Abstract:
Medical devices with novel spark gap electrode designs, able to control manually or automatically the electrodes gap are provided. These devices are used to generate a shock wave created by the rapid expansion and collapse of a plasma bubble that is formed between two spark gap electrodes placed in a special liquid medium, when a high differential voltage (kV) is applied to the electrodes. The resulting shock wave impacts a reflector to direct the energy into the body of an animal or a human toward the desired treatment location. This electro-hydraulic principle to create acoustic shock waves as a method of treatment is in use in the medical (lithotripsy, orthopedic use, wound treatment, burns, post-operative treatment, pain treatment, diagnosis, skin and organ transplantation supporting devices, arteriosclerosis treatment), cosmetic (treatment of scars and cellulite) and veterinary (treatment of musculoskeletal disorders) fields.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority of U.S. Provisional Application No. 61/663,016 filed Jun. 22, 2012, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Current devices used to generate acoustic shock waves using electro-hydraulic principles typically have a finite life with respect to the electrodes used to generate the shock waves. The primary reason for finite life is the increasing spark gap between the electrodes. As the number of shock waves generated between electrodes increases, the electrode surfaces (tips) facing each other are eroded. As the electrode surfaces erode the distance between the tips grow and the effectiveness of electro-hydraulic shockwave generation is diminished. The finite life of the eroding electrodes can require frequent manual adjustment or replacement of electrodes to maintain an effective spark gap. Thus it is desirable to have an electrode arrangement where the tip design allows a longer functional life and at the same time the electrodes&#39; gap distance is maintained automatically at a substantially constant distance to increase electrode life and reduce the need for manual adjustment or replacement of electrodes. 
     SUMMARY OF THE INVENTION 
     The acoustic shock wave produced in embodiments of this invention can be produced through the time-controlled plasma bubble formation and collapse across fixed electrodes placed in a special liquid medium. The formation of the plasma bubble can start with a purely thermal release, which may be generated by the high conductance between the electrodes. The relatively high conductance may produce a flow of electrons between cathode and anode electrodes, which heats the special liquid medium and contributes to plasma formation. The release of electrons and recombination of active atoms generated during high voltage discharge may be catalyzed by the substances present within the special liquid medium that may consist primarily of water with additives such as catalysts, buffer solutions and fine metals to increase conductivity. 
     During the plasma formation, the gap between the electrodes can be shortened by the leading charged particles, since plasma itself is populated by the charged particles. As the gap shortens, less energy may be needed to continue formation of the plasma arc (discharge) and as the voltage (potential energy) continues to be supplied to the electrodes this may generate a purely thermal release between the particles enclosed by the gap. The driven out electrons are freely mobile in the plasma gas, and the free electrons can ionize different particles on their way through impact resulting in a nuclear chain reaction that begins and forms the plasma channel between the electrodes. If an electron of an ion is caught in the plasma channel, its energy may be converted into oscillation energy (heat) and light (UV-RADIATION). The created energy can continue to heat the plasma and the surrounding environment. The environment adjacent to the plasma region between the two electrodes may heat so fast that water in the special liquid medium may evaporate forming a gas bubble that may grow rapidly and collapse rapidly once the bubble&#39;s internal pressure is overcome by the pressure of the surrounding liquid medium and the reduced potential between the two electrodes, thus producing the shock wave. The plasma formation and collapse may occur in less than a microsecond, and the liquid mixture surrounding the electrodes may remain sufficiently stable to sustain creating the next plasma bubble. 
     In various embodiments the combination of materials in the electrodes, the particular geometry of the electrodes and the composition of the special liquid medium can create the energy versus time reaction needed to produce the plasma bubble, which ultimately may produce the shock wave. In at least one embodiment of the present invention the combination of the electrode material, their geometry and special liquid medium in which the discharge occurs is optimized for at least one of:
