Cloak of invisibility
Encyclopedia
A cloak of invisibility
is a theme that has occurred in fiction
, and is a device which is under some scientific
inquiry.
s, such as The Twelve Dancing Princesses
, a more common trope is the cap of invisibility. The cap of invisibility
has appeared in Greek myth: Hades
was ascribed possession of a cap or helmet that made the wearer invisible. In some versions of the Perseus
myth, Perseus
borrows this cap from the goddess Athena
and uses it to sneak up on the sleeping Medusa
when he kills her. A similar helmet, the Tarnhelm
, is found in Norse mythology. In the Second Branch of the Mabinogi
, one of the important texts of Welsh mythology
, Caswallawn
(the historical Cassivellaunus) murders Caradog ap Bran
and other chieftains left in charge of Britain
while wearing a cloak of invisibility.
Edgar Rice Burroughs
uses the idea of an invisibility cloak in his 1931 novel A Fighting Man of Mars
. The movie, Erik the Viking
humorously depicts the title character using a cloak of invisibility, which he does not realize apparently works only on elderly men. In the Lord of the Rings, Frodo's elven cloak camouflaged him so that the enemy could see "nothing more than a boulder where the Hobbit
s were"; this magical item was used in the Dungeons & Dragons
game.
Camouflaging cloaks form a central plot element in Samuel R. Delany
's 1975 novel Dhalgren
and the Harry Potter
series of novels by J.K. Rowling. Harry uses the cloak to sneak into forbidden areas of the school.
More recently, cloaking devices have been used in videogames, for example Battlefield Heroes
and Team Fortress 2
, where they aid stealth-based characters. Also, Crossfire
has a game mode (appropriately called Ghost Mode) with the Black List Terrorists cloaked, and using stealth to detonate specific targets.
The cloaking device
s appearing in Star Wars
, Star Trek
and Stargate
, present a similar notion in a science fiction
form, but are generally used to hide larger scale objects, such as space ships. In science fiction cloaking, there is generally presented an assumed quasi-scientific, in-universe basis for the concept of achieving invisibility. Conversely, invisibility and cloaking is commonly presented in the science fantasy
genre as a magical phenomenon, rather than in forms that rely on pure science.
cylinder in a way that made them emerge almost as if there were nothing there. The cloak was made from metamaterials. It cast a small shadow, which the designers hope to fix.
The device obscures a defined two dimensional region and only at a particular microwave frequency. Work on achieving similar results with visible light is in progress. Other types of invisibility cloak are also possible, including ones that cloak events rather than objects.
However, cloaking a human-sized object at visible wavelengths appears to have low probability. Indeed, there appears to be a fundamental problem with these devices as "invisibility cloaks":
On the other hand, a group of researchers connected with Berkeley Lab and the University of California, Berkeley believe that cloaking at optical frequencies is indeed possible. Furthermore, it appears within reach. Their solution to the hurdles presented by cloaking issues are dielectrics. These nonconducting materials (dielectrics) are used for a carpet cloak, which serves as an optical cloaking device. According to the lead investigator:
Furthermore, a new cloaking system was announced in the beginning of 2011 that is effective in visible light and hides macroscopic objects ,i.e., objects that can be seen with the human eye. The cloak is constructed from ordinary, and easily obtainable calcite
. The crystal consists of two pieces configured according to specific parameters. The calcite is able to refract the light around a solid object positioned between the crystals. The system employs the natural birefringence
of the calcite. From outside the system the object is not visible "for at least 3 orders of magnitude larger than the wavelength of light
in all three dimensions." The calcite solves for the limitations of attempting to cloak with metallic inclusions - this method does not require a nanofabrication process as has become necessary with the other methods of cloaking. The nanofabrication process is time consuming and limits the size of the cloaked region to a microscopic area. The system works best under green light. In addition the researchers appear to be optimistic about a practical cloaking device in the future:
The design calls for tiny metal
needles to be fitted into a hairbrush-shaped cone at angles and lengths that would force light to pass around the cloak. This would make everything inside the cone appear to vanish because the light would no longer reflect off it. "It looks pretty much like fiction, I do realize, but it's completely in agreement with the laws of physics," said lead researcher Vladimir Shalaev
, a professor of electrical and computer engineering at Purdue. "Ideally, if we make it real it would work exactly like Harry Potter
's invisibility
cloak," he said. "It's not going to be heavy because there's going to be very little metal
in it."
