Since 1996 we have conducted a series of experiments in the ocean in which a time reversal mirror (TRM) is implemented in coastal water of approximately 100 m depth. Four frequency regimes were investigated: 450 Hz, 850 Hz, 3500 Hz, and most recently 15000 Hz. We have studied both the basic physics of the time reversal (phase conjugation in the frequency domain) process and the application of TRM to active sonar and underwater communications (Song et al.). In the case of the latter, we have found that the TRM process is sufficiently robust to reproduce ultrasonic laboratory results (Fink, Roux et al.) to the extent that we measured diffraction-limited focusing out to 30 km in the ocean. We have also investigated an assortment of potential sonar applications including echo-to-reverberation enhancement, reverberation nulling, barrier concepts, and coherent TRM-based undersea acoustic communications.
Marine Physical Laboratory, Scripps Institution of Oceanography, UCSD
291 Rosecrans Street
San Diego, CA 92106
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