Michio Hasegawa

Study of high power planar inductor

A method for planar inductor design has been established on the basis of a discussion of the magnetic flux density distribution. Planar inductors for miniature DC-DC converters have been developed using this design method. This converter is much smaller and thinner than conventional ones, and has an output power/volume ratio of 1.7 W/cc. A spiral coil with a very small distance between the conductors and a low loss magnetic sheet are required for the development of high Q planar inductors. >

Magnetostriction and magnetic core loss at high frequency in amorphous Fe‐Nb‐Si‐B alloys

Magnetostriction and magnetic core loss at high frequency up to 100 kHz were investigated together with crystallization temperature, saturation magnetization, and magnetic permeability for amorphous (Fe1−xNbx)zSi88−zB12 alloys. Crystallization temperature significantly rises with Nb addition, particularly in the high z region. Magnetostriction decreases with increasing Nb content and z value. Magnetic core loss decreases and magnetic permeability increases with decreasing magnetostriction. Magnetic core loss reduction due to Nb addition were analyzed to be mainly attributed to domain width reduction through the decrease of magnetostriction.

Magnetic properties of amorphous Fe-Cr-Si-B alloys

Substitution of Fe with Cr in amorphous (Fe 1-x Cr x ) z (Si 0.3 B 0.7 ) 100-z ( x=0\sim0.10, z=75\sim83 ) alloys was investigated. Cr decreases Curie temperature quite greatly, but it also slightly increases crystallization temperature. Cr improves soft magnetic properties, namely, it decreases coercive force and magnetic core loss, and increases initial magnetic permeability. An amorphous alloy, with (Fe 0.925 Cr 0.075 ) 83 Si 5 B 12 composition, is obtained which has superior soft magnetic properties comparable to Permalloy or Ferrites: coercive force 0.024Oe, initial permeability at 1 kHz 12,000 and magnetic core loss at f = 20 kHz and B= 3 kG 140 mW/cm3. The above magnetic properties can be achieved by annealing at 400°C for 15 minutes without magnetic field.

Low magnetostrictive amorphous Fe‐Nb‐Si‐B alloys

Magnetostriction and magnetic core loss at high frequency up to 50 kHz were investigated together with saturation magnetization, Curie temperature, and crystallization temperature for amorphous (Fe1−xNbx)83Si5B12 alloys. Magnetostriction decreases with Nb content, and becomes 1×10−6 for x=0.115. Magnetostriction was shown not to be proportional to the square of saturation magnetization unlike many Fe‐based amorphous alloys. Iron loss at high frequency was measured on the core before and after resin molding. Iron loss increase due to resin molding was reduced as magnetostriction decreases. The incremental rate of the loss due to resin molding was increased as frequency decreases.

Magnetostriction and related properties in amorphous Fe-Nb-Si-B alloys

Abstract A study was carried out to get Fe-based amorphous alloys with low magnetostriction. Magnetostriction (γ s ) was measured as functions of Nb and Fe content in Fe-Nb-Si-B amorphous alloys. It was found that Nb decreases γ s , particularly in Fe-rich region.

Substituted Amorphous Co–Fe–Si–B Alloys

The substitution effects of Cr, Nb and a commercial 42 at.% Nb–Ni on the magnetic properties of amorphous (Co–Fe)75Si10B15 alloys are studied. It is shown that substitutions of these metals increase the crystallization temperature. hardness and electrical resistivity, and improve soft magnetic properties. It is also shown that the appropriate Fe and 42 at.% Nb–Ni contents are beneficial for the improvement of the thermal stability of coercive force and of effective permeability.

Fabrication of an Amorphous Composite Alloy

An amorphous composite alloy connected with two different amorphous alloys is fabricated using a twin roll method. Crystallization temperature and the connected boundary for the amorphous composite alloy are investigated. The amorphous composite alloy thus obtained is verified to have a sharp connected boundary.

Influence of surface state on the magnetic core loss at high frequency in amorphous Fe-based alloys with low magnetostriction

Magnetic core losses at high frequency up to 100 kHz were investigated on low magnetostrictive amorphous Fe-based alloys annealed in various atmospheres (nitrogen, air and moderate vacuum). The lowest magnetic core loss was attained by the annealing in nitrogen atmosphere. The Auger electron spectroscopy showed oxidation for all the samples annealed at various atmospheres mentioned above, but oxygen concentration for the sample annealed in nitrogen atmosphere sharply drops at about 1000 A depth from the surface, which is quite different from the results of the samples annealed in air and moderate vacuum. The magnetic core loss of the sample annealed in nitrogen atmosphere becomes fairly large from chemical etching, which implies the importance of surface state for the magnetic core loss reduction at high frequency.

Planar inductor for very small DC-DC convertors

The authors describe the development of a planar inductor and its application to DC-DC converters. The planar inductor fabricated had a small size (11*11*0.8 mm), 33 mu H inductance, and a maximum quality factor of 14. The very small DC-DC converter, using the planar inductor as an energy storage element. had a 250 kHz switching frequency, a 5 V 2 W typical output, and a power/volume ratio of up to 1.7 W/cm/sup 3/.<<ETX>>

Magnetic Permeability and Thermal Stability of Low Magnetostrictive Amorphous Fe-Based Alloys

Introduction Fe-based amorphous alloys have large magnetostriction of up to 30xlO-6 and a small magnetic anisotropy that permits achievement of high permeability, making these alloys desirable to use as dynamic sensors. However, this large magnetostriction is an undesirable characteristic since it prevents their application in magnetic cores. The authors previously reported on an Fe-based amorphous alloy that exhibits a low magnetostriction of 10-6 order in which a portion of the Fe has been substituted with the elements Cr, Nb, and Mo, as well as discussing the relation between magnetostriction and high-frequency core loss [1] . This article reports on the permeability of low magnetostrictive amorphous Fe-based alloys, its thermal stability and the relation between magnetostriction and thermal stability.