Progress in high Tc magnetic sensors and their applications

We report recent progress on the development of components needed for high Tc SQUID magnetic sensors, and on some of the early applications which are appearing or can be foreseen. The SNS type edge junction, and the step edge and biepitaxial grain boundary junction technologies are considered and we include details of our own YBCO device based on steps which are Ar ion-milled in MgO substrates. A review of applications prospects for these detectors will be given in the light of the available noise performance which for high Tc DC SQUIDs, at much less than 10−4 0 Hz−1/2, is now better than for commercial low Tc RF SQUIDs. Illustrations are given from clinical biomagnetism and from non-destructive evaluation of conducting materials.