An Invisibility Cloak Made of Glass

Metamaterials, manmade structures that perform in ways that are rarely if ever seen in nature, are being developed theoretically and experimentally for optical and microwave applications. Metamaterials are periodic structures that are able to manipulate electromagnetic radiation, giving rise to the possibility of creating some type of cloak that could provide invisibility at different wavelengths of light, a superlens that could conceivably see the tiny structures in a living cell for the first time, and greatly improved miniaturized antennas and filters.

In an article in the June 10 online edition of Applied Physics Letters, Elena Semouchkina, Douglas Werner, George Semouchkin, and Carlo Pantano report on an attempt to develop an invisibility cloak in the infrared wavelength using nano-size chalcogenide glass resonators. Previous work by Pendry and Smith has shown cloaking effects are possible in the microwave regime, using metal structures.

This illustration shows cylindrical glass resonators designed to hide a metal cylinder of 15 micrometers in diameter. Image credit: Semouchkina, et al.
This illustration shows cylindrical glass resonators designed to hide a metal cylinder of 15 micrometers in diameter. Image credit: Semouchkina, et al.

In simulations, the team members from Penn State and Michigan Technological University created cylindrical glass resonators with a diameter twice their height (300 nm x 150 nm), which resonated at a frequency of 300 THz (1 micron in air). The feasibility of such structures was demonstrated by deposition of a thin film layer of chalcogenide glass etched into a grid pattern with 150 nm deep valleys and 300 nm wide plateaus at Penn State’s Nanofabrication Laboratory. The fabrication of a glass prototype was initiated, and will continue, through a collaboration with the NSF International Materials Institute for New Functionality in Glass.

Simulations showed the glass structures performed best when located along radial spokes that alternated the glass resonators with spacers made of a fused silica. The performance of the cloak was tested in simulations that hid a metal cylinder 5 microns in diameter inside the glass structure.

The uniqueness of their model lies in having simulated a true multi-resonator cloak structure and visualized the resonances in individual resonators. In many previous cases, modelers treated individual resonator arrays as though they were a uniform slab of material with uniform responses. This may easily give misleading results. “We also account for inter-resonator interactions, which is crucial for a correct design,” Semouchkina adds.

Finally, developing a design using resonators of identical size makes the possibility of fashioning real life resonators at the nanoscale far more feasible when they begin to fabricate their structures in the laboratory. In the future, the MRI researchers hope to develop metamaterials that will achieve equally good performance at the more interesting realm of visible light.

This work was supported in part by a grant from the National Science Foundation.

Elena Semouchkina is an associate professor of electrical and computer engineering at Michigan Technological University and an adjunct professor at Penn State; George Semouchkin is a visiting professor in the Materials Research Institute and a research professor at Michigan Technological University; Douglas Werner is professor of electrical engineering at Penn State; Carlo Pantano is distinguished professor of materials science and engineering at Penn State and director of the Materials Research Institute

This article was featured in Focus on Materials - Fall 2010.