Patent Publication Number: US-4920955-A

Title: Shock wave source

Description:
This is a continuation, of application Ser. No. 098,842, filed Sept. 21, 1987 ABd. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a shock wave source of the type suitable for treatment of calculi in the body of a patient, and in particular to such a shock wave source having a tube closed at one end by a flexible cover which can be pressed against the patient and closed at the other end by an electrically conductive membrane which is repelled by a flat coil supplied with high voltage pulses. 
     2. Description of the Prior Art 
     Shock wave sources are known which generate focused shock waves which can be directed at a calculus to be disintegrated in the body of a patient, for example a kidney stone. The calculus is shattered to such a degree that it can be eliminated naturally. The generation of the shock wave is undertaken by discharging a high voltage capacitor through a flat coil which may, for example, be in the form of a helical winding. An electrically conductive membrane is disposed adjacent to, but spaced from, the coil, and is repelled upon the occurrence of the high voltage pulse in the coil. The sudden movement of the membrane generates a shock wave in the volume between the membrane and the flexible covering. This shock wave is directed through a shock wave conducting medium in volume at the calculus by means of an acoustic lens in the shock wave tube. 
     Shock wave sources of this type are known wherein both one end of the coil and the membrane lie at ground potential. If a high voltage of, for example 20 kV is applied to the flat coil for generating a shock wave, the full high-voltage will be between a point of the flat coil and the membrane. The layer of insulation between the flat coil and the membrane must therefore have dimensions capable of insulating the entire high-voltage. Nonetheless, arcing is not always successfully avoided. A destruction of the membrane occurs as a result of such arcing. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a shock wave source of the type described above wherein the risk of voltage arcing between the flat coil and membrane is reduced in comparison to conventional devices. 
     The above object is achieved in accordance with the principles of the present invention in a shock wave source wherein the membrane is electrically insulated from both ends of the flat coil. In contrast to conventional shock wave sources, therefore, the membrane and one coil end are not grounded, so that the entire high-voltage is present between the membrane and the coil. As a result of the electrical insulation of the membrane from both coil ends, the insulating distance for the entire high-voltage is equal to twice the distance between the coil and the membrane, so that the risk of arcing is extremely slight. 
    
    
     DESCRIPTION OF THE DRAWING 
     The single FIGURE is a side sectional view, with a schematically indicated voltage source, of a shock wave tube constructed in accordance with the principles of the present invention showing the primary elements thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A shock wave tube 1 has a side thereof, which is to be applied to a patient, closed by an elastic cover 2. An opposite end of the shock wave tube is closed by a membrane 3 consisting of electrically conductive material. The volume surrounded by the shock wave tube 1, the cover 2, and the membrane 3 is filled with a shock-wave conducting coupling agent, such as water. An acoustic lens 4 for focusing the generated shock waves is disposed in this volume. Generation of the shock waves is achieved with a flat coil disposed opposite the membrane, which may be helically wound, and which is separated from the membrane 3 by a layer 7 of insulating material. One terminal of the flat coil is grounded, and the second terminal is connected to a high-voltage pulse generator 8. 
     Upon actuation of the high voltage pulse generator 8, the flat coil is briefly and rapidly energized, and the membrane 3 is rapidly repelled therefrom due to the eddy currents generated in the membrane 3 consisting of electrically conductive material. A shock wave thus propagates through the coupling agent in the shock wave tube 1 and is focused by the acoustic lens 4 at a calculus disposed in a patient. 
     The membrane 3 is electrically insulated from both ends 6a and 6b of the flat coil 6. The total insulating distance, which the maximum high voltage must withstand, is thus equal to twice the thickness of the layer 7 of insulating material. The risk of arcing between any location of the flat coil 6 and the membrane 3 is consequently extremely low. If an arcing were to occur, it would usually proceed between the coil end 6a, the membrane 3 and the coil end 6b. Thus the entire insulating distance is equal to the aforementioned, twice the distance between the flat coil 6 and the membrane 3, so that an adequate insulation is guaranteed, even if the layer 7 of insulating material is quite thin. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent worded hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.