MIグラジオメータ用アクティブ磁気シールドの環境磁界低減効果

抄録

We have developed the active magnetic shielding system, which a reference-type MI element output is fed back to a sensor-head with a feedback coil, to reduce the environmental magnetic noise around the sensor-head. Output properties of MI elements could keep linearity by adjusting the DC magnetic field in the feedback coil to less than 1 µT. Furthermore, the noise at 60 Hz related to the power source line was reduced by 1/10 with this system. We have measured a variation of magnetic field with a stainless steel metal ball (SUS304, 0.3 mm diameter) movement by using a new MI gradiometer with this system, and the magnetic signal of 700 pT was detected clearly compared with a previous MI gradiometer. Consequently, we considered that this type MI gradiometer is an effective method of a very weak magnetic measurement in the environmental magnetic noise.