Editing Cloaking device (section)

===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>