PHASE-CONJUGATION IN THE OCEAN - EXPERIMENTAL DEMONSTRATION OF AN ACOUSTIC TIME-REVERSAL MIRROR

An experiment conducted in the Mediterranean Sea in April 1996 demonst rated that a time-reversal mirror (or phase conjugate array) can be im plemented to spatially and temporally refocus an incident acoustic fie ld back to its origin. The experiment utilized a vertical source-recei ver array (SRA) spanning 77 m of a 125-m water column with 20 sources and receivers and a single source/receiver transponder (SRT) colocated in range with another vertical receive array (VRA) of 46 elements spa nning 90 m of a 145-m water column located 6.3 km from the SRA. Phase conjugation was implemented hv transmitting a 50-ms pulse from the SRT to the SRA digitizing the received signal and retransmitting the time reversed signals from all the sources of the SRA. The retransmitted s ignal then was received at the VRA. An assortment of runs was made to examine the structure of the focal point region and the temporal stabi lity of the process. The phase conjugation process was extremely robus t and stable, and the experimental results were consistent with theory . (C) 1998 Acoustical Society of America.