What is magnetic permeability and how is it calculated?

The magnetic permeability of a magnet is the relationship between the magnetic field and the magnetic flux density. See how to calculate permeability.

What is magnetic permeability?

The concept comes from the Latin "Permeare", which means "blown". This concept is used as a term to explain the permeability of materials for magnetic flux density. High permeability allows materials to become magnetic and increase magnetic flux density. High permeability materials have very low strength, such as ferromagnetic materials, such as iron.

Permanent magnets are basically ferromagnetic materials. Therefore, permanent magnets attract ferromagnetic materials. Permeability is the relationship between the magnetic field and the magnetic flux density.


Influence on magnetic permeability

Magnetic fields are heavily influenced by the matter forming a magnetic flux density in the external magnetic field. This depends on the magnetic permeability of the material. When the transmittance μ is very large, the magnetic flux density in the matter is large.

Permeabilidad magnética


Tips for taking magnetic permeability into account

It is indicated by the symbol μ. Can be used in combination with magnetic flux density (B) to calculate the size of the magnetic field (H). The following applies:

H = (1 / μ) * B.

To calculate the magnetic field in vacuum (H0), the flux density (B0) in vacuum must be divided by the field constant μ0. With a value of B0 = 1 Tesla or 1 Vs / m², a magnetic field of H0 = [(10 ^ 7) / (4 π}] * A / m is obtained.

The permeability number μr can be given by the formula B = μr * B is the density of the magnetic flux, which depends on the influence of matter, and if the μr of a matter is greater than 1, the magnetic field is amplified. If the matter μr is less than 1, the magnetic field weakens.

Both cases are known. Ferromagnetic materials have microscopic electron spins that line up in an indexed magnetic field. Due to the gain of this magnetic field it can sometimes be greater than the induced magnetic field.

When electron spins are aligned, the so-called exchange effect stabilizes this orientation in ferromagnetic materials. The permeability μr is very large due to the stabilization. Special ferromagnetic materials, called amorphous metals, have a transmission up to μr = 150,000. In comparison, iron has a transmission of 10,000. In the bibliographical references you often find the statement μ for simplification. Actually, this is intended for rent.


In addition to ferritic magnets, there are still paramagnets in which there are also electron gyres. These can also be aligned. However, unlike ferromagnetic materials, the orientation is not stabilized, so paramagnets only slightly improve the magnetic field. The permeability μr here is approximately 1.00001.


Then there are the diamagnets. These have a debilitating effect. This is because there are no permanent electron pins that can be aligned. When an induced magnet is applied, a current is induced. This is directed against the cause (according to the Lenz rule). This weakens the magnetic field.

This so-called diamagnetism occurs in any matter, but with para and ferromagnets this effect is superimposed by elementary magnets.

Another special case is the superconductor. These have a transmittance of zero, i.e. the density of the magnetic flux disappears. The field lines are completely removed from the material and run around this material.

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