Inductors can be designed using several types of materials. Two of the most common are Ferrite (with discrete gaps) and Powder Core (distributed gap materials). Ferrites are suited for low bias applications and have a couple of advantages. A relatively large selection of sizes and shapes are available and gapped tolerances typically fall in the +/- 3% range.
Powder Cores specifically Kool Mu have several advantages over ferrites. Ferrites exhibit sharp saturation requiring the designer to remain safely back from this point in the DC Bias curve to avoid saturating the core.
o Kool Mu has a soft saturation and can be used along the entire the DC Bias curve.
o Kool Mu has more than twice the flux capacity of ferrite and can offer a reduction in cores size when compared to ferrite.
o Kool Mu flux capacity is relatively stable as temperature increases while ferrite flux capacity decreases.
o Kool Mu does not have a discrete gap and as a result does not have fringing losses like gapped ferrite cores. The fringing flux around the gap in ferrite cores causes eddy currents in the windings.