Cloaking—What Is It?To cloak is to covering or conceal an object, to make it invisible. Invisible at least from a portion of the electromagnetic spectrum. Not only would the object be invisible, but the surroundings would be seen. It’s like something out of Star Trek.
Is cloaking possible?
Grasping the IdeaImagine you are outside. 25 feet in front of you is a French Poodle. You are looking at it, when a 2½- ton truck pulls between you and the dog. You no longer see the dog. If the truck is cloaked at a basic level, you would not see the truck. But neither would you see the dog. If the truck is cloaked at the highest level, you would see the dog!
Discerning the ConceptThe light bouncing off the truck must be manipulated or controlled to accomplish basic cloaking. The more advanced form, in which you would see the dog as well, requires manipulation of the light coming from the dog.¹
Some of the earlier efforts at cloaking were more like active camouflage, since they didn’t really render objects invisible but merely difficult to detect.² So in more recent times, what has been accomplished by way of true cloaking?
Is True Cloaking Possible?One approach involves so-called meta materials. These man made materials use repetitive surface features to affect radiation striking them. Some of these features are smaller than the wavelength of the radiation.
One form of meta material utilizes the idea of a negative refractive index. That concept is dramatized in this web media video.
One approach to basic cloaking, is plasma stealth. It is of interest to the military. It uses gaseous plasma confined between layers, perhaps of a membrane, that will absorb, or interfere with incoming signals such as radar.
Another Variety of CloakingAlthough most cloaking discussions refer to invisibility to waves of the electromagnetic spectrum, others refer to different kinds of waves. Waves such as those of the sea. Is it possible to make an object such as an offshore rig invisible to violent waves? Possibly so. That is the object of a discussion by David Szondy.
Fiction or Scientific Possibility?Based on gravitational lensing the idea of employing a gravitational device to bend light is appealing. How far away from Man’s grasp is the idea? Is it mere science fiction or is it a scientific possibility?
¹ This might remind the astronomer of the phenomenon of gravitational lensing. For further information, see Glass, Rubber and Gravitational Lenses
² See, for example, ADTIC: Active Camouflage for Infantry Headware Applications
- Science: Controlling Electromagnetic Fields, by Pendry, et. al.
- Duke Center for Metamaterials: Real life invisibility cloak perfected by Duke Researchers (Video)