Design And Application Of Flexible Piezoelectric Nanogenerator

Mechanical energy in the environment has many advantages,such as extensive distribution,diverse forms of expression,easy conversion,etc..The piezoelectric nanogenerators(NGs)could collect environmental mechanical energy and provide continuous energy for electronics,which has been widely applied in various fields of our life.With the expansion of the application fields,the demand for the development of piezoelectric NG is increasing.Especially in today's continuous innovation and development of stretchable and wearable electronics,it is of great significance and practical value to study piezoelectric NGs with flexible characteristics.However,the flexible NGs have some problems to be overcome: for example,low output performance,tensile orientation,easy stratification,loss of rigid lead and high cost.This thesis focuses on the researches about the material fabrication and structure design of flexible piezoelectric NGs.We have achieved the mechanism analysis of flexible piezoelectric transducer,simulation model construction,structure optimization and application expansion.The purpose of this study is to explore the variation of polarization strength of composite materials caused by the offset of the ferroelectric domains orientation of piezoelectric particles under the tensile and release excitation.Meanwhile,the piezoelectric material with high output performance and the electrode material with high conductivity are prepared in order to realize a multi-diretional stretchable piezoelectric transducer.Consequently,this research can lay a foundation for portable electronic device power supply and human motion mechanical energy collection.The main contents are described as follows:(1)A fabrication method of flexible piezoelectric NG with double arched structure is presented.In the whole device,the upper arched layer is the poly(vinylidene fluoride)(PVDF)film with designed optimum size;the lower arched layer is the PDMS film with the uniform trapezoid body micro-structures by MEMS process and mold process.The upper arched layer and the lower arched layer are connected in parallel by using a shared electrode,which can increase the charge amount of the middle shared electrode,thus improving electrical output performance of the piezoelectric unit.The piezoelectric layer of the double arched structure is used as the sensitive element of the sensor exhibiting the sensitivity of 2.21V/g and the linearity error of 5.91% under the vibration amplitude of 6mm.Furthermore,the test results show that the flexible piezoelectric NG based on double arched structure possesses stable output,heat –resistant,waterproof,and long lifetime,which can be usesd a sustainable energy supply and a self-powered vibration sensor applied in the wearable devices and flexible sensing systems.(2)An all-in-one no-wire stretchable piezoelectric NG is developed.The stretchable piezoelectric NG is composed of piezoelectric particles with 85wt% dispersed in silicone rubber as the stretchable piezoelectric layer and silver-coated glass microspheres with 75wt% dispersed in silicone rubber as the stretchable electrode layer.Because of the crosslinking property of the silicone rubber,the piezoelectric layer and the electrode layer can be completely integrated into one piece.Meanwhile,it is worth noting that the electrode layer offers remarkable abrasion and tear resistance,which can be used directly without any external encapsulation,successfully avoiding the mechanical coupling between whires and electrodes.The stretchable piezoelectric NG exhibits excellent output performances(Voc?34V,Isc?1?A)at the tensile strain of 50%,and can scavenge various dynamic deformations(e.g.,clusterled,folded,twisted).Therefore the device can be used as a power supply for commercial electronic equipments(such as LED light,LCD,electronic watch,etc.).In addition,the stretchable piezoelectric NG exhibits remarkable reliability and long lifetime under the uninterrupted stretching and releasing processes,which can be acted as stretchable intelligent energy-harvesting cloth to collect human limbs with varying degree of freedom mechanical energy,or also can be acted as self-powered sensor placing in stretchable fitness equipment to monitor dynamic tensile force.(3)In the above composite piezoelectric layer,the metal branch fibers are used to improve the output performances to form an energy conversion device with excellent tensile and electrical output property.The metal branch fibers(20g)/piezoelectric particle(130g)stretchable piezoelectric NG shows that the open-circuit output voltage peak-peak is about 61 V and the short-circuit output current peak-peak is about 1.11?A at the tensile strain of 50%.The device could be used as a portable power supply to directly drive five green light-emitting diodes in the stretching and releasing processes,or be stored in a capacitor for 800 s to dvire a digital thermometer.Furthermore,it could also be worn on the human body joints to accurately distinguish bending angles and bending frequencies.The detection method should be widely applied in the fields of artificial intelligence robot,activity trace and human health care.(4)In order to further promote the electrical output performances of the stretchable piezoelectric NG,a new smart textile with arched array structure is put forward,which can be used as a stretchable energy collecting device to collect mechanical energy for human limb movements.The output powers of the smart textile are about 402.8?W and 55.8?W under the contact-separate mode and stretch-release mode,respectively.It is worth noting that the output performance of the energy harvester increases by 33.9% in comparision with metal branch fiber/piezoelectric particle stretchable piezoelectric NG.In addition,the enhanced strechable piezoelectric NG based on arched array structure has multi-directional stretchable feature,which could be placed directly on the human body's joints.Consequently,this is able to replace the human body uncomfortability of the traditional flexible smart clothing due to the lacke of stretchable property,so as to achieve the high-efficiency acquisition for mechanical energy of human limbs.