Acoustical imaging by time reversal

Abstract

For the last few years, time-reversal techniques have been proved to be efficient for defect detection in materials without a priori knowledge on the defect. In the case of an extended target, an iterative time-reversal experiment allows focusing on the most reflective point of the defect. At this time, it was not possible to obtain an image of the defect after detection. Using PASS (phased array simulation software, developed in the laboratory), the time-reversal sequence is first iterated in order to be able to focus through a cylindrical interface separating a fluid and a solid. Then, the series of temporal signals is used in conjunction with time-delay laws, thus yielding spatial micro-angulations of the focused beam. Finally, the software is used to compute the back-scattered field due to several extended defects. After calibrating the focal spot displacement with the considered microangulation time delay law, it is shown how this technique allows one to obtain an image of the different defects in the material, even though the standard time-reversal method is only able to focus on the most reflective one. Starting from these numerical results, an experimental validation will start soon.