Recent progress with SQUID gradiometers, and their application to non-destructive evaluation and biomagnetism

Full text: SQUID gradiometers, both first and second order, are of great importance in those magnetometric measurements where the objects involved are at room temperature and cannot be screened by a superconductor. Essentially the gradiometers can discriminate in favour of nearby, but weak, sources and against distant but stronger ones, such as moving machinery. Fabricating such devices in HTS materials has been difficult because fabrication technologies are still more or less limited to single layer thin film methods. This paper will discuss new work on improving the fabrication and balance of such devices and present data from both HTS and LTS gradiometers on recent progress in flaw detection in aircraft structures, in fetal cardiography and in studies of the visual perception of stereopsis