         consistency and repeatability of the energy distribution created by the shock wave;   minimizing misfires (lack of plasma formation);   reducing the formation of gas bubbles (hydrogen and oxygen) within the special liquid;   reducing the erosion of the electrodes; and   maintaining the stability and life of the special liquid medium.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a conventional applicator treatment head containing two conventional electrodes. 
         FIG. 2  is a schematic diagram of an embodiment of an applicator treatment head containing two spring loaded electrodes separated by a fine mesh structure to control the gap spacing. 
         FIG. 3  is a cross-section plan view of an embodiment of an applicator treatment head containing two spring loaded electrodes each held at the proper spacing by their respective hollow non-conductive support. 
         FIG. 4  is a cross-section plan view of an embodiment of an applicator treatment head containing two spring loaded electrodes each held at the proper gap by the step feature in each electrode that aligns with the stop feature in a non-conductive support. 
         FIG. 5  is a cross-section plan view of an embodiment of an applicator treatment head containing two spring loaded electrodes each held at the proper gap by a detent feature in each electrode. 
         FIG. 6A  is a schematic diagram of an embodiment of an applicator treatment head containing two electrodes each designed as a cylindrical ring to increase the surface area of the discharge so that the electrode wear is reduced. 
         FIG. 6B  is a wireframe perspective view of the electrodes described in  FIG. 6A . 
         FIG. 7A  is a perspective view of an embodiment of two electrodes, each designed as a cylindrical ring having a large surface area and each having multiple radial holes that facilitate fluid circulation to the core of the electrodes, for improved heat dissipation from the electrodes. 
         FIG. 7B  is a cross-section plan view of the electrodes described in  FIG. 7A . 
         FIG. 8A  is a schematic diagram of an embodiment of an applicator treatment head containing two electrodes having a mirrored or complimentary tip profile with equal radiuses to increase the electrode life. 
         FIG. 8B  is a wireframe perspective view of the electrodes described in  FIG. 8A . 
         FIG. 9A  is a top plan view of an embodiment of the applicator treatment head containing two electrodes, center electrode cylinder and an outer electrode ring, that are concentric and coplanar so that the electrodes wear more evenly. 
         FIG. 9B  is a cross-section plan view of the applicator treatment head described in  FIG. 9A . 
         FIG. 10  is a cross-section plan view of an embodiment of an applicator treatment head containing multiple electrode tips for the Anode, which typically wears faster than the Cathode that is grounded to the metal reflector. 
         FIG. 11  is a cross-section plan view of an embodiment of an applicator treatment head with a manual adjustment mechanism using a handle for setting the electrode gap. 
         FIG. 12  is a cross-section plan view of an embodiment of an applicator treatment head with a manual adjustment mechanism using a threaded nut for setting the electrode gap. 
         FIG. 13A  is a top plan view of an embodiment of an applicator treatment head with a manual adjustment feature embodied in a rotating membrane assembly that adjusts one electrode toward the other. 
         FIG. 13B  is a cross-section plan view of the applicator treatment head described in  FIG. 13A . 
         FIG. 14  is a cross-section plan view of an embodiment of an applicator treatment head with a motor controlled adjustment mechanism for adjusting the electrode gap distance. 
         FIG. 15  is a diagram of an embodiment of a control system used to determine the electrode gap distance of various embodiments of the invention. 
         FIG. 16  is a diagram describing an embodiment of the control system used to determine the electrode gap distance and control the motor of  FIG. 14  to adjust the electrode gap. 
         FIG. 17  is a graph plot of test results for the sound output level with electrode wear using the conventional prior art electrode design described in  FIG. 1 . 
