A Simple Optical Fiber Sensor for Metal Defect Detection

Abstract

Based on the optical Faraday effect, a small fiber sensor is fabricated to detect the ferromagnetic defect. Experimental result shows its minimum diameter can reach 3 mm and its depth can reach 5%*t.(/p)(p)As we all know, if iron products are exposed to the air or humid environment, they have a strong tendency to be corroded. Many leakage accidents caused by corrosion have been occurred in the oil pipeline and nature gas pipeline, which bring about a series of problems such as environmental pollution and resource waste. Therefore, it is important to detect the iron pipes and vessels to prevent accidents. At present, there are many papers about applying optical methods to test metal defects. For example, optical variable imaging method [1], infrared optical imaging method[2], optical interference method[3], photonic crystal fiber sensor method [4], fiber Bragg grating (FBG)[5], etc. However, there are many shortcomings with these optical methods, including large size, difficult fabrication and signal affected by environmental weather. In this paper, based on the theory of magnetic flux leakage on ferromagnetic metal and the optical Faraday effect, the information of iron defects can be obtained by detecting the change of polarization state of incident light. Compared with other methods, it has incomparable advantages due to the optical signal without electromagnetic and temperature interference.