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Proceedings Paper

Limits to acoustic sensing and modal decomposition using FBGs
Author(s): Patrick Norman; Claire Davis; Cédric Rosalie; Nik Rajic
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Paper Abstract

Lamb-wave based structural health monitoring (SHM) approaches are typically constrained to operate below the first cut-off frequency to simplify the interpretation of the wave field in the time-domain. However from a diagnostic perspective, it is desirable to unlock the additional information encoded in the higher-order Lamb wave spectrum. Wave-mode decomposition is necessary for the extraction of useful information from multi-modal acoustic wave fields, which requires spatially dense sampling over the field. The instrument of choice for this task is the laser Doppler vibrometer, which is capable of producing detailed spectral decompositions. However vibrometry is not suited to in-situ measurement for SHM. Fibre Bragg gratings (FBGs) are capable of sensing Lamb waves and detection of higher order modes using FBGs has been previously demonstrated. The ability to multiplex multiple short-length gratings along a single fibre to create an FBG array gives rise to an in-situ sensor with sufficiently dense spatial sampling of an acoustic wave field to perform useful wave-mode decomposition. This paper explores some of the fundamental limits to modal decomposition resolution and bandwidth that exist for such sensors. Potential sources of noise and distortion encountered due to limitations of the sensor fabrication and interrogation methods are also discussed. In addition, modal decomposition of Lamb waves with frequencies up to 1.25 MHz is demonstrated in a laboratory experiment using an array of sixteen ~1 mm long gratings bonded to an aluminium plate. At least four modes are distinguishable in the resulting spectral decomposition.

Paper Details

Date Published: 20 April 2016
PDF: 12 pages
Proc. SPIE 9803, Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2016, 98033U (20 April 2016); doi: 10.1117/12.2219004
Show Author Affiliations
Patrick Norman, Defence Science and Technology Group (Australia)
Claire Davis, Defence Science and Technology Group (Australia)
Cédric Rosalie, Defence Science and Technology Group (Australia)
Nik Rajic, Defence Science and Technology Group (Australia)


Published in SPIE Proceedings Vol. 9803:
Sensors and Smart Structures Technologies for Civil, Mechanical, and Aerospace Systems 2016
Jerome P. Lynch, Editor(s)

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