Ultra-low resonant piezoelectric MEMS energy harvester with high power density

We demonstrate a microscale vibration energy harvester exhibiting an ultra-low resonance frequency and high power density. A spiral shaped microelectromechanical system (MEMS) energy harvester was designed to harvest ambient vibrations at a low frequency (<200 Hz) and acceleration (<0.25 g). High quality Pb(Zr_0.48Ti_0.52)O₃ (PZT) film with 1.8 µm-thickness exhibiting remanent polarization of 36.2 µC/cm² and longitudinal piezoelectric constant of 155 pm/V was synthesized to achieve high efficiency mechanical to electrical conversion. The experimental results demonstrate an ultra-low natural frequency of 48 Hz for MEMS harvester. This is one of the lowest resonance frequency reported for the piezoelectric MEMS energy harvester. Further, the position of the natural frequency was controlled by modulating the number of spiral turns and weight of the proof mass. The vibration mode shape and stress distribution were validated through a finite element analysis. The maximum output power of 23.3 nW was obtained from the five turns spiral MEMS energy harvester excited at 0.25 g acceleration and 68Hz. The normalized area and the volumetric energy density were measured to be 5.04 × 10⁻⁴ µW/mm² · g² · Hz and 4.92 × 10⁻² µW/mm³ · g² · Hz, respectively.