         FIG. 18  is a graph plot of test results for the sound output level with electrode wear using the electrodes described in  FIGS. 6A and 6B . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the electrodes in shock wave generation devices for extracorporeal therapy applications are of cylindrical shape and made of special alloys to increase their life expectancy, since in the electrochemical and thermal reaction that occurs during plasma formation some small amount of electrode materials is consumed. This principle is depicted in  FIG. 1  of an applicator treatment head  10  containing two electrodes  14  and  15 . The gap  12 , sometimes referred to as a ‘spark gap’, between the electrodes  14  and  15  is an important design and manufacturing variable that dictates the energy distribution versus time characteristics of the plasma bubble for producing the shock wave. The produced shock waves can be focused, unfocused, planar, pseudo-planar or radial. This electro-hydraulic principle to create acoustic shock waves as a method of treatment is in use in the medical (lithotripsy, orthopedic use, wound treatment, burns, post-operative treatment, pain treatment, diagnosis, skin and organ transplantation supporting devices, arteriosclerosis treatment), cosmetic (treatment of scars and cellulite) and veterinary (treatment of musculoskeletal disorders) fields. 
     As the number of shock waves increase, the electrode surfaces facing each other experience erosion and results in increasing the gap  12 . As the gap  12  increases from its nominal value, the efficiency and quality of plasma bubble formation decreases adversely affecting the intended use. At this point, the electrodes  14  and  15  must be readjusted for the proper gap. 
     Electrodes in Special Liquid Medium 
     The special liquid medium, enclosed in the applicator treatment head  10  by membrane  19 , in which electrodes are placed must be optimized for the intended application. The special liquid mixture is not only important to the formation of the plasma bubble, but it is also a primary factor to electrode tip erosion. The material of electrode tips (for example, DURATHERM ALLOY) and the composition of the liquid medium surrounding the tips must be considered together, because increased conductivity of the fluid will translate to a higher plasma arcing temperature and will increase erosion of the tip. The other equally important optimization is to reduce the formation of the hydrogen and oxygen gas bubbles (from electrolysis of water). Otherwise the medium will become overwhelmed with gas and cause misfiring of the electrodes or reduce the effectiveness of the shockwave due to large gas bubbles acting as an acoustic insulator for transmitting the shock wave to the body. The water used in the liquid mixture is degassed to an oxygen concentration of 2 mg/liter to minimize oxygen bubble formation. The addition of a hydrogenation catalyst will assist in recombining the hydrogen and/or oxygen back into water. An example of a catalyst for this purpose is palladium which has the ability to absorb hydrogen (1200 ml H 2 /ml Pd). Metals like magnesium or aluminum will act as oxygen absorbers. A common hydrogenation catalyst in industry is Pd/C consisting of an activated charcoal with palladium, the charcoal acts as a carrier for the palladium and is a good electrical conductor. The large porous structure of the charcoal provides a large surface (&gt;500 m 2 /g) for supplying the palladium (at the surface of the charcoal) for hydrogenation. The activated charcoal also acts to suspend and distribute the palladium throughout the liquid and increases the conductivity of the water. The other special liquid optimization is to reduce misfires that occur due to poor distribution of ions in the water. If the liquid were comprised solely of the water and catalyst, over time the catalyst settles or clumps and is distributed less uniformly (however it is not a homogenous mixture) throughout the liquid and the initial attempts of plasma formation between the electrodes would not occur. To improve the initial misfiring performance, a buffer is also needed in the liquid to set its pH (increase conductivity) and the affect of a buffer in water will remain stable. The amount of buffer and its pH will affect the erosion of the electrodes, with the more conductive medium allowing more electrode erosion. Also, the conductivity of the liquid affects the plasma formation (i.e., increasing the conductivity reduces the size of the plasma region). 
     Examples of catalysts that can be utilized:
         Nickel, Titanium, Magnesium, Aluminum, Silicon, Silica Gel, PdOH (palladium oxihydrate), PdCl 2  (palladium chloride), Pd/CaCO 3  (mixture of palladium with CaCO 3 —calcium carbonate), Pd/Silicate (mixture of palladium with silicate), Pt/C (platinum with active charcoal), Pd/C (palladium with active charcoal), PdO (palladium oxide—hydrated), HDK (pyrogenic silica)   An exemplary catalyst for an embodiment of the invention may be 15 to 30 mg Pd/C/ml water in the special liquid medium.       

