Amorphous wire MI micro magnetic sensor for gradient field detection

A 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/spl sim/40 MHz) multivibrator having a pair of amorphous wire MI heads each of 1/spl sim/3 mm in length. The resolution of field detection is 10/sup -6/ Oe for an ac field and the cut-off frequency is about 200 kHz. Stable detection of the surface field of a densely magnetized ring magnet with 19 mm diameter and 2000 poles (30 /spl mu/m in pole interval) for a high resolution rotary encoder was carried out with a sinusoidal waveform.