Timing strategy for boosting energy extraction from triboelectric nanogenerators

An unexpected additional energy generation by the triboelectric nanogenerator (TENG), due to its capacitive behavior, is discovered in this work. This discovery was inspired by some interesting interaction between the TENG and a power management system (PMS) developed in a recent paper (Harmon et al., 2020). After a desirable output was reported in (Harmon et al., 2020), an unusual output response with unexpectedly high output power was observed. This output response cannot be explained by the working principle of the PMS since it suggests a greater than 100% power conversion efficiency for the buck converter employed by the PMS. Detailed investigation reveals that the TENG has more energy to offer than expected from the original design of the PMS. As the buck converter transfers the energy stored in a temporary capacitor to the output, the TENG acts as a capacitor in parallel with the temporary storage capacitor, and contributes an additional amount of energy proportional to its capacitance. Since the internal capacitance of the TENG is time varying and takes the maximum value when the two triboelectric surfaces are in contact, the optimal timing for energy transfer is when the separation distance approaches 0. In practice, suboptimal timing strategies will be implemented via passive switches for simplicity and reliability.