Nonlinear interactions of sound fields generated by a focused annular array: application to vibro-acoustography

In ultrasound-stimulated vibro-acoustography (USVA) imaging method, one tries to form an image of the deformability of a tissue submitted to a low frequency (LF) stress field. The “coherent acoustic emission” resulting from the object vibration is detected by a sensitive hydrophone and used to form an image. In the present literature the origin of this stress field has been identified to the LF radiation pressure of the two primary beams driven at two close frequencies. This work analyses another possible contribution to the LF field which is distributed in the volume of the object and created by the nonlinear interaction of two high frequency primary beams. To do this, a calculation method of the nonlinear field has been developed and applied to the case of multiple rings annular arrays