The innovative material strengthens the signal in portable devices

A new material that moves like skin while maintaining signal strength in electronics could enable the development of next-generation wearable devices that provide continuous, consistent wireless and battery-free functionality.

According to a study published today in Nature, an international team of scientists from Rice University and Hanyang University developed the material by embedding clusters of high-dielectric ceramic nanoparticles in a flexible polymer. The material was reverse-engineered to not only mimic the elasticity of skin and the type of movement, but also adjust its dielectric properties to counteract the disruptive effects of movement on the connecting electronics, minimize energy loss and dissipate heat.

“Our team was able to combine simulations and experiments to understand how to design a material that can seamlessly deform like skin and change the way electrical charges are distributed within it when stretched to stabilize radio communications,” said Raudel Avila, assistant professor of mechanical engineering at Rice and the study’s lead author. “We’re sort of carefully crafting the electrical response to a mechanical event.”

Avila, who was responsible for conducting simulations to help determine proper material choices and design, explained that electronic devices use radio frequency (RF) components, such as antennas, to send and receive electromagnetic waves.

“If you’ve ever been in a place with poor cell service or a very spotty Wi-Fi signal, you probably understand the frustration of having a weak signal,” Avila said. “When we try to transmit information, we work on specific frequencies: two antennas communicate with each other on a specific frequency. So we need to make sure this frequency doesn’t change so that communication remains stable. The challenge this is achieved 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.

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 more time to figure out how to implement 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, noted that the research team took a creative approach to solving the problem of RF signal stability in stretchable electronics.

“Unlike previous research 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, emphasizing the importance of collaboration between the three different fields of knowledge for the development of ” such a multidimensional solution to a complex problem.”

“We believe 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 PhD student at the University of Tampere in Finland.

Wearable technologies are having a profound impact on healthcare, enabling new forms of personalized monitoring, diagnosis and care. Smart clothing market forecasts reflect the transformative potential of these technologies, with health and fitness driving the largest end-use application.

“Wireless, stretchable, skin-integrated electronic devices play a key role in health emergencies, e-health care and assistive technologies,” Basir added.

To test whether the material could help develop effective wearable technologies, researchers built several stretchable wireless devices, including an antenna, coil and transmission line, and then evaluated their performance both on a substrate they developed and on a standard elastomer without the added 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 demonstrated that our system supports stable wireless communication over distances of up to 30 meters (~98 feet) even under heavy 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.

For example, researchers 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% when worn on a small child’s head and up to 50% when worn on an adult’s head, effectively transmitting real-time EEG measurements over a distance of 30 meters wirelessly.

“Stretchable skin-connected RF devices that seamlessly adapt to skin morphology and monitor key physiological signals require critical design of individual material systems and electronic components to achieve mechanical and electrical properties and performance that do not interfere with user comfort,” Avila said. . “As wearable devices evolve and impact the way society interacts with technology, particularly in the context of health technology, the design and development of high-performance, stretchable electronics becomes critical for stable wireless connectivity.”

The research was supported by the Ministry of Science and ICT, Korean Government through the Institute of Information and Communication Technology, Planning and Evaluation (IITP-RS-2023-00253914, IITP-2022-0-00310) and through the National Research Foundation of Korea (NRF-2022R1C1C1003994, NRF-2019M3C7A1032076). The content of this press release is solely the responsibility of the authors and does not necessarily represent the official views of the funding organizations.

Reviewed article:

“Unchanging, stretchable radio frequency electronics” | Nature | DOI: 10.1038/s41586-024-07383-3

Authors: 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

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CAPTION: Raudel Avila is an assistant professor of mechanical engineering at Rice University and lead author of the study published in the journal Nature. (Photo: Jeff Fitlow/Rice University)

CAPTION: Raudel Avila, an assistant professor of mechanical engineering at Rice University, helped develop a new material that moves like skin while maintaining signal strength in electronics. (Photo: Jeff Fitlow/Rice University)

CAPTION: Pictured are stretchable wearable devices placed on a newly developed material substrate that can adjust its dielectric properties to counteract the disruptive effects of motion on connecting electronics. The system’s performance was tested under various types of deformation movements, including twisting (left) and poking (right). (Photo courtesy of Raudel Avila/Rice University and Sun Hong Kim/Hanyang University)

CAPTION: Cross-sectional stereomicroscopic images of a dielectric polymer showing deformed (left) and undeformed (right) clusters. Under the influence of tensile deformations, the cluster changes from a sphere into an ellipsoid. (Photo courtesy of Raudel Avila/Rice University and Sun Hong Kim/Hanyang University)