Improved Perforamance Of Optical Fiber Hydrogen Sensor Based On Controllably Optical Heating

Nowadays,the reserves of fossil fuels such as coal,oil and natural gas are in a state of depletion.It is crucial to find an alternative to fossil fuels that can lead to reduce environmental pollution at the same time.Hydrogen has been extensively researched and applied in the fields of automobile,material storage and aerospace due to its pollution-free combustion products and high energy conversion rate.However,the molecular size of hydrogen is the smallest molecule known at this stage,resulting in a high probability of leakage during production,transport,storage and use,and there is a risk of explosion when the hydrogen content in the air exceeds 4%.For the safety of hydrogen production,use and life,equipment safety,real-time monitoring of hydrogen concentration in the environment is necessary.Traditional hydrogen sensors are mostly developed based on electrical characteristics,and electric spark may be generated in the process of using,so there is a big security risk.The optical fiber hydrogen sensors have been widely studied due to the full use of the optical fiber's advantages of intrinsic safety,anti-electromagnetic interference,light weight and small size.The factors that affect the popularization and application of optical fiber hydrogen sensor are disadvantages in terms of long-term stability and reliability.In this paper,we combine the fiber grating with Pd / Ni hydrogen sensitive material,utilize the characteristic of volume expansion of Pd hydrogen absorption,and combine with the principle of monitoring the wavelength shift of the center of the fiber grating,to prepare a self-compensated FBG hydrogen sensor.For this type of hydrogen sensor,the full text mainly shows the following research contents and results:(1)Using the method of magnetron sputtering to coat different thickness of hydrogen-sensitive materials in the etching grating side plated.Placing the prepared different thickness of the hydrogen sensitive material sensing probe in the same test environment.The repeatability and gradient of the 1% hydrogen concentration of the probe were then tested in turn,and a comparison of the hydrogen response performance of probes of different thickness hydrogen-sensing materials resulted in a relatively optimal hydrogen-sensing material thickness.At the same time,the gratings are corroded to different diameters and are then coated with hydrogen sensing material with the same thickness.After that,hydrogen response performance under each corrosion diameter is compared to find the optimal grating corrosion diameter.(2)The temperature of the environment in which the probe is placed can affect the activity of the hydrogen sensitive material and thus the sensitivity of the sensing probe.In this paper,a 980 nm pump light source is introduced to heat the sensing probe,and the hydrogen response performance of the sensing probe under different heating intensities is compared to determine the influence of temperature on the sensing probe.Since the output power of the laser light source is not linear in the full range,in order to introduce the scheme of self-compensation of light heating temperature in the follow-up,the linear working area of the laser light source used in this paper is explored.(3)In this paper,double grating is used,one as a reference grating and the other as a sensing grating.Combining with PID control technology,under the premise of 980 nm pump light source working in the linear region,the working temperature of the sensing probe is controlled under a relatively stable condition.Then,the repeatability,gradient and long-term stability of 1% standard hydrogen before and after the introduction of temperature self-compensation were compared respectively,and then the influence of ambient temperature on the response performance of the hydrogen-sensing probe was obtained.So as to find an effective way to improve the hydrogen response performance of the sensing probe.