Broadband ultrasonic backscattering applied to nondestructive characterization of materials

A simple method based on the spectrum features of the backscattered signal is proposed to the assessment of scatterers size. The method takes advantage of the band-limited response of the scattering media to an incident broadband pulse. The single to multiple scattering regime transition determines this limited frequency content, which is strongly related to scatterer size. The method is applied to the estimation of graphite particle sizes in cast irons. Good quantitative correlation is obtained between graphite sizes measured by metallography and that obtained using this new ultrasonic method, in spite of the band limitations of the ultrasonic system used in the experiment. By this method, the absolute mean value of the scatterer size can be evaluated, provided that a reasonably good estimate of the concentration of particles is known.