Nonlinear harmonic imaging of solids

Abstract

Nonlinear ultrasonics has been shown to be sensitive to small scale damage and microstructural changes in solids. However, measuring the nonlinearity parameter of a solid requires complex calibrations and point-by-point measurements using contact transducers. This poses a challenge when it comes to applying this technique for imaging. The present work explores the use of immersion based nonlinear ultrasonics to perform nonlinear harmonic imaging of solids. A solid sample immersed in liquid (water) will form a “3-layer” structures (water-solid-water) when two ultrasonics transducers are used in through transmission mode. This work will explore the analytical modeling of such a structure using the KZK equation to model the combined effect of attenuation and diffraction of the three layers. The objective of the modelling effort is to develop an inversion model to invert the acoustic nonlinearity parameter from experimental results. The nonlinear model was further validated using experimental measurements carried out on a Steel sample with localized damaged.