First-order high- Tc SQUID gradiometer

Abstract

SQUID gradiometers are attractive for magnetic field measurements in noisy environments. A first-order planar gradiometer has been designed and fabricated. The layout of the planar gradiometer used to have two symmetric pickup coils; however, our design adopted one compensation loop with the same size as the SQUID loop at the symmetric position to reduce the imbalance caused by the SQUID. The gradient field resolution is up to 2.2 pT cm −1 Hz −1/2 (white noise) and 30 pT cm −1 Hz −1/2 at 1 Hz.