Documents / Official release
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/ fFOlil OFFI&Ilil l:ISE 8Hl¥ The split-ring resonators are electromagnetic circu its; they respond to the electromagnetic field of microwave rad iation. Their response depends on their shapes. For example, in the cloaking device shown in Figure 11, the double stripes in the middle of the split ring resonators vary from ring to ring. As these stripes form an electric capacitor, the capacitance of the resonators also varies. The colored curves show how the electromagnetic functions change over the distance from the center of the cloaking device as a result of the varied capacitance. As they are always positive, negative refraction is not required for cloaking. At the inner ring, the red curve reaches zero, defining the boundary of the cloaking device. The rings with their split-ring structures are designed to Figure 11. Cloaking Device for Microwaves14 perform an approximation of the coord inate transformation shown and explained in the previous section. How is this possible? The split-ring resonators act like the atoms or molecules of a normal optical or electromagnetic material : they absorb electromagnetic waves and re-emit them with a phase delay or advance that depends on their electromagnetic response. Like atoms or molecules, they are much smaller than the electromagnetic wavelength-3-mm cell size versus 3-cm wavelength in the case of the microwave cloaking device15- such that the waves cannot resolve them individually but, rather, react to them as if they were a bulk material with electromagnetic properties that may differ from point to point. Unlike atoms or molecules, the electromagnetic response of each sp lit-ring resonator is tailor made because it depends on the shape of the resonator that can be easi ly modified. For example, in the case of the microwave-cloaking device, 16 the electromagnetic response depends on the capacitance that is varied by changing the length of the double stripes in the resonators. An unstructured circuit board reacts completely differently to the microwave radiation: it would simply reflect it like the mesh in the window of a microwave oven. A material with electromagnetic or optical properties that depends on structures much smaller than the wavelength is called a metamaterial. Metamaterials per se are nothing new; the ancient Romans invented the first optical metamaterial: ruby glass. The Romans probably did not know it, but their recipe for ruby glass contained one crucial ingredient:17 tiny gold droplets, typically 5-60 nanometers (nm) in size. These gold particles color the glass in an extraordinary way, as demonstrated by the exquisite Lycurgus Cup shown in Figure 12. In daylight, the cup appears a greenish color, but illuminate it from the inside, and it glows ruby. The gold particles act like the split-ring resonators of the microwave-cloaking device, 18 but here on light, not on microwave radiation . Light consists of electromagnetic waves as well, but with significantly smaller wavelengths of around 500 nm. The gold particles are thus much smaller than the wavelength of light, and they turn out to be resonators as well: in them, electric currents flow in a way that is dictated by their shapes and sizes. When the light wave hits the resonance of the gold particle, most of its energy is UNCLASSIFIED//EOA: OEEICI C.. Uili OPU1¥ 10
Not linked to a story yet.
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.