Recognition Of Environmental Signals And Physiological Signals Based On The Internet Of Things

Environmental gas quality has a direct bearing on human safety and health.Therefore,it is crucial for human safety and health to perform research works on environmental gas monitoring and detection of human physiological signals.As one of the environmental signal detection methods,the gas sensor is quite important in the detection of various toxic and harmful gases.Nowadays,gas sensor based on metal oxide semiconductors has been widely studied due to the low cost,high response and simple operation.However,such gas sensor often needs a higher working temperature and shows poor gas sensing selectivity.For medical diagnosis and health testing,the emerging flexible pressure sensor has the advantages of flexibility,lightweight,and durability,which can be easily and tightly attached to the human skin for the detection of physiological health information such as heart rate and respiratory rhythm.To date,electronic textiles provide a good choice for constructing comfortable and intelligent wearable electronic devices owing to their advantages of flexibility,deformability,air permeability,and comfort.In fact,the textile-based flexible sensor device is easily interfered by human sweat or water vapor in the external environment,which reduces the sensor performance of the device and the comfort of human wearing.Regarding the above-mentioned problems,this thesis adopts methods of constructing heterostructures between the metal oxide and reduced graphene oxide（r GO）and introducing hydrophobic,waterproof materials into textiles,realizing the design and preparation of formaldehyde gas sensor and flexible pressure sensor.Also,the real-time monitoring systems based on the Internet of Things technology have been designed and performed.The main research work is as follows:（1）Sn₃O₄/r GO composite materials with different r GO content and pure Sn₃O₄ were prepared by a facile hydrothermal method.Then,sensing performances of both Sn₃O₄/r GO composite materials and pure Sn₃O₄ toward formaldehyde were systematically investigated.Compared with the pure Sn₃O₄ sensor,the Sn₃O₄/r GO composite sensor shows a greatly improved sensing response to formaldehyde at a relatively low temperature.By analyzing the sensing mechanism of pure Sn₃O₄ and Sn₃O₄/r GO composite materials,we attribute the enhanced formaldehyde gas sensing characteristics of the Sn₃O₄/r GO composite gas sensor to the heterostructure between Sn₃O₄ and r GO.（2）A waterproof and breathable Cotton/r GO/CNT composite sensing material were prepared by the solution infiltration method.Flexible pressure sensor and temperature sensor based on Cotton/r GO/CNT composite was developed.The proposed flexible pressure has a good linear sensing response toward the pressure in the range of 0-4 k Pa,and the sensitivity is as high as 1.042 k Pa^-1.The response and recovery time are less than 50 ms,and the pressure limit of detection is 1.5 Pa.More than 5000 cycle tests show the good long-term durability of the sensor.In addition,the designed flexible temperature sensor has a good linear response in the range of 28-40°C,fast response and recovery time（20 s/70 s）,and good performance repeatability,which can accurately distinguish 0.5°C changes.Finally,by constructing a sensor array of flexible pressure and temperature sensors based on Cotton/r GO/CNT composite sensing materials,we successfully mapped the pressure and temperature of items placed on it.（3）Relying on the Internet of Things technology,real-time monitoring systems have been designed and achieved.Based on the gas sensor,pressure sensor,and temperature sensor devices we designed and prepared,the micro-processing unit controls the collection and processing of harmful gas,pressure and temperature information in the environment,and sends sensor data through the Wi-Fi/Bluetooth communication module.The user’s mobile terminal will receive the sensor data through the Wi-Fi/Bluetooth communication module,and process and visualize these data to realize the remote and real-time monitoring of harmful gases,pressure,and temperature information in the environment.