technology:
According to Fermat’s Principle, light follows the trajectory of the shortest optical path, that is, the path over which the integral of the refractive index function is minimal. Therefore, the refractive index of an optical medium determines how light propagates within it. Consequently, by a suitable choice of refractive index profile for an optical medium, light rays can be bent around and made to propagate in closed loops…
Janos Perczel, 22, an undergraduate student at St Andrews University in Fife, has developed an optical sphere which could be used to create an "invisibility cloak". He said that by slowing down light by way of an optical illusion, the light can then be bent around an object to "conceal" it. Attempts have already been made to create invisibility cloaks but research shows that efforts are limited because any cloak would only work within certain backgrounds. But by slowing down the rays of light, Mr Perczel says the cloak wearer can move around ever-changing backgrounds.
Mr Perczel, from Hungary, came up with the idea under the guidance of "invisibility expert" Professor Ulf Leonhardt, who teaches at the university's school of physics and astronomy. The student recognised the potential of the invisible sphere and spent eight months fine tuning his project. The key development lies in the ability of the sphere, an optical device, to not only remain invisible itself but to slow light.
According to Prof Leonhardt, all optical illusions can slow down rays of light and the sphere can be used to bend this illusion around an object, reflecting off it and making it appear to be invisible. Mr Perczel added: "When the light is bent it engulfs the object, much like water covering a rock sitting in a river bed, and carries on its path, making it seem as if nothing is there. Light however can only be sped up to a speed faster than it would travel in space, under certain conditions, and this restricts invisibility cloaks to work in a limited part of the spectrum, essentially just one colour. This would be ideal if somebody was planning to stand still in camouflage. However, the moment they start to move, the scenery would begin to distort, revealing the person under the cloak. By slowing all of the light down with an invisible sphere, it does not need to be accelerated to such high speeds and can therefore work in all parts of the spectrum."
Invisibility
Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible . The term is usually used as a fantasy/science fiction term, where objects are literally made unseeable by magical or technological means; however, its effects can also be seen in the real...
is a theme that has occurred in fiction
Fiction
Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...
, and is a device which is under some scientific
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
inquiry.
Cloaks of invisibility in fiction
Cloaks of invisibility are relatively rare in folklore; although they do occur in some fairy taleFairy tale
A fairy tale is a type of short story that typically features such folkloric characters, such as fairies, goblins, elves, trolls, dwarves, giants or gnomes, and usually magic or enchantments. However, only a small number of the stories refer to fairies...
s, such as The Twelve Dancing Princesses
The Twelve Dancing Princesses
"The Twelve Dancing Princesses" is a German fairy tale originally published by the Brothers Grimm in 1812 in Kinder- und Hausmärchen as tale number 133...
, a more common trope is the cap of invisibility. The cap of invisibility
Cap of invisibility
In classical mythology, the Cap of Invisibility is a helmet or cap that can turn the wearer invisible. It is also known as the Cap of Hades, Helm of Hades, or Helm of Darkness. Wearers of the cap in Greek myths include the goddess of wisdom Athena, the messenger god Hermes, and the hero Perseus...
has appeared in Greek myth: Hades
Hades
Hades , Hadēs, originally , Haidēs or , Aidēs , meaning "the unseen") was the ancient Greek god of the underworld. The genitive , Haidou, was an elision to denote locality: "[the house/dominion] of Hades". Eventually, the nominative came to designate the abode of the dead.In Greek mythology, Hades...
