Cloaking devices

Simulation of how a cloaking device would work

Cloaking device deactivated: Light is reflected and absorbed by the object, causing it to be visible.

Cloaking device active: Light is deflected around the object, causing it to be invisible.

A cloaking device is an advanced stealth technology that causes an object, such as a spaceship or individual, 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, but developments in scientific research show that real-world cloaking devices can obscure objects from at least one wavelength of EM emissions.

Conceptual origins

In Star Trek, cloaking devices were first introduced and used by the Romulans in the Original Series episode "Balance of Terror", though the device was only referred to as "a practical invisibility screen."^{citation needed} The invisibility came as a surprise to the crew of the USS Enterprise, who considered it only a theoretical possibility. During a later episode, "The Enterprise Incident", the term "cloaking device" was first coined by writer D.C. Fontana. Decades later, the episode "Minefield" of Star Trek: Enterprise contradicted this by revealing that Romulans possessed a form of cloaking technology in the mid-22nd Century, suggesting that what was featured in "Balance of Terror" et al was some sort of improvement, or that, for some reason, Starfleet Intelligence (or perhaps agents in the Temporal Cold War) suppressed knowledge of the cloaking devices encountered a century earlier, after the 4th season opener which ended the temporal cold war thread, all references to cloaking devices were removed by the new show runner, this could be taken as part of the restored timeline. Enterprise also encountered several other races with cloaking technology, including briefly obtaining a cloak-capable pod belonging to the Suliban. In addition, the Mirror Universe Enterprise was also fitted with a Suliban cloaking device in the two "In a Mirror, Darkly" episodes. The Suliban cloaking device allowed the Mirror Enterprise NX-01 to fire weapons while cloaked.

Cloaking devices have also been used in many other science-fiction settings and games, including (but not limited to) Doctor Who, Star Wars, Predator, and StarCraft. When cloaking devices are used in games, they typically come with a drawback for balance, such as requiring a limited energy source to power them, or failing when the player initiates an attack while cloaked.

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 are more properly referred to as "active camouflage." Alternatively, metamaterials provide the theoretical possibility of making electromagnetic radiation appear to pass freely through the 'cloaked' object.

Philadelphia Experiment

The Philadelphia Experiment was an alleged secret experiment conducted by the U.S. Navy at the Philadelphia Naval Yards at Philadelphia, Pennsylvania, on or before October 28, 1943, which went horribly awry. The experiment was allegedly to cast a veil of radar and possibly optical invisibility or transparency around a ship. Though most mainstream experts argue the incident is an urban legend, a number of people argue that the Philadelphia Experiment could be genuine. Whether true or not, the Philadelphia Experiment has had a major ripple effect on conspiracy theory, and elements of the Philadelphia Experiment feature in many other conspiracy tales and provided the basis for various movies and miniseries.

Metamaterial research

Optical metamaterials have featured in several recent 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. (Opals are a well known example of a naturally occurring metamaterial.) It has been demonstrated that such materials can take on optical properties unattainable by natural substances. Most famously, a negative refractive index is possible.

Plasma

The United States Navy has been funding research into plasma based cloaking for several years.^{citation needed} So far, the experiments remain unsuccessful on visible light, but recently breakthroughs have been made on lower frequency electromagnetic cloaking, specifically radio. Basically, plasma is created then held in place by a magnetic field at a certain frequency and heat, and the fast moving particles suddenly take on a metamaterial like state taking in light, then distorting it around an object so it appears as if the object doesn't exist at all. Theoretically, a similar system could be made for other forms of electromagnetism as high frequency as gamma rays, but it becomes more difficult to achieve. The great challenges to implementing such a system are cheaply creating plasma, producing a large enough and precise enough magnetic field to contain it, and compensating for effects when things touch the field thereby disturbing the plasma.

Active camouflage

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.

Holographic Cloak

Holographic imaging could technically be used to generate a cloak by projecting the image behind the object being cloaked.

Optical camouflage

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 concept exists for now only in theory and in proof-of-concept prototypes, although many experts consider it technically feasible. It is an example of active camouflage (or adaptive camouflage). Recently it has been reported that the British Army has tested an invisible tank.^[1]

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