  Two novel classes of spherical invisibility cloaks based on nonlinear
transformation have been studied. The cloaking characteristics are presented by
segmenting the nonlinear transformation based spherical cloak into concentric
isotropic homogeneous coatings. Detailed investigations of the optimal
discretization (e.g., thickness control of each layer, nonlinear factor, etc.)
are presented for both linear and nonlinear spherical cloaks and their effects
on invisibility performance are also discussed. The cloaking properties and our
choice of optimal segmentation are verified by the numerical simulation of not
only near-field electric-field distribution but also the far-field radar cross
section (RCS).
