Tunable Metamaterial Created

Physicists at the California Institute of Technology (Caltech) have recently demonstrated that, by stretching metamaterials, they can dynamically change the wavelength of infrared light the structure naturally responds to.

Metamaterials are constructs put together by humans, a variety of materials that is able to influence the path and behavior of electromagnetic radiation in ways not possible in nature.

Such structures are generally used to create ultra-high-resolution microscope lenses that break the diffraction limit, and enable the production of highly absorbent coatings for solar cells.

But perhaps the most widely known application for metamaterials are invisibility cloaks, which redirects electromagnetic radiation around an object so that it appears invisible in that particular wavelength.

The issue with these materials is that they are naturally limited in their effects. Experts can produce a cloak for a particular color of visible light for example, but the object will remain readily visible in all other colors.

What the Caltech team demonstrated was that applying mechanical stress to a metamaterial-based optical filter can result in a shift in wavelength of light it responds to.

The new device that built was not solid, like other metamaterials, but rather based on a twisty polymer film. The active components were very tiny silver resonators, the group reveals.

The resonators are shaped as either a “C” or an “I”, and the two types are placed alternatively next to each other. The distance between their tips is normally around 50 nanometers.

Due to the fact that the structures were built on a stretching substrate, the new device could be made to feature a tip-to-tip length 50 percent higher than normal, Technology Review reports. 

This allowed researchers to dynamically change the wavelengths at which the resonators became high-efficiency filters, essentially changing the function of the nanomaterial.

“What's nice about this is, it's relatively easy to tune over a very broad band with simple mechanical means,” explains Boston College physics professor Willie Padilla, who was not a part of the study.

Details of the accomplishment appear online, in the latest issue of the esteemed scientific journal Nano Letters.

“A lot of this work is aiming to add to the tool belt. As we get closer to applications, someone will want a flexible material,” concludes Duke University professor of electrical and computer engineering Steven Cummer.