| Owing to the great reduction on power consumption of integrated circuits (ICs) and miniaturization during the past decades, the energy harvesting technique has gained much interest recently with the inspiration that more devices in wireless sensor networks as well as mobile electronics could power themselves by scavenging the ambient energy in different forms. Piezoelectric energy harvesting (PEH) is one of the most widely studied techniques to scavenge energy from ambient vibration sources. With the electromechanical nature, a PEH device can be divided into mechanical and electrical parts. The two parts are linked by the piezoelectric transducer. Literatures on PEH are reviewed and discussed. In the research of PEH, generally there are four different research foci on: mechanical part, electrical part, piezoelectric transduction, and system.;This thesis provides new insight into the research of piezoelectric energy harvesting from some systematic viewpoints. The modeling process of a single degree-of-freedom (SDOF) PEH system is firstly discussed. It shows how the model of a PEH device is built from the material level to element level, and then to device level. In the systematic analysis to PEH devices, the energy flow and impedance based analysis are highlighted. A detailed analysis on the energy flow within the PEH system provides good understanding on the system. However, up to now, most of the researches on PEH have been mainly concerned with the absolute amount of energy that can be harvested from vibrating structures; the detailed energy flow within the system as well as its effect on the vibrating structure, were seldom discussed. By studying the energy flow within three applications of standard energy harvesting (SEH), resistive shunt damping (RSD), and synchronized switching harvesting on inductor (SSHI), it can be concluded that, in a PEH system, the two functions of energy harvesting and dissipation are coexistent. Both of them bring out structural damping. New factors are defined to give a more comprehensive evaluation on the energy flow in PEH systems.;To enhance the harvesting power by using the impedance matching is not new; yet, previous literatures on impedance matching for PEH oversimplified the problem. Without clarification on the energy flow in the PEH system, their objectives on power optimization were ambiguous. Some literatures even assumed that the harvesting interfaces, which are nonlinear in nature, can be equalized to linear loads, and the load impedance can be arbitrarily set. With the understanding on energy flow within piezoelectric devices, we clarify the objective of impedance matching, and further demonstrate that the range of equivalent impedance of existing harvesting interfaces is in fact constrained, rather than unlimited. The analyses on system level provide guideline to improve the harvesting performances. Improvements can be made with innovative designs in either mechanical configuration, piezoelectric transducer, or interface circuit.;Besides system level analyses, some implementation issues on switching interface circuits are also investigated. These interfaces show a great potential on harvesting efficiency improvement. Based on the experimental observation, it is found that there is a voltage reversion after every inversion in SSHI, which weakens the harvesting performance. This influence is caused by the dielectric loss in piezoelectric material. A revised model as well as detailed analysis are proposed to evaluate the influence of dielectric loss over the harvesting power degradation.;Considering the practical implementation, a modified self-powered switching interface circuit is proposed. It can achieve better isolation among components and involve less dissipative components. Improved analysis on this self-powered switching interface circuit is also provided. It is shown that the higher the excitation level, the more beneficial for replacing the SEH interface with the self-powered switching interface; meanwhile, the closer between the performances of self-powered and ideal (external powered) switching interfaces. |
