I Permeability of Metglas and Propagation Velocity

[pete94857]

TL;DR Summary

Metglas. Speed of which the material reacts to the change.

I have conflicting information hence here I am. 2 different source that I believe to be credible have given me 2 different answers. And both actually make sense.

Does a higher permeability mean that the reaction through the material will actually travel (not travel but just in a descriptive sense) along the material slower than a lower permeability material.

One source describes it as because there's more of a reaction occurring in a higher permeability material then the "travel" will be slower such as in metglas being typically 3 to 10 m/s depending on environment and type of magnetism applied.

The other source put a higher permeability to a higher speed.

Both seems to make sense.

Example I had a 3 metre long bat of metglas with a cross section of 10mm by 10mm and applied a neodymium magnet (20mm cube 10kg pull) to one end it would take 1 second (approx) to reach the other end. With about 80% efficiency therefore 8kg pull at the far end. In a vacuum chamber with good contact between the magnet and the bar.

Thank you.

 

[Baluncore]

There are two velocities that are important.

The first is the velocity of wave propagation along the boundary between the material and air or space. That will be close to the speed of light, slowed down by the dielectric constant of the surface coating.

The second is the velocity of propagation into the material, perpendicular to the surface, which is much slower. It is often compared to the speed you can run, measured as a few meters per second.

If you laminate the magnetic material, with insulated gaps of about 5% of the lamination thickness, you will find that the full strength of the magnetic field propagates much faster along the laminations than through a solid bar.
https://en.wikipedia.org/wiki/Skin_effect
https://en.wikipedia.org/wiki/Skin_effect#Material_effect_on_skin_depth

 

[pete94857]

There are two velocities that are important.

The first is the velocity of wave propagation along the boundary between the material and air or space. That will be close to the speed of light, slowed down by the dielectric constant of the surface coating.

The second is the velocity of propagation into the material, perpendicular to the surface, which is much slower. It is often compared to the speed you can run, measured as a few meters per second.

If you laminate the magnetic material, with insulated gaps of about 5% of the lamination thickness, you will find that the full strength of the magnetic field propagates much faster along the laminations than through a solid bar.
https://en.wikipedia.org/wiki/Skin_effect
https://en.wikipedia.org/wiki/Skin_effect#Material_effect_on_skin_depth

Thank you.

 

[pete94857]

There are two velocities that are important.

The first is the velocity of wave propagation along the boundary between the material and air or space. That will be close to the speed of light, slowed down by the dielectric constant of the surface coating.

The second is the velocity of propagation into the material, perpendicular to the surface, which is much slower. It is often compared to the speed you can run, measured as a few meters per second.

If you laminate the magnetic material, with insulated gaps of about 5% of the lamination thickness, you will find that the full strength of the magnetic field propagates much faster along the laminations than through a solid bar.
https://en.wikipedia.org/wiki/Skin_effect
https://en.wikipedia.org/wiki/Skin_effect#Material_effect_on_skin_depth

So kind of both are correct. An almost instant but small reaction felt at the far end of the bar but a larger change that moves (kind of) along the bar at a much slower pace the higher the permeability the slower it will be ?

Have I understood it correctly.

Would the example on the efficiency be correct for metglas ?

 

[Baluncore]

Have I understood it correctly.

Probably.

Propagation into the body of the material is slowed, both by higher conductivity, and by higher permeability. Metglas fits that description, and so is best applied by bundling chemically insulated wires, tapes, or laminations. A thick metglas bar would be difficult to manufacture, because it cannot be cooled as quickly as a thin tape or wire.

 

[pete94857]

Probably.

Propagation into the body of the material is slowed, both by higher conductivity, and by higher permeability. Metglas fits that description, and so is best applied by bundling chemically insulated wires, tapes, or laminations. A thick metglas bar would be difficult to manufacture, because it cannot be cooled as quickly as a thin tape or wire.

OK thanks really appreciate it