Graphene-based Humidity Sensor And Its Application In Respiratory Monitoring

With the advancement of the era of portable healthcare systems,wearable respiratory sensors have become a research hotspot for scholars.Most of the current wearable respiratory sensors are made of flexible polymer substrates loaded with moisture-sensitive material films,which are not easy to degrade naturally and costly,and are not suitable for mass commercial production.Paper-based respiratory sensors loaded with graphene-based moisture-sensitive materials are green and environmentally friendly,and reduce the production cost of sensors,promoting the marketable range of wearable respiratory sensors.In this paper,we make an in-depth study of the moisture-sensitive characteristics of the sensor,starting from the structural parameters of the sensor,the type of paper substrate,the parameters of the moisture-sensitive material,the operating voltage frequency and the respiratory monitoring performance.The study is divided into three main parts as follows:(1)The paper-based humidity sensor was designed to determine the optimal sensor structure parameters using COMSOL software simulations,and the effects of different paper substrate types and operating voltage frequencies on the performance of the moisture-sensitive sensor were investigated.The moisture-sensitive sensors with A4 printing paper,Kodak photo paper and double-sided coated paper substrates were fabricated using screen printing process.The moisture-sensitive characteristics of the sensor under the operating voltage frequency of 100 Hz were studied,and the optimal operating voltage frequency of the sensor was determined to be 200 Hz,and the stability and respiratory monitoring performance of the sensor were tested;the sensor with Kodak photo paper substrate reached a maximum sensitivity of 7379% at the operating voltage frequency of200 Hz,and the response/recovery time was 108s/131 s.(2)The factors affecting the moisture-sensitive performance of graphene-based humidity sensors were systematically investigated,and GO capacitive paper-based humidity sensors and RGO resistive paper-based humidity sensors were fabricated using the spraying method and the thermal reduction method,respectively.The test results show that: the lower the GO concentration and the smaller the thickness of the moisture-sensitive film,the better the overall performance of the sensor,and the 1mg/m L GO sensor achieves a sensitivity of8504% and a response/recovery time of 177s/87 s at an operating voltage frequency of 500Hz;the sensitivity of the RGO sensor increases with the growth of the thermal reduction time and the concentration of the moisture-sensitive film,and at a thermal reduction time of 6h or more,the The maximum sensitivity of 140.3% was obtained for the RGO sensor with a moisture-sensitive film concentration of 5 mg/m L.(3)A miniaturized respiratory monitoring system was realized.By comparing the respiratory monitoring performance of GO sensor and RGO sensor,we found that GO sensor is more suitable for respiratory monitoring system.A miniaturized respiratory monitoring system with the GO sensor as the signal acquisition element and the STM32F103RCT6 chip as the microprocessor was made to communicate wirelessly with the Android smartphone terminal via Bluetooth;the test results of the respiratory monitoring system show that the GO sensor developed in this paper has a greater practical value.