Triboelectric nanogenerator (TENG) which converts ambient mechanical energy into electrical energy is a spotlighted energy harvesting technology for a portable power generator. In previous researches, the electrical power output of TENG has been improved via applying new materials or combining with other energy harvesting technologies. However, the electrical power generated by the sliding-type TENG is proportional to the size of the internal electrode, and the vertical contact-separation TENG requires a hollow space for moving the dielectric to create the electrical potential difference. Therefore, it is necessary to overcome the spatial limitation of TENGs for developing portable generators. Recently, many studies have shown miniaturization of TENG for portable applications, and there has been continuing efforts to invent portable generating devices which are capable of harvesting low input energy.
In this work, we demonstrate Roll-type sheet TENG (RTS-TENG) that can harvest mechanical energy through an extraction and self-retraction process without additional components for retraction. RTS-TENG utilizes the elastic force of the sheet itself and is thereby operate as a spiral spring. Besides, in the process of the extraction and retraction, it generates additional multiple power peaks in a single input, from a stacking/fluttering motion and changes of the sheet shape. We designed RTS-TENG considering two major factors for maximizing the output: the dimension of the casing cylinder and the length of the sheet. Furthermore, we established that the output energy is changed by patterning the electrodes of each part. And an electrical circuit is designed to efficiently combine the output harvested from each electrode. Finally, we demonstrate portable RTS-TENG which is applicable to any flat board devices without spiral springs for self-retraction process. This study shows possibility of practical applications for RTS-TENG which is usable when attached to portable electronic devices in the future. Additionally, it provides a potential solution as portable energy generators.