Energy Harvester for the Human Knee to Power Wearable Devices

Researchers from the Chinese University of Hong Kong have developed a device that can harvest energy from the human knee during walking, without a substantial increase in effort for wearers.

Their work demonstrates that the device generates up to 1.6 mW of power without significant change in breathing patterns or oxygen consumption by the wearer. One day, this device may power wearable electronics, body-worn sensors, and prostheses.

Previous work developing energy harvesters has resulted in a variety of devices (see flashbacks below). Some devices can generate a few watts, but they tend to be heavy. Other devices require substantial increase in effort by the wearer to power them. To address these limitations, the Hong Kong researchers developed a new smart-material-based energy harvester (SM-EH).

To work, the generator is strapped at the shin and the thigh, which positions the components close to the knee. When the user takes a step, a thin piezoelectric material is bent, which generates power. During walking motion, the device is bent and unbent, resulting in continous power generation.

The researchers performed tests with multiple users, where they measured power generation as a result of different walking speeds, and measured oxygen consumption and CO2 production by the users, with and without the device attached. The results led the researchers to conclude that the new generator did not require additional effort by the wearer to produce electric power. The device weighs less than one pound and can generate enough power for GPS devices and health monitoring equipment.

“Self-powered equipment can enable users to get rid of the inconvenient daily charge,” in a published statement said Wei-Hsin Liao, the senior author of the study. “This energy harvester would promote the development of self-powered wearable devices.”