Abstract:
A sparker array includes a plurality of sparker sources of sound and light emissions, the plurality of sparker sources arranged in a geometric pattern with respect to a region, the array configured to deliver a maximal acoustic output to the region. Sparker sources may include reflectors. A single electrical source to drive a sparker array may be employed. A sparker system may include two or more sparker arrays. A time delay may be employed to trigger electrical circuits of the sparker arrays. Sparker arrays may be used to deliver shock waves with increased operational life, consistency and efficacy for specific applications.

Description:
RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/289,125, filed on Dec. 22, 2009. The entire teachings of the above application is incorporated herein by reference. 
     
    
     GOVERNMENT SUPPORT 
       [0002]    This invention was supported in part in by the National Institutes of Health (NIH) Small Business Innovation Research (SBIR) program under Grant #2R44DK074231-02 and Grant #1R43DK089703-01. The Government has certain rights in the invention. 
     
    
     BACKGROUND 
       [0003]    Sparkers are pulsed sound and light sources known in the art which employ pulsed electric discharges in a liquid to generate high pressure shock waves and, simultaneously or separately, light emissions. A wide range of sizes and designs are used for various applications. For instance, a lithotripter comprising a single sparker placed at one focus of a semi-ellipsoid reflector is used to generate a shock wave which breaks up kidney stones located at the second focus (see  FIG. 1 ). This is a non-invasive extra-corporeal method for treating kidney stones. In another application, a single sparker placed at the focus of a paraboloid reflector is used to generate a shock wave that is directed into a pipe or at an area to control zebra mussels, an invasive species that clogs water supplies. 
         [0004]    In many sparkers known in the art, the pulsed electric discharge is generated between two electrodes separated by a gap. The output and/or life of this type of sparker are limited by electrode erosion, which may increase the gap separation, rendering the source output insufficient. For instance, conventional sparkers used in lithotripsy must be replaced during a medical procedure, since 2,000-3,000 pulses are required to break up the stone sufficiently, whereas the life of the sparker is about 1,500 pulses. This need for sparker replacement is an inconvenience to the procedure. Furthermore, the spark that generates the shock wave arises from a pulsed electric discharge jumping from one electrode to another, which “wanders” from pulse to pulse. The result is that the shock may not be generated precisely at the focus, causing imprecise focusing at the second focus which, in lithotripsy, is a likely contributor to unpleasant side effects in patients. This type of effect may be deleterious in any application in which the shock is generated at a focal region and transferred to another region. 
         [0005]    Also, in conventional shock wave lithotripters, the position of a kidney stone is not detected continuously during a procedure. Consequently, due to movement of the stone from the shock or from breathing by the patient, shocks may miss or only partially hit the stone. This increases the number of shocks needed to break up the stone and increases side effects from the shock hitting tissue in the vicinity of the stone. 
         [0006]    In addition, pressure pulses from conventional single sparkers have been use to tenderize meat, poultry and fish. Because of spreading of the pressure pulse, the tenderization effect may be non-uniform. 
       SUMMARY 
       [0007]    The present invention relates to a sparker array or multiple sparker arrays. Each sparker in the array can be a pulsed sound and/or light source. While embodiments of the invention are described primarily with respect to sound emissions and resulting pressure profiles, it will be understood that the same inventive concepts apply to light emissions and light intensity profiles. 
         [0008]    Each sparker array may be driven with a single pulsed power circuit. For a given pulsed power circuit there may be an optimum number of sparkers for maximizing efficiency and lifetime. The array is arranged so that the shock waves from each sparker element arrive at a specific location or region to provide a desired combined pressure profile in space and time. Embodiments of the invention may include the addition of acoustic reflectors, designed to deliver a desired combined pressure profile in space and time, the implementation of which may range from having a reflector for each sparker element of each array to having a single reflector for the entire array. Each reflector may be an ellipsoidal reflector having a first and second focus. Multiple reflectors may be positioned so that all of their second foci are at the same location, where, for instance, a kidney stone could be located in a medical procedure. Each sparker in the array may have an electrode positioned at the first focus of an ellipsoidal reflector. 
