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Robustness and Efficiency of Time Reversal Acoustics in Solid Media


Below we present three videos related to our work in robustness and efficiency of Time Reversal Acoustics (TRA) in solid media using a single-channel Time Reversal Mirror (TRM) with a sample geometry not leading to a chaotic/ergodic ray path dynamics and using single-mode transducers. The robustness is investigated by evaluating the level of reconstruction of a temporally symmetric source. (Click on each image to view the movie.)

 

Forward Propagation Simulation

Simulated temporal evolution of the norm of the displacement vector wave field (expressed in nm). The Gaussian modulated-sine wave is emitted by the line source on the bottom right boundary. The pulse propagates inside the specimen. The movie shows only the first 150 µsec of the forward propagation. In that time interval the single wave fronts due to multiple reflections at the boundaries are still recognizable. Then, inside the specimen many eigenmodes of vibration are increasingly set up. The sample starts to be a reverberant closed cavity. Random-like patterns of the norm of the displacement vector wave field appear, due to the superposition of the several excited modes.

 

Time Reversal Back-Propagation with the Big Time Reversal Mirror Transducer

Simulated temporal evolution of the norm of the displacement vector wave field (expressed in nm) during the time reversal backward propagation in the case with the big Time Reversal Mirror transducer, located on the bottom left boundary of the sample. Time t = 0 µsec corresponds to the theoretical retro-focal time.

One can see that a large amount of elastic energy is rebroadcasted inside the specimen and is redistributed about the medium. The retro-focusing is visible about t 0 = µsec, but only a small amount of energy is retro-focused at the source location, due to the energy redistribution.

 

Time Reversal Back-Propagation with the Small Time Reversal Mirror Transducer

Temporal evolution of the norm of the displacement vector wave field (expressed in nm) during the time reversal backward propagation in the case with the small Time Reversal Mirror transducer, located on the top right boundary of the sample. Time t = 0 µsec corresponds to the theoretical retro-focal time.

In this case, well before the retro-focal time, the back-propagating wave front is clearly visible. It does collapse exactly at the source location along its whole extension. Less energy is distributed about the medium, the retro-focus contains more energy.

M. Griffa, B. E. Anderson, R. A. Guyer, T. J. Ulrich, P. A. Johnson, "Investigation of the robustness of time reversal acoustics in solid media through the reconstruction of temporally symmetric sources", J. Phys. D: Appl. Phys. 41, 085415 (2008). (Abstract)

For more information, please contact Michele Griffa.

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