Epitaxially grown α'-(Fe_100-xCo_x)-C (x = 5, 10 at.%) films were synthesized by the sputtering method, and their structural and magnetic properties were investigated. The main results can be summarized as follows: (1) α'-FeCo-C single-phase films with bct crystal structure can be synthesized when prepared on MgO single-crystal substrates; (2) the saturation magnetization of α'-FeCo-C films is 5% larger than that of α'-Fe-C films; (3) α'-FeCo-C films are thermally stable up to 250°C, which is similar to the temperature for α'-Fe-C films; (4) α'-FeCo-C thin film with 5 at.% Co content shows superior soft-magnetic characteristics, and the coercive force is less than 5 Oe, which is almost identical to the value for α'-Fe-C film. Through this study, it was found that an increase in saturation magnetization can be realized by addition of 5 at.% Co to α'-Fe-C film while maintaining the latter’s thermal stability and the soft-magnetic properties.

View full abstract

Co₂MnGe is a full-Heusler alloy with L2₁ structure, theoretically predicted to be a half-metallic ferromagnet. In this paper the structural and magnetic properties of Co₂MnGe films with a Cr buffer layer were investigated. The magnetization at 20 kOe of the prepared Co₂MnGe film was 750 emu/cm³. The lattice parameter of the Co₂MnGe film annealed at 400°C was 5.704 Å, which was not in agreement with the value for a bulk sample (5.743 Å), but in nearly agreement with the value calculated from first principles (5.711 Å). The magnetization at 20 kOe was 970 emu/cm³ which was in nearly agreement with the theoretical value (1002 emu/cm³).

View full abstract

New half-metallic ferromagnets have been found in a zinc-blende crystal structure. The zinc-blende CrAs has been designed by ab initio calculations and the calculation predicts the highly spin-polarized electronic band structure. The zinc-blende CrAs thin film has been synthesized on GaAs (001) substrates by molecular-beam epitaxy. The film shows ferromagnetic behavior at room temperature and the magnetic moment per formula unit of CrAs is estimated to be about 3 μ_B, which agrees well with the theoretical prediction. The photoemission spectra of the CrAs film showed the Fermi edges indicating the metallic characteristics and the small band dispersion derived from Cr-3d bands.

View full abstract

In Fe₂O₃-Bi₂O₃-PbTiO₃ system thin films prepared by rf-reactive sputtering, the real part, ε_r', of dielectric permittivity, was changed by applying a magnetic field H. The Δε_r' vs. H curves of the films subjected to annealing at various temperatures were strongly correlated with their magnetization properties. The maximum relative value of |Δε_r'(H)/ε_r'| reached as much as 1.0%. A Δε_r'(H) curve can be reconstructed by a simple model based on uniform magnetization rotation.

View full abstract

A temperature-sensitive ferrimagnetic thin film (TFF) with 1.5 μm thickness was obtained by vacuum deposition of [Fe/Zn/Mn/Zn/Fe] multilayers on alumina substrates and subsequent sintering and annealing. The composition of the TFF is Mn_xZn_1-xFe₂O₄, The sputtering methods are the most typical procedures for obtaining magnetic thin films, while the new method has a low cost and does not require a special target like that used in the sputterig methods. The magnetization of TFF depends strongly on the sintering and annealing conditions. The TFF, which was sintered for 420 min in an atmosphere of oxygen with a partial pressure of 1% at 1200°C and annealed for 1 min in an atmosphere of argon at 400°C, exhibited a maximum saturation magnetization of about 105 emu/cm³ at room temperature. For the temperature change from 0°C to 60°C, the saturation magnetization of the TFF changed about 46%. TFF with sharp thermal response can be used as a micro-temperature sensor, a thermomagnetic transducer, an enzyme sensor, and a light-magnetic device. In this paper, the sintering and annealing conditions for the TFF are the focus of our attention.

