Invisibility has always been considered to be futuristic technology, but modern technology is very much on the cusp of making it real. One of the first appearances of this was in the technology that hides stealth aircraft. In terms of the total invisibility to visible light that sci-fi and fantasy fiction has talked about since H. G. Wells’ The Invisible Man, there are a couple of modern technologies that can achieve this.
One method that can be used to make an object invisible is the use of optical metamaterials. These are materials that have their refractive properties as a result of their structure rather than the substances they are composed of. This method means that invisibility can be achieved simply by restructuring a material rather than creating a new invisible material. Due to the structure, the material will guide light around an object in order to make it invisible. Currently this method can only be used in certain applications, and is not quite at the level of a practical invisibility cloak. Scientists managed to demonstrate that this method could make an object shrouded in some sort of fog completely invisible. For example, an object in clouds, fog or murky water could disappear completely with just a thin layer of this metamaterial. Perhaps in the future the method will be able to make all objects disappear, regardless of the environment it is in.
Active camouflage is camouflage that is able to very rapidly adapt to the surroundings of the object being hidden. This method of invisibility is already used in nature by groups of animals, for example reptiles, molluscs and flatfish. These animals achieve invisibility by countershading and by counterillumination, which means that they change colour either by changing their shading or changing their illumination. A technology called optical camouflage has been created around this and has an object wear a skin that has an image of the scene directly behind it, allowing the object to appear invisible. This technology is often achieved by using cameras and LEDs. With modern technology this form of invisibility is not totally achievable. The skin doesn’t adapt quickly enough to the image captured by the camera, so when the object is moving there is a visible distortion.
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