Research On Fluid-coupled Piezoelectric Energy Harvester

With the rapid development of microelectronics technology and wirelesstechnology, wireless sensors are widely used in many application areas. The mostlyused in energy supplication are traditional chemical batteries. As the problems ofchemical battery are increasingly prominent, such as short lifetime, requires periodicreplacement, large volume, difficult in recycling, environmental pollution, etc, it’sparticularly essential to pursue new method of energy supplication. Piezoelectric powergeneration, based on piezoelectric effect and can convert kinetic energy to electricenergy, is becoming a research hotspot for the reasons as follows: it can produce ahigher voltage, can directly supply energy to electronic devices, has simple structurewhich is easy in manufacturing, integration and miniaturization, and can adapt torelatively harsh environment. The convention effectiveness is better when the resonanceis achieved as the resonance frequency of the piezoelectric power generating device isclose to the external excitation frequency. However, the frequency of the environment isnot fixed generally, so it becomes particularly important designing the structureappropriately to change its resonant frequency to match the changing-frequencies of theenvironment. This paper presents a method of changing the natural frequency of thepiezoelectric energy harvester by changing the immersing depth ratio of in liquid. Inthat way, good results are achieved in certain broad frequency ranges.Firstly, the vibration model of piezoelectric cantilever beam is established, theparameters of influencing generation power are analysised. The natural frequency ofpiezoelectric energy harvester in vacuum and fluid are separately built. Treat thedifference between the two frequencies as frequency adjusting range, differentparameters influencing the frequency adjusting range are investigated using numericalmethod.Then the simulation analysis of piezoelectric energy harvester in the2differentkinds of medium is performed using the finite element analysis software ANSYS. Themodal analysis is conducted and natural frequencies are obtained of different situationin depth ratio. Comparison is made between the simulation and the numerical results toverifying the theoretical analysis. The energy harvesting properties of different depthratio are simulated mainly including the following aspects: open-circuit characteristic,internal impedance characteristic, optimal power, bandwidth and quality factor, etc. Theinfluence of structural parameters on power generation capacity is also investigated.Finally, the experimental system is established to validate the theoretical and thesimulation results. The resonant frequencies of different depth ratio are obtained andverification is made between experimental results, theoretical and the simulation results.The attenuation curve is recorded right after excitation through oscilloscope, and the damping ration of different cases are calculated. As with the simulation analysis, theenergy harvesting properties are obtained. And the influence of structural parameters onpower generation capacity is validated.