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AbstractThe generation of blast wave in extracorporeal shock
wave lithotripor (ESWL) takes advantage of the high-volt
capacitor to release electricity and to generate electric arc
between two electrodes. This arc heats the water around
electrodes quickly and generates blast wave owing to the water
volume expansion as well as the evaporated water bubbles. The
blast wave generated at the first focus of a truncated
ellipsoidal reflector will focus at the second focus which is
the position of human calculus through reflection. The high
pressure induced by shock wave focusing is the energy source of
calculus fragmentation.The use of water as medium for
lithotriptors is due to the fact that the sound impedance of
water is nearly the same as that of human tissue. Thus water and
tissue are viewed as the same medium. When a blast wave
generated in water which has good acoustic contact with human
tissue, only a little reflection occurs at the interface. The
purpose of this study is to investigate the phenomena of blast
wave focusing in water and the influence of different output
settings on the maximum pressure caused by shock wave focusing
on the lithotriptor LM 9200.Experiments were conducted mainly by
using a pressure transducer and an oscilloscope and a PC based
data acquisition system. It was found that the output voltage
setting has great influence on the maximum pressure, the
gasdynamic focus, and life time of the spark plug used.
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