Semi-analytical time-reversal imaging of a volume source in solids
Résumé
Based on the ability of acoustic waves to relive their past life, the time-reversal principle is of great interest for acoustic imaging. Many applications deal with focusing in soft materials. However, few applications concern solids because compressional- and shear-wave velocities are of the same order of magnitude, leading to mode conversion at interfaces. Moreover, only surface sources have been considered in solids. The purpose of this work is therefore twofold: imaging a volume acoustic source in a solid. The volume source is obtained by focusing a laser beam to a line with finite lateral dimension on the surface of a plate. The laser beam penetrates over a depth depending on the optical properties of the material. The normal displacements caused by acoustic waves generated by this volume source are measured at a surface of the plate. To analyze the optimal experimental configuration, normal displacements representing accurately the typical laser-ultrasonics data are computed. The time-reversal process, i.e., the playback of these normal displacements that leads to the reconstruction of the volume source, is experimentally complicated in laser-ultrasonics. A semi-analytical modeling is thus developed. Simultaneous imaging of the lateral dimension and penetration of the source is obtained and limitations are discussed.
Domaines
Acoustique [physics.class-ph]
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