Research On Fiber Bragg Grating Sensing Body Subjected To Ultrasonic Excitation

Ultrasonic detection is one of the popular ways in industrial nondestructive testing. As we know, the conventional piezoelectric sensors can't be used in harsh environment such as electromagnetic interference, high temperature and corrosion, and it only can be used for measuring one unit, so it is difficult to locate damage. Based on the above defects, we introduce FBG to replace piezoelectric sensors. Compared with other sensors, it has advantages of light mass, environmental adaptability and multiple measuring gratings that can be arranged on one optical fiber in order to realize multiple measurement multipoint or distributed real-time damage information monitoring. Due to the high frequency, ultrasonic is easy to decay in the propagation process. In the ultrasonic incentive, strain on the surface of FBG sensing body is very weak, so it must add elastic sensing body to enhance sensitizing effect.Based on the ultrasonic incentive mode, this paper gives optical fiber Bragg grating sensing body as the research object. First it studies the most suitable ultrasonic incentive way for damage detection. And then it establishes the basic mode of sensing body through the finite element method, according to the strain transferring theory of fiber Bragg grating sensor system in the ultrasonic field, and designs a composite sensing body which is sensitive to the perception of fiber grating ultrasonic micro stress. At last it analyzes its sensing properties through different experiments. The detailed content of this paper shows as follows:1. This paper gives the background of ultrasonic sensors based on FBG both at home and abroad, and it also proposes the good application prospect of this technology.2. It introduces the basic theory of ultrasonic, and based on characteristics of lamb wave propagation in the medium, it analyzes the suitable ultrasound incentive mode for damage detection.3. It discusses the basic principle of fiber grating sensor, and studies strain transfer laws of optical fiber grating sensor body in ultrasonic field from aspects of strain wave propagation and response to ultrasonic, offering certain guidance in FBG sensing body design. 4. According to the theory of elastic mechanics, the paper presents kinematics differential equation of ultrasound in solid medium. And it also designs the sensing body from three aspects of material, coupling agent and thickness. What's more, sensing body is modeled through the finite element software COMSOL. In that case, a kind of fiber grating sensor body is designed by analyzing the strain transfer characteristics, which has ability of good strain transfer.5. Through the contrast experiments of different materials, different coupling agent, different thickness and sensing body without elastic part, it has a research on the test performance of the FBG sensing body, and also it compares these test data with the results of the finite element calculation.Experiments results show that the new sensing body has advantage of simple structure and good strain transfer. What's more, the signal of ultrasonic transmitted through the FBG sensing body is detected clearly. In conclusion, this research not only provides theoretical basis to replace traditional electricity sensors, and also has high application value in fields of structural damage and realizing the dynamic monitoring online...