Norihiko Hamada

Development of a Co-free NdFeB anisotropic bonded magnet produced from the d-HDDR processed powder

The NdFeB anisotropic bonded magnet produced by the HDDR method, which was developed in 1990, has not found general popularity due to its high cost and low serviceable temperature of 353 K. The authors have developed a new production method that overcomes these barriers to decrease the cost and increase the serviceable temperature. The use of the dynamic HDDR (d-HDDR) process eliminates the need for Co, thus greatly reducing the production cost of NdFeB anisotropic bonded magnets with a (BH) max of 159 kJ/m/sup 3/. The anisotropy of the NdFeB magnetic powder is induced by the control of the reaction rate of the NdFeB alloy and hydrogen, by controlling the hydrogen pressure in the HDDR process. The serviceable temperature is increased by the addition of Dy after the application of the d-HDDR method. An increase in intrinsic coercivity, iHc, from 1.12 MA/m to 1.56 MA/m, corresponds to a proportional increase in the serviceable temperature to 413 K.

Development of Nd-Fe-B anisotropic bonded magnet with 27 MGOe

The maximum energy product of bonded magnets is advancing every year. The highest maximum energy product of any bonded magnet achieved is 25 MGOe (200 kJ/m/sup 3/) in the Nd-Fe-B system by d-HDDR treatment. There is a great demand for even higher energy bonded magnets with the desire for smaller, more efficient electric motors. Bonded magnets made from d-HDDR treated anisotropic magnet powder have low squareness due to low squareness of the powder. The authors developed a method to increase squareness of d-HDDR powder, and succeeded in developing the worlds highest energy bonded magnet with 26.6 MGOe (213 kJ/m/sup 3/). This was achieved through Dy-diffusion treatment followed by d-HDDR treatment, as well as an increase in the density of the bonded magnet. This magnet has little aging loss after being held at 393 K for 878 h.

Development of anisotropic bonded magnet applied to 150/spl deg/C use

An anisotropic bonded magnet (MAGFINE25), is about to be applied to dc motors for automobile use such as power seat motors and window motors. These dc motors have achieved a 50% reduction in weight and in volume, with the heat resistance of 120/spl deg/C. However, the heat resistance of 150/spl deg/C is required for motors near the engine, such as fan motors and wiper motors. We improved the heat resistance of the bonded magnet by the addition of Dy element to magnet powder, and succeeded in developing a bonded magnet with the heat resistance of 150/spl deg/C.

Auditory evoked field measurement using magneto-impedance sensors

The magnetic field of the human brain is extremely weak, and it is mostly measured and monitored in the magnetoencephalography method using superconducting quantum interference devices. In this study, in order to measure the weak magnetic field of the brain, we constructed a Magneto-Impedance sensor (MI sensor) system that can cancel out the background noise without any magnetic shield. Based on our previous studies of brain wave measurements, we used two MI sensors in this system for monitoring both cerebral hemispheres. In this study, we recorded and compared the auditory evoked field signals of the subject, including the N100 (or N1) and the P300 (or P3) brain waves. The results suggest that the MI sensor can be applied to brain activity measurement.

Highly Sensitive CMOS Magnetoimpedance Sensor Using Miniature Multi-Core Head Based on Amorphous Wire

We newly report a highly sensitive CMOS magnetoimpedance (MI) sensor based on a miniature multi-core head (~2 mm2). The miniature head consists of 13 μm diameter amorphous wires and pick-up coils totaling 250 turns. In this paper, the sensitivity and noise level of the prototype sensor is investigated. We showed that the noise floor of the prototype sensor is lower than 100 pT/Hz1/2 for the frequency range of 20-500 Hz. We estimated the peak-induced voltage at the pick-up coil on the basis of off-diagonal impedance theory. The results obtained in this paper will be useful for designing a highly sensitive MI sensor based on a miniature multi-core head with a CMOS pulse circuit.

Development of anisotropic bonded magnet with heat resistance

The Nd-Fe-B anisotropic magnet powder was prepared through d-HDDR (hydrogenation, disproportionation, desorption, recombination) treatment. The powder mixed with fine Dy-Fe alloy hydride is heat treated in vacuum (Dy diffusion treatment). The magnet powder properties are measured by vibrating sample magnetometer (VSM) after alignment. Particle size is measured by laser diffraction method. The magnet properties of anisotropic bonded magnets are measured using BH tracer. Flux of the radially aligned ring-shape bonded magnet is measured by flux meter.

Development of NdFeB anisotropic bonded magnet with 27MGOe

In this paper we present the development of the worlds highest energy bonded magnet with 27MGOe (213Jm/sup -3/) by the improvement of the AAM process.

Development of high sensitivity multi core MI element

MI sensor is a magnetic sensor based on the Magneto Impedance (MI) effect discovered by Mori et al. in 1993[1]. A small and highly sensitive magnetic sensor (AMI 306) based on above MI effect and used as an electromagnetic compass mainly in mobile phones and smart phones has been developed and commercialized by AICHI MICRO INTELLIGENT[2]. According to theoretical analysis, the MI sensor is foreseen to show the fT/√Hz level of noise density[3], and its performance would even be equal to SQUID. MI element (AMI306) with pickup coil fabricated by a plating process is used in electromagnetic compasses. Although it shows magnetic resolution in the micro Tesla order[4], higher performance in sensitivity and noise level is required.

Development of highly-sensitive mi sensor used for foreign particles inspection

Depending on applications, there were some problems that the sensor output will be easily saturated with geomagnetism owning to its high sensitivity. Therefore we present the design of MI sensor which is not saturated with geomagnetism, while retaining low noise density of 10 pT/Hz0.5 at 10 Hz . Then we verify that the particle with a size of 0.3 mm would be enough detected. In our presentation, we also introduce a demo unit for foreign body detection.

Development of BLDC motor with 3 times output

BLDC motors with high output are required. In these motors, some segment-shaped sintered ferrites with 4 MGOe were used. It is difficult to enhance output while keeping the same body size. Recently, a high energy anisotropic bonded magnet with 23 MGOe, called MAGFlNE, has entered the market. However, cogging torque in DC brushless motors generally increases as motor torque increases. Moreover, the increase in cogging torque in radially aligned magnets is extreme. We have solved this problem by developing a hybrid alignment using one ring-shaped MAGFINE25, and succeeded in developing a BLDC motor with 3 times greater output than current BLDC motors.