Air Core vs. Ferrite Core

Refers to the material inside a PEMF coil. An air-core coil has no magnetic material inside. It doesn't saturate regardless of drive current, making output predictable at high amplitudes. A ferrite or iron core multiplies flux density (relative permeability µr can be 100–1000x air), enabling higher Gauss with fewer turns. However, the core saturates at high currents. Above the saturation point the effective permeability collapses and output becomes nonlinear. Most high-peak PEMF devices use air-core coils to avoid saturation artifacts.