Alex Slocum of MIT has some great design tool spreadsheets.

Basics

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  • Energy in a magnetic field, Ramo et. al.:

 

  • For linear materials, where

 

 

 

 

  • Force is

 

 

  • Force per unit area (pressure) is

 

  • In the case of free space (air),  :

  @ B = 1 Tesla

  @ B = 2 Tesla

  • In a closed magnetic circuit:

 

  • Subsituting above,

 

To build a strong electromagnet, a short geometry, with large area is preferred. Note that most Ferromagnetic materials saturate around 1-2 Tesla. This occurs at a field intensity of:

 

For this reason, there is no point in building an electromagnet with a higher field intensity.