A ferrite core is a ceramic material made from iron oxide mixed with other metals (nickel, zinc, manganese). It's magnetic — it concentrates magnetic field lines the way a lens concentrates light. Winding a coil on a ferrite core dramatically increases its inductance compared to an air-core coil.
Mixes and frequency ranges
Different ferrite formulations ("mixes") are optimized for different frequency ranges:
| Mix | Material | Frequency range | Common use |
|---|---|---|---|
| Mix 43 | NiZn | 20–250 MHz | EMI suppression, broadband transformers |
| Mix 61 | NiZn | 200 MHz–2 GHz | High-frequency RF |
| Mix 31 | MnZn | 1–300 MHz | EMI suppression |
| Mix 77 | MnZn | DC–50 kHz | Power transformers, low-frequency inductors |
For the Open Energy experiments, Mix 43 (like the FT-50-43 toroid) is the standard recommendation — its operating range is well above the frequencies being measured, which prevents core saturation from confusing the results.
The non-linearity connection
At high enough drive levels, a ferrite core saturates — the magnetic material can't hold any more flux, and the inductance drops sharply. This is a non-linear behavior. Several of the patent-derived experiments deliberately drive ferrite cores into or near saturation to study what happens at the transition boundary.