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10 April 2014 Development of optical equipment for ultrasonic guided wave structural health monitoring
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This paper presents the development of optical equipment that is suitable for ultrasonic guided wave detection for active SHM in the hundreds of kHz range. In recent years, fiber Bragg grating (FBG) sensors have been investigated by many researchers as an alternative to piezoelectric sensors for the detection of ultrasonic waves. FBG have the advantage of being durable, lightweight, and easily embeddable into composite structures as well as being immune to electromagnetic interference and optically multiplexed. However, there is no commercially available product that uses this promising technology for the detection of ultrasonic guided waves because: (a) the frequency is high (hundreds of kHz); (b) the strains are very small (nano-strain); (c) the operational loads may also induce very large quasi-static strains (the superposition of very small ultrasonic strains and very large quasi-static strain presents a very significant challenge). Although no turn-key optical system exists for ultrasonic guided wave detection, we developed optical ultrasonic guided wave equipment using a tunable laser device. The measurement resolution and sampling speed were considered as the most important criteria in our test. We achieved high sensitive (nano-strain) and high sampling rate. Comparative measurements of low-amplitude ultrasonic waves have been done including FBG, strain gauge, and piezoelectric wafer active sensors (PWAS). Calibration and performance improvements for the optical interrogation system are also developed and discussed. The paper ends with conclusions and suggestions for further work.
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Bin Lin and Victor Giurgiutiu "Development of optical equipment for ultrasonic guided wave structural health monitoring", Proc. SPIE 9062, Smart Sensor Phenomena, Technology, Networks, and Systems Integration 2014, 90620R (10 April 2014);

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