Optimal dimensions of rectangular electromagnet for braking purposes

Electromechanical braking is based on the interaction of eddy currents and a magnetic field, with the former usually induced in a moving part. Although, in many cases, the currents are constrained and restricted by preferred conduction paths (eg., a squirrel cage in the case of induction braking), on occasion the induced part is designed with uniform conductivity, in which case the currents are “free”: their paths depend on the geometrical configuration of the device and on its electromagnetic properties. In practice, eddy-current brakes are frequently used for motor testing since the braking force lends itself to continuous control through the current flowing in the excitation winding of the electromagnet. The present paper deals with the braking effect on a conducting sheet moving in the field of an electromagnet having poles of rectangular cross-section. Its practical objective is improved pole design, with a view to minimized material cost for a specific braking force. The analysis is undertaken for two cases: a) a conducting sheet of infinite horizontal dimensions; b) a conducting sheet of finite width but infinite in the direction of motion.