Halbach Arrays

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Halbach Arrays are a very interesting arrangement of magnets. If you place them in a specific pattern you end up with most of the magnetic lines projected in one direction, and hardly any in the other.

This results in a magnet that sticks to a fridge one one side, but not on the other. Very weird! I put one inside a cylinder and it will always roll to one side on a metal object.

Making them is difficult, as they do NOT want to stay put together. You have to use force to keep them pressed together. I used superglue to make a fragile array and then wrapped them in a layer of aluminum tape. This made them sturdy enough to play with, and the tape is thin enough to not reduce the effect.

You can find more information and some nice digrams on the matchrockets.com site.

(Click on any image for a larger version)

The array, all wrapped up in tape. A fun little toy.
This is made of 1/4" cube magnets.

Iron filings over glass shows the effect with the array on it's side.
You can clearly see that the field is strong on the top edge, and the other side doesn't attract ANY filings.
This is a pile of filings on the top side where the field is strongest.
A normal array of magnets would collect them all at the ends.
Here is the bottom where the field lines are nearly absent.
It is hard to believe this is the same magnet as the image above!
Here we have it on it's side.
The magnet is actually near the bottom of the image under the white plastic.
All the filings are collected at the top.
Another view on the side.
This shows more of the field lines. The reason the shape is slightly diffrent than above is the Halbach array is closer to the surface this time.

I put a bit of saran wrap over the magnet to make cleanup easier and used some more filings to give a 3d view of the field.

This top view clearly shows the field lines coming out one side and not the other.
The "side" of the array is facing at the camera.

Another picture of the same angle with diffrent lighting.
This shows the top of the array from a good angle.
You can see where the field lines are squeezed out between each magnet on the side.
On the back side we can see how the field lines are so drawn inward that no filings at all litter the table behind it.
Only a few even stick to the back.
Thats impressive, as these are strong magnets.

I used some Ferrofluid to show the magnetic fields of the array. The Halbach array is under the plastic dish.

This is the top side of the magnet. It's the strong side that produces the intense magnetic field. It is a very "tight" field with clearly defined edges between the sections.

This is the weak side.. you can see the Ferrofluid is just kind of "slumped" and not very well defined.
HEre is the side of the Halbach array. Can you guess which side is the strong? It should be obvious if you compare it to the two above pictures.

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