This is a diagram of the slider-crank mechanism that generates energy during the knee's motion. Source: Gao et al.

Researchers from the Chinese University of Hong Kong have developed technology that harvests energy from the movement of a person’s knee.

The device consists of an energy harvester that attaches to a wearer’s knee. As the wearer walks, the harvester generates 1.6 microwatts of power — enough to power electronics like GPS devices and health monitoring equipment.

The harvester captures biomechanical energy from the movement of the knee, according to the device’s developers. To achieve this, researchers employed smart macrofiber material, which creates energy from bending motions, to devise a slider-crank mechanism. The researchers demonstrated that as the wearer walks and the knee flexes, the material experiences a constant back and forth movement, bending the device and subsequently generating electricity. The knee was selected due to its large range of motion.

Weighing just 0.68 lb, the prototype of the device was tested on individuals walking at speeds of 1-4 miles per hour. The device generates power without taxing the wearer. Researchers determined that the energy necessary to walk while wearing the device stayed the same with as walking without one by comparing the wearers' breathing patterns.

The research team is attempting to commercialize the device and lead study author Wei-Hsin Liao, professor in the department of mechanical and automation engineering, predicts that a self-powered GPS device would likely attract the attention of mountaineers and climbers.

"Self-powered equipment can enable users to get rid of the inconvenient daily charge," said Liao. "This energy harvester would promote the development of self-powered wearable devices."

The research is published in the journal Applied Physics Letters.