Invisibility has captured the human imagination for a long time. Stories and movies such as Harry Potter’s invisibility cloak and the Romulans’ starships in Star Trek have inspired scientists to make invisibility a possibility.
In 2003, scientists at the University of Tokyo developed optical camouflage technology to make things invisible. Scientists first filmed the background behind objects and later projected it onto objects. This approach is an outdated one.
Objects that are visible reflect light, and darkness is observed when the light is absorbed. For an object to become invisible, it should neither reflect nor absorb light. If the light is bent around an object without any reflection or casting of shadows, then the object cannot be seen. Naturally occurring materials do not have properties required to bend light. However, scientists today have created artificial nanostructures called metamaterials which are capable of doing just this. Metamaterials have a negative refractive index which enables them to control the way light waves are bent, reflected and absorbed. (More interesting details in our previous blog post Potter’s Invisibility Cloak is now Unfeelable)
Devices made from metamaterials are known as cloaking devices. These can cause objects to be partially or wholly invisible. A simple simulation of how a cloaking device would work is shown below:
Debashis Chanda, an optical and nanotech expert at the University of Central Florida, may have just cracked the puzzle to turn this science fiction into a practical reality. Chanda and fellow experts have developed a large strip of multilayer 3D metamaterial that operates in the visible spectral range using a nanotransfer printing technique. Metal/dielectric composite films are stacked together in a 3D architecture with nanoscale patterns and are capable of operating in the visible spectral range. Administrating electromagnetic resonances over the 3D space by structural manipulation allows explicit control over the proliferation of light. By improving this technique, larger pieces of the material can be created for real-life applications. For example, it can be used as a military camouflage, the team can create large-area metamaterial armor to enable fighter jets to remain invisible from radar or detection systems.
Fractal Antenna Systems Inc. was awarded the first patent on an invisibility cloak. Patent US8253639B2 titled Wideband electromagnetic cloaking systems relates to techniques for cloaking objects at certain wavelengths/frequencies or over certain wavelength/frequency ranges (bands). Operation at other frequencies, including those of visible light, infrared and ultraviolet, is also discussed. Other patents such as US9405118B1 also describe ways to optically hide an object in the visible light spectrum to make the object appear invisible.
Patent application US20170227781A1 filed by Toyota in June 2017 and titled Apparatuses and methods for making an object appear transparent focuses on making a car invisible from the inside. The patent describes a cloaking device designed to turn the car’s dashboard invisible, thus improving on-road visibility for the driver.
Light from an object on the cloaking device is directed around an article within a cloaking region. This light forms an image on an image facing side of the cloaking device in such a way that the article appears transparent to an observer.
Instead of the most popular way of making objects invisible, which is by bending light waves around objects, scientists are exploring newer techniques. Researchers from the Technical University of Vienna have developed a disparate approach to make an object invisible by using a beam of invisibility. The concept includes shining a beam, such as a laser, onto a material from above, pumping the material with energy. This alters the material’s properties, making it transparent to other wavelengths of light coming in from the side.
In course of time, invisibility cloaking might become more pragmatic. With the help of progressive manufacturing devices, the future of invisibility is bright. The best part about invisibility is that the greatest innovations in the field are still beyond our wildest dreams.
(Featured image is intended for representational purpose alone and has been sourced from https://commons.wikimedia.org/wiki/File:An_invisibility_cloak_using_optical_camouflage_by_Susumu_Tachi.jpg)