Passive acoustic fiber Bragg grating sensor measurements of Green function in an instrumented part

Abstract

The development of fiber Bragg grating (FBG) sensors for acoustic measurements permits the instrumentation of manufactured composite parts for the purposes of nondestructive evaluation (NDE) and lifetime monitoring. The parts can be designed from conception with an array of FBG acoustic receivers integrated into its internal structure for the purpose of multistatic data collection for NDE and monitoring of internal changes. The FBG array is accessed via a port on the outer surface and requires no additional power demands on the operation of the part. Data collection is accomplished by activating sources on the surface of the part and measuring the fields along the FBG array. We are particularly interested in Green function (GF) estimation of a FBG instrumented composite structure. By passively measuring diffuse acoustic fields throughout the volume, we use a technique developed by Lobkis and Weaver [J. Acoust. Soc. Am. 110(6), 3011–3017 (2001)] to estimate the GF within the part and monitor it over time. We describe FBG sensor array operation, review the theory of diffuse field GF estimation, and present examples in heterogeneous multilayered structures. [This work was performed under the auspices of the U.S. DOE by University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.]