Soft and Hard Piezoelectric Ceramics and Single Crystals for Random Vibration Energy Harvesting

Vibration-based energy harvesting for enabling next-generation self-powered devices is a rapidly growing research area. In real-world applications, the ambient vibrational energy is often available in non-deterministic forms rather than the extensively studied deterministic scenarios, such as simple harmonic excitation. It is of interest to choose the best piezoelectric material for a given random excitation. Here, performance comparisons of various soft and hard piezoelectric ceramics and single crystals are presented for electrical power generation under band-limited off-resonance and wideband random vibration energy-harvesting scenarios. For low-frequency off-resonance excitation, it is found that soft piezoelectric ceramics based upon lead zirconate titanate (e.g., PZT-5H and PZT-5A) outperform their hard counterparts (e.g., PZT-4 and PZT-8), and likewise soft single crystals based upon lead magnesium niobate and lead titanate as well as PZT (e.g., PMN-PT and PMN-PZT) outperform the relatively hard ones (e.g., manganese-doped PMN-PZT-Mn). Overall, for such off-resonance random vibrations, PMN-PT is the most suitable choice among the materials studied. For wideband random excitation with a bandwidth covering the fundamental resonance of the harvester, hard piezoelectric ceramics offer larger power output compared to soft ceramics, and likewise hard single crystals produce larger power compared to their soft counterparts. Remarkably, a hard piezoelectric ceramic (e.g., PZT-8) can outperform a soft single crystal (e.g., PMN-PT) for wideband random vibration energy harvesting.