We propose an "extended Landau free energy model", which can deal with the complex microstructure of magnetic domain structure and explain the magnetization reversal process using modern data science. The energy landscape is newly drawn in the information space by persistent homology (PH), principal component analysis (PCA), and Ising model for the magnetic domain structure big data of YIG. The PH and PCA analyses yielded high-quality features that explain the microstructure of the magnetic domain structure and magnetization. The energy landscape shows that the mode of domain formation changes sequentially with the energy gradient: nucleation, elongation, branching and widening of magnetic domain. In addition, small energy barriers were visualized, suggesting the extraction of hidden features difficult to recognize by human eyes. This model allows us to establish a relationship between the microstructure of the magnetic domain and the magnetization reversal process based on the energy.

  Nanocrystalline Fe-Si-B-Nb-Cu alloy ribbons were annealed in the magnetic field of 400 kA/m applied in the width direction of the ribbon to investigate the magnetic properties and structure. Induced magnetic anisotropy was obtained at all temperatures in the heat treatment range from 460 ˚C to 660 ˚C. The best magnetic properties were obtained in the high frequency region above 100 kHz in the magnetic field heat treatment at 550 ˚C. The relative permeability μr at 500 kHz was 9000. Magnetic core loss was very low value of 180 kW/m³ at 100 kHz after magnetic field annealing. The generated crystals had the structure of αFe (Si) and the grain size was 13 nm. It was also found that the induced magnetic anisotropy imparted to the core by the magnetic field heat treatment at 550 ˚C was maintained in an environmental test.

  As a novel method of vibration power generation, we propose a mechanism that utilizes the stress-induced phase transformation of ferromagnetic superelastic alloys. Since the parent phase of Fe-Mn-Al-Ni alloy is ferromagnetic and the martensite phase is antiferromagnetic, there is a possibility that the magnetic changes associated with phase transformation can be converted into electric power by electromagnetic induction. Therefore, the characteristics of Fe-Mn-Al-Ni alloy were measured with and without stress. It was confirmed that the magnetic flux density decreased when a compressive stress of about 450 MPa was applied to the sample but returned to the original state by unloading. In the observed microstructure, martensite appeared when a compressive stress of about 450 MPa was applied to the parent phase, but disappeared when unloaded, and a reversible change confirmed that the phase returned to the parent phase again. An analysis of the martensite phase fraction revealed that a magnetization change was obtained in accordance with the phase fraction. EBSD measurements also identified the crystal structure as bcc in the parent phase and fcc for the surface undulations caused by strain. From these results, it was clarified that the phase transformation occurs due to stress.

  Bulk CoFe_2-xMn_xO₄ samples were synthesized by using a solid-phase method at 900 ℃. Though a CoFe₂O₄ sample (x = 0.0) exhibited a cubic structure, a tetragonal structure was observed in the samples with x ≧ 1.2 due to the Jahn-Teller effect of Mn³⁺ ions. The lattice constants at the a and c axes of the tetragonal structure increased and decreased, respectively, as x increased. Thus, the degree of tetragonal distortion (c/a) became larger as x increased. Although the saturation magnetization decreased as x increased, the Mn concentration dependence of coercivity exhibited a maximum of approximately 600 Oe at x = 1.6. This value was larger than that of the x = 0.0 sample. It is clear that the partial substitution of Mn³⁺ for Fe³⁺ in CoFe₂O₄ is effective for improving the coercivity of bulk samples due to the Jahn-Teller effect.

  Our laboratory reports the characteristics of an inverse-magnetostrictive effect-type vibration sensor that detects high frequency vibrations. Our sensor has a sensitivity of 0.61 mrad/ppm when static strain is applied to it. However, we estimate that our sensor can detect high frequency vibration without deterioration in sensitivity. Therefore, we conducted an experiment to evaluate the capability of the sensor for high-frequency vibration detection. As a result, it is revealed that the sensor has a sensitivity of 1.09 mrad/ppm at, in this paper, 20 kHz. It can be said that this inverse-magnetostrictive effect-type vibration sensor has high sensitivity even in high-frequency vibration.

