Acoustic Emission Sensing System Of Fiber Bragg Grating

Along with the science and technology progress, the modern project construction structure, the machinery equipment, the electric power and the water conservation, the aerospace and so on have already developed to the large scale, the integration, the complication direction. In these integrated complex of structures, we can discover as soon as possible the position of the crack, the nature and the situation of expansion, discovered effectively the damage of the spot and the degree to prevent the accident from occurring. Compared with the traditional method of non-destructive testing, Acoustic emission testing technology has the advantages of no sensitivity to the test object, dynamic assessment and real-time diagnosis to the measured object, Therefore, acoustic emission detection technology is a very promising non-destructive testing technology.One of the most critical factors of the system overall sensing performance in the acoustic emission testing is the selection of the system sensors. The traditional piezoelectric sensor belongs to the resonant high-sensitivity sensor, has the advantages of the low impedance, high conversion efficiency, wave stability, low dielectric loss and small heat and so on. But its disadvantages are also quite obvious, the relatively narrow operating frequency, vulnerable to electromagnetic interference, can not contact with the corrosive environment and so on. Fiber Bragg grating sensors have good insulation, passive power, small size light weight, resistance, easy to achieve large-scale distributed measurement of electromagnetic interference, and other advantages, the advantages in the environment where inflammable and explosive, high corrosion are particularly obvious. But in the actual building of fiber grating sensing acoustic emission system faces some problems in the process:in practical engineering application, due to the causes of brittle texture of Fiber Bragg grating, we need to carry on the suitable seal protection for the optical fiber diffraction grating sensor. In the process of encapsulation, the encapsulation process will produce more or less affect on Fiber Bragg grating sensors by changing the fiber Bragg grating pass ability; sensor system make optical signals as the vector to perceive to and transmit the acoustic emission signals, because the luminous intensity change caused by the outside vibration is extremely weak, the improper operation of the optical signal in the hardware connection process will have a big influence; sensing system detects the signals of acoustic emission source by testing the change of t fiber grating optical power, Therefore, it has a quite high request to the power source of the system in order to improve the detection accuracy and signal-to-noise ratio. The thesis aims at the above existent problem and combine the physically applied background, develop a set of fiber grating sensing acoustic emission system which core is the optical fiber grating sensor, which including the research of sensing theory, design of sensor systems, the selection and construction of sensor systems devices, a large number of acoustic emission experiment and data processing after building the system and so on. The thesis’s main research work has the following sections:1. The thesis has analyzed the theory of Fiber Bragg grating sensing of acoustic emission. Detailed study of the modulation process of the acoustic emission stress waves on fiber Bragg grating center wavelength; Through the establishment of Fiber Bragg grating acoustic emission sensor model, studying the rule of the Fiber Bragg grating strain transmission, and analyze the important factors affecting the ability of the sensor strain transfer analysis of the packaging process.2. Under the direction of the Fiber Bragg grating strain transfer law, the thesis has analyzed the factors on by one which affect the optical fiber diffraction grating strain sensor transmission ability in the progress, and through experiments studied the technology such as the package base materials, adhesives and package size, and fiber Bragg grating sensor effect the fiber grating sensor strain transfer ability, and has provided the instruction for the optical fiber diffraction grating sensor design and the seal. 3. The thesis design fiber Bragg grating acoustic emission sensors which have a better acoustic emission signal detection capability, easy to install, and developed a set of fiber Bragg grating acoustic emission detection system which has stable performance. The system is good in system stability when the temperature has little change, the system realize the purpose of the system’s temperature compensation by instead of the narrow-band light source by Erbium-doped fiber ring laser when the temperature change is very big.4. As a comparison of conventional piezoelectric acoustic emission sensing system, the thesis has carried on the sine wave and the sound transmitting message examination experiment to the optical fiber diffraction grating sound launch sensing system. Though experiments the Fiber Bragg grating sensing acoustic emission system is able to reach the level of traditional acoustic emission detection system, and is superior to the traditional acoustic emission detection system in response speed, sensitivity, etc.