This model shows a three-dimensional metamaterial
Cloaking devices that hide planes from RADAR, microscopes that can see inside a single cell, and miniature antenna that measure only a few millimeters all sound like parts of an action movie. But, within the span of the decade since they were first created, metamaterials have moved these and other innovations from the realm of fiction closer to reality. In fact, metamaterials are better than real: they are fabricated to exhibit properties not possible in natural materials. At the Ames Laboratory, physicist Costas Soukoulis and his research team are working to improve metamaterials’ design, tailoring their properties for use in new technologies.
“Metamaterials have a few fundamental properties that may allow for many new applications,” says Soukoulis.
For instance, natural materials refract light to the opposite side of the incidence normal, while metamaterials can refract light to the same side, allowing imaging with a flat lens. Metamaterials are also capable of absorbing all light that hits them, reflecting none of it, creating perfect absorbers. The materials can even slow light. And what makes these properties even more interesting is that they can be adjusted to the needs of particular technologies.
“Usually, materials scientists are presented with a material, determine its properties and only then come up with a use for the material. But metamaterials work in the opposite direction,” says Soukoulis. “With metamaterials, we can think about what technology we’d like and what properties we want – perhaps properties unheard of before – and design the materials accordingly.”
Take, for example, the goal of creating super-efficient devices to harvest sunlight in solar energy products. Ideal materials for such a device would absorb a lot and reflect little of the light that hits it.
“In metamaterials, we can design both their magnetic and electric responses,” says Thomas Koschny, Ames Laboratory assistant scientist. “Therefore, we can control the reflection at the interface of the metamaterial, which you cannot easily do in normal materials. In regular materials, particularly with the types of waves like light, materials have only an electric response, and they are always reflective. But, in a metamaterial, we can arrange the parts of the material so that the electric response equals the magnetic response, and the surface is reflection free and all waves go into the material.”
Other possible applications are “superlenses” that would allow us to see molecules, like DNA molecules, in detail and devices that store large amounts of data optically. And many other potential uses exist because, unlike in natural materials, metamaterials can be designed to work at target frequencies, at least in principle, from radio frequencies to visible light.
But with such great potential also comes several challenges, some of which Soukoulis, Koschny and Martin Wegener’s research group at the Institute for Nanotechnology in Karlsruhe, Germany, have already made significant progress toward meeting. In 2006, the researchers were the first to fabricate a left-handed metamaterial, one with a negative index of refraction, in waves very close to visible light. In 2007, the group designed and fabricated the first left-handed metamaterial for visible light, and they recently fabricated chiral metamaterials that have giant optical activity.
Next up for Soukoulis and Koschny is creating building blueprints for 3D metamaterials, which, until now, have been so thin that they do not qualify as a “material.” Another aim is to reduce the energy losses in 3D metamaterials.
“Metamaterials may help solve the energy problems America is facing,” says Soukoulis. “There’s no shortage of new ideas in the field of metamaterials, and we’re helping make progress in understanding metamaterials’ basic physics, applied physics and possible applications.”
~ By Breehan Gerleman Lucchesi
Illustration of the refraction of a beam of light at the interface of a metamaterial (at left) in comparison
to a regular transparent material, such as window glass (at right). In a negative-index metamaterial
with both electric and magnetic responses close to negative unity there is no reflection, and the
light is bent “backwards.”