  We have developed highly sensitive thin-film sensor using a straight coplanar line structure. High-frequency characteristics were analyzed to improve the sensor’s impedance and S-parameter in consideration of transmission line theory, ferromagnetic resonance, and the complex permeability of magnetic thin film. A finite element method analysis was performed on the coplanar line-type thin-film sensor. The calculated S-parameters and impedance were in rough agreement with the measured value including the FMR frequency. The attenuation of S₂₁ was caused by an impedance mismatch inside the sensor element.

  Soft magnetic composite (SMC) is expected to be a next-generation motor cores since it has three-dimensional magnetic isotropy and excellent high-frequency characteristics. However, a metal die is required to manufacture an SMC-based motor core, which results in high costs. In particular, in the prototype evaluation stage, the high costs prevent the use of various cut-and-try procedures. This paper investigates the characteristics of an SMC-based SR motor manufactured by using wire electric discharge machining from an SMC bulk body.

  A switched reluctance motor (SRM) has a simple and robust structure since it consists of only stator cores, rotor cores and windings wounded around the stator poles. In previous papers, axial-flux-type switched reluctance motors (AFSRMs) were prototyped and installed into the rear wheels of a compact electric vehicle (EV). Driving tests were conducted with success. However, there was a difference between the losses calculated by electromagnetic field analysis and those measured from the prototype AFSRM. In this paper, the causes of the difference are investigated in experiments.

  Switched reluctance motors (SRMs), which consist of only iron cores and windings, are attracting attention as simple, robust, and inexpensive variable-speed motors. This paper presents a novel transverse-flux-type switched reluctance motor (TFSRM), that has permanent magnets in the rotor cores for applying a reverse bias magnetic field. The proposed TFSRM can expand the operating point from the 1st quadrant into the 3rd quadrant on B-H characteristic by the reverse bias magnetic field, which increases both torque and efficiency. The advantages of the proposed TFSRM is proved by using a three-dimensional finite element method (3D-FEM).

  Non-oriented silicon steel, which is commonly used as motor cores, is less expensive and has high flux density, while large iron loss under high-frequency region is a problem for high-speed applications. In contrast, NANOMET^®, one of the nanocrystalline soft magnetic alloys, is expected to be a next-generation motor core material since it has high flux density as almost the same as the conventional non-oriented silicon steel and lower iron loss. In a previous paper, prototype tests of a switched reluctance (SR) motor made of NANOMET^® laminated core were conducted, and it was clear that the iron loss is significantly reduced and the efficiency is improved. This paper presents the prototype tests results of an inset permanent magnet (InPM) motor made of NANOMET® laminated core.

  Variable inductors, which consist of magnetic cores and a primary dc and secondary ac winding, can control the effective inductance of the secondary ac winding continuously with the primary dc current due to the magnetic saturation effect. Therefore, they can be applied as reactive power compensators in electric power systems. Variable inductors have desirable features such as a simple and robust structure, low cost, and high reliability. This paper presents a novel orthogonal-core-type variable inductor composed of two types of cores: a cut core and a laminated core. By combining them, the lamination stacking of both cores can be aligned with each other, thereby preventing short circuits between laminations. In this paper, the basic characteristics of the proposed variable inductor are investigated by both simulation and experiment.

  In some cases, magnetic gears are required to have an integer gear ratio based on the design requirements of the entire system, which results in a larger cogging torque in a high-speed rotor that causes vibration, noise, and startup error. The conventional skew rotor structure is a well-known countermeasure for cogging torque. However, it is complicated and difficult to assemble, especially in an axial-flux magnetic gear. To solve this problem, this paper presents a new type of pole-pieces called the unequal-width type. The validity of the proposed pole-pieces is proved both with the three-dimensional finite element method (3D-FEM) and in an experiment.

  Magnetic gears can transmit torque and change speed without any mechanical contacts. Therefore, vibration and acoustic noise are very low, and maintainability is high. Various kinds of magnetic gears have been proposed. Among them, the flux-modulated-type magnetic gear has a higher torque density and efficiency compared to conventional magnetic gears. Magnetic gears have a torque limiter function that allows them to step out and shut off power when overloaded. However, after stepping out, they cannot transmit power again unless the load torque is removed to some extent. This paper presents a novel induction/synchronous magnetic gear with a cage rotor bar. In addition, the prototype induction/synchronous magnetic gears are tested.

