Development of Metallic Contaminant Detection System Using Eight-Channel High- $T_{c}$ SQUIDs

In this paper, a roll-to-roll eight-channel (8-ch) high-Tc superconducting quantum interference device (SQUID) detection system for magnetic contaminants in a lithium-ion (Li-ion) battery anode sheet was developed. Finding ultra-small metallic foreign matter is an important issue for a manufacturer because metallic contaminants carry the risk of an internal short. When contamination occurs, the manufacturer of the product suffers a great loss from recalling the tainted product. Metallic particles with outer dimensions smaller than 100 μm cannot be detected using a conventional X-ray imaging system. Therefore, a highly sensitive detection system for small foreign matter is required. We have already developed a detection system based on a single-channel SQUID gradiometer and horizontal magnetization. For practical use, the detection width of the system should be increased to at least 65 mm by employing multiple sensors. In this paper, we present an 8-ch high-Tc SQUID roll-to-roll system for inspecting a Li-ion battery anode with a width of 65 mm. A special microscopic type of a cryostat was developed upon which eight SQUID gradiometers were mounted. As a result, small iron particles of φ35 μm on a real Li-ion battery anode with a width of 70 mm were successfully detected. This system is practical for the detection of contaminants in a Li-ion battery anode sheet.