Broadband vibration energy harvesting for wireless sensor node power supply in train container

Wireless sensor nodes (WSNs) for temperature and humidity monitoring are commonly used in a cold chain logistics container. Energy harvesting technology is expected to realize the sustainable self-power supply for the WSN. Low amplitude and broadband vibration energy harvesting performance are the key points in train application. In this study, two piezoelectric vibration energy harvesters (PVEHs) are designed and simulated via COMSOL. Their low resonant frequencies and high electromechanical sensitivities are realized by big L-shaped mass blocks with different material densities. Their broadband vibration energy harvesting performance is achieved by the stopper and series connection. Experimental data are shown at an acceleration of 0.5 m/s²; PVEH-1 and PVEH-2 have maximum powers of 0.24 mW and 0.1 mW when excited at the resonant frequencies of 13.1 Hz and 18.8 Hz, respectively, and they both have the optimal load resistance of 40 kΩ. Two circuit design styles of two PVEHs, independent and series styles, are proposed for broadband vibration energy harvesting. Experimental results show that the series style has a wider operating frequency bandwidth and shorter charging time. Two PVEHs in series style can be effectively used for power supply of the temperature and humidity WSN in the broadband frequency range of 8.7-22.0 Hz above charging root mean square voltage of 5 V at the acceleration of 3.0 m/s². This scheme is promised to be applied to the cold chain logistics train container.