Invisibility

[2] Invisibility is often considered to be the supreme form of camouflage, as it does not reveal to the viewer any kind of vital signs, visual effects, or any frequencies of the electromagnetic spectrum detectable to the human eye, instead making use of radio, infrared or ultraviolet wavelengths.

[4] In filmmaking, people, objects, or backgrounds can be made to look invisible on camera through a process known as chroma keying.

Engineers and scientists have performed various kinds of research to investigate the possibility of finding ways to create real optical invisibility (cloaks) for objects.

Methods are typically based on implementing the theoretical techniques of transformation optics, which have given rise to several theories of cloaking.

[5][6] A 2006 theoretical work predicts that the imperfections are minor, and metamaterials may make real-life "cloaking devices" practical.

[7][8] The technique is predicted to be applied to radio waves within five years, and the distortion of visible light is an eventual possibility.

Xiang Zhang, of the University of California, Berkeley said: "In the case of invisibility cloaks or shields, the material would need to curve light waves completely around the object like a river flowing around a rock.

Valentine's team created their 'fishnet' material by stacking silver and metal dielectric layers on top of each other and then punching holes through them.

An invisibility cloak layout of a copper cylinder was produced in May, 2008, by physicist Professor Sir John Pendry.

In 2019, Hyperstealth Biotechnology has patented the technology behind a material that bends light to make people and objects near invisible to the naked eye.

The material, called Quantum Stealth, is currently still in the prototyping stage, but was developed by the company's CEO Guy Cramer primarily for military purposes, to conceal agents and equipment such as tanks and jets in the field.

Unlike traditional camouflage materials, which are limited to specific conditions such as forests or deserts, according to Cramer this "invisibility cloak" works in any environment or season, at any time of day.

The term was used in this manner in the title of the book Invisible Man, by Ralph Ellison, in reference to the protagonist, likely modeled after the author, being overlooked on account of his status as an African American.