Can a magnetic field be shielded passively?

[mreznicek]

Friends:

Can a magnetic field be shielded somehow by a passive material?

i.e. can I wrap a strong magnet in some thin material and impede the B field outside?

Thanks amigos! -MigsP.S. This is not a homework question! I finished M.E. a long time ago!

 

[genneth]

Yes -- superconductors exclude magnetic fields from penetrating, at least up to a limit.

 

[mreznicek]

Hi Genneth:

So what is a common household superconductor with which I could shield say my compass as it sits on the dash of my car so that the dash electronics don't affect it?

Migs

 

[genneth]

Hi Genneth:

So what is a common household superconductor with which I could shield say my compass as it sits on the dash of my car so that the dash electronics don't affect it?

Migs

Unfortunately, known superconductors need very low temperatures to work. If you've got some household ones, please tell! As far as shielding goes, a compass encased in a superconducting box wouldn't read *any* magnetic field, as the Earth's would be shielded as well. Added to that, I think superconductors are always opaque...

 

[mgb_phys]

You can also use any material with a high permeability.
The most common one is a special nickel alloy called mu-metal, I imagine it is expensive stuff - I've only ever used it in fancy physics experiments.

The normal way of sheilding out local constant fields is called hard iron correction and just involves positioning small magnets around the compass to cancel the effecs of the local field. If you see an old ships compass this is what the large metal balls around it do.

 

[mreznicek]

Thanks for the comments amigos! I kinda figured this was the case. I'ts always nice to have people in the know tell you exactly how it is ;) Migs

 

[LURCH]

In many industrial applications, magnetic fields are shielded by conductors. Try placing a piece of metal (any conductive metal) between your compass and the suspected origin of the interference. For example, a bit of flashing on the dashboard (shiny side down, of course).

 

[Video Eddie]

Friends:

Can a magnetic field be shielded somehow by a passive material?

i.e. can I wrap a strong magnet in some thin material and impede the B field outside?

Thanks amigos! -Migs


P.S. This is not a homework question! I finished M.E. a long time ago!

Yes, about any metal works well if it is an alternating field. If it is a fixed field then use mu-metal, or a ferromagnetic metal.

Any metal that is a conductor works well for alternating fields because an alternating field induces current in nearby conductors that it out of phase by 180 Degrees, therefore canceling the original field.

 

[mreznicek]

Good to know Eddie. I'm making a small 10x10cm robot vehicle and wanted to isolate the compass sensor from the electronics and motors. Another option will be to put the sensor on a small mast. -Migs

 

[rewebster]

Good to know Eddie. I'm making a small 10x10cm robot vehicle and wanted to isolate the compass sensor from the electronics and motors. Another option will be to put the sensor on a small mast. -Migs

well, here's my thinking:

it would have to have a 'sphere' shaped 'shield' to do the best job

but, the most critical factor is that since you're trying to 'shield' the magnetic field, I don't think your 'compass' is going to work too well

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you may want to try to 'shield' the other components