ACTIVE MAGNETIC SHIELDING DEVICE COMPATIBLE WITH ALTERNATING-CURRENT MAGNETIC FIELD

PROBLEM TO BE SOLVED: To provide an active magnetic shielding device that can highly accurately and surely cancel the disturbance magnetic field of an alternating-current magnetic field and a fluctuating magnetic field by eliminating the unnecessary canceling magnetic field applied to a magnetic sensor. SOLUTION: In order to eliminate unnecessary canceling magnetic field gradient sensor signals contained in the output signals of a magnetic sensor S, pseudo sensor signals that are very similar to the canceling magnetic field gradient sensor signals are formed by a current-voltage conversion circuit 15 for detecting the canceling current passed to a compensation coil 11 and a magnetic sensor pseudo circuit 10. The unnecessary canceling magnetic field gradient sensor signals in the signals are offset and erased by an adding/subtracting means 12. The magnetic sensor pseudo circuit 10 includes: a phase synchronizing means 17 for synchronizing the phase of the output signal of the current-voltage conversion circuit 15 with the phase of the output signal of the magnetic sensor; and an amplitude adjusting means 18 with a polarity switching function for switching the phase of the pseudo sensor signal in response to the phase of the canceling magnetic field gradient sensor signal. COPYRIGHT: (C)2010,JPO&INPIT