Elsevier, Physica C: Superconductivity and its Applications, (480), p. 10-13, 2012
DOI: 10.1016/j.physc.2012.04.023
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The performance of the direct readout schemes for dc SQUID, Additional Positive Feedback (APF), noise cancellation (NC) and SQUID bootstrap circuit (SBC), have been studied in conjunction with planar SQUID magnetometers. In this paper, we examine the NC technique applied to a niobium SQUID gradiometer module with an Nb wire-wound antenna connecting to a dual-loop SQUID chip with an integrated voltage feedback circuit for suppression of the preamplifier noise contribution. The sensitivity of the SQUID gradiometer module is measured to be about 1 fT/(cm vHz) in the white noise range in a magnetically shielded room. Using such gradiometer, both MCG and MEG signals are recorded.