AC losses in permanent magnets are becoming an important topic as these magnets are increasingly being used in rotating machines. To guarantee their performance, not only BH curves are relevant, but also the AC loss due to ripple fields needs to be properly characterized.

AC loss is largely due to eddy currents. To characterize this surface effect, we propose a single performance indicator: the delay time for the penetration of the magnetic field. This parameter can be used to easily predict the performance of the magnet.

For the practical point, we show the capabilities of our two measurement systems (HyMPulse and HyMAC).

The HyMPulse, a prominent pulsed field magnetometer, is being used for quality control of magnetic properties. Because it is developed to measure the end- product, it can also adequately measure the low- frequency AC losses.

In an AC magnetic properties tester – such as the HyMAC – the high- frequency losses are measured. This is done in closed-loop as well as open-loop sensors.