A cloaking device is a theoretical or fictional stealth technology that can cause objects, such as spaceships or individuals, to be partially or wholly invisible to parts of the electromagnetic (EM) spectrum.
Fictional cloaking devices have been used as plot devices in various media for many years.
Developments in scientific research show that real-world cloaking devices can obscure objects from at least one wavelength of EM emissions. Scientists already use artificial materials called metamaterials to bend light around an object.
Conceptual origins 
Inspired in part by the 1958 film Run Silent, Run Deep, Star Trek screenwriter Paul Schneider imagined cloaking as a space-travel analog of a submarine submerging, and employed it in the 1966 Star Trek episode "Balance of Terror". Another Star Trek screenwriter, D.C. Fontana, coined the term cloaking device for the 1968 episode "The Enterprise Incident".
Scientific experimentation 
An operational, non-fictional cloaking device might be an extension of the basic technologies used by stealth aircraft, such as radar-absorbing dark paint, optical camouflage, cooling the outer surface to minimize electromagnetic emissions (usually infrared), or other techniques to minimize other EM emissions, and to minimize particle emissions from the object. The use of certain devices to jam and confuse remote sensing devices would greatly aid in this process, but are more properly referred to as "active camouflage". Alternatively, metamaterials provide the theoretical possibility of making electromagnetic radiation appear to pass freely through the 'cloaked' object.
Metamaterial research 
Optical metamaterials have featured in several recent proposals for invisibility schemes. "Metamaterials" refers to materials that owe their refractive properties to the way they are structured, rather than the substances that compose them. Using transformation optics it is possible to design the optical parameters of a "cloak" so that it guides light around some region, rendering it invisible over a certain band of wavelengths. These spatially varying optical parameters do not correspond to any natural material, but may be implemented using metamaterials. There are several theories of cloaking, giving rise to different types of invisibility.
Active camouflage 
Active camouflage (or adaptive camouflage) is a group of camouflage technologies which would allow an object (usually military in nature) to blend into its surroundings by use of panels or coatings capable of changing color or luminosity. Active camouflage can be seen as having the potential to become the perfection of the art of camouflaging things from visual detection.
Optical camouflage is a kind of active camouflage in which one wears a fabric which has an image of the scene directly behind the wearer projected onto it, so that the wearer appears invisible. The drawback to this system is that, when the cloaked wearer moves, a visible distortion is often generated as the 'fabric' catches up with the object's motion. The concept exists for now only in theory and in proof-of-concept prototypes, although many experts consider it technically feasible.
Plasma stealth 
Plasma at certain density ranges absorbs certain bandwidths of broadband waves, potentially rendering an object invisible. However, generating plasma in air is too expensive and a feasible alternative is generating plasma between thin membranes instead. The Defense Technical Information Center is also following up research on plasma reducing RCS technologies. A plasma cloaking device was patented in 1991.
See also 
- Cloak of invisibility
- Philadelphia Experiment
- Physics and Star Trek
- Physics and Star Wars
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