The word ‘meta’ comes from the Greek meaning ‘to go beyond.’ In terms of metamaterials, this applies to characteristics that are beyond our capability to see, minute structures on the surface or interior of the material that can alter how it reacts to light.
Metamaterials gain their abilities from their internal microstructures, not their chemical compositions like naturally occurring materials. Most metamaterials are artificially crafted, specifically designed for function.
They work through microscopic patterns that interact with light in different ways. They can absorb or enhance light, which can be used for a variety of different purposes.
This is being applied to the field of optics, as metamaterials allow for existing optical technology to be miniaturised, and then can be customised to provide new properties or functions dependant on what they’re designed to do.
They can also be utilised to generate electromagnetic cloaking, or invisibility. So how were these seemingly magical materials created?
How Were Metamaterials Created?
The concept of metamaterials was first hypothesised by Victor Veselago in the 1960’s, who focused on the theoretical concept of negative index refraction. His theory was largely ignored because it all hinged upon a hypothetical material that was presumed impossible to construct.
Normal refraction occurs when light passes through one medium to another. You can see this when looking at a straw in a glass, the straw will seem to be closer below the surface of the water because the light that is allowing you to see it is being refracted, distorting how you perceive the glass.
Negative index refraction takes this further, bending light in such a way that simply couldn’t happen with mundane materials that naturally occur in nature.
The first negative-index metamaterial wasn’t created until the year 2000, but new materials quickly followed as scientists realised the potential of this new field of optics.
Metamaterials consist of multiple individual units known as meta-atoms, which are much smaller than the wavelength they interact with. These cells are built from conventional materials like metals and plastics, but their exact shape, geometry, and orientation can impact light on the scale of nanometres. This changes their electromagnetic parameters such as magnetic permeability and electric permittivity. The interatomic interaction can be finetuned on a scale previously unimaginable, giving scientists greater control over the materials they work with, and what they can do.
Metamaterials are also extremely resonant, meaning they can absorb light at a narrow range of frequencies, which can be entirely determined at the point of creation. This means that theoretically, new materials could be designed bespoke for new projects, implemented to a specific degree that was otherwise unthinkable.
How Metamaterials Can Make Existing Technology More Efficient
Energy efficiency is becoming more and more important, especially in renewable energy methods such as solar power. Until recently, there was a theoretical limit of 33.7% efficiency placed on photovoltaic panels, known as the Shockley-Queisser Limit. However, thanks to metamaterials, solar panels can now absorb light from wider angles, not just the light that falls directly onto it. Now, when light falls onto the panel, it can all be absorbed rather than being reflected away from it. This can increase their efficiency, meaning more power can be generated from the same amount of light.
Integrating metamaterials with clean technology can make it more efficiency, with higher longevity, meaning we can enjoy a cleaner future.