Abstract
Various nonlinear methods have been investigated in recent years offering improvements of over conventional B-mode in medical imaging and non-destructive testing (NDT) [1]. The most common include harmonic and overtone generation, inter-modulation product generation and resonant frequency shift, also known as Nonlinear Elastic Wave Spectroscopy (NEWS) methods. Furthermore, new optimized excitations such as Nonlinear Time Reversal (TR) based methods are needed and, thanks to the analysis of symmetry properties of cross-correlation generated functions, a wide range of innovation are classified within TR-NEWS methods [2]. This work proposes to unite the frequency-modulated constant-wave scatterer localization with TR-NEWS principles to enable the localization of scatterers distant from the transducers and the analysis of their nonclassical nonlinearity which often can be caused by microdamage or cracking. In this paper, using the found frequency of the defect, the delayed TR–NEWS can be leveraged to periodically excite the damaged region with the focused ultrasound. Resonance excitation results show potential for enhancing the wave motion more than a simple focused waves [3]. Thanks to the complexity of the acoustical propagation in a complex medium, the physical interpretation of the cross-correlation function used during the TR-NEWS analysis can be easily understood in terms of the acoustic energy focused in space and in time.
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