CUHK’s Latest Innovation Harvests Human Motion to Power Smart Devices


The Faculty of Engineering at the Chinese University of Hong Kong (CUHK) has developed an embedded energy harvester to sustainably power smartwatches and wristbands by converting kinetic energy from the arm swing into electricity.

From tracking workouts to staying connected to measuring your heart rate, there’s no end to what smartwatches can do, and their popularity has made them a verifiable daily companion. However, most smart devices are still limited by mediocre battery life. Thanks to the latest innovations from the Faculty of Engineering at the CUHK, soon, you may never experience an empty battery in your devices again.

Collecting Energy from a Walker’s Swinging Arms

A research team led by Professor Wei-Hsin Liao of the Department of Mechanical and Automation Engineering has developed an embedded energy harvester that is very efficient in generating electricity to sustainably power smartwatches and wristbands. By replacing mechanical gears with electromagnetic converters, the harvester works by converting kinetic energy from the arm swing into electricity, and the device can be embedded in a standard-sized smartwatch.

A typical mechanical gear and rotor inside an automatic watch fail to generate sufficient energy from a wrist movement. To overcome this challenge, Professor Liao and his team applied a magnetic frequency-up converter. By upping the frequency of human motion, the energy harvester can efficiently convert the human motion into electrical energy, resulting in a power output ten times that of devices currently available.

The research team came up with a highly compact embedded generator, equipped with a motion capture unit, a magnetic frequency-up converter, and a power generation unit. Thanks to the magnetic frequency-up converter, the energy harvester is highly compact and has a very high normalized power density. Although the total volume of the harvester is 5 cm3, it can still achieve a 1.74 mW power output.

An Embedded, Renewable Power Supply

Benefiting from high power output and power density, the energy harvesting system can be easily embedded in smartwatches and wristbands to provide a sustainable power supply. Unlike mechanical gears, the magnetic frequency-up converter uses magnetic force for transmission, avoiding the energy loss caused by mechanical friction. And magnetic transmission has the added benefit of protecting the device from impact. Furthermore, the magnetic frequency-up converter has the advantages of simple structure and low cost, which will help to commercialize the device in the future.

Professor Liao is an international expert in the area of mechanical engineering. A testament to his contributions in the field of sciences and technologies associated with adaptive structures and material systems, he was selected to receive the 2020 Adaptive Structures and Material Systems Award by the American Society of Mechanical Engineers – the first Hong Kong recipient of the award.

You can read more about the innovation here.