Apparatus for detecting an external magnetic field

摘要

Apparatus for detecting an external magnetic field comprises a magnetic sensor which produces para-magnetic oscillations and includes an elongated member of an electrically conductive material and a thin magnetic film disposed thereabout. Alternative embodiments of the invention are presented in each of which the detection of an external magnetic field by the sensor results in a change in the oscillating state. In a first embodiment, the sensor is maintained normally in an oscillating state of a given domain and thus a given phase; when the sensor is subjected to an external magnetic field of appropriate intensity and polarity, the magnetization of the sensor shifts from the first domain to the second domain and accordingly there is produced a change or reversal in phase of the oscillatory output derived from the sensor. In that change of phase, the sensor output passes through a zero voltage value which is detected for providing an indication of the sensing of the external magnetic field. In an alternative embodiment, the exciting magnetic field normally maintains the state of magnetization in a first domain producing a non-oscillating state of the sensor; an external magnetic field has the effect of switching the magnetization to an oscillation domain; the sensor accordingly switches from a non-oscillating state to an oscillating state in response to sensing the external magnetic field.