Abstract:
A combination capacitor and inductor employ a common volume of high permeability material for energy-storing electrical and magnetic fields thereby reducing the bulk of these components with respect to separate components of comparable value. Capacitor conductors are arranged so that while proximate to the high permeability material they provide countervailing current flows to minimize parasitic inductance exacerbated by the high permeability material.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    -- 
       CROSS REFERENCE TO RELATED APPLICATION 
       [0002]    -- 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to capacitors and inductors used in electrical circuits and in particular to an integrated capacitor and inductor sharing energy storage volumes. 
         [0004]    Inductors and capacitors arc fundamental building blocks in many common electrical devices. Unlike electrical resistors, another common building block component, inductors and capacitors can provide for electrical energy storage 
         [0005]    Inductors provide energy storage in the form of a magnetic field in the vicinity of a current-carrying conductor. The conductor is normally formed into a coil of multiple loops to concentrate the generated magnetic flux within the coil thereby increasing the inductance and energy storage. The coil may be further wrapped about a core of high magnetic permeability, such as a ferromagnetic or ferrimagnetic material, to further increase the coil&#39;s inductance. 
         [0006]    Capacitors provide for energy storage in the form of an electric field generated between two plates of different voltage separated by an insulator. The total area between the plates and their proximity may be increased to increase the capacitance and enemy storage. The insulator between the plates may further be selected to be a dielectric material, such as a plastic or ceramic, to further increase the capacitance. 
         [0007]    In many applications of inductors and capacitors, in both low-powered and high-powered electronics, the physical size of the inductor and capacitor may be a limiting factor in reducing the size of the circuit. 
         [0008]    Co-pending U.S. application Ser. No. 14/197,580 filed Mar. 5, 2014, assigned to the assignee of the present invention and hereby incorporated by reference, describes an inductor and capacitor configured to share an energy storage volume thereby substantially reducing the bulk of the device. In this regard, the capacitor may incorporate a high magnetic permeability material into its structure so that the capacitor may replace the normal high permeability core of the inductor. 
       SUMMARY OF THE INVENTION 
       [0009]    The present inventors have recognized that the process of increasing the magnetic permeability of the material within the capacitor structure with the purpose of creating an inductor core can undesirably increase a parasitic equivalent series inductance (ESL) of the capacitor degrading the capacitor performance at high frequencies. The present invention employs a loop-back terminal structure to moderate ESL in designs of this kind. The loop-back terminals of the capacitor aim to reduce the permeable volume enclosed by the capacitor conductors and minimize the net magnetic field induced by the capacitor current. 
         [0010]    Specifically, the present invention provides a combined inductor and capacitor having an inductor providing a conductor extending between a first and second terminal point through multiple loops defining a surrounded volume and a capacitor positioned within the surrounded volume and providing a capacitor structure including opposed conductive plates attached by conductors, respectively, to a third and fourth terminal and an insulator separating the opposed conductive plates. A high magnetic permeability material is distributed within the capacitor structure comprised of at least one of a ferromagnetic and ferrimagnetic material. The conductive plates and conductors are arranged so that current flow between the third and fourth terminals proximate to the high magnetic permeability material provides countervailing canceling magnetic fields within the high magnetic permeability material. 
         [0011]    It is thus a feature of at least one embodiment of the invention to provide a low-bulk combined inductor capacitor having low equivalent series inductance at the capacitor terminals. 
         [0012]    The capacitor plates may include a plurality of plates separated by a plurality of insulators in a stack extending along a first axis, with the plates extending parallel to a second axis perpendicular to the first axis, and a first subset of the plates may connect at first edges to a first conductive end cap and a second subset of the plates interleaved with the first subset of plates may connect at second edges to a second conductive end cap opposite the first conductive panel. The third terminal may connect to the first end cap and the fourth terminal may connect via a loop-back conductor to the second end cap, the loop-back conductor passing proximate to the high magnetic permeability material along the second axis toward the first end cap. The multiple loops of the inductor may spiral about an axis perpendicular to the first axis 
         [0013]    It is thus a feature of at least one embodiment of the invention to provide an extremely simple capacitor structure with low equivalent series inductance. 
