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8 April 2009 Adaptive imaging of damage from changes in guided wave signals recorded from spatially distributed arrays
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Several imaging algorithms are being considered for localizing damage in plate-like structures by analyzing changes in signals recorded from permanently mounted guided wave sensor arrays. Delay-and-sum type algorithms have been shown to be effective for damage localization, but exhibit side lobes that significantly reduce the signal-to-noise ratio. Adaptive algorithms such as MVDR (minimum variance distortionless response) can provide significant reduction in the amplitude of side lobes. Additional improvements in image quality are possible if assumptions can be made concerning the scattering characteristics of the damage site. In the work presented here, the efficacy of the adaptive imaging algorithms is evaluated using both simulated and experimental waveform data. The simulated waveform data is generated by ray tracing and incorporates edge reflections, nominal dispersion curves, and a variety of angular scattering patterns for scatterers with cylindrical symmetry. The effect on image quality of mismatch between actual and assumed scattering patterns is evaluated. Images generated from the simulated waveform data are compared to those generated from experimental data for scattering from a 6 mm through-hole in an aluminum plate. The images are in good agreement, and knowledge of scattering characteristics is shown to significantly improve imaging results.
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Jennifer E. Michaels, James S. Hall, and Thomas E. Michaels "Adaptive imaging of damage from changes in guided wave signals recorded from spatially distributed arrays", Proc. SPIE 7295, Health Monitoring of Structural and Biological Systems 2009, 729515 (8 April 2009);

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