Flexible Electret Generator And Its Application For Self-Powered Pressure Sensor

With the rapid development of flexible and wearable electronics as well as continuous progress of internet of things,environmental and renewable energy has become the research hot spot.As there has much random vibration energy of ambient environment and human body,mechanical energy harvesting from the above energy sources in order to design self-powered sensors for wearable and intelligent electronic system is of essential importance.This dissertation focuses on the electromechanical energy conversion of electret generators,and systematical studies of how to improve the power output,new applications of electret materials,and the fabrication of high performance and self-powered pressure sensors are presented.The main results are as following:(1)Sandwiched composite fluorocarbon electret film has been fabricated via hot-pressing method.The open pores of fibrous polytetrafluoroethylene can be closed through preparing two compact fluorinated ethylene propylene films on both sides,which hinders the fast degradation along the fiber attenuation of corona charges.Meanwhile,more residual charges can be stored in the interfaces between FEP and f-PTFE,thus results in larger surface charge density,which provides a proper method for the output power improvement of electret generators.Theoretical analysis using Paschen's law,Gauss's law and Kirchhoff's second law has been carried out,revealing the physical essence of increased surface charge density of the composite film.Experiments of surface charge densities based on dense,fibrous,and composite electret materials are also performed to verify the correctness of the theoretical analysis.Furthermore,the output performances of the electret generator basing on the composite film are carefully characterized.In addition,a self-powered breathing monitoring sensor based on the composite electret generator is introduced,which extends its application in the field of wearable electronics.(2)An electret generator is designed using green and biodegradable materials,which comprises of transparent poly lactic acid electret,flexible nanofibers transparent paper substrate,and conductive polymer PEDOT:PSS electrode.All of materials used are environmental benign,and waste treatment can be directly buried into soil to return to nature,reducing the generation of electronic waste.Meanwhile,the device also has a good flexibility and mechanical strength,and the transmittance in the visible band is 81%.The device could be used to power paper-based electronics,demonstrating its potential applications in the field of transparent and intelligent packaging systems.Furthmore,the whole self-degradation process in the natural soil of the electret generator is demonstrated,indicating that the device is recycled and will not pollute the environment.(3)A cellular composite fluorocarbon polymer piezoelectret is fabricated via three-step hot-pressing method.By constructing micron-sized voids in the inner cell,and combinating with outstanding charge storage ability of the fluorocarbon electrets,tremendous piezoelectric activity and high performance piezoelectret pressure sensor can be realized.The flexible piezoelectret pressure sensor shows remarkable sensitivity(7380 pC/N)in the subtle-pressure regime(<1 kPa),fast response time(50 ms),very low limit of detection(5 Pa)as well as high stability(30 000 cycles).In addition,the device owns the capability for detecting human motions such as wrist stretching,cheek motion from open-bite-open,and eyes blinking.It can be also used for monitoring human physiological signals such as radial artery pulse wave,indicating its promising applications in artificial intelligence and mobile healthcare monitoring systems.