ABSTRACT
Any real ultrasonic wave has a finite amplitude and to describe such a wave accurately the exact equations of hydrodynamics must be used from the start. This chapter discusses the consequences of including the nonlinear terms in the equations of hydrodynamics, neglecting for the time being dissipative processes. The propagation of ultrasound in liquids is likewise an adiabatic process, for which a theoretically well-founded equation of state does not yet exist in an explicit form. The distortion of the form of the wave during propagation in a fluid is also clearly observed in the diffraction of light by large-amplitude ultrasonic waves. When a finite-amplitude wave propagates in a real medium, the increase in the gradient of the particle velocity at the leading edge of the wave accompanying nonlinear distortions of the wave form must be accompanied by an increase in dissipative losses due to viscosity and heat conduction in the medium.
