Dose of STEM: Harry's Invisibility Cloak
The power of invisibility may sound like science-fiction, and the idea may be far fetched, but good news muggles - IT'S POSSIBLE! All we need is a bit of physics. Who wouldn't want to be invisible? Let's dive into the Physics of Invisibility cloaks!
Method #1
Some may have vaguely heard the words - REFLECTION! REFRACTION! INTERFERENCE! DIFFRACTION! Most of you may already know what they mean. But how are they related to the power of invisibility? We have to get into photonics! Photonics is the science of producing, detecting and manipulating light; the phenomena mentioned above all come under photonics.
Here's method #1 to get invisible - manipulating light using metamaterials. What are metamaterials? Hermione already has the answer.
Metamaterials, in general, are materials that are designed in such a way that they contain certain properties that are not found in naturally-occurring materials. Let's get to the context of usage of 'metamaterials' for cloaking later. Firstly, we need to understand how exactly can we make a cloak invisible. Picture this - we have a transparent sheet that would act as the cloak; would it work? Unfortunately, no - we cannot make it invisible by itself because light can pass through it and bounce of our body, making us visible. However, what we can do is manipulate the light to channel through the fabric i.e. bend it around the fabric unchanged. This is where metamaterials come into the picture.
The metamaterials are capable of bending electromagnetic radiation of particular frequencies and wavelengths. We all know that light is an electromagnetic wave, and this result was found out by James Clerk Maxwell. While naturally occurring materials only affect the electric part of the wave, metamaterials affect the magnetic part too resulting in the bending. The other cool thing about these metamaterials is that they have a negative refractive index for electromagnetic waves of a particular frequency. The metamaterials contain split-ring resonators, which produce that negative refractive index. Till now, scientists have only created metamaterials made of special polymers and minuscule coils of wire which contain a lattice-like structure with spaces in it less than the wavelength of light we want to bend. The most recent attempt at invisibility was by a Japanese scientist. You can read about it here - https://www.vice.com/en_us/article/wnzk7w/an-invisibility-cloak-you-have-to-see-to-believe-video https://news.bbc.co.uk/2/hi/asia-pacific/2777111.stm Method #2 There are other methods by which you can make an object invisible. The other method is by having your cloak made of multi-walled CNTs. CNTs or carbon nanotubes are an allotrope or a form of carbon. This method works on the principle of photothermal deflection the same principle which applies to the mirages we see in deserts and even roads. Researchers at the University of Texas and the Dallas Nanotech Institute (2011) have managed to make an object invisible through this method. They used sheets of CNTs which are good conductors of heat, so they are ideal for creating mirages. In order to create the effect, they heated the sheets using electricity, causing the light to bend away, creating the invisibility effect. There is another method of making an object appear invisible but it isn't something you can wear - using lenses. This is something for you to research on your own. Congratulations! You are a master of invisibility!
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