SIMULATION AND DESIGN OF A SUPERCONDUCTING EDDY-CURRENT PROBE FOR NONDESTRUCTIVE TESTING

Numerical modeling studies were carried out for the design and perform ance evaluation of an eddy current probe for superconducting quantum i nterference device (SQUID) based noncontacting electromagnetic nondest ructive testing. The probe utilizes high-T-c SQUID from electromagneti c interference and to focus magnetic flux due to the eddy current exci tation coil into the object under test (OUT). This is very important i n order to achieve ''self-nulling,'' where the probe responds only to the defects in the OUT. Simulations are carried out with the eddy curr ent probe located a finite distance above a defect free conducting hal f-space of infinite thickness. Eddy current densities in the OUT are t hen calculated for various probe designs, These eddy current densities give an indication of the flux focusing, and hence increased spatial resolution for combinations of HTS and mu-metal shielding. Shielding f actors an also calculated for the screening of the primary excitation field and the ''defect-free'' eddy current field. Agreement with the a nalytical solution of a simple solenoid above a conducting half-space verifies the numerical method. (C) 1998 American Institute of Physics.