A Theoretical Investigation of a Two-Degree-of-Freedom Vibro-Impact Triboelectric Energy Harvester for Larger Bandwidth

The efficiency of the energy harvesters can be improved by increasing the harvester bandwidth. Towards this, we presented a Two-Degree of Freedom (2-DOF) Vibro-impact Triboelectric Energy Harvester by combining multi-modality and piece-wise linearity of two close resonant frequencies. The harvester structure consists of a primary cantilever beam attached to a secondary cantilever beam through a tip mass. The secondary beam is attached in the opposite direction to the primary beam. The bottom surface of the secondary beam acts as an upper electrode of a triboelectric generator. A lower electrode with bonded Polydimethylsiloxane (PDMS) insulator is attached at some gap separation distance underneath the upper electrode to create an impact structure. When the system vibrates, an impact between the triboelectric layers generates an alternating electrical signal. A 2-DOF system with lumped parameter theoretical model was developed to extract the governing equations. The structure's dynamic behavior at different excitation levels, separation distance, and surface charge density were investigated theoretically. As a result, we achieved a wider bandwidth for the designed energy harvester. The proposed harvester demonstrated an increase in the maximum output voltage by more than 300 percent, and 250 percent increase in the bandwidth, by changing the excitation level from 0.1g to 0.7g. The result of this study can pave the way for an efficient energy harvester that can scavenge ambient vibrations over a wide range of excitation frequencies.