  The technique of applying form-invariant, spatial coordinate transformations
of Maxwell's equations can facilitate the design of structures with unique
electromagnetic or optical functionality. Here, we illustrate the
transformation-optical approach in the designs of a square electromagnetic
cloak and an omni-directional electromagnetic field concentrator. The
transformation equations are described and the functionality of the devices is
numerically confirmed by two-dimensional finite element simulations. The two
devices presented demonstrate that the transformation optic approach leads to
the specification of complex, anisotropic and inhomogeneous materials with well
directed and distinct electromagnetic behavior.
