Magnetic permeability confirmation 1

[tails009]

Following on from another thread I started, I also am not convinced my understanding of magnetic permeability is correct. I've attached a crude diagram of two situations:

The top view shows a magnet in a box of low permeability. My understanding is that the magnetic flux is free to pass through and attract the magnet outside towards the box?

The bottom view shows a magnet in a box of high permeability. Therefore the flux takes the easier route back to pole which is through the box material itself and does not reach the magnet outside the box and will have no attractive pull on it.

Is this correct?

My next question would be - does all diamagnetic material have low permeability? i.e. if I wanted to create a metal box that simulated the first scenario, would something like copper be a good design? I understand that diamagnetic material will try to repel the field but that these repelling forces are so small as to be negligible.

Thanks for your help.

 

[EdStainless]

Yes.

On a macro scale materials are ferromagnetic or not. The other classes of weak magnetic interactions are very important in labs or small scale devices, but not in the common world.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[tails009]

Thanks for that.

At least one thing I have clear in my head!

 

[electricpete]

My next question would be - does all diamagnetic material have low permeability? i.e. if I wanted to create a metal box that simulated the first scenario, would something like copper be a good design?

As long as it is not a dynamic experiment where induced currents can affect the result.

The relative permeability of copper is very close to 1 (0.999994 per wikipedia) so it is difficult to create an experiment where the diamagnetic properties will be visually obvious.

There is an experiment from some guy named electricpete here who shows a way to show that these small forces exist:

http://www.youtube.com/watch?v=2FvWtEdY4sE&playnext=1&list=PLA3288D5E0FDA9C4D&index=20

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(2B)+(2B)' ?

 

[electricpete]

By the way what is the objective of your experiment/demonstration?

=====================================
(2B)+(2B)' ?

 

[electricpete]

One more comment, in a static configuration, the copper box would be almost indistinguishable from air (since permeability is so close to 1) so copper box will appear to have no effect (compared to no copper box=air) unless you have figured out some way to show this very small difference. So depending on the objective of your experiment, maybe you can just get rid of the box in the upper diagram.

=====================================
(2B)+(2B)' ?

 

[tails009]

Thanks Pete,

The idea of a copper box was just to get the idea of permeability straight in my head, the application wont actually use a box but will utilise solid metal seperating a magnet and an electromagnet.

To simplify the idea to the most basic degree: I want to have permanent magnet attached to one side of a metallic material and upon activating the electromagnet, the permanent magnet is repelled. The thing is that this is the first time I have been dealing with magnetics so I'm finding some of the terminology confusing.

Naturally when I think of permeability, I think of permeability of rocks; thereby low permeability means fluid transfer through rock is harder. Permeability in magnetics is obviously different but It looks like I had the right idea.

Unfortunatley using copper for my application is not an option, so I'm looking for alternative low permeability, high strength material. Nickel Alloy was suggested but surely the Nickel in the Alloy would make this a higher permeability material?

 

[MikeMech]

316 or 310 Stainless might work for you. High strength and low permeabiltiy.

 

[IRstuff]

How about aluminum? You can buy aluminum boxes in hobby or electronics stores.

TTFN

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