*Article* **A Low-Frequency MEMS Piezoelectric Energy Harvesting System Based on Frequency Up-Conversion Mechanism**

**Manjuan Huang 1, Cheng Hou 1, Yunfei Li 1, Huicong Liu 1,\*, Fengxia Wang 1,\*, Tao Chen 1, Zhan Yang 1, Gang Tang 2 and Lining Sun 1**


Received: 22 August 2019; Accepted: 20 September 2019; Published: 24 September 2019

**Abstract:** This paper proposes an impact-based micro piezoelectric energy harvesting system (PEHS) working with the frequency up-conversion mechanism. The PEHS consists of a high-frequency straight piezoelectric cantilever (SPC), a low-frequency S-shaped stainless-steel cantilever (SSC), and supporting frames. During the vibration, the frequency up-conversion behavior is realized through the impact between the bottom low-frequency cantilever and the top high-frequency cantilever. The SPC used in the system is fabricated using a new micro electromechanical system (MEMS) fabrication process for a piezoelectric thick film on silicon substrate. The output performances of the single SPC and the PEHS under different excitation accelerations are tested. In the experiment, the normalized power density of the PEHS is 0.216 <sup>μ</sup>W·g<sup>−</sup>1·Hz−1·cm<sup>−</sup><sup>3</sup> at 0.3 g acceleration, which is 34 times higher than that of the SPC at the same acceleration level of 0.3 g. The PEHS can improve the output power under the low frequency and low acceleration scenario.

**Keywords:** MEMS; piezoelectric vibration energy harvester; frequency up-conversion mechanism; impact; PZT thick film
