Polyimide-coated fiber Bragg grating for relative humidity sensing

Abstract

A fiber-optic humidity sensor has been fabricated by coating a moisture sensitive polymer film to the fiber Bragg grating (FBG). The Bragg wavelength of the polyimide-coated FBG changes while it is exposed to different humidity conditions due to the volume expansion of the polyimide coating. The characteristics of sensors, including sensitivity, temporal response, and hysteresis, were improved by controlling the coating thickness and the degree of imidization during the thermal curing process of the polyimide. In the relative humidity (RH) condition ranging from 11.3% RH to 97.3% RH, the sensitivity of the sensor was about 13.5 pm/% RH with measurement uncertainty of ±1.5% RH.

Keywords

Fiber Bragg grating / humidity sensing / moisture sensitive

References

[1] Rao Y J. Recent progress in applications of in-fibre Bragg grating sensors. Optics and Lasers in Engineering, 1999, 31(4): 297-324.

[2] Rao Y J. In-fiber Bragg grating sensors. Measurement Science and Technology, 1997, 8(4): 355-375.

[3] Sutapun B, Tabibazar M, Kazemi A. Pd-coated elastooptic fiber optic Bragg grating sensors for multiplexed hydrogen sensing. Sensors and Actuators B: Chemical, 1999, 60(1): 27-34.

[4] Li W, Pang J, Lu X, Liu J. Rail expansion devices monitored by FBG sensors on an urban railway viaduct. Photonic Sensors, 2014, 4(2): 173-179.

[5] Pang D, Sui Q. Response analysis of ultrasonic sensing system based on fiber Bragg gratings of different lengths. Photonic Sensors, 2014, 4(3): 281-288.

[6] Saad S, Hassine L, Elfahem W. Hydrogen FBG sensor using Pd/Ag film with application in propulsion system fuel tank model of aerospacevehicle. Photonic Sensors, 2014, 4(3): 254-264.

[7] Teixeira J G V, Leite I T, Silva S, Frazão O. Advanced fiber-optic acoustic sensors. Photonic Sensors, 2014, 4(3): 198-208.

[8] Tan K M, Tay C M, Tjin S C, Chan C C, Rahardjo H. High relative humidity measurements using gelatin coated long-period grating sensors. Sensors and Actuators B: Chemical, 2005, 110(2): 335-341.

[9] Huang X F, Sheng D R, Cen K F, Zhou H. Low-cost relative humidity sensor based on thermoplastic polyimide-coated fiber Bragg grating. Sensors and Actuators B: Chemical, 2008, 127(2): 518524.

[10] Jun J Y, Bao L H, Liu H. Sketch of moisture sensitive polymer use with fiber Bragg grating based humidity sensor. College Physics, 2009, 28(7): 39-42.

[11] Yeo T L, Sun T, Grattan K T V, Parry D, Lade R, Powell B D. Polymer coated fiber Bragg grating for relative humidity sensing. IEEE Sensors Journal, 2005, 5(5): 1082-1089.

[12] Adhikari B, Majumdar S. Polymers in sensor applications. Progress in Polymer Science, 2004, 29(7): 699-766.

[13] Russell A P, Fletcher K S. Optical sensor for the determination of moisture. Analytica Chimica Acta, 1985, 170, 209-216.

[14] Hill K O, Meltz G. Fiber Bragg grating technology fundamentals and overview. Journal of Lightwave Technology, 1997, 15(8): 1263-1276..

[15] US Standard, ASTME104-02, Standard Practice for Maintaining Constant Relative Humidity by Means of Aqueous Solutions.