Papers by Author: Takashi Todaka

Abstract: New Hybrid (HB) type Active Magnetic Bearing (AMB) is proposed in this paper. It is intended to apply to high speed turbo machinery. This magnetic bearing is easily controlled by a standard linear power amplifier. The proposed magnetic bearing is analyzed and designed through Finite Element Method (FEM). The designed characteristics are compared with the standard electro-magnet type magnetic bearing. The results show good characteristics of high efficiency, good dynamic property and easy manufacturing. The proposed magnetic bearing is fabricated and the simple tests are carried out.

Abstract: The martensitic transformations (MT) in austenite stainless steel (SUS316) were observed by using a sensitive Flux-Gate (FG) sensor just after the magnetizations by the permanent magnet in the terrestrial field. MT in the small deformation range less than 5% elongation, was visualized by the 2-dimensional profile at each position together with the profile of the thickness deformations with an accuracy of several microns. We found the local MT enhancements up to 400[nT] at the positions along the changes of the thickness. In this experiment, the observations of MT were able to avoid the effects of the external fields or of the ac fields which was generated by the gating function in the FG sensor.

Abstract: This paper presents three-dimensional boundary element analysis for coupled magnetic field and moving problem. The method is applied to improve transmission characteristics of a magnetic gear and the usefulness is demonstrated. The gear has two movers consisting of permanent magnets and they rotate with different velocity. The double gap moving problem is very time consuming, because the mesh has to be regenerated at each time step or prepared many patterns previously. The use of the boundary element method is suitable for this problem, because meshes are required around only surfaces of considering objects and the objects can be rotated any angle according to the moving simulation. In this paper, the technique to reduce unknown variables in the boundary element equations utilizing symmetrical construction is proposed.

Abstract: This paper presents vibration characteristics of a hybrid magnetic suspension model combining functions of a magnetic spring and a magnetic damper. Dynamic simulations considering the moving equation are performed with the step-by-step method based on the time-domain three-dimensional axisymmetric finite element method. The results demonstrate that the proposed hybrid model is effective to improve the performance to attenuate vibrations.

Abstract: This paper presents a magnetic coupling for a large-sized mixer, which is separated by a vessel wall. In order to improve the transmission-torque, the magnetic material attached magnetic-flux concentrated surface permanent magnet (MCSPM) arrangement is applied to the magnetic coupling and the construction is optimized. The results show that the MCSPM arrangement is very effective to improve the air-gap magnetic flux density and the transmission torque even quantity of very few permanent magnets.

Abstract: This paper presents results of magnetic characteristic analysis of a three-phase three-leg transformer model core. In the analysis, the finite element method considering vector magnetic properties expressed by the integration-type E&S modelling is used. In this research, in order to reduce total iron loss, local vector magnetic properties for some different T-jointed models are compared in detail. Distributions of maximum flux density, maximum field strength, axis ratio and iron loss depending on the T-jointed position are clarified.

Abstract: In general, the magnetic properties of electrical steel sheets are strongly influenced by mechanical stress. We have reported the measurement results of vector magnetic properties of a non-oriented electrical steel sheet under stress conditions. From these results, it is possible to control the vector magnetic property by applying local mechanical stress. Therefore, we next focus on an induction heating technique that applies mechanical stress in a non-oriented electrical steel sheet. It is very important to control the eddy current distribution inside the non-oriented electrical steel sheet. This paper presents a magnetic flux concentration plate structure to control the eddy current in steel sheets by using an induction heating technique. The magnetic flux concentration plate structure is investigated in a three-dimensional magnetic field analysis by the finite element method.

Abstract: Magnetizations and optical Faraday effects have been intensitvely studied in transparent glasses of almost all Lanthanide elements with 20mol % in pulsed magnetic fields up to 30T in the temperature range between 1.8K-RT. The internal effective fields were investigated by observing Verdet constants as a function of applied fields and as a function of magnetizations in the wavelength range between 400nm and 2600nm, intensively for Nd, Pr , Tb and Dy glasses respectively. We obtained a magnet of Dy (30mol%) glass with optically transparent and adhesive to conventional magnet at the room temperature. The magnetizations of these glasses showed paramagnetism at the room temerature and showed super-paramagnetim at cryogenic temperatures below 4.2K.

Abstract: Magnetic gears are a force transmitter consisting of permanent magnets. The mechanical input can be transmitted to an output shaft without contact by magnetic forces. The magnetic gears are not worn out because there is no friction. As a result, the running costs such as the maintenance fee can be suppressed and the resources can be saved. However, the transmission torques of the conventional magnetic gears, which have so far been developed, are very low. Besides, new structure models designed for high torque density need a lot of permanent magnets and multi-pole constructions. Those structures are complex and the manufacturing is difficult. In this research, we applied a flux concentration type surface permanent magnet arrangement to a surface permanent magnet type magnetic gear in order to improve the transmission torque and to reduce the amount of permanent magnets. The magnetic flux distribution, the gap flux density and the transmission torque of the developed new models are numerically analyzed by using the two-dimensional finite element method. In this paper, a permanent magnet structure optimized to reduce its amount and influence of the flux concentration type surface permanent magnet arrangement on the gap flux density distribution and transmission torque are reported.

Abstract: This paper presents distributions of the local vector magnetic properties in a three-phase induction motor model core measured with a new vector hysteresis sensor (V-H sensor). The exciting conditions used in the measurements were common sinusoidal and PWM excitation. The influence of the modulation frequency on vector magnetic properties is made clear.