Two-Channel HTS SQUID Gradiometer System for Detection of Metallic Contaminants in Lithium-Ion Battery

A two-channel high-T_c SQUID gradiometer system for the detection of magnetic foreign matter in a lithium-ion battery was developed. Finding ultra-small metallic foreign particles can be a big issue for a manufacturer that produces commercial products such as lithium-ion batteries. If the presence of such particles is detected in its products, the manufacturer has to recall the products and thereby suffers a significant loss. Previously, we developed a detection system based on a single-channel SQUID gradiometer and horizontal magnetization. For practical use, we need to increase the detection width of the system by employing multiple sensors. In this paper, we present a two-channel high-T_c SQUID gradiometer system for the inspection of a lithium-ion battery. In order to increase the inspection width, two SQUID gradiometers were employed along with a specially designed cryostat. As a result, small iron particles with a diameter of less than 100 μm were detected by the system with a width of 22 mm. This is the first multi-channel high-T_c SQUID gradiometer system for detection of the contaminants in a lithium-ion battery.