Reflected shockwave shielding device

In an extracorporeal lithotripter comprising a truncated ellipsoidal reflector open at one end, said one end being downwardly directed substantially toward the surface of the earth, a rubber diaphragm closing said open end;

• said reflector having a first focus point within said reflector and a second focus point outside said reflector and beyond said diaphragm, said reflector having an axis of rotation which passes through both of said focus points, said reflector and said diaphragm comprising a volume filled with water, a pair of electrodes in said reflector and having ends in spaced relation providing a spark gap at said first focus point, an electrical spark between said electrodes across said gap producing a shockwave focused by said reflector on said second focus point, an ultrasound transducer within said reflector and aimed toward said second focus point, and a housing for said transducer, said housing being supported from said reflector adjacent said reflector open end and having a rounded upper end disposed toward said spark gap to deflect shockwaves, said housing having an open end and a bore opening at said housing end toward said second focus point, said transducer being mounted in said bore and aimed downwardly thereof, the improvement comprising means extending downwardly from said housing toward said diaphragm and defining a downwardly opening space, means opening into said space and selectively operable to effect filling of said space with water or a gas, water in said space conducting soundwaves to and from said transducer, and gas being nonconductive of shockwaves to guard said transducer against reflected shockwaves from below.