Nonlinear acoustic holography for characterization of therapeutic transducers

A method is presented for nonlinear acoustic holography for the study of powerful ultrasound sources and the corresponding radiated fields. The approach is based on measuring two-dimensional distributions of amplitude and phase of acoustic pressure for harmonics present in the signal spectrum. The obtained distributions are used to calculate the back-propagation of the acoustic field for a mathematical reconstruction of the vibrational velocity on the surface of the source. Calculation of the nonlinear propagation is based on the numerical solution of the Westervelt wave equation. The developed method of nonlinear acoustic holography is an effective tool for the characterization of therapeutic ultrasound sources operating at high power levels, when the source vibration characteristics may differ significantly from the vibration characteristics at low power levels. The paper presents the basis of a numerical model for the calculation of the nonlinear propagation of the time-reversed acoustic field. Physical experiments on nonlinear holography of real therapeutic sources are also described.