Detection of a Deep Flaw Inside a Conductor Using a Squid Magnetometer

Abstract

<p>In general, eddy current techniques are suitable for finding surface-breaking flaws in conductors. Subsurface cracks are very difficult to detect due to the skin depth effect. Acoustic techniques are effective at detecting subsurface voids, but cracks immediately beneath the surface are difficult to discriminate from the surface signal. Superconducting QUantum Interference Device (SQUID) magnetometers, very sensitive instruments for measuring DC and low frequency fields, have been used for detection of flaws in conducting objects [1,2,3]. By injecting DC and low frequency AC currents into a brass bar, we have detected a subsurface flaw using a SQUID magnetometer, and shown these data to be consistent with our theoretical calculation.</p>