Optical fiber sensor encapsulated by polyurethane

Fiber Bragg gratings (FBGs) are ideally suited for monitoring strain in civil structures, aircrafts, ocean engineering due to their low cost, reliable and high accuracy. A new encapsulation technology for FBG using polyurethane is proposed to help the sensor withstand large displacement in hash environment. This paper aims to provide experimental packaging procedures, calibration and field tests of developed FBG sensors for strain measurement. The principles, basic chemical reaction processes and prepare procedures of polyurethane are demonstrated. Suitable protective encapsulation to the bare fiber by polyurethane ensures that there is no relative slip at the interface. The encapsulated FBG sensor has good linearity from the result of calibration test conducted on a universal testing machine. Further the sensor is embedded into the freezing soil to evaluate the performance in severe environment.