Wei Hsin Liao is thinking about people in a pickle. “If hikers get lost in remote mountains, off the power grid, what they need is something that derives energy from motion and converts it to electricity,” he says. You can understand why this is on his mind.
Liao is a professor in CUHK’s Department of Mechanical and Automation Engineering and from his laboratory in the University he can look up into a range of hills behind, criss-crossed by hiking trails which have developed into an attractive recreational network, so the popularity of hiking has shot up. So too has the number of hill walkers who fear they will lose the trail and find power to their electronic devices exhausted.
“In a situation like that”, continues Professor Liao, “what they need is a device they can wear which gives enough electricity for them to monitor their vital signs, know their position, or even send out an SOS signal if they need help.”
Liao, founding director of the University’s Smart Materials and Structures Laboratory, is the man who is delivering it. He has turned his area of research towards how technology could help self-survival. Over six months, he and his research team have made an extraordinary breakthrough with a device which harvests energy from the ordinary movement of the human body itself; to be precise, from the knee. All you have to do is simply walk. Biomechanical energy is captured by the knee’s movement. That is then converted to electricity which can be used to power wearable electronics such as pedometers, health monitors, and GPS.
How is the conversion made? “The lightweight smart materials used in the energy harvester are piezoelectric macro fibre composites (MFC) which create electricity when they are repeatedly bent and crumpled, as they would be by a bending and unbending joint.” explains Professor Liao. “The knee’s action is captured by a bending beam with a slider-crank, which the team devised. Patches of the MFC are attached to it so that when the knee flexes or expands, the material is deformed, and electricity is generated.” The knee is the most productive joint to choose and because the harvester is so light and easy to wear, it can be applied to other joints if need be.
The harvester is featherweight. The prototype weighs only 307 grams, creating very little extra burden. The metabolic cost is almost the same as walking without it. It can be with you almost anywhere you like, all the time. It attaches to your leg by two simple bands, one on the shank and the other on the thigh. As long as you are walking, the harvester keeps giving. Depending on how energetic the wearer is feeling, it can be almost inexhaustible.
Moving at normal speed, 4 km/h, will produce an average of 1.6 mW which is enough to power wearable electronic devices such as smart bands and more than enough for the hapless hiker to reopen a mobile phone to send out an SOS signal. If you are in pitch darkness then the energy produced by the harvester can light up your lamp.
The electricity the harvester generates can be transmitted to the devices that you are carrying, in various ways. “I think that wireless transmission like Internet of Things (IoT) technology is preferable but a physical connection between the harvester and the device, such as a cable connector, is possible if necessary,” says Professor Liao. He expects that the energy will be directly transferred into your phone or a monitor as you walk, or it can be sent to a storage device you are carrying and transferred later.
You will be able to wear this for hiking soon. Professor Liao’s team is planning to commercialise it and launch it in the retail market by cooperating with garment manufacturers to embed the device in sportswear. Currently, they are filing patents in the US and China. Our information prone society is now asking for instant readouts on the body’s performance, such as blood pressure and heart rate, especially during exercise and sport. It is going to be a tremendous attraction to people in competition, training or doing plain private exercise to have the biomechanical energy harvester on their bodies, compact and unobtrusive.
Photo by Stanley Yip