Defense Intelligence Reference Document Invisibilty Cloaking Theory And Experiments

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depend on their lengths and on their arrangement, which, in principle, can be tailor-
made and controlled using the tools of modern nanotechnology. The thin wires will have
lower electric losses than split-ring resonators, and their radiation losses by the
equivalent of spontaneous emission are reduced as well. Such optical cloaking devices
do not yet exist, but one can gauge the progress in the required technology by
considering the progress in negatively refracting optical materials.
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Figure 13. Idea for a Cloaking Device for Visible Light. Metal nanowires replace the split-ring resonators of
the microwave cloaking device. Coordinate transformation and structure of the optical cloak. a: The coordinate
transformation that compresses a cylindrical region r < b into a concentric cylindrical shell a< r < b. There is no
variation along the vertical direction. The radii rl and r2 define the internal and external radius of a fraction of the
cylindrical cloak. b: A small fraction of the cylindrical cloak. The wires are all perpendicular to the cylinder's inner
and outer interfaces, but their spatial positions do not have to be periodic and can be random.'n
Figure 14 below 21 illustrates the route toward achieving negative refraction in the
visible range of the spectrum. Losses typically are a greater problem for negatively
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