Design and Fabrication of HTS-SQUID Gradiometer With Imbalance of 10–4 Using a Gradiometric SQUID Structure

We have succeeded in fabricating a high-temperature superconducting (HTS) thin-film gradiometer with small imbalance by applying an HTS multilayer process, including crossovers, superconductive contacts, and ramp-edge Josephson junctions. The gradiometer consists of a series pickup coil and a gradiometric superconducting quantum interference device (SQUID) structure. Since the intrinsic imbalance of the series pickup coil is found to be small, a highly balanced gradiometer can be obtained by selecting the gradiometric SQUID inductor with imbalance that cancels the imbalance of the pickup coil out. The fabricated gradiometer showed the imbalance better than 10
^–4
by applying a homogeneous magnetic field using a large circular coil in an outdoor experiment.