View full abstract

Barium ferrite thin films with lanthanum ions and cobalt ions substituted for barium ions and iron ions were prepared by the conventional sputtering method. To crystallize a hexagonal barium ferrite phase, the as-deposited films were annealed at a temperature of 900°C for 5 hours in air. The crystal orientation of La-Co substituted barium ferrite thin films was changed by controlling their compositions. The c-axis direction of the hexagonal structure was changed from perpendicular to parallel to the film surface by increasing the Co concentration. An attempt was also made to reduce the film thickness of La-Co-substituted barium ferrite thin films, in order to utilize them as perpendicular magnetic recording media. However, when the thickness of the films was decreased, the coercivity of the films also decreased because of their poor crystallinity. It was considered that the poor crystallinity was caused by the diffusion of barium ions into substrates. Therefore, a Ba-rich buffer layer was used to prevent the loss of barium ions. The La-Co-substituted barium ferrite thin films with a Ba-rich buffer layer had good crystallinity at a film thickness of 20 nm, and their magnetizations were larger than those of single-layer barium ferrite thin films.

View full abstract

We succeeded in synthesizing M_xFe_3-xO₄ (M = Cu, Zn, Fe, Ni, Co, Mn, and Mg) ultra fine particles from an aqueous solution, utilizing Fe²⁺ → Fe³⁺ oxidation by air (oxygen). The synthesis was performed at room temperature, in open air, and on near neutral condition of pH = 7−9. Their particles were ∼ 10 nm in size and of spinel structure. All the particles had saturation magnetizations that compared favorably with those of bulk samples. The solubility limit in x in the M_xFe_3-xO₄ particles increased as the ratio Fe³⁺ / Fe²⁺ in the reaction solution increased.

View full abstract

We developed a new deposition method for ultrafine particles (UFP), which is based on the vibration of particles in the electrostatic field between parallel electrodes. Fe, Ni, and Co UFP were deposited onto ZnO/glass and Cu substrates at a dc voltage of 20 kV. The film structure changed from a small-grained to a large-grained structure. Films with a large-grained structure show high reflectivity. From SEM observation of films, it was found that the main deposition process is heating and fusion of ultrafine particles by discharge in the charge exchange that occurs on collision. This deposition method can be used to prepare films with various structures, such as small-grained and large-grained structures.

View full abstract

Initial permeability, permittivity and resistivity spectra of Mn-Zn-Ti ferrite with Fe-poor composition (less than 50 mol% of Fe₂O₃) (FPF) are compared with Fe-rich Mn-Zn ferrite and Ni-Zn ferrite.
Analysis of the electromagnetic characteristics shows that the skin effect and dimensional resonance can be disregarded for FPF of the measured sample size below 1 MHz.
The contribution of the domain wall and spin rotation resonance to the permeability spectra was estimated by numerical fitting of the permeability data. It was found that natural resonance occurred in FPF, as in Ni-Zn ferrite. In addition, FPF has a damping factor β smaller than the conventional Fe-rich Mn-Zn ferrite, because it does not contain Fe²⁺ ions that have non- zero orbital moment, and large magnetic anisotropy factor.

View full abstract

The core loss of conventional MnZn ferrite varies with temperature. Therefore, for use in a trans-former, the main composition must be chosen so that the loss is lowest between 80°C and 100°C. Substitution of Co for Fe in an MnO-ZnO-Fe₂O₃ ternary system gives a smaller variation in loss with temperature. The gradient of the loss-temperature curve in the lower temperature region becomes steadily gentler upon substitution of CoO up to 0.5 mol%, irrespective of the ZnO concentration. However, excess substitution gives rise to a steep increase in the loss as the temperature decreases. According to analysis using the Globus’ model, both the improvement in the temperature dependence and the abrupt change in core loss in the lower temperature region accompanying Co replacement could result from a change in the magnetocrystalline anisotropy constant K₁.

View full abstract

Ni-Zn ferrite films 0.2-1.2 μm in thickness were prepared by spraying a reaction solution of FeCl₂(+FeCl₃)+NiCl₂+ZnCl₂ (pH = 6.95) and an oxidizing solution of NaNO₂ + CH₃COONH₄ (+NH₃) simultaneously onto spinning glass substrates at a substrate temperature of 90°C. Films with a thickness of 0.48 μm deposited by the conventional spin-spray method using only Fe²⁺ as iron ions exhibited a high permeability μ' of 42 and a high magnetic resonance frequency f_r of 650 MHz. This was 5 times as high as the value for Ni-Zn ferrite bulk. Film plated by adding NH₃ to an oxidizing solution and film deposited by using a mixture of Fe³⁺(10%) and Fe²⁺(90%) as iron ions exhibited higher f_r values of 900 MHz and 1.2 GHz, respectively. Since not only the real part μ' but also the imaginary part μ'' had large values of about 30 at 1 GHz, the films prepared in this study will be applicable to rf inductors as well as wave absorbers for suppressing EMI in the quasi-microwave range exceeding 1 GHz.

