Improving the efficiency of energy harvesting, by investigating different techniques to increase the harvester bandwidth, as well as by exploring the influencing factors and adjusting them to optimal setups. Towards this, multiple Vibro-impact energy harvesters were proposed in this study. First, a Two-Degree of Freedom (2DOF) Vibro-impact Triboelectric Energy Harvester with a single and a double impact configuration is proposed. Multi-modality and piecewise linearity were combined to improve the harvesting bandwidth of triboelectric energy harvesters utilizing two resonant frequencies. The harvester structure consists of a primary cantilever beam attached to a secondary cantilever beam through a tip mass in the opposite direction to the primary beam. An aluminum layer is attached to The bottom surface of the secondary beam, acts as an electrode of a triboelectric generator, and the other electrode is an aluminum layer bonded with Polydimethylsiloxane (PDMS) insulator, which is placed at some gap separation distance underneath the upper electrode to create a single impact structure. When the system is subjected to vibration excitation, the beams will vibrate, resulting in an impact between the triboelectric layers, generating an alternating electrical signal. To enhance the resonator's bandwidth, we modified the structure to have a double impact by adding another triboelectric generator for the primary beam. The two beams are designed to have close frequencies, and under the effect of the impact, the bandwidth of the resonators is combined to create a very wide bandwidth. A 2DOF lumped parameter theoretical model was developed to extract the governing equations of both single and double impact systems. Then, a simulation analysis was conducted to examine the structure's dynamic behavior at different excitation levels, separation distance, and surface charge density. Finally, experimental results were extracted to validate the simulation results. 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. Second, a harvester under rotational magnetic excitation is proposed for wind energy harvesting applications. The triboelectric beam generates electricity using magnetic impact-induced vibration. The triboelectric energy harvester consists of a clamped-clamped (CC) beam embedded in an outer case. The lower side of the beam acts as an upper electrode that will undergo a contact-separation motion with another lower electrode with a bonded PDMS layer. A permanent magnet will be attached to the beam's upper side facing another magnet attached to a rotating rigid shaft blade at the same polarity. While the fan rotates, a repulsive magnetic force created between the two magnets will excite the CC-beam, leading to the contact-separation motion and generation of electricity. A Single-Degree of Freedom (SDOF) model is presented and simulated to extract the dynamic behavior and the generated electrical signal. The relationship between the output voltage and excitation rotational frequency is analyzed. In addition, the relationship between the output voltage and the distance between magnets and its effect on the bandwidth is also discussed. Finally, the effect of the surface charge density on the amplitude of the generated output voltage signal is examined. The rotational wind triboelectric energy harvester can effectively scavenge wind energy.
Date of publication
Thesis Chair: Alwathiqbellah Ibrahim, Ph.D. Member: Neal Barakat, Ph.D. Member: Tahsin Khajah, Ph.D.
Masters of Science in Mechanical Engineering
Hassan, Mostafa, "Experimental and Theoretical Investigation of Vibro-Impact Triboelectric Energy Harvesters" (2022). Mechanical Engineering Theses. Paper 20.