         [0014]    Alternatively, the surrounded volume may be substantially toroidal and the capacitor plates may extend parallel to an axis of the toroid, and the first and second conductive end caps may provide opposite bases of a toroidal capacitor structure each respectively to interconnect different subsets of the capacitor plates. At least one conductive ring may conform to an outer periphery of the toroidal capacitor structure or an inner diameter of the toroidal capacitor structure electrically connected to the second conductive end cap. The third terminal may connect to the first end cap and the fourth terminal may connect to at least one conductive ring, and the multiple loops of the inductor may spiral about the toroid to pass repeatedly through the inner diameter of the toroid and around the outer periphery. 
         [0015]    It is thus a feature of at least one embodiment of the invention to provide a toroidal combined inductor and capacitor with low series resistance. 
         [0016]    Alternatively, when the surrounded volume is substantially toroidal, the capacitor plates may extend perpendicularly to an axis of the toroid and the first conductive end cap may be a conductive ring conforming to an outer periphery of a toroidal capacitor structure and the second conductive end cap may be a conductive ring conforming to an inner diameter of the toroidal capacitor structure. The structure may further include at least one conductive base plate conforming to at least one base of the toroidal capacitor structure and electrically connected to at least one of the end caps to communicate electricity with at least one of the third and fourth terminals. The multiple loops of the inductor may spiral about the toroid to pass repeatedly through the inner diameter of the toroid and around the outer periphery. 
         [0017]    It is thus a feature of at least one embodiment of the invention to provide a toroidal combined inductor and capacitor that may make use of a spiral winding of the capacitor plates. 
         [0018]    Alternatively, the capacitor plates may include at least two conductive plates separated by an insulator rolled in spiral about the first axis to create a laminated, or “tape wound” structure with laminations separated along lines of radius from the first axis and the third terminal may connect to at least one plate and the fourth terminal may connect to at least a second plate separated from the first plate by the insulator so that instantaneous current flow in the first and second plates provides countervailing canceling magnetic fields. In this case the multiple loops of the inductor spiral about the first axis but are decoupled from ESL of the capacitor terminals. 
         [0019]    It is thus a feature of at least one embodiment of the invention to provide a simple capacitor structure that inherently provides countervailing current flows and/or whose layout provides minimal enclosed permeable material 
         [0020]    The first and second terminals may be galvanically isolated from the third and fourth terminals. 
         [0021]    It is thus a feature of at least one embodiment of the invention to provide a combined inductor/capacitor with inductive and capacitive elements that may be used independently in contrast, say, to the systems that may use parasitic capacitances or inductance having a fixed predetermined configuration to the element on which they are parasitic. 
         [0022]    The combined inductor and capacitor may have plates that extend along an axis substantially parallel to magnetic field lines from the inductor. 
         [0023]    It is thus a feature of at least one embodiment of the invention to provide a combined inductor and capacitor with minimized induced eddy currents in the capacitor plates by making the plates thin and ensuring that plates run in parallel to the magnetic field lines. 
         [0024]    The combined inductor and capacitor where the high magnetic permeability material operates to increase an inductance of the inductor by a factor of no less than 2 when compared to the inductance of the inductor without the high magnetic permeability material. 
         [0025]    It is thus a feature of at least one embodiment of the invention to provide a specially constructed capacitor that may serve as a high permeability inductor core. The high permeability material may be distributed in a plurality of layers in the capacitor structure. 
         [0026]    It is thus a feature of at least one embodiment of the invention to provide a simple method of integrating high permeability material into a capacitor structure during manufacture. 
         [0027]    The high permeability material may be iron or an iron alloy with a nonferrous metal coating. It is thus a feature of at least one embodiment of the invention to permit a flexible combination of ferrous and nonferrous metals to provide both conduction and high permeability in the conductive plates of the capacitor. 
         [0028]    The combined inductor and capacitor may have a high magnetic permeability material that is a plurality of granules incorporating inter-granular gaps of low magnetic permeability. 
         [0029]    It is thus a feature of at least one embodiment of the invention to promote magnetic energy storage of the inductor within the same surrounded volume as the electrostatic energy storage of the capacitor. 
         [0030]    The combined inductor and capacitor may contain conductive plates that comprise a material selected from the group consisting of copper and aluminum. 
         [0031]    It is thus a feature of at least one embodiment of the invention to provide a combined inductor and capacitor that may use highly conductive yet low permeability materials. 
         [0032]    The insulator may be a dielectric material increasing a capacitance of the capacitor by at least a factor of two when compared to the capacitor without the dielectric material. 
