A cloaking device is a hypothetical or fictional
stealth technology
Stealth technology, also termed low observable technology (LO technology), is a sub-discipline of military tactics and passive and active electronic countermeasures. The term covers a range of military technology, methods used to make personnel ...
that can cause objects, such as
spaceships
Spaceship may refer to:
Spaceflight
* Space vehicle, the combination of launch vehicle and spacecraft
* Spacecraft, a craft, vehicle, vessel or machine designed for spaceflight
* Starship, a spacecraft built for interstellar flight
Computing
...
or individuals, to be partially or wholly
invisible
Invisibility is the state of an object that cannot be seen. An object in this state is said to be ''invisible'' (literally, "not visible"). The phenomenon is studied by physics and perceptual psychology.
Since objects can be seen by light fr ...
to parts of the
electromagnetic (EM) spectrum. Fictional cloaking devices have been used as
plot device
A plot device or plot mechanism
is any technique in a narrative used to move the plot forward.
A clichéd plot device may annoy the reader and a contrived or arbitrary device may confuse the reader, causing a loss of the suspension of disbelief ...
s in various media for many years.
Developments in scientific research
show that real-world cloaking devices can obscure objects from at least one
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
of EM emissions. Scientists already use artificial materials called
metamaterial
A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is a type of material engineered to have a property, typically rarely observed in naturally occu ...
s to bend light around an object. However, over the entire spectrum, a cloaked object scatters more than an uncloaked object.
[
]
Fictional origins
Cloaks with magical powers of invisibility appear from the earliest days of story-telling. Since the advent of modern
Science fiction
Science fiction (often shortened to sci-fi or abbreviated SF) is a genre of speculative fiction that deals with imaginative and futuristic concepts. These concepts may include information technology and robotics, biological manipulations, space ...
, many variations on the theme with proposed basis in reality have been imagined. ''
Star Trek
''Star Trek'' is an American science fiction media franchise created by Gene Roddenberry, which began with the Star Trek: The Original Series, series of the same name and became a worldwide Popular culture, pop-culture Cultural influence of ...
'' screenwriter
Paul Schneider, inspired in part by the 1958 film ''
Run Silent, Run Deep,'' and in part by ''
The Enemy Below
''The Enemy Below'' is a 1957 American DeLuxe Color war film in CinemaScope about a battle between an American destroyer escort and a German U-boat during World War II. It stars Robert Mitchum and Curt Jürgens as the American and German comm ...
,'' which had been released in 1957, imagined cloaking as a space-travel analog of a
submarine
A submarine (often shortened to sub) is a watercraft capable of independent operation underwater. (It differs from a submersible, which has more limited underwater capability.) The term "submarine" is also sometimes used historically or infor ...
submerging, and employed it in the 1966 ''Star Trek'' episode "
Balance of Terror
"Balance of Terror" is the fourteenth episode of the first season of the American science fiction television series ''Star Trek''. Written by Paul Schneider and directed by Vincent McEveety, it first aired on December 15, 1966.
The series, ...
", in which he introduced the
Romulan
The Romulans () are an extraterrestrial race in the American science fiction franchise ''Star Trek''. Their adopted home world is Romulus, and within the same star system they have settled a sister planet Remus. Their original home world, Vulcan ...
species, whose space vessels employ cloaking devices extensively. (He likewise predicted, in the same episode, that invisibility, "selective bending of light" as described above, would have an enormous power requirement.) Another ''Star Trek'' screenwriter,
D.C. Fontana, coined the term ''"cloaking device"'' for the 1968 episode "
The ''Enterprise'' Incident", which also featured Romulans.
''Star Trek'' placed a limit on use of this device: a space vessel cannot fire weapons, employ defensive
shields
A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry like spears or long ranged projectiles suc ...
, or operate
transporters while cloaked; thus it must "decloak" to fire—essentially like a submarine needing to "surface" in order to launch torpedoes.
Writers and game designers have since incorporated cloaking devices into many other science-fiction narratives, including ''
Doctor Who
''Doctor Who'' is a British science fiction television series broadcast by the BBC since 1963. The series, created by Sydney Newman, C. E. Webber and Donald Wilson (writer and producer), Donald Wilson, depicts the adventures of an extraterre ...
'', ''
Star Wars
''Star Wars'' is an American epic film, epic space opera media franchise created by George Lucas, which began with the Star Wars (film), eponymous 1977 film and Cultural impact of Star Wars, quickly became a worldwide popular culture, pop cu ...
'', and ''
Stargate
''Stargate'' is a military science fiction media franchise owned by Amazon MGM Studios. It is based on Stargate (film), the film directed by Roland Emmerich, which he co-wrote with producer Dean Devlin; production company StudioCanal owns the ...
''.
Scientific experimentation
An operational,
non-fiction
Non-fiction (or nonfiction) is any document or content (media), media content that attempts, in good faith, to convey information only about the real life, real world, rather than being grounded in imagination. Non-fiction typically aims to pre ...
al 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
Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those ...
), 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 is more properly referred to as "
active camouflage
Active camouflage or adaptive camouflage is camouflage that adapts, often rapidly, to the surroundings of an object such as an animal or military vehicle. In theory, active camouflage could provide perfect concealment from visual detection.
Acti ...
". Alternatively, metamaterials provide the theoretical possibility of making electromagnetic radiation pass freely around the 'cloaked' object.
Metamaterial research
Optical
metamaterial
A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is a type of material engineered to have a property, typically rarely observed in naturally occu ...
s have featured in several 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
Transformation optics is a branch of optics which applies metamaterials to produce spatial variations, derived from coordinate transformations, which can direct chosen bandwidths of electromagnetic radiation. This can allow for the construction o ...
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
A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is a type of material engineered to have a property, typically rarely observed in naturally occur ...