     Examples of conductive agents that can be utilized:
         Citrate Buffer pH 4 to 10, Graphite, Charcoal, HCl/THF (hydrochloric acid or hydrochloride salt (HCl) and tetrahydrofuran (THF) solution), HCl/H 2 O (hydrochloric acid or hydrochloride salt (HCl) and water (H 2 O) solution)       

     An exemplary conductive agents for an embodiment of the invention may be 4 to 4.5 μl pH6/ml water 
     Examples of colloidal or solubility agents for the catalyst that can be utilized:
         Soap, Glycerin, Coupling gel, PEG (polyethylene glycol),       

     An exemplary colloidal or solubility agents for a catalyst used in an embodiment of the invention may be 15 to 30 μl liquid soap/ml water 
     Test results for different combinations of catalysts and buffers are presented in Table 1 below: 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Performance 
                   
               
               
                   
                   
                 as Number 
                 Number 
               
               
                   
                   
                 of Shots 
                 of Shots 
               
               
                   
                   
                 Required to 
                 where Gas 
               
               
                   
                   
                 Destroy 
                 Formation 
               
               
                   
                   
                 Artificial 
                 was 
               
               
                   
                 Formulation 
                 Stones 
                 Observed 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Pd/C 10/50 2.5 g 
                 480 
                 100,000 
               
               
                   
                 Pd0 0.75 g 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 1,150 
                 95,000 
               
               
                   
                 Citrate Buffer 0.3 ml 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 428 
                 93,000 
               
               
                   
                 PdO 0.1 g 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 595 
                 90,000 
               
               
                   
                 PdO 0.2 g 
               
               
                   
                 Pd/C 10/50 3.5 g 
                 650 
                 80,000 
               
               
                   
                 PdO 0.3 g 
               
               
                   
                 Citrate Buffer 0.45 ml 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 588 
                 65,000 
               
               
                   
                 Citrate Buffer 0.66 ml 
               
               
                   
                 Pd/C 10/50 4 g 
                 650 
                 60,000 
               
               
                   
                 PdO 0.36 g 
               
               
                   
                 Pd/C 10/50 2.5 g, 
                 760 
                 60,000 
               
               
                   
                 15-Drop Buffer PH-6 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 460 
                 58,000 
               
               
                   
                 Pd 0.6 g 
               
               
                   
                 Pd/C 10/? 1.5 g 
                 600 
                 56,000 
               
               
                   
                 Pd/C 10/50 4 g 
                 600 
                 55,000 
               
               
                   
                 PdOH/C 20/50 2.5 g 
                 620 
                 55,000 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 440 
                 51,000 
               
               
                   
                 Pd/C 10/50 4 g 
                 700 
                 50,000 
               
               
                   
                 PdO 0.5 g 
               
               
                   
                 Pd/C10/50 2.5 g 
                 480 
                 45,000 
               
               
                   
                 Pd/C 5/50 2.5 g 
                 600 
                 45,000 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 600 
                 42,000 
               
               
                   
                 Pd/C 5/50 2.5 g 
                 740 
                 35,000 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 480 
                 35,000 
               
               
                   
                 PdOH/C 20/50 2 g 
                 740 
                 17,000 
               
               
                   
                 C 1 g 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 560 
                 8,009 
               
               
                   
                 HC1/H 2 O 
               
               
                   
                 Pd/C 10/50 2.5 g; 
                 550 
                 5,000 
               
               
                   
                 HC1/THF 
               
               
                   
                 Pd/C 10/50 2.5 g 
                 470 
                 5,000 
               
               
                   
                 PdC12 0.1 g 
               
               
                   
                 Pd/C 10/50 
                 540 
                 75,000 
               
               
                   
                   
               
               
                   
                 NOTE: 
               
               
                   
                 XX/YY denotes the ratio of the different components in the formulation. 
               
             
          
         
       
     
     The following are optimal liquid mixtures for exemplary embodiments of the special liquid mixture of the invention:
         Special Liquid Mixture Embodiment 1 includes a first catalyst with 22 to 28 mg Pd/C/ml of water, a second catalyst with 1.9 to 2 mg Palladium Oxide-Hydrated PdO/ml of water, and a buffer with 4 to 4.5 μl buffer at pH6/ml of water.   Special Liquid Mixture Embodiment 2 includes a first catalyst with 22 to 28 mg Pd/C/ml of water, a second catalyst with 2 to 3 mg HDK/ml of water, and a buffer with 5 to 6 μl buffer at pH10/ml of water       

