We carried out measurement of somatosensory evoked fields (SEFs) by applying an electric stimulus to different right fingers (the thumb, fourth finger, and little finger), using three-dimensional second-order gradiometers connected to 39-channel SQUIDs, which can detect magnetic components perpendicular to the scalp (Br) and tangential to the scalp (Bθ, Bφ) simultaneously. A singular value decomposition method was applied to the SEF data for preprocessing. To discriminate the activities of multiple nerves (the median nerve and ulnar nerve) in the fourth finger, time-frequency analysis (wavelet transform) was applied to each set of SEF data. The dominant distribution of power spectrum to the thumb (median nerve) stimulation was different from the distribution of the little finger (ulnar nerve) stimulation (thumb: 16-18 Hz, little finger: 13-15 Hz). However, the fourth finger showed the distribution that combined the results of the thumb and little finger. Furthermore, coherence between each set of SEF data showed a high value in that frequency range. Source localization was also examined by the SEF data with different frequency ranges. We conclude that the proposed method is useful for detecting the frequency component of the SEF data obtained by stimulation of different fingers and for discriminating multiple sources of SEF data in the fourth finger.

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We have developed a way of making TMR heads that are free from thermal damage. We found that during the annealing stage in the write head process the resistance area (RA) product increased and the magnetoresistance ratio (MR) decreased. This degradation depended on the kind of insulator material on both sides of the TMR junction. Because Al₂O₃ has a relatively high Gibbs free energy, it suppressed the degradation, and thus oxidation at the sensor edge caused less thermal damage. To prevent thermal damage, we developed a TMR head with a Damascene coil process in the write head. It showed no degradation after the write head process, and, furthermore, had good readback performance.

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The fabrication of highly (100) oriented Co₂MnGe thin film by using a Cr buffer layer and an underlayer deposited under various conditions on a thermally oxidized Si substrate was investigated. The main results are as follows : (1) The Cr buffer layer deposited under optimized conditions had a strong (100) orientation on the Ni-Ta underlayer. (2) The Co₂MnGe layer had a strong (100) orientation on the (100) oriented Cr buffer layer with a large saturation magnetization of 860 emu/cc, which is almost the same as the case of the (100) epitaxial Co₂MnGe layer fabricated on an MgO (100) substrate. As a result, we succeeded in fabricating a magnetic tunnel junction of MnIr(100)/Co₂MnGe(100)/MgO(100)/Co₂MnGe(100)/Cr(100) with a low surface roughness on a thermally oxidized Si substrate.

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A new magnetic method of motion capture is proposed. To produce reference magnetic fields, this method uses a simple coil system which consists of two pairs of square coils, which are placed along the sides of two sets of opposite surfaces of a cubic frame where one pair of the coils is rotated through 90 degrees from the other. Two quasi-uniform magnetic fields and one gradient magnetic field are successively generated by these coils and are measured by a triaxial magnetic sensor attached to the moving object. The coordinates of the object are calculated by the Gauss-Newton method from several scalar functions defined by scalar products of the measured magnetic field vectors. The effective area where motion capture can be stably performed was numerically estimated to be a little larger than a cubic area with an edge length of 60 percent of that of the cubic frame.

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Recently, various types of vernier motor have been developed. The variable-reluctance vernier motor (VRVM) is a three-phase reluctance motor whose stator has slots and distributed three-phase windings. The rotor is a slotted iron core without windings. The relationship between S, R, and P is S = R ± P, where S and R are the numbers of stator and rotor slots and P is the number of poles. The rotor of the VRVM moves at a sub-multiple of the angular velocity of the stator mmf. The multiplying factor is P/R. The authors previously reported that a VRVM can be analyzed as a three-phase reluctance motor, and obtained the voltage equations on the γ−δ axis and an expression for the torque. However, the loss separation of a VRVM is not yet clear. In this paper, the iron loss of VRVM is analyzed by the finite element method and compared with experimental values.

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We studied an electric power transmission system for implanted medical devices, such as cardiac pacemakers. We examined improvements to transmission efficiency by reducing the eddy current loss of the titanium case and fabricated a prototype charger system that has 50% efficiency. The secondary rechargeable battery is charged outside the body. The eddy current loss heats through the titanium case and decreases transmission efficiency in an alternating magnetic field. We designed power transmission coils for a rechargeable cardiac pacemaker. The proposed secondary coil is located within the inner wall of the titanium case. The transmission efficiency was 26 - 40% at 10 - 20 mm of gap. We examined improvements in transmission by changing the shape of the titanium case, using a magnetic field simulator. The eddy current loss in the divided model (two divisions) was 40% less than that in the basic model in one simulation results. We found the efficiency increased 40 to 50% at 10 mm of gap by measuring the transmission efficiency of the divided model. We fabricated a prototype charger system based on our simulation results. The system achieved maximum efficiency of 50% after the battery was recharged.

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We measured three-dimensional (3D) magnetocardiograms (MCGs) of rest time (Rest MCGs) and exercise-induced MCG (ex-MCGs) using a second-order gradiometer connected to a 39-channel superconducting quantum interference device (SQUID). This system can detect the magnetic field component perpendicular to the chest (Bz) and tangential to the chest (Bx and By). Time-frequency analysis (wavelet analysis) was applied to the rest and ex-MCGs to examine the frequency distribution of the QT segment. These results were reconfirmed in a t-test. Spatial distribution of the ST segment with a power map showed a more significant change than the QRS complex (Bz and Bx components). Singular value decomposition (SVD), having a time window (48 ms) and a shift time (5 ms), was applied to both MCG data. The ST segments of both MCG data were divided into 10 intervals to examine the spatial distribution between the rest MCG and the ex-MCG in detail. We found that the Bx component showed more significant change in power maps than the Bz and By components in the ex-MCG.

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