### Time-Reversal Movie (14 Megs!)

### NB: You've got to wait until it stops rotating

### Here are some explanations on the Time Reversal
experiment.

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Initial condition at time t=0:

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Acoustic signal at time t=T-0 after propagation through a random medium:

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Acoustic signal at time t=T+0 after truncation and time-reversion (where
pressure is kept constant and the velocity field (or equivalently the
time derivative of the pressure field) is reversed):

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Acoustic pulse at time 2T after propagation through the same random medium.
Notice the peak in the center at the location of the initial pulse:

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Zooms of the same pulse at time 2T near the origin:

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Rotation of the pulse in the vicinity of the origin:

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Unlike the initial pulse (a peaked Gaussian which is positive everywhere),
the repropagated signal has essentially mean zero. The time-reversal
procedure is a filter that kills low frequencies.

###
You can get more information on time reversal from the following papers
and their references: