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​Origami batteries and accordion sensors could power smart clothes

The kirigami lithium-ion battery sewn between two elastic bands (c) at the upper arm with elbow straightened, (d) at the upper arm with elbow bent. The next two images show the kirigami LIB removed from the elastic bands and stretched directly, (e) at the compact state and (f) at the stretched state. Hanqing Jiang/Scientific Reports

The ancient art of origami is helping to inspire the next generation of wearable technology.

In a study published last week in the journal Scientific Reports, engineers at Arizona State University in Tempe demonstrated how a cleverly folded stretchable battery could be used to power a smartwatch.

Hanqing Jiang, an associate professor of mechanical and aerospace engineering at Arizona State, used a particular type of origami called kirigami, which involves both folding and cutting in strategic ways, to create a lithium-ion battery that can be stretched to 150 percent its original length -- and still work.

Jiang and his team created the battery by coating a piece of Reynolds Wrap aluminum foil with conductive material to create positive and negative electrodes. He then folded and cut the foil into particular kirigami configurations. Think of it as precision paper dolls.

The team made a battery in a "cut-n-twist" pattern created by folding the foil into a stack and cutting out small symmetrical bits at each crease. When stretched and twisted at either end the battery ends up looking roughly like a telephone cord.

They sewed it into an elastic band and swapped out the original battery in a Samsung Gear 2 smartwatch. The makeshift battery wristband was able to power the watch, even when stretched from the wrist to the upper arm.

Jiang noted that in tests, a battery made with a more intricate "cut-n-shear" pattern had double the energy capacity and was stretchable up to one and a half times its starting length.

"The kirigami-based methodology can be readily expanded to other applications to develop highly stretchable devices and thus deeply and broadly impact the field of stretchable and wearable electronics," Jiang wrote in the study.

Meanwhile, in North Carolina, researchers have created a see-through stretchable conductor inspired by an accordion.

Abhijeet Bagal, a Ph.D. student in mechanical and aerospace engineering at NC State and lead author of a paper describing the work in the journal Materials Horizons, said the "nano-accordion" geometry mirrors the original.

"The only thing different is that we made it much smaller," Bagal said in a statement.

The NC State researchers transferred an array of evenly spaced rectangles of conductive zinc oxide onto a transparent elastic polymer. The resulting ridges of zinc oxide allow the structure to expand and contract like the bellows of an accordion.

The researchers hooked the conductor up to a battery and an LED bulb and stretched it. The LED stayed lighted -- until the stretching broke the wire connection to the power source.

Chih-Hao Chang, an assistant professor of mechanical and aerospace engineering at NC State and corresponding author of the paper, said, "We're now working on ways to improve the conductivity of the nano-accordion structures. And at some point we want to find a way to scale up the process."

The conductor could be used in flexible electronics, stretchable displays or wearable sensors. Perhaps it could one day help track your heart rate on an origami-powered smartwatch.

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