Fair-rite’s ‘new’ #43 permeability data (2020)

Fair-rite publishes spreadsheets of the complex permeability characteristic of many of the ferrite mixes. This note is about #43 mix and clarification I sought from Fair-rite.


I note that recently, the published table of #43 permeability changed subtly but significantly. Does this table apply to historical product, or does it only apply to new product, ie was there an actual change in the mix, or what it the result of better measurement of characteristics?

Fai-rite’s response (Jan 2021)

Hi Owen, It is a little bit of both. We have acquired new more accurate test and measurement equipment since the previous curves have been published. Additionally due to availability of raw materials over time; there has been some drift relative performance in some of our materials.

The actual compositions of the materials are the same but, in some cases the composition/concentrations of some of the impurities or differences in some of the processing parameters of the various oxides our materials are comprised of has seen changes.

We use average recent lots for producing curves for our catalog and website.

It is a little difficult to separate out exactly what change can be attributed to the measurement equipment versus what is due to the material. What I can say is that; In general, the shift due to equipment changes were most pronounced at higher test frequencies.

Thanks, Michael Arasim Product Manager for Power and Inductive Applications.

I have published various tools and articles based on the undated pre 2020 published data, and measurement results reconciled quite well with that data, taking into account the tolerance on the products.

I have added the #43 data I downloaded in 2020 (fortunately the files do contain a date), and included the data in Ferrite permeability interpolations as shown in the above screen shot.