An international team of researchers from Rice University, Texas and Hanyang University, South Korea developed the material by embedding clusters of highly dielectric ceramic nanoparticles into an elastic polymer. Their findings are published in Nature.
The material was reverse engineered to mimic skin elasticity and motion types, and also to adjust its dielectric properties to counter the disruptive effects of motion on interfacing electronics, minimise energy loss and dissipate heat.
In a statement, Raudel Avila, assistant professor of mechanical engineering at Rice and a lead author of the study, said: “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 distribute inside it when it is stretched so as to stabilise radio-frequency communication. In a way, we are carefully engineering an electrical response to a mechanical event.”
Avila explained that two antennas communicating with each other do so at a given frequency.
“So we need to ensure that that frequency does not change so that communication remains stable,” he said. “The challenge of achieving this in systems designed to be mobile and flexible is that any change or transformation in the shape of those RF components causes a frequency shift, which means you’ll experience signal disruption.”
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According to Rice, the nanoparticles embedded in the substrate served to counteract these disruptions, with a key design element being the intentional pattern of their distribution. Both the distance between the particles and the shape of their clusters played a critical role in stabilising the electrical properties and resonant frequency of the RF components.
“The clustering strategy is very important, and it would take a lot longer to figure out how to go about it through experimental observations alone,” said Avila.
Sun Hong Kim, a former research associate from 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 the design of a high-dielectric nanocomposite for the substrate where the wireless device is located,” said Kim.
“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.
To test whether the material could support the development of effective wearable technologies, the researchers built several stretchable wireless devices, including an antenna, a coil and a transmission line, and evaluated their performance on the substrate they developed and on a standard elastomer without the added ceramic nanoparticles.
“When we put the electronics on the substrate and then we stretch or bend it, we see that the resonant frequency of our system remains stable,” said Avila. “We showed that our system supports stable wireless communication at a distance of up to 30m, even under strain. With a standard substrate, the system completely loses connectivity.”
The wireless working distance of the far-field communication system exceeds that of any other similar skin-interfaced system. Moreover, the new material could be used to enhance wireless connectivity performance in a variety of wearable platforms designed to fit various body parts in a wide range of sizes.
The researchers developed wearable bionic bands to be worn on the head, knee, arm or wrist to monitor health data across the body, including electroencephalogram (EEG) and electromyogram (EMG) activity, knee motion and body temperature. The headband, which was shown could stretch up to 30 per cent when worn on the head of a toddler and up to 50 per cent on the head of an adult, successfully transmitted real-time EEG measurements at a wireless distance of 30m.
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