Flexible Piezoelectric Thin Films And Acoustic-electric Sensing And Energy Conversion Devices

With the explosive development of information science,Internet of Things（Io T）and wearable electronics flexible devices drew significant attentions.Compared with the traditional touch interface,the voice interface based on speech recognition can help the users to communicate with devices more intuitively,and the acoustic-electric conversion device is the key of the whole system.In this case,researchers are working on high-sensitivity,self-powered and flexible acoustic-electric conversion device.In this thesis,poly（vinylidene fluoride）（PVDF）and lead zirconate titanate(Pb(Zr_0.52Ti_0.48)O₃,PZT)piezoelectric materials,incorporated on flexible silicone-based membrane（PDMS）are investigated.On basis of the above,different types of acoustic-electric sensing and energy conversion devices have been developed.Their performances are characterized,and the practical application of the device in acoustic sensing and acoustic energy harvesting are evaluated.Main results of our study are as follows:1.In order to improve the electrical output of the device,mechanical clamping structure and the mechanical free structure are designed,and their frequency responses,signal output and vibration performance are comprehensively studied.Data filtering have been carried out to reduce the noise of the output signal to improve data accuracy.Since mechanical free structure exhibits better output performance,structure stability and convenience in assembly,subsequent experiments are carried out based on mechanical free structure.2.High performance PVDF film is prepared by solution casting method,after integration on flexible PDMS substrate,flexible acoustic-electric conversion device is obtained.The best response bandwidth of the device is 0-600 Hz,and the best response sound pressure level（SPL）is 55-115 d B.Under a 115 d B SPL,the device shows maximum sensitivity of 1029.9 m V/Pa at140 Hz.Under the 140 Hz sound incentive,device exhibits a maximum sensitivity of 3960m V/Pa（aiming to the SPL of 90 d B）.The horizontal distance limit during detection is 25 cm,and the detection limit in the vertical direction is 6 cm.The minimum frequency resolution gap of the device is 0.5 Hz.In this research,the performances in speech recognition and music recording of the device are also demonstrated.As for the acoustic energy harvesting performance,under the excitation frequency of 140 Hz and SPL of 115 d B,the device exhibits an open-circuit voltage of 11.5 V and a short-circuit current of 16μA.The maximum instantaneous output power is found to be 11.3μW.Consequently,the energy harvester can directly power three commercial LED bulbs without external electrical suppliers.Electronic clock can operate for short periods powered by acoustic harvester with rectifiers and capacitors.3.PZT thin films are successfully prepared on Mica substrates by the sol-gel method.After being integrated on flexible PDMS,the acoustic sensing application using PZT thin films grown on Mica is realized for the first time to the best of our knowledge.The best response bandwidth of the device is 0-500 Hz,and the best response SPL is 55-115 d B.Under the SPL of 115 d B,the device shows a maximum sensitivity of 702.04 m V/Pa at 140 Hz.Under the 140Hz sound incentive,device exhibits maximum sensitivity of 3451.6 m V/Pa（aiming to the SPL of 90 d B）.The detection distance limit in the horizontal and vertical direction is 6 cm and 3 cm,respectively.In this thesis,the application of flexible piezoelectric thin film in acoustic-electric sensing and energy conversion is systematically studied,which is expected to provide new strategy for the development and innovation of acoustic-electric sensing and energy conversion devices.