Research On Technologies Of Harvesting Vibrational Energy By Miniature-piezoelectric Vibrator With Broad-band Response

Wireless sensor network (WSN) nodes are generally powered by batteries, and limited energy of battery is the key factor to influence the lifetime of WSN nodes. With the development of low-power integration circuit technology and power management technology, it is possible for using the energy scavenged directly from the ambient energy source to power this kind of device. Power supply by scavenging energy from environment can avoid changing batteries frequently and lengthen the lifetime of WSN. Harvesting vibration energy from environment is one of the fundamental modes for ambient energy harvesting technology. Increasing the bandwidth of resonance frequency and the efficiency of energy conversion and storage is very important for harvesting vibration energy from environment based on piezoelectric principle.In order to apply the energy harvesting to WSN, the mathematical expression of power output is deduced in this thesis, based on analyze of the static and dynamic model and the electrical equivalent model of the miniature-piezoelectric vibration energy generator. The selection of materials under different vibration condition and the effects of the structure parameters on performance are investigated based on the limitation of geometrical dimensions and admissible stress, the structural optimization design is developed with power output as the optimization objectives based on genetic algorithm. the finite element analysis tool is used to simulate the piezoelectric vibrator. In order to widen the frequency bandwidth of piezoelectric vibrator of generator, a two-degrees-of-freedom piezoelectric vibrator is designed, which can effectively increase the band of resonance frequency comparing with a single piezoelectric vibrator, and the parameters optimal method of the two-degrees-of-freedom piezoelectric vibrator is presented. Finally, according to the characteristic of the high output voltage of piezoelectric generator and the small eclectic current, the power conditioning circuit of piezoelectric transducer with low power consumption is designed which the output voltage can be regulated, and Pspiceis tool is used to simulate the power conditiong circuit, and the applicability of circuit is analyzed on basis of the simulation results.The simulation results demonstrate that the two-degrees-of-freedom piezoelectric vibrator can effectively increase the bandwidth of resonance frequency, and the higher conversion efficiency is obtained by the power conditioning circuit of piezoelectric transducer.