K. Yamasawa

High-frequency operation of a planar-type microtransformer and its application to multilayered switching regulators

The operation of a multilayered microtransformer composed of planar zig-zag coils and amorphous magnetic film is described. The transformer has a maximum efficiency of 77.5%. Its equivalent circuit is approximated by the parallel connection of the winding inductance and of the stray capacitance. Variable magnetic coupling is obtained between the primary and secondary windings by shifting the relative position of the two coils. The microtransformer is used in a magnetically controlled multilayered switching regulator. The regulator has an output of 1.4 W and an efficiency of 24%. The magnetization loss in the circuit is the same as that of the semiconductors. A two-output-type multilayered switching regulator is also proposed that has an acceptably good output characteristic at each port even though a common magnetic film is used. >

Experimental considerations on a new automatic cooling device using temperature-sensitive magnetic fluid

An automatic cooling device to eliminate the waste heat of machinery has been made by utilizing a temperature-sensitive magnetic fluid. This cooler requires no pump for flowing the fluid, since a part of the thermal energy is converted to the kinetic energy. If a permanent magnet is used, power supply is unnecessary. The cooler is expected to be maintenance-free and simple in shape.

A new wideband common-mode noise filter consisting of Mn-Zn ferrite core and copper/polyimide tape wound coil

A new wideband common-mode noise filter for switching power supplies has been developed. The filter consisted of an Mn-Zn ferrite core and a copper/polyimide tape wound coil. The tape wound coil had two signal lines, two ground lines, and a polyimide dielectric film. The filter exhibited a common-mode rejection of over 30 dB in the wide frequency range of 100 kHz to 100 MHz. The wideband common-mode filtering was due to the high-frequency magnetic loss of the Mn-Zn ferrite core and the optimum ground point selection for the ground lines.

New applications of nanocrystalline Fe(Co–Fe)–Hf–O magnetic films to micromagnetic devices

New applications of high resistivity magnetic films, such as Fe–Hf–O and Co–Fe–Hf–O as thin film inductors and flux gate magnetic sensors, were investigated. These soft magnetic films with nanocrystalline structure and high resistivity were deposited on glass substrate by using the oxygen reactive sputtering method. Planar sandwich thin film inductors developed by using Fe–Hf–O or Co–Fe–Hf–O films had a higher quality factor than that of an amorphous Co–Ta–Hf film inductor. The dc–dc converter using the Fe(Co–Fe)–Hf–O film inductor had higher conversion efficiency. These high resistivity magnetic films were also applied to a flux gate magnetic sensor operated at high frequencies over 1 MHz. Both high frequency excitation and high permeability (owing to the low eddy current loss) enabled us to increase the sensitivity, e.g., 39 mV/Oe/turn at 5 MHz when using a 3 μm thick Fe–Hf–O film (12×6 mm2 area).

Preparation and characterization of Mn-Ir/Fe-Si exchange-coupled multilayer film with Ru underlayer for high-frequency applications

Fe-Si magnetic film and Mn-Ir/Fe-Si exchange-coupled film with an Ru underlayer were fabricated and evaluated. Both coercivity and anisotropy dispersion were reduced due to the Ru underlayer effect on the magnetic properties of Fe-Si magnetic film and Mn-Ir/Fe-Si exchange-coupled film. Even in the Mn-Ir/Fe-Si exchange-coupled multilayer film with an Ru underlayer, the coercivity of the upper Fe-Si layer was reduced.

Application of nanocrystalline Fe(or Co-Fe)-Hf-O magnetic films with high electrical resistivity to micro DC-DC converters

High resistivity magnetic films, such as reactive sputtered Fe-Hf-O and Co-Fe-Hf-O, were applied to multilayered micro reactors for high frequency operation dc-dc converters. For a comparison, an amorphous Co-Ta-Hf film with good soft magnetic properties was also investigated. The micro reactor had the highest quality factor (the lowest loss) when using Co-Fe-Hf-O film with the highest resistivity. In 5 MHz operation of dc-dc converters using these micro reactors, the highest conversion efficiency was obtained when using Co-Fe-Hf-O film.

Development of an Electromagnetic Wave Shielding Textile by Electroless Ni-Based Alloy Plating

A polyester nonwoven textile with Ni-based alloy coating was fabricated, and the effect of electromagnetic wave shielding was evaluated. The Ni-based was coated by electroless plating on the textile. The electromagnetic wave shielding effect of the textile with Ni-B coating was about 99.98% over the induction range of 6-13 GHz. Because the textile has thin, light, flexible, and breathable characteristics, it will be versatile for the various electromagnetic wave shielding applications.

Preparation and Characterization of Nanofiber Nonwoven Textile for Electromagnetic Wave Shielding

A nanofiber nonwoven textile with metallic magnetic material coating was fabricated, and the effect of electromagnetic wave shielding was evaluated. The nanofiber nonwoven textile with an average diameter of about 500 nm was spun by electrospinning. The metallic magnetic material was coated by sputtering on the textile surface. EMI shielding effect of the textile with metallic magnetic material coating was about 90% in the GHz band. Because the textile has thin, light, flexible, and breathable characteristics, it will be versatile for various electromagnetic wave shielding applications.

A thin film type magnetic/dielectric hybrid transmission-line with a large wavelength shortening

A novel thin film type hybrid transmission-line device with a magnetic/dielectric multilayer structure was developed. The magnetic/dielectric hybrid micro strip-line consisted of a top aluminum strip line, the CoZrNb/polyimide multilayer structure, and bottom aluminum ground plane on the Al/sub 2/O/sub 3/ substrate. The hybrid microstrip-line exhibited a large wavelength shortening effect. For example, the wavelength ratio of the hybrid transmission-line and free space was below 7%. Therefore, a quarter wavelength distributed constant line device, such as impedance converter, balun and filter, will be miniaturized using the new hybrid transmission-line, because of its large wavelength shortening effect.

High frequency soft magnetic properties of nanocrystalline Fe-(Co)-Hf-O films with high electrical resistivity and their application to micro DC-DC converter

We have developed nanocrystalline Fe-(Co)-Hf-O films which exhibit high electrical resistivity (ϱ) more than 4 μ Ωm as well as high magnetization (Is) more than 1T and also good soft magnetic properties even in as-deposited states. Furthermore, real part of complex permeability μ′ of these films exhibit more than 1000 up to 100 MHz by annealing in an uniaxial magnetic field. The layered inductor using nanocrystalline Fe61-Hf13-O26 film and Co44-Fe19-Hf15-O22 film show the Q of 8.4 and 12.3 at 5 MHz. The micro DC-DC converter using the nanocrystalline Fe61-Hf13-O26 film and Co44-Fe19-Hf15-O22 film inductor show the maximum efficiency of 83.5% and 86% in the boost converter driving at 5 MHz. So, it was evident that high resistive nanocrystalline Fe-(Co)-Hf-O films were effective for the highfrequency micro DC-DC converter.