Flip-chip-type high-T-c gradiometer for biomagnetic measurements in unshielded environment

A flip-chip-type gradiometer has been constructed with a 10 mm x 5 mm plana r DC-SQUID gradiometer fabricated on a SrTiO3 bicrystal substrate and a flu x transformer made from a YBCO* //YBCO/CeO2/YSZ multilayer on a phi 50.8 mm Si wafer. The coupling coefficient between the flux transformer and the pl anar gradiometer is 0.18. The transformer increases effectively the resolut ion of the gradiometer. A magnetic field gradient resolution of 73 fT. cm(- 1).Hz(-1/2) in the white region and 596 fT.cm(-1)Hz(-1/2) at 1 Hz has been obtained. High quality magnetocardiogram signals have been successfully mea sured by using this flip-chip-type gradiometer in an unshielded environment .