| Nowadays,as the pace of life accelerates,people’s life pressure is gradually increasing,more and more people have symptoms such as depression,anxiety,and insomnia.As known,nearly one-third of people’s life is spent in sleep.Sleep is a critical period for the body to carry out physical and psychological repair.Long-term sleep disorders will degrade or even deteriorate the functions of various organs and tissues in the body.In view of this insight,sleep monitoring is of great significance for the early warning and regulation of human health state.Polysomnography（PSG）,as the most commonly used monitoring method,has the advantages of high accuracy and comprehensive monitoring parameters,but its structure is complex,cost is high,and comfort is low.Therefore,how to design a new type of sleep monitoring system with low cost,high sensitivity and high comfort is the focus of current research.The self-powered flexible electret-based pressure sensor has the advantages of high sensitivity and simple preparation process,which can be used to build a sleep monitoring device to detect the fretting of human body and realize the non-invasive monitoring of sleep.On the other hand,the human body characteristics monitored by the sensor are the superposition of a variety of physiological signals,so it is necessary to combine the corresponding electronic hardware platform,digital signal processing system and signal separation algorithm to realize the real-time monitoring of sleep state.Therefore,this paper proposes a sleep monitoring device based on the self-driven electret pressure sensor of hemispherical micro-projectile body and matches the corresponding hardware platform,software and algorithm to construct a complete non-invasive sleep monitoring system.The main research contents of this paper are as follows:（1）Combined with the theoretical analysis and calculation of the electrostatic electret pressure sensor,the paper made a highly sensitive self-powered electret pressure sensor which is based on the hemispherical micro-elastic film,and explored the height,diameter and center distance of the hemispherical micro-elastic film on the sensitivity of the sensor.Through simulation and experimental data analysis,it is found that the sensor constructed by hemispheric microprojectile with the height,diameter and center distance of 300μm,1.5 mm and 2.5 mm respectively has the best performance.As expected,the sensor has good electrical output characteristics with an output open-circuit voltage of 32 V,a short-circuit current peak-to-peak value of 1.2μA,and a transferred charge of 16 n C under the condition of an external pressure of 1 N and 3 Hz.At the same time,this sensor has excellent stability,in which the electrical output performance is basically unchanged after 20,000 cycles.Moreover,the sensitivity of the sensor reached 6.22 V k Pa-1 under the initial pressure condition（<2 k Pa）,which is about 150 times that of commercial PVDF film.Without touching the body surface,the monitoring of respiration,cough,heartbeat and body movement was successfully realized by using this sensor.（2）From three aspects of hardware,software and algorithm,an integrated non-intrusive sleep monitoring system based on the pressure sensor of hemispherical microprojectile electret is constructed to realize the extraction and analysis of physiological signals.In terms of hardware platform construction,AD9226 analog-to-digital conversion chip,AX7Z020core board and HC-06 Bluetooth chip are selected as three main parts of sampling conversion,processing storage and wireless transmission respectively.In terms of software and algorithm deployment,the signal processing algorithm and data flow coordination control algorithm are designed to achieve the separation of physiological signals.The details are listed as follows:the body motion signal is extracted by threshold monitoring;Respiratory signals were separated by finite impulse response（FIR）filter.This thesis proposes a separation algorithm based on difference,which can separate the heartbeat signal.Compared with the FIR filter,the delay can be reduced by nearly 50 times,and at the same time,it has higher fidelity.Through data mining,the time-domain analysis and nonlinear analysis of heart rate variability（HRV）,as well as the monitoring of central sleep apnea are realized.Finally,based on the Universal Asynchronous Transceiving and Receiving Protocol（UART）,a set of expandable private protocols were designed for real-time mode and all-night monitoring mode,respectively,to realize data transmission from terminal to mobile terminal,and a non-invasive sleep monitoring system based on electret pressure sensor was developed. |
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