  Eddy current separation (ECS) is a process used throughout the scrap
recycling industry for separating nonferrous metals from nonmetallic fluff. To
date, however, the physical theory of ECS has generally been limited to
empirical approximations and numerical simulations. We therefore introduce a
simplified, two-dimensional model for ECS based on a cylindrical array of
permanent, alternating magnets. The result is a Fourier-series expansion that
describes the total magnetic field profile over all space. If the magnets are
then rotated with constant angular velocity, the magnetic fields vary as a
discrete series of sinusoidal harmonics, thereby inducing electrical eddy
currents in nearby conductive particles. Force and torque calculations can then
be used to predict the corresponding kinematic trajectories.
