HIGH-TEMPERATURE RF SQUID GRADIOMETER APPLIED TO NONDESTRUCTIVE TESTING

This paper reports the utilization of a high temperature superconducting (HTS) RF SQUID gradiometer in non-destructive testing (NDT), A two-hole HTS RF SQUID, capable of working in a noisy environment without any magnetic shielding, is employed as a gradiometer sensor without using flux transformer coils. This gradiometer, maintained at LN2 temperature, is sensitive enough to detect small mock cracks in an aluminium alloy slab covered by another 25.4 mm thick solid aluminium alloy slab. Such an NDT device should have a significant impact on metal fatigue detection technology and demonstrates an important practical usage of high temperature superconductors.