     Spring-Loaded Electrodes 
     A device generating acoustic shock waves using electro-hydraulic principle shown in  FIG. 1  has a finite life with respect to generating effective shock waves. The primary reason for finite life is the increasing spark gap  12  between the electrodes, when the electrodes  14  and  15  are energized via the power source  11  controlled by a controller  13 . 
     In one embodiment of the invention the electrodes may be arranged where each electrode is supported by a spring-loaded mechanism on one end and a fine mesh structure on the other end as shown in  FIG. 2 . Electrodes  214  and  215  may be closely encased in cylinders  20  and  21  respectively, and may be supported on one end by a compression spring  18  inside the encasing cylinder. The other end of each electrode may be supported by a rigid porous structure  16 . When fully assembled, the distance  212  between the electrode tips is controlled by the rigid porous structure  16 . The electrodes  214  and  215  are energized via the controlled power source  11 . 
     As the number of shock waves generated by the device increases, the surfaces at the tips of electrodes  214  and  215  experience erosion. As the erosion increases, each compression spring  18  moves the corresponding electrode  214  and  215  towards the supporting structure  16  thus maintaining a constant distance  212  between the tips of electrodes  214  and  215 . Since the distance  212  stays constant, the finite life of the electrodes can be greatly increased providing for less frequent adjustment or replacement of electrodes. This type of electrode arrangement can increase the finite electrode life. 
     An alternative embodiment of electrodes supported by springs is shown in  FIG. 3 . Electrodes  314  and  315  have a hollow center and are supported by a non-conductive members  22  in the center of each electrode and a compression spring  318  on one end. As each electrode  314  and  315  erodes around its circumference, the force from the spring  318  pushes the electrode towards the end stop of the non-conductive member  22  maintaining a nominal ‘spark gap’ distance  312 . 
     Another alternative embodiment of spring-loaded electrodes is shown in  FIG. 4 . The profiles of electrodes  414  and  415  have multiple tapered steps in which a hollow non-conductive member  22  encases each electrode  414  and  415  and provides an end stop against the tapered feature of the electrode  414  or  415  under compression by the spring  418  on the other end. As the electrode material erodes the top of the electrode  414  or  415  to a point where the tapered step is removed, the electrode  414  or  415  will be pushed forward by the spring and stop at the next tapered step. Once this happens the nominal ‘spark gap’ distance  412  is restored. 
     A different embodiment for the electrode geometry that utilizes similar in function to  FIG. 4  is shown in  FIG. 5 . The profile of each electrode  514  and  515  has multiple detents or steps in which a hollow non-conductive member  22  encases each electrode  514  and  515  and provides an end stop against the step feature of the electrodes  514  and  515 . Once the electrode material erodes the step, the electrode  514  or  515  will be pushed forward by the spring  518  and stop at the next step. Once this happens the nominal ‘spark gap’ distance  512  is restored. 
     Ring Shaped Electrodes 
     As shown in  FIGS. 6A and 6B  another embodiment where electrodes  614  and  615  may have cylindrical ring-shaped parallel planar surfaces  26  and  27  respectively at their respective tips  616  and  617 . The outer diameters of the cylindrical ring-shaped parallel planar surfaces  26  and  27  may be greater than the diameter of the base of the electrodes  614  and  615 . The electrode shape shown in  FIG. 6B  provides for larger tip surface areas of the cylindrical ring-shaped parallel planar surfaces  26  and  27  for discharge to occur when electrodes  614  and  615  are energized by the power provided by the power source  11  controlled by a controller  13 . Electrodes  614  and  615  may include a bore  618  and  619  in the center of each electrode to allow heat to conduct more efficiently to the special liquid medium surrounding the electrodes. 
     The electrical discharge, when the design shown in  FIGS. 6A and 6B  is powered from the controlled power source  11 , can occur across one or multiple points  28  and  29  on the cylindrical ring-shaped parallel planar surfaces  26  and  27 , respectively. The location of discharge points  28  and  29  is dictated by path of least resistance to electrical discharge provided by the controlled power source  11 . As the number of voltage discharges increase, the location of 28 and 29 will change because the surfaces  26  and  27  experience localized material erosion. The gap  612  across the electrodes shown in  FIG. 6A  decreases at a lower rate than that of  FIG. 1  due to a larger electrode tip surface area, which increases heat dissipation and provides a random change in the discharge path. The outer diameter of the ring shaped end of the electrode cannot be too large as that it will cause incorrect focusing of acoustic shock waves. 
     Modified Ring Shaped Electrodes 
     The electrode geometry shown in  FIGS. 6A and 6B  may be further modified as shown in  FIG. 7A  and  FIG. 7B . The ratio of electrode tip surfaces  26  and  27  is greater than one ( 26 : 27 &gt;1). This can be beneficial to embodiments of the electrodes because the surface of the anode electrode  26  wears faster than the surface of the cathode electrode  27  and different dimensions may allow a uniform gap adjustment from both ends. Both electrodes  714  and  715  have multiple radial holes  30  that facilitate fluid circulation to the core of the electrodes. Better fluid circulation may improve heat dissipation from the electrodes  714  and  715  into the special liquid medium. 
