Abstract:
The invention relates to a flexible flat electrode arrangement for a dielectrically limited gas discharge, comprising a central region ( 3 ), an edge region, and a flat electrode ( 14 ) which conducts a high-voltage potential and which is embedded in a flat dielectric that forms an upper face ( 10 ) and a contact face ( 6 ). The invention allows the active surface of the electrode arrangement to be matched to the size of a surface to be treated in that the flat dielectric is in the form of a flat strip ( 1 ) wound into a spiral at least in the edge region, and the electrode ( 14 ) is formed by at least one electric conductor which runs in the longitudinal direction of the wound strip ( 1 ) and which leads into an end surface ( 13 ) of the strip ( 1 ).

Description:
FIELD OF THE INVENTION 
     The invention relates to a flexible, flat electrode arrangement for a dielectric barrier gas discharge. 
     BACKGROUND 
     Dielectric barrier plasma discharges are used for numerous applications. DE 195 32 105 C2 discloses treating, for example activating or cleaning, the surface of three-dimensional workpieces. By virtue of a so-called barrier discharge, it is possible to reduce a layer of oil to minimum quantities of oil per unit length. It is essential here, however, that uniform treatment of the surface takes place. For this, a homogeneous formation or the plasma is required, wherein the idea consists in that the plasma discharges take place in thin filaments which are spaced apart from one another. This is problematic in the case of surfaces with an irregular three-dimensional shape. Therefore, DE 195 32 105 C2 provides for a negative form with the dielectric to be formed by the surface of the workpiece, which negative form therefore consists of a shapeable, for example pressable or deep-drawable plastic. Provision is also made here for an intermediate layer to be used, with the result that the dielectric can be shaped with the intermediate layer directly on the surface of the workpiece. The intermediate layer is then removed in order to ensure an interspace between the dielectric and the electrode, in which the plasma can form. On its side facing away from the surface to be treated, the dielectric is coated with a conductive material, to which the required high voltage in the form of an AC voltage can be supplied. 
     DE 10 2007 030 915 A1 discloses forming hollow fibers from a dielectric material, which hollow fibers are provided with a metallically conductive coating in the interior of said hollow fibers, with the result that the hollow fibers form a dielectric with an inner shielded electrode which, together with the surface acting as mating electrode of a conductive body, can form a plasma field. In this case, provision is also made for a fabric to be formed with hollow fibers which can be laid flat onto an irregular surface, in particular surface of the skin of a human body. This results in the advantage of an electrode arrangement which can be matched to the irregular topology of the surface of the skin for performing a plasma treatment. However, one disadvantage with this consists in the high manufacturing complexity for the formation of the hollow fibers forming the fabric, which hollow fibers are intended to have a flexible electrode in their cavity in order no ensure the flexibility of the electrode fabric required for matching to the surface of the skin. 
     SUMMARY 
     According to the invention, a dielectric barrier gas discharge or plasma treatment is also intended to be possible for bodies with as irregular three-dimensional shape, in particular also for the surface of the skin of a living organism. In this case, the surface to be treated can act as mating electrode by virtue of it being connected electrically to ground, for example. However, it is also possible to form a dedicated mating electrode with the electrode arrangement, with the result that a dielectrically impeded plasma treatment for flat bodies with an irregular shape is also possible in an intermediate space between the electrode arrangement and the mating electrode. 
     A problem in terms of production technology consists for the flat electrodes is that the size of the surface to be treated is often not known in advance. It is therefore known to produce flat electrodes in predetermined, possibly several, sizes. In this case, if appropriate, a discrepancy between the size of the electrode and the size of the surface to be treated needs to be accepted. In order to treat the entire surface, if appropriate the electrode arrangement needs to be laid several times in different positions. If in the reverse case the laid electrode arrangement is too large for the surface to be treated, an unnecessarily large field for the generation of the plasma is built up. 
     Therefore, the present invention is based on the object of providing a flat, flexible electrode arrangement which can be produced easily and inexpensively and, in terms of its effective area, can be matched easily to the size of the surface to be treated. 
     This object is achieved according to the invention by a flexible, flat electrode arrangement comprising a central region and a peripheral region and comprising a flat electrode conducting a high voltage potential, which electrode is embedded in a flat dielectric forming an upper side and a resting side. The flat dielectric has, at least in the peripheral region, the form of a flat strip wound in helical fashion, and the electrode is formed by at least one electrical conductor which runs in the longitudinal direction of the wound-up strip and opens out into an end face of the strip. 
