Hi Mike,

I did a quick and dirty run with FEMM, just mirroring one of the 
designs I had done before.

  http://bnordgren.org/seismo/Mike001.pdf

You should probably have the viewer scale at 200% to see it properly 
as it's kind of small.  The structure is made of a steel cylinder and 
discs with their axis running up the left side of the paper and is a 
cross-section view.  Only one half is shown as the left side is just 
a mirror image.  The two magnets are set as N pole to N pole and the 
whole thing is surrounded by a vertical steel tube with steel disks 
on the top and bottom.

The field looks good, nice and linear around the coil winding (the 
rectangle in the open space).  Only problem is how do you connect 
anything, physically or electrically to the coil, as it's now 
entirely surrounded by iron.  You'd have to cut some holes somewhere, I guess.

Regards,
Brett 


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