         [0033]    It is thus a feature of at least one embodiment of the invention to make use of the capacitor insulators as well as conductors for the purpose of increasing magnetic permeability of a core formed by the capacitor. 
         [0034]    The insulator may incorporate a granular high magnetic permeability material selected from the group consisting of ferromagnetic materials and ferrimagnetic materials. 
         [0035]    It is thus a feature of at least one embodiment of the invention to provide a method of augmenting the permeability of common insulators that may be used in the capacitor. 
         [0036]    The capacitor structure may provide a ring of laminated conductive plates and insulators extending perpendicularly to an axis of the ring, the ring including radially inwardly extending pole elements and the inductor providing loops around each pole element. It is thus a feature of at least one embodiment of the invention to provide an integrated inductor and capacitor that form a stator of a motor. 
         [0037]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  is a perspective view of a first embodiment of the present invention having a toroidal form factor, the view providing a partial cutaway and an expanded cross-section of a capacitor layer structure; 
           [0039]      FIG. 2  is a simplified electrical schematic of the electrical equivalent of the embodiment of  FIG. 1  showing an independent inductor and capacitor; 
           [0040]      FIG. 3  is an expanded and rotated view of the cross-section of  FIG. 1  showing a first embodiment using ferrous capacitor plates separated by an insulating dielectric; 
           [0041]      FIG. 4  is a figure similar to that of  FIG. 3  showing laminated ferrous and nonferrous metals used for the capacitor plates; 
           [0042]      FIG. 5  is a figure similar to that of  FIG. 3  showing the use of a high permeability layer interposed between capacitor plates and the insulating dielectric; 
           [0043]      FIG. 6  is a figure similar to that of  FIG. 3  showing nonferrous capacitor plates and a high permeability insulating layer having permeable and permittive properties; 
           [0044]      FIG. 7  is a perspective view of an alternative embodiment to that of  FIG. 1  showing a linear form factor; 
           [0045]      FIG. 8  is a perspective view of an alternative embodiment to  FIG. 7  showing a spiral capacitor plate configuration; 
           [0046]      FIG. 9  is a figure similar to that of  FIG. 7  showing an embodiment of the invention producing a combination capacitor and transformer; 
           [0047]      FIG. 10  is a figure similar to that of  FIG. 2  showing a simplified electrical schematic of the equivalent circuit of  FIG. 9   
           [0048]      FIG. 11  is a figure similar to that of  FIG. 9  showing in simplified form an alternative winding producing an auto transformer; 
           [0049]      FIG. 12 a    is an equivalent circuit of the embodiment of  FIG. 1  showing an equivalent series inductance promoted by the high permeability core material; 
           [0050]      FIG. 12 b    is a figure similar to  FIG. 12 a    showing a loop-back terminal connection that substantially reduces the equivalent series inductance; 
           [0051]      FIG. 13  is a cutaway perspective figure showing a core construction of the embodiment of  FIG. 1  incorporating a loop-back terminal together with an enlarged inset showing construction of the loop-back terminal by a central conductive ring; 
           [0052]      FIG. 14  is a figure similar to  FIG. 13  showing alternative lamination orientation of the capacitor layers as may provide for the current loop-back terminal connection; 
           [0053]      FIG. 15  is a perspective figure showing a core construction of the embodiment of  FIG. 8  showing an alternative loop-back connection integrated into the capacitor plates that produces countervailing capacitive current flows; 
           [0054]      FIG. 16  is a perspective figure showing a core construction of the embodiments of  FIGS. 7 and 9  providing current loop-back by side panel connections; and 
           [0055]      FIG. 17  is a fragmentary perspective view of a motor stator showing use of the present invention to incorporate motor capacitors into the stator structure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiment I 
       [0056]    These embodiments are taught in co-pending U.S. application Ser. No. 14/197,580 cited above. 
         [0057]    Referring now to  FIG. 1 , an integrated capacitor inductor unit  10  of the present invention, in one example, may provide a toroidal core  12  having a generally rectangular cross-section, the latter cross-section which when swept in a circle about the toroid axis  17  defines a core volume  19 . 
