My Joy of Life

Topics: Phase, Sonar, Complexity Pages: 1 (287 words) Published: October 7, 2012
A recent experiment1 first demonstrated an acoustic
time-reversal mirror ~TRM! in the ocean. A TRM2,3 also
referred to as the process of phase conjugation in the frequency domain,4–8 focuses sound from a source–receive array
~SRA! back to the probe source ~PS! which ensonified
the SRA. The SRA receives the probe-source field, time reverses it ~phase conjugation in the frequency domain!, and
then uses the time-reversed data as the excitation for an array of sources which are collocated with the receiving hydrophones. If the ocean environment does not change significantly
during the two-way travel time, the phase-conjugate
field will refocus, regardless of the complexity of the medium, with the caveat that excessive loss in the system degrades
the process. The focus is both spatial and temporal,
recombining the multipaths from the first part of the
transmission.9 Since this process offers an approach to compensate for multipath interference and other distortion
through a complex medium, it may be applicable to various
adaptive sonar and communication concepts.
This paper describes a second phase-conjugation experiment
conducted in May 1997. The new results reported in
this paper include: ~1! extending the range of focus from the earlier result of 6 km out to 30 km, ~2! validating a new
technique to refocus at ranges other than that of the probe
source, and ~3! demonstrating that probe-source pulses 1
day, 2 days, and as much as 1 week old can be successfully
The second TRM experiment was performed off the
west coast of Italy in May 1997 at the same location as the
previous experiment.1
Figure 1 is a schematic of the experiment, and indicates
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