the preconditioning in the case of the A method.

Native application of finite-element method (FEM) to the analysis of skin and proximity effects in multi-turn coils results in large equation systems, whose solution needs long computational time. This paper proposes a semi-analytical approach to overcome this problem. For the analysis of the proximity effect, the complex permeability of a round conducting wire immersed in uniform time-harmonic magnetic fields is represented in a closed form. Then, the homogenized complex permeability over the cross section of the multi-turn coil is analytically evaluated using the Ollendorff formula. The magnetoquasistatic problem is thus replaced by the magnetostatic one, in which the multi-turn coil is treated as a uniform material with the homogenized complex permeability. The skin effect is taken into consideration by introducing the corresponding impedance in the circuit equation. The proposed method is shown to give the impedance of multi-turn coils, which is in good agreement with that obtained by the conventional FEM as well as experiments.

This paper discusses robustness of the multigrid (MG) method against distortion of finite elements. The convergence of MG method becomes considerably worse as the finite elements become flat. It is shown that the smoother used in the MG method cannot effectively eliminate the high-frequency component of the residue for flat elements, and this gives rise to deterioration in the convergence. Moreover, the multigrid method with conjugate gradient (CG) smoother is shown to be more robust against mesh distortion than that with Gauss-Seidel smoother.

This paper describes a computer simulation study for estimating the multiple sources in the brain based on a three-dimensional measurement of magnetoencephalogram (3-D MEG). We propose a new source analysis method using spatio-temporal data of 3-D MEG and singular value decomposition analysis. The number of estimation sources is decided by the number of dominant singular values of spatio-temporal 3-D MEG data. The source localization is done as pattern matching by signal subspace of singular vectors and projection of an estimating source. In order to assess this algorithm, inverse calculation to the MEG model consisting of three sources located in the brain was performed. The results showed that three sources were dearly discriminated, and that the estimation error was less than 1 mm with SNR=5. The proposed method is useful for estimating multiple sources overlapping in time.

This paper proposes a stator design that consists of a combination of an alternate slot winding and dummy slots to minimize pulsating torque in surface-mounted permanent magnet synchronous motors. The alternate arrangement of winding coils is designed to eliminate a harmonic component of back electromotive force that gives rise to a harmonic component of pulsating torque. However, the non-uniform arrangement of slots decreases the frequency of the cogging torque by half and may aggravate torque pulsation. To compensate for the drawback or the decrease in the frequency of the cogging torque, dummy slots are introduced in the alternately slotted stator. A theoretical method is developed for the proposed stator combination. The proposed stator design is applied to a prototype in combination with other rotor magnet design techniques, such as magnet shifting and the adjustment of magnet width, to minimize pulsating torque. The results show that the designed motor reduces the ripple factor of the torque by approximately 30% relative to the original value. In addition, the proposed alternate slot winding is validated by comparing the design with equal slot-winding designs optimized through finite-element method analysis., IEEE Transactions on Magnetics, 51(6), 8202911; 2015

A time-domain boundary element method (TDBEM) provides one more possibility of potential numerical schemes for a time domain microwave simulation in addition to the finite difference time domain method. However, it is known that the TDBEM requires very large memory of order of 100 GB. As one of the solutions to effective memory reduction, this paper presents a 4-D domain decomposition method for the TDBEM. It is shown that the 4-D domain decomposition method of the TDBEM works well for the effective memory reduction in a particle accelerator wake field analysis.

This paper presents the topology optimization of a synchronous reluctance motor using the normalized Gaussian network. In the optimization, the average torque and iron loss are considered. In the resultant motor, the area of the rotor surface adjacent to the stator is found to be reduced when the weight for the iron loss is sufficiently large. On the other hand, large flux barriers are present in the rotor when the average torque is maximized without considering the iron loss.

This paper presents a topology optimization method for multimaterial models based on the normalized Gaussian network. In this method, one can determine optimal shapes of machines that are composed of various materials, such as iron, magnetic, and non-magnetic material. The present method is applied to the optimization of the average torque for interior permanent magnet motor to determine the distributions of magnetic core and flux barrier as well as magnets. The optimization results show that average torque can be improved using as small amount of magnet as possible. In addition, the characteristic of the present method is discussed in detail.

This paper presents parameter and topology optimizations of wideband antennas for microwave energy harvesters based on finite difference time-domain computations. The antenna shapes are optimized to reduce return losses in a specific frequency band using micro-genetic algorithm. The shape parameters of a two-arm planar spiral antenna are optimized. In addition, the topology optimization is performed using normalized Gaussian network, where spatial symmetries are assumed. It is shown that the return losses of the optimized antennas are

When a magnet generating highly homogeneous magnetic field is designed, a shimming is required. The shimming is usually performed so that the magnetic field only in the axis direction is compensated by iron pieces and/or coils. The compensation is commonly achieved by eliminating the coefficients of the spherical harmonics expansion of the magnetic field generated by the main magnet. Some papers showed the coefficients of the spherical harmonics expansion in only the z-direction for passive shimming. However, recently some magnets generate a magnetic field tilted from the z-axis, such as a magic-angle-spinning nuclear magnetic resonance/MRI. It is, therefore, necessary to eliminate the coefficients of the spherical harmonics expansion in the x- and y-direction.

This paper proposes a two-step method for topology optimization, in which after global search is performed by the on-off method, and then local search is carried out by the level set approach. The genetic and gradient-based algorithms are employed for the former and latter optimizations, respectively. This present method is applied to two numerical examples; topology optimizations of a magnetic shield system and interior permanent magnetic motor. It is shown that this present method can find solutions with better performances in comparison with the conventional on-off method.

International audience; This paper studies many Genetic Algorithm strategies to solve hard-constrained optimization problems. It investigates the role of various genetic operators to avoid premature convergence. In particular, an analysis of niching methods is carried out on a simple function to showadvantages and drawbacks of each of them. Comparisons are also performed on an original benchmark based on an electrode shape optimization technique coupled with a charge simulation method.

International audience; When the frequency of power converters increases, the wound components like inductors or transformers can no longer be supposed ideal. In this paper a formulation using 2D finite elements is presented for studying the high frequency coupled magnetic and electric field problem (eddy currents, proximity effects and stray capacitance). This formulation is based on a particular division of the 3D spatial domain which enables a 2D calculation.