Developing advanced techniques on modeling and system identification of piezoelectric energy harvesting systems

Ambient vibration is the most available and promising source of energy that can be converted into electrical energy through several techniques and be used for powering small electronic devices. The advantage of harvesting ambient vibration energy is the removal of external power sources like batteries with maintenance cost and chemical waste. Among the diverse methods for vibration-based energy harvesting, piezoelectric materials stand out for their impressive power density and adaptability in manufacturing across desired geometries and scales. Piezoelectric energy harvesters, also, enable the researchers to develop self-powered devices and systems, such as structural health monitoring of 2D components in marine, aerospace, and automotive structures. Vibration-based piezoelectric energy harvesting consists of a piezoelectric transducer structurally coupled with a vibrating host structure which provides kinetic energy to be converted into electrical energy. A harvesting circuit is also connected electrically to the piezoelectric for regulating the harvested electrical energy. The vibrating host structure has been extensively studied for beams with variable cross sections and several shapes. Plate structures, as an alternative to beams, are more suitable for piezoelectric energy harvesting not only because of their availability in practical applications but also because of capability of providing broadband energy harvesting. On the other hand, advanced electrical circuits have been introduced to provide stable electrical power flow i.e., DC power output, and improve the efficiency of the energy harvesting system. However, the research in the mechanical part overlooked the use of advanced harvesting circuits and also the studies in the electrical part is limited to simple vibrating structures considering only one vibration mode of structure as an equivalent mass-stiffness-damper system. Therefore, this thesis is dedicated to bridge the research gap between the electrical advancements and mechanical studies on piezoelectric energy harvesting. The first part of this work focuses on developing an analytical model for multi-modal piezoelectric energy harvesting on a thin plate structure integrated with an advanced harvesting circuit i.e., synchronized switch harvesting on inductor (SSHI). The analytical solution is developed based on an equivalent impedance approach to predict the steady-state electrical response of the harvester as a closed-form solution. The experiments are conducted to validate the analytical solution for the system's first and second vibration modes. The energy harvesting performance of the SSHI circuit is compared against the standard rectifier, showing 183% and 134% power output enhancement for the first and second vibration modes, respectively. Additionally, the experimental results reveal that integration of SSHI to a plate-like harvester introduces a multi-switching behavior rather than a standard single-switching behavior due to the multimodal vibrational characteristics of the plate. Equivalent circuit modeling (ECM) is a useful tool for piezoelectric energy harvesters to analyze the electromechanical response of the system especially when complex host structure geometries and nonlinear circuits are used in the harvesting systems. At the second part of the thesis, we present an experimental admittance-based system identification method that allows us to identify the multi-modal ECM without prior knowledge of the host plate's geometry and/or physical properties of the piezoelectric patches. Using the proposed experimental method, we obtain the electromechanical frequency-response admittance of the PEH system at each vibration mode, and thereby, we calculate the equivalent system parameters. Additionally, a novel experimental technique is presented for the identification of the equivalent voltage sources associated with each LCR branch of the ECM. The derived ECM is experimentally validated for single and multiple piezoelectric patch harvesters on a plate. The electrical frequency response of the system has been validated for standard AC and rectifier circuits using SPICE software. Overall, the proposed admittance-based system identification is an accurate and robust method to identify the equivalent system parameters, making it a practical and reliable tool for modeling piezoelectric energy harvesting systems.