         [0009]    In another embodiment, each reflector may be a paraboloid, with the sparker placed at the focus. Alternatively, the entire array may have a single reflector to increase the efficiency of utilizing the omnidirectional pressure from the sparkers in the array. In general, the array may be arranged to deliver pressure to a region or planar surface where, for instance, meat, fish, poultry or the like may be located for the purpose of tenderization and/or disinfection. For applications such as tenderization, the sparker array can provide a more uniform pressure pulse than a single sparker. In general, both the light and pressure pulse emitted from the sparker array may work together to effect a particular result in a target region. 
         [0010]    The sound and light emissions may occur in a liquid, such as a coupling liquid. The salinity of the liquid may be greater than 1 millisiemens per centimeter. Because of the salinity of the liquid, each sparker can have a single electrode, with the liquid acting as the second electrode. 
         [0011]    Also, the geometrical arrangement of the sparkers may be selected in order to deliver a desired pressure distribution to a specific region. In addition, the sound and light emissions can include pulses having an adjustable temporal pulselength and the pulselength may be adjusted to adjust the pressure profile delivered to the region. For example, the temporal pulselength of the sound emission may be adjusted to adjust the size of the focal region. Furthermore, in instances in which the sparker electrode is in the vicinity of an electrically conducting material, e.g., as in the case of a metal reflector, the sparker design may include an electrical insulator to assure proper operation and long lifetime. For multiple array arrangements, embodiments of the present invention may include configuring firing of the arrays simultaneously to increase the pressure delivery to a region. Alternatively, embodiments of the present invention may include the capability to trigger shock waves from each array with controlled time separations. For example, two sparker arrays may be triggered to deliver one pulse each, the pulses separated by a time interval. Sparker arrays used in a two-pulse or multi-pulse mode, in which the time between pulses may range over 1-1000 microseconds, may be more efficient at breaking up kidney stones. Furthermore, the sparker array or multiple sparker arrays may be arranged to allow for observation of a specified region. For example, the array elements, including any reflectors, may be arranged to allow for observation of the second focus (of all the array elements), so that a sensor can track the position of a kidney stone at that focus. 
         [0012]    Embodiments of the present inventive sparker array can be used to improve consistency and efficiency, while increasing the useful life of the sparker system. The inventive improvement increases the capability of the source and/or reduces the requirements&#39; on the emissive source to accomplish an intended objective. For lithotripsy, the sparker array can increase the life of the sparker, reduce side effects in the patient, provide for using two or more pulses to break kidney stones, and allow for tracking the position of kidney stones during a medical procedure. 
         [0013]    Furthermore, it is thought that the size of the focal region is an important feature in achieving comminution, or pulverization, of kidney stones. 
         [0014]    Embodiments of the present invention are amenable for use in a wide variety of industrial, commercial, military, academic, and environmental applications such as, in addition to lithotripsy and meat tenderization, surface treatment (e.g. cleaning, barnacle removal), protection against unfriendly divers, sterilization, geophysical exploration, anti-biofouling, underwater surveillance, ballast water control, mine sweeping, submarine countermeasures, controlling zebra mussels and the like. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
           [0016]      FIG. 1  illustrates a conventional single sparker lithotripter. 
           [0017]      FIG. 2  illustrates an embodiment of a sparker array lithotripter. 
           [0018]      FIG. 3  is a schematic diagram of an array of sparkers arranged to provide a specific pressure level to a specific region including a single electrical circuit to drive all the sparkers in the array. 
           [0019]      FIG. 4  illustrates different optimal number of sparkers for different pulsed power circuits. 
           [0020]      FIG. 5  illustrates an array in which each sparker includes a reflector, increasing the pressure level delivered to a specific region. 
