MEASURING CAVITATION AT 1.5MHz

Ultrasound, in the megahertz frequency range, is being used increasingly for medical purposes at peak intensities (particularly in therapeutic applications) where the possibility of biological damage to tissues or circulating blood cells by cavitation must be considered a potential hazard.Cavitation is defined in this context as bubbles driven into non linear oscillation in the sound field and which may be responsible for certain physical, chemical or biological effects.At low sonic amplitude, the process known as rectified diffusion may also take place to provide gas nuclei of appropriate size for cavitation to occur.The subsequent process has been referred to as "stable gaseous cavitation".No programme for the investigation of this phenomenon can proceed without some means for its monitoring, and the work reported here is the first step towards that goal.The'e erimental arrangement is shown schematically in Figure 1.A 1&5 ml sample holder is suspended in the path of the beam, which may be focused, using a concave faced transducer, or plane wave, in either standing or travelling save mode, using either an acoustic .mi-rroror absorbing horn.The generator can supply either continuous or pulsed ultrasound over a wide range of frequencies, pulseulengths-and duty ratios, and at intensities Well in excess of those encountered in