Mechanical energy harvesting using triboelectric nanogenerators

Abstract

During the last two decades, mechanical energy harvesting has seen a surge in research. The interest comes from the rapid development of low-power-consumption small-scale electronics such as wireless sensors and portable electric devices, which can be self-powered by harvesting electrical energy from diverse ambient sources. Wind energy harvesting and biomechanical energy harvesting are the two main focuses of this thesis. Firstly, the fundamental knowledge and the most recent research progress in the field of wind and biomechanical energy harvesting are reviewed in the introduction. Although flag flapping in open flow is a well-known phenomenon that has been studied extensively for several decades, little is known about the flag flutters in channels and their interactions with sidewalls. Therefore, the flag flutter in confinement with and without electrostatic force is studied. The results of critical velocities, flapping frequency, amplitude, contact modes, and energy conversion lay the groundwork for the subsequent chapters. Some fundamentals of flutter-driven triboelectric nanogenerators (FTENG), such as energy flow, governing equations, and the comparison of three structures, are introduced. Based on the low power output of FTENG, a flexible flagpole is proposed to replace the rigid flagpole to enlarge the contact areas for triboelectrification and electrostatic induction. The results show that the flexible flagpole design reduced the critical velocity and enhanced the power output by two orders of magnitudes. A temperature and humidity wireless sensor is successfully powered using a commercial power management circuit. However, the FTENG still has a high impedance issue. Therefore, an auto-switch structure is designed. That is enabled by a top electrode. An effective working velocity domain with larger energy output is found. The new device can deliver an ultrahigh instantaneous power of 55 kW m$^{-2}$. A resistor–capacitor circuit model is used to explain the energy output. For biomechanical energy harvesting, a smart textile that can harvest biomechanical energy while keeping the body warm is introduced. The textile has a high solar absorptivity and low thermal emissivity. Therefore, it can warm the body both in indoor and outdoor environments. Electricity generation originates from the contact and separation between skin and textile. Finally, several potential directions are discussed, including the suggestion of theoretical modeling and alternative FTENG configurations. The work presented in this thesis has the potential to lead the way toward self-powered smart electronic systems, which will be required for future sustainable and intelligent cities.