View full abstract

Ceramics made from a series of room-temperature ferrimagnetic mixed oxides, Ba₃Co₂Gd_xFe_24-xO₄₁ (x = 0-1.0), with Z-type structure, were prepared by the conventional powder metallurgy method. A series of Ba₃Co₂Gd_xFe_24-xO₄₁ samples were made with BaCO₃, CoO, Gd₂O₃, and α-Fe₂O₃ as starting materials. The frequency dependence of the initial permeability of all samples was measured. The initial permeability of Ba₃Co₂Gd_0.1Fe_23.9O₄₁ was 22.3 (at 0.1 GHz), which was the highest of all the samples. It was a remarkably high value compared with those reported for isotropic samples. The crystal structure was determined by the x-ray diffraction method; a single phase of the Z-type structure was obtained for Ba₃Co₂Gd_xFe_24-xO₄₁ (x = 0.01, 0.1). Gadolinium ions formed a solid solution of Co₂Z ferrite. This is one of the reasons for the high initial permeability. The other reasons are higher densification and the change in magnetic anisotropy caused by a small quantity of Gd ions forming a solid solution of the Z-phase.

View full abstract

In order to develop a magnetic/dielectric hybrid material for high-frequency transmission-line devices, a ferrite/polyimide composite thick film was fabricated by using a Mn-Zn ferrite particle and poryimide precursor. The microstructure of the composite thick film was characterized by using SEM observation and X-ray micro analyzer. In addition, the magnetic and dielectric properties of the same film were evaluated. The composite thick film exhibited a large effect on the wavelength shortening up to 1/20 and large absorption for high-frequency electromagnetic energy.

View full abstract

We studied the feasibility of electronic components manufactured from recycling powder composed of a MnZn ferrite grinding sludge and commercially available clay for earthenware and carbon powder. The effects of the mixing ratios, matching thickness, and matching frequency on the high-frequency magnetic properties and dielectric properties of rubber sheeted samples of added carbon powder were investigated. As a result, we found it possible to utilize the mixtures as composite materials for producing electromagnetic wave absorbers that exhibited value of peak frequency (f₀) increase by adding carbon powder. It is possible to design electromagnetic wave absorbers for an arbitrary frequency between several hundred MHz and a few GHz.

View full abstract

The magnetic properties and resistivity of granular CoFe/Al₂O₃ films with various Al₂O₃ preparation conditions were investigated. The films came to have good soft magnetic properties and their resistivity increased as the Ar gas pressure used in the Al₂O₃ preparation decreased. The surface roughness of these films also became large when a low Ar gas pressure was used in the Al₂O₃ preparation. In view of the above results, the coverage of CoFe granules with Al₂O₃ was thought to be different when various Ar gas pressures were used in the Al₂O₃ preparation.

View full abstract

We demonstrate that Ni-Fe-fine-particle films have potential for use as high-frequency conduction noise suppressors in the quasi-microwave band. Ni-Fe- Sm₂O₃, MgF₂, and B₂O₃ films with different volume fractions of Ni₈₀Fe₂₀ were produced. Samples with soft magnetic properties and electrical resistivity (ρ) higher than 10⁴ (μΩcm) were obtained. Their resistivity is hundreds of times higher than that of Fe-Al-O granular films, and the magnetic resonance loss is several tens of times higher than that of commercially used noise suppressors in the quasi-microwave band. These results suggest that thin-film current noise suppressors that can be integrated into micron-scale electric-devices could be produced by using these films.

View full abstract

The soft magnetic properties of NiFe/FeCo/NiFe sandwich films with high saturation magnetization are discussed in relation to the microstructure. Ta/NiFe/FeCo/NiFe/Ta films prepared using the UHV sputtering process show bcc-(110) preferred grain orientation with the <110> direction sharply perpendicular to the film plane in the FeCo layer. It was revealed that thin NiFe film with a thickness of only 3 nm works effectively as a seed layer of FeCo film to control the microstructure, resulting in a significant reduction of the coercivity. The best thickness of the FeCo layer in order to realize both soft magnetic properties and high saturation magnetization was found to be ∼100 nm. Film deposition in Ar + N₂ plasma reduced the grain size, but did not lead to further improvement of the soft magnetic properties. The large lattice strain induced by N₂ addition is likely to degrade the soft magnetic properties.

