Yasuo Okazaki

A large thermal elasticity of the ordered FeRh alloy film with sharp magnetic transition

Thermal elasticity and electrical resistivity with the magnetic phase transition were studied in FeRh alloy films prepared by ion-beam sputtering and subjected to post-annealing. Fe/sub 49.7/Rh/sub 50.3/ and Fe/sub 48.9/Rh/sub 51.1/ films deposited on conventional glass substrate and subjected to post-annealing at 600/spl deg/C for 90 min, respectively. Both films show a considerably sharp transition. In particular, Fe/sub 49.7/Rh/sub 50.3/ film exhibits small thermal hysteresis of about 20/spl deg/C width, which is only about 2 times over than that of bulk. Furthermore, a large abrupt thermal strain over 2/spl times/10/sup -3/ was observed with the magnetic transition. These results indicate that strictly controlled an equiatomic composition is an effective way to obtain the FeRh film with abrupt magnetic phase transition under low temperature and short time annealing.

Loss deterioration in amorphous cores for distribution transformers

Abstract The loss deterioration mechanism and building factor of amorphous cores for distribution transformers are discussed. The building factor (BF), the ratio of core loss to material loss, is analyzed by means of separating various loss deterioration factors. Among the five factors examined, two major factors, residual stress and interlaminar eddy currents in the core, are shown to be inevitable and deteriorate the core loss.

AC magnetic properties of electrical steel core under DC-biased magnetization

Abstract AC magnetic properties of electrical steel core under DC-biased magnetization have been measured and discussed. The biased magnetization Δ B depends not only on DC-biased field H DC but also on AC magnetization B m and the magnetic losses increase with Δ B at the same B m . We discuss this loss increase from the viewpoint of frequency dependence of losses.

Vibration analysis of a 3-phase model transformer core

Noise generated by a transformer core has been reduced by improving material and design, but further reduction is still required. To obtain the reduction, the comprehension of noise generating mechanism is important. It is achieved by detailed investigation of core vibration. A vibration measuring system utilizing a laser Doppler vibration meter was developed, and the vibration of a 3-phase 3-limb transformer core was measured. The following results were obtained. The vibration on the front and back of the core was two or three times higher than the other surfaces. The vibration occurred mainly in the limbs of the core, and the vibration direction was perpendicular to the core surface. The vibration waveforms were out of phase between the center limb and both of the side limbs. These results reveal that the principal cause of the vibration on the core was resonance. On the upper surface of the yoke, the vibration was higher in the right and left part and the middle. It is likely that the vibration on the right and left parts is derived from the magnetostriction of the side limbs. The vibration in the middle was considered to be generated by the magnetostriction under the rotational magnetization which occurs in the T-joint area of a 3-phase transformer core.

Harmonic analysis of AC magnetostriction measurements under non-sinusoidal excitation

A new system for analyzing ac magnetostriction of electrical steel sheets, has been developed. This system has the following advantages: (a) AC magnetostriction waveforms can be precisely measured up to 4 kHz, and analyzed to harmonic components. (b) Non-sinusoidal flux density can be excited to simulate the distorted waveform in an actual transformer core.

Development of real-time and highly accurate wireless motion capture system utilizing soft magnetic core

Highly accurate wireless motion capture system using LC resonant magnetic marker has been developed. The marker consists of soft magnetic core with wound coil and a chip capacitor without battery or electric wires, driven wirelessly by the action of electromagnetic induction. The system realized the position accuracy is less than 1 mm within the space of 150 mm from the pickup coil array. Compared with dc magnetic system, the proposed system is applicable for precision motion-capturing under optically isolated space without magnetic shielding because the system is not influenced very much by the earth field noise.

Wireless Magnetic Motion Capture System—Compensatory Tracking of Positional Error Caused by Mutual Inductance

A wireless magnetic motion capture system using an LC resonant magnetic marker was developed and has been studied. The positional error of the system caused by mutual inductance between the exciting coil and the LC marker was examined. It has been found that the impedance change of the exciting coil due to a resonance of the LC marker perturbs the strength of the magnetic field which is used for marker excitation. The more a marker approaches the exciting coil, the larger it becomes. This fluctuation induces an error in the marker signal which is measured by the pickup coils and is necessary for positional calculation. Then, the compensatory process in consideration of the mutual inductance has been employed for positional calculation in order to improve the positional accuracy. From the compensation, the absolute positional accuracy is less than 2 mm within 140 mm of the pickup coil array

Wireless Magnetic Motion Capture System for Multi-Marker Detection

A wireless multi-motion capture system using five LC resonant magnetic markers has been developed and is demonstrated. Each marker has an individual resonant frequency, 157, 201, 273, 323, and 440 kHz, respectively. A new measuring technique is applied in order to reduce the acquisition time. In this new technique the markers are excited by a superposed wave corresponding to the all resonant frequencies, while the voltage signals induced through pick-up coils are separated in a frequency spectrum by FFT analysis. Regardless of the number of markers, the voltage amplitude for each resonant frequency can be easily obtained simultaneously and thus the proposed system can detect multiple markers. The positional accuracy for five markers is less than 2 mm within 100 mm of the pick-up coil array

Magnetic shielding by soft magnetic materials in alternating magnetic field

Abstract The magnetic shielding effect of an alternating field up to 20 kHz was examined in 3% Si steel sheets and amorphous ribbons. Not only the permeability but also the domain configuration was found to affect the shielding effects. The annealed Fe-based amorphous shield without field showed exceedingly high shielding effectiveness for higher frequencies.

Magnetic properties of electrophoretic deposited ferrite particulate films

To fabricate ferrite films, electrophoretic deposition (EPD) of magnetite fine particles, synthesized by Fe/sup 2+//spl rarr/Fe/sup 3+/ oxidation, in water dispersion mixtures was carried out at room temperature. It is shown that densely packed ferrite films with a thickness of 9.2 /spl mu/m can be deposited via EPD from magnetite fine particles with a size of 10-30 nm onto a copper substrate. The film exhibited soft magnetic properties almost the same as raw magnetite particles.