Piezoelectric circular diaphragm with mechanically induced pre-stress for energy harvesting

This paper presents the results of a piezoelectric circular diaphragm harvester utilising a unique measurement setup with tailored input force (walk profile), adjustable mechanical pre-stress, and simultaneous measurement of the harvested energy output and input force pressure. The harvester, incorporating the pre-stressing mechanism, consisted of a 191 mu m thick PZ-5A piezoelectric disc (empty set 34.5 mm) and a 100 mu m thick steel plate (empty set 45.5 mm). Its performance was measured with pressure cycles at a frequency of 0.96 Hz. Harvested energy was measured as a function of the pre-stressing state, the applied force, and the pressure profile. The optimal bending pre-stress was found to improve the efficiency of harvesting by similar to 141% compared to the case without pre-stress. The maximum obtained efficiency was 14.7%, and the maximum average power density of 6.06mW cm(-3) was measured for a unimorph diaphragm energy harvester. The results show that the pre-stressing technique is an effective method to improve the efficiency and generated power in this type of piezoelectric harvester, potentially enabling it to power different portable devices and sensors in future applications.