Mobile NDE System Utilizing Robust HTS-SQUID Magnetometer for Use in Unshielded Environments

In this paper, we demonstrated detection of deep-lying defects in aluminum alloy samples utilizing an eddy current technique while moving a robust HTS-SQUID magnetometer integrated on a robot-based NDE system in an unshielded environment. A bicrystal-Josephson-junction-based HTS-SQUID magnetometer, which was covered by an alternative HTS film as a superconducting shield, both having a mesh structure with a 5-μm line width, was used in the system. An active magnetic shield scheme was also utilized in order to cancel magnetic flux coupling to the magnetometer during motion. For comparison, detection of the same defects using a ramp-edge-Josephson-junction-based HTS-SQUID gradiometer, which has the roughly equivalent area with the magnetometer, was also carried out. Experimental results showed that the magnetometer had better capability to detect deeper defects in conductive materials than the gradiometer.