A first simulation (Figure 2a) showed the fields for the ideal cloaking shell that has continuously variable permittivity and permeability prescribed by the original theory. As it travels from left to right, the plane wave is smoothly deformed by the cloaking shell, much like river water flowing around a rock. An observer on the right side would thus see only the undisturbed wave, rendering the scattering object transparent and effectively invisible. The next step was to see the effects of adding energy absorption as is expected in real-world materials. The model added substantial energy absorption to the shell’s permittivity and permeability, and Figure 2b shows that the cloaking effect does not fall apart in the face of losses. The object would now cast a shadow because the incident electromagnetic power is partially absorbed before it can exit the shell, but the wave is otherwise undisturbed and thus the object does not reflect in any other direction.

Figure 2: The Electric Field Distribution near the cloaked object (the white center). Electromagnetic power flows from left to right. The x-axis extends across±0.6m, and the y-axis extends across ± 0.4m. Shown are: (a) ideal parameters, (b) ideal parameters with loss, (c) 8-layer stepwise approximation, and (d)reduced material parameters.

To find out how it would work in practice, the team designed and fabricated an eight-layer metamaterial structure with the simplified cloaking shell parameters described above. The experimentally measured fields were in almost exact agreement with the simulated fields, which confirmed that the fabricated metamaterial structure achieved the target electromagnetic parameters.

This article is based on work done by Steven A. Cummer, David Schurig, and David Smith of Duke University using multiphysics software from COMSOL, Inc. For more information, click here.