A stretchable antenna that can be designed into wearable technologies has been developed by researchers at North Carolina State University.
The researchers were looking to create an antenna that can be stretched, rolled, or twisted and always bounce back to the original shape since wearable systems are subject to a range of stresses as patients move around.
“Many researchers – including our lab – have developed prototype sensors for wearable health systems, but there was a clear need to develop antennas that can be easily incorporated into those systems to transmit data from the sensors so that patients can be monitored or diagnosed,”
said senior author Dr. Yong Zhu.
Nanowire Polymer Composite
To develop a sufficiently resilient and effective antenna, researchers applied silver nanowires in a specific pattern, using a stencil. They then poured a liquid polymer over the nanowires.
As the polymer sets, it forms an elastic composite material with the nanowires embedded in the desired pattern. The resulting patterned material forms the radiating element of a microstrip patch antenna.
By manipulating the form and size of the radiating element, the researchers are able to control the frequency at which the antenna sends and receives signals. The radiating layer is then bonded to a “ground” layer, which is made of the same composite, except with a continuous layer of silver nanowires embedded.
Frequency Bandwidth Stability
The researchers observed that, while the flexible nanowire antenna’s frequency does change as it is stretched because stretching changes its dimensions, the frequency stays within a defined bandwidth.
“This means it will still communicate effectively with remote equipment while being stretched,” Adams says. “In addition, it returns to its original shape and continues to work even after it has been significantly deformed, bent, twisted or rolled.”
This antenna can be used as a wireless strain gauge as well since the frequency changes almost linearly with the strain.
“Other researchers have developed stretchable sensors, using liquid metal, for example. Our technique is relatively simple, can be integrated directly into the sensors themselves, and would be fairly easy to scale up,”
Reference: Lingnan Song, Amanda C. Myers, Jacob J. Adams, Yong Zhu. Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires. ACS Applied Materials & Interfaces, 2014; 140317111111009 DOI:10.1021/am405972e