           [0021]      FIG. 6  illustrates an array in which each sparker includes a semi-ellipsoidal reflector, with an electrode at one focus, and the array arranged so that all the reflectors have the same second focus. 
           [0022]      FIG. 7  illustrates an array with a single reflector for the entire array. 
           [0023]      FIGS. 8A-8C  show examples of different geometrical configurations for the elements of the array. 
           [0024]      FIG. 9  illustrates an example configuration for a sparker with an electrically conducting reflector. 
           [0025]      FIG. 10  shows a configuration of two sparker arrays, each of which can be triggered electronically at different times. 
           [0026]      FIG. 11  illustrates an array arrangement including a sensor for observing the region with the maximum pressure level. 
           [0027]      FIG. 12  illustrates an example pulsed electrical driver circuit for a single sparker array. 
           [0028]      FIGS. 13A and 13B  show exemplary simulation data from a model of a sparker array. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Shown in  FIG. 2  is an embodiment of a sparker array lithotripter. Sparker array  10  includes multiple sparkers  12  arranged in a geometric pattern to provide a maximum pressure level in specific region  16 . In a preferred embodiment, the geometric pattern may be the surface of a sphere  20 . The center of the sphere of spherical surface  20  may lie within specific region  16 . Furthermore, sparkers  12  may include reflectors  14 , which may be ellipsoid reflectors. Ellipsoid reflectors  14  may be arranged on spherical surface  20  with the second foci of all ellipsoid reflectors  14  located at the center of the sphere. In a preferred embodiment, sparkers  12  may generate pulsed electrical discharges in coupling liquid  22  to generate high pressure shock waves  24 . Shock waves  24  may comprise direct and reflected shock waves, or rays, as described below with reference to  FIG. 5 . Only direct show waves are illustrated in  FIG. 2 . The salinity of liquid  22 , which is a measure of the conductivity of the liquid, may be greater than 1 millisiemens/cm. When used as a lithotripter, an embodiment of sparker array  10  may be placed adjacent to the animal body  26  such that region  16  is located within the body  26 . Region  16  located in body  26  may include a kidney stone  28 . In a preferred embodiment, shock waves  24  from each sparker  12  arrive at specific location  16  to provide a desired combined pressure profile in space and time for the treatment of kidney stone  28 . 
         [0030]    Shown in  FIG. 3  is a schematic diagram of an embodiment of sparker array  310  having sparkers  312 , positioned so that a specific pressure is produced in specific region  316 . Any number of sparkers  312  can be included in array  310  and their positions selected to produce a variety of maximal regions. For simplicity, the sound emitted from each sparker  312  is illustrated as a single and direct shock wave  24  from each sparker  312  to region  316 . 
         [0031]    As shown in  FIG. 3 , a single electrical circuit  305  may drive all of the sparkers  312  in array  1 . As illustrated, all sparkers  312  are connected in parallel to circuit  305  via connections  325   a  and  325   b . Connections  325   a  and  325   b  illustrate a completed circuit. For example, either connection  325   a  or connection  325   b  can be a positive lead with the other a negative lead. In general, circuit  305  may have a capacitance of between 0.002 and 128 microfarads (uF), and the charge voltage may be between 3 and 32 kilovolts (kV). In an embodiment, circuit  305  may have a capacitance of between 0.002 uF and 0.64 uF, and the charge voltage may be between 16 and 32 kilovolts (kV). In another embodiment, the capacitance may be between 32 uF and 128 uF with a charge voltage between 3 kV and 12 kV. Other embodiments may feature different capacitance and charge voltage values. Sparkers  312  or array  310  may be positioned to produce a maximum pressure in specific region  316 . For simplicity, the sound emitted from each sparker  312  is illustrated as a single and direct shock wave  24  from each sparker  312  to region  316 . 
