Quantitative roughness characterization of non-gaussian random rough surfaces by ultrasonic method using pitch-catch and pulse-echo configurations

Fundamental study to quantitatively evaluate not only the root-mean-square (rms) roughness Rq but also skewness Rsk of non-Gaussian random rough surfaces by ultrasonic method is presented. In this work, Johnson distribution together with Kirchhoff theory have been employed to derive a newly proposed Johnson characteristic function, which provides a theoretical relationship among ultrasonic reflection coefficient, Rq and Rsk. Based on the characteristics of such relationship, an effective ultrasonic measurement method consisting of a pitch-catch and a pulse-echo configuration to quantitatively characterize Rq and Rsk has been proposed. A general guideline for such characterization method has also been suggested. The validation of the proposed method has then been conducted numerically in the case of an air-coupled ultrasound. Good agreements between the numerically estimated Rq and Rsk and the corresponding reference values thus confirm the validity of the proposed method