Structural And Circuit Design Of Cantilever Based Piezoelectric Energy Harvester

As the rapid development of Micro-Electro-Mechanical System and high integration digital equipment,the sensor with small volume,low consumption and low cost can be implemented and spread quickly.And the traditional chemical battery used in this sensor has short life,large volume,low reliability and the other fatal problems.So the piezoelectric energy harvester which can directly capture energy from the environment vibration becomes a research hotspot in recent years.In this paper,the piezoelectric energy harvester is divided into three units,including piezoelectric unit,energy harvesting circuit unit and energy storage unit.And those three units are studied from the theoretical calculation,the simulation analysis and the experiment test.In consideration of theoretical relationship between output characteristic and structure parameters of the piezoelectric unit,the structure of piezoelectric unit can be optimization designed from the thickness of the piezoelectric layer and the surface shapes of the cantilever beam.Then,from the perspective of piezoelectric material fatigue,the theoretical relationship between piezoelectric material fatigue and amplitude of piezoelectric unit can be analyzed,which can further optimization design the reliability of the piezoelectric unit structure.The energy harvesting circuit,of which the commutating and voltage-stabilizing function can make the output of piezoelectric unit charge the energy storage unit and supply the MEMS sensor,is a very important component unit of the piezoelectric energy harvester.The energy harvesting circuit based on LTC3588 chip,designed in this paper,can realize high efficient commutating and output stable DC voltage.In terms of energy storage unit,the charging features of the super capacitor and lithium ion battery are contrast analyzed.And the piezoelectric energy harvester model machine is used to charge them respectively.Finally,the experiment that uses the piezoelectric energy harvester model machine to supply the low-cost Bluetooth is also designed in this paper,which can verify the feasibility of the piezoelectric energy harvester.The conclusions are as follows:In the terms of structure design,there are two optimal thickness of the piezoelectric layer,one of it makes piezoelectric unit output maximum voltage,and the other one makes piezoelectric unit output maximum power;when the surface shape of cantilever beam is triangle,the output voltage is largest,and the gradient of the trapezoidal beam is greater the output voltage is larger;the critical amplitude of piezoelectric material fatigue crack extension equals equivalent amplitude of 1.5 times the coercive electric field,and the amplitude of piezoelectric unit is greater the speed of fatigue crack extension is faster.In the other terms of circuit design,the energy harvesting circuit based on LTC3588 chip can output stable DC voltage,which is verified by the experiment;the super capacitor can charge to 95% after 100 minutes,while the lithium ion batteries need more than three hours;the piezoelectric energy harvester model machine makes low-cost Bluetooth working time extending,which proved that the piezoelectric energy harvester has a practical value.