Multimodal MEMS vibration energy harvester with cascaded flexible and silicon beams for ultra-low frequency response

Abstract

Scavenging energy from ambient vibrations has become a promising energy supply for autonomous microsystems. However, restricted by device size, most MEMS vibration energy harvesters have much higher resonant frequencies than environmental vibrations, which reduces scavenged power and limits applicable scenarios. Herein, we propose a MEMS multimodal vibration energy harvester with specifically cascaded flexible PDMS and zigzag silicon beams to lower the resonant frequency to Hertz level and to broaden the bandwidth simultaneously. A two-stage architecture is designed, in which the primary subsystem consists of suspended PDMS beams characterized by low Young’s modulus, and the secondary system consists of zigzag silicon beams. We also propose the PDMS lift-off process to fabricate the suspended flexible beams, a compatible microfabrication method with high yield and good repeatability. The fabricated MEMS energy harvester can operate at ultra-low resonant frequencies of 3 Hz and 23 Hz, achieving maximum normalized voltage density of 200 V/cm3/g2 @ 3 Hz. The reasons for output power degradation in the low frequency range and the potential enhancement strategies are discussed. This work offers new insights for achieving MEMS scale energy harvesting with ultra-low frequency response.