Doug Lung / RF Report
03.24.2014 02:22 AM
North Carolina State University Researchers Develop ‘Stretchable’ Antennas
Devices operate in GHz range and are intended for health monitoring
I've reported on "stretchable" antennas before, but in that application their ability to stretch was used to tune them to different frequencies. Researchers at North Carolina State University have developed a "stretchable" antenna for use with wearable health monitoring devices.
The NCSU researchers created the antenna by using a stencil to apply silver nanowires in a specific pattern and then pouring a liquid polymer over the nanowires. When the polymer sets, it forms an elastic composite material with the nanowires embedded in it with the desired pattern, allowing the pattern to be used as the radiating element of a microstrip patch antenna. The shape and dimensions of the radiating element determine its resonant frequency.
By now, you’re probably wondering what happens to that resonant frequency when the antenna is stretched. Dr. Jacob Adams, an associate professor of electrical and computer engineering at NC State explains that while the resonant frequency does change, it stays within a defined bandwidth.
"This means it will still communicate effectively with remote equipment while being stretched. In addition, it returns to its original shape and continues to work even after it has been significantly deformed, bent, twisted or rolled," said Adams.
More details on the stretchable antenna are available in the North Carolina State University news release and in a paper published on-line in ACS Applied Materials & Interfaces, "Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires." Lead author of the paper is Lingnan Song, an undergraduate at Zhejiang University who worked on the project at NC State during an exchange program. Co-authors include Amanda Myers, a Ph.D. student at NC State; and Dr. Jacob Adams, an assistant professor of electrical and computer engineering at NC State.
The antennas developed by the researchers include a 3-GHz microstrip antenna and a 6-GHz 2-element patch array. While these aren't close to broadcast frequencies, I wonder if a modified design might not be used to receive UHF TV or perhaps even VHF FM or TV if the fabric was large enough. Use of the stretchable antenna for two-way communications over commercial wireless networks seems unlikely unless the absorbed RF power on the skin could be reduced below FCC exposure limits.

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