Abstract:
An RF heating system for generating precision stray RF fields that can be used to heat materials. The RF heating system includes an RF power supply for generating RF signals and an electrode apparatus that is coupled to the RF power supply. An electrode apparatus according to the present invention has many advantages over existing electrode apparatuses. For example, the electrode apparatus is easier to manufacture, easier to duplicate, easier to control the manufacturing tolerances on the electrode system, and easier to correctly place and design the resulting RF stray field.

Description:
[0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/364,737, filed Mar. 18, 2002, and also claims the benefit of U.S. Provisional Patent Application No. 60/365,120, filed Mar. 19, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention is related to the field of electrode apparatuses for stray field radio frequency (“RF”) heating.  
           [0004]    2. Discussion of the Background  
           [0005]    A conventional electrode apparatus for stray field heating typically includes at least two parallel electrodes. The electrode apparatus is electrically connected to an RF generator that generates an RF signal. When the RF generator generates an RF signal, an RF field is generated between the two electrodes and a stray RF field is also radiated from the electrodes. The RF field is typically strongest in the region within the overlapping space between the electrodes, with a stray component of the field extending beyond the overlapping area of the electrodes. Stray field RF heating refers to the technique of heating a material by exposing the material to the generated stray field.  
         SUMMARY OF THE INVENTION  
         [0006]    In one aspect, the present invention provides an RF heating system for generating precision stray RF fields that can be used to heat materials. The RF heating system includes an RF power supply for generating RF signals and an electrode apparatus that is coupled to the RF power supply. An electrode apparatus according to the present invention has many advantages over existing electrode apparatuses. For example, the electrode apparatus is easier to manufacture, easier to manufacture duplicate electrode systems, easier to control the manufacturing tolerances on the electrode system, and easier to correctly place and design the resulting RF stray field. Other advantages exist.  
           [0007]    According to one embodiment, an electrode apparatus of the present invention comprises two elements: a first element and a second element. The first element and the second element are each energized by a radio frequency signal that is typically at a phase angle of 0° and 180° respectfully, to produce a voltage potential between the electrodes that varies between zero and a maximum potential at the frequency provided by the power supply. In addition, the first element could be energized by a radio frequency signal and the second element could be equivalent to ground, still providing a voltage potential between the electrodes that varies at the frequency of the source supply.  
           [0008]    In one embodiment, the first element comprises a first elongated member and a second elongated member. The first element further comprises an elongated electrode having one end connected to the first elongated member and the other end connected to the second elongated member. The elongated members and the elongated electrode are preferably formed from a single mass of material (such as, but not limited to, a copper sheet or plate), but this is not a requirement.  
           [0009]    The second element comprises a base and an electrode plate that is connected to and extends outwardly from a surface of the base. The electrode plate is rectangular in shape having two lateral sides and a distal side. Like the first element, the second element is preferably formed from a single mass of material, but this is not a requirement.  
           [0010]    The first element and the second element are positioned such that the elongated electrode and the electrode plate are aligned so that, when the RF power supply produces an RF signal, an RF field is generated between the elongated electrode and the electrode plate, and a stray RF field radiates from the elongated electrode and the electrode plate. In one embodiment, the first element and the second element are positioned such that the elongated electrode and the electrode plate are spaced apart and interdigitated or interlaced or “laterally adjacent” such that the elongated electrode is not directly over any portion of the electrode plate. That is, the distal side of the electrode plate runs substantially parallel with the elongated electrode and is spaced apart from the elongated electrode. Preferably, the distance from the top surface of the elongated electrode to the surface of the base is equal to or about equal to the height of the electrode plate, but this is not a requirement.  
           [0011]    Advantageously, the first element may include a plurality of elongated electrodes. Each of the plurality of elongated electrodes having one end connected to the first elongated member and the other end connected to the second elongated member. Preferably, the plurality of elongated electrodes are evenly spaced apart and are parallel with each other. In this embodiment, the second element includes a plurality of electrode plates that are attached to and extend outwardly from the surface of the base. Like the elongated electrodes, the electrode plates are also preferably spaced evenly apart. In this embodiment, the first element and the second element are aligned so that the elongated electrodes and the electrode plates are interdigitated. Preferably, the distance from the top surface of an elongated electrode to the surface of the base is equal to or about equal to the height of the electrode plate(s) that are adjacent to the elongated electrode.  
