Harry Potter's invisibility cloak has always amazed people as it seems to be both magical and scientifically fictitious. While Star Trek popularized the concept of cloaking devices, it was Harry Potter who popularized the invisibility cloak. However, there are not many implementations of invisibility-based technology.
In reality, the closest invisibility device is introduced through stealth technology, which provides effective invisibility in certain wavelengths that are longer than human eyes can see.
Significance of the Development of Metamaterial
Scientists know that the first step in making invisible objects is using materials that are undetectable under microwave to radio wavelengths. Perhaps, the closest advancement that could make invisibility cloak a reality happened in 2018. The material called broadband achromatic metalens could render an object invisible under the visible light spectrum.
The fusion of broadband achromatic metalens and metamaterial cloaking, a nanotechnology advancement, could perhaps enable the first-ever invisible cloak.
According to Freethink*, the typical behavior of light of any wavelength could either be absorption or reflection. When absorbed, background light and signals will be obscured and the object will be visible. On the other hand, reflected light bounces and illuminates the object, allowing it to be observed directly.
That means the only way for transparency to be possible is if the light comes from behind the object and could somehow still arrive in front of the object at some trajectory. The way a true invisibility cloak works then means to hide a material that was not intrinsically transparent to divert light around an object from all directions.
A new nanotechnology on metamaterials created metalenses that are recognized for their ability to change the angle at which background rays of light emerge. Metalens would shape the wavefronts of incoming light waves regardless of wavelength to allow light to be focused on a single point.
Metalens' appealing features include being thin to allow a single wavelength, being simple to make, and may concentrate the light of several wavelengths onto the same place.
A 2018 breakthrough uses titanium-based nanofins that will guide light through a different part of the material to allow it to bend by the necessary amount to wind up where it needed to be. Researchers said that it allows for the development of cheaper, lighter, and more effective lenses.
Biggest Challenge in Making Invisibility Cloak
As Freethink* reports, the biggest challenge in making invisibility cloaks a reality is the incorporation of a large variety of wavelengths. The cloak's material should vary from point to point to bend and unbend the light. Metamaterials may have made a significant advancement but it is still exclusive to visible light.
So far, existing materials have not yet managed to penetrate the visible light portion of the spectrum with a cloak. On the other hand, metalenses could be applied to nanofin technology to extend the wavelength covered. Experts think that the fusion of metalenses with concurrent advances in metamaterials would make visible-light cloaking devices a reality.
But just like Star Trek in which it took centuries to build a cloaking technology, humans might need decades to successfully apply metalens to metamaterial cloaks or a 3D cloaking device.
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