I Questions related to magnetic shielding separating two like poles

[Freddie Dinsdale]

TL;DR Summary

Are there any equations that help describe a sheet of magnetic shielding that successfully reduces the repulsive forces between two like poles, furthermore are there any equations that tell us the work required to move said sheet between the magnets.

Hi! I’m working on a little project and I’ve run into a rut. Supposing I placed two perfectly aligned cylindrical magnets with like poles facing one another and I wanted to significantly reduce the repulsive force between them by a value x using magnetic shielding, are there any equations that describe the amount the repulsive forces between the two are reduced by, depending on the characteristic of the magnets, shielding and the locations of both the magnets and the sheet. Furthermore, is there anything that would describe the work I’d need to do to move the sheet from completely outside to between the magnets (ignoring the normal F=ma, obviously).

Thank you very much for your time!

 

[berkeman]

I don't think I'll be able to help with your quantitative question, but qualitatively it seems that since magnetic shielding material is ferrous, it will attract the magnets instead of repelling them. Is that what you want, or do you want to try to reduce all magnetic forces to zero?

Here is a good tutorial on magnetic shielding by a company that I have used for many years:

https://www.magnetic-shield.com/all-about-shielding-faqs/

 

[Freddie Dinsdale]

I don't think I'll be able to help with your quantitative question, but qualitatively it seems that since magnetic shielding material is ferrous, it will attract the magnets instead of repelling them. Is that what you want, or do you want to try to reduce all magnetic forces to zero?

Here is a good tutorial on magnetic shielding by a company that I have used for many years:

https://www.magnetic-shield.com/all-about-shielding-faqs/

Thanks for your reply

Are there any tools that could help me find the exact force of attraction and the point where the forces flip?

 

[berkeman]

Are there any tools that could help me find the exact force of attraction and the point where the forces flip?

I only know of fairly expensive simulation tools like COMSOL. I don't know if there are free/inexpensive alternatives that will do what you want.

https://www.comsol.com/blogs/quick-intro-permanent-magnet-modeling

Have you tried any experiments to start getting an idea?

 

[Freddie Dinsdale]

I only know of fairly expensive simulation tools like COMSOL. I don't know if there are free/inexpensive alternatives that will do what you want.

https://www.comsol.com/blogs/quick-intro-permanent-magnet-modeling

Have you tried any experiments to start getting an idea?

No I’ve not. If there’s nothing available I can use to calculate it then I guess this is my best bet. Thank you for your time and have a good day

 

[Baluncore]

Furthermore, is there anything that would describe the work I’d need to do to move the sheet from completely outside to between the magnets (ignoring the normal F=ma, obviously).

Since the initial fields are separated by a plane of total cancellation, half-way between the magnets, it would take no energy to insert a sheet of material into the gap. No field lines would be cut when the sheet was inserted or removed.
You can use the same analysis, to show that such a sheet, could not provide any shielding between the two magnets.

Supposing I placed two perfectly aligned cylindrical magnets with like poles facing one another and I wanted to significantly reduce the repulsive force between them by a value x using magnetic shielding, ...

As argued above, a sheet could not work as a boundary wall.
Introduce instead, two other identical bar magnets, one from each side, also with opposed poles, to make a neutral middle-ground. If you started with two S poles, one above and one below, place two N poles, one on each side. The attraction of the two N poles will cancel the repulsion of the original S poles, so the inter-magnet forces would completely disappear at the point of symmetry. Partial symmetrical insertion of the two N poles, would partially cancel the force between your originally opposed S poles, with only the required force of x remaining.

 

[berkeman]

Since the initial fields are separated by a plane of total cancellation, half-way between the magnets, it would take no energy to insert a sheet of material into the gap. No field lines would be cut when the sheet was inserted or removed.
You can use the same analysis, to show that such a sheet, could not provide any shielding between the two magnets.

I'm not sure that I agree with this. It's only true for an intervening ferrous sheet of infinitesimal thickness. With reasonable thickness, there is a non-zero field on both halves of the intervening sheet, and that will generate an attraction on each of the magnets. It seems like there would be a thickness that would provide a balance between the repulsive and attractive fields.

It may help to provide an explicit external return shield piece for each cylindrical magnet, but I don't know if that's needed.