# Magnetic shielding question

1. Feb 2, 2013

### sonlinh

First I am sorry if this question is not quite related to this forum. But I have not where to go So I just post it here hopfully one can help.

I have two strong magnets. Each has around BrMax: 13200 gauss and pull force 27 lbs.
I am looking for a magnetic shield product (off the shelf) to redirect the magnetic fields in such a way that two magnets no longer attracting each other when N and S of the magnets near by each other(place the magentic shield in the middle of both magnets).

Requirement: don;t need to shield 100%, above 70% is acceptable. The two magnets can place 1/4 inch apart.

From http://www.lessemf.com/mag-shld.html, they have the GIRON that can shield the magnetic. With Initial permeability 500, Relative permeablity 7000, Saturation induction 2.0 T. I plan to buy around 1 square foot of this product!

As I understand product has the higher staturation point, the better.

1. I have problem of based on magnet, how do I know what saturation point is needed.

2. does the magnetic shield I plan to buy will work? Maybe it need multiple layers will work?

3. If it is not working, What if I select a less strong magnets? what max gauss, max pull force I can buy
Any suggestion would help.
thanks again.

2. Feb 2, 2013

### Staff: Mentor

Magnetic shields do not work like regular shields (for bullets or similar). They can redirect the field, but they need some "target" for that. If you build a shield from one pole of a magnet to the other pole (or at least in that direction), it can work. If you just place some material between the magnets, it will do the opposite: It will increase the force between the magnets.
It would be interesting to see the application, or the precise requirements.
The force will be weaker. Taking the limit: if you buy nonmagnetic materials, the force is zero. I doubt that this is the target.

3. Feb 6, 2013

### sonlinh

Let me try to understand the basic here...
ex: magnet 1 shield around S pole, the N pole shield around like a pipe and redirect to target magnet 2, S pole.
Magnet 1 eventually will die out?? and what happen to magnet 2 will it increase the magnet fields magnet 2. I am trying to understand if there is anything effect to the permanent magnets.

If I remove the sheild from S pole of magnet 1, does the magnetic field at N pole penentrate around the sheild and try to go back to S pole of maget 1?
Thanks.

4. Feb 6, 2013

### Staff: Mentor

Can you draw a sketch? I don't understand that.

5. Feb 6, 2013

### sonlinh

I am very bad at drawing.

Imagine 2 magnets, places on the same line facing east, both N poles also facing east, 3 inches apart, magnet 1 behind magnet 2, . Both magnets start attracting each other when near together say 2 ins.

1. shield the S pole of magnet 1. Just using shield material grap around the S pole.

2. Make a another magnetShield like a cylinder (2 inch). One side tie to the N pole of magnet 1, the other side near the S of maget 2.

Will the field from N pole of magnet 1 able to reach the S pole of magnet 2? Or what will happen.

6. Feb 6, 2013

### Staff: Mentor

It sounds like you just need a "keeper" around each magnet. The keeper can be of iron, and for bar magnets like you describe, the keeper should be a "C" shape, so that the two ends of the C cover the ends of the bar magnet. That confines the magnetic field to the keeper, so there is no external magnetic field to interact with outside objects.

If you magnet is horseshoe shaped, a straight flat keeper bar can be placed across its exposed N/S ends.

.

7. Feb 6, 2013

### sonlinh

Not really. I would like to understand the relationship between magnets, and magnetic fields. For example does the characteristics of magnet changes, fields changes in this case if any.

8. Feb 8, 2013

### Graniar

If not applying too big fields, you may assume characteristics of hard magnets (such as NeFeB) to be constant.

Soft magnets (like iron,ferrits) magnetises in direction of external field, and so increases it.

Superconductors has Meissner effect, it generates equal controversal field, and repell it.

9. Feb 8, 2013

### Staff: Mentor

You would increase the attraction between the magnets. And yes, if you draw field lines, those from the N-pole of magnet 2 would (mainly) go to the S-pole of magnet 1. The shielding material there is not relevant, as there are no field lines which could follow it as in a keeper.