We have developed a scanning SQUID microscope using a conventional niobium dc SQUID, which can be produced easily and reproducibly. The sensor has an effective area of about 45 micron x 45 micron and a magnetic field resolution on the order of 1 pT/(Hz0.5. The SQUID is attached to a copper rod inside the insulating vacuum of a liquid helium cryostat. A 50 micron thin sapphire window separates the SQUID from the sample at room temperature. The sample is scanned using a motor driven x-y-stage. The SQUID sensor is read out using conventional DC-SQUID electronics with a bandwidth of 1 kHz and a slew rate of 200 mT/s. A personal computer drives the sample stage and generates the scan image from the SQUID signal. This scanning SQUID microscope can be operated without magnetic shielding in a normal lab environment and has a spatial resolution of about 50 micron. We have shown the usefullness of our scanning SQUID microscope for practical applications such as measurements on bills, data storage media, geological samples, and static field or eddy current NDE of stainless steel samples and aircraft parts.
Eddy current measurements with a high spatial resolution SQUID system
Wirbelstrommessungen mit einem hochauflösenden SQUID-System
2000
9 Seiten, 11 Bilder, 10 Quellen
(Nicht paginiert).
Aufsatz (Konferenz)
Englisch
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