Single layer YBa2Cu3O7radio frequency SQUID magnetometers with directhyphen;coupled pickup coils and fliphyphen;chip flux transformers

摘要

Our aim has been to further improve the magnetic field resolution,BN, of singlehyphen;layer rf SQUID magnetometers operating in liquid nitrogen. Following the approaches recently introduced in dc SQUIDs, we tested designs with directhyphen;coupled pickup coils having an areaAp=0.6 to 0.8 cm2, and a singlehyphen;layer thinhyphen;film fliphyphen;chip flux transformer withAp=16 cm2. In conditions of still suboptimal coupling between SQUID and the 150 MHz tank circuit, we attainedBNbartil;90 fT/Hz1/2above 3ndash;4 Hz atAp=0.8 cm2, andBNbartil;24 fT/Hz1/2above 0.5 Hz whenAp=16 cm2. For rf SQUID with lumpedhyphen;element tank circuit, we project the lowerBNlimit to be le;50 fT/Hz1/2atAple;1 cm2. This might be attainable through further coupling optimization, and increase of tank frequency to the highest possible value of ge;500 MHz. copy;1994 American Institute of Physics.