The effects of local nonlinearities on the ultrasonic second harmonic waves

In most previous works, the ultrasonic nonlinearity is assumed to be uniformly distributed throughout the material. However, the effects of local nonlinearity are attracting interests recently. In this work, the quadratic nonlinearity parameter field is built with a sufficient number of Gaussian kernels, then the single Gaussian beam model of second harmonic wave is developed considering random local nonlinearities. The results show that the degree of nonlinear ultrasonic beam fluctuation depended strongly on the complex microstructure of the inhomogeneous material.