Design Dynamic Analysis and Power Measurement of a Bistable Piezoelectric Energy Harvester Driven by Finger Pressing

Abstract

Based on frequency up-conversion this study presents the design dynamic analysis fabrications and measurements of a bistable piezoelectric energy harvester (PEH) driven by finger pressing The energy harvester is composed of a bimorph piezoelectric beam two sliders six springs a push button and the housing The design forms a bistable potential field including two potential wells and a potential barrier The piezoelectric beam initially rested at one potential well moves in responding to the button press by finger overcomes the potential barrier accelerates to another potential well and then collides the housing at high velocity A transient vibration is excited due to the collision and then converted into electrical energy by piezoelectric effect The bistable potential field depends on the slider angles which is the key factor to be discussed in this study For the dynamic analysis the piezoelectric coupling coefficient d31 was corrected based on experiment The finite element software ANSYS was used to establish a transient dynamic model to evaluate the dynamic behavior and harvested power of the PEH For the prototype fabrication and measurement most parts were made by 3D printing except the piezoelectric beam and springs By considering issues of slider angle four prototypes were assembled with various slider angles of 15° 22 5° 30°and 37 5° As the finger pressed the button the voltage across a resistor connected with the PEH was generated and monitored by an oscilloscope By knowing the resistance and the voltage the generated power was calculated The measurements results showed that for both low resistance and high resistance the PEH can not deliver high power The maximum power occurs at an optimum resistance of 30 kΩ This optimum resistance is independent of the slider angle For slider angle being 15° 22 5° and 30° the maximum powers generated by the PEH were measured to be 1 8 mW、5 3 mW and 8 7 mW respectively under the optimum resistance For the case of the slider with the angle of 37 5° the PEH failed to complete the pressing due to the limitation of the spring compressed displacement The power measurements data were compared with numerical simulation by the finite element model Except for the case of slider with the angle of 15° showing some error due to the low power level the comparisons resulted in small errors of 1 89% and 0 33 % for the cases of 22 5° and 30° respectively It concluded that the finite element model developed by this study can predict the PEH power in a high accuracy In the final part of this study a full-wave rectifier was connected to the PEH to store the charges in a capacitance through ten successive presses The charges were released to form a current to light a LED During the discharging the instantaneous power was measured to be 1 35 mW

Date of Award	2020
Original language	English
Supervisor	Chung-De Chen (Supervisor)