New measurement techniques developed on the basis of nonlinear acoustics

When nonlinear interactions between a medium and acoustic waves are used in addition to linear interactions, two main directions can be expected in the development of new measurement techniques: (i) the extraction of new characteristics of the medium, and (ii) the construction of completely new or more compact measuring systems. In this paper, a few applications are shown of nonlinear acoustics, picked up from a method based on the use of impulsive and high‐pressure pumping waves to generate the required nonlinear effects and high‐frequency, small amplitude continuous probing waves to detect the results. The applications include (i) measurements of gas flow velocity and temperature distributions, (ii) nondestructive measurement of the stress distribution in metals, and (iii) imaging of dynamic characteristics, including the nonlinear parameter of soft tissues as a new means of medical diagnosis. The exact construction of each system and the corresponding experimental results are shown in detail.