High intensity ultrasound waves from a strongly focused circular source

To verify the effectiveness of the spheroidal beam eguation (SBE) [J.Acoust. Soc.Am. 107, 3035-3046 (2000)] that is promisingly applicable to a theoretical pre-diction of strongly focused nonlinear beams, experiments are carried out in water using a 1.6MHz focused transducer with a circular aperture of 73mm in diameter and a focal length of 75mm. The aperture half-opening angle becomes 29o, which exceeds the upper limit of the applicability of the KZK model eguation. At the maximum, peak pressure attains about lOMPa at the focus. For such intense waves, the pressure levels of the first three harmonics are in fairly good agreement with the theory. The focused source is highly excited by a sinusoidal tone-burst signal with. three periods to study nonlinear propagation of an ultrasonic pulse. For such a transient wave, the SBE theory agrees well with experiments. Significant distortion appears in the direct wave than the edge wave in the post-focal region, in particular, for the wave passing through a sheet of silicone rubber near the focus.