Fiber Bragg Grating (FBG)-Based Pore Pressure Sensor Utilizing Bellows System

This study presents the design, fabrication, and performance evaluation of an optical fiber Bragg grating (FBG)-based pore pressure sensor for geotechnical borehole applications. The sensor comprises a cylindrical body, 3-D, printed from polylactic acid (PLA) material, with dimensions of 40 mm in diameter and 155 mm in length. The transducer holding the FBG utilizes a square bellows design and was 3-D printed using thermoplastic polyurethane (TPU) material, taking advantage of its good flexibility. This transducer was positioned inside a cylindrical housing to allow pore pressure measurement to take place effectively. Two FBGs, denoted FBG P and FBG T, were used to measure pore pressure and temperature, respectively. The experimental results demonstrate a pressure sensitivity of 1.224 pm/kPa for FBG P with a linearity of 99.41%. Besides that, the results also demonstrate FBG T’s effectiveness in giving temperature compensation to FBG P during pore pressure measurement. This innovative sensor design offers a compact and versatile solution for pore pressure measurement in geotechnical applications, combining the benefits of FBG technology with 3-D printing capabilities.