An Impact-based Broadband Low-frequency Vibration Energy Harvester And Its Applications

A vibration energy harvester has such advantages as small volume, maintenance free and long lives. The energy harvester is an ideal solution to power the wireless sensor network nodes. As the vibration energy in most natural environments is characterized by low-frequency, wideband and weak, it is siginificant to develop low-frequency and broadband energy harvesters.According to the requirements of the optimization of the impact-driven vibration energy harvester, a mathematical model of the impact-based vibration energy harvester with a ball was established and the effects of the environmental excitation and the structutural parameters on the output performance of the harvester was analyzed. The circuit of a self-powered wireless temperature and humidity sensor node was designed. A wireless sensor node was fabricated and tested. The main context includes:① The advance in vibration energy harvesting and frequency band expending methods was summarized and analyzed.② The lumped parameter model and the distributed parameter model of the cantilever was established. And the equations of the ball motion, the impact motion and output voltage of the cantilever were presented. With this, the mathematical model of the impact-based vibration energy harvester with a ball was obtained.③ Based on above model, the effects of the amplititude and frequency of the base excitation, the length of guiding channel and the diameter of stee l rolling mass on the output of the harvester were analyzed. A vibration energy harvester with relatively high scavenging efficiency for wideband and low frequency vibration energy from environments. The measured output power of a piezoelectric bimorph on an 130 kΩ resistor was 0.572 m W under a base acceleration with the amplitude of 9.8 m/s2 and frequency of 20.2 Hz, and the half power bandwidth was about 27.8% or 5.6 Hz.④ The circuit of power management for the harvester, the circuit for temperature and humidity detecting and wireless transmiting were designed. A self-powered wireless sensor node which consist of a detection circuit, a power management circuit and a vibration energy harvester was fabricated. The experimental results show that the wireless sensor node worked normally when the frequency of the base acceleration excitation with the amplitude of 1 g is between 7 Hz and 19 Hz. If two piezoelectric cantilevers were used to power the node, the minimum time interval for the node to measure and send out the temperature and humidity is about 34.2 s.