Stretchy batteries and solar cells take wearable technology to next level
Scientists have developed thin, soft stretchy batteries and solar cells that can be applied to the skin like a band-aid. New device uses miniaturised batteries and solar cells connected with wires sandwiched between layers of rubber. The device, which is about 0.25 millimetres thick, can be applied to the skin. It can be used to measure health indicators in medical, sports and defence settings. 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 modest 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 milliwatt levels needed to operate realistic forms of electronics, sensors and radios", he added.
The device, developed by Dr Rogers and an international team of researchers from the US, China and South Korea is based on miniaturised 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. "When such arrays are embedded, above and below, into a thin layer of a super-soft rubber material and then coated on top and bottom with a slightly stiffer rubber, the systems have soft, stretchy characteristics.
"The active components [effectively] 'float' in the super soft core layer in a way that mechanically decouples them from the surroundings; [and] the shell layer establishes a robust interface to the skin." The resulting system could stretch up to 30 per cent without detectable loss in solar power generation, the researchers said.
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.
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