| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 89 === Blast waves on electrohydaulic extracorporeal shock wave lithotriptors are generated by a high-voltage capacitor that releases electrical current to generate sparks between two electrodes. This spark heats the water around the electrodes quickly, and evaporates water to form bubbles owing to expansion of the bubble volume. The blast waves generated at the first focus of a truncated ellipsoidal reflector will focus at the second focus where is the position of human calculus through reflector’s reflection. The peak pressures induced by shock wave focusing are the energy source of calculus fragmentation. The objective of this study is to design gap-controlled electrodes so that their gap can be controlled in order to generate more uniform-strength peak pressures. There is greatly different performance between the non-gap-controlled electrodes such as the traditionally imbedded electrodes and the improved gap-controlled electrodes. The non-gap-controlled electrodes can’t produce uniform-strength peak pressures at different operating voltage settings, but the gap-controlled electrodes can. It was found that our designed gap-controlled electrodes produced more stable, uniform-strength peak pressures at the second focus than the non-gap-controlled electrodes did. The performance of the gap-controlled electrodes was evaluated by testing their capability of stone disintegration in water. Two electrode materials composed of bronze and tungsten were studied.
For underwater explosions, the cavitation phenomenon of gas bubble generation often occurred in water when the pressure of water was decreased to its vapor pressure at a constant temperature. A bubble acts like an expanding spherical piston to generate a shock wave. Tap water that usually contained a little gas was often used for electrohydraulic lithotriptors, resulting in energy loss. Consequently, the focused peak pressures in tap water were lower than those in degased water. In this study, experiments were conducted to test the extent of stone disintegration in the degased and tap water in order to examine the performance of our designed gap-controlled electrodes.
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