Permeability: The ability of a material to conduct magnetic fields

The permeability (µ) describes the ability of a material to conduct or amplify a magnetic field. It is one of the fundamental properties of magnetism and is expressed in units of Henry per metre (H/m). Permeability is decisive for the behaviour of materials in magnetic fields and determines how strongly a material can be magnetised.

Types of permeability

• Absolute permeability (µ): The permeability of a specific material in a magnetic field.
• Vacuum permeability (µ₀): A universal constant that describes the magnetic conductivity in a vacuum. Its value is 4π × 10-⁷ H/m.
• Relative permeability (µᵣ): The ratio of the absolute permeability of a material to the permeability of the vacuum: µᵣ = µ / µ₀. It indicates how much stronger or weaker a material conducts a magnetic field than a vacuum.

Permeability in different materials

Materials can be divided into three categories according to their permeability:

• Ferromagnetic materials: Have a very high relative permeability (µᵣ > 1.000), e.g. iron, cobalt and nickel. These materials amplify magnetic fields extremely strongly.
• Paramagnetic materials: Have a low relative permeability (µᵣ ≈ 1.01), e.g. aluminium and platinum. They weakly amplify magnetic fields.
• Diamagnetic materials: Have a relative permeability of less than 1 (µᵣ < 1), e.g. copper and water. They slightly attenuate magnetic fields.

Mathematical description

Permeability is a central parameter in the relationship between magnetic flux density (B) and magnetic field strength (H):

B = µ × H

Where:

• B: Magnetic flux density (in Tesla, T)
• H: Magnetic field strength (in amperes per metre, A/m)
• µ: Absolute permeability of the material (in henry per metre, H/m)

Applications of permeability

Permeability is a key parameter in many technical and scientific applications:

• Electromagnet: Materials with high permeability are used for magnetic cores to generate strong magnetic fields.
• Transformers: Iron cores with high permeability minimise energy losses during energy transmission.
• Magnetic shielding: Materials with high permeability, such as mu-metal, are used to protect sensitive devices from external magnetic fields.
• Memory technology: Magnetic permeability plays a crucial role in storing information on hard drives and in memory chips.

Interesting facts about permeability

Did you know that superconductors have a permeability of zero? This means that they can completely shield magnetic fields. This phenomenon, known as the Meissner-Ochsenfeld effect, is used in technologies such as magnetic resonance imaging (MRI) and magnetic levitation applications. In addition, materials with extremely high permeability, such as special alloys of nickel and iron, enable the development of extremely sensitive magnetic field sensors.