[Phys-L] Halbach array magnets : simple yet clever

[John Denker <jsd@av8n.com>]

Here's something interesting that is in some sense very simple
yet was not invented until 1973:
  *Halbach arrays*
  http://en.wikipedia.org/wiki/Halbach_array

It's a way of combining permanent magnets to produce especially
uniform fields, or especially lopsided fields, et cetera.
Applications include motors, refrigerator door seals, and lots 
more.

I like to think of the one-sided version as the superposition
of many small horseshoe magnets.

You might have thought that everything having to do with
macroscopic permanent magnets was figured out in the 1800s, 
but not so.