Amorphous wire MI micro magnetic sensor for gradient field detection

Sensitive and quick response micro magnetic sensor for detection of a very localized field (gradient field) cancelling background disturbance field is presented using a high frequency (20 similar to 40 MHz) multivibrator having a pair of amorphous wire MI head of 1 similar to 3 mm length each. The resolution of field detection is 10(-6) Oe for ac field and the cut-off frequency is about 200 kHz. Stable detection of a surface field of a densely magnetized ring magnet with 19 mm diameter and 2000 poles (30 mu m in pole interval) for a high resolution rotary encoder was carried out with a sinusoidal waveform.