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Metamaterials, a unique class of materials with properties not found in nature, play a crucial role in creating invisibility cloaks. By designing these materials with carefully arranged nanostructures, scientists can control the behavior of light waves, allowing for the manipulation of light around an object, making it appear invisible.
On the other hand, Metamaterials also serve as thin lenses that can converge light with different wavelengths to the same point, overcoming the limitations of traditional lenses.
Another method used to create invisibility cloaks is light redirection. These techniques require precise control of the speed, direction, and intensity of light waves to achieve the desired effect.
Examples of invisibility cloaks
While invisibility cloaks are still undergoing research and scientific development, there have been significant advancements and notable evidence in this field.
Quantum Stealth - Quantum Invisibility
By layering multiple layers of different refractive indices, this material can refract light at various angles, creating 'dead spots' that block light from passing through and effectively conceal the subject while maintaining an unaffected background.
In 2019, Hyperstealth Biotechnology, a military camouflage uniform manufacturer based in Canada, unveiled a prototype of 'quantum stealth', a thin, paper-like material capable of bending light around it. Moreover, the stealth cloak not only works against visible light but also can counter infrared and shortwave infrared, making it a broadband stealth cloak.
Developed in 2014 at the University of Rochester, it can operate in multiple directions in a 3D environment, thanks to a system of 4 lenses.
This means the device can hide objects from view from any position of the viewer relative to the object. The team achieved this feat by carefully selecting the type of lenses, power, and distance between the lenses.
Although the current device demonstrates significant advancements, there are still areas for improvement. Firstly, this setup cannot be transformed into a stealth suit due to the complex and inflexible optical system.
Aside from addressing the perspective issue, the 'Rochester cloak' allows for maintaining a natural state for the background scene, without distorting the surrounding visual scenery around the object.
Invisible cloak for security cameras
A group of Chinese students has found a breakthrough to bypass security cameras. And the result is they have created a garment designed to make the wearer almost invisible to AI-monitored cameras - InvisDefense.
InvisDefense has the ability to render the wearer invisible to surveillance cameras while still being visible to the naked eye.
'Security cameras using AI technology are everywhere. They pervade our lives,' Wei Hui, a computer science graduate student at Wuhan University, who designed the core algorithm of the cloak, said.
'We designed this product to counter the possibility of malware detection, aiming to protect the privacy and safety of people in certain situations,' he added.
During daylight hours, the camera primarily relies on motion detection and outlines to identify human bodies. By adorning the surface of InvisDefense with specially designed camouflage patterns, the garment can flawlessly disrupt the visual machine's recognition algorithm, rendering the wearer indistinguishable to the camera.
As darkness falls, the challenge escalates as cameras switch to infrared imaging. To counter this, InvisDefense incorporates temperature control modules with unconventional shapes on its inner surface, creating a unique thermal pattern that can deceive infrared cameras.
Metal Stealth
This flat metalens is the first single lens capable of converging the entire visible light spectrum - including white light - to the same focal point at high resolution. It utilizes arrays of nano titanium dioxide fibers to uniformly focus light wavelengths and eliminate chromatic aberration.
A breakthrough in 2018 involved the use of nano titanium fibers in metal tubes, allowing them to bend light at the necessary level to achieve stealth capabilities. While previous metamaterials could not cover visible light wavelengths, the combination of Metalens and metamaterials shows promise in expanding stealth capabilities across the visible light spectrum.
This advancement in metal technology brings the ability to create visible light concealment devices, where light with different wavelengths can be controlled to make objects invisible. Although this technology is still not fully developed, it is an important step towards achieving real-world stealth cloaks in the near future.
Stealth Shield
The stealth shield utilizes a precise array of lenses to cleverly manipulate light. By redirecting the majority of reflected light from the object away from the observer, it can effectively camouflage the person standing behind it. Subsequently, this redirected light will spread across the surface of the shield, creating an illusion of the background.
The Future of Stealth Cloaks
In the military domain, stealth technology could revolutionize stealth operations, making military assets invisible to radar or surveillance systems. Additionally, in the field of optics, stealth techniques could enhance the efficiency of telescopes, microscopes, and other imaging devices.
While we may not soon witness invisibility cloaks akin to those in Harry Potter, the undeniable progress in this field is incredibly impressive.
Research and collaboration are underway among scientists, engineers, and materials experts promising further breakthroughs in the future. Stealth technology may one day become an indispensable part of our lives, revolutionizing various industries and altering our perception of the world.