. There are several
theories of cloaking
Theories of cloaking discusses various theories based on science and research, for producing an electromagnetic cloaking device. Theories presented employ transformation optics, event cloaking, dipolar scattering cancellation, tunneling light tr ...
, giving rise to different types of invisibility.
[
][
][
]
In 2014, scientists demonstrated good cloaking performance in murky water, demonstrating that an object shrouded in fog can disappear completely when appropriately coated with metamaterial. This is due to the random scattering of light, such as that which occurs in clouds, fog, milk, frosted glass, etc., combined with the properties of the metamaterial coating. When light is diffused, a thin coat of metamaterial around an object can make it essentially invisible under a range of lighting conditions.
Active camouflage

''
Active camouflage
Active camouflage or adaptive camouflage is camouflage that adapts, often rapidly, to the surroundings of an object such as an animal or military vehicle. In theory, active camouflage could provide perfect concealment from visual detection.
Acti ...
'' (or ''adaptive camouflage'') is a group of
camouflage
Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
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.
It has been reported that the
British Army
The British Army is the principal Army, land warfare force of the United Kingdom. the British Army comprises 73,847 regular full-time personnel, 4,127 Brigade of Gurkhas, Gurkhas, 25,742 Army Reserve (United Kingdom), volunteer reserve perso ...
has tested an invisible tank.
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
The Defense Technical Information Center (DTIC, ) is the repository for research and engineering information for the United States Department of Defense (DoD). DTIC's services are available to DoD personnel, federal government personnel, federa ...
is also following up research on plasma reducing
RCS
RCS may refer to:
Organizations Arts and entertainment
* Radio Corporation of Singapore
* Radcliffe Choral Society, a choral ensemble at Harvard University
*RCS MediaGroup (Rizzoli-Corriere della Sera), an Italian publishing group
*Royal Conserva ...
technologies. A plasma cloaking device was patented in 1991.
Metascreen
A prototype Metascreen is a claimed cloaking device, which is just few
micrometers
The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...
thick and to a limited extent can hide
3D objects from microwaves in their natural environment, in their natural positions, in all directions, and from all of the observer's positions. It was prepared at the
University of Texas at Austin
The University of Texas at Austin (UT Austin, UT, or Texas) is a public university, public research university in Austin, Texas, United States. Founded in 1883, it is the flagship institution of the University of Texas System. With 53,082 stud ...
by Professor
Andrea Alù.
The metascreen consisted of a 66 micrometre thick polycarbonate film supporting an arrangement of 20 micrometer thick copper strips that resembled a
fishing net
A fishing net or fish net is a net (device), net used for fishing. Fishing nets work by serving as an improvised fish trap, and some are indeed rigged as traps (e.g. #Fyke nets, fyke nets). They are usually wide open when deployed (e.g. by cast ...
. In the experiment, when the metascreen was hit by 3.6 GHz microwaves, it re-radiated microwaves of the same frequency that were out of phase, thus cancelling out reflections from the object being hidden.
[ The device only cancelled out the scattering of microwaves in the first order.][ The same researchers published a paper on " plasmonic cloaking" the previous year.
]
Howell/Choi cloaking device
University of Rochester physics professor John Howell and graduate student Joseph Choi have announced a scalable cloaking device which uses common optical lenses to achieve visible light cloaking on the macroscopic scale, known as the " Rochester Cloak". The device consists of a series of four lenses which direct light rays around objects which would otherwise occlude the optical pathway.
Cloaking in mechanics
The concepts of cloaking are not limited to optics but can also be transferred to other fields of physics. For example, it was possible to cloak acoustics for certain frequencies as well as touching in mechanics. This renders an object "invisible" to sound or even hides it from touching.
See also
*Cloak
A cloak is a type of loose garment worn over clothing, mostly but not always as outerwear for outdoor wear, which serves the same purpose as an overcoat and protects the wearer from the weather. It may form part of a uniform. People in many d ...
*Invisibility
Invisibility is the state of an object that cannot be seen. An object in this state is said to be ''invisible'' (literally, "not visible"). The phenomenon is studied by physics and perceptual psychology.
Since objects can be seen by light fr ...
*Cloak of invisibility
A cloak of invisibility is an item that prevents the wearer from being seen. In folklore, mythology and fairy tales, a cloak of invisibility appears either as a magical item used by duplicitous characters or an item worn by a hero to fulfill a q ...
*Metamaterial
A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is a type of material engineered to have a property, typically rarely observed in naturally occu ...
* Philadelphia Experiment
*Stealth technology
Stealth technology, also termed low observable technology (LO technology), is a sub-discipline of military tactics and passive and active electronic countermeasures. The term covers a range of military technology, methods used to make personnel ...
References
*
*
*
MSNBC: Can objects be turned invisible?
External links
University of Texas at Austin, Cockrell School of Engineering
''Researchers at UT Austin Create an Ultrathin Invisibility Cloak'', 26 March 2013.
''New Journal of Physics''
"Demonstration of an ultralow profile cloak for scattering suppression of a finite-length rod in free space", by JC Soric, PY Chen, A Kerkhoff, D Rainwater, K Melin, and Andrea Alù, March 2013.
''New Journal of Physics''
"Experimental verification of three-dimensional plasmonic cloaking in free-space", by D Rainwater, A Kerkhoff, K Melin, J C Soric, G Moreno and Andrea Alù, January 2012.
''Physical Review'' X
"Do Cloaked Objects Really Scatter Less", by Francesco Monticone and Andrea Alù, October 2013.
{{Science fiction, state=collapsed
Fictional technology
Hypothetical technology
Invisibility
Science fiction themes
Star Trek devices
Theoretical physics
Fiction about invisibility
Stealth technology