Low-T-c magnetometer used for active shielding in the frequency range dc-500 Hz in biomagnetic measurements

Ultra low-noise de SQUIDS have been used to detect disturbances in biomagne tic measurements and to feed an active shielding system that compensates th ese disturbances. This work describes some properties of the SQUIDs used an d the principle of active shielding that has been improved for frequencies from de to 500 Hz. So far an additional attenuation of up to 50 dB for near -de and almost 20 dB for 50 Hz magnetic disturbances has been achieved.