Structural health monitoring system for detecting impact events and acoustic emissions

Y. Qiao*, Sridhar Krishnaswamy

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution


A structural health monitoring system designed to monitor unpredictable, nonrepeating events such as impact and acoustic emission in aircraft structures is described. Such systems require a large number of sensors that have to be active at all times or need to be dynamically activated as an event occurs. While the sensors themselves are relatively inexpensive, the overhead costs in terms of sensor demodulation and data acquisition can be overwhelming as the number of sensors increases. This paper discusses work at NU in the area of array demodulators and dynamic focusing techniques to help minimize sensor demodulation and data acquisition costs. Our efforts to reduce sensor demodulation costs focus on Fiber Bragg Grating (FBG) sensors where standard demodulation methods are not applicable for high frequency applications. At NU, we are developing an adaptive spectral demodulation method using two-wave mixing in photorefractive crystals. The unique features of this scheme include (i) adaptivity to low frequency drifts caused by thermal or quasistatic strains without the need for active stabilization, (ii) dynamic strain sensitivity into the MHz range, and (iii) easy multiplexability of several tens to hundreds of sensors in one demodulator. We then demonstrate a method to dynamically distribute the limited number of channels in a data acquisition system (DAQ) among several acoustic sensors. The structure to be monitored is divided into N zones, with each zone containing M acoustic sensors plus one trigger sensor. The proposed dynamic focusing scheme would allow a system of M sensors distributed over each of N zones to be monitored by a DAQ with (N+M) channels, rather than one with N *M channels as would be needed if all the sensors had to be monitored simultaneously. In this paper, we will demonstrate a SHM system for monitoring impact-induced Lamb waves in multiple thin plates (representing different zones of a large structure) by using multiple piezoelectric and FBG sensors using the above approaches.

Original languageEnglish (US)
Title of host publicationProceedings of the 3rd European Workshop - Structural Health Monitoring 2006
Number of pages8
StatePublished - Dec 1 2006
Event3rd European Workshop on Structural Health Monitoring 2006 - Granada, Spain
Duration: Jul 5 2006Jul 7 2006


Other3rd European Workshop on Structural Health Monitoring 2006

ASJC Scopus subject areas

  • Civil and Structural Engineering
  • Safety, Risk, Reliability and Quality


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