Magnetic materials for high rotational velocity machines: a fresh look at an old problem

The diameter and speed of rotors in electromagnetic machines are limited by materials. Machines having high tip-speed rotors demand materials performance in both magnetic and mechanical behaviors. As a result, soft magnetic materials are used both for energy conversion and for structural support. Unfortunately, desirable magnetic characteristics are linked to materials with inferior mechanical properties. Furthermore, a material’s magnetic characteristics change with temperature, mechanical stress, frequency, laminate thickness, etc., complicating direct comparison between materials candidates. Two new metrics for materials comparison under such multifactoral conditions are presented. A “next generation” category of magnetic materials is identified and some issues facing machine designers for the effective use of these materials are suggested.