Operation of HTS dc-SQUID sensors in high magnetic fields

For HTS dc-SQUID sensors operating in high magnetic fields we have used quasiplanar HTS Josephson junctions, HTS films prepared at optimized conditions with a high oxygen pressure dc-sputtering technique, a capsulation with a heater, and a proper dc-SQUID layouts. DC-SQUIDs tested in magnetic fields up to about 1 kG demonstrate no reduction of the critical current. A model is proposed, which gives a satisfactory explanation of the experimental results. With the use of a digital feedback a dynamic range of about 160 dB was achieved. Highly sensitive devices were prepared with flip-chip flux antennas. For the magnetometers a resolution of about 40 fT//spl radic/Hz was obtained in unshielded environment.