A high-Tc
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 µm
cannot be detected by conventional x-ray imaging. Therefore we developed a detection system based on
a high-Tc
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 µm. This detection level was hard to achieve using a conventional x-ray detection method.
We have designed and constructed a computer controlled food contaminant detection system for practical use, based on high-T c SQUID detectors. The system, which features waterproof stainless steel construction, is acceptable under the HACCP (Hazard Analysis and Critical Control Point) programme guidelines. The outer dimensions of the system are 1500 mm length × 477 mm width × 1445 mm height, and it can accept objects up to 200 mm wide × 80 mm high. An automatic liquid nitrogen filling system was installed in the standard model. This system employed a double-layered permeable metallic shield with a thickness of 1 mm as a magnetically shielded box. The distribution of the magnetic field in the box was simulated by FEM; the gap between each shield layer was optimized before fabrication. A shielding factor of 732 in the Z-component was achieved. This value is high enough to safely operate the system in a non-laboratory environment, i.e., a factory. During testing, we successfully detected a steel contaminant as small as 0.3 mm in diameter at a distance of 75 mm.
A PC controlled food contaminant detection system for practical use was designed and constructed. The system we have developed is the High-Tc SQUID based system, which is covered with waterproof stainless steel plates and acceptable to HACCP (Hazard Analysis and Critical Control Point) program. The outer dimension of the system is 1500L mm x 477W mm x 1445H mm and the acceptable object size is 200W mm x 80H mm. This system employed a double-layered permeable metallic shield with thickness of 1 mm as a magnetically shielded box. The distribution of the magnetic field in the box was simulated by FEM; the gap between each shield layer was optimized before fabrication. Then the shielding factor of 732 in Z-component was achieved. This value is good enough to operate the system in a factory. As a result, we successfully detected a steel ball as small as 0.3 mm in diameter with a distance of 75 mm.
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