Time-reversal.md

+<table>
+  <tr>
+    <th colspan="2">Time reversal of acoustic waves</th>
+  </tr>
+  <tr>
+    <td style="text-align:center"><img src="Time-reversal_screenshot1.png" width=100%></td>
+    <td style="text-align:center"><img src="Time-reversal_screenshot2.png" width=100%></td>
+  </tr>
+  <tr>
+    <th colspan="2"> Browse <a href="https://gitlab.onelab.info/doc/models/tree/master/TimeReversal/">model files</a></th>
+  </tr>
+</table>
+
+## Quick start
+
+To run the model, open `TR.pro` with Gmsh.
+
+## Additional information
+
+This model showcases the time reversal of acoustic waves.
+
+The principle of time reversal
+(https://en.wikipedia.org/wiki/Time_reversal_signal_processing) is to use the
+reversibility of the wave equation in non dissipative media to back-propagate a
+signal on the source that first emitted it. Time Reversal Mirrors (TRM),
+designed by Matthias Fink and his team in the 1990's, are composed of a large
+number of transducers which can play alternatively the role of emitters and
+receivers. Associated to a numerical treatment module, they are able to record a
+signal, time reverse it, and back propagate it into the medium. The applications
+are numerous, such as submarine communication or kidney stone destruction.
+
+Several analyses are predefined: time reversal in free space or with
+randomly-distributed obstacles between the source and the TRM, using either a
+monochromatic or a broadband signal.
+
+----
+*Model developed by @bthierry*