Stretchy batteries and solar cells take wearable technology to next level

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Scientists have developed thin, soft stretchy batteries and solar cells that can be applied to the skin like a band-aid.

The flexible power system overcomes barriers experienced by current wearable technologies, according to a report in the Proceedings of the National Academy of Sciences.

Co-author Professor John Rogers, at the Department of Materials Science and Engineering, at the University of Illinois, said these barriers included most electrical performance and the rigid nature of current systems.

“If you think about conventional electrical devices they are all rigid as a consequence of the fact they are all formed on wafers of silicon,” Dr Rogers said.

He said this was a large reason why technology such as smart phones had a stiff construction.

“The question is how do you get from that to something that looks like the skin that matches the shape of the physical body,” Dr Rogers said.

The power levels in many current technologies were also often in the “range of microwatts, far short of the milliwat levels needed to operate realistic forms of electronics, sensors and radios”, he added.

Anatomy of the stretchy system

The device, developed by Dr Rogers and in international team of researchers from the US, China and South Korea is based on miniaturized solar cells and lithium batteries.

“Our batteries and solar cells consist of a tiled array of thin, millimetre-scale components, interconnected together with spring-like wiring,” he said.

“Which such arrays are embedded, above and below, into a thin layer of super-soft rubber material and then coated on top and bottom with a slightly stiffer rubber, the systems have soft, stretchy characteristics.

The researchers tested the device, which is about 2.5 millimetres thick and applied to the skin like a band-aid, in a range of scenarios such as monitoring skin temperature during physical exercise and bathing.

They said the device could be used for a range of practical and medical applications.

“We are envisioning … full vital signs measurements, via ECG, temperature, blood pressure, respiration rate and blood oxygenation — all with data streams that match up with clinical gold standards,” he said.

He said ongoing monitoring by wearable technologies would also be able to aid patients with muscular or neurological disorders, such as motor neuron or Parkinson’s disease.

In the paper the researchers also suggest the ability to monitor temperature could help in the prevention of conditions such as hyperthermia and frostbite in extreme conditions.

Dr Rogers said the technology also had possible applications in monitoring of athletes and possible military applications.

Its versatility was enhanced by the fact the battery could be recharged wirelessly and the laboratory experiments had shown the device maintained its accuracy while completely submerged and was waterproof.