Wearable electronics could be powered by body motion

South Korean researchers have been investigating the ability of triboelectric nanogenerators (TENGs) — small devices that convert movement into electricity — to create wearable electronics powered solely by the wearer’s day-to-day body motion. And they have some good news.

Hyeon-Jin Shin, research master at the Samsung Advanced Institute of Technology (SAIT), explained that he and his collaborators wanted to address the real-world feasibility of TENGs for wearable applications and, in particular, how to optimise the energy conversion.

“Over the past several years, many researchers have demonstrated a potential for energy harvesting using triboelectricity, and TENGs’ expectations as an energy source for wearable or portable devices have increased,” Shin said. “It is important to confirm that the mechanical energy from human motion can cover the energy consumption of the devices to utilise a TENG for small devices.”

The research team compared the achievable TENG energy produced in one minute by typical body movements, such as typing or arm swinging, to that consumed in the same time by a range of commercial electronics and wearables. Although such movements would not yield enough energy to support an active tablet device, the theory showed the semi-passive activities could power smaller phones and smart watches by TENG power alone.

“We confirmed that if the mechanical energy is entirely converted into electrical energy, the energy generated by the daily motion of an arm can sufficiently cover the energy consumption of a smart watch and even the standby energy consumption of a smartphone,” said Shin.

Investigating the mechanism that produces electricity in a device, they also discovered that its elasticity, not normally factored into calculating a TENG’s maximum possible energy, can offer a boost to the value. Shin explained, “To fully utilise the mechanical energy from human motion for the TENG, it is very important to increase the maximum possible energy of a TENG based on understanding the factors related to the motion in an aspect of the velocity (kinetic energy) and elasticity (impulse).”

With the study now published in the journal APL Materials, from AIP Publishing, Shin and his fellow researchers are poised to keep refining the practical realisations of the technology and use their findings to push the boundaries of what TENG devices can power — and for how long.

“The optimisation of output energy of a TENG in actual use remains a task for future work because a real system has many limitations, such as impedance matching, frequency control and the stability of the structure,” Shin said. “Nevertheless, the results of this study give insight into the design of a TENG to obtain a large amount of energy in a limited space.”