University of Tokyo, Japan
Department of Mechanical Engineering


Plenary Talk

Wearable/skin-attached Energy Harvesters with High-performance Amorphous Polymer Electrets

Wearable/skin-attached electronics have great potential in healthcare, sports, and biomedical
applications. The development of these devices has led to a significant increase in the use of coin batteries,
increasing their environmental impact. Energy harvesting is a method to capture ambient energy such as
environmental vibration, ambient light, and body heat. Among them, energy harvesting from human motion
is suitable for powering battery-less wearable devices and skin electronics.
In such applications, electret energy harvesters (EH) have advantages over other types of EHs due to
the fact that low-frequency motion is dominant. In this talk, the development of new amorphous polymer
electret materials based on quantum chemical analysis and machine learning as well as a novel stretchable
electret material is presented. In addition, their application to rotational/stretchable electret EHs is
introduced.

In the last 90 years since the first development of electret using Carnauba wax, electret materials have
been developed by heuristic approaches. In the present study, for the first time, a novel high-performance
amorphous fluorinated polymer electret based on quantum chemical analysis and machine learning is
proposed. A new electret material based on CYTOP thus obtained offers a record-high surface charge
density with extremely-high thermal stability of implanted charges. Novel stretchable electret material
based on a cross-linked amorphous fluorinated polymer is also discussed.

As an application of the developed CYTOP electret, a novel low-profile rotational electret EH is
prototyped. Output power up to 1 mW has been obtained at a low rotational speed of 1 rps with only 3 mm
in thickness. Evaluation of the rotational EH for human walking and activities of daily living (ADL) is also
discussed.