     The flat electrode arrangement according to the invention can therefore be produced in a maximum required size and, for a specific application case, reduced in size by virtue of the fact that a piece of the helically wound strip is cut to length. The electrode formed by the at least one electrical conductor extends into the end face of the strip and contact can be made with said electrode safely and reliably at the end of the strip in order to ensure the connection to the high voltage source. For this, it is conceivable to remove the insulation from one electrical conductor by removing the flat dielectric in order then to produce a contact with conventional connection means. However, it is preferred to keep the dielectric unchanged and to produce the contact with the aid of insulation displacement contacts, which cut through the dielectric in the end region of the strip from a large surface in order thus to produce a metallic contact with the electrical conductor. Such a contact arrangement has the advantage that safe insulation of the electrode arrangement with respect to the high voltage supplied to the electrical conductor is ensured in a simple manner. 
     The electrical conductor embedded in the flat dielectric can have numerous embodiments. It is thus possible, for example, to embed the conductor as a metallic grid-like strip in the helically wound flat dielectric strip. 
     In an embodiment that is advantageous in terms of production technology, the conductor is at least one narrow conductor running in the strip from the end face to the central region and from there back to the end face. Such a narrow conductor, in particular when it is in the form of a conductor wire with a round or oval cross section, can easily be matched to the curvature of the helically round dielectric strip and can furthermore make contact in a simple manner in the same way as a core of an electrical cable. Contact is preferably made with the electrode according to the invention in the region of the end face with a contact arrangement and the electrode is electrically insulated from the surrounding environment. This is achieved in a simple manner with a contact arrangement known per se, which has a housing which is open on one side and into which the end face of the helically wound strip is pushed in such a way that the housing surrounds in insulating fashion the end face, an upper side and lower side and narrow side of an end region of the strip, which end region is adjacent to the end face, and the contact arrangement is provided with insulation displacement contacts for making contact with the flat electrode, which insulation displacement contacts penetrate into the dielectric in self-cutting fashion from the upper side and/or the lower side. 
     The flexible flat electrode arrangement according to the invention in a preferred embodiment is designed to rest on a surface to be treated, wherein the surface forms a mating electrode with respect to an electrode which is contained in the electrode arrangement and conducts a high voltage. It is advantageous here if the strip has integrally formed elevations on its resting side, which elevations define a resting plane and have interspaces which are suitable as the gas space for forming a plasma. The plasma is therefore produced in the interspaces between the elevations of the dielectric. In a further preferred embodiment, the strips have through-openings which pass through the dielectric from the resting side to the upper side and are preferably connected to a suction removal device for fluids from the gas space formed by the interspaces. As a result, it is possible in particular for a plasma treatment of a wound surface to be performed and, for example, for secretions from the wound to be removed by suction via the through-opening during the plasma treatment. It is of course also conceivable for suitable materials to be introduced into the plasma space between the elevations, in particular gaseous materials, via the through-opening. 
     The electrode arrangement according to the invention also makes it possible to form a dedicated mating electrode which is part of the electrode arrangement. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The arrangement will be explained in more detail below with reference to the exemplary embodiments illustrated in the drawing, in which: 
         FIG. 1  shows a schematic perspective view of a resting side of the electrode arrangement with a schematically illustrated connection to a high-voltage supply; 
         FIG. 2  shows a schematic perspective view of an upper side of the electrode arrangement shown in  FIG. 1 ; 
         FIG. 3  shows a plan view of the resting side of the electrode shown in  FIG. 1  with an illustration of the conductor wires which run in the interior of the electrode arrangement and form an electrode; 
         FIG. 4  shows a section along the line A-A on  FIG. 3 ; 
         FIG. 5  shows a schematic perspective illustration of a further exemplary embodiment of a flat electrode arrangement comprising a special contact-making element for making contact with the conductor wires running through the strip forming the electrode arrangement in the region of an end face; 
         FIG. 6  shows a vertical section along the line A-A and a plan view of the contact-making arrangement in a first state; 
         FIG. 7  shows an illustration of the contact-making arrangement shown in  FIG. 6  in an inserted state of the strip; 
         FIG. 8  shows an illustration of the contact-making arrangement shown in  FIG. 7  in a folded-down position of a pivotable holder for insulation displacement contacts; 
         FIG. 9  shows an illustration as in  FIG. 8 , in which the pivotable holder is locked by a slide engaging over said pivotable holder; 
         FIG. 10  shows a schematic perspective illustration as shown in  FIG. 5  with a contact element with which contact has been made and which is locked. 
