Measurement Criteria for the Magnetic Characterization of Magnetic Materials

Ferromagnetic materials exhibit nonlinear magnetic behavior, and many are anisotropic. Their magnetic characterization requires a mapping-in excitation and measurement-of the magnitude and direction of the magnetic field H or magnetic induction B. While many previous works have treated different parts of the characterization problem, the question of measurement reliability was not always adequately addressed. This work relies on key assumptions made in characterization experiments to propose three criteria that form a necessary and sufficient condition for reliable measurements: 1) material properties are assumed homogeneous in the measurement region (uniformity criterion); 2) measured H is assumed to be equal to that giving rise to the measured B (correspondence criterion); and 3) B&H directions are assumed known (direction criterion). Both theory and simulation are used to quantitatively assess the fulfillment of these assumptions using various apparatuses found in the literature along with new setup designs. Both alternating and rotating field loadings are considered for linear and nonlinear behaviors, using isotropic and anisotropic materials in both 1-D and 2-D excitation and measurement systems, with and without applied mechanical stress. The derived criteria are then used to establish guidelines for accepting, rejecting, and improving experimental apparatuses and offer clear insight into the measured data. In general, and when the application allows it, surface measurements of both B&H are recommended, 1-D excitation systems-though limited to certain applications-fulfill the criteria the most, and finally, while the excitation can be 1-D or 2-D, the measurement should always be 3-D.

Automated summary

This study proposes criteria for the reliable measurement of the magnetic characteristics of ferromagnetic materials, including the uniformity criterion, the correspondence criterion, and the direction criterion, and quantitatively evaluates these criteria using theory and simulation. The results indicate that surface measurements and 1-D excitation systems are more suitable for fulfilling the criteria, and provide guidelines for accepting, rejecting, and improving experimental apparatuses.