Abstract
Active shielding effect was examined in a negative feedback circuit system consisting of a magneto-impedance effective sensor, an amplifier and a canceling coil to compensate external magnetic field noise. The frequency dependent active shielding effectiveness depends on the phase difference between the input and output sensor signals in a loop, whch were less than 90 degree up to 20,000 Hz. An excellent characteristic of active shielding effectiveness of 48 dB was obtained for the external magnetic field noise from dc field to the frequency of 2,000 Hz.
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