Energy harvesting from vibro-impact of structures using triboelectric materials

• Main Author: Zhao, Chaoyang
• Other Authors: Yang Yaowen
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2023
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/169397
• Institution: Nanyang Technological University

In the past few years, the remarkable progress of wireless sensing technology has raised a huge demand for the miniature of electronics and distributed power supply strategies, which leads to tremendous attention to be focused on the energy harvesting techniques that generate continuous electricity from the ambient environment. There are several energy sources in nature for energy harvesting, such as solar, thermal gradient, wind/water flow and vibration. Among them, the wide existence of vibration makes it an ideal energy source to be harvested through transduction mechanisms. Triboelectricity has long been regarded as a negative effect until it was first utilized for energy harvesting in 2012. Triboelectric energy harvesters (TEHs) have a lot of merits including good flexibility, wide material availability, high power density and low cost. Therefore, it is worth investigating triboelectric energy harvesting for low-frequency vibrations and wind-induced vibrations energy harvesting, aiming at powering wireless sensors for infrastructure monitoring. In this thesis, a novel cantilever TEH working on the contact-separation mode is proposed for low- frequency vibration energy harvesting. An electromechanical model of TEH with non-parallel contact surfaces is derived by evaluating the total electrical energy between two surfaces. One merit of the proposed harvester lies in its simple design for easy implementation. The performance of TEH is investigated theoretically and experimentally, and the results show that it can harvest energy from not only low-frequency base excitation but also broadband vibration sources. A peak output voltage of 25 V is achieved from the harvester under a base acceleration of 0.5 g with an excitation frequency of 8 Hz. Good agreement is observed between the experimental results and analytical predictions. The performance of TEH can be improved by adjusting the gap distance between the top plate and the beam. The proposed TEH is shown to be cost-effective to scavenge the low-frequency vibration energy from the ambient environment. Fluid-induced vibration caused by aerodynamic instability is also a very common energy source that can be converted into electricity using harvesters. In this thesis, a cantilever-type harvester with a square shape bluff body is proposed for wind energy harvesting based on the galloping effect. The prototypes of the harvester with different contact areas of the triboelectric pair were fabricated. Experiments were conducted in a wind tunnel and the results indicate that the harvester is effective in power generation especially when the contact area is large. It can charge a capacitor with a capacitance of 47 μF to 3.3 V in 60 seconds. In addition, the harvester shows its capability of integrating with piezoelectric material to increase its energy conversion efficiency. Governing equations considering the aerodynamic force and non-parallel configuration of the triboelectric layer are established and validated. Note that the external vibration source may have a random magnitude of excitation and fluctuates in a wide frequency range. Wide bandwidth characteristic of the harvester plays a key role in judging its performance. To some extent, the cantilever type TEH has already achieved wide bandwidth due to the impact nonlinearity. This thesis proposes a wide-bandwidth triboelectric energy harvester (UBTEH) by using the multimodal method. It was found that the frequency locking phenomenon occurs for the UBTEH with narrow gaps and under large acceleration. By combining the multimodal techniques and impact, the strong resonance at the locking frequency delivers the best power output and continuous wide bandwidth. The modified UBTEH has an overall bandwidth of 8.2 Hz even in the low-frequency range. In summary, this thesis focuses on the design and analysis of a cantilever-type TEH for energy harvesting from harmonic vibrations. An electromechanical model considering the non-parallel configuration of triboelectric layers is proposed and experimentally validated. The thesis also explores the concept of a wide-bandwidth TEH by incorporating the multimodal technique. Additionally, the cantilever-type TEH is redesigned by introducing a bluff body for galloping wind energy harvesting. A theoretical model is formulated by taking into account the aerodynamic force. Future work will concentrate on the performance enhancement of the harvester, followed by the circuit simulation when integrating with electronics for wireless sensing. Furthermore, TEHs with multilayer structures and other working modes will be explored.