was ascribed possession of a cap or helmet that made the wearer invisible. In some versions of the Perseus
Perseus
Perseus ,Perseos and Perseas are not used in English. the legendary founder of Mycenae and of the Perseid dynasty of Danaans there, was the first of the mythic heroes of Greek mythology whose exploits in defeating various archaic monsters provided the founding myths of the Twelve Olympians...
myth, Perseus
Perseus
Perseus ,Perseos and Perseas are not used in English. the legendary founder of Mycenae and of the Perseid dynasty of Danaans there, was the first of the mythic heroes of Greek mythology whose exploits in defeating various archaic monsters provided the founding myths of the Twelve Olympians...
borrows this cap from the goddess Athena
Athena
In Greek mythology, Athena, Athenê, or Athene , also referred to as Pallas Athena/Athene , is the goddess of wisdom, courage, inspiration, civilization, warfare, strength, strategy, the arts, crafts, justice, and skill. Minerva, Athena's Roman incarnation, embodies similar attributes. Athena is...
and uses it to sneak up on the sleeping Medusa
Medusa
In Greek mythology Medusa , " guardian, protectress") was a Gorgon, a chthonic monster, and a daughter of Phorcys and Ceto. The author Hyginus, interposes a generation and gives Medusa another chthonic pair as parents. Gazing directly upon her would turn onlookers to stone...
when he kills her. A similar helmet, the Tarnhelm
Tarnhelm
Tarnhelm is the name of a magic helmet in Richard Wagner's Der Ring des Nibelungen. It is used as a cloak of invisibility by Alberich in Das Rheingold...
, is found in Norse mythology. In the Second Branch of the Mabinogi
Mabinogion
The Mabinogion is the title given to a collection of eleven prose stories collated from medieval Welsh manuscripts. The tales draw on pre-Christian Celtic mythology, international folktale motifs, and early medieval historical traditions...
, one of the important texts of Welsh mythology
Welsh mythology
Welsh mythology, the remnants of the mythology of the pre-Christian Britons, has come down to us in much altered form in medieval Welsh manuscripts such as the Red Book of Hergest, the White Book of Rhydderch, the Book of Aneirin and the Book of Taliesin....
, Caswallawn
Cassivellaunus
Cassivellaunus was an historical British chieftain who led the defence against Julius Caesar's second expedition to Britain in 54 BC. The first British person whose name is recorded, Cassivellaunus led an alliance of tribes against Roman forces, but eventually surrendered after his location was...
(the historical Cassivellaunus) murders Caradog ap Bran
Caradog ap Bran
Caradog ap Bran is the son of the British king Bran the Blessed in Welsh mythology and literature, who appears most prominently in the second branch of the Mabinogi, the tale of Branwen ferch Llŷr. He is further mentioned in the Welsh Triads and in certain medieval Welsh genealogies...
and other chieftains left in charge of Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
while wearing a cloak of invisibility.
Edgar Rice Burroughs
Edgar Rice Burroughs
Edgar Rice Burroughs was an American author, best known for his creation of the jungle hero Tarzan and the heroic Mars adventurer John Carter, although he produced works in many genres.-Biography:...
uses the idea of an invisibility cloak in his 1931 novel A Fighting Man of Mars
A Fighting Man of Mars
A Fighting Man of Mars is an Edgar Rice Burroughs science fiction novel, the seventh of his famous Barsoom series. Burroughs began writing it on February 28, 1929, and the finished story was first published in Blue Book Magazine as a six-part serial in the issues for April to September, 1930...
. The movie, Erik the Viking
Erik the Viking
Erik the Viking is a 1989 feature film written and directed by Terry Jones. The film was inspired by Jones's children's book The Saga of Erik the Viking , but the plot is completely different. Jones also appears in the film as King Arnulf....
humorously depicts the title character using a cloak of invisibility, which he does not realize apparently works only on elderly men. In the Lord of the Rings, Frodo's elven cloak camouflaged him so that the enemy could see "nothing more than a boulder where the Hobbit
Hobbit
Hobbits are a fictional diminutive race who inhabit the lands of Middle-earth in J. R. R. Tolkien's fiction.Hobbits first appeared in the novel The Hobbit, in which the main protagonist, Bilbo Baggins, is the titular hobbit...
s were"; this magical item was used in the Dungeons & Dragons
Dungeons & Dragons
Dungeons & Dragons is a fantasy role-playing game originally designed by Gary Gygax and Dave Arneson, and first published in 1974 by Tactical Studies Rules, Inc. . The game has been published by Wizards of the Coast since 1997...
game.
