Rotational energy harvester powers devices using human motions

Kinetic energy harvesting is a sustainable method for powering small devices such as wristwatches. However, the mismatch between low-frequency human motions and the higher resonant frequencies of vibrational energy harvesters makes the conversion from mechanical energy to electricity a complicated process.

Using a rotational energy harvester, Zhang et al. demonstrate the applicability of converting mechanical energy from irregular human motion to usable electrical energy. The small device is composed of two systems that work together to convert low-frequency linear motion into high-speed rotational motion. The rotating component induces a current in the copper coils attached to the system, which is then stored in a capacitor.

After installing the device on a wood floor, human footsteps were used to demonstrate its effectiveness. With a walking frequency of about 1 Hz and a device compression of about 8 mm, the device can generate a stable voltage of 2.2 V, enough to light up to 70 green LEDs simultaneously.

Though the output power of the technology is still low, it can be used in a variety of low-power applications from environmental monitoring, such as temperature and humidity sensors, or motion trackers.

Aside from placing the device underneath the floor or beneath a person’s shoes to harvest energy from walking motions, there are a number of creative ways the technology can be used.

“It may also be set on the road – energy could be generated when automobiles run over it,” said author Fei Wang. “We are also planning to set it in a buoy to harvest energy from waves.”

Source: “Rotational electromagnetic energy harvester for human motion application at low frequency,” by Yulong Zhang, Anxin Luo, Yifan Wang, Xiangtian Dai, Yan Lu, and Fei Wang, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/1.5142575 .