Cloaking device

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Cloaking device simulation (inactive).jpg
Simulation of a hypothetical cloaking device. Normally, incident light waves on an object are absorbed or reflected, causing the object to appear visible.
Cloaking device simulation (active).jpg
With the cloaking device active, light is 'deflected' around the object to make it appear as if it did not exist, rendering it invisible.

A cloaking device is a hypothetical 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.

Contents

Developments in scientific research [1] 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. [2] However, over the entire spectrum, a cloaked object scatters more than an uncloaked object. [3]

Fictional origins

Cloaks with magical powers of invisibility appear from the earliest days of story-telling. Since the advent of modern Science fiction, many variations on the theme with proposed basis in reality have been imagined. Star Trek screenwriter Paul Schneider, inspired in part by the 1958 film Run Silent, Run Deep, and in part by The Enemy Below, which had been released in 1957, imagined cloaking as a space-travel analog of a submarine submerging, and employed it in the 1966 Star Trek episode "Balance of Terror", in which he introduced the Romulan 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, or operate transporters while cloaked; [4] thus it must "decloak" to fire—essentially like a submarine needing to "surface" in order to launch torpedoes. [5]

Writers and game designers have since incorporated cloaking devices into many other science-fiction narratives, including Doctor Who , Star Wars , and Stargate .

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 is more properly referred to as "active camouflage". Alternatively, metamaterials provide the theoretical possibility of making electromagnetic radiation pass freely around the 'cloaked' object. [6]

Metamaterial research

Optical metamaterials 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. [7] [8]

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. [9] [10] [11] 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. [12] [13]

Active camouflage

A coat using optical camouflage by Susumu Tachi. 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. An invisibility cloak using optical camouflage by Susumu Tachi.jpg
A coat using optical camouflage by Susumu Tachi. 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. [14]

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. [15] The Defense Technical Information Center is also following up research on plasma reducing RCS technologies. [16] A plasma cloaking device was patented in 1991. [17]

Metascreen

A prototype Metascreen is a claimed cloaking device, which is just few micrometers 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, Austin by Professor Andrea Alù. [18]

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 GHz microwaves, it re-radiated microwaves of the same frequency that were out of phase, thus cancelling out reflections from the object being hidden. [18] The device only cancelled out the scattering of microwaves in the first order. [18] The same researchers published a paper on "plasmonic cloaking" the previous year. [19]

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. [20]

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. [21]

See also

Related Research Articles

<span class="mw-page-title-main">Invisibility</span> State of a matter that cannot be seen

Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible. The phenomenon is studied by physics and perceptual psychology.

<span class="mw-page-title-main">Metamaterial</span> Materials engineered to have properties that have not yet been found in nature

A metamaterial is a type of material engineered to have a property, typically rarely observed in naturally occurring materials, that is derived not from the properties of the base materials but from their newly designed structures. Metamaterials are usually fashioned from multiple materials, such as metals and plastics, and are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Their precise shape, geometry, size, orientation, and arrangement give them their "smart" properties of manipulating electromagnetic, acoustic, or even seismic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.

<span class="mw-page-title-main">John Pendry</span> British physicist

Sir John Brian Pendry, is an English theoretical physicist known for his research into refractive indices and creation of the first practical "Invisibility Cloak". He is a professor of theoretical solid state physics at Imperial College London where he was head of the department of physics (1998–2001) and principal of the faculty of physical sciences (2001–2002). He is an honorary fellow of Downing College, Cambridge, and an IEEE fellow. He received the Kavli Prize in Nanoscience "for transformative contributions to the field of nano-optics that have broken long-held beliefs about the limitations of the resolution limits of optical microscopy and imaging.", together with Stefan Hell, and Thomas Ebbesen, in 2014.

Nanophotonics or nano-optics is the study of the behavior of light on the nanometer scale, and of the interaction of nanometer-scale objects with light. It is a branch of optics, optical engineering, electrical engineering, and nanotechnology. It often involves dielectric structures such as nanoantennas, or metallic components, which can transport and focus light via surface plasmon polaritons.

<span class="mw-page-title-main">Cloak of invisibility</span> Mythical object that grants 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 quest. It is a common theme in Welsh mythology and Germanic folklore, and may originate with the cap of invisibility seen in ancient Greek myths. The motif falls under "D1361.12 magic cloak of invisibility" in the Stith Thompson motif index scheme.

