Résumé:
Thanks to the Time Reversal theory, a technique of
localization of an impact generated by a simple finger knock on
plate-shaped solid objects has been developed. It is shown that
the technique works with only one cheap accelerometer, and that
adding sensors increases the contrast of the localization pattern
but not the resolution. To better understand the phenomenon
and to know exactly the nature of the created waves, a 2D elastic
simulation is used, showing that in a very good approximation
the A0 Lamb mode is the only propagating one. Moreover, at
around 1 cm from the edges, even the non–propagating modes
are negligible compared with the A0 mode. Furthermore, the
stability of the technique to temperature changes is studied.
Indeed, the TR theory predicts that the localization is effective
only if the acoustic medium reciprocity has not been broken by
any change in the medium including wave speed variation due to
temperature change. To this end, a laser interferometer coupled
to a low frequency demodulator measures the impulse responses
created by a knock on a plate during the cooling. Given that
there is only one propagating wave (A0), it is expected that
temperature variations lead to a stretching of acoustic signatures
that can be compensated for thanks to a simple contraction: this
is observed experimentally. This shows the feasibility of the
technique for outdoor Time Reversal interactive experiment.

Mots-clés: Time Reversal, impact localization, A0 Lamb mode,