Study On Fiber Optic Fabry-Perot Acoustic Sensor And Its Application

As the development of the industry and technology, high-performance measurements on static and dynamic pressure have becoming more and more important in many industrial areas, such as petrochemical industry, fluid engineering, wind tunnel test, biomedicine and industrial safety, etc. Because of the advantages of compact size, high sensitivity, high frequency response and immunity to electromagnetic interference, diaphragm-based extrinsic Fabry-Perot Interferometer (EFPI) optical fiber sensor is a good choice to detect the low pressure and acoustic wave in harsh environment with high temperature and strong electromagnetic interference. In this dissertation, systematic and intensively study on the theory, devices and applications of the diaphragm-based EFPI optical fiber sensor is presented. The major research works are outlined as followings:Based on the theoretical study of the diaphragm-based EFPI optical fiber sensor, an all silica diaphragm-based EFPI optical fiber differential pressure sensor with the pressure balance structure is designed. A capillary with cone-shaped cup and two holes is employed as the alignment and support component of the diaphragm-based EFPI optical fiber sensor, which use a silica diaphragm with 30μm thickness as sensing element. The silica diaphragm is bonded with the capillary by carbon dioxide laser. Due to the vent structure and the low thermal expansion coefficient of the silica material, this sensor has low temperature response and high sensitivity. The demodulation algorithm based on the minimum mean square error estimation is used. Experimental results show that the resolution of this system is 0.12nm, corresponding to a pressure resolution of 4.7Pa. The sensitivity is 25.89nm/KPa in the range of 0-3KPa with a linear correlation coefficient of 0.99958.The novel polymer poly(phthalazinone ether sulfone ketone, PPESK) diaphragm is used as the sensing element of diaphragm-based EFPI fiber optical acoustic sensor for the first time. The self-stabilized quadrature point of optical acoustic sensor (optical microphone) interferometer/intensity systems based on tunable incoherent light source and a tunable fiber laser are designed and studied in this thesis. Based on this self-stabilized system, the polymer diaphragm-based EFPI fiber acoustic sensor can be used to detect the acoustic wave in air with high sensitivity. Experimental results show that the fiber acoustic sensor has a linear response in the range of 0-3Pa at 1 KHz with linear correlation coefficient of 0.99979. The sensitivity of fiber acoustic sensor is 31mV/Pa and its signal-to-noise ratio is 29dB. This sensor can be used for acoustic measurements in a frequency range from 100 Hz to 12.7 KHz and the sensitivity is-30.54±0.88dB (Re.1V/Pa) corresponding to this frequency range. The photoacoustic spectroscopy trace gas detection system based on the PPESK diaphragm EFPI fiber acoustic sensor are designed and studied based on the acoustic characteristics of the resonant photo-acoustic cell. This system is passive and can realize all-optical detection. The diameter of the PPESK diaphragm is 2.75mm. The sensor has a flat response in a range of 200Hz to 2500Hz with a sensitivity of -16.65±0.63dB and the signal-to-noise is 35dB at 1KHz. Using wavelength modulation and second harmonic detection method, the acetylene and ammonia are chosen for the demonstration of this photoacoustic spectroscopy system. The acetylene was detected at the absorption peak of 1530.37nm with the modulation frequency of 802Hz and modulation amplitude of 14mV. The linear relationship between the photoacoustic signal and the acetylene concentration in a range of 0.05ppm to lppm is obtained and the linear correlation coefficient is 0.99981. The signal-to-noise of acetylene absorption spectrum for 50ppb concentration is 32dB and the detection limit is 1.56ppb. The ammonia was detected at an absorption peak of 1531.7nm with the modulation frequency as 818Hz and modulation amplitude of 14mV respectively. Experimental results demonstrate that there is a linear relationship between the photo-acoustic signal and the ammonia in a range from 0.3ppm to 2ppm and its linear correlation coefficient is 0.99976. The signal-to-noise of ammonia absorption spectrum for 500ppb concentration is 48dB and the detection limit is 10.4ppb. This system would have great potential applications in biomedicine and safety monitoring of electric power systems, etc.