Camouflaging cloaks form a central plot element in Samuel R. Delany
Samuel R. Delany
Samuel Ray Delany, Jr., also known as "Chip" is an American author, professor and literary critic. His work includes a number of novels, many in the science fiction genre, as well as memoir, criticism, and essays on sexuality and society.His science fiction novels include Babel-17, The Einstein...
's 1975 novel Dhalgren
Dhalgren
Dhalgren is a science fiction novel by Samuel R. Delany. The story begins with a cryptic passage:to wound the autumnal city.So howled out for the world to give him a name.The in-dark answered with wind....
and the Harry Potter
Harry Potter
Harry Potter is a series of seven fantasy novels written by the British author J. K. Rowling. The books chronicle the adventures of the adolescent wizard Harry Potter and his best friends Ron Weasley and Hermione Granger, all of whom are students at Hogwarts School of Witchcraft and Wizardry...
series of novels by J.K. Rowling. Harry uses the cloak to sneak into forbidden areas of the school.
More recently, cloaking devices have been used in videogames, for example Battlefield Heroes
Battlefield Heroes
Battlefield Heroes is a cartoon-style action video game developed by DICE initially—now developed by —and published by EA for Microsoft Windows. It is played from a third-person EA are calling it FPS perspective. The game is less demanding on computer specifications than the previous games of the...
and Team Fortress 2
Team Fortress 2
Team Fortress 2 is a free-to-play team-based first-person shooter multiplayer video game developed by Valve Corporation. A sequel to the original mod Team Fortress based on the Quake engine, it was first released as part of the video game compilation The Orange Box on October 10, 2007 for Windows...
, where they aid stealth-based characters. Also, Crossfire
Crossfire
A crossfire is a military term for the siting of weapons so that their arcs of fire overlap. This tactic came to prominence in World War I....
has a game mode (appropriately called Ghost Mode) with the Black List Terrorists cloaked, and using stealth to detonate specific targets.
The cloaking device
Cloaking device
Cloaking devices are advanced stealth technologies still in development that will cause objects, such as spaceships or individuals, to be partially or wholly invisible to parts of the electromagnetic spectrum...
s appearing in Star Wars
Star Wars
Star Wars is an American epic space opera film series created by George Lucas. The first film in the series was originally released on May 25, 1977, under the title Star Wars, by 20th Century Fox, and became a worldwide pop culture phenomenon, followed by two sequels, released at three-year...
, Star Trek
Star Trek
Star Trek is an American science fiction entertainment franchise created by Gene Roddenberry. The core of Star Trek is its six television series: The Original Series, The Animated Series, The Next Generation, Deep Space Nine, Voyager, and Enterprise...
and Stargate
Stargate
Stargate is a adventure military science fiction franchise, initially conceived by Roland Emmerich and Dean Devlin. The first film in the franchise was simply titled Stargate. It was originally released on October 28, 1994, by Metro-Goldwyn-Mayer and Carolco, and became a hit, grossing nearly...
, present a similar notion in a science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
form, but are generally used to hide larger scale objects, such as space ships. In science fiction cloaking, there is generally presented an assumed quasi-scientific, in-universe basis for the concept of achieving invisibility. Conversely, invisibility and cloaking is commonly presented in the science fantasy
Science fantasy
Science fantasy is a mixed genre within speculative fiction drawing elements from both science fiction and fantasy. Although in some terms of its portrayal in recent media products it can be defined as instead of being a mixed genre of science fiction and fantasy it is instead a mixing of the...
genre as a magical phenomenon, rather than in forms that rely on pure science.
