Research on Fiber Bragg Grating Acoustic Emission Sensor
A kind of sensible fiber grating acoustic emission (AE) signal sensor based on acrylic substrate is designed. The influence of encapsulation material and structure on the sensing characteristics was investigated experimentally. Firstly, the theory of FBG
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Abstract A kind of sensible fiber grating acoustic emission (AE) signal sensor based on acrylic substrate is designed. The influence of encapsulation material and structure on the sensing characteristics was investigated experimentally. Firstly, the theory of FBG mode and the principle of fiber-optic Bragg grating (FBG) sensing are studied theoretically, and two kinds of encapsulation structures are proposed. FBG AE sensor converts the detected AE signal into the wavelength change of optical signal and converts it into electrical signal voltage change through photoelectric detector. The Advantech PCI-1712 card was used to voltage data acquisition. The software of FBG AE system is designed with LabVIEW to realize multichannel high-speed signal acquisition, data storage, data analysis, and data display and playback. Keywords AE · FBG · Sensor design · LabVIEW
1 Introduction In the integrated and complex structure of the engineering test, the location and extent of damage could be found by early detection of the location of crack and its nature and expansion to prevent the accident occurrence. Compared with the traditional nondestructive testing technology, AE detection technology has the advantages of insensitive to the geometric shape of the detection object, dynamic evaluation, and real-time diagnosis of the measured object, so the AE detection technology is a promising nondestructive testing technology. In the AE detection system, the selection of sensors is one of the most important factors that affect the overall sensing performance of the system. Recently, as a new type of passive optical device, fiber grating has been developed gradually in the Y. Yu (*) · G. Wang · B. Liu School of Information Science and Engineering, Shenyang University of Technology, Shenyang, China e-mail: [email protected] © Springer Nature Switzerland AG 2019 G. Shen et al. (eds.), Advances in Acoustic Emission Technology, Springer Proceedings in Physics 218, https://doi.org/10.1007/978-3-030-12111-2_4
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monitoring of engineering structures due to its advantages of anti-electromagnetic interference, strong chemical resistance, long lifetime, and good reusability. But bare fiber grating has poor shear resistances, so encapsulation of bare fiber gratings is an important step in the practical application of FBG sensors. Two kinds of encapsulation structures with acrylic substrate and steel were advanced. The theory of FBG mode and the principle of FBG sensing were studied theoretically.
2 FBG AE Sensor Package 2.1
Mechanism of Interaction Between Fiber Grating and AE Wave
The fiber grating is a spatial phase grating formed by exposing the optical fiber to the spatial interference fringes formed by ultraviolet light and utilizing the photorefractive index of the photosensitive fiber [1]. In general, the refractive index change of waveguide modes is represented by (1): 2π z þ ϕðzÞ Δneff ðzÞ ¼ Δ neff ðzÞ 1 þ s cos Λ
ð1Þ
where Δneff is the effective refractive index of the fiber, s is related to the modulation of the frin
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