A diaphragm based Fiber Bragg Grating (FBG) type pressure sensor for ocean applications

In this paper, a low-cost diaphragm based Fiber Bragg Grating (FBG) pressure sensor design for ocean applications is presented. The pressure with different thickness of copper diaphragms have been measured. A single bare FBG is mounted on top of the circular diaphragm so that maximum pressure is exerted at center of the diaphragm and it will cause the diaphragm lateral shape variation so that a strain will develop on FBG. In order to measure the pressure variation a compact design is made by using stainless steel disks and rubber "O" rings with closed air cavity setup. The pressure in static freshwater column ranging from 0 to 0.04 Mpa was gauged, using closed air cavity setup. In addition to that, another "T" shaped design, for testing has been made with solid stainless steel tube with open air cavity setup for an extended range of pressure sensing. By using an oil pressure pump and open air cavity setup, the value of pressure ranged from 0 to 0.5 Mpa with the step size of 0.01 Mpa. In both setups same thickness of copper material is used to measure the pressure and to compare the results. Furthermore, a range of experiments are carried out to test both the setups. Experimental results indicated that the pressure sensitivities in closed air cavity setup are 0.2286 and 24.95 nm/Mpa with linearity 96.29% and in open air cavity setup is 5.458 and 16.22 nm/Mpa with linearity 99.34% achieved. Open air cavity setup is more sensitive than closed air cavity method and also reported good linearity comparatively with closed air cavity method. The repeatability of the sensor has been tested 3 times and showed less hysteresis. This type of pressure sensor could be used to measure static and dynamic pressure sensing in oceanography, gas and liquid environments.