Study On Interferometric Optical Fiber Sensors Applied In Acoustic And Acceleration Measurement

The thesis is supported by the national key project of 863: The optical fibersensing system for measuring the seismic time shift signal, which is focused on therealization of a fiber optic sensing system suitable for oil well logging and reservoirmonitoring. In these applications, the main sensing objects are the acoustic pressureand the vibrating acceleration, which can reflect the distribution information of oillayers. Compared with the traditional piezoelectric sensors, the fiber optic sensorshave notable advantages such as good performance, wide operation frequency range,wide dynamic range, high signal transmission capacity, ease in multiplexing andmulti-parameter detection, electrical insulation, and immunity to electromagneticinterference etc.Among different modulation type fiber optic sensors, phase modulation typesensors based on optical interference theory exhibit high sensitivity, high resolution,geometric versatility and can be employed in many sensing fields. Therefore this kindof fiber optic sensors can play an important role in military and civil applications, andresearch on new sensing structure meeting the demands of practical operation willbecome one of key work in the practicality of interferometric fiber optic sensors.The work in this thesis aims at the interferometric fiber optic sensors suitable foroil well logging and reservoir monitoring. First of all, we illustrate the transducingtheory based on elasto-optic effect in acoustic and acceleration measurement. Andthen we introduce several demodulation technology by which we can obtain the phaseinformation from the interferometric intensity. The major work in this thesis is tostudy diaphragm type interferometric sensing heads applied in acoustic pressuremeasurement and vibrating acceleration measurement, shown as follows:1)Based on elastic mechanics, we analysis the response of the diaphragm typesensing element in acoustic field. The design, manufacturing and experimental testingof a diaphragm type fiber optic acoustic sensor have been completed and described indetail. Experimental results show good linear relationship between output signal andthe acoustic pressure to be measured. In the operating frequency range between 100Hz and 5 kHz, the sensitivity and the minimum detectable level are -139 dB re V/μPaand 82 dB re μPa, respectively。2)Based on vibration mechanics model, we analysis the response of thediaphragm type sensing element in vibration field. The design, manufacturing andexperimental testing of a diaphragm type fiber optic accelerometer have beencompleted and described in detail. Experimental results show good linear relationshipbetween output signal and the acceleration to be measured. The suitable operatingfrequency range is from 10 Hz to 5 kHz, the sensitivity and the minimum detectablelevel are 40 dB re V/g and 83 dB re ng/Hz1/2, respectively。According to the theoretical derivation and experimental results,the diaphragmtype sensors can be believed to have good prospect due to light weight, flexibility,simplicity, high sensitivity and directional response,...