  Coordinate-transformation cloaking is based on the design of a metamaterial
shell made of an anisotropic, spatially inhomogeneous "transformation medium"
that allows rerouting the impinging wave around a given region of space. In its
original version, it is generally believed that, in the ideal limit, the
radiation cannot penetrate the cloaking shell (from outside to inside, and
viceversa). However, it was recently shown by Chen et al. that electromagnetic
fields may actually penetrate the cloaked region, provided that this region
contains double-negative transformation media which, via proper design, may be
in principle used to (partially or totally) "undo" the cloaking transformation,
thereby acting as an "anti-cloak." In this paper, we further elaborate this
concept, by considering a more general scenario of cloak/anti-cloak
interactions. Our full-wave analytical study provides new insightful results
and explores the effects of departure from ideality, suggesting also some novel
scenarios for potential applications.
