Time reversal in ultrasound focusing transmitters and receivers

The ability of a single-channel time reversal acoustic systems to focus and receive ultrasound radiation is considered. The basic element of these systems is a liquid-filled acoustic reverberator. Two types of the reverberators have been experimentally studied; one of them is a thin-wall cylindrical balloon used in ultrasound catheters for treatment of cardiac fibrillation, and the other consists of plane-parallel foil layers. It is demonstrated that such systems can effectively focus ultrasound using only one radiation channel. Random deformation of balloon walls and foil layers leads to a noticeable improvement of focusing quality and helps to overcome the limitations imposed by a spatial symmetry of a system. The use of a binary radiation mode increases the focal field intensity as compared to the conventional mode. The possibility of spatial localization of external sources with the use of the time reversal focusing system as a receiver is demonstrated.