# Encyclopedia Magnetica

Encyclopedia of magnetics and electromagnetics.

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magnetic_permeability

# Magnetic permeability

 Stan Zurek, Magnetic permeability, Encyclopedia-Magnetica.com, {accessed on 2019-05-19}

Magnetic permeability, denoted by μ - a property of a given medium quantifying its magnetic response of flux density $B$ when subjected to magnetic field strength $H$.1)

Permeabilities of magnetic materials (e.g. ferromagnets) are much higher than those of non-magnetic materials (e.g. vacuum, diamagnets and paramagnets)

by S. Zurek, E. Magnetica, CC-BY-3.0

Permeability of free space (or vacuum) is a universal physical constant defined in the international system of units (SI) denoted as $μ_0$ and its value defined exactly2)3) as $μ_0 = 4 × π × 10^{-7}$ henry per metre which is approximately $μ_0 \approx 1.2566 × 10^{-6}$ H/m.

The term “name” was proposed in 1885 by Olivier Heaviside.

## Practical significance of permeability

From a practical viewpoint permeability is one of the basic parameters which allows categorising all materials as “magnetic” (permeability much greater than that of vacuum $μ >> μ_0$) and “non-magnetic” (permeability similar to that of vacuum $μ \approx μ_0$). In reality all materials are magnetic because they always exhibit some magnetic response to the magnetic excitation so that:

 (1) $$B = μ · H$$ (T)

Ferromagnetic and ferrimagnetic materials have their permeabilities significantly greater than vacuum and are used for construction of magnetic cores in magnetic circuits.

However, at sufficiently high excitation all magnetic materials exhibit magnetic saturation, with which the permeability reduces to that of vacuum.

Permeability of ferromagnetic materials is a non-linear function of the applied excitation and reduces when approaching saturation

by S. Zurek, E. Magnetica, CC-BY-3.0

## Types of permeability

There are several types of magnetic permeability:

## References

magnetic_permeability.txt · Last modified: 2016/06/27 14:54 by Stan Zurek