Experimental demonstration of the focused acoustic field in the ocean

Abstract

An experiment conducted in the Mediterranean Sea in April1996 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 (SM) spanning 77 m of a 125 m water column with 20 sources and receivers and a single source/receiver transponder (SFU) co-located in range with another vertical receive array (VRA) of 46 elements spanning 90 m of a 145 m water column located 6.3 km from the SM. 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 dl the sources of the SRA. The retransmitted signal then was received at the VRA. An assortment of runs was made to examine the structure of the focal point region and the temporal stability of the process. The phase conjugation process was robust and stable and the experimental results were consistent with theory.