  Transformation optics is used to design a gateway that can block
electromagnetic waves but allows the passage of other entities. Our conceptual
device has the advantage that it can be realized with simple materials and
structural parameters and can have a reasonably wide bandwidth. In particular,
we show that our system can be implemented by using a magnetic photonic crystal
structure that employs a square ray of ferrite rods, and as the field response
of ferrites can be tuned by external magnetic fields, we end up with an
electromagnetic gateway that can be open or shut using external fields. The
functionality is also robust against the positional disorder of the rods that
made up the photonic crystal.
