T-Shaped Piezoelectric Structure for High-Performance MEMS Vibration Energy Harvesting

In the recent decades energy harvesting from ambient vibration by the micro-electromechanical systems (MEMS) has been recognized as a promising solution to boosting lifespan of low-power electronic devices. Apparently, highly efficient MEMS vibration harvesters with lower operational frequencies are advantageous. In this paper we propose a new mechanical structure to aim for energy conversion efficiency enhancement and operational frequency reduction for the piezoelectric MEMS vibration energy harvesters. The proposed structure has a T-shaped geometry with integration of two identical proof masses at the T-segment. Thanks to two degrees-of-freedom, in this structure both bending and torsional mode frequencies can be located close to each other. Its analytic model of frequency response is derived and then validated by finite element modeling (FEM) simulations and prototype measurements. Compared to the conventional straight cantilever configuration, our proposed T-shaped piezoelectric cantilever structure can help distribute mechanical strain in broader areas with higher magnitude and lower resonant frequency. Our analytical, numerical, and experimental studies show that the normalized power density of the proposed T-shaped harvester is 4.8 times higher than that of the conventional one, in addition to 36% resonant frequency reduction.