Modeling eddy currents with boundary conditions by using Coulomb's law and the method of images

Abstract

Since the eddy-current problem usually depends on the geometry of the moving conductive sheet and the pole shape, there is no general method for solving it analytically. This paper presents a method for analysis of the eddy current in the special case of a rotating disk in a time-invariant field. The analysis uses Coulomb's law and the method of images to consider the boundary conditions. First, the surface charge generated in the rotating disk is obtained and Coulomb's law is applied to calculate the electric field intensity, assuming an infinite disk radius. Second, the finite disk radius is taken into account by introducing an imaginary electric field intensity to satisfy the boundary condition that the radial component of the eddy current is zero at the edge of the rotating disk. Third, the braking torque is calculated by applying the Lorentz force law. The paper compares the computed braking torque with the experimental results to establish the validity of the model.