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Time Reversal in Solids (Linear and Nonlinear Elasticity)


Source Reconstruction Using Time Reversal

One of the focuses of our group is to study time reversed acoustics in solid media with application to earthquakes, nuclear explosion monitoring, non-destructive evaluation, and biomedical applications. Two movies are displayed here which illustrate sample results obtained using time reversal. Each of these movies display velocity measurements obtained with a laser vibrometer while scanning a 6 by 6 square centimeter scan area on an aluminum plate (1/8 x 12 1/4 x 19 inches in size). In both movies, the upper subplot displays the spatial velocity distribution as time evolves, and the lower subplot displays the amplitude versus time at the source location and a tracer dot traces the plot in time.

Forward Propagation

In the first movie, a 3 mm diameter piezoelectric transducer (placed on the other side of the plate) is emitting a pulse signal centered around 200 kHz. (Click the image to the right to play the movie.)

 

Backpropagation of Time Reversed Signals

In the second movie, four time reversal mirror channels are rebroadcasting the time reversed version of the forward signals they each detected and a focus is created. Note that in the second movie that in the beginning there is no obvious structure to the field. Then annular rings are formed around the initial source location which propagate inward. At a certain point a maximum amplitude occurs at the initial source location which corresponds to the peak of the focal time. After the focal time, the rings begin to propagate away from the initial source location and finally the structure in the field dies away. (Click the image to the right to play the movie.)

For more information, contact Brian Anderson.


 

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