Research On Diaphragm Based EFPI Fiber-Opitc Acoustic Sensor And Sensing System

Compared with the traditional electric acoustic sensor,the optical fiber acoustic sensor has the advantages of high sensitivity,anti-electromagnetic interference,low transmission loss and light weight,and has a wide application prospect.The diaphragm-based Extrinsic Fabry-Perot fiber-optic acoustic sensor is recognized as one of the most sensitive acoustic sensors in the present study so far.The current research focus mainly on its material selection,structural design,signal processing and practical application.In this paper,this type of sensor and its system was studied,the main work is reflected in the following aspects:(1)In order to solve the problem of signal fading caused by the drift of the working point of the interferometric sensors,the dual-wavelength orthogonal demodulation method for signal compensation is studied.The demodulation method is classified into two cases:small signal and large signal.And the application range of the diaphragm vibration amplitude of the two cases is analyzed and discussed.For the situation that the two signals are not completely orthogonal,the demodulation algorithm is improved.We discussed and analyzed the relationship between the demodulation effect and the phase difference in the present of noise in the signals when it comes to practical application.It is concluded that,when the phase difference deviates from the orthogonal condition within ±20°,the signal after demodulation is basically the same.And when the value is over ±60°,the demodulation method is basically ineffective.(2)An EFPI acoustic sensor is designed and fabricated by using the acoustic sensitive polymer film.The acoustic sensing system is built based on the dual wavelength demodulation method.The characteristics of the sensor are tested and the feasibility of the demodulation theory is verified.And the sensor is used to detect the ultrasonic wave in an aluminum plate.The experiment proves that the detection effect is higher than that of an FBG type acoustic sensor attached to the aluminum plate.This kind of detection method has a great application prospect.(3)An optical path structure is designed,which is extended based on the dual-wavelength orthogonal demodulation method,for the construction of quasi-distributed acoustic sensing system.The system can achieve not only quasi-distributed measurement,but also the stability of the signals after demodulation.The experiment verifies the feasibility of this system.