Graphene foam is the future of IoT power, maybe

An electrically charged spring in your step

A group of Scottish engineers claim to have come up with a new way to harvest the electricity wasted by everyday human movement: electrically conductive foam.

The team from the University of West Scotland reported their findings in a recently published paper detailing the addition of three-dimensional graphene (3DG) foam to triboelectric nanogenerators (TENGs) that researchers have traditionally been trying their best to miniaturize in order to add it to things like clothing and smartphones

By moving away from wearability and pocketable miniaturization, the team was able to create a floor sensor that could detect and draw enough electricity from a human step to power an Arduino computer. The sensor was also connected to software able to determine if someone was entering or leaving a room and who they were "based on measuring their unique temporal pressure profile," the team said in their paper.

3DG-TENG floor sensors could be used to manage energy usage in smart buildings by, for example, adjusting heating and cooling systems based on room occupancy, turning lights and other systems off and on when the first/last person enters/leaves, and the like. 

"We have proven that using … 3DG foam as an active layer in TENGs can work as a reliable and cost-effective energy harvesting power source for autonomous sensors and electronics," said Dr Carlos Garcia Nuñez, a lecturer in engineering and physical sciences at UWS and one of the authors on the research paper. "This discovery has enormous potential for the booming global IoT industry."

A new take on old tech

Research into TENGs has been fairly constant in the decade since they were discovered, but a number of drawbacks and shortcomings have limited the technology. According to the team behind the 3DG-TENGs, low durability, high internal impedance, limited short-circuit current, and structural problems are all stumbling blocks.

TENGs work relatively simply, using static electricity to convert mechanical energy into electric power. They are made of two electrically dissimilar materials that, when touched together and separated, create a small bit of electrical energy. As such, surface area is a key part of getting good electrical generation, and the boffins said their 3DG foam "possesses a unique porous structure enhancing the contact surface." That, in turn, is why they were able to get their 3DG-TENGs doorway sensor generating around 10.37 watts per square meter, which are "record values for carbon-based TENG." 

Integrated Graphene, the company behind the 3DG foam used in the experiment, said the sensors could also be used to harvest energy from cars driving over smart roads, generate performance data for athletes, and for wearable biosensors used to diagnose various health conditions. The Scottish researchers said they were also able to use the foam sensor to charge batteries.

Whether graphene foam will hold up better over time is unclear – the researchers said in their paper that their 3DG-TENGs foam is "a very promising mechanical energy harvester in terms of output characteristics," but also noted that "material transfer … due to several contact-separation cycles could hinder … stability." ®

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