Wearable electrical circuit has the need for 5G speed

Novel design elements, such as the interlocking segments, are fundamental to the stretcable, wearable circuit's high performance(Credit: Yei Hwan Jung and Juhwan Lee)

Today's fitness trackers cram an impressive amount of functionality into some small packages, but if current wearables research is any indication they could come to look pretty clunky pretty quickly. The scientists behind the latest flexible electronics that can be worn on the skin like a tattoo claim to have developed the world's fastest stretchable circuit, providing what they see as a platform for the forthcoming era of blazing-fast 5G wireless communications.

Numerous research teams are working on ultrathin skin-mounted electronics that could work as everything from medical sensors, to sports tickets to human-machine interfaces. Among these is a team from the University of Wisconsin-Madison, which has developed a new type of flexible circuit with one eye on the next generation of wireless communications technologies.

The team notes a few novel design elements as fundamental to the circuit's high performance. Inspired by twisted-pair telephone cables, the circuits are made up of two interlaced power transmission lines that are fashioned into repeating S-like bends. The researchers claim this form allows the transmission lines to be stretched without compromising performance, while also protecting them from external interference.

These shapes, which are made in two layers of segmented metal blocks, also serve to better contain the electromagnetic waves running through the circuit, almost entirely avoiding current loss. The researchers say the circuits can operate at radio frequency levels of up to 40 GHz in their current form.

It is still a little ways off, but 5G technology could see wireless signals shift to higher bands on the radio spectrum, such as the microwave frequencies in the 0.3 gigahertz to 300 gigahertz range. This could open up bandwidth to accommodate an unprecedented amount of yet-to-be connected devices, including everything from smartphones to light globes.

The circuits measure 25 micrometers in thickness, a girth the researchers say seriously undercuts other stretchable transmission lines which can go as wide as 640 micrometers. This slender form would lend itself particularly well to a so-called second skin, or electrical systems that can be worn like a tattoo for a variety of applications.

This might mean sensors that wirelessly track certain health parameters, relaying data to doctors to avoid the need for regular visits to the clinic. Or perhaps more inconspicuous ways to monitor sun exposure or even charge our other mobile devices.

"We've found a way to integrate high-frequency active transistors into a useful circuit that can be wireless," says Zhenqiang Ma leader of the research. "This is a platform. This opens the door to lots of new capabilities."

The research was published in the journal Advanced Functional Materials.

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