         [0058]    The toroidal core  12  may be wrapped with a conductor  14  leading from a first terminal  16  (designated I 1 ) and passing, in each of multiple loops  18 , through a center opening of the toroidal core  12  and around its outer periphery to terminate at a second terminal  16  (designated I 2 ). The loops  18  together form a solenoid around the core volume  19  so that electrical current passing through the conductor  14  from one terminal  16  to the other terminal  16  will generate a circumferential magnetic field B of flux lines passing through the core volume  19  and circling around the axis  17 . 
         [0059]    The toroidal core  12  comprises a number of planar layers  20  each extending circumferentially along and around axis  17  in height and length, respectively. Generally the planar layers  20  may be wound about a cylindrical form describing the center opening of the toroidal core  12  in a spiral outward to the outer circumferential periphery of the toroidal core  12  to provide a laminated structure. 
         [0060]    The planar layers  20  include conductive plates  22  separated by interleaving insulating layers  24 . Alternate conductive plates  22  may be attached to a first terminal  26  (designated C 1 ) and the remaining conductive plates  22  attached to a second terminal  26  (designated C 2 ). As such, the conductive plates  22  form opposite plates of a capacitor each separated by an insulating layer  24  so that voltage applied to the terminals  26  will generate a radial electric field E with field lines generally perpendicular to axis  17 . 
         [0061]    Referring now also to  FIG. 2 , it will be appreciated that the capacitance between terminals  26  provides a capacitor  23  electronically independent of the inductor  25  between terminals  16 . Generally the current through the inductor  25  will be independent of the current through the capacitor  23  and the terminals  26  of the capacitor  23  need not be connected to the inductor  25  and may be separately accessed from the terminals  16  of the inductor  25  and vice versa. In this regard, the capacitor  23  and inductor  25  may be readily distinguished from a parasitic capacitor between inductor windings or parasitic inductance of capacitor leads. 
         [0062]    In this embodiment, the electrical field E of the capacitor  23  will be perpendicular to the magnetic field B of the inductor  25  and the broad area of the conductive plates  22  (local surface normals) will also be perpendicular to the local magnetic field B reducing induced eddy currents in the conductive plates  22  caused by fluctuations of the magnetic field B such as may cause heating or energy loss. 
         [0063]    Referring now to  FIG. 3 , in a first embodiment, the conductive plates  22  may be ferrous materials  27  such as a metallic iron or steel or other ferrous alloy or conductive ferromagnetic material. The ferrous high permeability material  27  may be ductile so that it may be wound in the annular form of toroidal core  12  as discussed above. The ferrous high permeability material  27  may provide both a conductive medium for the capacitor plates and a high permeability material increasing the inductance of the inductor  25 . 
         [0064]    The insulating layers  24  may be, for example, a polymer such as polyester, Teflon or the like to provide a dielectric material having a high relative permittivity, for example, greater than 2, to increase the capacitance between the conductive plates  22 . Other dielectric materials known for use in capacitors may also be used. 
         [0065]    Referring now to  FIG. 4 , in an alternative embodiment, the conductive plates  22  may be constructed of a ferrous high permeability material  27  laminated to a conductive nonferrous material  28  such as copper or aluminum together to provide a continuous conductive path between the conductive plates  22  and the terminals  26 . Although only one side is shown laminated in  FIG. 4 , it will be appreciated that opposite sides and edges of the ferrous high permeability material  27  may be laminated with more conductive metal and other lamination orders and numbers may also be used. 
         [0066]    Referring now to  FIG. 5 , in an alternative embodiment, the conductive plates  22  may be a wholly nonferrous material such as aluminum or copper coated with a particulate or granularized high permeability material  27 . The granularized high permeability material  27  provides gaps of low permeability and thus sites of magnetic energy storage. In this case, the granularized high permeability material  27  may be a ferrous material such as iron, an alloy, or an iron compound such as exhibits ferromagnetic properties for high permeability and/or a ferrite material such as magnesium and zinc ferrite or nickel-zinc ferrite, exhibiting ferrimagnetic properties and high permeability. 
         [0067]    Alternatively, the granularized high permeability material  27  may be coated in a film on a surface of the insulating layer  24  or may be formed in its own layer to be laminated or layered between the insulating layer  24  and conductive plate  22 . In each of the examples of  FIGS. 4 and 5 , the insulating layer  24  may be as described with respect to  FIG. 3 . Again although a coating of granularized type high permeability material  27  is shown on only one side of the conductive plate  22  it will be understood that the coating may be placed on both sides and edges of the conductive plate  22  attached to either the conductive plate  22  or the insulating layer  24 . 
