On the thermoelectric magnetic field of spherical and cylindrical inclusions

It was recently discovered that inclusions and other types of inhomogeneiti es can be nondestructively detected by thermoelectric measurements in an en tirely noncontact way by using high-sensitivity superconducting quantum int erference device magnetometers to sense the weak thermoelectric currents ar ound the affected region when the specimen is subjected to directional heat ing or cooling. In this article we present theoretical models capable of pr edicting the magnetic field produced by thermoelectric currents around sphe rical and cylindrical inclusions under external thermal excitation. We inve stigated how the magnetic signal to be detected depends on (i) the relevant physical properties of the host and the inclusion, (ii) the size of the in clusion, (iii) the depth of the inclusion below the surface of the specimen , (iv) the polarization of the magnetometer, (v) the lift-off distance of t he magnetometer from the specimen, and the (vi) direction and (vii) strengt h of the external heating or cooling applied to the specimen. The analytica l models presented are numerically evaluated to illustrate the strength and polarization of the magnetic field for different lift-off distances and in clusion depths. (C) 2000 American Institute of Physics. [S0021-8979(00)0661 0-X].