CNT INVISIBILITY CLOAK

Metamaterials are no longer the only option for invisibility. For years that technology has been the source of hope for some future invisibility cloak, but so far only certain frequencies of light can be affected. Carbon nanotubes, on the other hand, can be used to bend all frequencies of visible light right now. Researchers at the University of Texas have used a sheet of carbon nanotubes to artificially create the mirage effect.

The mirage effect can often be seen on hot days when the sun heats paved roads. Sometimes you can see a puddle of water far down a road, but you know it is just an illusion. How does it happen? The air in contact with the pavement is much hotter than surrounding air. This temperature difference bends light so that instead of seeing the road, you see a warped image of the sky (which closely resembles reflecting water). Wherever there is an extreme temperature difference, there will be this mirage effect. The metallic bodies of cars can effectively heat the air around them, but carbon nanotubes (CNTs) are better. When an electric current passes through a sheet of CNTs, heat is quickly produced and dissipated. In the demonstration video, water was used instead of air. Like flicking a switch, the mirage effect can be activated and deactivated at will. This is a very convenient quality of the technology.

The CNTs seem a preferable alternative to metamaterials. The main drawbacks are excessive heat and possibly limited angles of cloaking. On the positive side, CNTs are much more durable than metamaterials and can bend all colors at once. Metamaterials have difficulty bending more than one color of light at a time. Indeed, it is hard to make a metamaterial that works with visible light at all. Rather than a small sheet, imagine a blanket of CNTs. With the press of a button that blanket becomes a personal wall of invisibility. With some advanced insulation on the inner side, the blanket might be able to hide a person, small car, or other item of interest. The main obstacles to this dream are the high cost of producing CNTs and supplying the energy necessary for what is essentially a high-tech electric heater.