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From Tolkien's ring of power in The Lord of the Rings and Star Trek's Romulans (who could make their warships disappear from view) to Harry Potter's magical cloak, the power to turn someone or something invisible has often fascinated mankind. But whoever thought that a scientist at Michigan Technological University would be serious about building a working invisibility cloak?
That's exactly what Elena Semouchkina, an associate professor of electrical and computer engineering at Michigan Tech, is doing. She has found a method to use magnetic resonance to capture rays of light and route them around objects, thus rendering those objects invisible.
Glass ResonatorsSemouchkina and colleagues at Pennsylvania State University, where she is also an adjunct professor, recently reported on their research in the journal Applied Physics Letters, published by the American Institute of Physics. Co-authors included Douglas Werner and Carlo Pantano, both of Penn State, and George Semouchkin, who works at Michigan Tech and Penn State.
The researchers describe the development of a nonmetallic cloak that uses identical glass resonators made of chalcogenide glass (a type of dielectric material that does not conduct electricity). In computer simulations, the cloak made objects hit by infrared waves-approximately 1 micron long-disappear from view. Earlier attempts by other researchers used metal rings and wires. "Ours is the first to do the cloaking of cylindrical objects with glass," Semouchkina said.
Her invisibility cloak uses metamaterials, which are artificial materials with properties that do not exist in nature; these metamaterials are made of tiny glass resonators arranged in a concentric pattern in the shape of a cylinder. The "spokes" of the concentric configuration produce the magnetic resonance required to bend light waves around an object and make it invisible.
Metamaterials, which use small resonators instead of atoms or molecules from natural materials, straddle the boundary between materials science and electrical engineering. They were named one of the top three physics discoveries of the decade by the American Physical Society. A new researcher specializing in metamaterials is joining Michigan Tech's faculty this fall.
Ongoing WorkSemouchkina and her team now are testing an invisibility cloak re-scaled to work at microwave frequencies and made of ceramic resonators. They're using Michigan Tech's anechoic chamber, a cave-like compartment in an Electrical Energy Resources Center lab that is lined with highly absorbent charcoal-gray foam cones. There, antennas transmit and receive microwaves, which are much longer than infrared light (up to several centimeters long). They have cloaked metal cylinders 2-3 in. in diameter and 3-4 in. high.
"Starting from these experiments, we want to move to higher frequencies and smaller wavelengths," the researcher said. "The most exciting applications will be at the frequencies of visible light."
For more information, visit www.mtu.edu.