A high-Tc flip-chip SQUID gradiometer for mobile underwater magnetic sensing

Abstract

We report on the development of a magnetic gradient tensor sensor based on high-Tc SQUIDs for marine surveying applications. The proposed system uses sixplanar gradiometers incorporated into a hexagonal pyramid structure wherethe combined output will provide a measure of the gradient tensor. Thisreport focuses on the development and characterization of long baseline high-Tc SQUID gradiometers for this purpose. We compare the performance of twoseparate fabricated gradiometer designs. These devices both consist of a large40 mm × 20 mm gradiometric pickup loop antenna flip-chip coupled to a small readout SQUIDgradiometer. We have thus far demonstrated an unshielded gradient sensitivity of∼29 fT cm−1 Hz−1/2 at 1 kHzand ∼170 fT cm−1 Hz−1/2 at 10 Hz through optimizing the coupling inductances of our device.