Wearable Antennas Designed for Medical Applications

Researchers from Penn State, in collaboration with academic institutions abroad, are developing wearable antennas for medical applications. Typically, wearable medical devices are outfitted with sensors to collect specific data, then utilizes a wired connection to transmit that collected information. Flexible electronics have paved the way for wireless sensors that can be worn on the body in the form of patches, but the transmission range is usually limited and often requires mobile devices to act as a bridge between the transmitter and receiver.

The engineers are currently looking at ways to outfit those wearable devices with flexible antennas, which need to be robust enough to handle the natural movements when worn directly on the skin. Therein lies a unique challenge — when antennas stretch or compressed, their resonance frequency changes and their wavelengths may not match those of the intended receiver. To mitigate that issue, the team designed a flexible antenna using layers, with the bottom outfitted with a copper mesh arranged in overlapping, wavey lines. The top layer serves as the antenna's radiating element, creating a double arch when compressed, and stretches when pulled. Those motions move in a series of steps — arches, flattens and stretches, which improves the antenna's overall flexibility and reduces RF fluctuations.

The stretchable antenna's bottom layer also prevents radio signals from interacting with the skin, preventing any tissue damage. Since the antenna can maintain a steady RF signal, it can also collect energy from radio waves, potentially lowering the energy costs when used with other devices. The transmitter also has a range of around 300 feet, making integration easy with any number of processors and sensors.

The researchers analyzed the prototype and began looking at ways to fine-tune the antenna for customized performance. Instead of making the three-step approach (arch, flatten, stretch), the team measured the antenna's deformation at different intervals. They then used computer simulations to identify the relationship between the deformation and antenna performance. The team found that the normalization of different variables provided several paths for customizing performance. They also found that varying the copper mesh layer design could produce different outcomes, even if the same variables were used. It will be interesting to see how these new stretchable antennas evolve over the coming months.