If you’ve ever done research into cloaking devices, or ultra-precise microscopy, you may have come across the word meta-material.
A meta-material is defined as a synthetic material with a composite structure that exhibits characteristics that are not normally found in natural materials. Such materials, to the untrained eye, would appear to defy the laws of physics, having such possible applications as complete invisibility, sound-manipulation, and superior optics.
But, as Arthur C. Clarke so eloquently said, “Any sufficiently advanced technology is indistinguishable from magic,” and this particular case is no different.
The scientific explanation for why meta-materials are capable of their seemingly law-breaking abilities is understandably complicated, but with a basic understanding of chemical structure and light (the visible light portion of the electromagnetic spectrum), one can come to a logical conclusion as to how these materials operate.
Now, if you’ve taken grade 10 science, you understand that all things in nature are composed of atoms, and those atoms come together in structures called molecules. These molecules compounded together produce larger structures, which give rise to the macro-objects we see in our day-to-day lives.
With meta-materials, the characteristics of these molecular structures can be fine-tuned. Everything from the shape and size of the molecules to the lattice constant (the spacing between adjacent unit cells) and interatomic interactions can be tailored to fit and meet a specific end-goal.
UC Berkeley researcher Jason Valentine, who works with meta-materials that affect light near the visible spectrum, stated in an interview with Reuters that the most necessary characteristic of meta-materials is that they must have a structural array smaller than the wavelength of the electromagnetic radiation being used, for what is known as negative refraction to occur; aka the ‘holy grail’ of meta-material research.
And so, it is of no surprise that one of the main areas of research into meta-materials is manipulation of the refraction index.
Natural materials have a positive refraction index, which means that the light that interacts with the object is slightly bent in the direction of propagation. Air for example, has a refraction index just above one, water is 1.33 and a diamond is 2.4. Meta-materials on the other hand, have a negative refraction index. This means that light is bent backwards when interacting with the meta-material.
This was how meta-materials, in the year 2000, were first truly produced with practical applications in mind by Sir John Brian Pendry, an English theoretical physicist. It was he who theorized the meta-material-derived invisibility cloak, which would make an object invisible by forcing incident light to go around the object and return to its original trajectory undisturbed.
But before you Potter fans go crazy, this particular invisibility cloak would be nothing like the one you see in the films. In a 2011 interview he stated:
“I think it’s pretty sure that any cloak that Harry Potter would recognize is not on the table. You could dream up some theory, but the very practicality of making it would be so impossible. But can you hide things from light? Yes. Can you hide things which are a few centimeters across? Yes. Is the cloak really flexible and flappy? No. Will it ever be? No. So you can do quite a lot of things, but there are limitations. There are going to be some disappointed kids around, but there might be a few people in industry who are very grateful for it.”
As incredible as a functioning invisibility cloak sounds, there are also many other applications for meta-materials.
The super-lens is one such other application, whereby the meta-material of the lens is altered in such a way as to allow the observer to view objects much smaller than the 200 nm diffraction limit. For those of you who have taken biology courses, the average mitochondria is 0.5 to 1 nm in length. Perhaps this imaging technique will one day permit researchers the ability to view this organelle in unprecedented detail, as well as the others that are contained within cells.
Seismic protection is another area of hot research into meta-materials. Through the use of seismic meta-materials, which direct the destructive seismic waves produced by earthquakes around buildings, one could save thousands of lives, and millions in damages.
Sound suppression and on-the-fly colour changes are also possible with meta-materials. The material in question would be textured with nanoscale wrinkles that manipulate sound or light waves based on their spacing. With such a material, one can imagine a car that changes color with the touch of a button.
But, as with most technological marvels that make great promises, these inventions will take some time to come to fruition. Until then, I’ll be waiting intently for my invisibility cloak; even if it’s a box, and not all “flexible and flappy”, as Pendry so dishearteningly explained.