  Cooling fans are widely used in communication base station servers since they have a good balance between performance and cost. Cooling fan motors generally have an outer rotor structure because the fan can be directly mounted on the rotor. However, the outer-rotor-type motor has a low degree of freedom in design since the rotor core is thin. Therefore, most of the cooling fan motors have a surface permanent magnet (SPM) structure, and thus, it has ferrite magnets to prevent eddy current losses in magnets and cannot use a reluctance torque. This paper presents a novel outer-rotor-type high-speed PM motor with a segmented-shaped rotor. It can efficiently use reluctance torque in addition to magnet torque, and reduce eddy current loss in magnets even though the rotor has sintered Nd-Fe-B magnets. The usefulness of the proposed motor is proved by comparing it with an inset PM motor using a three-dimensional finite element method (3D-FEM) and prototype tests.

  In this paper, we designed an axial gap induction motor with a synchronous speed of 6000 rpm and a power density of more than 1 kW/L for drones by applying the proportional increment method, which decides the allocation of electric loading and magnetic loading, to the axial gap induction motor. The designed motor was analyzed by reluctance network analysis (RNA), which has a proven to be a useful method for analyzing induction motors. It was confirmed that an axial gap induction motor with a rotational speed of 5850 rpm and a power density of 1.39 kW/L could be designed.

  In the thin steel plate production line that is widely used for industrial products, contact conveyance is performed with rollers, but deterioration in the quality of the plates is a problem because scratches and irregularities occur on the surface of the plates. Therefore, non-contact magnetic levitation transfer of thin steel plates done using the attractive force of electromagnets has been proposed. So far, studies have been conducted on changing the bending angle and the conveying direction of thin steel plates with the magnetic levitation system that uses a horizontal positioning control system and the curved magnetic levitation system. Therefore, in this study, the distance between the centers of the horizontal electromagnets was changed. It was confirmed that the levitation performance was improved by increasing the distance between the centers of these electromagnets.

  Deterioration in the surface quality of steel plates is a problem because steel plates are transported by contact with a roller. A non-contact way of transporting steel plates using electromagnetic force has been proposed as a solution to these problems. In the previous system for magnetically levitating flexible steel plates, it was difficult to levitate thinner steel plates because of the deflection of the steel plates during levitation. To solve this problem, an edge-supported electromagnetic levitation system was proposed. This system is suitable for flexible steel plates and uses electromagnets installed in the horizontal direction. These electromagnets create tension force and suspension force that acts on the steel plates. It is possible to reduce the vibration of flexible steel plates because the tension force suppresses the deflection of the plates. In this paper, the characteristics of tension force on steel plates were investigated by electromagnetic field analysis. Moreover, the relationship between tension force and the reduction in vibration was investigated by experiments using a magnetic levitation system.

  In thin steel plate production lines, contact conveyance by rollers is used, so scratches on the surface of the plates and plating defects are problems. Therefore, non-contact magnetic levitation conveyance of thin steel plates using the attractive force of electromagnets has been proposed. We studied a magnetic levitation system for thin steel plates that uses both electromagnets and permanent magnets. While a thin steel plate was magnetically levitated, we investigated the effect of changing the position where tension is applied by a magnetic field from the horizontal direction on the placement of permanent magnets optimized by a genetic algorithm. From the result, we found that this change had a positive effect on levitation performance.

  Magnetic hyperthermia (MH) is a promising cancer therapy in which the heating temperature is expected to be a key determinant for its success. A therapeutic system with high-accuracy temperature control is of vital importance to avoid overheating in normal tissues surrounding a tumor. We previously developed a PID-based temperature control system and verified its validity in vitro. In this study, we validate our control system in vivo. First, we investigated both the improvement in heat generation by high-density Resovist^® (Ferucarbotran) and the optimal PID tuning method for the high-density Resovist^® in vitro. Next, we injected the high-density Resovist^® into mice and then performed PID-based temperature control in vivo. We demonstrate that by using our PID-based control system, it is possible to accurately control the therapeutic temperature (e.g., 50°C) in vivo with a standard deviation of 0.05°C in the steady-state. Our system has the potential to be used for MH either alone or together with other cancer treatment modalities for basic and clinical studies.