Re: Helmholtz coil - model with permanent magnets
- From: pmb <pmb61@xxxxxxxxxxx>
- Date: Wed, 29 Apr 2009 08:03:54 -0700 (PDT)
On Apr 28, 12:55 pm, phil-news-nos...@xxxxxxxx wrote:
On Tue, 28 Apr 2009 09:25:48 -0700 (PDT) pmb <pm...@xxxxxxxxxxx> wrote:
| On Apr 27, 2:56?pm, phil-news-nos...@xxxxxxxx wrote:
|> On Sun, 26 Apr 2009 03:42:23 -0700 (PDT) michael3d2...@xxxxxxxxx wrote:
|> | On Apr 26, 4:31?am, phil-news-nos...@xxxxxxxx wrote:
|> |> If the Helmholtz coil, which is really two circular coils next to each other,
|> |> produces a uniform magnetic field, then shouldn't two flat disk permanent
|> |> magnets also do the same thing?
|> |>
|> |> --
|> |> |WARNING: Due to extreme spam, googlegroups.com is blocked. ?Due to ignorance |
|> |> | ? ? ? ? by the abuse department, bellsouth.net is blocked. ?If you post to ?|
|> |> | ? ? ? ? Usenet from these places, find another Usenet provider ASAP. ? ? ? ?|
|> |> | Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |
|> |
|> | Yes, most definitely
|>
|> So how wide an area could I make a uniform field by either of these methods?
|> I'm thinking somewhere between 1 to 4 cm spacing needed between the two disk
|> magnets. ?Assuming magnets are big enough, or separate magnets can be tiled
|> together (the slight imperfections shouldn't be an issue), how wide (in the
|> other two dimensions, like radius if kept circular) could this be done?
|>
|> What if the magnets have small holes in the middle, like a flatten donut?
|> Of course I would expect the field near the holes to be different.
|
| The specs you're seeking depend on how uniform you want the field to
| be. Therefore you need to specify the allowed variation in the
| uniformity of the magnetic field.
I'm taking this in the opposite approach. Variations in uniformity won't
matter as to the principle of the design. Changes in orientation would..
Variations in uniformity will have an effect on the efficiency of a particular
cunstructed design. But for now I want to just see if this will work at all.
If it works, then it will be worth it to explore all the math to evaluate the
efficiency with different variations.
|> I'm still thinking up designs around the Faraday homopolar generator. ?I think
|> I need to do these designs around having the field produced by two magnets as
|> in the Helmholtz coil arrangement, with the electrical windings in between.
|> And this might be multiple sandwiched layers alternating between magnets and
|> windings. ?The magnets would be rotated and the windings would be stationary.
|
| Why do you want a uniform magnetic field? Any magnetic field will do.
| Unless you want a uniform magnetic field so as to make the field known
| and thus allow the calculations to be easy and therefore let the
| comparison between theory and experiement to be easy?
What is critical is that the _orientation_ of the field not change, ...
The magnetic field is a vector quantity and as such as both a
magnitude and a direction. Therefore changes in orientation are
considered to be changes in the magnetic field.
Pete
.
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