         [0068]    Referring now to  FIG. 6 , any of the materials described with respect to  FIGS. 3, 4, 5  may be used for the conductive plates  22  and the insulating layers  24  may incorporate a granularized high permeability material  27 , for example, as a filler material in a polymer thermoplastic. 
         [0069]    Generally the amount of high permeability material  27  will be such as to provide an effective amount of inductive energy storage by the inductor. Such an effective amount, for example, may increase the inductance of the inductor  25  by a factor of no less than 10 or at least no less than 2 in comparison to the inductor  25  operating without this material (for example, with an air core) but otherwise identical in construction. The high permeability material  27  will preferably have a permeability equal or exceeding that of nickel in the same magnetic environment. As noted, the high permeability material  27  may include ferrous materials including alloys and compounds as well as ferrite materials. 
         [0070]    Generally the insulating layer  24 , as noted, will be a dielectric, having a high relative permittivity of at least 2 and be in amount and quantity such as to increase the capacitance of the capacitor  23  by a factor of no less than two in comparison to the capacitor  23  operating without this material (for example, with an air gap between conductive plates  22 ) but otherwise identical in construction. The qualities of the dielectric of the insulating layer  24  will typically be at least as effective as polyethylene. 
         [0071]    Referring now to  FIG. 7 , the integrated capacitor inductor unit  10  may alternatively provide a linear core  12  that extends without curvature along an axis  30 . In this case the linear core  12  may have many planar parallel rectangular layers  20  extending along the axis  30 . 
         [0072]    It will be appreciated that the linear core  12  need not use planar laminations of layers  20  but for manufacturing convenience (as shown in  FIG. 8 ) may provide layers  20  wrapped in a spiral about axis  30  to create a cylindrical core  12 . A single pair of conductors and a single pair of insulators may be wrapped in an Archimedean spiral to create multiple layers simplifying the wiring of the capacitor  23 . Generally the invention may provide an inductor with an inductance of at least 0.01 μH and/or a capacitor with a capacitance of least 0.0001 μF and in some embodiments an inductor with an inductance of at least 0.1 μH and a capacitor with a capacitance of at least 0.01 μF. 
         [0073]    Referring now to  FIG. 9 , it will be appreciated that the same cores  12  described above may be used for the construction of a transformer  36 . In one example, the core shown in  FIG. 7  may be wrapped with two conductors  38  and  40  each passing in multiple loops around the core  12  and axis  30 . The conductors  38  and  40  may each terminate in separate terminals  42  (for conductor  38 ) and terminals  44  (for conductor  40 ) to provide primary winding  50  and secondary winding  52  of the transformer  36 . 
         [0074]    In these applications, the cores  12  may be characterized as described above with respect to the permeability and permittivity with one exception. While the conductors  38  and  40  (and thus primary winding  50  and secondary winding  52 ) are intended to be fully flux coupled through the core  12  of the capacitor  23 , they will exhibit some leakage flux giving them each an inductive quality. An increase in inductance of the conductors  38  and  40 , however, is not necessarily desired, so the characteristics of the core  12  applicable to inductors, in increasing the inductance of inductors, will not apply to the cores  12  used for transformers Instead the permeability of the core  12  will generally be selected to reduce the leakage flux of the transformer  36 , for example, in one measure to provide a short circuit leakage reactance impedance of less than 15 percent or the 5% of typical transformers. 
         [0075]    Referring to  FIG. 10  it will be appreciated that the capacitance between terminals  26  will be electrically independent of the transformer primary winding  50  operating between terminals  42  and the transformer secondary winding  52  operating between terminals  44 . Further, although the number of turns of each winding  50  and  52  are shown to be approximately the same, it will be appreciated that in general the ratio between the number of turns of the primary winding  50  and secondary winding  52  will vary providing the transformer “turns ratio” defining a voltage or current “step up” or step down”. It will also be appreciated that the direction of winding of the primary winding  50  and secondary winding  52  may be the same direction or opposite direction. 
         [0076]    It will be understood that other transformer cores  12 , including a toroidal core  12  such as shown in  FIG. 1  and the spiral core  12  shown in  FIG. 8 , may also be used for a transformer  36 . In addition, the invention contemplates that other traditional transformer core structures may be used including so-called E-I cores and the like while still providing capacitance as taught by this application. 
