# Cylindrical Halbach array with a vertical magnetic field?

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## Summary:

Is it possible to have a cylindrical halbach array with a magnetic field concentration that goes through the vertical center of the axis?

## Main Question or Discussion Point

Similar to what is shown here, except the south side would be the weak side of the array.

A link to purchase one of these or at least the magnetic field arrangement would be very helpful. Thanks in advance.

## Answers and Replies

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No. It would require magnetic monopoles. Linear Holbach arrays alternate poles.

So if I took this array and wrapped it into a cylinder I wouldn't get the same magnetic field?

That is, take the ends and connect them, with the strong and weak sides maintained in their current position.

The same field as what? You could make an annular ring with an open center and many alternating poles yes.
That is not what you had drawn!

The magnet on the right is exactly the geometry at the base of any conical loudspeaker. The field goes into the page at the center and out at the periphery. The magnet is annular with axial field and there is a soft magnetic plate with center "axle" and backing plate to complete the "magnetic circuit". What are you trying to make?

berkeman
worlds simplest electric train

I'd like to try this experiment but with a halbach array to see if I can increase the speed without increasing weight. The doubled strength of a halbach array, along with the fact that the magnetic field is already unbalanced means I can have a lighter more compact magnet (array) on each end.

etotheipi and hutchphd
So I guess what I am asking is if I could make the desired halbach array simply by wrapping a planar array.

That is fantastic video.....I've not seen that trick before.
Not sure I understand your plan though. The fields from those permanent magnets already is axial as is the field from the coil. Plus each end of the battery "car" actually gives forward thrust. I don't understand your picture of the "existing magnet" field.
Great stuff.

The strong side would be where the greatest magnetic flux density from the coil is which would create a net force. The fact that the halbach array can be more compact and deliver twice the magnetic field strength would make this a more efficient machine.

If I understand the physics here the front and back magnets must be in the same direction (NSbatteryNS) not (NSbatterySN).
If that is true Halbach array is not what you want here. All the leaky flux is your friend.

For this to work properly the arrangement is (NSbatterySN) since one of the poles must be exposed to more flux to create a net force.

at 3:50 it is explained

I stand corrected....what an interesting system.
But i still do not know what you want . What does the "undesirable" geometry picture represent? The magnets as purchased already look like the "desirable" geometry in your picture (the flat ends are pole faces).

The cylindrical halbach arrays I'm finding have their poles oriented so that they point upward and not into the page. This poses a problem because a sideways cylinder will not fit in the coil. I need cylindrical halbach arrays that behave similar to a cylindrical magnet, with their pole facing into the page.

The cylindrical halbach arrays I'm finding
Can you please specify??
And why do you think an array will do any better here?? They are not necessarilly better...they just redirect flux......with this symmetry I don't see the utility. Convince me.

an example

I believe the performance will be improved because rather than wasting magnetic flux on the outer facing poles, it is redirected towards the middle where it will push back harder against the solenoid field, which according to newtons third law will cause a greater force.

You do realize that thing is two inches in diameter? I am impressed by the uniformity of the interior field however.
My attempts to make these arrays do anything particularly useful have been singularly unimpressive. I think the highest flux density face pole magnets will better serve you. And perhaps a more conical pole face. I just do not see how to make a Halbach geometry do anything like what you want.
So thanks for the question.....what a great toy!