<span class="mw-page-title-main">Nader Engheta</span> Iranian-American scientist

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<span class="mw-page-title-main">Negative-index metamaterial</span> Material with a negative refractive index

Negative-index metamaterial or negative-index material (NIM) is a metamaterial whose refractive index for an electromagnetic wave has a negative value over some frequency range.

<span class="mw-page-title-main">Terahertz metamaterial</span>

A terahertz metamaterial is a class of composite metamaterials designed to interact at terahertz (THz) frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz.

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<span class="mw-page-title-main">Photonic metamaterial</span> Type of electromagnetic metamaterial

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A nonlinear metamaterial is an artificially constructed material that can exhibit properties not yet found in nature. Its response to electromagnetic radiation can be characterized by its permittivity and material permeability. The product of the permittivity and permeability results in the refractive index. Unlike natural materials, nonlinear metamaterials can produce a negative refractive index. These can also produce a more pronounced nonlinear response than naturally occurring materials.

<span class="mw-page-title-main">Metamaterial cloaking</span> Shielding an object from view using materials made to redirect light

Metamaterial cloaking is the usage of metamaterials in an invisibility cloak. This is accomplished by manipulating the paths traversed by light through a novel optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible. Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself.

A metamaterial absorber is a type of metamaterial intended to efficiently absorb electromagnetic radiation such as light. Furthermore, metamaterials are an advance in materials science. Hence, those metamaterials that are designed to be absorbers offer benefits over conventional absorbers such as further miniaturization, wider adaptability, and increased effectiveness. Intended applications for the metamaterial absorber include emitters, photodetectors, sensors, spatial light modulators, infrared camouflage, wireless communication, and use in solar photovoltaics and thermophotovoltaics.

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<span class="mw-page-title-main">Theories of cloaking</span>

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 transmittance, sensors and active sources, and acoustic cloaking.

<span class="mw-page-title-main">Transformation optics</span> Branch of optics which studies how EM radiation can be manipulated with metamaterials

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 of new composite artificial devices, which probably could not exist without metamaterials and coordinate transformation. Computing power that became available in the late 1990s enables prescribed quantitative values for the permittivity and permeability, the constitutive parameters, which produce localized spatial variations. The aggregate value of all the constitutive parameters produces an effective value, which yields the intended or desired results.

A plasmonic metamaterial is a metamaterial that uses surface plasmons to achieve optical properties not seen in nature. Plasmons are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs). Once launched, the SPPs ripple along the metal-dielectric interface. Compared with the incident light, the SPPs can be much shorter in wavelength.

Andrea Alù is an Italian American scientist and engineer, currently Einstein Professor of Physics at The City University of New York Graduate Center. He is known for his contributions to the fields of optics, photonics, plasmonics, and acoustics, most notably in the context of metamaterials and metasurfaces. He has co-authored over 650 journal papers and 35 book chapters, and he holds 11 U.S. patents.

Illusion optics is an electromagnetic theory that can change the optical appearance of an object to be exactly like that of another virtual object, i.e. an illusion, such as turning the look of an apple into that of a banana. Invisibility is a special case of illusion optics, which turns objects into illusions of free space. The concept and numerical proof of illusion optics was proposed in 2009 based on transformation optics in the field of metamaterials. It is a scientific disproof of the idiom 'Seeing is Believing'.

<span class="mw-page-title-main">Electromagnetic metasurface</span>

An electromagnetic metasurface refers to a kind of artificial sheet material with sub-wavelength features. Metasurfaces can be either structured or unstructured with subwavelength-scaled patterns.

