Study On Organic Humidity Sensing Film And Optical F-P Relative Humidity Sensor

At present,with the rapid development of industry and agriculture,environmental protection,construction,petrochemical industry,medical treatment,aerospace and other fields,people put forward higher requirements for the performance of humidity sensors.Among many humidity monitoring methods,the fiber-optic F-P relative humidity sensor has been favored and valued by researchers because of its unique advantages.The core of the humidity sensor is the humidity sensitive film with specific adsorption of water molecules.Its adsorption performance,mechanical properties and optical properties directly determine the performance of the sensor.Therefore,the selection of humidity sensitive membranes with good optical properties and adsorption properties is of great significance for the development of humidity relative sensors with high sensitivity,long life,fast response,low cost,large range and wide temperature range.The main research contents of this thesis are as follows:?1?The optical properties of humidity sensitive membranes and Fabry-Perot?F-P?sensing principles.The calculation principle of composite refractive index after humidity sensitive membrane adsorption of water molecules is discussed.The solid-gas thermodynamic system composed of humidity sensitive membrane and water molecules is described to achieve the equilibrium adsorption model.The relationship between cavity length of F-P sensor and initial film thickness,fringe contrast in interference spectrum and refractive index of sensitive film was simulated.?2?The preparation and characterization of polyimide sensitive membranes doped.First,the pure PAA,PAA doped by LiCl and PAA doped by CH₃OH were spin-coated on the cover glass by a rubber leveler and sintered at 220?.Then they were characterized by means of FI-IR,AFM,optical microscopy,etc.?3?Research on fiber-optic F-P relative humidity sensor doped with PI and determination of adsorption model.The F-P sensing cavity of single-layer structure is prepared on-line by splicing method.The relationship between the initial film thickness and sensitivity of pure PI is discussed.The wavelength modulation type fiber F-P humidity sensor is used to explore the humidity response of doped PI and judge its Adsorption model.The results show that the humidity sensitivity fitting curves of the three sensing probes?pure PI,PI+LiCl and PI+CH₃OH?are linear in the range of 20⁹5%RH,and the sensitivity of these sensing probe are 0.095 nm/%RH,0.164.nm/%RH,0.100 nm/%RH,respectively;low hysteresis,low temperature sensitivity and good repeatability.In addition,the adsorption model of PI sensitive membrane to water sensitive molecules belongs to the Langmuir model.?4?The PI/Nafion multilayer membrane structure was used to study the humidity response of the Nafion sensitive membrane.The interference spectra generated by FP sensing probes based on Nafion,PI/Nafion and PI/Nafion/PI were simulated,and the difference of fringe contrast in their interference spectra was analyzed.The double-layer and three-layer film structure were prepared by the spin coating and casting method.A F-P sensing cavity of multi-layer structure is prepared on-line by splicing method.The wavelength modulation type fiber F-P humidity sensor is used to explore the humidity response of Nafion sensitive membrane.The results show that the humidity sensitivity fitting curves of the sensing probe PI/Nafion is nonlinear in the range of 30⁹0%RH,and the extremum wavelength drifts 91.68 nm;the humidity sensitivity fitting curves of the sensing probe PI/Nafion/PI is linear,but the extreme wavelengths drifts 6.32 nm and the sensitivity is only 0.096 nm/%RH.