Electromagnetic Scattering Analysis for Crack Depth Estimation

Hidenori SEKIGUCHI  Hiroshi SHIRAI  

IEICE TRANSACTIONS on Electronics   Vol.E86-C   No.11   pp.2224-2229
Publication Date: 2003/11/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Analytical and Simulation Methods for Electromagnetic Wave Problems)
crack depth estimation,  radar cross section,  RCS,  time domain gating process,  dip frequency,  

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A simple non-destructive depth estimation method for a crack on a metal surface has been proposed. This method is based on our finding that the electromagnetic back scattering from a narrow trough (crack model) on the ground plane causes periodical nulls (dips) as the frequency changes, and the first dip occurs when the depth of the crack becomes nearly one half of the incident wavelength. Dependencies of the crack's aperture and the incident angle have also been studied from rigorous and numerical analyses, and considered as our depth estimation parameters. A simple estimation formula for a crack depth has been derived from these studies. Test measurement has been made to check the accuracy of our estimation formula. Time domain gating process is utilized for isolating the crack scattering spectra buried in the measured frequency RCS data. Tested crack types are a narrow rectangular, a tapered, and a stair approximated crack shapes. It is found that the depth of these cracks can be measured within 3 percent error by our estimation method.