Simulation of a mixed wave and definition of nonlinearity parameter with diffraction correction

The measurement of acoustic nonlinearity parameter typically employs a toneburst signal of single frequency for harmonic generation during its propagation in through-transmission mode. A two wave mixing technique can be considered and the difference frequency components can be used in determining the nonlinearity parameter. One important advantage of using the difference frequency component is to minimize the source nonlinearity and to acquire low attenuating nonlinear signal. In this work, expressions for the fundamental and difference frequency components are presented, and beam fields are simulated. Explicit expressions for diffraction and attenuation corrections are derived, and the nonlinearity parameter is newly defined with these corrections included.