Time reversal acoustic approach for non-lethal swimmer deterrent

One of the most challenging aspects of port security is to provide protection against surface and underwater threats. In particular, a significant terrorist threat might be posed to the domestic harbors in the form of an explosive device delivered underwater by a scuba diver. Along with improving swimmer detection technology, the question arises of how to respond to underwater swimmer threats once they are detected. One of the possible approaches is an application of high intensity acoustic waves utilized as non-lethal weapons. This paper discusses the possible application of Time Reversal Acoustic (TRA) focusing to enable the acoustic localization and precision sound targeting of a hostile diver with minimum impact to the marine environments. The acoustic noise radiated by a diver is used to focus the acoustic energy back to the diver. The diver acts as an active self disclosing acoustic beacon. The advantages and main parameters of the TRA focusing system are demonstrated using the model of shallow sea, where propagation of high frequency acoustic waves is affected by numerous reflections from surface and bottom. The developed model was used to estimate an effective zone of the diver deterrence. Special attention was paid to estimation of acoustic field outside the focal region to be sure the TRA system does not produce acoustic intensities that are harmful to marine life.