A study of linear piezoelectric vibration energy harvesting technique and its optimisation

The study is conducted to address the research questions proposed from the existing research gaps through literature review. Firstly, a study of single degree-of-freedom piezoelectric vibration energy harvesting model is carried out to provide a basic guideline for further two degree-of-freedom and multiple degree-of-freedom piezoelectric vibration energy harvester study. It is found that the harvested power of the single degree-of-freedom piezoelectric vibration energy harvester is limited by the mass and damping of the harvesting system, and the external excitation amplitude. The harvested power limit is independent from the properties of piezoelectric materials.

The study of single degree-od-freedom piezoelectric vibration energy harvester connected with four different energy extraction and storage circuits is performed. Both the harvested resonant power and the energy harvesting efficiency have been normalised as functions of dimensionless variables and compared for the harvester with the four different circuits. Furthermore, the two degree-of-freedom and generalization of multiple degree-of-freedom piezoelectric vibration energy harvesting models are studied. A hybrid of the time and frequency domain analysis methods is developed and to provide the tunning strategy for optimization of harvesting performance and harvesting frequency bandwidth. The effect of the coupling coefficient between the electrical system and mechanical system has been discussed and analysed, especially in that case of the harvesting system connected with multiple electrical interface circuit systems which are not studied in previous literatures.

The results from the analysis method have been validated by the simulation (Matlab Simulink) and the results obtained from experimental tests. An enhanced piezoelectric vibration energy harvesting system is then developed and studied. It is believed that the enhanced piezoelectric vibration energy harvesting model can scavenge 9.78 times more energy than that of the conventional system. It is also found out that the harvesting resonant frequency can be lowered by increasing the number of degree-of-freedom of piezoelectric vibration energy harvester without increasing the total mass of the system. Finally, the parameter uncertainty has been investigated by the Monte Carlo Simulation on the single degree-of-freedom piezoelectric vibration energy harvester, two degree-of-freedom piezoelectric vibration energy harvester and the enhanced two degree-of-freedom piezoelectric vibration energy harvester.