Experiments on eddy current NDE with HTS rf SQUIDS

HTS SQUIDs are promising sensors for applications in eddy current NDE. Due to their high field sensitivity at low frequencies, they are especially suitable for applications, where a large penetration depth is required. We have set up two SQUID systems for low frequency eddy current NDE. 3 GHz rf SQUIDs made from YBCO are used as sensors with a field resolution of about 1pT//spl radic/(Hz). One system, where the SQUIDs are cooled by immersing them in liquid nitrogen, is optimised for testing fellows of aircraft wheels. The fixed cryostat is mounted close to the outer surface of the rotating fellow. The second system uses a cryocooler for SQUID cooling. A motorised x-y stage is used to move the SQUIDs above the plane specimen to be tested. Due to the high slewrate of the SQUID electronics, both systems can easily be operated in an unshielded environment. A double-D shaped coil is used to reduce the excitation field at the location of the SQUID. We report on first results of measurements on aircraft parts.