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Fiber Bragg grating seismic sensor using inverted spring-mass system

A simple seismic vibration sensor is designed using fiber Bragg grating (FBG) with aid of an inverted spring-mass system. An inertial mass is attached to the spring enables to oscillate in axial direction only when it is subjected to seismic vibration (P-wave). The spring mass system facilitates free motion only in one direction that is parallel to the base. An interrogation system is developed using Single mode-Multimode- Single mode (SMS) configuration to monitor the Bragg wavelength shift of FBG into its equivalent optical intensity modulation corresponding to the seismic vibration. The experimental results show that proposed sensor is capable of measuring the vibrations of frequency over the range of 2-20Hz. Further, it is evident from the results that the sensor is highly sensitive at 7.5Hz represents the resonance frequency of the designed sensor system. The range of the frequency measurement can be optimized by changing the spring parameters or overhead weight (mass) and also the position of the FBG attached between the spring and support. Thus designed sensor head enables low-cost measurement and fast response in real time applications.