     Complementary Profile Electrodes 
     An alternate embodiment for the shape of the electrodes shown in  FIGS. 8A and 8B  will provide longer electrode life due to the complementary tip shape of the electrodes. Electrode  31  has a convex tip profile and electrode  32  has a concave tip profile, which are complementary to one another with convex radius  35  being equal to concave radius  36 . The complementary tip profiles create equidistant electric field lines  34  for setting up an equipotential electric field across the gap  812 , when the electrodes  31  and  32  are powered by the controlled power source  11 . The gap  812  across the electrodes  31  and  32  may decrease at a lower rate than that of prior art the electrodes  14  and  15  of  FIG. 1  due to the equipotential electric field lines  34  and the larger tip surface area. This is different when compared to the prior art electrodes  14  and  15  of  FIG. 1  whose point to point gap  12  varies over the tip surface yielding electric field lines of varying intensity between the electrodes that is further exacerbated by tip erosion. 
     Concentric Coplanar Electrodes with Cylindrical Spark Gap 
     An alternative embodiment to extend the life of the electrodes is shown in  FIGS. 9A and 9B . By distributing the spark gap radially along the entire circular/cylindrical gap  912  region erosion of the material of electrodes  46  and  48  should be minimized. If any portion of the material  38  of the inner electrode  46  or the material  40  of the outer electrode  48  become eroded, the gap will be maintained by the other positions around the circumference of the electrode cylinders  46  and  48  allowing continued firing and a much longer useful life than current single/point gap designs as previously shown in prior art  FIG. 1 . 
       FIG. 9B  illustrates the cylindrical spark gap arrangement inside the applicator body  42 . The top view of the spark gap assembly, shown in  FIG. 9A , contains an inner electrode  46 , a center electrode cylinder  50 , and an outer electrode ring  48 . Both electrodes may be mounted to the applicator body  42  and conductive reflector  44  of  FIG. 9B  via snap-on locking pins or other mounting mechanism, which allows precise positioning of the electrodes. Power to the inner electrode  46  of  FIG. 9B  is supplied via a wire cable  54  whereas the outer electrode is connected to the mounting struts  52  that provides a return path to ground via a conductive reflector  44 . 
     Multiple Electrode Tips 
     In general, referring back to  FIG. 1 , the electrode  14  may have the less mass is designated as the cathode, and experiences faster erosion compared to the erosion by the other electrode  15 , the anode. In one embodiment, as shown in  FIG. 10 , increasing the mass of the cathode electrode  1014  along with utilizing multiple anode tips  56  can be arranged such that electrical discharge takes place alternatively across the cathode  1014  and each Anode  56 . This configuration effectively decreases the net electrode erosion resulting in reducing the rate of spark gap  1012  increase. Power to each anode tip  56  is supplied through separate wire cables  54  so that each anode tip  56  can be alternately powered as another means of controlling tip erosion. In alternative embodiment of this design the cathode electrode may consist of multiple tips as opposed to the anode electrode. 
     Position Adjustable Electrodes 
     The shock wave device may include a user adjustable electrode positioning device as shown in  FIG. 11 . A user adjustable electrode positioning device can increase the overall useful life of the electrodes. In one embodiment electrode  1115  is assembled such that user can adjust the ‘spark gap’  1112  distance. Electrode  1115  is assembled to a movable mechanism  64  interfacing with a spring-loaded one directional latch  58  and a position adjustment handle  60 . The interaction between the latch  58  and detents  62  of the movable electrode supporting body  64  allows positioning the electrode  1115  at a nominal location. The user can move the position adjustment handle  60  until both electrodes  1114  and  1115  come in contact with each other and then move the handle  60  in the opposite direction until the latch  58  engages into the detent  62 . This user performed operation may reset the ‘spark gap’ distance  1112  to a nominal value. 
     Alternatively, in another embodiment shown in  FIG. 12  a user adjustable positioning nut  66  that is integrated with the moveable electrode supporting body  64  can be adjusted to set the ‘spark gap’ distance  1212  to a nominal value. The user can turn the adjustable positioning nut  66  until both electrodes  1214  and  1215  come in contact with each other and then turn the positioning nut  66  in the opposite direction until the spring loaded latch  58  engages into the detent  62 . 
     In another arrangement shown in the  FIGS. 13A and 13B , electrode  1314  is assembled to a spring-loaded mechanical member  70 . The mechanical member  70  is captured by a hard plastic membrane  68 . The hard plastic membrane  68  has a ramp geometry  72 , shown in top view  FIG. 13A , on part of its surface such that when rotated will force the electrode  1314  towards the electrode  1315 . This user performed operation will restore the nominal ‘spark gap’ distance  1312 . 
