Assessment of HTS step-edge thin-film RF SQUIDs for NDT

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Abstract
The authors describe the fabrication of straightforward YBa2Cu3O7- delta thin-film step-edge Josephson junctions and RF SQUIDS on (100) MgO by pulsed laser deposition. At 77 K, a typical SQUID has a transfer function of 8 mu V/ Phi O. The SQUID has been operated in the open loop and flux-locked modes to assess the potential of HTS devices in NDT applications. Some attractive characteristics are apparent: the SQUIDS already have adequate field sensitivity and excellent spatial resolution, while the use of liquid nitrogen is convenient and has fundamental advantages over liquid helium in terms of cryostat design. However, experimental results also highlight the problems faced by HTS SQUID NDT including the need for reasonably low 1/f noise and gradiometric operation. Further work is necessary, particularly in the areas of device configuration and system design.