Eddy current probe patterned in YBCO

Superconductive quantum interference devices (SQUIDs) coupled to arrays of small pickup loops can give images of millimeter fatigue cracks deep inside structures, using eddy currents. Coupling magnetic flux from a pickup loop to a SQUID commonly leads to a thousand fold loss. An eddy current probe, patterned in YBCO, uses 37 parallel turns to couple magnetic flux from a pickup loop 8 mm in diameter to give an expected gain in flux transfer of about six, instead of a loss.