Abstract
We have studied the planar-type single-layer second-order high-Tc SQUID gradiometer that detects the transverse field gradient, d2Bz/dx2. The gradiometer consists of three parallel-connected rectangular pickup loops that are directly coupled to a SQUID. The pickup loops are designed in such a way that the SQUID measures the difference in the differential screening currents of neighbouring pickup loops. The SQUID has either step-edge or bicrystal Josephson junctions. The gradiometer was made from a single layer of YBa2Cu3O7 film on a 1 cm × 1 cm chip. The response of the gradiometer was tested in various flux distributions generated by three identical multiturn film coils patterned on the same chip in parallel with each pickup loop. The balanced gradiometer responded sensitively only to the second-order field gradient. Reduction of the inductive coupling between loops improved the intrinsic balance.
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