Editing Cloaking device (section)

==Scientific experimentation==
An operational, [[non-fiction]]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]]), 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]]". Alternatively, metamaterials provide the theoretical possibility of making electromagnetic radiation pass freely around the 'cloaked' object.<ref>{{cite journal|first1= Robert F. |last1=Service | first2= Adrian |last2= Cho |title= Strange New Tricks With Light |journal= Science |pages= 1622 |volume= 330 |date= 17 December 2010|bibcode = 2010Sci...330.1622S |doi=10.1126/science.330.6011.1622 |issue=6011 |pmid=21163994}}</ref>

===Metamaterial research===
{{main|Metamaterial cloaking}}
Optical [[metamaterial]]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]] 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.<ref name="pendry2006controlling">
{{Cite journal
 |author      = Pendry, J.B.
 |author2     = Schurig, D.
 |author3     = Smith, D.R.
 |title       = Controlling electromagnetic fields
 |journal     = Science
 |year        = 2006
 |volume      = 312
 |number      = 5781
 |pages       = 1780–1782
 |url         = http://courses.washington.edu/phys322/Pendry.pdf
 |bibcode     = 2006Sci...312.1780P
 |doi         = 10.1126/science.1125907
 |pmid        = 16728597
 |s2cid = 7967675
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20161006013943/http://courses.washington.edu/phys322/Pendry.pdf
 |archive-date = 2016-10-06
}}
</ref><ref name="leonhardt2008focus">
{{Cite journal
 |author = Leonhardt, Ulf
 |author2 = Smith, David R.
 |title = Focus on Cloaking and Transformation Optics
 |journal = [[New Journal of Physics]]
 |year = 2008
 |volume = 10
 |issue = 11
 |pages =  115019
 |doi = 10.1088/1367-2630/10/11/115019
 |bibcode = 2008NJPh...10k5019L
|doi-access = free
 }}
</ref>

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.<ref name="inami2003optical">
{{Cite book
 |chapter-url         = http://www.computer.org/csdl/proceedings/ismar/2003/2006/00/20060348.pdf
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20160426122636/https://www.computer.org/csdl/proceedings/ismar/2003/2006/00/20060348.pdf
 |archive-date = 2016-04-26
 |doi     = 10.1109/ISMAR.2003.1240754
 |citeseerx     = 10.1.1.105.4855
 |isbn     = 978-0-7695-2006-3
 |chapter = Optical camouflage using retro-reflective projection technology
 |title = The Second IEEE and ACM International Symposium on Mixed and Augmented Reality, 2003. Proceedings
 |pages = 348–349
 |year = 2003
 |last1 = Inami
 |first1 = M.
 |last2 = Kawakami
 |first2 = N.
 |last3 = Tachi
 |first3 = S.
 |s2cid = 44776407
 }}
</ref><ref name="alu2008plasmonic">
{{Cite journal
 |author      = Alù, A.
 |author2     = Engheta, N.
 |title       = Plasmonic and metamaterial cloaking: physical mechanisms and potentials
 |journal     = Journal of Optics A: Pure and Applied Optics
 |year        = 2008
 |volume      = 10
 |number      = 9
 |pages       = 093002
 |url         = http://repository.upenn.edu/cgi/viewcontent.cgi?article=1491&context=ese_papers
 |doi         = 10.1088/1464-4258/10/9/093002
 |bibcode     = 2008JOptA..10i3002A
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20160420235219/http://repository.upenn.edu/cgi/viewcontent.cgi?article=1491&context=ese_papers
 |archive-date = 2016-04-20
|citeseerx     = 10.1.1.651.1357
 }}
</ref><ref name="gonano2016perspective">
{{Cite book
 |author      = Gonano, C.A.
 |title       = A perspective on metasurfaces, circuits, holograms and invisibility
 |year        = 2016
 |publisher   = Politecnico di Milano, Italy
 |url         = https://www.politesi.polimi.it/bitstream/10589/116524/3/2016_01_PhD_Gonano.pdf
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20160424141054/https://www.politesi.polimi.it/bitstream/10589/116524/3/2016_01_PhD_Gonano.pdf
 |archive-date = 2016-04-24
}}
</ref>
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.<ref>{{cite journal|author=Smith, David R. |title= A cloaking coating for murky media |journal=Science|pages= 384–385 |volume= 345 |issue= 6195 |date= 25 July 2014 |doi=10.1126/science.1256753|bibcode = 2014Sci...345..384S |pmid=25061192|s2cid= 206559590 }}</ref><ref>{{cite journal|author=Schittny, Robert et cl. |title= Invisibility cloaking in a diffuse light scattering medium |journal=Science|pages= 427–429 |volume= 345 |issue= 6195 |date= 25 July 2014 |doi=10.1126/science.1254524|pmid= 24903561 |bibcode = 2014Sci...345..427S |s2cid= 206557843 |doi-access= free }}</ref>

=== Active camouflage ===
{{main|Active camouflage}}

[[File:An invisibility cloak using optical camouflage by Susumu Tachi.jpg|thumb|A coat using optical camouflage by Susumu 
Tachi.<ref name="inami2003optical"/>
 Left: The coat seen without a special device. Right: The same coat seen though the half-mirror projector part of the Retro-Reflective Projection Technology.]]
''[[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.

