HIGH-EFFICIENCY SHOCK-WAVE GENERATOR FOR EXTRACORPOREAL LITHOTRIPSY

In extracorporeal lithotripsy, the electro-acoustic efficiency of elec trohydraulic generators is limited by the inductance of the electrical discharge circuit. A new shock wave generator is described that uses a coaxial discharge line enabling electro-acoustic efficiency to be gr eatly increased. The line is built using a para-electric ceramic with a relative dielectric constant of 1700, manufactured for use in high-v oltage impulse mode. A Coaxial spark gap, with minimal inductance, has been developed to obtain the triggered breakdown of the discharge lin e. Shock waves are created with a coaxial electrode plugged directly i nto the spark gap and immersed in an electrolyte of degassed saline. E lectrode gap and electrolyte resistivity are adjusted to match the res istivity of the electrolyte volume between the underwater electrodes t o the characteristic impedance of the line. The discharge line generat es in the medium a rectangular current pulse with an amplitude of abou t 6000 A and a rise time of 50 ns. Compared with conventional generato rs, measurements of the expansive peak pressure pulse show an increase of 105% at 10 kV, 86.5% at 12 kV and 34.5% at 14 kV charging voltage. Electro-acoustic efficiency is found to be 11% instead of 5.5% for a conventional discharge circuit.