Transmission Imaging: Forward Scattering and Scatter Reconstruction
We give here a theory for the nature of the image if produced by the scanning laser acoustic microscope (SLAM) at a surface in the far field of the flaw. A physical model and an exact calculation of scattering of longitudinal acoustic waves by spherical defects are presented. The total displacement field (incident plus scattered) is evaluated at planes at a distance from the defect by using the Ying and Truell scattering theory. It is found that evaluation of the exact type and size of a defect is not possible from direct observation of the total field. A holographic type reconstruction technique using either 2-dimensional Fourier transform, or Rayleigh-Sommerfeld diffraction formulae, was used to reconstruct the field at the location of the defect from a knowledge of the field at an observation plane, a distance z away from the defect. It is found that accurate defect characterization can be made using this reconstruction technique.
KeywordsScattered Field Total Field Transmission Imaging Observation Plane Spherical Void
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- la.T.E. McGraw, D.E. Yuhas, and L.W. Kessler, “Flaw Characterization in Silicon Nitride at 100 MHz.” ARPA/AF Review of Progress in Quantitative NDE, July 8-31, 1979, Scripps Institute of Oceanography.Google Scholar
- lb.Sonomicroscope™, Sonoscan Inc., Bensenville, IL 60106.Google Scholar
- 5.J.E. Goodman, “Introduction to Fourier Optics”, McGraw-Hill, 1968.Google Scholar