Research On The Characteristics And Experiment Of Humidity Sensors Based On Micro-fiber Structure

With the rapid development of science and technology, many fields need real-time monitoring of the humidity. Fiber optic humidity sensors emerged in recent years have received much attention, for their high temperature resistance, corrosion resistance, and working in harsh environments with strong electromagnetic interference. However, most traditional optical fiber humidity sensors which are bound by fiber structure and the thickness of humidity sensitive film have low response speed and small sensitivity, and can not be used widely.This thesis presents two kinds of micro-fiber humidity sensor with high sensitivity and high response rates, mainly as follows:Firstly, we propose a fiber optic humidity sensor based on micro-fiber Bragg grating(MFBG). In the sensor structure, the fiber Bragg grating(FBG) is etched into tens of microns, with polyimide humidity film coated on the MFBG. Researching on its sensitivity and response speed, we find that Compared with the ordinary FBG humidity sensor, the sensitivity of MFBG humidity sensor can be increased by more than 50%. What is more, the response speed can be improved greatly, and the response time of MFBG humidity sensor can be shorted to 8.3% of that of FBG humidity.Secondly, an improved humidity sensor based on dual fiber Bragg grating and micro fiber structure is proposed. The structure is a optical fiber have two fiber Bragg gratings with the same diameter, and polyimide, a humidity material, coated on the area between the two gratings which is corroded into tens of microns. Experiments prove that the use of micro fiber can improve the sensitivity of response of the sensor, and the fiber humidity sensor can monitor changes of the temperature and the humidity simultaneously by introduce dual fiber Bragg grating structure, which solved cross sensitivity problem of the humidity sensor based on MFBG to temperature and humidity. Due to its reflection spectrum consist of a plurality of successive reflection peaks, this kind humidity sensor is more suitable for smaller change of humidity in environmental monitoring.This paper studies on these two kinds structure of fiber optic humidity sensors, mostly focusing on the innovation of design, manufacturing, and characteristics testing. The produced microfiber humidity sensor has higher sensitivity and response speed than the normal humidity sensor. What is more, dual fiber Bragg grating with micro fiber connected structure can solve cross sensitivity problem of optical fiber humidity sensor to temperature and humidity. So they will further widen the road of fiber grating sensing in the development of humidity areas.