Region division in transformation electromagnetics

In the past decade, transformation optics (or transformation electromagnetics), which is based on the property of metric invariance in Maxwell's equations, has been developed rapidly. Transformation electromagnetics allows metamaterials to be tailored according to practical requires. In this paper, we review some kinds of special transformation devices based on region division, including the arbitrarily-shaped invisibility cloaks and concentrators, localized invisibility cloaks, and functional illusion devices. The technique of region division can also be applied to other fields of electromagnetics.