Metamaterial Behaves Like a Chameleon

Infrared image of metadevice composed of vanadium dioxide with gold patterned mesh. Device without any electric current (right) showing the PSU cut from the pattern and reflective. Device with 2.03 amps of current. The PSU and background now appear the same (middle), the PSU has faded into the background. Device with 2.20 amps of current. The background is now reflective (left) while the PSU is not. (Source: D. Werner / PSU)

Infrared image of metadevice composed of vanadium dioxide with gold patterned mesh. Device without any electric current (right) showing the PSU cut from the pattern and reflective. Device with 2.03 amps of current (middle). The PSU and background now appear the same, the PSU has faded into the background. Device with 2.20 amps of current (left). The background is now reflective while the PSU is not. (Source: D. Werner / PSU)

An electric current will not only heat a hybrid metamaterial, but will also trigger it to change state and fade into the background like a chameleon in what may be the proof-of-concept of the first control­lable meta­material device, or metadevice, according to a team of engineers.

“Previous meta­materials work focused mainly on cloaking objects so they were invisible in the radio frequency or other specific frequencies,” said Douglas H. Werner, John L. and Genevieve H. McCain Chair Professor of electrical engineering, Penn State. “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. These composites derive their func­tionality by their internal structure rather than by their chemical composition. Existing meta­materials have unusual electromagnetic or acoustic pro­perties. Metadevices take meta­materials and do something of interest or value as any device does.

“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,” said Lei Kang, research associate in electrical engineering, Penn State. The meta­material is composed of a base layer of gold thick enough so that light cannot pass through it. A thin layer of aluminum dioxide separates the gold from the active vanadium dioxide layer. Another layer of aluminum dioxide separates the vanadium from a gold-patterned layer that is attached to an external electric source. The geometry of the patterned mesh screen controls the functional wavelength range. 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 materials represents a major step forward by providing a universal approach to creating self-sufficient and highly versatile nano­photonic systems,” the researchers said. As a proof of concept, the researchers created a .035 inch by .02 inch device and cut the letters PSU into the gold mesh layer so the vanadium dioxide showed through. They photo­graphed the device using an infrared camera at 2.67 microns. Without any current flowing through the device, the PSU stands out as highly reflec­tive. 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.

The response of the vanadium dioxide is tunable by altering the current flowing through the device. According to the researchers, vanadium dioxide can change state very rapidly and it is the device confi­guration that limits the tuning. (Source: PSU)

Reference: L. Liu et al.: Hybrid metamaterials for electrically triggered multifunctional control, Nat. Comms. 7, 13236 (2016); DOI: 10.1038/ncomms13236

Link: Center for Nanoscale Science, Pennsylvania State University, University Park, USA

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