Permeability & Relative Permeability

In this post, we will discuss Permeability & Relative Permeability with their definition, relationship, equations, formula, the permeability of air, examples, etc.

Permeability

The ability of a material to conduct magnetic lines of force through it is called the permeability of that material.

It is generally represented by μ (mu, a Greek letter). The greater the permeability of a material, the greater is its conductivity for the magnetic lines of force and vice versa.
The permeability of air or vacuum is the poorest and is represented as μ₀ (where μ₀ = 4 x pi × 10^–7 H/m).

Relative permeability

The absolute (or actual) permeability μ of a magnetic material is much greater than the absolute permeability of air μ₀.

The relative permeability of a magnetic material is given in comparison with air or vacuum.
Hence, the ratio of the permeability of material μ to the permeability of air or vacuum μ₀ is called the relative permeability μ_r of the material.

Therefore,
μ_r =μ/μ₀
or, permeability of material μ = μ_rμ₀

Relative permeability – values

• Obviously, the relative permeability of air would be 1.
• The value of relative permeability of all the non-magnetic materials is also 1.
• However, the relative permeability value is as high as 8,000 for soft iron.
• Whereas the relative permeability value for Mu metal (iron 22% and nickel 78%) is as high as 120,000.

The closed path followed by magnetic flux is called a magnetic circuit. A magnetic circuit usually consists of magnetic materials having high permeability (e.g., iron, soft steel, etc.).