Development of Metallic Contaminant Detection System Using RF High-Tc SQUID With Cu Pickup Coil

We developed a metallic contaminant detector using a high-Tc rf-SQUID with a Cu pickup coil for industrial products. For manufacturers producing industrial products, problems arising from metallic contaminants are critical issues. A detection system using a SQUID is a powerful tool for sensitive inspections. However, since the detection width is dependent on the size of the SQUID, multiple sensors are required for practical use. However, such devices are costly and complicated. This is the reason as to why the SQUID system has not been widely used in the field. Therefore, we have recently proposed a new detection system using Faraday's law of electromagnetic induction. The detection section consists of a pair of permanent magnets surrounded by copper wound pickup coils. The output of the pickup coil is remotely connected to a copper wound input coil. The input coil couples magnetically with a SQUID. In this case, the width of the pickup coil can be widened as to be as large as 27 mm in diameter. As compared with 1-ch SQUID direct detection, the width of the new method is three times larger. In this paper, we describe the performance of the system with a conveyor, which uses an LC resonant circuit. By applying the LC resonance, the amplitude increased and the signal to noise ratio (SNR) was improved by a factor of two.