Experimental demonstration of an acoustic time reversal mirror in the ocean

Abstract

An experiment conducted in the Mediterranean Sea in April 1996 demonstrated that a time reversal mirror (or phase conjugate array) can be implemented to spatially and temporally refocus an incident acoustic field back to its origin. The experiment utilized a vertical source–receiver array (SRA) spanning 77 m of a 125-m water column with 20 sources and receivers and a single source/receiver transponder (SRT) co-located in range with another vertical receive array (VRA) of 46 elements spanning 90 m of a 145-m water column located 6.5 km from the SRA. Phase conjugation was implemented by 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 signal was then received at the VRA. An assortment of runs were made to examine the structure of the focal point region and the temporal stability of the process. The phase conjugation process was extremely robust and stable. There was also excellent agreement between experiment and theory.