Actuators with permanent magnets having variable in space orientation of magnetization

The force between a permanent magnet and a coil can be increased if the magnetization orientation of the magnet is suitably varying in space. The force is greatest if the magnet is magnetized along coil field lines ('optimal' magnet). In this article, is studied how the optimisation effect depends on the magnet proportions and coil-magnet distance in case of cylindrical magnets and coaxial planar coils. The dependence of the force on the magnet height and coil-magnet distance for differently magnetized magnets (axial, radial, optimal) is presented. Magnetization of the magnet in the direction of the coil's field can provide a more than two-fold force compared to axial magnetization, especially at thin magnets and small coil-magnet distances. The measured force values differed from the calculated values maximum 2% for a milli-size radial-axial composite magnet. (C) 2002 Elsevier Science B.V. All rights reserved.