         [0077]    Referring now to  FIG. 11 , in one embodiment, the primary winding  50  may share a length of conductor with the secondary winding  52  in the manner of an auto transformer or variable transformer (where the terminal  44  of the secondary winding may slide along the windings to change the relative turns ratio between the primary winding  50  and secondary winding  52 ). 
       Embodiments II 
       [0078]    Referring now to  FIGS. 1 and 12   a , current flow from capacitor terminal  26  (C 1 ) to capacitor terminal  26  (C 2 ) will produce a magnetic field Bp encircling the conductors  60  forming a path leading between capacitor terminals  26  according to the right-band rule. Conductor  60  includes generally the conductive material proximate to the core  12  including the conductive plates  22  in those conductors interconnecting the plates  22  to the terminals  26 . 
         [0079]    For normal capacitor designs, where the conductors  60  connected between the terminals  26  of the capacitance  23  are removed from high permeability material, the energy stored in this magnetic field Bp and hence the inductance caused by the magnetic field Bp may be relatively low. In the present design, however, the conductors  60  communicating current between the terminals  26  are proximate to high permeability material  27  so that they increase the equivalent series inductance  62 . 
         [0080]    In practice, the high permeability material  27  increases the equivalent series inductance  62  caused by the field Bp to the point of significantly affecting the capacitance of the devices at frequencies less than 100 kilohertz, well within the domain of current solid-state switching elements that may make use of the integrated capacitor inductor unit  10  of the present invention. This inductance  62  will be termed “parasitic” inductance because it differs from the inductance of inductor  25  provided by the loops  18  (for example, shown in  FIG. 1 ) such as is galvanically isolated from the capacitor  23 . For two conductors to be galvanically isolated, as used herein, means that there is substantially no ohmic connection between the conductors and hence no path for DC current. 
         [0081]    Referring now to  FIG. 12   b,  this parasitic inductance  62  may be substantially reduced by employing a loop-back conductor  60 ′ being a portion of conductor  60  that passes backwards with respect to the remainder of conductor  60  (formed of the plates  22  and interconnecting conductors to one of the terminals  26 ) in close proximity to the high permeability material  27 . The flux concentration provided by the high permeability material  27  is the principal cause of the excessive equivalent series inductance  62  (the ESL) of the capacitor  23 , and hence the configuration of the loop-back conductor  60 ′ in the vicinity of the high permeability material  27  is of principal interest with portions of the loop-back conductor  60 ′ away from the high permeability materials  27  being of less concern. 
         [0082]    In operation, the loop-back conductor  60 ′ provides a countervailing magnetic field to field Bp (depicted as −Bp) that operates to effectively cancel the magnetic energy stored in the high permeability material  27  thereby greatly reducing the parasitic inductance  62 . 
         [0083]    Referring now to  FIG. 13 , the loop-back conductor may be implemented in the design of  FIG. 1  by passing the conductor  60  leading to terminal C 2  backward through the center of the toroid of the core  12  as a loop-back conductor  60 ′ as generally depicted in  FIG. 12 b   . Desirably, but less critically, the conductors  60  to each of the terminals C 1  and C 2  will be kept closely proximate. 
         [0084]    In the embodiment shown in  FIG. 13 , alternate conductive plates  22  of the core  12  may be connected to a bottom end cap  66  adjacent to a lower base of the toroid of the core  12  and the remaining conductive plates  22  connected to an upper end cap  68  fitting against the upper base of the toroid of the core  12 . Part of the loop-back conductor  60 ′ may be formed by a conductive ring  70  fitting against the inner cylindrical bore of the toroid of the core  12  or a conductive ring  72  fitting against the outer periphery of the toroid of the core  12 . The upper end cap  68  attaches to one terminal  26  and the lower end cap  66  is extended up the side wall and/or the outer peripheral wall by either or both of the conductive ring  70  or conductive ring  72  to attach at its upper edge to the remaining terminal  26 . The loops  18  of the inductor circle the toroid of the core  12  to pass repeatedly through the center of the toroid and around its outer periphery in successive windings, one of which is shown by arrow  74 . The result is a magnetic field B generally aligned with a plane of the plates  22  and circling around axis  17 . 
