Tuesday, September 14, 2010

A lasing wavelength stabilized simultaneous multipoint acoustic sensing system using pressure-coupled fiber Bragg gratings

Jung-Ryul Leea, Corresponding Author Contact Information, E-mail The Corresponding Author, See Yenn Chonga, Chang-Yong Yuna and Dong-Jin Yoonb

a Department of Aerospace Engineering, Chonbuk National University, 664-14 Duckjin-dong, Duckjin-gu, Jeonju, Chonbuk 561-756, Republic of Korea

b Safety Measurement Center, Korea Research Institute of Standards and Science, 209 Gajeong-ro Yuseong-gu, Daejeon, Republic of Korea

Received 5 June 2010;
revised 17 July 2010;
accepted 15 August 2010.
Available online 30 August 2010.

Abstract

A fiber Bragg grating (FBG) sensor head, using a pressure coupling mechanism, was designed for broadband frequency response and structural strain-free characteristic. The pressure-coupled sensor heads were connected to a simultaneous multipoint acoustic sensing system based on a tunable laser. An intelligent lasing wavelength stabilization algorithm capable of identifying the direction of spectrum movement, the wavelength shifting speed, and a fiber bending event was developed so that the simultaneous multipoint acoustic sensing system could be used in environments with rapid temperature variations. The lasing wavelength feedback control algorithm updated the lasing wavelength into the steep slope of the FBG spectrum even under conditions of rapid temperature change. The averaging lasing wavelength updating time was only 21 s because the system can decide a minimal size in scan window by finding the FBG spectrum shifting speed and direction in real time. The system was able to update the lasing wavelength which missed the steep slope of the FBG spectrum under maximum temperature variation rates 0.3014 and −0.3246 °C/s. The proposed system detected simultaneous impact waves at multiple points under conditions of rapid temperature change and change in dynamic strain.

Keywords: Fiber Bragg grating; Tunable laser; Lasing wavelength stabilization; Integrated structural health management; Acoustic emission

Note: The journal paper has published in Optics and Lasers in Engineering (impact factor 1.262, 2010)

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