Grain noise power spectrum estimation for weak scattering polycrystalline materials using experimentally estimated backscatter coefficients: normal incidence

Single Scattering and Diffusive Limits of the Ultrasonic Radiative Transfer Equation

“…Both multiple scattering limits of the URTE have been discussed in this paper. The single scattering limit of the URTE was shown to be valid at early times and was also shown to be equivalent to the independent scatterer model [1,2,3]. Multiple scattering effects became significant when compared with the single scattering at times on the order of or less than the mean free times of the scattering medium.…”

“…The multiple scattering problem has two limits. In the limit of early times or weakly scattering materials, and for experiments involving focussed transducers, a single scattering approximation has been successful for modeling grain noise [1,2,3]. This assumption implies that the incident wave strikes, on average, a single scatterer before being detected.…”

“…Microstructural characterization of polycrystalline metals is often performed using ultrasonic backscatter techniques [1,2,3]. The backscattered diffuse or incoherent signals, also called grain noise, contain microstructural information about grain size, orientation, and composition which is useful for materials characterization.…”

Experimental Evidence of Single and Multiple Scattering in Polycrystalline Materials

“…The material is first interrogated with uhrasound to obtain an ensemble of backscattered signals that are used to estimate the ensemble average backscattered signalpower spectrum (the numerator in Equation (5)). The measurement system related effects are then modeled by H(m) and removed through the frequency domain division shown in Equation (5). When this experimental approach is properly applied, the resulting estimate of 77(w) is independent of the configuration of the measurement system that was used to obtain the backscattered signals.…”

“…Current methods for properly estimating 7](m) are lirnited to cases in which the single scattering assumption is valid. Many models for grain noise also rely upon the validity of the single scattering assumption [5][6][7][8][9]. When attempting to validate models based upon the single scattering assumption, one must frrst verify that the single scattering assumption is valid.…”