     
    
    
     DETAILED DESCRIPTION 
     In the first embodiment of a flat electrode arrangement according to the invention illustrated in  FIG. 1 , said electrode arrangement comprises a helically wound flat strip  1 , which, with a rounded-off end  2 , forms a central region  3  of the electrode arrangement and is then shaped in such a way that it forms helical turns  4  resting against one another, by means of which turns a peripheral region is defined. The turns of the strip rest against one another via integrally formed spacer pieces  5 . 
     The strip  1  consists of a dielectric material and forms a dielectric of the electrode arrangement. The side shown in  FIG. 1  represents a resting side  6 , on which the strip  1  is provided with a multiplicity or elevations  7 , which in the exemplary embodiment illustrated are in the form of round knobs. The elevations  7  all have the same height and, with their upper side, define a resting surface for a mating electrode (not illustrated), which can be formed by the surface to be treated when said surface is connected to ground, for example. The elevations  7  only take up a small surface area component of the resting surface  6 , with the result that a much greater proportion of the resting surface consists of interspaces  8  between the elevations  7 . The surface proportion of the elevations can be between 5 and 40% of the resting surface  6 , while the interspaces  8  take up a surface proportion of 60 to 95%, preferably between 75 and 95%. 
       FIG. 1  also shows that small through-openings  9  have been introduced in the strip  1 , which through-openings are preferably distributed uniformly over the surface of the strip. The through-openings  9  extend from the resting side  6  toward the opposite upper side  10  (cf.  FIG. 2 ). The through-openings  9  advantageously enable removal by suction of fluid from the interspaces  8  in which a plasma is intended to form during operation of the electrode arrangement. 
     For the formation of the plasma, an electrode, which is represented schematically as being connected to a high voltage supply  12  by means of two conductor wires  11  in  FIG. 1 , is embedded in the dielectric formed by the strip  1 . 
       FIG. 2  shows a view of the upper side  10  of the electrode arrangement formed by the strip  1 . Only the through-openings  9  are visible from the upper side  10 . 
     The illustration in  FIG. 3  shows that the conductor wires  11  run within the strip  1  in the longitudinal direction thereof, to be precise as far as into the central region  3  formed by the rounded-off end  2  of the strip  1 . In the central region  3 , the conductor wires are bent through 180° so as to match the rounded-off end  2  and run parallel to one another through the conductor back to an end face  13 . The end face  13  represents the outer free end of the strip  1  and can be aligned at right angles (radially) with respect to the longitudinal extent of the strip  1 . However, it is also possible for the end face to be formed with any desired angle with respect to the longitudinal extent of the strip  1 . 
       FIG. 3  shows that the two conductor wires  11  which run to and fro in the longitudinal direction of the strip  1  form an electrode  14  which is embedded in the dielectric formed by the strip and which is therefore formed by four sections of the conductor wires  11  running parallel to one another in the exemplary embodiment illustrated. 
     The conductor wires  11  of the electrode  14  are connected to an identical high-voltage potential in the high-voltage supply  12 . They therefore form an electrode connected to a high-voltage potential which, with a mating electrode which is formed, for example, by the surface to be treated which is connected to ground, a treatment space which is formed in the case of the electrode illustrated by the interspaces  8  between the elevations  7 . The electrode  14  is delimited on all sides by the dielectric of the strip  1 , with the exception merely of the end face  13 . 
     In the case of the connection of the conductor wires  11  to the high-voltage supply  12  as illustrated schematically in  FIGS. 1 to 3 , insulation of the conductor wires  11  is of course required outside of the end face  13  in the same way as is required at the end face  13  itself. 
     The sectional illustration in  FIG. 4  shows a view of the end face  13 , and also the interspace running in helical fashion and formed by the spacer pieces  5  between the turns  4  of the strip  1  and the multiplicity of elevations  7 , whose identical heights form a resting plane  15 . 
     Contact-making of the conductor wires  11  running within the strip, which contact-making is not only schematic but also realistic, is illustrated in  FIG. 5 . In this case, the high-voltage supply  12  is connected to a contact-making element  17  via an insulated high-voltage cable  16 , which contact-making element  17  has a pivotably mounted holder  8  and a locking slide  19 . The holder  18  and the locking slide  10  are located on a housing  20 , which is closed in insulating fashion on all sides and has an insertion slot  21  for an end region of the strip having the end face  13 .  FIG. 5  illustrates that the end region of the strip has been inserted into the insertion slot  21 . 
     The illustration in  FIG. 6  shows the end region of the strip  1 , which has been inserted into the insertion slot  21  of the housing  20  against a stop  22 , which is mounted longitudinally displaceable in the housing  20  and is held in a rest position by a compression spring  23 . The sectional illustration in  FIG. 6  also shows that the pivotable holder  8  can be pivoted about a rotary spindle  24 , which is aligned in parallel with the insertion slot  21 , but transversely with respect to the longitudinal extent of the strip. A compression spring  25  presses the holder into a pivoted-up position illustrated in  FIG. 6 , in which metallic insulation displacement contacts  26  held at the end of the holder  18  on its lower side are above the stop  22 . 
