Hybrid energy harvester from Kwangwoon University shows promise as a wearable charger for portable electronic devices

How many electronic devices do you carry with you on a typical day? Between laptops, mobile phones and smart watches, there is an ever-growing need for reliable, portable power sources. Battery packs can provide that functionality, but they too need to be recharged. So, the race is on to develop built-in energy harvesters that can continuously recharge portable electronics.

The latest breakthrough in this effort comes from researchers at Korea’s Kwangwoon University. Writing in Nano Energy [DOI: 10.1016/j.nanoen.2017.12.046], they report on a hybrid energy harvester which can convert the mechanical energy of ‘human-induced motion’ (i.e. handshaking, walking, and slow running) into electrical energy. Their design combines two complementary technologies that operate under the same mechanical motion – a Halbach magnet array in an electromagnetic harvester (EMG), and a nanostructured PTFE triboelectric device (TENG) that scavenges mechanical energy from contact/separation and sliding friction. They wanted to determine if the hybrid system could deliver higher electrical output than existing, individual mechanical energy harvesters.

Their final device measured 6.5 x 2.6 x 1.8 cm3 – comparable to battery ‘power packs’ currently available on the market. The theoretical modelling of their system determined that the EMG acts as a voltage source, with its output dependent on magnetic flux density, coil length, and velocity. In addition, the TENG was shown to act as a current source, with its output dependent on triboelectric charge density, surface area, and sliding velocity.

To determine the device’s real-world performance, the authors tested it in-situ, as the wearer carried out various activities. They were particularly interested in its performance at vibrations similar to those that characterise handshaking, i.e. almost harmonic, with a frequency of 2.5–6 Hz and an amplitude with peak acceleration of 15–20 ms-2. The resulting output powers were 5.8 mW (handshaking), 2.6 mW (walking), and 3.4 mW (slow running).

The team also connected their generator to electronic devices, including Lithium-ion batteries and capacitors, and achieved the maximum charging voltage when the EMG and TENG were being used simultaneously. This result suggested that the hybrid device outperforms either of the individual harvesters. In addition, the device’s electrical output remained stable, even after 150k cycles. The authors say that this work “takes a significant step toward hybrid energy harvesting from human induced motion and its potential applications in powered portable electronics.”


Md Salauddin, R.M. Toyabur, Pukar Maharjan, Jae Yeong Park “High performance human-induced vibration driven hybrid energy harvester for powering portable electronics” Nano Energy, 45 (2018) 236–246. DOI: 10.1016/j.nanoen.2017.12.046