Gas-liquid Two-phase Optical Fiber Sensor For Acetone Based On Cholesteric Liquid Crystal

Acetone--one of the common volatile organic compounds,is a common industrial production raw material,studying acetone concentrations in breath and urine is clinically relevant in medicine.Acetone is toxic,and its leakage will pollute the air and water sources,posing a threat to life and health,so the monitoring of acetone is of great significance.At present,the research on the detection of acetone concentration in a gas-liquid two-phase environment has attracted much attention,in past studies,traditional sensors were complicated to manufacture and could not quantitatively detect the concentration of acetone,therefore,according to actual needs,this paper integrates cholesteric liquid crystals on optical fibers to study and prepare a gas-liquid two-phase sensor,the sensor combines the advantages of optical fiber and liquid crystal sensor,and can quantitatively measure acetone at room temperature.The main contents of the study are as follows:(1)Volatile organic gases(VOCs)can change the pitch of cholesteric liquid crystals(CLC),therefore,CLC is used to sense VOCs.In this paper,the sensor is designed as a dual probe,which can sense acetone and temperature at the same time.Two kinds of CLCs with different pitches are filled at the fiber end of the 2×2 multimode fiber coupler to form a double probe,the acetone probes were encapsulated using polydimethylsiloxane(PDMS)and the temperature probes were encapsulated using glycerol and UV glue.Subsequently,the effects of different thicknesses of PDMS and CLC on acetone were explored,the results show that PDMS has no effect on the sensitivity of the sensor,and different CLC thicknesses also have no effect on the sensitivity of the sensor.the highest sensitivity can reach 4.11 nm/%,and the linear fitting degree is 0.999.(2)The detection range,actual detection limit and theoretical detection limit of acetone were explored in the gas phase environment,the results show that the theoretical value of the experiment is consistent with the actual value.Subsequently,the response and compensation of the sensor to temperature were studied,when the temperature fluctuates ±5°C in a short time,after temperature compensation,the linear fitting degree of the sensor is still as high as0.950.(3)The influence of humidity change on the sensor in the gas phase environment was explored,the results show that humidity has no effect on it.In the liquid phase environment,the detection limit and detection range of acetone concentration were explored.Finally,continuous tracking randomly measured the response of the sensor to acetone in the air within32 days,which has good repeatability and reversibility,and the maximum deviation within 32 days is 7.1%,which proves that the sensor has very good stability.