Halbach arrays

Posted on January 23, 2008

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– EDIT –
I’ve redone this study afterwards, with much better results. Check it out!
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I got a very interesting tip today about a technology I didn’t know: Halbach magnetic arrays. Thanks to Nick Schlensky for that.

Halbach magnet array
(copyright Wikimedia Commons)

I’m hoping I can use it to remove the iron cores from my design and make it a lot lighter. But let’s get a clearer notion of what a Halbach array is and how it can help us.I modeled such a creature in FEMM, comparing it to a normal sequence of magnets to see the difference. Here are the photos. In all photos I placed exactly the same 5 cubic magnets, I just changed the orientation of their magnetization field.

simple-nohalbach5-air.png

simple-halbach5-air.png

As you can see, it is true that the Halbach layout creates a field that is very predominant on one side of the magnet row, and nearly non-existent on the opposite side. Very promising. :)

I put in a bit of soft-magnetic iron to see how the flow changed:

simple-steel-nohalbach5.png

simple-steel-halbach5.png

Again it is obvious the powerful asymmetry caused by this layout. It would be perfectly possible to make the iron core on top a lot thinner or even remove it altogether without losing performance.

Now let’s see how this behaves when facing another magnet… after all, the interesting point is the interaction with other fields.

interaction-left-air-nohalbach5.pnginteraction-right-air-nohalbach5.png
Fig 5/6: Forces caused by homogeneous sequence.
interaction-left-air-halbach5.pnginteraction-right-air-halbach5.png
Fig 7/8: Forces caused by Halbach sequence.

Now I’m disappointed!! :( The Halbach magnet layout seems to improve very much the forces in the direction we don’t care about (radial, here the Y), and makes the ones we do care about (tangential, here the X) a lot smaller.

You can see in Figs 5 through 8 the following changes:
  • X force (tangential in the motor, produces torque): from 46N down to 4 N
  • Y force (radial in the motor, produces material stress): from 10N up to 80N
This is definitely not the thing we’d like to have in our motors…
So the question now is: am I using this Halbach array in the correct way? Should I change something else to make it work?
Or, putting it in another way: what do the guys at CSIRO and PowerCroco know that I don’t?!…
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– EDIT –
I’ve redone this study afterwards, with much better results. Check it out!
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Posted in: Motorfemmulator