Paper Generators: Harvesting Energy from Touching, Rubbing and Sliding
We present a new energy harvesting technology that generates electrical energy from a user’s interactions with paper-like materials. The energy harvesters are flexible, light, and inexpensive, and they utilize a user’s gestures such as tapping, touching, rubbing and sliding to generate energy. The harvested energy is then used to actuate LEDs, e-paper displays and other devices to create interactive applications for books and other printed media.
Paper Generators are based on electrets: materials that hold quasi-permanent electric charge. Our implementation makes use of PTFE (Polytetrafluoroethylene) sheets, commonly known by the brand name Teflon®. When the PTFE sheet is rubbed with ordinary paper, opposite-polarity charges accumulate on the surfaces of the paper and the PTFE due to the triboelectric effect, forming the electret (Figure a). Because PTFE has a lower electron affinity than paper, charge on the PTFE is negative. When the PTFE sheet is stacked with conductive layers that serve as electrodes, such as silver coated polyester sheets or paper with printed conductive ink, the charge on the PTFE attracts free charges of opposite polarity, which then accumulate on the surface of the conductors, as shown in Figure b. This structure forms the basis of Paper Generators.
The operation of the Paper Generators relies on the movement of the two conductive sheets relative to each other and the electret, PTFE. Energy is created when a user moves electrodes. As the relative positions of the sheets change, the distribution of the induced charges, the electric field, and the total capacitance between the conductors change, resulting in an electric potential difference between the conductors (Figure c). Hence, the movements of the sheets and the field source are converted into electrical potential energy that can do work.
The same principle of operation applies to the horizontal movement of the top electrode (sliding). It is also possible to replace the top electrode with the user’s hand. In this scenario, the user holds and rubs the PTFE sheet on and off the bottom electrode, while touching the other end of the voltmeter with his free hand. The circuit is completed through the users body. These different Paper Generator configurations and structures allow for energy generation using different user gestures, such as tapping, rubbing, touching, rotating and sliding.