Thermoelectric detection of spherical tin inclusions in copper by magneticsensing

Inclusions and other types of imperfections in metals can be nondestructive ly detected by noncontacting magnetic measurements that sense the thermoele ctric currents around such flaws when the specimen is subjected to directio nal heating and cooling. This article presents experimental data for the ma gnetic field produced by thermoelectric currents around surface-breaking sp herical tin inclusions in copper under external thermal excitation for diff erent lift-off distances between the sensor and the surface of the specimen . The diameter of the inclusions and the lift-off distance varied from 2.4 to 12.7 mm and from 12 to 20 mm, respectively, A fairly modest 0.7 degreesC /cm temperature gradient in the specimen produced peak magnetic flux densit ies ranging from 1 to 250 nT. These results were found to be in good agreem ent with recently published theoretical predictions [P. B. Nagy and A. H. N ayfeh, J. Appl. Phys. 87, 7481 (2000)]. (C) 2000 American Institute of Phys ics. [S0021-8979(00)01824-7].