This paper describes the principle of AC resistance reduction using magnetic flux path control technology and its application. Applying magnetic flux path control technology to each coil in power transmission can improve the transmission efficiency and reduce the heat generation of the coil. By increasing the relative permeability of the magnetic composite material used for the magnetic flux path control technology from around 10, further improvement in efficiency and lower heat generation can be expected.

　The seas around Japan are rich in energy and mineral resources. Autonomous Underwater Vehicles (AUVs) that can move freely in the sea are effective for efficient investigation and utilization of these resources. AUVs are battery capacity-dependent and have a short time of activity, and must be pulled out of the sea each time they are recharged. This paper has examined the wireless power transfer technology in the sea for the efficient operation of AUVs. Experiments on wireless power transfer of high power in salt water have been conducted using a metal pressure vessel such as an AUV and transfer and receiving coils. We have shown that the proposal method has high degree of freedom of position and transfer efficiency. We also have studied the loss of wireless power transfer in the sea by simulation.

　The magnetic resonant wireless power transfer (WPT) system has been applied to electrically-driven mobile systems. Although the magnetic resonant WPT system is relatively robust against the misalignment between a transfer (Tx) coil and receiver (Rx) coil, it is difficult to keep the energy transfer when the relative position of the coils changes significantly. This will be a technical issue in the WPT for wearable and implantable devices. To solve this, WPT system with a function of human tracking has been proposed. A simple and fast algorithm using the gradient ascent to calculate optimal coil position based on the position and attitude of a Rx coil was developed. In this paper, basic principle of this system and evaluation results are introduced.

　In order to reduce the weight of the onbord pickup coil for the wireless power transfer for railway vehicles, the core shape of the pickup coil was optimized by multiobjective optimization using a genetic algorithm with topology optimization. The optimaization results provide a guideline for core reduction.

　Recent research and development activities for industrial application of inductive wireless power transfer are introduced. Rapid wireless charger for heavy duty vehicles, such as electric buses, with several tens or even a hundred kilowatt charging power, has been evaluated by public road operation. Recent wireless charger for automated guided vehicle can supply as large as 115 A at 24 V to reduce charging time and increase operation rate. Drone frustum wireless charging port will provide an easier automated drone operation for various industrial applications in near future.

　There are two types magnetic bearings in general, heteropolar-type magnetic bearing (Heteropolar-type MB) and homopolar-type magnetic bearing (Homopolar-type MB). For each type of magnetic bearing, it has its own disadvantage. Heteropolar-Type MB cost low because of the low usage of the magnet, but high iron loss decides it is difficult to be cooling down. Homopolar-type MB has a low iron loss and can be cooling down easily, but cost is high because of high usage of magnet and has a complex structure. In this paper, our research group focused on the problem and proposed a new Homopolar-Type MB structure unifying four C-shaped cores, which can suppress the iron loss with a low usage of magnet and can be cooling down easily. What’s more, we also considerate the influences by the change of the structure and proposed the optimal one. The excellent characters of the new type Homopolar-Type MB will be shown by 3D-FEA.

　This paper proposes small size angle sensor with Vernier pattern. Angle sensors play an important role in improving the functionality and workability of machine tools, industrial robots and mounting equipment. In that situation, angle sensors are required to be smaller, have higher accuracy and have functional safety. In response to these requirements, the aim is to develop a magnetic angle sensor with a 30 mm diameter, 19 bit resolution and redundant system by using a new mechanism. A rotor with a copper foil pattern and a stator with a meander coil pattern are prototyped and evaluated for angle error. As a result, 19 bit resolution and ± 1° angle error was obtained. This showed the possibility of further miniaturization and higher accuracy of the sensor by using the Vernier pattern.

　In order to develop a high-efficiency, low-loss, small, high-power, high-speed rotating motor, it is necessary to accurately measure the magnetic properties of electrical steel sheets under PWM excitation. A shunt resistor is generally used for measuring magnetic characteristics, but non-contact current measurement is required. However, iron cores are used in commercially available current measurement sensors, and it is necessary to consider the effects of core characteristics on high-frequency currents. The authors are focusing on Rogowski coils and developing small current / magnetic field sensors specialized for motor and electrical steel sheet evaluation. In this paper, we make a prototype of Rogowski coil, and report on the evaluation of basic electrical characteristics and the results of application to the measurement of magnetic characteristics of electrical steel sheets under sinusoidal excitation and PWM excitation.