Editor’s Note: This is the second installment of a five part series about the technologies of yesterday’s science fiction becoming the reality of tomorrow. The first installment on flying cars can be viewed here.
The concept of invisibility is mind-boggling. How can you make something disappear at the snap of a finger? But, when we examine the idea scientifically, it doesn’t seem crazy after all. We’ve all learned in physics class that we see in the visible light portion of the electromagnetic spectrum. We are able to see because luminous objects, i.e. the sun, a lightbulb, your laptop, produce light, thus illuminating other objects that absorb, transmit and/or reflect light, such as you and me. But, turn off all the lights in your room and prevent any light from coming through the window and suddenly you can no longer see anything. The objects haven’t disappeared. Rather, sight is impossible without visible light.
In the Harry Potter universe, Harry possesses an invisibility cloak spun from the hair of a demiguise, a magical creature that possesses the power to become invisible. But because in our comparatively boring universe there are no such creatures, scientists have looked elsewhere for the ability to create a cloaking device. Enter metamaterials.
First conceptualized in 1967 by a Russian physicist, metamaterials are artificial structures that are nanometers in size and exhibit properties not found in nature. Their precise shape, geometry, size, orientation and arrangement allow metamaterials to affect light and sound in a way that is impossible with natural materials. While natural materials only affect the electro portion of light, metamaterials can also affect the magnetic portion. It is these properties that give metamaterials the ability to bend electromagnetic radiation around an object. If this effect can be achieved within the visible portion of the electromagnetic spectrum, then a metamaterial-shielded object would essentially be rendered invisible. Picture a rock in a river. Just as the water flows around the rock, light flows around the object. With no reflected light to illuminate the object, we would never know it was there.
This is not to say that a scientist out there currently has a perfect invisibility cloak hanging in his closet. Still, there are no doubts that this technology is possible. Duke University’s David Smith proved the principle of cloaking in 2006. Smith created a metamaterial that, when activated, steered microwaves around a cylinder. Although humans obviously don’t see in the microwave portion of the electromagnetic spectrum, this demonstration showed that energy waves could indeed be routed around an object, rendering it invisible to those specific waves.
In 2007, University of Maryland’s Igor Smolyaninov took this concept even further. He created a metamaterial capable of bending visible light around an object. Unfortunately, this material was only micrometers in size and only worked in a two-dimensional space.
The two main challenges with creating a device capable of cloaking a user from visible light are the need to create meta-atoms, the constituent parts of metamaterials, which are smaller than the wavelength of visible light (ranging from 400 nanometers to 700 nanometers), and the fabrication of metamaterials that can be detached from the hard surfaces they are developed on to create flexible constructs. The most exciting development in the history of metamaterials came in 2010, when researchers at St. Andrews University tackled both these obstacles and took one step closer to creating a real life invisibility cloak. They developed a form of material called Metaflex, which not only manipulates visible light, but can also be used on a flexible surface. Metaflex membranes can be stacked to create flexible and three-dimensional metamaterials, like a cloak. As we continue to improve this technology, a cloaking device straight out of fantasy appears likely in the coming decades.
Imagine the implications of such a cloak. Want to take a quick nap at work? Throw on your invisibility cloak and kick back. Stuck in the peanut gallery at your favorite sporting event? Become invisible and waltz right up to the front row to get the best view in the house. In all seriousness, such an object in the hands of the average consumer would probably be a terrible idea. I can’t speak from experience but I’d imagine it’d be pretty easy to get away with a crime if you’re invisible. On the other hand, a cloaking device could be extremely useful in the hands of our military. Top-secret operations would truly take the word covert to a whole other level.
The uses for metamaterials don’t stop with just invisibility. The potential applications within fields such as optics, engineering and nanoscience are endless. With the potential application of metamaterials in mind, institutions across the world, including Harvard, MIT, University College London and even departments within the US Government, continue to research the abilities of metamaterials to control and manipulate electromagnetic energy.