Nonlinear problems in the generation, propagation and measurement of high intensity ultrasonic waves in air

This paper in memory of Leif Bjorno deals with the non-linear acoustic problems linked to high-intensity ultrasonics, an area that he deeply cultivated. The generation, propagation and measurement of high intensity ultrasonic waves in air is highly conditioned by the nonlinearities that are inherent with high intensities such as wave distortion and saturation. Particularly in air the propagation of high-intensity ultrasonic waves is greatly affected by the strong non-linearity introduced by the medium itself which notably limits the attainable acoustic pressure levels. On the other hand the power capacity of the sources is also limited by nonlinear effects such as modal interactions and fatigue failure of its components. Finally, the characterization and measurement of the acoustic field of finite amplitude waves by means of probes of very small diameter with respect to the wavelength poses specific issues on the signal capture and the distortion introduced by the probe itself. All these problems will be ...