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

Abstract

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//spl Phi//sub 0/ field sensitivity and <20 /spl mu//spl Phi//sub 0///spl radic/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.