Abstract
In conventional ultrasound detection in structures, a fiber Bragg grating (FBG) is glued on or embedded in the structure. However, application of strain to the structure can influence the sensitivity of the FBG toward ultrasound and can prevent its effective detection. An FBG can work as a strain-insensitive ultrasound sensor when it is not directly glued to the monitored structure, but is instead applied to a small thin plate to form a mobile sensor. Another possible configuration is to affix an FBG-inscribed optical fiber without the grating section attached to the monitored structure. In the present study, sensitivity to ultrasound propagated through an aluminum plate was compared for a strain-insensitive FBG sensor and an FBG sensor installed in a conventional manner. Strains induced by ultrasound from a piezoelectric transducer and by quasi-acoustic emission of a pencil lead break were also quantitatively evaluated from the response amplitude of the FBG sensor. Experimental results showed that the reduction in the signal-to-noise ratio for ultrasound detection with strain-insensitive FBG sensors, relative to traditionally-installed FBG sensors, was only 6 dB, and the ultrasound-induced strain varied within a range of sub-micron strains.
Highlights
In a fiber Bragg grating (FBG), the core of a single-mode optical fiber is subjected to periodic modulation of its refractive index
The sensitivity of strain-insensitive FBG sensors toward ultrasonic vibrations and the strain induced by ultrasonic vibrations were quantitatively evaluated in this study
The following conclusions may be drawn from these results: (1) An FBG sensor affixed to the surface of a thin plate had higher sensitivity to symmetrical-mode waves than asymmetrical-mode waves
Summary
In a fiber Bragg grating (FBG), the core of a single-mode optical fiber is subjected to periodic modulation of its refractive index. Nm Strain-insensitive FBG ultrasound sensing systems that incorporate broadband light sources and optical filters used as demodulators have been proposed [10,11]. These systems employ optical filters that feature periodical optical characteristics such as arrayed waveguide gratings and Fabry-Perot filters. The Bragg wavelength shift induced by ultrasound can be detected by monitoring the change in intensity of light transmitted through the filters, irrespective of the Bragg wavelength These systems still have a critical drawback; the sensitivity toward ultrasonic vibration is too low to acquire a sufficient amplitude response without averaging the response signal. Strains induced by ultrasound vibration and quasi-AE were quantitatively evaluated from the FBG sensor responses
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
