Second order gradiometer and dc SQUID integrated on a planar substrate

摘要

An integrated system of a thinhyphen;film niobium dc superconducting quantum interference device (SQUID) and a second order gradiometer on a planar substrate is described. The system consists of a dc SQUID with eight loops in parallel, each sensitive to the second derivative part;2Bz/part;x2of the magnetic field. The calculated SQUID inductance is 1.3 nH. With an overall size of 16times;16.5 mm2a sensitivity of 1.5times;10minus;9Tmminus;2thinsp;Hzminus;1/2is obtained. The measured transfer function for uniform fields perpendicular to the plane of the gradiometer is 2.1times;10minus;7thinsp;Tthinsp;Fgr;minus;10.