Internal defects detection by ultrasound non destructive testing is widely used in industry. Ultrasonic time signal data are diffi cult to interpret since they require continuous signal analysis for each point of the piece. Inverse problem in materials analysis puts some challenges because the composition variables are both discrete and continuous and because the engineering properties are highly nonlinear functions. In this paper we address the non linear features of back scatted ultrasonic waves from steel plate, for understanding its micro structural behaviour. The experiments show a challenging interface between material properties, calculations and ultrasonic wave propagation modelling
