Nikolai Shervashidze 5.1.201810/2Cloaking DevicesFinal draftAbstractThis Article will walk you through the ways something is is made to appear invisible for the eye or for a detector, scanner or other type of a detector. To see something your eye must catch the light reflected from the object and process it, so to make this object invisible you must no let the reflected light to enter your eye or to bend the light around the object so i does not reflect from it. Scientist do this using different tools, like metamaterials, superlenses or active camouflages. Down below you will read in debt how this is done and about the physics phenomenons that allow this to happen.IntroInvisibility has been a subject in science fiction and fantasy for a long time now, from the invisible cloak of Harry Potter to the cloaking devices of the ships in Star Wars and Star Trek. Film industry has exploited those concept for nearly a century, which led to the idea of invisibility very popular. However, now scientist are beginning to believe that they can achieve the same result by using complex technologies, which help object disappear from sight or from detectors. To make something disappear you first need to see it. When you see something the light bouncing from the object enters your pupils and interacts with the rods and cones from your eyes, which results in a electrical impulse sent to your brain. This tells the brain that there is an object and helps you perceive it. The rods detect only black and white and the cones detect colors, so the color of the object depends on the frequency of the light interacting with the cones.So if something is invisible that means that your eyes or a machine can’t see it or detect it. In order to do that we need to make the light of the object not to interact with our eyes. To achieve this we need to bend the light around the object so it doesn’t scatter around, and doesn’t reflect from it in a way that the light doesn’t get in any kind of a detector. Also if the reflected light from the object enters our eyes but it’s not recognised, that again means that the object is cloaked or camouflaged. So the perfect cloaking device bends the light around the object, which allows you to see right through it. This concept, however, doesn’t apply only for light and things you can see with your eyes, it applies for magnetic and acoustic waves as well. This led the scientist to find ways to hide those waves from radars and other kind of detectors. However, building something that is invisible for detectors isn’t new at all. Military organisations from around the globe have been building machines and more specifically aircrafts, which are undetectable for radars. Such aircraft is the stealth bomber B-2, which was built during the cold war by USA. This plane is nearly invisible for radar and also has reduced magnetic, electrical, acoustic and infrared detection.MetamaterialsPhysicists are working very hard to make such materials that bend the waves around a object. Those materials are called metamaterials. Metamaterials usually have highly conducting metal, such as copper or gold, and which are then arranged in specific shapes and structure. These specifically arranged structures lead to an effective type of reflection, which leads to the so called negative reflection index, that means that they don’t have the power to reflect certain kind of waves. Most of the materials we know have a positive reflection index, that determines how the light(or other types of waves) will reflect from it and how the light will interact after it’s reflected. To create invisibility the metamaterial or the cloaking device has to bend the electromagnetic waves around the objects it’s hiding and around itself. To achieve this the cloaking device must not cause distortions to the electromagnetic waves.SuperlensOther use for the metamaterials other than to create cloaking devices is to make superlenses. The superlens is a type of lens that is made of metamaterials and this helps us to see thing much smaller than they really are. Also this allows the lens to go beyond the diffraction limit. Most of the lenses that we use are ordinary and they can’t go beyond the diffraction limit. Those lenses can only project objects bigger than half of the wavelength of the light they interact with. The diffraction limit is what makes possible for the lense to limit and control the fineness of the resolution. Going beyond this diffraction limit will help scientists project a object, which is smaller than half of the wavelength. Active CamouflageAnother type of cloaking device used today is the active camouflage. This is a technology used mainly by the military. Active camouflage or also adaptive camouflage is a technology allows certain person or object to blend in into its surroundings, using panels and coatings which are capable of changing colors in order to become indetectable for human eye. Optical camouflage is type of active camo, which consists of someone wearing a clothing, which has the surrounding projected onto it, so that the person wearing it will appear invisible. However, a negative aspect of this technology is that, when the person wearing the camouflage moves a distortion is created, because the clothing struggles to keep up with the wearer’s pace. Those technologies no longer exist only is the science-fiction, as there are prototypes testing the active camouflage of people and on vehicles . ConclusionIn conclusion the cloaking devices are real and they put in good use by the governments around the globe, since those types of technologies help their military programs to expand. This leeds to new types of devices to be tested very often.