Construction and measurements of HTS DC SQUID electronic gradiometer to be used in NDE systems

We have designed a non-destructive evaluation system by using an electronic gradiometer constructed with two DC SQUID magnetometers. Typical flux modulation of the SQUIDs used in this work was about 30 /spl mu/V and the noise at 10 Hz was about 14 /spl mu//spl Phi//sub 0///spl radic/Hz. The system includes a non-magnetic stainless steel dewar and a set of coaxial exciting coils, which was used to induce an eddy current in the test piece. The sample motion stage and the SQUIDs were computer controlled and the output data from the electronic gradiometer was obtained by using Labview software.