It has been reported that the [[British Army]] has tested an invisible tank.<ref>Clark, Josh. [http://science.howstuffworks.com/invisible-tank.htm "Is the army testing an invisible tank?"] {{webarchive|url=https://web.archive.org/web/20120301121221/http://science.howstuffworks.com/invisible-tank.htm |date=2012-03-01 }}, ''HowStuffWorks.com'', 3 December 2007. accessed 22 February 2012.</ref>

===Plasma stealth===
{{Main|Plasma stealth}}
[[plasma (physics)|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.<ref>[http://adsabs.harvard.edu/abs/1990sri..reptQ....V Plasma cloaking: Air chemistry, broadband absorption, and plasma generation] [http://www.stormingmedia.us/44/4402/A440222.html backup] {{webarchive|url=https://web.archive.org/web/20090802184503/http://www.stormingmedia.us/44/4402/A440222.html |date=2009-08-02 }}, February 1990.</ref> The [[Defense Technical Information Center]] is also following up research on plasma reducing [[Radar cross-section|RCS]] technologies.<ref>Gregoire, D. J. ; Santoru, J. ; Schumacher, R. W.[http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA250710 Abstract] {{webarchive|url=https://web.archive.org/web/20090802062206/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA250710 |date=2009-08-02 }} [http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA250710&Location=U2&doc=GetTRDoc.pdf Electromagnetic-Wave Propagation in Unmagnetized Plasmas] {{webarchive|url=https://web.archive.org/web/20090802062201/http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA250710&Location=U2&doc=GetTRDoc.pdf |date=2009-08-02 }}, March 1992.</ref>  A plasma cloaking device was patented in 1991.<ref>Roth, John R. "Microwave absorption system" {{US patent|4989006}}</ref>

===Metascreen===
A prototype Metascreen is a claimed cloaking device, which is just few [[micrometers]] thick and to a limited extent can hide [[Three-dimensional space|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]] by Professor [[Andrea Alù]].<ref name=physicsworld.com>{{cite web|url=http://physicsworld.com/cws/article/news/2013/mar/28/ultrathin-metascreen-forms-latest-invisibility-cloak|work=PhysicsWorld.com|date=28 March 2013|title=Ultrathin "metascreen" forms latest invisibility cloak|author=Tim Wogan|url-status=live|archive-url=https://web.archive.org/web/20130817232220/http://physicsworld.com/cws/article/news/2013/mar/28/ultrathin-metascreen-forms-latest-invisibility-cloak|archive-date=17 August 2013}}</ref>

The metascreen consisted of a 66 micrometre thick polycarbonate film supporting an arrangement of 20 micrometer thick copper strips that resembled a [[fishing net]].  In the experiment, when the metascreen was hit by 3.6&nbsp;GHz microwaves, it re-radiated microwaves of the same frequency that were out of phase, thus cancelling out reflections from the object being hidden.<ref name=physicsworld.com/>  The device only cancelled out the scattering of microwaves in the first order.<ref name=physicsworld.com/> The same researchers published a paper on "[[Theories of cloaking#Plasmonic cover|plasmonic cloaking]]" the previous year.<ref>http://iopscience.iop.org/1367-2630 New Journal of Physics, March 2013.</ref>

=== 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]].<ref>{{cite web|title=Cloaking' device uses ordinary lenses to hide objects across range of angles|work=Science Daily|date=29 September 2014|url=https://www.sciencedaily.com/releases/2014/09/140929085221.htm|access-date=15 August 2021|archive-url=https://web.archive.org/web/20141001000527/https://www.sciencedaily.com/releases/2014/09/140929085221.htm|url-status=live|archive-date=2014-10-01}}</ref>

===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.<ref>{{ cite journal | last = Bückmann | first = Tiemo | year = 2014 | title = An elasto-mechanical unfeelability cloak made of pentamode metamaterials | journal = [[Nature Communications]] | volume = 5 | issue = 4130 | pages = 4130 | doi = 10.1038/ncomms5130 | pmid = 24942191 | bibcode = 2014NatCo...5.4130B | doi-access = free }}</ref>