ABSTRACT
This chapter discusses the propagation of ultrasonic waves in an ideal medium without energy losses. In a real medium, however, due to the presence of dissipative processes, part of the energy of the ultrasonic wave is transformed into heat. At the same time the intensity and amplitude of the ultrasonic wave continuously decrease as it propagates and the wave is attenuated. The chapter describes the relations between the quantities varying in the field of ultrasonic waves with infinitesimal amplitude, i.e., in the linear approximation. Viscous losses, in particular, can arise at the boundary of a real ultrasonic beam surrounded by unperturbed liquid, since under the condition of continuity at the boundary the oscillating particles in the liquid in the boundary layer of the beam will create viscous stresses in the unperturbed medium. Non-dissipative processes such as diffraction, scattering by inhomogeneities in the medium, etc. can also attenuate ultrasound.
