Single transmitter time reversal focusing characterization using cross-correlation method

Acoustic focusing with reverberating acoustic cavities based on the time reversal acoustic principle has been demonstrated in a range of medical applications from three-dimensional imaging to the generation of high pressure therapeutic pulses for the destruction of kidney and gallbladder stones in the human body. We investigate acoustic focusing in a system comprised of a single transmitter and a layered membrane reverberator. The system is capable of achieving focal peak acoustic pressures up to 0.4 MPa with less than 1 mm focal spot and steering range up to 20 mm. Focusing in the frequency range between 0.5 and 4 MHz is investigated. The parametric investigation of various membrane configurations is performed by a conventional time reversal technique with a hydrophone. In addition, we propose the cross-correlation of hydrophone signals as a method of evaluating the system focusing properties without conducting the actual time reversal focusing experiment. The cross-correlation method predicts the focal spot dimensions for the layered reverberator single transmitter system that compares well with experiment and theory. An important implication is the possibility to use inverse filtering to construct signals of the desired waveform with a low spatial peak pressure amplitude that can enhance the cell’s permeability toward macroparticle uptake.