In a message dated 2006/10/01, gmvoeth@........... writes:

> Hello Chris;
> Can you tell us how to get a uniform magnetic field
> to cut the coil at right angles (normal) to the windings ?

Hi Geoff,

       I use 4 off 1" sq x 1/8" rectangular NdFeB magnets on two 3.5" x 2" x 
1/4" thick mild steel backing plates and mount the coil in between. You have 
N+S magnets on one face opposite to S+N magnets on the other face. This gives a 
high central field and a linear movement response. I use a rectangular 
pancake coil of about 2000 turns. It is quite effective!

       See  http://jclahr.com/science/psn/chapman/lehman/index.html

> can you use two opposing horse shoe magnets
> with a coil in the middle ?

       This is likely to give a lower sensitivity and is more difficult to 
make / mount. Large Alnico U magnets are quite expensive. You benefit from the 
relatively high flux of the NdFeB magnets.

       Regards,

       Chris Chapman
In a me=
ssage dated 2006/10/01, gmvoeth@........... writes:



Hello Chris;

Can you tell us how to get a uniform magnetic field

to cut the coil at right angles (normal) to the windings ?




Hi Geoff,



       I use 4 off 1" sq x 1/8" rectangular Nd=
FeB magnets on two 3.5" x 2" x 1/4" thick mild steel backing plates and moun=
t the coil in between. You have N+S magnets on one face opposite to S+N magn=
ets on the other face. This gives a high central field and a linear movement=
 response. I use a rectangular pancake coil of about 2000 turns. It is quite=
 effective!



       See  http://jclahr.com/science/psn=
/chapman/lehman/index.html



can you use two opposing horse=20=
shoe magnets

with a coil in the middle ?




       This is likely to give a lower sensitiv=
ity and is more difficult to make / mount. Large Alnico U magnets are quite=20=
expensive. You benefit from the relatively high flux of the NdFeB magnets.


       Regards,



       Chris Chapman