View full abstract

(CoFeB)-(SiO₂) soft magnetic film with an electrical resistivity of over 5000 μΩcm (0.5 Ωm) was deposited on glass substrates by using synchronous triple-rf magnetron sputtering. The magnetostatic properties and high-frequency permeability characteristics of the films were investigated.
The film in as-dep. state exhibited a maximum electrical resistivity of about 115,600 μΩcm (11.56 Ωm), with a uniaxal anisotropy field H_k of about 250 Oe, a hard axis coercivity H_ch of 5.6 Oe and a saturated magnetization 4 πM_s of 8.3 kG. In the permeability characteristics of the film, the real part of the relative permeability was 50, which exhibited a good flat frequency dependence until 2 GHz. The resonance frequency was more than 3 GHz.
It was found that a drastic increase in the resistivity was possible to the range over 100,000 μΩcm (10^-3 Ωm).

View full abstract

Amorphous Fe-Cr-Si-B-C powder cores with glass binders were produced by cold-pressing and sintering at relatively high temperatures below crystallization temperature. The density of the core obtained was about 80%. The magnetic properties of toroidal samples 30 mm in diameter were measured. For the core pressed at 2 GPa, room temperature and sintered at 460°C × 20 min in air, the initial permeability in the frequency range up to 1 MHz for H_m = 5 mOe was about 100, and the core loss at 100 kHz for B_m = 0.1 T was 500 kW/m³. These values were comparable with those of hot-pressed amorphous powder cores, which had been previously reported. Compared with a commercial Sendust powder core widely used for choking coils and fly-back transformers, the initial permeability was approximately equal and the core loss was 30% lower. Furthermore, the domain patterns of the amorphous core were observed and their relation to the magnetic properties was discussed.

View full abstract

The stress-magnetization properties of Co-based amorphous ribbons due to heat treatment were investigated. A sample was annealed with a longitudinal magnetic field applied to its ribbon axis. Examination of the stress-magnetization change revealed a stress-insensitive region that depended on the annealing temperature. To apply further stress, the magnetization of the sample was decreased to zero. However, examination of the magnetization change revealed a unique behavior due to a stress application at a lower exciting magnetic field (< 5 A/m). The stress-magnetization change showed irreversibility, with a maximum slightly larger than the initial magnetization value while the stress was decreased and then restored to the initial value. The results could be interpreted as implying a model of combined effects: a magnetic field parallel to the ribbon axis, an induced anisotropy field due to field annealing, and magnetoelastic anisotropy due to the applied tensile stress.

View full abstract

This paper describes domain patterns in grain-oriented silicon steel after the application of rectangular wave induction in the easy and hard magnetization directions. More lancet domains appear after application of rectangular wave induction than after demagnetization by ac induction in the easy magnetization direction.
In the hard magnetization direction, the 180° wall spacing and lancet domain density do not change after ac and rectangular wave demagnetization. The domain pattern suggests that the increase in the lancet domain and its deviation cause the ac magnetostriction deviation after application of rectangular wave induction.

View full abstract

We already devised a method for detecting cracks nondestructively by using direction of the magnetic field measured by the ring arranged with the sensors. However, cracks cannot be detected when the ring arranged with the sensors leans to the distribution line. We devise detecting cracks, even if the ring arranged with the sensors leans to the distribution line. We introduce a parameter ΔLm and standard deviation that vary with the existence of cracks and confirmed the probability of the nondestructive detection with ΔLm and standard deviation.

View full abstract

Gamma-ray irradiation tests of High-Tc SQUIDs were carried out to examine their workability in nuclear reactor environments. The SQUIDs were made of a HoBa₂Cu₃O_7-x superconductive thin film on SrTiO₃ substrates. Some were encapsulated in separate cases of glass-fiber-rein- forced epoxy resin.
Gamma-ray irradiation was performed with a Co-60 gamma-ray source. Irradiation dose rates were (8.1 to 12.1) x 10³ Gy/h (i.e., (1.0 to 1.5) x 10⁶ R/h), and the maximum absorption dose was about 10.4 MGy. During and after irradiation, noises of SQUIDs were measured with a power spectrum analyzer. Changes in modulation voltage were also investigated. No gamma-ray induced noise was observed during irradiation. The noise level and modulation voltage did not change until a total irradiation dose of about 3 MGy, and after that it decreased slightly.
We concluded that the tested high-Tc SQUIDs are very resistant to gamma-ray irradiation, and thus the application of high-Tc SQUIDs in inspection of reactor components seems promising.

