Role of entropy perturbations in third-order nonlinear acoustic tomography problems

Abstract

The effect of the entropy perturbations on the acoustic pressure, which arises due to third-order nonlinear interaction, has been considered. The contribution to entropy perturbation due to the presence of viscosity and thermal conductivity (by means of the general equation of heat transfer) and also due to the nonlinearity of the considered medium has been estimated. It has been shown that when all possible factors responsible for the change in entropy are taken into account, the third-order contribution to the acoustic pressure due to density perturbations in primary waves strongly exceeds that due to entropy perturbations. It has been concluded that an isoentropic mathematical description of third-order nonlinear effects in nonlinear acoustic tomography problems is appropriate.