Are metamaterials electric: Infrared imaging

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  • Published: Nov 1, 2016
  • Author: David Bradley
  • Channels: Infrared Spectroscopy
thumbnail image: Are metamaterials electric: Infrared imaging


This is an infrared image of metadevice composed of vanadium dioxide with gold patterned mesh. (Top) Device without any electric current showing the PSU cut from the pattern and reflective. (Middle) Device with 2.03 amps of current. The PSU and background now appear the same, the PSU has faded into the background. (Bottom) Device with 2.20 amps of current. The background is now reflective while the PSU is not. Credit: Douglas Werner, Penn State

A hybrid meta material behaves like an electric version of the chameleon's skin, changing colour when a current is applied but also becoming warmer, at least when viewed in the infrared. This could be the first proof-of-principle of a controllable metamaterial device, according to engineers at Penn State University.

"Previous metamaterials work focused mainly on cloaking objects so they were invisible in the radio frequency or other specific frequencies," explains Douglas Werner, John L. and Genevieve H. McCain Chair Professor of electrical engineering, PSU. "Here we are not trying to make something disappear, but to make it blend in with the background like a chameleon and we are working in optical wavelengths, specifically in the infrared."

Metamaterials are synthetic, composite materials that possess qualities not seen in natural materials. Commonly, they have functionality derived from their structure whether internal or surface structure rather than endowed to them by virtue of their chemical composition, which is the usual source of a material's properties. There are several experimental metamaterials around that have unusual electromagnetic or acoustic properties bending light waves or sound waves, for instance, however, there are no real-world applications as yet in the form of metadevices that take metamaterials and do something of interest or value with that structure and its properties.

Non-chemical key

"The key to this metamaterial and metadevice is vanadium dioxide, a phase change crystal with a phase transition that is triggered by temperatures created by an electric current," explains Lei Kang, research associate in electrical engineering. The team's metamaterial is composed of a base layer of gold that is sufficiently thick to be opaque. A thin layer of aluminium dioxide is then used to separate this gold layer from the active vanadium dioxide layer. A second layer of aluminium dioxide separates the vanadium from a gold-patterned layer, which is in turn attached to an external electric source.

It is the geometry, rather than the chemistry of the substances from which the metamaterial is made that then give rise to its properties. The patterned mesh screen controls the functional wavelength range and then the amount of current flowing through the device controls the Joule heating effect, the heating due to resistance. "The proposed metadevice integrated with novel transition metal materials represents a major step forward by providing a universal approach to creating self-sufficient and highly versatile nanophotonic systems," the researchers explain in the journal Nature Communications.


In their prototype metadevice, the team has cut the letters PSU into the gold mesh layer so the vanadium dioxide shows through. They then photographed the device using an infrared camera at 2.67 micrometres wavelength. Without any current flowing through the device, the PSU stands out as highly reflective. However, with a current of 2.03 Amps, the PSU fades into the background and becomes invisible, while at 2.20 Amps, the PSU is clearly visible but the background has become highly reflective. This effect due to the patterned vanadium dioxide is tuneable by changing the current flowing through the device. According to the researchers, vanadium dioxide can change state very rapidly and it is only the device configuration that limits the tuning.

"We believe that the unit-cell nature of metamaterials and the active tuning capability demonstrated here can be combined to provide unprecedented flexibility for pixelated light manipulation in the subwavelength regime," the team concludes. They also add that the way in which photonic nanostructures and the active materials family of two-dimensional transition-metal dichalcogenides interact could be exploited in new functionalities in various kinds of metadevices.

Related Links

Nature Commun 2016, 7, 13236: "Hybrid metamaterials for electrically triggered multifunctional control"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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