View full abstract

We measured radio frequency electromagnetic noise in a cylindrical magnetic shield using a developed monopole antenna RF noise entering the shield through its open ends affects the SQUID operation. In flux-locked mode, it causes the feedback circuit to unlock or increases the noise floor. First, we examined the effect of RF noise reduction using dc-SQUID first-order gradiometers and copper mesh shield. RF noise was also measured using a conical log spiral antenna and a developed monopole antenna. Second, we investigated the reduction of RF noise in a cylindrical magnetic shield by filling its open ends with metal-coated cloth using a fabricated antenna. The RF noise level was decreased inside the shield; as a result, the low-frequency signal-to-noise performance of the SQUID sensors were improved.

View full abstract

VR resolvers were developed as angle sensors for the motors of hybrid electric vehicles. Because the angle error of the resolver affects motor efficiency, the angle accuracy of the resolver must be improved. Results of investigations up to now showed the major cause of angle error of the resolver to be determined by imbalance of induced voltages on the coils caused by uneven distribution of magnetic flux around the coils. We, therefore, searched for a shape core that makes the distribution of magnetic flux more even around the coils. Finally we found that a thicker core stack, a smaller minimum air gap between the rotor and stator, and wider tooth tips of the core are effective for reducing the angle error.

View full abstract

We studied a giant magnetostrictive thin film for use in high- sensitivity microsensors and microactuators. It is important to have even lower magnetic coercive force for the sensor application. We, therefore, aimed to decrease the magnetic coercive force by selecting an appropriate ratio of Tb(RE)-Fe(TM) alloys. The resulting giant magnetostrictive thin film was applied to a force sensor with a meander coil.
This paper describes the following : (1) The influence on magnetic characteristics of magnetron-sputtered film by sputtering condition is described for the force sensor ; (2) the magnetostriction of the film showed 702 ppm at 80 kA/m when processed at the appropriate annealing temperature ; (3) we constructed the force sensor with a meander coil and the thin film was used for the sensor ; (4) a change in impedance of 7% was observed on the meander coil. We have shown the possibility of using this design as a sensor.

View full abstract

This paper deals with arail joint gap sensor having two detecting coils across to the exciting coil. The sensor, designed for ordinary railways, is able to detect flux change due to eddy current in the rail. The key points of this paper are as follows: (1) principle of measurement by the rail joint gap sensor with two detecting coils across to the exciting coil, (2) rail joint gap sensor use of resonance, (3) and the possibility of rail joint gap measurements for track inspection car with in high lift-off.

View full abstract

This paper presents a new switch-type MI sensor using amorphous wire and a CMOS inverter IC with a positive feedback loop. The MI (Magneto-Impedance) chip is composed of a single amorphous wire (30 μm diameter and 2 mm length) and two coils (feedback coil and pickup coil). This sensor circuit has high sensitivity and low power consumption. A switching magnetic field is set up using the variable resistance of a positive feedback loop. A switching magnetic field is independent of the frequency and amplitude of the external magnetic field. This on/off MI sensor will be useful for application to automobile anti-lock braking systems (ABS) and to magnetic stripe card readers.

View full abstract

An innovative eddy current test (ECT) probe for inspection of printed circuit boards (PCB) is reported. The proposed ECT probe has a meander exciting coil and a solenoid pickup coil. This paper reports a multi-ECT probe, which is useful to shorten the time of inspection. The probe consists of a number of solenoid coils on a single core, with coil characteristics matched with each other. Using the developed multi-ECT probe, we showed the results of scanning a PCB having some solder points and a disconnection point on an 0.8-mm conductor.

View full abstract

This paper discusses a wall-pinned, high-frequency carrier-type, thin-film magnetic field sensor, which can decrease the area of closure domains and reduce wall displacement of the sensor element. The sensor element was annealed at 350°C for 20 minutes without any magnetic field, thus inducing wall pinning. We examined the relationship between the domain structure and impedance change of the wall-pinned sensor element. The decrease in the sensitivity around a high-sensitivity area was suppressed owing to the reduction of growth of the closure domains.