           [0012]    In one embodiment, the RF power supply includes an RF generator, an impedance matching circuit and an above described electrode apparatus. In this embodiment, the first element of the electrode apparatus is connected to a first node within the impedance matching circuit and the second element of the electrode apparatus is connected to a second node within the impedance matching circuit. In one embodiment, an element having an inductance (e.g., a conductive coil) is connected between the first node and the second node.  
           [0013]    In another embodiment, the second element of the electrode apparatus is placed within a housing and the first element rests on a surface of the housing. The housing is preferably constructed from a non-conducting or low dielectric constant or low dissipation factor material such as, but not limited to Teflon® (polytetraflouroethylene), polypropylene, polyethelene, Kapton®, and polystyrene.  
           [0014]    In another aspect, the invention provides an electrode apparatus for generating stray fields that includes an elongated electrode and an electrode plate having a first face and a second face. The first face of the electrode plate faces in a direction that is substantially perpendicular to the longitudinal axis of the elongated electrode. The elongated electrode is spaced apart from the first face of the electrode plate. The height of the electrode plate is greater than the thickness of the elongated electrode. And the length of the electrode plate is shorter than the length of the elongated electrode.  
           [0015]    In another aspect, the invention provides a method for making a product, wherein the product has one or more components. The method includes the steps of: generating a stray field using one of the electrode apparatuses described above and exposing a component of the product to the stray field for the purpose of heating the component. The component may be an adhesive that heats when exposed to certain RF fields or any other component.  
           [0016]    The above and other features and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.  
         [0018]    [0018]FIG. 1 is a top view of an electrode apparatus according to one embodiment of the invention.  
         [0019]    [0019]FIG. 2 shows a perspective view of the electrode apparatus.  
         [0020]    [0020]FIG. 3 is a perspective view of a first element of the electrode apparatus.  
         [0021]    [0021]FIG. 4 is perspective view of a second element of the electrode apparatus.  
         [0022]    [0022]FIG. 5A illustrates an RF heating system.  
         [0023]    [0023]FIG. 5B is a circuit diagram of an impedance matching circuit according to one embodiment.  
         [0024]    [0024]FIG. 6 is a cross-sectional view of the electrode apparatus.  
         [0025]    [0025]FIG. 7 illustrates a stray RF field.  
         [0026]    [0026]FIG. 8 is a top view of a portion of the electrode apparatus.  
         [0027]    [0027]FIG. 9A illustrates one alternative embodiment of an electrode apparatus according to the present invention.  
         [0028]    [0028]FIG. 9B is a cross-sectional view of the alternative embodiment of the electrode apparatus.  
         [0029]    [0029]FIG. 10 is an exploded view of the alternative embodiment of the electrode apparatus.  
         [0030]    [0030]FIG. 11 is another cross-sectional view of the alternative embodiment of the electrode apparatus.  
         [0031]    [0031]FIG. 12 is a cross-sectional view of another embodiment of an electrode apparatus according to the present invention.  
         [0032]    FIGS.  13 - 18  illustrate additional embodiments of an electrode apparatus according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    While the present invention may be embodied in many different forms, there described herein in detail an illustrative embodiment with the understanding that the present disclosure is to be considered as an example of the principles of the invention and is not intended to limit the invention to the illustrated embodiment.  
         [0034]    [0034]FIG. 1 is a top view of an electrode apparatus  100 , according to one embodiment of the invention, for use in an RF heating system  500  (see FIG. 5A). As shown FIG. 1, electrode apparatus  100  includes a first element  102  a second element  104 . FIG. 2 shows a perspective view of electrode apparatus  100 . FIG. 3 is a perspective view of first element  102 , and FIG. 4 is perspective view of second element  104 .  
         [0035]    Referring now to FIG. 5A, RF heating system  500  includes an RF power supply  501  and electrode apparatus  100 , which is coupled to RF power supply  501 . RF power supply includes an RF generator  502  and may include an impedance matching circuit  504 . As shown in FIG. 5, both first element  102  and second element  104  of electrode apparatus  100  are connected to impedance matching circuit  504 , which is connected to RF generator  502 . When RF generator  502  generates an RF signal a stray RF field is generated by electrode apparatus  100 . This stray RF field can be used to heat a material. As shown in FIG. 5, an optional coil  506  may be connected between first element  102  and second element  104  for impedance matching. Coil  506  can be made hollow, thus enabling electrode apparatus  100  to be water cooled.  
         [0036]    For illustration, FIG. 5B is a circuit diagram of one possible embodiment of impedance matching circuit  504 . As shown in FIG. 5B, circuit  504  includes a transformer  560 , a first capacitor  570 , a second capacitor  571 , an inductor  580  connected between capacitors  570  and  571 . In this embodiment, first electrode element  102  may be connected to node  590  and second electrode element  104  may be connected to node  591 , or vice-versa.  
