Flexible, Light-Bending Metamaterial Developed

A group of scientists from the United States announced the development of a new type of metamaterial, that is capable of bending both light and itself, opening up the way for a new host of applications, such as advanced camouflages.

The achievement is significant because it operates in the developing field of metamaterials, man-made structures that have interesting physical properties. The most important is the ability to bend electromagnetic waves in manners that are impossible in nature.

As such, these materials have been proposed as the logical choice for constructing invisibility cloaks for various portions of the electromagnetic spectrum, as well as for generating artificial black holes.

But investigators at the University of St. Andrews took the field one step forward when they managed to develop a type of metamaterial that is flexible, and still retains its innate ability to bend light around.

“It's a pretty significant step forward. At radio frequencies we know how to make a lot of these things. But at optical wavelengths, things have been very fabrication-limited,” says Stephen Cummer.

The investigator holds an appointment as a professor of electrical and computer engineering at the Duke University. He is also the inventor of the first invisibility cloak based on metamaterials.

The thing about these materials is that they need to be fashioned out of components that are smaller than the particular wavelength of light they are designed to manipulate.

Until now, this meant that metamaterials designed for optical wavelengths could only be built of rigid surfaces in the lab. The team at the University of St. Andrews changed that with their flexible metamaterial, which they now call Metaflex.

It too is originally manufactured on a solid, rigid substrate. The first layer of the material is placed on top of the substrate, so that the next layers do not adhere to the solid base.

The researchers then add a layer of flexible transparent polymer, made out of plastic. Through a subsequent lithographic process, a lattice of nanoscale gold bars is created over the polymer.

These gold nanorods are 40 nanometers (billionths of a meter) in diameter each, and have a length of 100 to 200 nanometers, Technology Review reports.

After this layer is added, the material is submerged in a bath of chemicals that separate the first layer from the solid substrate, and the polymer from the first layer. The result is a flexible polymer sheet featuring an array of gold nanorods.

Additionally, the new material can also be made to interact with various wavelengths of light, by simply changing the spacing and the length of the gold nanorods, the team concludes.