View full abstract

A high-frequency carrier type thin-film magnetic field sensor was combined with a high-frequency carrier suppressing circuit to increase detection sensitivity. The carrier-suppressing circuit was designed and tuned to suppress the carrier, thus reducing the phase noise level of thermal noise (-174 dBm) at room temperature. The carrier was suppressed by about 60 dB, enabling detection of a very low signal from the sensor. As a result, high sensitivity of 7.2 × 10^-6A/m (9 × 10^-8 Oe) was demonstrated at 501 kHz.

View full abstract

Over current detection characteristics based on magnetic saturation of an outer magnetic core type planar inductor were analyzed. The planar inductor had two planar windings: an inner planar coil connected to the main electrical circuit, and an outer planar search coil on the top surface of the outer thin magnetic core. The planar inductor was used as an energy storage element for high-frequency power conversion equipment, such as switching dc-dc converters. The basic operation of the over current mode due to magnetic core saturation was simulated by a nonlinear finite element method.

View full abstract

We previously proposed a Magnetic-Flux-Control transformer (MFC transformer). The MFC transformer has simple construction and high reliability because it consists of only a core and its windings. The MFC transformer can control output voltage and net inductance easily and continuously.
For wide application and practical use, it is necessary to establish a design method for the MFC transformer. In this paper, we present an analytical method for the MFC transformer using Reluctance Network Analysis (RNA) and examine the characteristics of an MFC transformer.

View full abstract

We proposed a three-phase variable inductor for control equipment in an electric power system. The three-phase variable inductor is constructed with three orthogonal cores that have wedge gaps for reduction of harmonics. When the three-phase variable inductor is connected to a power line in parallel, a simple and reliable var compensator results. A trial three-phase, 100-kVA variable inductor was demonstrated in a 6.6-kV ac distribution system. In order to expand the application of the variable inductor, it is necessary to clear the operation of the variable inductor under various conditions in the electric power system. It is generally difficult, however in general to carry out field tests on an actual electric power system. Numerical simulation is an effective method for analysis of an electric power system. In particular, EMTP is one of the most widely used programs in the analysis of electric power systems. In this paper, we present an EMTP model of the orthogonal core variable inductor and apply the model to the analysis of an orthogonal core SVC.

View full abstract

We propose a desk-type design for a contactless power station (CLPS) using spiral formed coils. In this system, in order to supply electrical power efficiently to portable equipment on the desk, the primary coils are arranged to cover the desk. A configuration using several primary coils for each secondary coil was therefore proposed. We examined improvement of transmitted characteristics in this coil configuration. We improved transmitted characteristics of the electric supply and charging circuit to book-size personal computer as an applied example. As a result, we confirmed we kept the efficiency high of electric power transmission everywhere. From this fact, we confirmed the effectiveness of using several primary coils.

View full abstract

The magnetic enzyme sensor (MES) is a thermal biosensor utilizing temperature-sensitive ferrimagnetic thin film with a composition of Mn_xZn_1-xFe₂O₄, prepared by sputtering and annealing processes. Temperature-sensitive ferrimagnetic thin film with a marked temperature dependence has the ability to detect temperature variations of as little as 10^-3°C, so application of the film to an enzyme sensor is possible. The conventional enzyme sensor is an electronic device using a semiconductor, such as a thermistor, whereas MES is a magnetic detector utilizing temperature dependence of the temperature-sensitive ferrimagnetic thin film. The temperature rise due to an enzyme reaction is less than 10^-2°C, and it is difficult to detect with a conventional magnetic sensor because of the large heat of the capacitor and the instability of the magnetic signal readout. The MES is, accordingly, proposed for detecting chemical substances and the metabolites due to enzyme reactions. The MES can be used in the fields of biochemistry and biomagnetics for clinical chemical analysis, process measurement, and hygiene management of foods. This paper describes construction of the MES, and a logic circuit expression for response characteristics.

