Clifton Labs / Technical Articles

Permeability and Ferrite Material

Since the article was written in 2008, other types of ferrite material have been introduced with different characteristics over the MF and HF frequency ranges.  Type 31 has become popular for HF transmission line chokes, for example.  You can find more information about the various types of ferrite made by Fair-Rite at https://www.fair-rite.com/materials/ along with the applications for which they are optimized.

Note that the materials may be optimized for EMI suppression (energy dissipation) or for inductive (energy storage) applications.  These materials appear in both the Suppressive Materials and Inductive Materials tables.  These materials, such as Type 43 used in this article, have frequency ranges where they are primarily inductive and frequency ranges where they are primarily dissipative.  As shown in the graph on page 7, below 10 MHz Type 43 material is primarily inductive but at higher frequencies, it becomes increasingly dissipative.  That is why beads of Type 43 material are used for EMI suppression at VHF and UHF but can be used as transformer cores in the MF and lower HF ranges.

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