Colpitts-Oscillator-Type Micro-Magnetic Sensor Using Amorphous MI Elements.

A Colpitts-oscillator-type field sensor was constructed using Ml-elements (amorphous FeCoSiB wire and CoFeB film) as the inductive components. The oscillation voltage of the circuit changes with the applied magnetic field, owing to the change of impedance of the MI element. Therefore, this sensor operates with amplitude modulation. The sensitivity of a sensor with a 1 mm-long wire head was 0.1 V/Oe, and the resolution of the field detection was about 10-4 Oe. The temperature stability of the sensor was improved by adding an emitter resistance Re to the Colpitts circuit.