HTS Rf-SQUID Microscope for Metallic Contaminant Detection

We have developed metallic contaminant detection systems using HTS-SQUIDs. In this study, we designed and fabricated a single-chip HTS rf-SQUID using SQUID microscope techniques to reduce both the lift-off and cooling temperature as compared with the substrate resonator HTS rf-SQUID. The HTS rf-SQUID was a washer-type rf-SQUID without a flux focuser. By lengthening and narrowing the SQUID hole, we showed that the inductance of the SQUID ring was reduced, and the effective area and the field noise were improved consequently. By introducing a single-chip HTS rf-SQUID with hole size of 800 μm × 50 μm into the detection system, we obtained a field sensitivity of 150 fT/Hz^1/2 and a lift-off of 1.5 mm. Since this SQUID has advantages in the reduction of lift-off and cooling temperature, its detectability and magnetic field resolution are superior to that of the substrate resonator SQUID. Finally, we showed the single-chip SQUID can detect 20 μm in diameter iron balls.