Vibration energy harvester for self-charging wearable devices

Osaka Metropolitan University scientists have made a significant advance towards self-charging wearable devices with the creation of a dynamic magnifier-enhanced piezoelectric vibration energy harvester that can amplify power generated from impulsive vibrations, such as from human walking, by about 90 times, while remaining as small as currently developed energy harvesters. The results were published in Applied Physics Letters.

The rising demand for more efficient recharging of wearable devices has increased the attention paid to energy harvesting, a technology that converts energy such as heat and light into electricity that can power small devices. One form of energy harvesting called vibration energy harvesting is deemed highly practical, given that it can transform the kinetic energy from vibration into electricity and is not affected by weather or climate.

A research team led by Associate Professor Takeshi Yoshimura from Osaka Metropolitan University has developed a microelectromechanical system (MEMS) piezoelectric vibration energy harvester that is approximately 2 cm in diameter with a U-shaped metal component called a dynamic magnifier. Compared with conventional harvesters, the new harvester allows for an increase of about 90 times in the power converted from impulsive vibrations, which can be generated by human walking motion.

The researchers are working on developing vibration energy harvesters that utilise the piezoelectric effect, a phenomenon in which specific types of materials produce an electric charge or voltage in response to applied pressure. They have succeeded in generating microwatt-level electricity from mechanical vibrations with a constant frequency, such as those generated by motors and washing machines. However, the power generation of these harvesters drops when the applied vibrations are nonstationary and impulsive, such as those generated by human walking. In response, the researchers developed and incorporated the U-shaped vibration amplification component under the harvester. The component allowed for improvement in power generated without increasing the device size. The technology is expected to generate electric power from non-steady vibrations, including walking motion, in order to power small wearable devices such as smartphones and wireless earphones.

“Since electronic devices are expected to become more energy-efficient, we hope that this invention will contribute to the realisation of self-charging wearable devices,” Yoshimura said.

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