Machinbird,
Your idea and comment could be used in next generation of CSMU location devices (pingers, etc)
If you could excite this with a pulse of the appropriate frequency, and if it were nearby, you might receive a slight signal back from the oscillating element after the exciting signal cut off. This signal would have a characteristic amplitude decay over time which should be easy to characterize from experiment with similar pingers. You would also receive echos of the original pulse as it bounced off more distant items, but these would not have the characteristic decay signature.
Our discussion, a world wide public one precludes the big companies to patent it and can be used for the aviation safety in the future.
Kudos!
I will comment the technical advantages of your solution for underwater box location. Will use messages area,. Who become interested i can copy.