Soft-magnetic terms

Soft-magnetic terms

Definitions of the soft-magnetic parameters used on this site.

FeNi powder core

A soft-magnetic core pressed from iron-nickel (permalloy) alloy powder, roughly 50 % Fe and 50 % Ni, with a distributed air gap. It combines high saturation flux density with low core loss and soft saturation behaviour, which suits high-current DC-bias power inductors.

Permeability (μ)

The ratio of magnetic flux density to applied magnetic field strength, describing how easily a material carries flux. In powder cores a moderate permeability is deliberate: it is set by the alloy and the amount of distributed air gap, and it trades inductance per turn against DC-bias capability.

Saturation flux density (Bs)

The maximum magnetic flux density a material can carry before it saturates and its inductance collapses. FeNi alloy reaches Bs ≥ 1.5 T, materially higher than ferrite, which is the main reason FeNi powder cores hold their inductance under heavy DC bias.

Saturation current (Isat)

The DC current at which an inductor’s inductance has fallen by a specified percentage — commonly 20 % or 30 % — from its nominal value. It is the governing limit when sizing a power inductor for a DC-biased rail.

DC resistance (DCR)

The ohmic resistance of an inductor’s winding, which sets its conduction loss as I²R. In high-current converters DCR drives efficiency directly, so cores that allow fewer turns and thicker wire are preferred.

Core loss

Power dissipated in the core as heat, from hysteresis and eddy currents, growing with frequency and flux swing. It is always quoted at a stated frequency, flux density and temperature — a figure without those three conditions means nothing.

Distributed air gap

Instead of one discrete gap, the non-magnetic regions are spread throughout the core volume by coating each powder particle with insulation. This raises the saturation limit, gives soft saturation, and avoids the localized fringing flux and hot spots of a discrete gap.

Soft magnetic material

A material that is easy to magnetise and demagnetise — narrow hysteresis loop, high permeability, low coercivity — used to guide and shape magnetic flux in inductors and transformers. FeNi alloy powder, ferrite and silicon steel are the common families.

Automotive qualification (IATF 16949 / AEC-Q200)

Two separate requirements. IATF 16949 certifies a manufacturer’s quality management system for automotive supply; AEC-Q200 qualifies a specific passive component through a stress-test sequence, and is assessed per part number.