Stretchable Antenna Enables Reliable Wearable ECG Monitoring During Motion

This instability hampers clinical use for long-duration physiologic monitoring during daily life, rehabilitation, and exercise. Reliable connectivity is essential when clinicians depend on real‑time electrocardiogram and vital sign streams outside controlled settings. To help address this challenge, researchers have developed a soft, stretchable antenna engineered to remain tuned and communicate steadily even as the body moves.

Developed at Penn State with international collaborators, the stretchable radiofrequency antenna is intended for wireless links used by Bluetooth and similar systems, and it can also harvest ambient radiofrequency energy to power components. The work was published in Nature Communications. The design targets the common mismatch between flexible sensors and rigid antennas that disrupts signal quality during motion.

The antenna is fabricated from tiny liquid metal particles dispersed in Ecoflex, a soft, rubber‑like elastomer. A cross‑shaped opening at the center of the circular layout guides the internal signal path so that changes in shape do not simply lengthen the path and detune the device. In testing, the antenna maintained functional stability when stretched in multiple directions by up to 45%, limiting frequency shifts that typically interrupt connectivity.

Two demonstrations evaluated practical performance. In one, the antenna harvested radio waves and generated enough electricity to power a small LED while stretched about 30% in different directions; a conventional stretchable antenna lost stable power output after roughly 5% strain. In a second, a related version integrated into a smart T‑shirt with electrocardiogram electrodes and a Bluetooth Low Energy system transmitted stable electrocardiogram signals from approximately 6 feet to more than 300 feet. The system continued to acquire recognizable electrocardiogram, heart rate, and acceleration signals during arm raises, upper‑body stretches, and an outdoor run from more than 300 feet toward the receiver.

The investigators noted immediate opportunities in healthcare, where motion‑resilient communication could support more continuous and reliable wearable monitoring during daily activity, exercise, or rehabilitation.

“The medical application is the top priority for us, because we see the great potential for this in monitoring human health,” said Huanyu “Larry” Cheng, the James L. Henderson Jr. Memorial Professor of Engineering Science and Mechanics at Penn State and a corresponding author of the study.

“Practical application will require the actual use of the antenna in the sensing and integration of the system. Here, the demonstration shows we can get this integrated so the energy can be harvested, and the data can be transmitted,” said Cheng.

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