Distributed external cloak without embedded antiobjects

We propose a distributed external cloak without embedded antiobjects, which contains tunable windows and a cloaking area. It consists of closed and standalone systems whose positions and parameters can be separately controlled by the design purpose and folded geometry. Such an external cloak does not rely on either cloaked material or the concept of the antiobject [Phys. Rev. Lett. 102, 093901 (2009)] in the complementary material, and can thus be kept unchanged when different objects are considered. The object lies outside the cloak and is not blinded in terms of multiple open windows desired by specific designs. Such a distributed cloak enables us to conceal arbitrary objects of varying shape in center areas, which may exceed the inner boundary of a perfect closed cloak. (C) 2010 Optical Society of America