Correlations between Microstructure and Backscattered Ultrasonic Energy

  • John Mittleman
  • David W. Mohr
Part of the Review of Progress in Quantitative Nondestructive Evaluation book series


Scattering of ultrasonic energy by discrete and random discontinuities has been studied on a number of scales in geophysics, submarine warfare, mine-hunting, weld inspection, medicine, and materials characterization, to name but a few application areas. This study belongs to the latter category, materials characterization, and is specifically directed towards establishing correlations between metallurgical microstructure and the observable backscatter that is produced when high frequency ultrasonic energy interacts with crystalline grain structures in an immersion test. Wave propagation near liquid-solid interfaces has been described in considerable mathematical detail [2–4], as has propagation in crystalline solids [5–7], but the scattering of sound from grain structure into a liquid half-space is complex, and has received little theoretical treatment. Adler and Bolland [8] measured backscattering from isotropic and anisotropic materials, but with beam diameters and wavelengths far greater than common metallic grain sizes. In studies of backscattering from annealed aluminum samples Bridge and Bin Saffiey [9] presented theoretical and empirical results relating attenuation to microstructure for relatively low frequencies. They noted that leaky waves, propagating both forward and backward, were generated at all angles of incidence; this finding complements the observation by Diachok and Mayer [10] that leaky waves propagate in a conical pattern (not just forward and backwards) when a liquid-solid interface is excited by a longitudinal wave incident at the Rayleigh angle. Because backscattered energy can exist in an acoustic environment which is free from specularly reflected signals, relatively high signal-to-noise ratios can be easily achieved, even from scatterers of microscopic dimensions. A wide range of signal processing tools are available to extract from the backscattered signals features which may correlate with microstructure [11–12]. Saniie and Bilgutay [13] applied several of these tools, including homomorphic deconvolution, to backscattered signals produced in normal incidence contact testing of stainless steel samples with a variety of grain sizes, with some success. The homomorphic deconvolution technique was also used by Kechter and Achenbach [14] to extract single-scatterer characteristics from the complex sound field produced by multiple scatterers.


Surface Wave Frequency Index OFHC Copper Leaky Wave Quantitative Nondestructive Evaluation 
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Copyright information

© Springer Science+Business Media New York 1990

Authors and Affiliations

  • John Mittleman
    • 1
  • David W. Mohr
    • 1
  1. 1.Naval Coastal Systems CenterPanama CityUSA

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