Engineer – New material enables stretchable wearables

An international team of scientists from Rice University in Texas and Hanyang University in South Korea developed the material by embedding clusters of high-dielectric ceramic nanoparticles in a flexible polymer. Their findings were published in Nature.

The material was reverse-engineered to mimic the elasticity of skin and the type of movement, and also tuned its dielectric properties to counteract the disruptive effects of movement on connecting electronics, minimize energy loss and dissipate heat.

In a statement, Raudel Avila, assistant professor of mechanical engineering at Rice and lead author of the study, said: “Our team was able to combine simulations and experiments to understand how to design a material that can smoothly deform like skin and change the way electrical charges they unfold within it when stretched to stabilize radio communications. In a sense, we are carefully crafting the electrical response to a mechanical event.”

Avila explained that two antennas that communicate with each other do so at a specific frequency.

“We therefore need to make sure that the frequency does not change so that communication remains stable,” he said. “The challenge with achieving this in systems designed for portability and flexibility is that any change or transformation in the shape of these RF components causes a frequency shift, which means you will experience signal interference.”

According to Rice, the nanoparticles embedded in the substrate were intended to counteract these disruptions, and a key element of the design was the intended pattern of their distribution. Both the distance between the particles and the shape of their clusters played a key role in stabilizing the electrical properties and resonance frequency of the RF components.

“The clustering strategy is very important, and it would take much longer to figure out how to apply it based on experimental observations alone,” Avila said.

Sun Hong Kim, a former research fellow at Hanyang and now a postdoctoral researcher at Northwestern University, said the research team took a creative approach to solving the problem of RF signal stability in stretchable electronics.

“Unlike previous studies that focused on electrode materials or design, we focused on designing a high-dielectric nanocomposite for the substrate on which the wireless device is placed,” Kim said.

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

To test whether the material could support the development of effective wearable technologies, researchers built several stretchable wireless devices, including an antenna, coil, and transmission line, and then evaluated their performance on a substrate they developed and on a standard elastomer without the addition of ceramic nanoparticles.

“When we place electronics on a substrate and then stretch or bend them, we see that the resonant frequency of our system remains stable,” Avila said. “We have shown that our system supports stable wireless communication over distances of up to 30 m, even under load. With a standard substrate, the system completely loses connectivity.”

The wireless operating distance of the long-range communication system is longer than any other similar skin-connection system. Moreover, the new material can be used to improve wireless performance in a variety of wearable platforms designed to fit different body parts and a wide range of sizes.

Scientists have developed wearable bionic wristbands to be worn on the head, knee, arm or wrist to monitor whole-body health data, including electroencephalogram (EEG) and electromyogram (EMG) activity, knee movement and body temperature. The headband has been shown to extend up to 30 percent when worn on a small child’s head and up to 50 percent when worn on an adult’s head, effectively transmitting real-time EEG measurements over a distance of 30 m wirelessly.