Comprehensive Study of Energy Capturing, Conversion, and Transportation Behaviors in a Piezoelectric Vibration Energy Harvesting System

Piezoelectric vibration energy harvester (PEH) is one of the hottest research areas to address renewable energy issues with over 10,000 journal articles published in the last two decades. However, several critical issues, such as the proof mass effects, electrical impedance, mechanical resonance, and energy charging processing, remain open. This dissertation presents a comprehensive study addressing the above issues. To obtain reliable results, a professional quality flextensional PEH (FPEH) and multiple comprehensive experimental methods were developed, and ANSYS FEM modelling was used. Study of the proof mass effect indicated that the generated voltage linearly increased with the weight ratio of the proof mass over the FPEH while the resonance frequency linearly decreased with the square root of the mass ratio. The resonant electrical impedance behaviors were studied through both electrical and mechanical excitations in accordance with the impedance matching principle. This study discovered that under mechanical excitation i) the capacitive impedance of PEH dominated at the resonance frequency while the inductive impedance of PEH dominated at the anti-resonance frequency, ii) the resonance frequency by mechanical excitation was slightly lower than electrical excitation, iii) the peak of the generated voltage was at the anti-resonance frequency of the mechanical excitation, iv) two power peaks at the anti-resonance and resonance frequencies were captured under the umbrella of the voltage peak. Finally, an innovative method for charging a super-capacitor from a PEH was developed in this study. This study found that during the charging process, i) the lowest voltage point in the PEH was the negative of the forward voltage of the rectifier, and ii) the highest voltage point was limited to the voltage of the super-capacitor plus the forward voltage of the rectifier. The optimized charging condition was the key to increase energy storage efficiency.