A stretchable antenna that can be incorporated into wearable technologies, such as health monitoring devices, has been developed by researchers from North Carolina State University.
The researchers wanted to develop an antenna that could be stretched, rolled or twisted and always return to its original shape because wearable systems can be subject to a variety of stresses as patients move around. In doing so, they learned that, while the antenna's frequency does change as it is stretched, since that changes its dimensions, the frequency stays within a defined bandwidth.
The researchers detailed their work in a paper, "Stretchable and Reversibly Deformable Radio Frequency Antennas Based on Silver Nanowires," which was published online in ACS Applied Materials & Interfaces.
The antenna is well-suited for applications such as wireless strain sensing. The material and fabrication technique reported in the paper could then theoretically be extended to achieve other types of stretchable antennas with more complex patterns and multilayer structures.
"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," Dr. Yong Zhu, an associate professor of mechanical and aerospace engineering at NC State and senior author of the paper describing the work, said in a statement.
To create an appropriately resilient, effective antenna, the researchers used a stencil to apply silver nanowires in a specific pattern and then poured a liquid polymer over the nanowires.
When the polymer sets, it forms an elastic composite material that has the nanowires embedded in the desired pattern.
The work on the new, stretchable antenna builds on previous research from Zhu's lab to create elastic conductors and multifunctional sensors using silver nanowires.
This patterned material forms the radiating element of a microstrip patch antenna. By manipulating the shape and dimensions of the radiating element, the researchers can 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 it has a continuous layer of silver nanowires embedded.
"Other researchers have developed stretchable sensors, using liquid metal, for example," Zhu continued. "Our technique is relatively simple, can be integrated directly into the sensors themselves, and would be fairly easy to scale up."
The 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.