         [0032]    Shown in  FIG. 4  is a graph of the total pressure output as a function of the number of sparkers in a sparker array, for two different pulsed power circuits. In each circuit A and circuit B, the same sparker design is used. As shown in  FIG. 4 , the pressure output, shown on the vertical axis, changes as a function of the number of sparkers driven by each circuit, shown on the horizontal axis. First, the pressure output increases as the number of sparkers driven by each circuit increases, but only up to a point, after which the pressure output decreases as a function of increased number of sparkers. The point at which the pressure output reaches an optimal value is different for circuit A than for circuit B. In  FIG. 4 , the optimal points for circuits A and B are characterized by number of sparkers N A  and N B  and pressure outputs P A  and P B , respectively. The graph shown in  FIG. 4  illustrates the principle that for optimal maximum pressure, the number of sparkers and the pulsed power circuit must be electrically matched. For a given circuit, too few or too many sparkers may result in the circuit not being well matched to the sparker array. 
         [0033]    In the embodiment shown in  FIG. 5 , each sparker  512  of array  510  has a reflector  514  to provide directionality of the sound emission, which, along with the positions of the sparkers in array  1 , provides a maximum pressure in a specific region  3 . Both direct rays  24  and reflected rays  25  are shown in  FIG. 5 . The term ray as used herein refers to a ray of light as well as a shock wave or pressure pulse travelling in a specific direction. The direct rays  24  from each sparker travel a different distance from the reflected rays  25 , which travel to the reflector first and then are reflected. Depending on the temporal length of the pulse and the extra distance the reflected pulse travels, the pulse profile in region  516  may have a single pulse consisting of an overlap of the direct  24  and reflected  25  rays, or have two pulses, one from the direct rays  24  and the other from the reflected rays  25 . Suitable materials for reflectors include air, metal, and plastics, such as Teflon® polytetrafluoroethylene (PTFE) and Delrin® polyoxymethylene (POM), which are highly reflective to sound and light. Teachings of reflectors and reflector systems are disclosed in U.S. Pat. No. 6,672,729 and U.S. Pat. No. 7,593,289, incorporated herein by reference in their entirety. 
         [0034]    Shown in  FIG. 6  is an embodiment in which each sparker source  612  of array  610  includes a reflector  614 . Each reflector  614  is positioned to form a section of an ellipse  606 , and each sparker  612  is located at the first focus  607  of associated reflector  614 . The second focus  608  of each reflector is positioned to provide a maximum pressure in specific region  616 . In one preferred embodiment, second focus  608  of each reflector may be at the same location so as to provide a maximum pressure in the region of all the second foci  608 . For an ellipsoidal reflector  614 , the reflected energy, e.g., the energy of the reflected shock wave, is the major portion of the energy delivered to region  616 . For simplicity, the sound emitted from each sparker  612  is illustrated as a single and direct shock wave  24  from each sparker  612  to focus  8  located in region  616 . 
         [0035]    Shown in  FIG. 7  is a sparker array  710  with a single reflector  714  that encompasses the array. Both direct rays  24  and reflected rays  25  from the sparker array arrive at region  716  to provide a combined pressure profile in space and time. The shape of the reflector  714  is shown in  FIG. 7  to follow the geometric arrangement of sparkers  712 , but that need not be the case. As shown in  FIG. 7 , the geometric arrangement of sparkers  712  in array  710  is such that sparkers  712  are located on a curved line, such as a section of a circle whose center is located in region  716 . Other geometric arrangements of the sparkers  712  of array  710  are possible. In general, the geometric arrangement of the sparkers of array  710  may be one dimensional, e.g., along a straight line, two-dimensional, e.g., along a curve, arc, or in a plane, or three-dimensional, e.g., on a spherical surface. 
