Flux Focusing

[sreid]

Clerly, flux intensity in an air gap can be increased by tapering iron pole pieces. If the magnets are the "pole pieces", can the magnets be tapered to increase the gap field strength?

 

[MagMike]

Unfortunately, they don't work that way. Tapering magnets can help shape a magnetic field (e.g. to improve uniformity), but because of the reduced magnet volume the output is reduced.

Tapering the pole pieces works because the flux is concentrated by a high permeability material. Most permanent magnets work at permeabilities close to 1.

The best way to increase the flux in the air gap of a dipole is a Halbach array or closed-loop permanent magnet configuration assembly as suggested by gphatch in an earlier thread (thread340-122602). Note, these ways are more expensive and are more difficult to assemble. You have to calculate if those trade-offs are worth it.