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 array 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 make up the photonic crystal.
Very recently, it has been demonstrated that the double negative medium (DNM) can be realized with a simple array of ferrite rods without any metallic components, which can be used to implement the present gateway. The original isotropic material (the blue region in the picture has a large value of permittivity, “0 = −10 000 and μ0 = 1, which may be treated approximately as a perfect electric conductor (PEC).
The amplified scattering effect can be utilized to make an invisible gateway . Suppose that a PEC wall separates the whole space into two regions, the upper domain and the lower domain. If there are channels (or gateways) opened in the PEC wall, people in the two different spaces can communicate with each other, both physically and through electromagnetic (EM) waves. However, if we replace the doors with the described configuration at a specific frequency, the communication for that frequency will be blocked because the systems behave like PECs. The most amazing fact is that the channel is in fact physically empty. There is nothing but air in the channel so objects can ‘walk through’ but the channel is blocked as perceived by the eye because light at the designated frequency cannot penetrate