         [0036]    Shown in  FIGS. 8A-8C  are exemplary geometrical arrangements of the sparkers of the array  810 . Each array configuration may deliver a different spatial profile of sound or light output in the region  816 . The array may be configured to deliver a maximal acoustic or light output to region  816 . At least one sparker  812  of array  810  in  FIGS. 8A-8C  may include a reflector (not shown), such as reflector  514  described with reference to  FIG. 5 . Alternatively or in addition, each array  810  of  FIGS. 8A-8C  may also include a reflector (not shown) associated with at least two sparkers, such as reflector  714  of  FIG. 7 . For simplicity, the sound emitted from each sparker  812  is illustrated as a single and direct shock wave  24  from each sparker  812  to region  816 . 
         [0037]    As shown in  FIG. 8A , array  810  includes a plurality of sparkers  812  located on a concave line with respect to region  816 . As shown in  FIG. 8B , sparkers  812  of array  810  may be located on a curved surface, such as a section of the surface of a sphere, with respect to region  816 . As shown in  FIG. 8C , array  810  may include a plurality of sparkers  812  arranged in a plane with respect to region  816 , which may be a planar surface. The planar configuration shown in  FIG. 8C  may be particularly suited for meat tenderization, where the meat can be located at region  816 . For instance, meat products can move along through region  816  under the array, which may be pulsing, so as to provide the right amount of pressure to accomplish tenderization by the time the meat products leave region  816 . 
         [0038]    Shown in  FIG. 9  is a sparker head design for sparker  912  in which a dielectric material  930  separates and insulates the sparker electrode  932  from surrounding electrically conducting material of the sparker source, such as metallic reflector  914 . The tip of electrode  932  is exposed to the environment, for example, a coupling liquid. The separation distance  934  between the tip of electrode  932  and the metallic reflector  914  can be adjusted to control the path of discharge of the sparker  912 . The distance  934  may be set large enough to avoid discharge to metallic reflector  914 . 
         [0039]    Shown in  FIG. 10  are two sparker arrays  1010  and  1010 ′, each with a separate electrical driver circuit  305  and  305 ′. Each circuit  305  and  305 ′ is triggered with a specified time delay  1009 , so that two pressure pulses are delivered to region  1016 . The two pressure pulses may be maximal pressure pulses spaced in time. One pulse, e.g., the second pulse, may be smaller than the other. Each sparker array  1010  and  1010 ′ may include one or more reflectors (not shown), such as reflectors  414  described with reference to  FIG. 4 . In a preferred embodiment, each array includes ellipsoid reflectors, such as reflectors  614  described with reference to  FIG. 6 . Furthermore, sparkers  1012  and may be located at first focus of the reflectors and the second focus of all the reflectors may be located in the same region. For simplicity, the sound emitted from each sparker  1012 ,  1012 ′ is illustrated as a single and direct shock wave  24  from each sparker  1012 ,  1012 ′ to region  1016 . 
         [0040]    In lithotripsy, the use of two sparker arrays delivering two pulses separated by a time delay may accelerate breaking up of the kidney stone. A small interpulse interval, e.g., between 1 and 1000 microseconds, may be used to accelerate breaking up of the stone. In addition, the second pulse may be smaller than the first pulse, or vice versa, which may reduce the risk of tissue damage, yet the double pulse may still accelerate kidney stone breakup when compared to conventional single pulse techniques. 
         [0041]    Shown in  FIG. 11  is an embodiment of an array  1110  of sparkers sources  1112 , including reflectors  1114 , configured to provide an opening  1136 , which allows a probe  1138  to interrogate and/or observe region  3 . Region  1116  encompasses a target, such as kidney stone  28 . Probe  1138  may be an ultrasound probe and may be located in-line with focal region  1116 . Such an arrangement of sparkers  1112  and probe  1138  can allow for continuous monitoring the position of a kidney stone during a lithotripsy procedure. Consequently, movement of the stone from the shock or from breathing by the patient can be detected and the delivery of shocks adjusted in order to avoid shocks that may miss or only partially hit the stone. Adjustment of the delivery of shocks may include adjustment of the timing, amplitude, or temporal pulselength of the shocks, or a combination of thereof. In general, the sparker array may be positioned at the start of the lithotripsy procedure so that the kidney stone is at a focus of one or more reflectors of the sparker sources. During the procedure, the position of the sparker array may be adjusted in response to a detected position or detected movement of the kidney stone. 