     In a further embodiment, the spark gap distance  1412  can be adjusted automatically through a mechanical drive train  76  coupled to a stepper motor  74  as shown in  FIG. 14 . The drive train  76  is coupled with the electrode supporting body  1416  so that as the stepper motor  74  rotates the electrode  1415  will move either toward or away from the opposing electrode  1414  based on direction of motor rotation. A control system (not shown) for stepper motor  74  can be used to adjust the electrode  1415  by first closing the gap  1412  and then moving the electrode  1415  in the opposite direction to a fixed distance. Alternatively, the stepper motor  74  can be controlled based on automatically estimating the spark gap distance  1412 . A method to automatically estimate the spark gap distance  1412  is shown in  FIG. 15  and described later in this document. 
     Spark Gap Sensing and Compensating System 
     An embodiment for a system to sense the gap distance  1512  is shown in  FIG. 15 . A control system  1500  that may also be responsible for generating the high voltage applied between the electrodes  1514  and  1515 , can utilize different controls of a high voltage generator  80  and high voltage switch  84  to apply a specific voltage impulse or multiple voltage impulses at a much lower voltage to the electrodes  1514  and  1515 . Using the relationship of impulse voltage  108  to impulse current  110  in the applied signal to the treatment head  1510 , the electrode gap  1512  of the applicator treatment head  1510  can be determined. This may be performed prior to starting treatment, during a treatment session or in between treatment sessions. If the gap  1512  increases significantly the control system may alert the user. In a further embodiment, the gap measurement system can be integrated with a treatment head with the manually or automatically adjustable electrode gap shock wave applicators, which were described earlier in this specification. 
     In the case of a shock wave device with manually adjustable electrodes the user is provided an external means to adjust the gap distance of the applicator treatment head as described in  FIGS. 11-13B , and may be provided with a viewing aid displayed on the control system&#39;s display  100 . The adjustment is made by the user to set the optimum distance. The user may be further assisted with the manual adjustment of the electrode gap distance  1512  by instructions that may be shown on display  100  instructing the user to adjust the tips until they touch followed by using the adjustment in the opposite direction a specific number of turns. Another method of gap adjustment may use the equivalent capacitance measurement by the Gap Sensing Interface  106  of  FIG. 15  and  FIG. 16 , which is described later in this specification. 
     In an embodiment where the adjustment is automated, the control system  1600  may be coupled to a shock wave device with an electromechanical drive  76  as depicted in  FIG. 14  and a motor drive and control system  112 , as shown in  FIG. 16 , to set the electrode gap with the feedback from the Gap Sensing Interface  106 , or can be based off a position encoding of the electrode tips that is integrated into the stepper motor  74 . Using an embodiment with the position encoded electrode tips, the stepper motor  74  would be commanded via the motor control  112  and position sensing signal  116  from the microcontroller  96  to move the adjustable electrode until it touches the tip of the other electrode, this is detected using the feedback from the Gap Sensing Interface  106 . After electrodes  1614  and  1615  are in contact with each other the stepper motor  74  would be controlled to move the adjustable electrode in the opposite direction to the nominal gap distance  1612 . Controlling the stepper motor  74  rotation occurs by the motor control and position sensing signal  116  from the microcontroller  96  to the motor driver  112  and the motor drive and sensing interface cable  114 . 
     In both  FIG. 15  and  FIG. 16 , microcontroller  96  can be responsible for controlling the high voltage to the treatment head  1510  and  1610  respectively, using the Generator Enable signal  102  and the HV Switch Enable  104  that will provide the impulse voltage via the HV Connector  88  and HV Cable  78  to the treatment head  1510  or  1610 . The Gap Sensing Interface  106  measures the impulse voltage and current to the treatment head  1510  or  1610  using the Voltage and Current Signal Processor  90 , the Microcontroller  96 , and the Display  100 . 
     The microcontroller  96  may initiate the measurement of the electrode gap  1512  or  1612  by generating a particular impulse voltage or combination of impulse voltages from the HV Generator  80  using the Microcontroller interface Generator Control  102 . The voltage generated by the HV Generator  80  would be less than normally used to create a shock wave. The HV Switch  84  is enabled to apply the Generator Output  82  to the treatment head  10  by the control signal HV Switch Enable  104 . The impulse voltage and impulse current on the output  86  of the HV Switch  84  is sensed by a Voltage and Current Signal Processor  90 . The Voltage and Current Signal Processor  90  converts the impulse voltage and impulse current applied to the treatment head into a digital form  92  and  94  respectively, which is processed by the Microcontroller  96 . The Microcontroller software determines the electrode gap distance  1512  or  1612  through the derivation of the Equivalent Capacitance (“EC”) of the treatment head. 
     The microcontroller  96  may derive the EC by correlating it to the standard electrical capacitance formula for a parallel plate capacitor as shown below:
 
