Low noise HTS dc-SQUID flip-chip magnetometers and gradiometers

We have fabricated HTS dc-SQUID flip-chip sensors with a large area multilayer flux transformers. Different layouts of the flux transformers provide a large variety of magnetometers and planar gradiometers. For the magnetometers a resolution similar to 6 fT/root Hz end the planar gradiometers a resolution of about similar to 30 fTcm(.)root Hz were routinely obtained at 77 K. The noise was nearly white down to frequencies of few Hz. The sensors were vacuum-tight encapsulated together with a heater and a feedback coil. This makes the handling of the sensors more reproducible and convenient. Production of the magnetometers end gradiometers in small series was proven.