       FIG. 6  furthermore shows that both parallel ribs  27  are formed on the holder  18  and parallel ribs  28  are formed on the locking slide on the upper sides in order to facilitate manipulation. 
       FIG. 7  illustrates that, in comparison with the first position illustrated in  FIG. 6 , the strip  1  is inserted further into the insertion slot  21  and in the process presses the stop  22  axially in counter to the force of the compression spring  23  illustrated in  FIG. 6  until the end of the strip  1  with the end face  13  pressing against the stop  22  comes to lie beneath the insulation displacement contacts  26 . 
       FIG. 8  illustrates that the contact-making with the conductor wires  11  running within the strip  1  is now performed by virtue of the fact that the pivotable holder  18  is pivoted downwards by pressure being exerted on its upper side counter to the force of the compression spring  25 , as a result of which the insulation displacement contacts  26  cut into the material of the strip  1  from the upper side  10  until a metallic, i.e. electrically conductive, connect is produced with the metallic conductor wires  11 . Whilst maintaining the pressure on the holder  18 , the locking slide  19  is moved in the longitudinal direction, as shown in  FIG. 9 , so that it now protrudes beyond the holder  18 , with the result that said holder is locked in the contact-making position counter to the restoring force of the compression spring  23 . The holder  18 , the locking slide  9 , the housing  20 , etc. of the contact-making elements  17  of course consist of a nonconductive material, for example plastics, with the result that safe insulation is ensured on all sides and there is no risk of unimpeded dissipation of the high voltage by virtue of touching contact with parts of the electrode  14 . 
     The position of the contact-making element  17  in which full contact has been made, which contact-making element makes contact with the electrode  14  of the strip  1 , is illustrated in  FIG. 10 . 
     The high-voltage potential supplied by the high-voltage supply  12  via the high-voltage cable  16  is conducted within the contact-making element in a manner known per se to the insulation displacement contacts  26 , with the result that the electrode  14  is connected to a high-voltage potential via the insulation displacement contacts  26 . 
     It can readily be seen that the contact-making implemented by the contact-making elements  17  is simple and safe, but that other contact-making possibilities which are conventional to a person skilled in the art likewise meet all requirements for the safe insulation of the high-voltage potential with respect to discharges as a result of touching contact. 
     The particular advantage of the electrode arrangement illustrated consists in that the strip can be cut to length at any desired point in a simple manner in order to enable matching of the size of the resting side  6  to the size of a surface to be treated. The process of cutting the strip  1  to length is possible without impairing the function of the electrode  14  because the electrode extends in the longitudinal direction of the strip in said strip, preferably as far as into the central region  3 . Contact can be made with the electrode  14  in a simple manner at the end region of the strip having the end face  13  formed by the process of cutting to length, preferably with the aid of a contact-making element  17 . The matching of the surface size of the electrode arrangement to the effective surface required for the treatment of a surface can therefore be realized in a simple manner without any complications merely by the strip  1  being cut to length. 
     The strip  1  preferably consists of a flexible dielectric material, with the result that the electrode arrangement formed by the strip  1  can be matched to irregular three-dimensional surfaces. The short distance between the turns  4  of the strip  1  which is defined by the spacer pieces  5  and is running helically also contributes to this. 
     It can be seen that through-openings  9  provided in the exemplary embodiments illustrated are not absolutely necessary when, for specific application cases, removal by suction of a fluid from the treatment area which is formed by the interspaces  8  is not required. However, it is known that the removal by suction of fluid can be advantageous, for example, for the treatment of a wound for encouraging sealing of the wound. 
     The embodiment of the electrode shown in the exemplary embodiments illustrated by means of at least one conductor wire  11  is not absolutely necessary for implementing the invention. It is possible, for example, for the electrode to be implemented by a flexible wire grid embedded in the strip, with it being possible for contact to be made with the wire grid in a similar manner to the conductor wires  11 , for example by means of insulation displacement contacts  26  of a contact-making element  17 . 
     Any material which is flexible in an expanding and insulating manner, for example plastics material, can be used for the dielectric material of the strip  1 , in particular foamed material, wherein a closed-cell plastic or elastomer foam is preferred because the risk of electrical short circuits by liquids penetrating open pore structures is ruled out thereby. Suitable plasmas material is, for example, foamed polyurethane or silica or a closed-cell natural rubber, without such a list intending to be exclusive.