Researchers from Penn State and elsewhere are developing devices to explore the possibilities of wearable, flexible antennae that could have applications in health monitoring and clinical treatments.
Researchers believe that current research on flexible electronics is paving the way for wireless sensors that can be worn on the body and collect a variety of medical data. But where does the data go? Without a similar flexible transmitting device, these sensors would require wired connections to transmit health data, they note.
As such, researchers in the Penn State College of Engineering, along with two international teams of investigators, are developing devices to explore the possibilities of wearable, flexible antennae. In April, they published two papers about it in Nano-Micro Letters and Materials & Design.
They explain that like wearable sensors, a wearable transmitter needs to be safe for use on human skin, functional at room temperature and able to withstand twisting, compression and stretching. The flexibility of the transmitter, though, poses a unique challenge: When antennae are compressed or stretched, their resonance frequency (RF) changes and they transmit radio signals at wavelengths that may not match those of the antenna's intended receivers.
As a workaround, the research team created the flexible transmitter in layers. Building upon previous research, they fabricated a copper mesh with a pattern of overlapping, wavy lines. This mesh makes up the bottom layer, which touches the skin, and the top layer, which serves as the radiating element in the antenna. The top layer creates a double arch when compressed and stretches when pulled -- and moves between these stages in an ordered set of steps.
The structured process through which the antenna mesh arches, flattens and stretches improves the overall flexibility of the layer and reduces RF fluctuations between the antenna's states, according to Huanyu "Larry" Cheng, Ph.D., Dorothy Quiggle Career Development Professor in the Penn State Department of Engineering Science and Mechanics.
"Changing the geometry of an antenna will change its performance," Cheng said. "We wanted to target a geometric structure that would allow for movement while leaving the transmitting frequency unchanged."
The transmitter, which can send wireless data at a range of nearly 300 feet, can easily integrate a number of computer chips or sensors, Cheng said. With further research, it could have applications in health monitoring and clinical treatments, as well as energy generation and storage.
"We've demonstrated robust wireless communication in a stretchable transmitter," Cheng said. "To our knowledge, this is the first wearable antenna that exhibits almost completely unchanged resonance frequency over a relatively large range of stretching."
Cheng and his collaborators will continue to research ways to facilitate the development of these devices through application-based studies as well as further fundamental explorations to optimize the design process.
"We are really excited that this research could one day lead to networks of sensors and transmitters worn on the body, all communicating with each other and external devices," Cheng said. "What we're imagining is science fiction at the moment, but we are working to make it happen."
