Influence of different magnetic field profiles on eddy- current braking

The formulas usually employed to describe the forces acting during eddy-current braking contain only one numerical value for magnetic-field strength at the site of the eddy-current disk, namely, its maximum or average value above the magnetic poles. The author investigates the influence of different magnetic-field profiles at the site of the eddy-current disk on braking force. For this purpose a number of magnetic systems using barium-ferrite magnets, which supplied different magnetic fields in the eddy-current disk, were developed. These fields varied from a nearly straightforward sinusoidal shape to fields which existed practically only at the poles, beyond which they dropped very steeply. The braking forces measured at these systems are compared with calculated braking forces. In the calculations a formula which establishes a relationship between the measured magnetic-field profile and the braking force is used. The formula was developed for a rectangular, a cosine and a cosine-squared distribution of magnetic-field strength perpendicular to the measured magnetic-field profile, allowing for the boundary conditions prevailing at the edge of the eddy-current disk.