Electronics > Projects, Designs, and Technical Stuff
Do we have any magnet/magnetism gurus here?
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ejeffrey:

--- Quote from: strawberry on September 27, 2019, 07:57:06 pm ---how a magnetic sphere with poles on inner and outer face can work?

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It can't.  The field lines have to get from the north to the south pole.  That's also the problem  T3sl4co1l was explaining about the flat plane.  The field lines in the center have to go *much* farther to get back to the other side than the ones at the edge.  It isn't mathematically impossible like the sphere question but it is get very hard very quickly as your requirements on area, field strength, and uniformity go up.

Its much more practical to create a uniform field in a gap between pole pieces than on the surface of a plate.
RandallMcRee:

--- Quote from: Zero999 on September 27, 2019, 08:13:26 pm ---Are you talking about somethign like this?
(Attachment Link)

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Yeah, thanks for illustrating. So reviewing the halbach orientation it seems that there is not predominantly north or south, so not red and blue. Instead we have a linear orientation. So, we could, for example have one side oriented in one direction and the flip side oriented 90 degrees to it.

Perhaps that would be useful to the OP. Hard to say.
cvanc:

--- Quote from: Zero999 on September 27, 2019, 08:13:26 pm ---Are you talking about somethign like this?
(Attachment Link)

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Yes.  Imagine this the size of a sheet of plywood.  Thickness is undefined.

Can a Halbach array be made such that the entire face of the plane is North?  The asymmetric pattern would be helpful as I only care about the field on one side.

Thanks everyone.
ejeffrey:

--- Quote from: cvanc on September 29, 2019, 03:06:23 pm ---
--- Quote from: Zero999 on September 27, 2019, 08:13:26 pm ---Are you talking about somethign like this?
(Attachment Link)

--- End quote ---

Yes.  Imagine this the size of a sheet of plywood.  Thickness is undefined.

Can a Halbach array be made such that the entire face of the plane is North?  The asymmetric pattern would be helpful as I only care about the field on one side.

Thanks everyone.

--- End quote ---

No. The whole point of the halbach array is that the alternating polarity allow closing flux loops to stay local.  It is basically a bunch of horseshoe magnets stacked in a row.

If you make a plate with all north on one side the field has to return to the back.  A uniformly magnetized plate will always fall to half at the edge and 1/4 at the corner so you will need nonuniform magnetization to get an approximately uniform field.
IanB:

--- Quote from: cvanc on September 27, 2019, 06:01:48 pm ---I want to build a large flat "sheet" magnet.  A mathematical plane.  It needs to be strong, have a smooth even field, and be North on the front side and South on the back side.
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Take any small magnet and measure the field at one of its poles. You will find the field is strongest at the center. For example, anything you stick to the edge of the magnet will tend to get pulled to the center. So even a small, ordinary magnet doesn't have an even field over its very small area of flat surface. Now imagine scaling up the small magnet to ever larger sizes. As you scale it up the uneven field will scale with it.

From an engineering perspective, what you are asking would seem to be impossible, or at least, hugely infeasible.
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