SENSITIVE AND QUICK RESPONSE MICRO MAGNETIC SENSOR USING AMORPHOUS WIRE MI-ELEMENT COLPITTS-OSCILLATOR

A new high performance micro magnetic sensor using an amorphous wire M I element (30 mu m diameter, 1 similar to 3 mm length) is presented. T he MI element works as an inductive element in the Colpitts oscillator circuit with an oscillation frequency of about 50 similar to 100 MHz and changes its voltage amplitude with about 100 %/0e. The amplitude m odulation-demodulation type field sensor circuit having a negative fee dback loop shows sensing performances with a high linearity of 0.1 %/F S (+/- 1 Oe), quick response at a cut off frequency of about 300 kHz a nd a temperature stability of about 0.06 %/degrees C (RT similar to 70 degrees C). The weak surface field of about 0.1 Oe of a densely magne tized ring magnet with 19 mm diameter and 1,000 poles for an accurate rotary encoder was stable detected using the MI sensor.