| With the rapid development of current society and the continuous improvement of living standard of the people,health problems have become well-known hot issues.However,as China is stepping into aging society,all kinds of chronic and cardiovascular diseases have gradually become the main factors affecting the health of the people.According to the statistical data,by 2019,50%of the elderly population in China suffers from more than one chronic disease.Due to the long onset period of the chronic diseases,the symptoms of immediate clinical monitoring are not obvious,which greatly affects the diagnosis and treatment of the chronic diseases.If the physiological data for the patient in daily life can be obtained,it will be of great help to the prevention and diagnosis of the diseases.With the application of intelligent techniques and the Internet of Things(IoT),the wearable health monitoring system has also been further developed.In particular,the pulse sensor will play an important role in the field of health care.However,the existing wearable health monitoring system generally possesses some problems,such as low sensitivity,poor system integration,unstable physiological feedback signal,and poor biocompatibility.Due to its unique flexibility,the flexible sensor can receive signals more effectively on the surface of the object,and it is more effective for the feedback of physiological signals such as heart rate and pulse.Therefore,this thesis investigated the material,structure,and algorithm optimization aimed at improving the sensitivity of the sensor,optimizing the wearable health monitoring system and analyzing the pulse data.The main research results are summarized as follows,1.Based on the advantages of composite materials and the high sensitivity of the electrospinning structure in pressure sensing,the nano-composite fibers of piezoelectric ceramics and PVDF were prepared by the water medium electrospinning process,and the materials were characterized.The effect of ceramic particles on the piezoelectric properties of PVDF fiber was investigated under the condition of low filling content.The results show that the electrospinning process could induce the formation of β-phase of PVDF,and the good interfacial effect could further improve the piezoelectric properties of the composites.After testing,the relative ratio of β-phase of 1.5wt%PZT/PVDF composite fiber could be increased to 79%.In the force/electric test,the sensitivity was as high as 560 mV/N,and the system exhibited a stable performance and improved linearity in multiple cyclic loading test cycles,demonstrating good macro piezoelectric properties.2.Combined with the transmission characteristics of the human cardiovascular system,a flexible wireless pulse sensing system was designed and manufactured based on the PZT/PVDF piezoelectric composite fiber.In the study of the circuit,the charge acquisition module,the filter module,and the voltage lifting module were designed reasonably to make the matching circuit work reliably.The wireless function of the sensor was realized,and the pulse rate of the human body could be monitored for a long time,and the physiological abnormal signals could be given an alarm.The traditional pulse sampling law was investigated,and the dynamic threshold method was used to optimize the pulse rate information collection so that the pulse rate collection speed of flexible wireless pulse sensor system was faster and the data confidence was higher.The system is expected to be suitable for telemedicine monitoring application.3.To further realize the effective extraction of radial artery pulse information,the sensing characteristics of piezoelectric material in D33 mode were investigated,and a flexible pressure sensing array based on PVDF piezoelectric element was designed.Considering that the flexible design of the array was more conducive to pulse information acquisition,the flexible electrode was fabricated by magnetron sputtering technology.The PDMS unit with a round table structure was fabricated by using 3D printed composite polyurethane resin and organosilicon mold.The flexible array had a 10×10 piezoelectric element with an area of only 3.75×3.75 cm.The distributed measurement principle of dynamic force was explored,and the 3D recognition function of contact force was realized.Through effective data collection,it has practical significance in the objective imaging of the pulse.4.The pulse detection effect of the PVDF flexible piezoelectric sensor array was investigated.This thesis explored the objectification of pulse diagnosis in Chinese medicine through a flexible array.The pulse data were filtered,sliced,and interpolated to optimize the imaging effect.The pulse recognition algorithm is designed to make the diagnosis of pulse information more convenient for future medical staff.Through the training model,the neural network based on deep learning was used to effectively identify the four typical pulse images that were feedback from the array:Fu pulse,Hua pulse,Chi pulse,and Ru pulse.The result showed that the array could recognize the pulse pattern well at the scanning rate of 100 Hz.From the point of view for practical applications,this work systematically investigated the wearable health monitoring system of the human cardiovascular system. |
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