Design of a piezoelectric–electromagnetic hybrid vibration energy harvester operating under ultra-low frequency excitation

In this paper, we proposed a novel piezoelectric-electromagnetic hybrid vibration energy harvester (HVEH). The HVEH has a unique structure, which enables it to work in an ultra-low frequency environment. An amplification structure amplifies the input displacement, increasing the displacement distance of the magnets. The motion of the magnets causes the frequency up-conversion of the piezoelectric cantilever beam. As the magnets move back and forth, the piezoelectric vibration energy harvester (PVEH) generates a stable output energy. A closed magnetic circuit is designed for electromagnetic vibration energy harvester (EVEH) with a pair of magnets and a soft magnetic core. The pair of magnets with opposite polarities changes the direction of magnetic flux in the coil by 180°, resulting the EVEH to harvest more energy. The combination of piezoelectric and electromagnetic energy harvesters makes the energy harvester obtain higher output energy. The experimental results show that, in the cycle experiments with a frequency of 5 Hz, the maximum peak-to-peak open-circuit voltage of the PVEH and the EVEH is 40.39 V and 36.87 V, respectively. The optimal load resistance and the maximum output power of the PVEH are 398.7 kΩ and 87.9 μW, while the EVEH’s are 3.2 kΩ and 2.173 mW, respectively. In addition, the charging characteristics of the HVEH through a 3300 uF capacitor indicated that the voltage growth of the HVEH is faster than that of the single energy harvester at the same time. The experimental results demonstrate great potential of the proposed energy harvester in various applications.