For an amorphous core or a nanocrystalline core, mean magnetic path (Lm) and iron cross section (Ac) are two important parameters. Here we’ll introduce them and the calculation method for a finished soft magnetic core.

Mean Magnetic Path and Iron Cross Section

The Lm is the mean length of a magnetic core, and the Ac is the effective section area of it. The resistance value of a conductor is proportional to its length and inverse proportional to its section area. Similarly, the reluctance of a magnetic core is proportional to Lm and inverse proportional to Ac.

Then, how to calculate them when the shape and dimensions of a core are given? Take the toroidal core (ring core) for mini current transformer as an example. The Lm is the mean value of the circumference of its outer and inner circle. The Ac is equal to the external cross section multiply the stacking factor, range from 0.75 to 0.8 for nanocrystalline or amorphous cores.

For special shape cores, the Ac and Lm value cannot be sorted out easily, thus, we’ll provide all the information to customers. Usually, our common mode choke core has small Ac and Lm value, due to its small size.