References

  1. ↑ John Schwartz (October 20, 2006). "Scientists Take Step Toward Invisibility". The New York Times .
  2. ↑ Sledge, Gary. "Going Where No One Has Gone Before", Discovery Channel Magazine #3. ISSN   1793-5725
  3. ↑ Monticone, F.; Alù, A. (2013). "Do Cloaked Objects Really Scatter Less?". Phys. Rev. X. 3 (4): 041005. arXiv: 1307.3996 . Bibcode:2013PhRvX...3d1005M. doi:10.1103/PhysRevX.3.041005. S2CID   118637398.
  4. ↑ Okuda, Michael; Okuda, Denise (1999). The Star Trek Encyclopedia. Simon and Schuster. ISBN   9781451646887.
  5. ↑ Sopan Deb (November 12, 2017). "Star Trek: Discovery, Season 1, Episode 9: Sloppy Showdowns". The New York Times . The Klingons have to decloak to fire
  6. ↑ Service, Robert F.; Cho, Adrian (17 December 2010). "Strange New Tricks With Light". Science. 330 (6011): 1622. Bibcode:2010Sci...330.1622S. doi:10.1126/science.330.6011.1622. PMID   21163994.
  7. ↑ Pendry, J.B.; Schurig, D.; Smith, D.R. (2006). "Controlling electromagnetic fields" (PDF). Science. 312 (5781): 1780–1782. Bibcode:2006Sci...312.1780P. doi:10.1126/science.1125907. PMID   16728597. S2CID   7967675. Archived (PDF) from the original on 2016-10-06.
  8. ↑ Leonhardt, Ulf; Smith, David R. (2008). "Focus on Cloaking and Transformation Optics". New Journal of Physics . 10 (11): 115019. Bibcode:2008NJPh...10k5019L. doi: 10.1088/1367-2630/10/11/115019 .
  9. 1 2 Inami, M.; Kawakami, N.; Tachi, S. (2003). "Optical camouflage using retro-reflective projection technology" (PDF). The Second IEEE and ACM International Symposium on Mixed and Augmented Reality, 2003. Proceedings. pp. 348–349. CiteSeerX   10.1.1.105.4855 . doi:10.1109/ISMAR.2003.1240754. ISBN   978-0-7695-2006-3. S2CID   44776407. Archived (PDF) from the original on 2016-04-26.
  10. ↑ Alù, A.; Engheta, N. (2008). "Plasmonic and metamaterial cloaking: physical mechanisms and potentials". Journal of Optics A: Pure and Applied Optics. 10 (9): 093002. Bibcode:2008JOptA..10i3002A. CiteSeerX   10.1.1.651.1357 . doi:10.1088/1464-4258/10/9/093002. Archived from the original on 2016-04-20.
  11. ↑ Gonano, C.A. (2016). A perspective on metasurfaces, circuits, holograms and invisibility (PDF). Politecnico di Milano, Italy. Archived (PDF) from the original on 2016-04-24.
  12. ↑ Smith, David R. (25 July 2014). "A cloaking coating for murky media". Science. 345 (6195): 384–385. Bibcode:2014Sci...345..384S. doi:10.1126/science.1256753. PMID   25061192. S2CID   206559590.
  13. ↑ Schittny, Robert et cl. (25 July 2014). "Invisibility cloaking in a diffuse light scattering medium". Science. 345 (6195): 427–429. Bibcode:2014Sci...345..427S. doi: 10.1126/science.1254524 . PMID   24903561. S2CID   206557843.
  14. ↑ Clark, Josh. "Is the army testing an invisible tank?" Archived 2012-03-01 at the Wayback Machine , HowStuffWorks.com, 3 December 2007. accessed 22 February 2012.
  15. ↑ Plasma cloaking: Air chemistry, broadband absorption, and plasma generation backup Archived 2009-08-02 at the Wayback Machine , February 1990.
  16. ↑ Gregoire, D. J. ; Santoru, J. ; Schumacher, R. W.Abstract Archived 2009-08-02 at the Wayback Machine Electromagnetic-Wave Propagation in Unmagnetized Plasmas Archived 2009-08-02 at the Wayback Machine , March 1992.
  17. ↑ Roth, John R. "Microwave absorption system" U.S. patent 4,989,006
  18. 1 2 3 Tim Wogan (28 March 2013). "Ultrathin "metascreen" forms latest invisibility cloak". PhysicsWorld.com. Archived from the original on 17 August 2013.
  19. ↑ http://iopscience.iop.org/1367-2630 New Journal of Physics, March 2013.
  20. ↑ "Cloaking' device uses ordinary lenses to hide objects across range of angles". Science Daily. 29 September 2014. Archived from the original on 2014-10-01. Retrieved 15 August 2021.
  21. ↑ Bückmann, Tiemo (2014). "An elasto-mechanical unfeelability cloak made of pentamode metamaterials". Nature Communications . 5 (4130): 4130. Bibcode:2014NatCo...5.4130B. doi: 10.1038/ncomms5130 . PMID   24942191.
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