Flexible Electret Transducer And Its Application For Self-powered Sensor And Low Frequency Energy Harvester

Sensors,as the terminal of the intelligent interconnection,have raised increasingly concerns in the era of Internet of Things?IOT?.Among them,wearable sensors own the advantages of portable,easy-to-use and high accuracy,will be of great help to human healthcare in the future.However,the drawback of batteries has restrained modern wearable electronics in many aspects.For instance,wearable electronics devices cannot be used when they are charging.As a result,building a self-powered system by electrostatic mechanical energy transducers and self-powered wearable sensor based on space-charge electret might be a solution.In this doctoral dissertation,we focus on improving the performance of flexible electret mechanical energy transducers,the performance of wearable sensors based on space-charge electret and electrostatic effects.We also developed new applications for space-charge electret.The main results of this doctoral dissertation include:1.We have theoretically studied the corona charging technology for space-charge electrets and discussed the main reason of the space-charge leakage in electrets.The output and stress/strain model for cellular piezoelectret was established.We also studied how the structrual parameters influence the performance of electret mechanical energy transducer.2.A cellular polypropylene piezoelectret film was fabricated from biaxially oriented polypropylene via corona charging and gas expansion method.The process of fabricating cellular polypropylene piezoelectret was studied and optimized,which enables the cellular polypropylene piezoelectret has gained large piezoelectric coefficient d₃₃ at²10 pC/N.The performance of cellular polypropylene piezoelectret maintains stable under 60 degree centigrade and cyclic test more than 9000 times.The cellular polypropylene piezoelectret was further fabricated as the self-powered wearable sensors for detecting human pulse and thorat vibration detection,which realized the preliminary application of cellular polypropylene piezoelectret in human health monitoring.3.A structual/performance controllable PFA piezoelectret was fabricated via hot press process.The open-circuit voltages of PFA piezoelectret under different structual parameters were discussed in detail.The non-linear stress-strain model for piezoelectret was established,which was verified by test results.The optimized PFA piezoelectret reach the sensitivity of15 V/kPa in the range of 0-2.5 kPa.The PFA piezoelectret was further fabricated as wearable sensors for monitoring human pulse,sound,respiration,runtastic speed,which demonstrates the fine application prospect of PFA piezoelectret in wearable human health monitoring.4.The structure of high performance electrostatic energy transducer based on electret was designed.The power density of a 2 mm thick,4×4 cm² FEP mutli-layer electrostatic energy transducer reached 2.5?W/cm² under the stimulation force of 5 N and the frequency of 5 Hz.The device also owns high stability?27000 cycles?.By virtue of the output characteristic of the FEP mutli-layer electrostatic energy transducer,we demonstrated a self-powered remote system in order to control a fan without using extra energy source.5.We have designed a structure for flexible mechanical energy transducer,which could maximum the space utilize effiency and owns large output performance.We have analyzed the working principle of this energy transducer and compare the output performance of this transducer with two other mentioned transducers.The transducer was fabricated by FEP and COC electret films with contain negative and positive space charges,respectively.The current output reached 1?A under the stimulation of 5 N,which would continue increase with the stimulation force.This research would have a profound effect on the design of flexible electret transducer under contain volume.