A high-Tc SQUID micro-detector with a high performance magnetic shield for contaminant detection in industrial products

A high-T-c superconducting quantum interference device (SQUID) system for the detection of magnetic foreign matter in industrial products was developed. There is a possibility that ultra-small metallic foreign matter has been accidentally mixed with industrial products such as lithium ion batteries. Metallic particles with outer dimensions less than 100 mu m cannot be detected by conventional x-ray imaging. Therefore we developed a detection system based on a high-T-c SQUID microscope with a high performance magnetic shield. The use of SQUID microscopes with a 0.5 mm thick vacuum window was proposed. This design enables the SQUID to approach the object to be measured as close as 1 mm and enhances the sensitivity. A new magnetic shield with sleeves was carefully designed and built. As a result, we could successfully measure small particles sized 100 mu m. This detection level was hard to achieve using a conventional x-ray detection method.