Bulletin No. 2, 2019

25 The Force is with Us The Force is with Us LiaoWei-hsin harvests energy fromhumanmotion Anxiety over dying battery is a syndrome of our times. Thanks to the ingenious invention by mechanical engineers led by Prof. Liao Wei-hsin , chairman of Department of Mechanical and Automation Engineering, our paranoia about charging will soon be cured. By donning the human knee energy harvester, we can duly capture the kinetic energy generated by the joint and power electronics simply by walking, any time any place. ‘The human body is a rich source of energy, especially kinetic energy, which can be harvested for the generation of electricity,’ remarked Dr. Gao Fei , Postdoctoral Fellow in the Department of Mechanical and Automation Engineering who is the main inventor. To capture the knee’s energy and convert it into electricity, the human motion researchers fashion their human knee energy harvester after the slider-crank mechanism ( see Figure 1 ). To begin with, we have two fixing bands at the thigh and shank which fasten the device to our limb. From the thigh and shank human knee energy harvester generates 1.6 milliwatts of power, i.e., 1.6 millijoules per second. This would be sufficient to power small devices such as health monitoring equipment and GPS devices. ‘The power generated by the harvester can either be stored, or put through to other portable and wearable appliances as in the Internet of Things. It offers a good solution to the battery problem, as it allows us to utilize energy locally. In mountaineering, for example, where charging may be a problem, we do not have to rely on batteries, as we can get energy direct from our own motion. It would be good for safety and emergency purposes,’ said the professor. Weighing only 307g, this modern- day talaria produces energy at no cost to us. The research team had performed experiments and found out it does not increase the users’ metabolic effort. Using ball joints at the bearings of the thigh and shank fixing bands, the harvester caters to all knee movements, issuing even more energy in intense activities like running and in soccer games. Following the publication of the invention as a featured article in Applied Physics Letters in July, the team has been greeted with wide media and commercial interests. It is looking to improve its energy efficiency, enhance the design, increase its comfort and lower the cost, while filing patents in the US and China. In two years’ time, we will see the prototype developed into a full-fledged product in the market, soothing our nerves and affording us the boon of streaming energy at no extra effort. Amy L. Figure 2. MFC-based human knee energy harvester fixing bands extend the thigh and shank links, respectively, which meet at a movable bearing at the knee. A linear guide, moreover, connects the thigh and shank links at their ends at the corresponding fixing bands, and a slider glides along it. ‘When walking, our leg flexes and extends, causing the slider to move back and forth. The rotary motion of the knee is thus transformed to linear motion along the slider,’ explained Professor Liao. On top of the above, a carbon fibre plate with smart materials on it arches over the design, with one end of it hinged on the thigh fixing band and another on the moving slider. The slider’s movement arising from our gait would cause the carbon fibre plate to bend and the smart materials on it would deform, converting the pressure it receives into electricity. Such smart materials are macro- fibre composite (MFC) slices that are piezoelectric in nature, meaning the materials can generate electricity once they come across pressure and deformation. At a normal walking speed of 4 km per hour, the MFC Shank fixing band Carbon fibre plate MFC Ball joint Thigh fixing band Slider Linear guide