Nondestructive evaluation of flaws using SQUIDs

Abstract

Using high-T c SQUIDs, we have designed a nondestructive evaluation system to probe buried flaws. The frequency of the excitation magnetic fields was varied from 10 to 800 Hz and the magnetic fields generated from the eddy current was lock-in detected. The SQUIDs output data revealed the most effective excitation frequencies for the flaws with different depths and widths. The signal-to-noise ratio of the deep flaws can be further enhanced either by using higher excitation fields or using the SQUIDs with higher low-frequency sensitivity.