December 19, 2013
Battery-Powered Cloaking Device In The Works At U Texas
Gerard LeBlond for www.redorbit.com - Your Universe Online
The first battery-powered cloaking device is being designed by researchers at the University of Texas. The use of an external source of power will greatly expand its bandwidth of operation.
Andrea Alu is the associate professor in the Department of Electrical and Computer Engineering at the Cockrell School of Engineering in Austin, Texas. He and his team have proposed the design of a cloaking device (active cloak) powered by a battery. This will allow objects to be undetectable to radio sensors at a wider range of frequencies.
The study, by Pai-Yen Chen, a team researcher, and co-authored by Christos Argyropoulos, a postdoctoral researcher, and Alu, was published Dec. 3 in Physical Review Letters under the title “Broadening the Cloaking Bandwidth with Non-Foster Metasurfaces."
The applications of this device will be numerous; besides being able to cloak, it will improve cellular and radio communications, as well as biomedical sensing.
Up until this new development, typical cloaks (passive cloak) had not been designed to use an external power source. The passive cloak suppresses the scattering of light that bounces off an object, which makes it less visible. When the cloak’s scattered fields and the object interfere, they cancel each other out, resulting in the object being transparent to radio-wave detectors. In the future, cloaks could be designed to let the object be more difficult to see with the naked eye, but currently they only work on radio waves.
“Many cloaking designs are good at suppressing the visibility under certain conditions, but they are inherently limited to work for specific colors of light or specific frequencies of operation,” Alu said in a statement.
On the contrary,in this paper Alu explains, “we prove that cloaks can become broadband, pushing this technology far beyond current limits of passive cloaks. I believe that our design helps us understand the fundamental challenges of suppressing the scattering of various objects at multiple wavelengths and shows a realistic path to overcome them,” added Alu.
By using batteries, circuits and amplifiers to boost signals, the active cloak can be used over a wider range of frequencies. Also, the cloak can be thinner, making it less obvious then typical cloaks.
In October, Alu and his graduate student, Francesco Monticone, published a related paper in Physical Review X proving that existing cloaks are limited in bandwidth operation and cannot provide broadband cloaking. Passive cloaks, when viewed with certain frequencies, may become transparent, however, under white light they become more visible.
The active cloak design started as a passive cloak made from a collection of metal square patches, then the team properly inserted amplifiers powered by a battery to broaden the bandwidth.
“In our case, by introducing these suitable amplifiers along the cloaking surface, we can break the fundamental limits of passive cloaks and realize a ‘non-Foster’ surface reactance that decreases, rather than increases, with frequency, significantly broadening the bandwidth of operation,” Alu said.
The team is continuing to work on the design of the active cloak and plan to build a prototype. The team is also working on active cloaks that will improve wireless communications by suppressing the disturbance of neighboring antennas. Another use proposed by the team is to improve biomedical sensing, near-field imaging and energy harvesting devices.
Funding for this project came from grants provided by The Air Force Office of Scientific Research, the Defense Threat Reduction Agency and a National Science Foundation, along with various government, private and nonprofit agencies.