A method of testing acceleration to assess instability in GMR and TMR heads was developed. Head instability appears as the output of change in signal amplitude and/or signal distortion with spike noise in both heads. A new tool for testing instability in hard disk drives (HDDs) with various acceleration-condition functions was developed to characterize the relation between instability and acceleration conditions. Classification of head instability in HDDs is proposed with the use of this new tool.

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  This paper describes a new type of actuator composed of a shape-memory-alloy coated magnetic ribbon that detects any deformation of the shape memory alloy. The ribbons reversibly deform by heating or cooling in the temperature region from 10°C to 80°C. The deformation causes a change in the mechanical resonant frequency, which can be detected wirelessly with a pick-up coil. The deformation of the ribbons is confirmed to be proportional to the mechanical resonant frequency with an accuracy of ±0.58%. A heat-driven actuator with a high positioning resolution will be realized by monitoring the resonant frequency and feeding back it to the heating power.

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  This paper describes results obtained from analysis and experiments done on a fluxgate dc earth leakage current sensor for electric vehicles and photovoltaic power generation systems. As fluxgate current sensors are extremely sensitive to room temperature, various applications need this characteristic. However, conventional fluxgate current sensors have a problem in that they can only measure a narrow range of currents. To address this issue, we propose that the turns of the excitation coil be optimized with a simulator. This new sensor consists of a coiled wire that is wound around a toroidal amorphous core and through a bus bar. The sensor detects variations in excitation current according to dc current. The sensor was analyzed with a simulator. The magnetic field simulator was used to calculate the excitation current, and the output voltage according to the excitation current was calculated with a circuit simulator. We found that the results from simulations almost corresponded to those from measurements, and were able to verify the validity of the basic analytical model. As a result of analysis with the simulator, 35 turns of the excitation coil were used to achieve a wide range of measurements of ±600 mA.

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  A strain sensor with an optical signal using a magnetic Kerr effect and an inverse magnetostrictive effect on a Fe/Mn-Ir exchange-coupled single-domain magnetic thin film was fabricated and evaluated. The optical sensing technique has the advantage of not inducing noise from external electromagnetic interference. In addition, since the proposed method using the magnetic Kerr effect on single-domain exchange-coupled magnetic thin film utilizes only utilizes magnetization rotation, Barkhausen noise due to domain wall pinning can be excluded. The strain sensor was consisted of a linearly polarized He-Ne laser and various optical devices such as a prism beam splitter and a differential amplifier as well as exchange-coupled magnetic thin film. The compressive stress was measured with the strain sensor in SiO₂ (40 nm)/Fe (50 nm)/Mn-Ir (10 nm)/Fe (50 nm)/Ru (1 nm) exchange-coupled magnetic thin film. The sensor output voltage was proportional to the applied compressive stress of σ<100 MPa in the strain sensor. The sensing range and sensitivity to the stress in the strain sensor was also easily changed by varying the Fe ferromagnetic layer thickness.

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  We applied a four-legged transformer that integrates a transformer and an output choke function on a hybrid-type dc-dc converter that alternately operates forward and flyback conversions and successfully reduced the footprint of the magnetic devices used in the converters. To further miniaturize hybrid-type dc-dc converters, it is necessary to reduce the output smoothing capacitors’ footprint. In turn, reducing the size of output smoothing capacitors requires the ripple current that flows though them to be reduces. As a result of analyzing the magnetic circuit of four-legged transformers, we found that a transformer has an air-gap length that reduces the ripple current of the output smoothing capacitors to zero during forward operations. In addition, we found that the initial value of the ripple current during flyback operations matched the last value under this condition of air-gap length. In this paper, we discuss the design conditions for a four-legged transformer and the experiments we conducted to verify the effects of the design.

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