Cloaks of invisibility in science
On October 19, 2006, a cloak was produced that routed microwaves of a particular frequency around a copperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
cylinder in a way that made them emerge almost as if there were nothing there. The cloak was made from metamaterials. It cast a small shadow, which the designers hope to fix.
The device obscures a defined two dimensional region and only at a particular microwave frequency. Work on achieving similar results with visible light is in progress. Other types of invisibility cloak are also possible, including ones that cloak events rather than objects.
However, cloaking a human-sized object at visible wavelengths appears to have low probability. Indeed, there appears to be a fundamental problem with these devices as "invisibility cloaks":
On the other hand, a group of researchers connected with Berkeley Lab and the University of California, Berkeley believe that cloaking at optical frequencies is indeed possible. Furthermore, it appears within reach. Their solution to the hurdles presented by cloaking issues are dielectrics. These nonconducting materials (dielectrics) are used for a carpet cloak, which serves as an optical cloaking device. According to the lead investigator:
Furthermore, a new cloaking system was announced in the beginning of 2011 that is effective in visible light and hides macroscopic objects ,i.e., objects that can be seen with the human eye. The cloak is constructed from ordinary, and easily obtainable calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...
. The crystal consists of two pieces configured according to specific parameters. The calcite is able to refract the light around a solid object positioned between the crystals. The system employs the natural birefringence
Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
of the calcite. From outside the system the object is not visible "for at least 3 orders of magnitude larger than the wavelength of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
in all three dimensions." The calcite solves for the limitations of attempting to cloak with metallic inclusions - this method does not require a nanofabrication process as has become necessary with the other methods of cloaking. The nanofabrication process is time consuming and limits the size of the cloaked region to a microscopic area. The system works best under green light. In addition the researchers appear to be optimistic about a practical cloaking device in the future:
The design calls for tiny metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
needles to be fitted into a hairbrush-shaped cone at angles and lengths that would force light to pass around the cloak. This would make everything inside the cone appear to vanish because the light would no longer reflect off it. "It looks pretty much like fiction, I do realize, but it's completely in agreement with the laws of physics," said lead researcher Vladimir Shalaev
Vladimir Shalaev
Vladimir M. Shalaev , the Robert and Anne Burnett Professor of Electrical and Computer Engineering and Professor of Biomedical Engineering at Purdue University, specializes in metamaterials, transformation optics, nanophotonics and plasmonics...
, a professor of electrical and computer engineering at Purdue. "Ideally, if we make it real it would work exactly like Harry Potter
Harry Potter
Harry Potter is a series of seven fantasy novels written by the British author J. K. Rowling. The books chronicle the adventures of the adolescent wizard Harry Potter and his best friends Ron Weasley and Hermione Granger, all of whom are students at Hogwarts School of Witchcraft and Wizardry...
's invisibility
Invisibility
Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible . The term is usually used as a fantasy/science fiction term, where objects are literally made unseeable by magical or technological means; however, its effects can also be seen in the real...
cloak," he said. "It's not going to be heavy because there's going to be very little metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
in it."
- On April 30, 2009, two teams of scientists developed a cloak that rendered objects invisible to near-infrared light. Unlike its predecessors, this technology did not utilize metals, which improves cloaking since metals cause some light to be lost. Researchers mentioned that since the approach can be scaled down further in size, it was a major step towards a cloak that would work for visible light.
Problems of refraction and opacity
The headlined claims that laboratory results with metamaterials are demonstrations of prototype invisibility cloaks conflicts with two facts resulting from fundamental characteristics of the underlying metamaterialMetamaterial
Metamaterials are artificial materials engineered to have properties that may not be found in nature. Metamaterials usually gain their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior....
technology:
- These materials are, by nature, highly dispersiveDispersion (optics)In optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency.Media having such a property are termed dispersive media...
, hence light passing around a "cloaked" object would be strongly refractedRefractionRefraction is the change in direction of a wave due to a change in its speed. It is essentially a surface phenomenon . The phenomenon is mainly in governance to the law of conservation of energy. The proper explanation would be that due to change of medium, the phase velocity of the wave is changed...
