This is a preliminary report of an application of underwater shock wave focusing to the so-called extracorporeal shock wave lithotripsy, ESWL. Underwater spherical shock waves were initiated by microexplosions at one of two focus points of an ellipsoidal cavity. Consequently, the reflected shock waves were focused at the second focus point outside the ellipsoidal reflector, and high pressure was generated for a few microseconds. To the shock wave propagation, human tissue has a character very similar to that of water, and we can generate high pressure inside the human body by shock wave focusing sufficient to disintegrate human calculi. This paper reports an experimental and numerical approach of determining the most effective shape of ellipsoidal reflector for the lithotriptor and clarifying the mechanism of focused high-pressure generation by microexplosions. It was found that a half-ellipsoidal shape having a major and minor axis ratio of about 1.4∼1.5 was very suitable for the lithotriptor.
