Subject: How do I Create a Strong Electromagnetic Field

I am currently in my final year of univesity at Lancaster (England) and 
doing my final year project which is to stimulate human nerves ot help 
multiple sclerosis.
I am trying to produce a field from a coil which is connected up to an 
alternating supply of 15 Volts, 4Amps, frequencies min 1Hz and max 100Hz 
although I am having problems choosing the type of core and coil shape.  I 
have looked into E cores but it looks as though it wouldnt be possible to 
get a large enough airgap where the flux density is greatest.  I have also 
been looking into toroidal coils but it looks like all of the flux stays 
in the core and is not emitted. Is this true?
I would be very grateful if you could recommend the best types of core and 
core format for me to gain the best electromagnetic field possible.
Many thanks!
Paul

Re: How do I Create a Strong Electromagnetic Field