This study reports on a magnetic sensor composed of a Cu wire sandwiched between Co-based amorphous ribbons. The impedance of the Cu wire largely depends on the permeability of the amorphous ribbons and changes with an external field. This phenomenon results in a change in the voltage at the fundamental frequency (V 1st) and that at the second harmonic frequency (V 2nd) at both ends of the Cu wire. The maximum V 2nd variation rate was ∼150%/Oe which is about 15 times larger than that of V 1st. The detection of the second harmonic voltage offers the potential for a great improvement in the magnetic field sensitivity.

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A tunable MR sensor with variable sensitivity and measuring range is fabricated and characterized. The sensor has been fabricated using a combination of Ni-Fe soft magnetic film, Fe-Co-Sm hard magnetic film. The sensor is placed in a magnetizing coil for the process of magnetizing the hard magnetic film. The sensitivity and the measuring range of the sensor are tuned by bias magnetic field produced by the magnetic poles of the hard magnetic film. The sensitivity change was about 60 %, and the measuring range change was about 30 % in the tunable MR sensor from the experimental results. The bias magnetic field is controlled by changing amplitude of the pulsed magnetic field in the magnetizing for the hard magnetic film. The control power for one time tuning is about 18 Wh.Index Terms-Tunable magnetic sensor, variable sensitivity and measuring range, hard magnetic film, soft magnetic film, pulsed magnetic field magnetizing method.

This article describes the use of a magnetic ribbon to create a highly sensitive magnetic sensor. The sensor employs the impedance change in a magnetic ribbon when a radio frequency (RF) current is passed through it and an external magnetic field is applied. To achieve a highly sensitive magnetic sensor, we had to increase the impedance change. We examined stacked magnetic ribbons, each isolated with thin plastic sheets, and interpreted the results by calculating the impedances and relative current in each ribbon. The impedance change was enhanced by stacking the ribbons. However, the effective permeability, which greatly affects the sensitivity, decreased as the number of ribbons increased. Consequently, the double-layered structure provided the maximum sensitivity, which was about three times higher than that of a singlelayered structure.

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