The Ferrite permeability interpolations calculator performs interpolations of tables of complex permeability data.
From manufacturer’s curves
Some of the data is derived from manufacturer’s published complex permeability curves. The plot above shows the Ferroxcube’s published curve for 3C81 material, and points at which it was digitised to extract a table of µ’ and µ”.
The calculator result is a cubic spline interpolation of the tabulated data.
From manufacturer’s tables
Some data is derived from manufacturer’s published complex permeability tables, most or all of the Fair-rite data is sourced in this way.
Above is a plot of Fair-rite’s published complex permeability table for #77 mix. Note that µ’ has negative values from 7-1140MHz which raises concern for the quality of the data, it may be the result of blind extrapolation.
Whilst I prefer to use data traceable to the manufacturer, I favor a solution that discards data that is on the face of it suspect.
So, in processing these tables data is discarded where µ'<0.95 or µ”<0. Only interpolation is done (ie no extrapolation). Note that this would include some data from the plot above that is probably extrapolated by Fair-rite, but not obviously wrong. It would be better if they published just what they measured. This change took effect on 07/09/2019.
The calculator result is a cubic spline interpolation of the tabulated data.
From measurement
The calculator includes data for some cores for which published data could not be found. They are mostly characterised by my own measurement.