| 摘要 |
PURPOSE:To enlarge the range of action by setting a pair of spiral coils in parallel on a substrate and alternatively electrifying either of them. CONSTITUTION:Either of a pair of spiral coils 22 and 23 alternatively circularized. Namely a continuous line A shows a read output characteristic on the spiral coil 22 side and a broken line B shows the read output characteristic on the spiral coil 23 side. Now, an aberrations delta which occurs when the magnetic gap of a reading head position just between spiral coils 22 and 23 is set as zero and the aberration delta when it position near the spiral coil 23 side is set as positive, and also the aberration delta when it position near the spiral coil 22 side is set as negative. Within the ranges R1 and R4 in figure, the spiral coil 22 is electrified, within the ranges R2 and R5 the spiral coil 23 is electrified and within the R3 either the spiral coil 23 or the spiral coil 24 (spiral coil whose read output level is larger) is electrified so that reading can be possible within all the ranges from R1 to R5.
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