Structural Monitoring by Fiber Optic Sensor


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Technical Information


Followings are technical principles of our system.

FOD sensor can detect ultrasonic wave (vibration at the same time) that cannot be heard by human ear. Conventionally, several kinds of ceramics are used, where FOD can compete. In material science, by hearing very small ultrasonic, material destruction process is observed from micro crack till further degradation.

By combining FOD and magnetic, metal thickness is measured. According to Flemming law, EMAT generates vibration into metal, where FOD sensor detects such vibration frequency. The strongest frequency is corresponding to metal thickness.

By making grating inside core of fiber optic, such grating shall reflect particular wavelength of laser, correlating to period of grating. Grating period expands or shrinks to strain and temperature change.

FBG sensor is advantageous of being able to have many sensors in one line of fiber optic. To recognize the position of each FBG, there are several methods like WDM (wavelength division multiplex) and TDM (time division multiplex). OFDR (Optical Frequency Domain Reflectometry) is a third option, that can divide FBG by interferometric approach. OFDR makes possible to measure several hundreds of FBG and also to measure with less-than-1mm spatial resolution, both of those are impossible by WDM and TDM.

Damage of rotating machine comes from bearing, shaft, etc that are represented from high frequency ultrasonic to low frequency vibration. By using FOD wide coverage of frequency (10Hz to 1MHz), preventive diagnosis is possible.

Conventionally, there are several methods to detect thermal neutron, such as Geiger-Muller. SOF is utilizing scintillation phenomena to detect thermal neutron which passes through sensor probe, and such scintillated light is led by fiber optic to photo-detector.