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This Defense Intelligence Reference Document, dated 2 March 2010 and produced by the Defense Intelligence Agency under its Advanced Aerospace Weapon System Applications (AAWSA) Program, is a technical survey of invisibility. It covers camouflage, including stealth aircraft and optical camouflage, then transparency, cloaking by coordinate transformation, metamaterials and non-Euclidean broadband cloaking. It concludes that perfect cloaking is impossible but imperfect microwave cloaks are within reach of present technology. Whether cloaking will work at visible wavelengths remains unclear.
“red lights”6 pages
UNCLASSIFIED/ ,SFIHl 8FFHil.t.k Wfili IH.k\f 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. t] y• I ----- 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 12 UNCLASSIFIED/ ,u;oAt OFFIGIPk IP&'i Ollk¥
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Report, from the dia collection. The PDF is mirrored here; the original link is under it. 29 pages are in the text index: search them above, or from the library's search.