         [0042]    As shown in  FIG. 11 , reflectors  1114  can be semi-ellipsoidal reflectors. Each sparker  1112  can include one electrode  1132 . Sparkers  1112  can be located at the first focus  1107  of semi-ellipsoidal reflectors  1114 . As shown in  FIG. 11 , the electrode  1132  of each sparker  1112  can be located at the first focus  1107 . The second focus  1108  of all the reflectors  1114  may be located in the same region  1116 . For simplicity, the sound emitted from each sparker  1112  is illustrated as a single, direct shock wave  24  from each sparker  1112  to region  1116 . 
         [0043]      FIG. 12  shows a general circuit configuration for the pulsed electrical driver for the sparker array, such as for circuit  305  that drives array  310  of  FIG. 3 . A power supply  1240  charges a capacitor C to a specific voltage, and the circuit is characterized by an inductance L and resistance R, as is known in the art. The sparkers in the array  1210  are connected in parallel, each having an effective resistance, inductance and capacitance (not shown). 
         [0044]    The temporal pulselength of a pressure pulse emitted from a sparker source can be increased or decreased by increasing or decreasing, respectively, the temporal pulselength of the electrical discharge produced by the electrical circuit driving the sparker source. For arrangements such as shown in  FIG. 11 , this adjustment of the temporal pulselength of one or more sparkers in the array can produce an adjustment in the size of the focal region at the second focus. Increasing the size of the region at the second focus may increase the capability of the pulse to break up a kidney stone. In single and multiple array systems, the pulselength can vary independently of the pulse intensity. 
         [0045]    The way by which adjusting the temporal pulselength can adjust the pressure profile delivered to a region can be understood by considering an instructive example of two pulses. In this example, increasing the pulselength of two pulses also increases the size of the focal region. At the focus, two pulses (with the same peak pressure) arrive simultaneously and combine to produce a peak pressure double that of a single pulse. For locations away from focus, the path length of the two pulses is different, so that the peak pressure is less than double that of a single pulse. The boundary (and hence size) of the focal region is often specified as the location where the peak pressure has fallen to one-half the peak pressure at focus. For two pulses, this occurs when the two pulses no longer overlap. This occurs when the difference in path length (Lp) of the two pulses is equal to the product of tp and c, where tp is the temporal pulselength and c is the propagation speed of a pulse. Consequently, doubling the pulselength tp also doubles the size of the path length which defines the size of the focal region. Thus, the size of the focal region is doubled. Note that the path length difference is related to but does not necessarily coincide with the spatial width of a pulse. 
         [0046]      FIGS. 13A and 13B  show exemplary simulation data from a model of a sparker array demonstrating that doubling the pulselength also doubles the spatial width of the pulse.  FIG. 13A  shows a plot of the pressure at the focus for a 1 microsecond pulse (thin line) and a 2 microsecond pulse (thick line), each pulse delivered to the focal region from an array of fourteen sparkers. Pressure in megapascal (MPa) is shown in the vertical axis and time in microseconds (vs) is shown on the horizontal axis.  FIG. 13B  shows the spatial pressure profiles at the focal region corresponding to the pressure pulses of  FIG. 13A . Pressure in megapascal (MPa) is shown on the vertical axis and position in millimeters (mm) is shown on the horizontal axis. The focus is located at the 0 mm position. The boundary for each of the pressure profiles, and hence the size of the focal region, is indicated by circles that mark the position away from the focus at which the pressure is at one-half peak pressure. As shown in  FIG. 13B , the size of the focal region changes from 4 mm to 8 mm when the pulselength is doubled from 1 to 2 microseconds. For the simulation data shown, the pulse propagation speed c is 1.5×10 5  cm/sec. 
         [0047]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.