High-performance Nonlinear Piezoelectric Energy Harvesting in Compressive Mode

With the rapid development of low-power electronic devices such as wireless sensor networks, wearable devices and medical implants, the need for long-lifespan and high-efficiency power sources has become more and more pressing. The commonly used electrochemical batteries cannot meet the demand due to their limited capacity, low energy density, and maintenance and disposal requirements, which has spurred interest in the vibration energy harvesting technique. Over the past decade, many endeavors have been undertaken to improve the performance of energy harvesters, especially those using piezoelectric materials. Piezoelectric energy harvesters (PEHs) however, are still in the laboratory stage and cannot be widely deployed in practice. The main blocking factors stem from their low power output and poor environmental adaptability. This thesis aims to explore new methods to improve energy harvester performance in terms of power output, frequency bandwidth and directional sensitivity. Specifically, by taking advantage of the nonlinear dynamics of thin beams and the compressive mode of piezoceramics, a high-performance compressive-mode piezoelectric energy harvester (HC-PEH) is proposed. A multi-stage force amplification mechanism is embedded into the coupling system, which significantly increases the voltage responses. Finite element analysis and analytical modeling are conducted to analyze the stress state, the force amplification effect and the nonlinear characteristics of the system. Prototypes are fabricated and tested . The experimental data, closely matched with the analytical estimations, demonstrates great performance enhancement. The bandwidth is effectively extended by the strong nonlinear responses. A maximum power 54.7 mW is generated under an acceleration of 4.9 m/s^2, which is about one order of magnitude higher than the state of the art. Furthermore, this study proposes a simple method to enhance the tailorability of energy harvesters by shifting the dynamic responses between the hardening and softening nonlinearity. To deal with the unidirectional sensitivity issue, a multi-directional compressive-mode piezoelectric energy harvester (MC-PEH) is developed. Theoretical and experimental studies demonstrate that the MC-PEH is capable of isotropically harnessing vibration energy from multiple directions. Apart from the structural aspect, new piezoelectric materials (PMN-PT PZN-PT) and interface circuits (SSHI) have also been investigated to improve the efficiency of whole energy harvesting systems.Ph.D