流体媒质三次谐波及三阶非线性声参量研究

Theoretical study of third-order harmonics and third-order nonlinear pamameter in fluid media

从流体动力学的基本方程出发，采用逐级近似微扰法，建立了理想流体媒质一至三级近似的波动方程，并得到三次谐波声压的积累解与声波传播距离的平方成正比.在此基础上进而求得三阶非线性声参量C/A与三次谐波声压之间的关系，这为下一步用有限振幅法测量和研究流体媒质的三阶非线性声参量C/A提供了理论基础.而三阶非线性参量预期在医学超声参数成像技术中有重要的应用前景.

Based on the basic equation of fluid dynamics, the wave equations in the first order,second-order and third-order approximations are established by the perturbation method. The accumulation solution of third-order harmonics sound pressure has a term proportional to the square of the distance. The solution gives explanation to the relationship between nonlinear parameter C/A and the sound pressure of third-order harmonics, thus providing a theoretical foundation for the measurement and study of the nonlinear parameter C/A of fluids by the finite amplitude method. It is expected that the third-order nonlinear parameter will have a good future in medical ultrasonic imaging.