A permanent magnet structure for maximizing the flux density per weight of magnetic material comprising a hollow body flux source for generating a magnetic field in the central gap of the hollow body, the magnetic field having a flux density greater than the residual flux density of the hollow body flux source. The hollow body flux source has a generally elliptic-shape, defined by unequal major and minor axis. These elliptic-shaped permanent magnet structures exhibit a higher flux density at the center gap while minimizing the amount of magnetic material used. Inserts of soft magnetic material proximate the central gap, and a shell of soft magnetic material surrounding the hollow body can further increase the strength of the magnetic field in the central gap by reducing the magnetic flux leakage and focusing the flux density lines in the central gap.
Available at: http://works.bepress.com/david_jiles/14/