A cloaking device is a hypothetical or fictional stealth technology that can cause objects, such as spaceships or individuals, 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.
Simulation of a hypothetical cloaking device. Normally, incident light waves on an object are absorbed or reflected, causing the object to appear visible.
With the cloaking device active, light is 'deflected' around the object to make it appear as if it did not exist, rendering it invisible.
A coat using optical camouflage by Susumu Tachi. Left: The coat seen without a special device. Right: The same coat seen though the half-mirror projector part of the Retro-Reflective Projection Technology.
Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible. The phenomenon is studied by physics and perceptual psychology.
Alberich puts on the Tarnhelm and vanishes; illustration by Arthur Rackham to Richard Wagner's Das Rheingold