First results for a novel superconducting imaging-surface sensor array

A superconducting imaging-surface system was constructed using 12 coplanar thin-film SQUID magnetometers located parallel to and spaced 2 cm from a 25 cm diameter lead imaging-plane. Some measurements included two additional sensors on the "back" side of the superconducting imaging-plane to study th e field symmetry for our system. Performance was measured in a shielded can and in the open laboratory environment. Data from this system has been use d to: (a) understand the noise characteristics of the dewar-SQUID imaging p late arrangement, (b) to verify the imaging principle, (c) measure the back ground rejection factor of the imaging plane, and (d) compare superconducti ng materials for the imaging plane. A phantom source field was measured at the sensors as a function of phantom distance from the sensor array to verify the imaging theory. Both the shap e and absolute values of the measured and predicted curves agree very well indicating the system is behaving as a gradiometer in accordance with theor y. The output from SQUIDs located behind the imaging surface that sense bac kground fields can be used for software or analog background cancellation. Fields arising from sources close to the imaging plane were shielded form t he background sensors by more than a factor of 1000, Measurement of the sym metry of sensor sensitivity to uniform fields exactly followed theoretical predictions.