Reconstruction of inclusions in solids using ultrasonic Born inversion

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Abstract
Voids and inclusions in elastic solids are characterized experimentally using scattered ultrasonic waves. The flaws are reconstructed using a one-dimensional elastic wave inverse scattering algorithm based on the Born–Neuman expansion. This method emphasizes the role of low and intermediate frequency longitudinal waves. The utility of the inverse Born approximation is tested for several new circumstances. First the algorithm is tested for pitch-catch (bistatic) geometries. Secondly the effects of resonant excitation of the scatterer on flaw characterization are measured for several spherical flaws. The third and major result shows that the one-dimensional algorithm can be used to determine the size, shape and orientation of nearly ellipsoidal flaws when access angle is limited. The effects of varying access aperture on the reconstruction are reported. Another common experimental limitation in flaw characterization arises from interferences of the flaw signal with nearby surfaces. We briefly report that the same algorithm was successful in inverting several near surface flaws. In particular, we have successfully reconstructed, in the bulk of the sample, an approximately prolate spheroidal inclusion imbedded in plastic, an oblate spheroidal void in titanium, and in the near surface region an approximately prolate spheroidal inclusion.

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