Theoretical analysis of localized magnetic flux measurement by needle probe

Abstract
Analytical study of the needle probe measurement of magnetic flux was performed on the basis of the electromagnetic theory to provide an advanced theoretical backbone for the measuring method. Provided that the flux change in the specimen is homogeneous, the electromotive force induced between the needles represents exactly the flux change in the area between the needles. The measuring error in the needle probe measurement is caused by lack of homogeneity in the flux change postulated in the theory. Among several possible causes of flux non-homogeneity, the existence of domain structure is most intrinsic in localized area measurements, so that in this study the measuring error due to this cause was calculated theoretically in detail. It can be concluded that even in the cases of large domain size often occurring in oriented core materials, the localized measurements by the needle probe provide fairly reliable measure of the flux change in the area.