POWER DIFFERENCE IN SPECTRUM OF SOUND RADIATION BEFORE AND AFTER BREAK OF PHANTOM BY PIEZOELECTRIC EXTRACORPOREAL SHOCK-WAVE LITHOTRIPTOR

This paper investigates the difference in the spectrum of sound radiat ed before and after the break of a phantom at a focal point of the pie zoelectric extracorporeal shock wave lithotriptor (ESWL) in order to i dentify the break time or to examine whether a calculus exists exactly at the focal point or not. From the preliminary experiments using a p iece of chalk as a phantom of a calculus to measure the sound radiated when impact is applied to the chalk by an impact hammer, it is found that the bending vibration component of the vibration is exhibited in the spectrum of sound. However, for small-sized chalk shorter than 3 c m, the peak frequency of the bending vibration is higher than 20 kHz. From the experiments using a piezoeletric ESWL, it is found that there is clear difference in the power spectra among the sound radiated bef ore the break. that radiated just after the break in the breaking proc ess, and that radiated when the chalk does not exist at the focal poin t of the ESWL. These characteristics will be effective for the examina tion of the existence of the calculus at the focal point.