Nonlinear acoustics

The basics of nonlinear acoustics and its application to medical ultrasound imaging are introduced. First, a little historical introduction is given, and next, the coefficient of nonlinearity is introduced, together with a variety of equations, which step by step develop from simple to more sophisticated models. Starting from sinusoidal plane waves in lossless nonlinear media (Fubini solution), the models are gradually expanded to include the effect of absorption (Keck–Beyer), pulsed plane waves (Burgers), quasiplanar wave (Khokhlov–Zabolotskaya–Kuznetsov), diffraction (Westervelt), and local nonlinearity (full nonlinear wave equation). Next, the application of nonlinear acoustics to medical ultrasound imaging is discussed. The peculiarities of harmonic beams are introduced and an example of fundamental and second harmonic ultrasound images is given.