Non-destructive evaluation with a linear array of 11 HTS SQUIDs

A linear array of 11 High Temperature Superconducting (HTS) SQUIDs was used for non-destructive evaluation (NDE) applications. The array consists of 11 SQUID magnetometers arranged linearly along a single substrate with 0.75 mm spacing. The SQUIDs have 105 nT/Φ₀ field sensitivity and <20 μΦ₀/√Hz noise values at 1 kHz with DC bias current. We used an eddy current NDE technique. The eddy current induction coils were arranged such that there was a null in the induction field at the SQUIDs. Single Frequency and white-noise (frequency-continuum) induction schemes were used. Both SQUIDs and induction coils were placed at the bottom of a liquid nitrogen dewar with a 4 mm hot-to-cold distance. Flawed and unflawed samples were scanned beneath the array. The phase and amplitude of the SQUID´s response relative to the induction signal were acquired. This paper presents experimental results and their interpretation