View full abstract

Hyperthermia is a therapeutic technique against cancer. It necrotizes cancer cells by applying heat at about 43°C, at which the survival rate of cancer cells drastically drops. However, in case of a substantially large tumor, there is a possibility that cancer cells may survive when there is a difference in the temperature between the central part and marginal region. For this condition, high-temperature hyperthermia is proposed as a way to ensure that the malignant tumor is necrotized. In this study, using the soft heating method, which is a kind of inductive heating method, with hybrid heaters, we examined the temperature distributions of hybrid heaters that varies with the configuration of metal rings for the thermosensitive magnetic material.

View full abstract

A real-time monitoring system utilizing linearly polarized light was developed for observing intracellular cytoskeleton protein motion and the possible effects of strong static magnetic fields on cell behavior. Smooth muscle cells of a rat were cultured in a petri dish for one day, then were set between a pair of light-polarizing plates, whose polarizing directions were normal to each other and inclined almost 45 degrees against the direction of the magnetic field. The polarized light transmission through the adhering cell layer was measured in real time under magnetic fields of up to 14 T. During the magnetic field exposures, the light transmission increased 50% and reached a stable level within 3 hours. The results indicated that the intracellular cyto-skeleton proteins rotated due to the diamagnetic torque force acting on them.

View full abstract

This paper describes a method of source estimation for a magnetic alpha wave, using a combination of singular value decomposition (SVD) analysis and measurement of the tangential magnetic field component in a 3-D vector magnetoencephalogram (MEG).
First, we found, as a result of singular value decomposition analysis, that two dominant singular values exist in not only the perpendicular component but also the tangential components (B_θ, B_Φ). To discuss the source structure of the right and the left hemisphere in the brain, we calculated the singular value with the data obtained from each the right and the left head. Two singular values with score proportion (>80 %) were also obtained to both of the right and the left. The second, using the isofield contour map of tangential component of magnetic alpha wave, it was found that there are two extreme values.
These results indicated that there were two sources in the magnetic alpha wave. Further, we could confirm that SVD analysis and measuring tangential component were useful to separate sources of magnetic alpha wave overlapping in time.

View full abstract

We measured somatosensory evoked fields (SEFs) by electric stimulation to the right thumbs of five subjects, using a three dimensional, second-order gradiometer connected to 39-channel SQUIDs, which can simultaneously detect the magnetic field components perpendicular to the scalp (Br) and tangential to the scalp (B_θ, B_Φ). To assess the relationship between phase lag and stimulation repetition frequency (SRF), we detected the delay time of a component synchronous with stimulation interval (27 to 1007 ms) by convolution of the reference signal and SEF wave. Phase lag was linear to SRF for at least two different SRFs in both Br and B_θ. It was calculated by the test for significance of the linear regression slope (β≠0 : P <0.05). Response latencies calculated from the slope were ranged from 200.9±16.2 ms to 46.4±2.2 ms in Br and from 189.3±34.3 ms to 45.5±5.2 ms in B_θ. We also analyzed the power spectrum of SEF waves by time-frequency analysis.

View full abstract

We performed three-dimensional vector measurement of magnetocardiograms (MCGs) of normal subjects and subjects with hypertrophic cardiomyopathy (HCM) and myocardial infarction (MI), using three-dimensionals second-order gradiometer connected to 39-channel SQUIDs, which can detect magnetic field components perpendicular to the chest wall (Bz) and tangential to the chest wall (Bx, By) simultaneously.
To compare the MCGs of normal subjects with those of patients, We analyzed MCG data for normal subjects using the ratio power. High correlation was obtained in MCG between normal subject and normal subject who was averaged, but data for patients HCM and MI displayed low correlation.
The power map of a normal subject was compared with those of patients based on correlation coefficient. Results confirmed the difference in heart activity.

View full abstract

An implantable micro-pump for treatment of fetal hydrocephalus has been designed, fabricated, and tested. The moving part of the pump consists of a magnet attached to an elastic film. When an external alternating magnetic field is applied, the elastic film vibrates angularly and can produce a unidirectional movement of fluid. The pump requires no power supply cables and can be easily driven by the coil placed outside the mother’s body. The 2-cm-long prototype satisfied the pumping conditions required for treatment under a low magnetic field. This result demonstrates that the pump proposed here is applicable for the shunt system for fetal hydrocephalus.

