Measurement Criteria for the Magnetic Characterization of Magnetic Materials

Abstract

Ferromagnetic materials exhibit nonlinear magnetic behavior, and many are anisotropic. Their magnetic characterization requires a mappingin excitation and measurementof 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. The present 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 1D and 2D 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, 1D excitation systemsthough limited to certain applications -fulfill the criteria the most, and finally, while the excitation can be 1D or 2D the measurement should always be 3D.