Saturation (magnetic)

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For magnetic materials, saturation is the state when the material cannot absorb a stronger magnetic field, such that an increase of magnetization force produces no significant change in magnetic flux density.
The relation between the magnetic field H and the magnetic flux density B is expressed in terms of the magnetic permeability μ : B = μH.
The permeability of many materials is not constant, but depends on H. For example, in a ferromagnet the permeability is increasing with H, inverts at a certain point then decreases significantly. Further increase in H will not cause an increase in B as the permeability is too small.

Different materials have different saturation level. For example, iron reaches magnetic saturation at 2.2 teslas.

Saturation limits the minimum size of transformer cores. To lower its effects, an air gap is created in some kinds of transformer cores.

The hysteresis curve shows the dependence of B upon H in different materials and therefore the saturation.

cgs units: emu per gram.