         [0037]    Referring now to FIG. 3, first element  102  includes a frame  302  and one or more bars  304  that extend from a first lateral member  310  of frame  302  to a second lateral member  311  of frame  302 . Frame  302  and bars  304  may be solid or hollow. Bars  304  are referred to herein as “elongated electrodes  304 ”. Frame  302  and elongated electrodes  304  are made from an electrically conductive material or materials (such as, but not limited to, copper). In one embodiment, frame  302  and elongated electrodes  304  are formed from a single body, but this is not a requirement, as elongated electrodes  304  may be connected to lateral members  310  and  311  by, for example, welding, brazing or soldering or other connection technique.  
         [0038]    Elongated electrodes  304  are generally of an elongated rectangular or cylindrical shape. If elongated electrodes are rectangular in shape, then, to suppress the potential for arcing, the edges of elongated electrodes  304  may be rounded. The dimensions of frame  302  and elongated electrodes  304  vary depending on the heating application. A first connector  312  is connected to frame  302  and is used to electrically connect frame  302  to an RF power supply. An optional second connector  314  is also connected to frame  302 . This connector is used to connect frame  302  to coil  506  or to other circuit elements.  
         [0039]    Referring to FIG. 4, second element  104  includes a base  402 . Base  402  is made from an electrically conductive material or materials. Second element  104  also includes one or more electrode plates  404 . Electrode plates  404  are attached to a top surface  410  of base  402  and extend outwardly from top surface  410 . Like base  462 , electrode plates  404  are made from an electrically conductive material or materials. In one embodiment, electrode plates  404  are integral with base  402 , but this is not a requirement, as electrode plates  404  may be connected to top surface  410  by, for example, welding, brazing or soldering or other connection technique. In one embodiment, electrode plates  404  are generally of a rectangular shape and have a first lateral side  480 , a second lateral side  481 , a distal side  482 , a first face  483  and a second face  484 . The specific dimensions of base  402  and electrode plates  404  will vary depending on the heating application. To suppress the potential for arcing, the edges of electrode plates  404  may be rounded. A first connector  412  is connected to base  402  and is used to electrically connect base  402  to an RF power supply. An optional second connector  414  is also connected to base  402 . This connector is used to connect base  402  to coil  506  or to other circuit elements.  
         [0040]    As shown in FIG. 2, first element  102  is spaced apart from top surface  410  of base  402 . Preferably, first element  102  and second element  104  are aligned so that elongated electrodes  304  and electrode plates  404  are interdigitated. Additionally, it is preferable that the distance from a top surface  615  of an elongated electrode (see FIG. 6) to top surface  410  of base  402  is equal to or about equal to the height (h) of the electrode plate(s)  404  that are adjacent to the elongated electrode. This is best illustrated in FIG. 6, which illustrates a side cross-sectional view of electrode apparatus  100 . As shown in FIG. 6, first element  102  and second element  104  are aligned such that a distal portion  610  of each electrode plate  404  is laterally adjacent to at least one elongated electrode  304 .  
         [0041]    To avoid potential arcing problems and to concentrate charge density in the area between adjacent distal portions  610  and elongated electrodes  304 , the distance from the bottom surface of elongated electrodes  304  to top surface  410  of base  402  should be at least twice the distance (X) from distal portion  610  to elongated electrode  304 , but this is not a requirement. Consequently, in one embodiment, the height (h) of electrode plates  404  is greater than the thickness (t) of elongated electrodes  304 . In one embodiment, as described above, h&gt;=t+2X. Preferably, the distance (X) from the distal portion  610  to the elongated electrode  304  is determined by the specific heating application, thus defining the distance from the bottom surface of elongated electrodes  304  to the top surface  410  of base  402 .  
         [0042]    [0042]FIG. 7, like FIG. 6, is a side cross-sectional view of one embodiment of electrode apparatus  100  and illustrates a stray field  700  that is generated when the RF generator generates an RF signal and the RF signal is provided to electrode apparatus  100 . As shown in FIG. 7, stray field  700  is created in the region of space that is above the space between distal portion  610  and elongated electrode  304 .  
