Investigating the effects of auxetic structures on galloping energy harvesting performance

Galloping, a type of self-excited flow-induced vibration, is utilised as a power source for flow energy harvesting. Recent advancements have introduced auxetic structures to potentially enhance energy harvesting by modifying the shape of the substrate beam. However, current research mainly focuses on strain, acoustics, and base excitation as energy sources, with minimal attention paid to flow-induced vibrational energy. This study, therefore, investigates the effects of auxetic structures on the performance of galloping energy harvesters. Comparative analysis is performed using two beam types: a conventional plain beam and an auxetic beam. An electromechanical mathematical model, using the extended Hamilton’s principle, is developed to predict the dynamic responses of these harvesters. Wind tunnel experiments are conducted to validate the simulations and demonstrate the design. The findings indicate that while the auxetic energy harvester exhibits higher vibration amplitudes than the plain energy harvester, its output voltage is paradoxically lower. Further impedance matching tests determine that the optimal load resistance for the auxetic energy harvester is 300 kΩ, compared to 200 kΩ for the plain energy harvester. Moreover, at the maximum tested wind speed of 5.1 m/s under optimal resistance conditions, the auxetic energy harvester achieves a maximum output power of 0.067 mW, which is lower than the 0.239 mW generated by the simple plain energy harvester. These results show that auxetic structures may not enhance galloping energy harvesting performance as anticipated.