Design of improved integrated thin-film planar dc SQUID gradiometers

Abstract

Key issues in the design of improved first and second derivative, thin-film, planar dc SQUID gradiometers are discussed. The introduction of a planar coupling scheme to optimally couple the planar dc SQUID to the gradiometer pickup loops leads to significantly increased sensitivity as well as elimination of the sensitivity differences between series and parallel gradiometer loop configurations. Two-hole and figure-8 SQUID designs are presented which are consistent with intrinsic gradiometer balance ≲10−4 against uniform field changes. Straightforward calculations together with data from existing low-noise SQUIDs suggest improvements in gradient sensitivity on the order of 102 over existing planar gradiometers.