Finite difference time domain investigation of interior sound fields generated by parametric acoustic arrays

Abstract

Parametric acoustic arrays enable tight beams of audible sound through the nonlinear collimation and mixing of ultrasonic acoustic waves. Previous investigations have considered parametric array characterization when operated in free field environments and in the presence of rigid planar reflectors, so that the opportunity to leverage parametric arrays in more realistic environments with diffusive scatterers and absorptive surfaces remains unexplored. To fill the knowledge gap, this research establishes a finite difference time domain (FDTD) model of a parametric array in an interior environment with a combination of reflective, absorptive, and diffusive bounding surfaces. The modeling framework builds upon existing FDTD models of nonlinear ultrasound wave propagation used in the life sciences and medicine. Here, the studies seek to elucidate how the sonic sound field is manipulated when the reflective surfaces that receive the nonlinear ultrasonic waves are neither planar nor perfectly reflective. The relative ability to take advantage of such interaction between incident ultrasound and reflected energies, when compared to a perfectly rigid plane for reflection, is examined in detail. All together, this work establishes and harnesses an FDTD modeling framework to examine the use of parametric acoustic arrays in conventional interior environments having reflective, absorptive, and diffusive surfaces.