What is an Invisibility Cloak?

There are two versions of an invisibility cloak that scientists are working to perfect. The first uses augmented reality, or a combination of computers, cameras and reflective surfaces to make a person appear invisible. The second invisibility cloak is made of metamaterials using nanotechnology.

The first invisibility cloak is sometimes called optical camouflage. A person wears a cloak made of a special reflective material. When viewed by an observer from a particular angle, that cloaked person disappears from the view.

This invisibility cloak uses parts of a scientific offshoot called augmented reality technology. This technology provides useful information to supplement the real world. An example of this is a portable Global Positioning System (GPS) that tells useful information about a particular location or a pair of goggles that overlaps computer generated information to the real world picture viewed by the wearer. Using some ideas behind this technology, scientists have been able to make someone appear to disappear into the background.

The invisibility cloak itself is made from retro-reflected material. This special material has a beaded surface as opposed to the standard flat surface of most reflective materials. Most reflective surfaces make light bounce back at a different angle than it came in at or spreads it out into many smaller beams. The beading on the cloak allows it to reflect light out directly back in the same direction in a single light beam.

Effectively, the coat is turned into a wearable movie screen. The wearer has a movie camera pointed behind him. The camera gives a live video feed to a remote computer. This computer processes the image and sends it into a pinhole sized projector. The projector filters the image through an iris diaphragm, which controls the passage of light and clears the image. The image is finally projected onto the cloak, making the person an exact reflection of what is occurring behind them.

Another version of the invisibility cloak is in the works from Duke University. This alternative cloak uses metamaterials, or materials with strange properties. In this case, reflective metamaterials created by nanotechnology work to create an object with a negative refractive index, making objects unaffected by light waves. The materials must have a smaller wavelength of than light in order for this to be effective, which is why nanotechnology is an essential part of the science. If completed as planned, the fabric would reflect light directly off the image and the object would essentially be cloaked.