         [0043]    Although it is not a requirement, in one embodiment, the following configuration is preferable: electrode plates  404  are spaced evenly apart from each other and all have the same height with respect to top surface  410 , first lateral member  310  of frame  302  is parallel with second lateral member  311 , and elongated electrodes  304  are perpendicular to both first lateral  310  member and second lateral member  311  and are also spaced evenly apart from each other. The dimensions of base  402 , frame  302 , electrode plates  404 , and elongated electrodes  304  vary depending on the heating application. Thus, there are no preferred dimensions. Similarly, the distance between electrode plates  404  and the distance between elongated electrodes  304  also varies depending on the heating application. However, in one embodiment, it is preferred that the distance between electrode plates  404  is equal to the distance between elongated electrodes  304 .  
         [0044]    [0044]FIG. 8 illustrates a top view of a portion of electrode apparatus  100 , according to one embodiment, to illustrate preferred relative distances from an electrode plate  804  to its laterally adjacent elongated electrodes  806  and  808  and to lateral members  310  and  311 . It is preferred that electrode plate  804  be equally distant (or about equally distant) from elongated electrode  806  and elongated electrode  808 . It is also preferred that electrode plate  804  be equally distant (or about equally distant) from lateral member  310  and lateral member  311 . Lastly, it is preferred that the distance (D4) from electrode plate  804  to lateral members  310  and  311  be greater than or equal to two times the distance (D1) from electrode plate  804  to an adjacent elongated electrode  806  or  808 . Consequently, as shown in FIG. 8, the length (L1) of elongated electrodes  806  and  808  is greater than the length (L2) of electrode plate  804 . In one embodiment, as described above, L1=L2+D4+D4. It is preferred that the distance (D1) from electrode plate  804  to an adjacent elongated electrode  806  or  808  be determined by the heating application, thus defining the distance (D4) from electrode plate  804  to lateral members  310  and  311 .  
         [0045]    [0045]FIG. 9A illustrates an electrode apparatus  900  according to another embodiment of the invention. Electrode apparatus  900  comprises a housing  902  for housing second element  104  of electrode apparatus  100 . First element  102  of electrode apparatus  100  rests on (or is secured to) the top of housing  902 . The material out of which housing  902  is constructed is preferably a non-electrically conducting material with a low dielectric constant and low dissipation factor, such as, but not limited to Teflon® (polytetraflouroethylene), polypropylene, polyethelene, Kapton®, and polystyrene.  
         [0046]    [0046]FIG. 9B illustrates an end cross-sectional view of electrode apparatus  900 . As shown in FIG. 9B, housing comprises a bottom piece  910  for receiving second element  104  and a cover  911  for covering second element  104 . First element  102  may be placed on top of cover  911 . FIG. 10 is an exploded view of electrode apparatus  900 . As shown in FIG. 10, bottom piece  910  includes a channel  1002  for receiving base  402  of second element  104 , and cover  911  includes channels  1004  for receiving elongated electrodes  304 .  
         [0047]    [0047]FIG. 11 further illustrates cover  911  according to one embodiment. FIG. 11 is a side cross-sectional view of electrode apparatus  900 . As shown in FIG. 11, not only does cover  911  include channels 1004 for receiving elongated electrodes  304 , but also includes channels 1102 for receiving distal side  482  of electrode plates  404 . Preferably, the thickness of the portion of cover  911  that covers distal side  482  is thin enough so that a stray field radiating from electrode plate  104  can penetrate through cover  911 . In one embodiment, the thickness is about 0.05 inches.  
         [0048]    [0048]FIG. 12 illustrates a cross-sectional view of an additional embodiment of electrode apparatus  100 . In this embodiment, a cover  1202  is used to insulate and protect electrodes  304  and  404 . As shown in FIG. 12, it is possible to remove cover  911  from the electrode apparatus assembly  900 , and cover element  102  and element  104  with a continuous sheet of material  1202 . Preferably, the thickness (t) of the cover sheet  1202  is thin enough so that the stray field can penetrate through the sheet. In addition, the thickness of the cover  1202  is thick enough to act as a focusing material for the stray RF field  700 . In one embodiment, the thickness of the cover  1202  is about 0.050 inches, but the invention is not limited to this or any particular thickness. The material out of which cover  1202  is constructed is preferably a non-electrically conducting material with a low dielectric constant and low dissipation factor, such as, but not limited to Teflon® (polytetraflouroethylene), polypropylene, polyethelene, Kapton®, and polystyrene.  
         [0049]    To illustrate the some of the possible variations of electrode apparatus  100 , FIGS.  13 - 18  are provided. These figures illustrate just a few of the possible alternative embodiments of the invention.  
         [0050]    While various illustrative embodiments of the present invention described above have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.