Characterization of Nonlinear Ultrasonic Diffuse Energy Imaging

Nonlinear ultrasonic diffuse energy imaging is a highly sensitive method for the measurement of elastic nonlinearity. While the underlying principles that govern the technique are understood, the precise behavior and sensitivity have not previously been quantified. This paper presents experimental, theoretical, and numerical modeling studies undertaken to characterize nonlinear diffuse energy imaging. The influence of incoherent noise, elastic nonlinearity, and instrumentation error are quantified. This paper enables the prediction of spatial sensitivity, aperture, and amplitude dependence of the measurement, all of which moves the technique toward industrial viability. Furthermore, while previous studies have focused on the detection of closed cracks, the ultimate aim for nonlinear ultrasonic imaging in application to material testing is the detection of damage precursors, which requires a sensitivity to weak classical nonlinearity. This paper identifies the experimental requirements necessary for this to be achieved, greatly expanding the potential applicability of nonlinear ultrasonic array imaging.