Magnetic Permeability Overview

Magnetic permeability is a property of materials that lets them form a magnetic field inside them and support it. Introduced by Oliver Heaviside in 1885, it’s a measure of how easily magnetic lines of force go through a material. I like to think of it as how much a material wants to be magnetized. It determines how much magnetic flux a material can sustain.

Definition and Formula

Magnetic permeability (μ) is defined as the ratio of magnetic induction (B) to magnetic intensity (H). It’s expressed with the following formula:

μ=B/H

This scalar quantity measures how much a material doesn’t want to let magnetic fields in and how much it does let them in. A higher magnetic permeability means the material supports a stronger magnetic induction and lets magnetic fields penetrate more.

 

Factors Influencing Magnetic Permeability

Permeability changes based on:

  • The nature and structure of the material
  • Temperature and humidity
  • The strength and frequency of the applied magnetic field

Materials with higher permeability have a stronger magnetic response, and materials with lower permeability have less magnetic interaction. Permeability is always a positive value and can change based on the external magnetic conditions.

 

Magnetic permeability comes in several flavors:

  • Permeability of Free Space (μ₀): The base level of permeability in a vacuum. We often use this as a reference in other permeability calculations.
  • Permeability of Medium (μ): This tells you how much a material doesn’t want to let magnetic fields in and how much it does let them in.
  • Relative Permeability (μr): A ratio with no units that tells you how much a material doesn’t want to let magnetic fields in and how much it does let them in.

 

Different materials have different levels of magnetic permeability. They’re grouped into:

  • Diamagnetic Materials: These materials reduce the magnetic flux density a little bit because their relative permeability is a little bit less than 1. An example is bismuth.
  • Paramagnetic Materials: These materials are weakly magnetized when you expose them to an external magnetic field. They have a relative permeability a little bit greater than 1. Platinum is one example.
  • Ferromagnetic Materials: These materials have a high magnetic permeability (often more than 100,000) and have the strongest magnetic properties. Iron is one example.

 

Induced Magnetic Fields and Material Interaction

How magnetic fields interact with materials depends on the magnetic permeability of the material. When you apply an external magnetic field, some materials, especially ferromagnetic materials, create an internal magnetic field, or induced magnetism. This induced field interacts with the external field, and you get magnetic attraction. That’s why a permanent magnet can attract ferrous materials.

But materials like wood don’t support the induction of a magnetic field (they have very low magnetic permeability). So they don’t interact with magnets and don’t get attracted to them. On the other hand, materials like steel (which have high permeability) interact strongly with external magnetic fields and get attracted to magnets.

 

Magnetic Permeability in Practical Applications

Magnetic permeability becomes important when you’re picking materials for systems that have magnetic fields. For example, in robotics, you might have a magnetic handling device that picks up mild steel tubing because mild steel has high permeability. But if you’re trying to pick up 410 stainless steel tubing (which has low permeability), you might not get enough force to pick it up. You’ll have a weaker magnetic grip or might not be able to pick it up at all.

When you design systems or products that rely on magnetic properties, you have to think about the permeability of the material you’re working with to make sure it works the way you want it to. Whether you want materials with high permeability or low permeability, you need to understand how they behave in magnetic environments.

 

Magnetic Permeability in Practical Applications

Magnetic permeability becomes important when you’re picking materials for systems that have magnetic fields. For example, in robotics, you might have a magnetic handling device that picks up mild steel tubing because mild steel has high permeability. But if you’re trying to pick up 410 stainless steel tubing (which has low permeability), you might not get enough force to pick it up. You’ll have a weaker magnetic grip or might not be able to pick it up at all.

When you design systems or products that rely on magnetic properties, you have to think about the permeability of the material you’re working with to make sure it works the way you want it to. Whether you want materials with high permeability or low permeability, you need to understand how they behave in magnetic environments.

 

Conclusion

Magnetic permeability is important because it tells you how materials react to external magnetic fields. It affects how strong things get attracted to each other. And if you’re designing products or systems that use magnets, you have to think about the permeability of the materials you’re working with. You might want materials with high permeability or low permeability.

The permeability of a material can change based on things like temperature and how strong the field is that you’re applying to it. So when you’re working with magnets and designing products, you have to think about how that permeability can change so you can get your magnets to work the way you want them to.