Development of High-T c SQUID and Application to Ultra-Sensitive Contaminant Detection System

We have developed magnetic metallic contaminant detectors using multiple high-T c SQUIDs (superconducting quantum interference devices) for food and industrial products. For manufacturers producing items such as processed food and industrial products, problems with metallic contaminants are critical issues. When contamination occurs, the manufacturer of the product suffers a great loss from recalling the tainted product. The lower detection limit for practical X-ray usage is on the order of 1 mm. A detection system using a SQUID is a powerful tool for sensitive inspections. For practical use, the detection width of the system should be increased by employing multiple sensors. We designed and set up a multi-channel high-T c SQUID inspection system with a width of at least 130 mm for food and 70 mm for industrial products. As a result, a small ϕ0.3-mm stainless steel particle for food and a ϕ27-μm iron particle for industrial products were successfully detected.