Feb 2020     Issue 12
Harvesting Energy from the Human Body as It Walks

Prof. Wei Hsin Liao, Department of Mechanical and Automation Engineering

A research team led by Prof. Wei-Hsin Liao from the Department of Mechanical and Automation Engineering has developed a lightweight energy harvester composed of smart materials that scavenges energy from human motion, generating an inexhaustible and sustainable power supply just from a person walking. Specifically, the device can capture biomechanical energy from the motion of the human knee and convert it into electricity, which can be used to power wearable electronics such as pedometers, health monitors and GPS trackers . The team’s work was published in Applied Physics Letters and recommended as a featured article by the editors.

Researchers have already developed large devices that use human motion to generate electricity, such as electromagnetic generators that capture energy when people walk on treadmills or ride bicycles. However, these bulky devices hamper users’ movement and increase the burden on the wearer, because of their considerable weight and the large forces interacting between the harvesters and the human body. These challenges significantly restrict the wider use of these devices. To overcome this, a research team led by Professor Liao proposed and developed a lightweight energy harvester that employs piezoelectric macro-fibre composites, integrated with novel mechanical structures.

Piezoelectric macro-fibre composites are lightweight materials that can produce electricity as they deform . The proposed energy harvester employs a bending beam and a slider-crank mechanism to capture the motion of the human knee when the user is walking. It then uses the captured motion to deform piezoelectric macro-fibre composite pieces bonded to the bending beam, producing electricity 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 or hip, enabling energy harvesters to capture motion more easily and generate more electricity. The prototype harvester, made from piezoelectric macro-fibre composites, can generate an average power output of 1.6mW, from a wearer walking at between 2km/h and 6.5km/h. The generated electricity is sufficient to power common wearable electronic devices such as smart bands. Furthermore, the prototype weighs just 307g . When walking with the device, the wearer’s metabolic cost is almost the same as when walking without it. Unlike existing electromagnetic generator energy harvesters, the lightweight, smart-materials-based energy harvester can capture energy from human motion without increasing the burden on the wearer. It is expected to significantly encourage the use of biomechanical energy harvesters.

This apparatus will attract much attention from mountaineers and hikers. If they get lost in remote mountain areas or in the wilderness where the power grid is unavailable, the device can derive energy from their motion and convert it into electricity, enabling the wearer to continuously monitor their vital signs, know their position, or even send out an SOS signal. At present, we are focusing on improving the performance of the harvester by reducing the weight of the device and increasing its energy-harvesting efficiency. We plan to commercialise the harvester and market it through cooperation with garment manufacturers to embed the device in sportswear.

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