A research team at the Chinese University of Hong Kong (CUHK) has developed an energy harvesting system to power wearable devices from the movement of the knee.
The energy harvesting system developed by Professor Wei-Hsin Liao from the Department of Mechanical and Automation Engineering is based around a piezoelectric macro fibre composite integrated with novel mechanical structures.
It uses a bending beam and a slider-crank mechanism to capture the motion of the human knee when walking. Then, the captured motion is used to deform piezoelectric macro fibre composites pieces bonded to the bending beam so that electricity is produced when the human knee flexes or extends.
“The human knee joint has a larger range of motion than other lower limb joints such as the ankle and hip, which enables energy harvesters to capture the motion more easily and generate more electricity,” said Prof Liao. The prototype energy harvesting system generates an average power of 1.6 mW, when the wearer walks at about 2-6.5 km/h. The generated electricity is efficient to power common wearable electronic devices such as smart bands.
As the prototype weighs only 307 grams, the wearer’s metabolic cost is almost the same as that when walking without the device. Unlike the existing electromagnetic generator-based energy harvesters, the lightweight smart materials-based energy harvesting system can capture energy from human motion without increasing the wearer’s burden. It is expected to significantly promote the use of biomechanical energy harvesters.
“This apparatus will attract much attention from mountaineers and hikers. If they get lost in remote mountains or a wilderness where the power grid is unavailable, the device can derive energy from their motion and convert it to electricity, enabling wearers to continuously monitor their vital signs, know their position, or even send out an SOS signal at any time when they need help,” said Prof Liao.
“At present, we are focusing on improvement in the performance of the harvester by reducing the weight of the device and increasing energy harvesting efficiency. We plan to commercialise the harvester and market it through cooperating with garment manufacturers to embed the device in sportswear.”
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