Magnetizing a ferrimagnetic core at megahertz frequencies

The average flux densities and their phases through different cross sections of the toroidal core made of ferrimagnetic material have no obvious difference at low frequencies even if the core is excited by several turns of winding current that cover only a very small part of the circumference of the core. However, with the increase of the frequency into the MHz range and the enlargement of the core size, it is observed that the flux densities through two different cross sections and the phases between them are different. The bigger the core, the more obvious the phenomenon is. This experimental phenomenon may hint that time is needed to make the whole core uniformly magnetized and the magnetizing time increases with the enlargement of the core sizes. When the time is comparable to the period of the exciting current, this nonuniformly magnetizing phenomenon occurs.