Skin-mimicking material paves way for consistent wireless and battery-free wearable devices

Wearable technologies are revolutionizing healthcare by enabling new forms of individual monitoring, diagnosis, and care. These technologies, which include smartwatches, fitness trackers, and wearable medical devices, are designed to collect data on various health metrics such as heart rate, physical activity, sleep patterns, and even blood oxygen levels. This data can be used to monitor patients in real-time, providing valuable insights that can aid in the early detection of diseases, management of chronic conditions, and overall health maintenance.

According to industry reports, the smart wear market is expected to grow significantly in the coming years, with health and fitness applications owning the largest share in terms of end use.

Now, a groundbreaking development paves the way for battery-free next generation of wearables - a game-changing material that mimics skin's elasticity while preserving signal strength in electronics.

Researchers from Rice University and Hanyang University have created this revolutionary material by embedding clusters of highly dielectric ceramic nanoparticles within an elastic polymer. This ingenious design not only replicates the skin's flexibility and movement but also adjusts its electrical properties. This adjustment counters the negative effects of movement on connected electronics, minimizing energy loss and heat dissipation.

The team combined simulations and experiments to design a material that seamlessly deforms like skin and changes the way electrical charges distribute inside it when it is stretched to stabilize radio-frequency communication, explained Raudel Avila, assistant professor of mechanical engineering at Rice and a lead author on the study.

Electronic devices use radio frequency (RF) elements like antennas to send and receive electromagnetic waves. In mobile and flexible systems,  ensuring that that frequency does not change so that communication remains stable is challenging. Any change or transformation in the shape of those RF components causes a frequency shift, which means you’ll experience signal disruption, Dr. Avila explained.

To address this, the researchers focused on the high-dielectric nanocomposite substrate supporting the wireless device, rather than the electrodes or design which have been traditionally focused on. 

The researchers envision broad applications for this technology, including wearable medical devices, soft robotics, and high-performance antennas. To validate its effectiveness, they built several stretchable wireless devices – an antenna, a coil, and a transmission line – and tested them on their newly developed substrate as well as a standard elastomer (without the nanoparticles).

"We believe that our technology can be applied to various fields such as wearable medical devices, soft robotics and thin and light high-performance antennas,” said Abdul Basir, a former research associate from Hanyang and now a postdoctoral researcher at Tampere University in Finland.

"We showed that our system supports stable wireless communication at a distance of up to 30 meters (~98 feet) even under strain. With a standard substrate, the system completely loses connectivity," Avila said.

Furthermore, the novel material can enhance wireless connectivity in various wearable platforms designed for different body parts and sizes. The researchers created bionic bands for the head, knee, arm, and wrist to monitor various health data, including brainwave activity (EEG), muscle activity (EMG), joint movement, and body temperature. The headband, designed to stretch 30% on a toddler's head and 50% on an adult's, successfully transmitted real-time EEG data over 30 meters.

"As wearables continue to evolve and influence the way society interacts with technology, particularly in the context of medical technology, the design and development of highly efficient stretchable electronics become critical for stable wireless connectivity," Dr. Avila concluded.

This breakthrough paves the way for a future where wearable health devices seamlessly integrate with our bodies, continuously monitoring our health and transmitting data without compromising signal strength or battery life.

A paper describing the materials, fabrication and design strategies is published in Nature. The study authors include Sun Hong Kim, Abdul Basir, Raudel Avila, Jaeman Lim, Seong Woo Hong, Geonoh Choe, Joo Hwan Shin, Jin Hee Hwang, Sun Young Park, Jiho Joo, Chanmi Lee, Jaehon Choi, Byunghum Lee, Kwang-Seong Choi, Sungmook Jung, Tae-il Kim, Hyoungsuk Yoo and Yei Hwan Jung.