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 /spl sim/6 fT//spl radic/Hz and the planar gradiometers a resolution of about /spl sim/30 fT/cm./spl radic/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 and gradiometers in small series was proven.
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Faley et al. (2001) studied this question.
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