EC≈∈ r ( A   tip   /d   gap )  Equation 1
 
     The formula of Equation 1 can be replaced by other mathematical models that may be a more complex model of the EC for the treatment head. In the simplest case of Equation 1, “∈ r ” is the dielectric value of the special liquid medium within the treatment head. The electrode tip surface area (“A tip ”) can be considered constant as it is less of a factor compared to the electrode gap distance (“d gap ”) in calculating the EC, and the dielectric value can also be assumed to be constant, so the gap distance can be derived by knowing the EC. The microcontroller will measure the voltage (“V”) and current (“I”) applied to the treatment head and from that derive EC using the formula: 
     
       
         
           
             
               
                 
                   EC 
                   = 
                   
                     
                       ∫ 
                       
                         I 
                         · 
                         
                           ⅆ 
                           t 
                         
                       
                     
                     V 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
               
             
             
               
                 
                   
                     d 
                     gap 
                   
                   ≈ 
                   
                     
                       
                         ɛ 
                         r 
                       
                       · 
                       
                         A 
                         tip 
                       
                     
                     
                       
                         ∫ 
                         
                           I 
                           · 
                           
                             ⅆ 
                             t 
                           
                         
                       
                       V 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
               
             
           
         
       
     
     In Equation 3, the microcontroller  96  may integrate the measured current (“I”) applied to the treatment head or can measure current decay over a finite period, from that the charge stored in the capacitance of the electrodes is determined which is required to derive the EC. In conclusion, the microcontroller can measure the voltage (“V”) and current (“I”) applied to the treatment head to monitor the distance between the electrodes. 
     Empirical Electrode Life Span Estimation 
     Acoustic shock wave pulses produce a distinct audible sound that can be measured using a Sound Pressure Level meter. The measured sound level of continuous pulses falls within a tight range when the ‘spark gap’ is within the design limits. As the ‘spark gap’ distance increases, the measured sound level from continuous pulses starts to diverge from the tight range described earlier. This is an indication of inconsistent plasma bubble formation.  FIG. 17  shows empirical data for a ‘spark gap’ of the prior art shock wave device of  FIG. 1 . The data shows a clear divergence of sound level measurements as the number of continuous pulses (life span) increases. The divergence of sound level data can be delayed by changing the geometry of electrode tips as described in this specification (i.e., the spark gap useful lifespan can be increased). 
     When a combination of optimized catalysts and buffers combined with tip shape and material is used, in accordance with embodiments described in this specification, the data shows an increased longevity of the applicators&#39; lifespan as can be seen in  FIG. 18 . This suggests that for medical applications, where the spark generating electrodes are used in a non-consumable fluid that incorporates optimal amounts of catalysts, buffers and conductive particles and are combined with optimal materials and shape for the electrodes as shown in the various embodiments of the invention, the longevity of the shock waves applicators can be increased. 
     The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications, combinations and variations are possible in light of the above teaching. 
     The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. 
     Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.