Kinematic design for high performance triboelectric nanogenerators with enhanced working frequency

Triboelectric nanogenerators (TENGs) can harvest a variety of environmental energies including sound, waves, wind, and human motions, but low input energies nomally generate low output power although TENGs have high power conversion efficiency (PCE). In this study, we report the kinematic design of TENGs for improving the PCE. By adopting a gear train in a TENG system, the frequency (f_w) at the working gear could be larger than that (f_in) at the input gear. Finally, the output energy of TENGs with a higher working frequency could be improved, thus providing enhanced PCE. We investigated the output performance of our gear-based TENG system under input frequencies of 1.5, 3, and 4.5Hz by controlling the gear ratio (i.e. 1, 1.7, and 5). Under the input frequencies, the output voltage and current from our gear-based TENG system were enhanced up to the maximum of 3.6 times and 4.4 times, respectively. It was analyzed that the PCE was improved up to 7.57 times at the gear ratio of 5 under the input frequency of 1.5Hz. In order to clearly understand improved performance of the gear-based TENG system, we used our TENG system to charge a capacitor by rectifying the output voltage. Under the input frequency of 4.5Hz, we obtained a 3 times enhanced rectifying voltage at a gear ratio of 5. Interestingly, capacitor charging voltage was enhanced up to about 8 fold in using our TENG system. It is attributed that our gear-based TENG system could improve simultaneously the magnitude as well as the generation time of output power, finally enhancing output energy. Therefore, our gear-based TENG system provided an effective way to enhance the PCE of TENGs operating at a given input energy.