(prismsPrism (optics)In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
are not invisible). - Currently light passing through these materials is partially absorbed, making the shield partially opaque.
- Perfect cloaking by materials may be problematic, when taking causalityCausalityCausality is the relationship between an event and a second event , where the second event is understood as a consequence of the first....
into account.
Acoustic Cloaking
Though perfect cloaking based on invisible paint is impossible if detectors (such as microphones) and sources (such as loudspeakers) are placed round a volume and if a particular formula is used to calculate the signals to be fed to the sources, perfect cloaking is possible. Such perfect cloaking does require that the information can flow through the volume fast enough and the calculations can be performed fast enough so that the necessary information can get to the sources on the far side of the volume fast enough. As a result, perfect cloaking for light is still probably at least very difficult if not impossible. For sound waves, though, such perfect cloaking is possible in principle; an object could therefore be made invisible to sonar, for example.According to Fermat’s Principle, light follows the trajectory of the shortest optical path, that is, the path over which the integral of the refractive index function is minimal. Therefore, the refractive index of an optical medium determines how light propagates within it. Consequently, by a suitable choice of refractive index profile for an optical medium, light rays can be bent around and made to propagate in closed loops…
Janos Perczel, 22, an undergraduate student at St Andrews University in Fife, has developed an optical sphere which could be used to create an "invisibility cloak". He said that by slowing down light by way of an optical illusion, the light can then be bent around an object to "conceal" it. Attempts have already been made to create invisibility cloaks but research shows that efforts are limited because any cloak would only work within certain backgrounds. But by slowing down the rays of light, Mr Perczel says the cloak wearer can move around ever-changing backgrounds.
Mr Perczel, from Hungary, came up with the idea under the guidance of "invisibility expert" Professor Ulf Leonhardt, who teaches at the university's school of physics and astronomy. The student recognised the potential of the invisible sphere and spent eight months fine tuning his project. The key development lies in the ability of the sphere, an optical device, to not only remain invisible itself but to slow light.
According to Prof Leonhardt, all optical illusions can slow down rays of light and the sphere can be used to bend this illusion around an object, reflecting off it and making it appear to be invisible. Mr Perczel added: "When the light is bent it engulfs the object, much like water covering a rock sitting in a river bed, and carries on its path, making it seem as if nothing is there. Light however can only be sped up to a speed faster than it would travel in space, under certain conditions, and this restricts invisibility cloaks to work in a limited part of the spectrum, essentially just one colour. This would be ideal if somebody was planning to stand still in camouflage. However, the moment they start to move, the scenery would begin to distort, revealing the person under the cloak. By slowing all of the light down with an invisible sphere, it does not need to be accelerated to such high speeds and can therefore work in all parts of the spectrum."
Further reading
- Cloaking and Invisibility: Fact and Fiction by Professor David R. Smith - Electrical and Computer Engineering - Duke University (May 28, 2006)
- Three-dimensional optical metamaterial with a negative refractive index by Jason Valentine, Shuang Zhang, Thomas Zentgraf, Erick Ulin-Avila, Dentcho A. Genov, Guy Bartal, and Xiang Zhang. Nature advance online publication 11 August 2008.
- Optical Negative Refraction in Bulk Metamaterials of Nanowires by Jie Yao, Zhaowei Liu, Yongmin Liu, Yuan Wang, Cheng Sun, Guy Bartal, Angelica M. Stacy, and Xiang Zhang. Science 15 August 2008: Vol. 321. no. 5891, p. 930.
External links
- Vanishing point - The Guadian Info on "stealth suit"
- Invisibility Cloak Created in 3-D - BBC News
- Invisibility Cloak One Step Closer - BBC News
- How Invisibility Cloaks Work - HowStuffWorks
- Plasmonic invisibility effect - Live Science
- Scientists Aim to Duplicate Harry Potter's Invisibility Cloak - Live Science