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Time Reversal (TR) concept is based on the symmetry of vibrations and acoustics phenomena associate to direct end reversed time. The main consequence of this time symmetry is the possibility of creating, from a measured response, time reversed waves travelling from the measurement locations to the place where the primary waves were created. In the lecture, bases and limitations of Time Reversal concept are presented. Contrary to standard inverse method, no reguralization is needed. Applications in bio mechanics, military purposes and ultrasonics have been developed in literature, this lecture focuses on engineering applications in the field of acoustics and structural vibration. The phenomenon of focalization is presented experimentally and it is shown that, contrary to standard inverse problems for source detection, structural complexity renders Time Reversal technique more efficient. Automotive industry is a field of interest for source detection. The application of TR technique to detect vibro acoustic sources responsible of the noise produced in a car in operating conditions is of major interest . As an example, with TR technique one can clearly detect if the noise is coming from airborne or structure borne path, results on this case is presented. A second application of TR, is defect detection: when a structure has no defect, playing recorded time reversed signals produce focalization of vibrations at primary source locations, when the structure has defects the wave propagation travel is modified and the focalization is no more observed, indicating the presence of defect. Results obtained on a wind turbine blade are presented. A third application is related to the concept of perceptive mechanical media that can detect if a modification is occurring in its environment. This opens a gate to a lot of applications in particular the communication with tactile structures. Some experimental results on structural transmission are shown.
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