PZT/MFC Based Piezoelectric Flexible Pressure Sensor Development And Wearable Application Research

Flexible pressure sensors are the most important components of wearable electronics,which can convert external pressure into electrical signals and are used for monitoring human movement and physiological signals.Among them,piezoelectric nanogenerator(PENG),as a special kind of flexible pressure sensor,shows great development potential as a sensing element for next-generation wearable electronic devices,and meeting the requirements of high flexibility,good mechanical strength and high sensitivity of wearable devices.In order to achieve similar high piezoelectric performance as rigid piezoelectric ceramic materials while meeting the flexible requirements of wearable electronic devices,microfibrillated cellulose(MFC)was introduced as the matrix phase for the first time in this subject to develop piezoelectric flexible pressure sensors,the contents of the research are as follows:Ⅰ.Lead zirconate titanate(PZT)piezoelectric particles were dispersed in MFC matrix,and high mechanical performance of PZT/MFC piezoelectric composite films were prepared by solution blending method,characterized microscopic morphology,and tested mechanical,electrical and output performance.The results showed that the compatibility of PZT piezoelectric particles with MFC was enhanced and the longitudinal distribution density was increased;the tensile strength of the piezoelectric composite film was 60 MPa and the piezoelectric constant was 27 p C/N;under a stress of 30 k Pa,the PZT/MFC piezoelectric flexible pressure sensor had an open-circuit voltage of 6.5 V,a short-circuit current of 0.56 μA,an output power of 1.02 μW at a load resistance of 7 MΩ,and a sensitivity of 0.21 V/k Pa.Ⅱ.MFC@PVA composites were prepared using MFC modified polyvinyl alcohol(PVA)to optimize the piezoelectric potential distribution and polarization electric field distribution of PZT/MFC two-phase composites.The results showed that MFC reacted with the hydroxyl groups on the molecular chain of PVA to form a hydrogen bonding network structure,the interface between the two phases was blurred,PVA filled the defects and cracks inside MFC,and MFC promoted the crystallization of PVA.The content of 50% MFC could increase the elastic modulus of pure PVA by 63 times,yield strength by 318%,elongation at break reduced to 1/7 of the original;conductivity by 768 times,relative dielectric constant by 154%;glass transition temperature by 14.2 ℃,and crosslink density by 1.5 times.Ⅲ.MFC@PVA composites were used as the matrix phase and PZT as the piezoelectric phase to prepare PZT/MFC@PVA piezoelectric composites with high flexibility and output performance.In the piezoelectric composites,the three materials PZT,MFC and PVA were highly compatible,and the PZT piezoelectric particles existed in a calcium titanite structure;the elastic modulus of the piezoelectric composite film was 789 MPa,the tensile strength was41.9 MPa,the elongation at break was 7.4%,and the piezoelectric constant was 40.3 p C/N.Under a stress of 40 k Pa,the PZT/MFC@PVA piezoelectric flexible pressure sensor had an open-circuit voltage of 16.2 V,a short-circuit current of 0.87 μA,an output power of 3.37 μW at a load resistance of 10 MΩ,and a sensitivity of 0.4093 V/k Pa.Ⅳ.The above-mentioned piezoelectric flexible pressure sensor was studied for practical application,the high mechanical performance PZT/MFC piezoelectric pressure sensor was used for plantar pressure monitoring,and the test results showed that the sensor could distinguish the motion state and identify the stress concentration area on the plantar surface of the foot,and the human plantar pressure range was between 33-47 k Pa,and the maximum pressure area was located in the first metatarsal region.The highly sensitive PZT/MFC@PVA piezoelectric pressure sensor was used for dynamic stress monitoring of facial and thoracic muscle groups,and the frequency and peak of the output waveform characterized the amplitude and number of muscle activities,sensing small muscle spasms of about 500 Pa with a response time of 54 ms.In conclusion,MFC was used as the matrix phase of piezoelectric composites in this subject.The hydrophilic,three-dimensional mesh structure and high mechanical properties of MFC solved the problems of uneven dispersion,poor compatibility and poor mechanical properties of piezoelectric composites.MFC was used to modify PVA to construct PZT/MFC@PVA piezoelectric composites.The application study of the piezoelectric flexible pressure sensor showed that the sensor could be used for the detection of pressure sores in diabetic complications,prevention of varicose veins in lower limbs with prolonged foot support,gait rehabilitation for hemiplegic patients and detection of sleep apnea hypoventilation syndrome.The piezoelectric flexible pressure sensor developed in this subject will show a broad application prospect in the field of biomechanical signal monitoring such as medical diagnosis,medical rehabilitation and portable wearable devices.