| With the rapid development of social economy and industrial technology,the consumption of fossil fuels such as coal oil increases,which has led to the continuous increase of greenhouse gas emissions and the greenhouse effect.As global warming worsens,extreme weather becomes more frequent around the world and biodiversity is under serious threat.Carbon dioxide(CO2)is the largest contributor to global warming among several greenhouse gases,but the detection of CO2 has been in a slow development stage.But the shortcomings of existing sensors are more obvious,such as cumbersome preparation process,small detection range,complex detection process,etc.A CO2 sensor that can cope with multiple use scenarios has become a research hotspot.In order to actively respond to the environmental protection policies of "peak carbon dioxide emissions" and "carbon neutrality" and better monitor CO2 emissions online in real time.In this paper,based on the advantages of fiber Bragg grating(FBG),a polymer-coated FBG gas sensor for CO2 detection has been studied with simple preparation,low cost,and convenient operation.It also has features such as short response/recovery time,excellent selectivity and long service life.What’s more,it can carry out stable and effective online monitoring under different temperatures and humidity.Based on the principle that the axial deformation of FBG causes the reflection wavelength shift and the phenomenon of volume expansion of polyether sulfone(PES)in CO2,a gas sensor based on polymer coating/FBG for CO2 detection is designed.Through the volume expansion of the polymer coating in CO2,the grating is elongated to change the period,and finally makes the Bragg reflection wavelength shift.According to the wavelength shift,the concentration of CO2 can be calculated,and the on-line monitoring of CO2 can be realized.In order to prepare the designed sensor conveniently and repetitively,this paper presents a low-temperature spin and high-temperature curing process.Through the hot spin coating process,uniform and smooth PES coating is coated on the surface of the gate area,which greatly ensures the reliability of the detection results of different batches of sensors.We analyzed and discussed the factors that affect the test results of the CO2 gas sensor in detail,and investigated the influence of spin coating process,temperature,and humidity on the sensor’s response value.Although the number of revolutions of the grating at different positions in the sensor spin-coating process is very small,the effect on the response value is negligible.It is found that the maximum response value of the sensor decreases with the increase of test environment temperature,but the time to reach the equilibrium state also decreases.It is concluded that the sensor can be used stably between-5℃-55℃.In addition,the influence of humidity on the sensor is explored.Although the developed gas sensor is affected more and more obviously with the increase of humidity in the test environment,it can still perform stable and reliable detection at 80%RH.Finally.we studied the performance of the CO2 gas sensor,and tested the sensitivity and limit of detection(LOD),selectivity,response/recovery time and durability of the sensor.The performance of our sensor is compared with that of the existing sensors.In addition,in order to make the sensor more practical application value and to comply with the development trend of industrial intelligence,an over-concentration alarm system was demonstrated and it can generate sound and light alarm automatically when CO2 exceeds the safety threshold.In summary,a simple,easy-to-operate and low-cost sensor preparation process is designed,and the influence factors of sensor response value are analyzed in detail,the performance parameters of the sensor are tested,and a CO2 gas sensor with simple preparation,strong anti-interference ability and low-cost is developed. |
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