View full abstract

We developed a new motion-capture system for jaw movement using two magnets and two-axial fluxgate sensors. Two magnets are fixed to a tooth in the lower jaw and to the forehead. The system can naturally detect the jaw movement as a rigid body because the system has no need for attachments such as a clutch inside the mouth or a magnetic field sensor array in contact with the head.

View full abstract

We designed a new contactless power and signal transmission device using electromagnetic coupling for functional electrical stimulation (FES) system. The system consists of two coils which are arranged outside and inside the body respectively. Implanted coil follows electrode to stimulate muscles. Stimulating wave forms is generated at the integrated controller which is connected on the electrode. We discussed the characteristics and the coil shape in which we reduce the noise without using filter in signal transmission.

View full abstract

We performed three-dimensional vector measurement of magnetocardiograms (MCGs) for normal subjects and subjects with Wolff-Parkinson-White (WPW) syndrome, using a three-dimensional second-order gradiometer connected to 39-channel SQUIDs, which can simultaneously detect magnetic field components perpendicular to the chest wall (Bz) and those tangential to the chest wall (Bx,By). In order to analyze the accessory pathway of WPW syndrome, source estimation to the delta wave was performed using the equivalent current dipole (ECD) method.
Magnetic field pattern Bz of the delta wave for WPW syndrome was not a dipole pattern, and it was difficult to estimate sources. Magnetic field patterns Bx and By, however can provide information on constraint conditions for estimation of multiple sources. It was found by three-dimensional measurement that the estimation of the accessory pathway received the effects of a repolarization process of the heart atrium when the accessory pathway was located far from a sinoatrial node. It was shown that three-dimensional MCG measurements are effective for detailed analysis of heart activity.

View full abstract

A magnetic micro-machine with a heating device, which can run in gel, was fabricated. The machine is composed of a screw tip, a rod-shaped NdFeB magnet, and a rod-shaped permalloy unit. The machine is 2 mm in diameter and 19 mm in length. The NdFeB magnet is magnetized to the direction of the diameter. When a rotational magnetic field with rotation frequency of 10 Hz is applied, the machine rotates and moves in agar. In addition, a machine placed in an alternating magnetic field, at 100kHz, produces heat by iron loss. It was demonstrated that the machine can move 20 mm and be heated above 50°C. This means a wireless heating mechanism could be obtained using an alternating magnetic field and a rotational magnetic field. This machine has the great possibilities for local medical operations for cancer.

View full abstract

In this paper, we propose a new analytical model for brushless dc motors that is based on the magnetic circuit. The magnetic circuit is constructed with magnetic reluctances of stator and rotor cores and magnetomotive force of the stator winding currents and permanent magnets. Combining the magnetic circuit, electrical circuit, electronic circuit, and control circuit, we can accurately analyze the dynamic characteristics of the brushless dc motor.

View full abstract

We developed a linear induction motor (LIM) that can generate thrust in arbitrary directions on a two dimensional plane, and we studied the basic characteristics of that motor.We already reported switching characteristics for such a transport and switch system when the carrier weight is constant and the center of gravity is variable. This paper, shows results when the weight of a carrier is variable. The following items we are examined when the travel direction thrust - to - function ratio in the carrier is constant and switching direction thrust - to - function ratio in the carrier is variable: (1) influence on the switching angle to the thrust of X-Y LIM when the weight of a carrier is variable, and (2) relationship between the switching angle in weight change of a carrier and the change of the center of gravity position of a carrier.

View full abstract

Electromagnetic suspension (EMS) is widely used in conveyor systems because of the various advantages in practical use. U-type magnets are often used to generate the levitation force in the EMS system. A conventional electromagnet, however, can only control one degree of freedom. It cannot constitute a levitation system by itself alone.
A four-pole yoke hybrid electromagnet is proposed instead of the usual U-type magnet; its magnetic levitation control is a zero power control method. We propose an X-Y linear synchronous motor (X-Y LSM) composed of an iron core and two windings in the horizontal x and y directions.

View full abstract

The swimming properties of miniature magnetic micro-machines with spiral structures were analyzed theoretically employing a two-dimensional finite volume method. Based on the analysis results, a miniature machine was fabricated. The miniature machine was found to be able to swim in a fluid with Reynolds numbers of 10^-5 to 0.2. This result shows that the machine is suitable as a micro-size swimming machine. Good agreement was obtained between experimental and theoretical results. This method made it possible to design an optimum machine structure.

View full abstract