Mu-Metal core?

[Visionary]

Can Mu-Metal be used as a core for an electromagnet? It has a very very high relative permeability, good advantage!

And other wonderful properties, what problems could it cause if ti was indeed a core for an electromagnet?

Unfortunately, it saturates a very low fields, how can this be solved? By increasing the size maybe?

 

 

V.

Edited July 21, 2013 by Visionary

[Visionary]

Um...

Anyone has an idea about this?

Edited July 21, 2013 by Visionary

[swansont]

Could you? Yes. But the reason you wouldn't is one you have already pointed out: it saturates way too easily, which is the exact reason it's used as a shielding material rather than a core.

 

The way you "solve" this is by using a material with a smaller permeability.

[Visionary]

Could you? Yes. But the reason you wouldn't is one you have already pointed out: it saturates way too easily, which is the exact reason it's used as a shielding material rather than a core.

 

The way you "solve" this is by using a material with a smaller permeability.

 

I know that it's a problem, but never understood why... Even if it did saturate really quick whys is it a problem?

By increasing the size of the core maybe it can withstand a greater external field without saturating quickly, also by limiting external B of course it could help too.

Mu-metal's permeability is above the thousands, in fact! Could be in the tens of thousands, adding its B + External B = a total B far more greater than Ext.B which is amazing, mu® is very very high that's why I'm trying to create a possible way to use Mu-metal cores,is it impossible? Or possible but very complicated?

Edited July 21, 2013 by Visionary

[swansont]

Changing the size won't do anything, since it's the field per unit area (flux) that's important. If you make the coil bigger but leave the current the same, you still have the same field everywhere.

 

Saturation is a problem because the role of the core is to contain the flux lines, so that they are concentrated at the end face, and if you saturate, then any additional field will have a different spatial profile. Instead of a dipole that is based on the physical dimensions of the core, you have one that's from the dimensions of the coil. A saturated core means there is a limit to the current you can run through the magnet and have it be effective, which typically makes it a bad electromagnet. Unless you have an application where you actually want that to happen.

[Visionary]

By increasing the area we allow more flux to pass, I don't understand how increasing the total size of the Mu-metal will not solve the saturation problem.

I understand that making the coil bigger( thicker wire or more turns) and I is the same hence B is the same.

 

In reality, there is a limit to everything. In all electromagnets there has to be a limit. The limit of how much current we can apply is fine with me, the point that I'm emphasizing, is the fact the magnetic field from the coil is amplified by the thousands with a core. If Mu-metal is the core its could potentially increase the magnetic field by the ten's of thousands.

 

"The saturation point is the flux density at which the material can not contain any more magnetic flux. Steel saturates around 22,000 Gauss, while MuMetal saturates at about 8,000 Gauss."

 

I think the larger the material the more flux lines it should contain.

Only if the surface area where the flux lines penetrate is increase, only then can the saturation change.

 

Just got to solve the saturation problem and Mu-Metal could be used in stronger magnetic fields.

 

Relative permeability: 20,000+

I have got to use this!

It can amplify a magnetic field x20,000 times!

What are the best known cores?

Edited July 21, 2013 by Visionary

[swansont]

Flux is the number of lines per unit area. Changing the area does not change the flux.

[Visionary]

No no no... Changing the area allows more FLUX from the external field to pass.

A source.

Turn's out... When they use Mu-metal shields its important to increase length and thickness why is that? Well, to allow more of the external magnetic field to penetrate the material.

Assuming that if a materiel saturates rapidly because of all the moments being alined... Increasing the "size" would mean more moments have to be alined which means, a higher saturation.

I read multiple resource that deal with magnetic fields, when using a certain ferromagnet to shield/test a field. The material has to withstand the magnetic field fully(i.e covers its total flux's).

 

Hope that made sense.

[swansont]

That's not the same situation as an electromagnet.

 

If you have a constant number of flux lines, making the mumetal thicker will help. That's why it's useful in shielding.

 

But in an electromagnet, the core already fills the available area. Making it bigger means making the coil bigger, so with the same current you have more flux lines, as I said above. The density stays the same, so you have more flux lines, in exact proportion to the increased size of your core. In that situation, there is no advantage.

[Visionary]

That's not the same situation as an electromagnet.

 

If you have a constant number of flux lines, making the mumetal thicker will help. That's why it's useful in shielding.

 

But in an electromagnet, the core already fills the available area. Making it bigger means making the coil bigger, so with the same current you have more flux lines, as I said above. The density stays the same, so you have more flux lines, in exact proportion to the increased size of your core. In that situation, there is no advantage.

 

 

Well, in case of the electromagnet using a Mu-metal core is great, but the only problem was saturation. I suggested increasing the thickness or area of the core in order for it to handle more of the applied external magnetic field of the coil to create a higher total magnetic field.

If we made the coil bigger but with the same current(I)...There is more area for the flux lines to pass through before saturating, and more electron spins for it to be aligned, causing a greater total magnetic field to be created by those aligned electrons + the magnetic field of the coil. So there is possibly an advantage, lowering the saturation rate for it to handle the applied magnetic field, and possibly increasing the magnetic flux lines due to the presence of more domain's(i.e electron spins) possibly not differently.

 

So now I guess the saturation issue is solved .

Edited July 22, 2013 by Visionary

[Enthalpy]

A wider core would increase the flux for the same saturation induction, yes, and this would avoid to increase too much the number of turns. Ultimately, it would have allowed to use Permalloy in a transformer core.

 

But we don't desire it!

 

We want small transformers, because laminations and copper have a price, and transformers are always too heavy. What designers desire is a higher induction at saturation.

 

We want a small core so the copper windings are short hence dissipate less. (The rationale as well is shortened here, but it's the proper direction and ultimate reason).

 

A wider and longer core dissipates more due to its volume, lessening the advantage of Permalloy.

 

Incidentally, the permeability defines the reactive current (the magnetizing current) that passes the primary when the secondary delivers no current; this reactive current is not directly a dissipation in the transformer, but it has drawbacks. The power losses in the core relate instead with the material's hysteresis (which Permalloy would be good as well) and laminations' eddy currents (3% silicon in transformer iron is as good as much nickel).

 

One excellent reason against Permalloy is that nickel is expensive. Silicon in transformer iron is cheap.

[swansont]

Well, in case of the electromagnet using a Mu-metal core is great, but the only problem was saturation. I suggested increasing the thickness or area of the core in order for it to handle more of the applied external magnetic field of the coil to create a higher total magnetic field.

If we made the coil bigger but with the same current(I)...There is more area for the flux lines to pass through before saturating, and more electron spins for it to be aligned, causing a greater total magnetic field to be created by those aligned electrons + the magnetic field of the coil. So there is possibly an advantage, lowering the saturation rate for it to handle the applied magnetic field, and possibly increasing the magnetic flux lines due to the presence of more domain's(i.e electron spins) possibly not differently.

 

So now I guess the saturation issue is solved .

Larger coil area = more flux lines, by the exact same proportion as you have increased the area of the core. The saturation has not changed.

[Visionary]

Larger coil area same current. Thus, equal magnetic field strength + flux density.

It's possible to increase the core size to decrease the quick saturation at the same applied current + field + flux density.

Only thing that changed now... The rate of saturation change is much slower.

Edited July 22, 2013 by Visionary

[swansont]

Same flux density x more area = more flux lines. Saturation depends on flux density, which you have not decreased. (Unlike with shielding)