Solar power could be future of wearable sensors

A new way of harnessing the sun’s rays to power synthetic skin could help to create advanced prosthetic limbs capable of returning the sense of touch to amputees.
(c) University of Glasgow

Professor Ravinder Dahiya and colleagues from the University of Glasgow’s Bendable Electronics and Sensing Technologies (BEST) have developed a promising new type of solar-powered supercapacitor which could be used in the next generation of wearable health sensors. The group’s initial goal was to create a synthetic and touch-sensitive covering for prosthetic hands made from graphene.

Currently, wearable systems generally rely on relatively heavy, inflexible batteries, which can be uncomfortable for long-term users. The BEST team have built on their previous success in developing flexible sensors by developing a supercapacitor which could power health sensors capable of conforming to wearer’s bodies, offering more comfort and a more consistent contact with skin to better collect health data.

Their new supercapacitor uses layers of flexible, three-dimensional porous foam formed from graphene and silver to produce a device capable of storing and releasing around three times more power than any similar flexible supercapacitor. The team demonstrated the durability of the supercapacitor, showing that it provided power consistently across 25,000 charging and discharging cycles.

They have also found a way to charge the system by integrating it with flexible solar powered skin already developed by the BEST group, effectively creating an entirely self-charging system, as well as a pH sensor which uses wearer’s sweat to monitor their health.

Synthetic skin for prosthetics

Professor Dahiya said: “We’re very pleased by the progress this new form of solar-powered supercapacitor represents. A flexible, wearable health monitoring system which only requires exposure to sunlight to charge has a lot of obvious commercial appeal, but the underlying technology has a great deal of additional potential. This research could take the wearable systems for health monitoring to remote parts of the world where solar power is often the most reliable source of energy, and it could also increase the efficiency of hybrid electric vehicles. We’re already looking at further integrating the technology into flexible synthetic skin which we’re developing for use in advanced prosthetics.”

Update February 18, 2019:
In a new paper the researchers discuss how they have used layers of graphene and polyurethane to create a flexible supercapacitor which can generate power from the sun and store excess energy for later use. They demonstrate the effectiveness of their new material by powering a series of devices, including a string of 84 power-hungry LEDs and the high-torque motors in a prosthetic hand, allowing it to grasp a series of objects.

The top touch sensitive layer developed by the BEST group researchers is made from graphene, a highly flexible, transparent ‘super-material’ form of carbon layers just one atom thick. Sunlight which passes through the top layer of graphene is used to generate power via a layer of flexible photovoltaic cells below. Any surplus power is stored in a newly-developed supercapacitor, made from a graphite-polyurethane composite.

In laboratory tests, the supercapacitor has been powered, discharged and powered again 15,000 times with no significant loss in its ability to store the power it generates. “This is the latest development in a string of successes we’ve had in creating flexible, graphene based devices which are capable of powering themselves from sunlight. Our previous generation of flexible e-skin needed around 20 nanowatts per square centimetre for its operation, which is so low that we were getting surplus energy even with the lowest-quality photovoltaic cells on the market,” Dahiya said. “We were keen to see what we could do to capture that extra energy and store it for use at a later time, but we weren’t satisfied with current types of energy storages devices such as batteries to do the job, as they are often heavy, non-flexible, prone to getting hot, and slow to charge. Our new flexible supercapacitor, which is made from inexpensive materials, takes us some distance towards our ultimate goal of creating entirely self-sufficient flexible, solar-powered devices which can store the power they generate. There’s huge potential for devices such as prosthetics, wearable health monitors, and electric vehicles which incorporate this technology, and we’re keen to continue refining and improving the breakthroughs we’ve made already in this field.”

Source: University of Glasgow