Sensitivity to Off-Axis Vector Components of Typical Wire Wound Flat H-Coil Configurations

Power loss in magnetically soft magnetic materials can be measured by detecting magnetic field strength H and flux density B. H can be detected with the so-called H-coil sensor, which is an induction coil wound on a thin flat non-magnetic former. The accuracy of H measurement directly affects the measurement of power loss. For alternating (uni-directional) magnetization, H is applied mainly along the symmetry axis of the sample under test and the normal component is small due to magnetically closed circuit. So any off-axis H components usually have small amplitude and do not cause significant errors. However, under 2-D or rotational magnetization, the H-coils are exposed to strong H in all directions. It is shown in this paper that such off-axis H components can introduce significant amplitude and phase errors, which contribute to the differences in the calculated clockwise and anticlockwise power loss values. Theoretical analysis of order of magnitude of such off-axis sensitivity is given in this paper for three typical configurations of H-coils (with the return wire positioned along one side, diagonally and through the center). Experimental verification is also presented for the side wire configuration.