Experimental estimation of the remanent induction for the study of functional fatigue in permanent magnets

The magnetization of new generation hard ferromagnetic materials is difficult to access experimentally without the use of advanced and expensive instruments. This article proposes two novel, easily implementable techniques for measuring the remanent induction of permanent magnets: a variant of the extraction method and a residual magnetic field method. Both methods are validated on hard Ferrites by comparison with hysteresis loop measurements taken as a reference measurement. The advantages and disadvantages of each method are discussed. Subsequently, the proposed techniques are applied to measure the remanent induction of rare-earth magnets, specifically Neodymium–Iron–Boron (NdFeB) and Samarium-Cobalt (Sm-Co). The obtained results exhibit consistency with manufacturer-provided data, attesting to the accuracy of the proposed measurement methodologies. Furthermore, the research investigates the effect of cyclic mechanical loading on the remanent induction of permanent magnets. The magnets are subjected to a set of 10⁶ sinusoidal uniaxial compression cycles at a frequency of 30 Hz and at stress amplitudes representative for practical conditions in electrical machine applications. The remanent induction of the mechanically cycled magnets is subsequently measured. The investigation reveals no significant fatigue effect on the remanent induction in the studied hard materials. Overall, this study provides insights into the magneto-mechanical coupling effects in hard ferromagnetic materials and into the performance analysis of magnet properties under time-varying mechanical loadings.