copper magentic "shield"?

[eserf]

Gentlemen,

A quick thought: When a magnet is run over copper, or if copper is moved past a magnet, a mirrored counter field is set up where the magnet will float over the copper. Case in point, the "magnet dropped down a copper pipe" trick, along with variants on this (spinning copper plate levitating a magnet)... and of course, the current crop of MagLev train technology using Halbach arrays....

So, what if we were to use an outer stator ring of magnets (perhaps a Halbach array to concentrate available force), and an inner rotor with sections of thick cubes of copper, with a laminate of steel on one side?

In effect, when this is spun, the copper would repel from the magnets, and the imbalance of force would come from the steel laminated to the side of the copper (attraction side).

I do realize this would not do anything as far as self starting, as the effect does not happen until it is in motion... but I wonder if there would be a critical speed (much like the MagLev trains which are said to have less and less friction as the speed increases) at which it would turn on it's own?

If nothing else, have I missed any device that has used copper for it's ability to REPEL a magnetic force?


Thank-you for reading, and I look forward to any insight !

[AB Hammer]

eserf

Interesting thoughts, but have you considered that the magnet field in the copper tube could be more of an amplification effect of the field?. I have done shielding test from an eye witness point of view and I did copper shielding test and it was like the shielding attempt was not even there.

[gyulasun]

@eserf,

When a non ferromagnetic metal like copper (or aluminium, silver etc) is placed into a changing magnetic field, eddy currents are induced in it and the magnetic fields created by these currents will counteract the changing field and results in phenomena you also refer to.  As a side effect, this current in the copper (or aluminium etc) will heat up the metal surface, the heat developed depends on the distance, thickness etc.

So even if the effect could be utilized in motion as you think, the heat has to be "digested" somehow, not to cause problems (think of induction heaters how severe heating effect eddy currents may have!).

And when there is no changing magnetic field then copper (and aluminium etc) are useless as magnetic shields I agree with AB Hammer  (simply because the permeability of these materieals are near to unity (like for the air).

But all this should not discourage you from thinking on these ideas because there must be found a best shape, thickness etc where the heating is at a minimum and could also be conducted away by air blowing. 

rgds,  Gyula

[eserf]

AH, good point all.

I'll chalk this on up to do some pendulum tests at some point, just to check merit.

Basically I just noticed that we always try to shield the magnets... so I'm starting to lean in the direction of making the runner in a device out of materials that aren't magnetic... perhaps large chunks of Bismuth with thin bits of steel on one side, and the idea of copper or aluminum intrigued me as it has effect discussed above....

just jotting down more stuff to play with at some point and wanted to see if it had all-ready been investigated 

Thanks-guys!

[pese]

Reference
When a non ferromagnetic metal like copper (or aluminium, silver etc) is placed into a changing magnetic field, eddy currents are induced in it and the magnetic fields created by these currents will counteract the changing field and results in phenomena you also refer to.  As a side effect, this current in the copper (or aluminium etc) will heat up the metal surface, the heat developed depends on the distance, thickness etc.


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Do not wonder about that.
That is the same (with strongest "eddy cirrent", IF you take an normal Transoforer, and brin onöy ONE Winding of copper alumin or other wire
on the coil in SCHORT.
.
The same "short" circuit , if you have an Disk, an tube or other
in an AC field of an Transformer , even in an changing (moving field)=
from an permanent magnet.


(Find that exeriment , that let you see, thatt an falling magnet - falls some times longer IF it fall in an copper tube.
.
The eddy current needs power, so the magnet must wok against it , an need nor time to pass the tube.

feel free to discuss about it. 
GP