Study Of Portable Intelligent Environmental Monitoring System And Device Design

Metal oxide semiconductor（MOS）gas sensors play a key role in the use of environmental monitoring systems owing to their simple structure,low production cost,good stability and ease of integration.Among the many MOS gas sensors,WO₃-based gas sensors show great potential due to their high electrical conductivity,high response activity and stable performance.However,due to the poor selectivity and high operating temperature among many WO₃sensors,they are far from satisfying requirements for practical applications.In order to improve the response of WO₃-based sensors as well as to achieve the goal of real-time monitoring,the study aims to optimize the performance of WO₃-based gas sensors by changing the morphology and surface structure of WO₃gas sensing materials through the addition of organic acids,and to produce the corresponding tungsten oxide para-thermal gas sensing elements,by preparing the sensitive layer of gas sensing elements.Finally,the self-developed tungsten oxide gas sensing sensor was used in combination with the STM32 microcontroller system to construct an environmental monitoring device.The main research results are as follows.（1）Sea urchin-like WO₃nanospheres were obtained by hydrothermal method with different levels of malonic acid.On this basis,different organic acids were optimally added to prepare WO₃gas-sensing materials with different structures.The results showed that the sea urchin WO₃nanospheres prepared with malonic acid as the morphology modifier achieved a response value of 70 to 50 ppm acetone at a working temperature of 200°C,which was 1.75 and 2.8 times higher than those prepared with ethanedioic acid and succinic acid,with a response/recovery time of 11 s/13 s,respectively.The smaller diameter of the WO₃nanospheres compared to the other two acids resulted in a larger specific surface area and enhanced response to acetone gas.This provides a new idea for the manufacture of breath detectors for clinical diagnosis and monitoring of diabetes by doctors and patients,allowing the sensors to be used in the medical field as well.（2）WO₃nanomaterials with different morphologies were obtained by hydrothermal reaction and calcination with different levels of citric acid.The heterocrystalline interface of the self-assembled nanosheets with a bicrystalline,flower-like graded structure of tungsten oxide nanospheres resulted in a highly desirable response to the Listeria monocytogenes biomarker dimethyl trisulfide gas.In order to investigate the effect of different organic acids on the morphology of WO₃nanomaterials,WO₃nanomaterials were also prepared using the organic acid malic acid as a structural modifier.The sensor has far-reaching market applications in aquaculture detection,energy conservation and environmental protection,microbial contamination and food quality detection.（3）Design and build a portable intelligent environment monitoring system based on STM32,according to the needs of the monitoring system the whole system mainly includes environment detection module,sensor signal conditioning module and data processing module.The sensor signal conditioning module is mainly designed for the new WO₃gas-sensing sensor.This environmental monitoring system accomplishes the detection of Listeria monocytogenes biomarker dimethyl trisulfide gas,and can be realized through the host computer to monitor the relevant data in the environment in real time,a preliminary exploration of its practical applications is also presented.