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This Defense Intelligence Reference Document, dated 2 March 2010, was prepared by the Defense Intelligence Agency's Defense Warning Office under the Advanced Aerospace Weapon System Applications program. It reviews invisibility through camouflage, transparency, and cloaking, covering metamaterials, transformation optics, and non-Euclidean broadband cloaking designs. It concludes that perfect cloaking is impossible, but imperfect devices could be made. Microwave cloaking is within reach of present technology, while visible-light invisibility remains uncertain and depends mainly on new theoretical research.
From the source:Release of 2026-09-18 Incident: 3/2/10, Las Vegas, Nevada. Released with redactions. This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD surveys the theory and early experiments behind invisibility cloaking, describing several ways an object might be hidden from visual or sensor detection, including camouflage, transparency effects, and optical cloaking that bends light around an object. It focuses mainly on metamaterials, negative refraction, and transformation optics, and reviews experiments that had already demonstrated limited cloaking at microwave frequencies. The report argues that “imperfect” cloaking is physically achievable in some parts of the electromagnetic spectrum, especially for microwaves, but that “perfect” cloaking is not practical because it would require material properties that conflict with the underlying physics. Its overall conclusion is that cloaking is a scientific field with plausible narrow applications, but that useful visible-light cloaking depends more on future theoretical breakthroughs than on conventional advances in materials science.
UNCLASSIFIED/ /FOR: errl@IAL YSI: e .. tv hemisphere invisible and creating the same illusion as shown in A. Alternatively (D), one could expand the red line that light never crosses to create a hidden space. Why are such curved optical spaces of any practical advantage? They seem more complicated, but the distortion of space in such spaces is always finite, never infinite as in the conventional Euclidean cloaking devices. As the spatial distortions directly correspond to the required refractive ind ices, the required optical properties are never infinite, and hence such devices can, in principle, operate in a broad band of the spectrum. Curved space is more practical than flat space, although the theory is more complicated. These ideas can be extended from the two-dimensional toy model to the three-dimensional world, but they can no longer be visualized. Figure 21 below shows some ray trajectories in three-dimensional non-Euclidean cloaking devices. Figure 21. Three-Dimensional Cloaking. One can extrapolate the ideas illustrated in the previous figure to three-dimensional space, replacing the plane by flat space and the sphere by a hypersphere. The lentil-shaped object indicates the hidden interior of the device; the partly shaded grid, the boundary of the invisibil ity device. For better contrast, light rays are shown in red . A: Rays are bent around the invisible reg ion . B: In three dimensions, some rays turn out to perform two loops in hyperspace that appear in physical space as light wrapped around the invisible interior. Such non-Euclidean cloaking devices are imperfect because they delay the light traveling through the cloak. With sensitive timing or wave-front sensing one could, in principle, detect the presence of the cloaking device. Perfect cloaking is impossible, but as long as time delays and wave-front dislocations are of no concern, invisibility could become reality. Implementation Non-Euclidean cloaking devices do not have an obvious symmetry like the Euclidean microwave-cloaking device. 36 They require materials with an electromagnetic response that varies from cell to cell and is anisotropic. Most probably, such cloaking structures can be made for microwaves. A precursor of the necessary technology is the recently demonstrated ground-plate cloak. 37 This device implements the coordinate transformation shown below (that already appeared in the first paper on cloaking by UNCLASSIFIED/ /&OR OFFICI.t.k WS& 8,.LY 20
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Official release, from the pursue collection. The PDF is mirrored here; the original link is above. 29 pages are in the text index: search them above, or from the library's search.