Abstract： This paper proposes a MEMS piezoelectric energy harvesting system (PEHS) working with the impact-based frequency up-conversion mechanism. By using this mechanism, the problem that the natural frequency of the piezoelectric cantilever does not match the external excitation frequency is solved and the efficiency of energy harvesting is improved. The PEHS mainly consists of a low frequency stainless-steel cantilever with resonant frequency of 25 Hz and a high frequency piezoelectric cantilever with resonant frequency of 935 Hz. These two cantilevers are placed in parallel. The conversion of low frequency environmental vibration to high frequency piezoelectric beam vibration is realized through the collision between the bottom stainless-steel cantilever and the top piezoelectric cantilever. During one collision cycle, the bottom stainless-steel cantilever is firstly triggered to resonate under the external low frequency vibration excitation, then the stainless-steel cantilever collides with the top piezoelectric cantilever and they move upwards together. The models of an energy harvesting system in which a low frequency driving cantilever impacts a high frequency generating cantilever are established and discussed. The output performances of the single piezoelectric cantilever at different accelerations and the output performances of the PEHS under different initial distances are tested. Experimental results demonstrate that under the external vibration of 935 Hz, the maximum output voltage of the single piezoelectric cantilever is 74 mV and the maximum output power is calculated to be 0.11 μW at 1.0 g acceleration. While the maximum open-circuit output voltage of the PEHS can be 1220 mV at a relatively low excitation frequency of 25 Hz, the operating bandwidth of the PEHS is widened to 4.7 Hz and the maximum output power is calculated to be 8.6 μW at an acceleration of 1.0 g. It indicates that the impact-based frequency up-conversion mechanism can effectively reduce the operating frequency, widen the operating bandwidth and improve the vibration energy harvesting efficiency of the PVEH under low frequency and low acceleration vibration environment.
2019, Vol. 40 