         [0085]    Referring now to  FIG. 14 , in an alternative embodiment, the plates  22  of the toriodal core  12  may be generally perpendicular to axis  17 . Here alternate conductive plates  22  of the core  12  may be connected to conductive ring  70  fitting against the inner cylindrical bore of the toroid of the core  12 , and the remaining conductive plates  22  may be connected to a conductive ring  72  fitting against the outer periphery of the toroid of core  12 . An upper end cap  68  fitting against the upper base of the toroid of the core  12  may attach to the inner ring  70  and in turn attach to terminal  26  of C 1  near the outer periphery of the toroid of the core  12 . The remaining terminal  26  of C 2  may attach to the outer ring  72 . Here the loop-back conductor  60 ′ is formed by the upper end cap  68  providing a current flow counter to that between the plates  22 . The loops  18  of the inductor circle the toroid of the core  12  again passing repeatedly through the center of the toroid and around its outer periphery as shown by arrow  74 . The result is a magnetic field B generally aligned with the plane of the plates  22 . 
         [0086]    Referring now to  FIG. 15 , a loop-back conductor can be implemented in the embodiment of  FIG. 8  by constructing the core  12  from a rolled sheet  80  having a flexible insulating layer  24  supporting on its opposite broad faces plates  22   a  and  22   b.  An additional insulator  24 ′ may be adhered to the upper plate  22   a.  One terminal  26  may be attached to the upper plate  22   a  and the other terminal  26  may be attached to the lower plate  22   b  by conductors extending parallel to axis  30 , one of which provides conductor  60  and the other of which provides loop-back conductor  60 ′. The axial portions of the conductors  60  and  60 ′ communicating between terminals  26  and the plates  22   a  and  22   b  provide a countervailing magnetic field. In addition, the helical plates  22   a  and  22   b  provide a similar countervailing magnetic field generation when the sheet  80  is rolled in a spiral around axis  30 . As shown in  FIG. 8 , the loops  18  of the inductor circle the axis  30  as shown by arrow  74 . The result is a magnetic field B generally aligned with the plane of plates  22  extending along axis  30 . 
         [0087]    Referring now to  FIGS. 7, 9, and 16 , alternate conductive plates  22  of the core  12  may be connected to a bottom end cap  66  adjacent to a lower face of the core  12  and the remaining conductive plates  22  connected to an upper end cap  68  fitting against the upper face of the core  12 . Part of the loop-back conductor  60 ′ may be formed by a conductive side panel  82  along one or both vertical sides of the core  12  in a direction parallel to the plates  22 . An upper edge of this conductive side panel  82  may connect to terminal C 2  and terminal C 1  may connect to the upper end cap  68 . Desirably, but less critically, the conductors  60  to each of the terminals C 1  will be kept closely proximate. Leads to the terminals C 1  and C 2  may also extend along axis  30  so as not to interfere with the loops  18  winding around the core as indicated by arrow  74 . The loops produce a magnetic field B generally aligned with the plates  22  along axis  30 . 
       Embodiment III 
       [0088]    Referring now to  FIG. 17 , the core  12  in one embodiment may be given a shape providing a planar ring  88  with teeth  90  extending radially inward from an inner diameter of the planar ring  88  as along the plane of the planar ring  88 . Each of the teeth  90  may be positioned at an equal angle about an axis  92 , the latter defining the center of the ring  88 . The ring  88  and teeth  90  may be constructed of a set of layers  20  extending parallel to the plane of the ring  88  and comprising alternating conductive plates  22  and insulators  24  generally in the manner of the construction of the core described in  FIG. 14  above. Terminals  26  may be attached to outer ring  72  and inner ring  70  communicating with alternate plates  22  at an inner periphery and outer periphery of the planar ring  88  as discussed above with respect to  FIG. 14  to provide capacitor terminals  26 . 
         [0089]    Each of the teeth  90  may be wound with conductive loops  18  in the manner of a conventional motor stator to provide multiple inductors  25  operating for the purpose of generating a magnetic field for influencing a motor rotor. The capacitance provided by terminals  26  may be used, for example, for a motor starting or phasing capacitor. 
         [0090]    Certain terminology is used herein for purposes of reference only, and thus is not intended to be limiting. For example, terms such as “upper”, “lower”, “above”, and “below” refer to directions in the drawings to which reference is made. Terms such as “front”, “back”, “rear”, “bottom” and “side”, describe the orientation of portions of the component within a consistent but arbitrary frame of reference which is made clear by reference to the text and the associated drawings describing the component under discussion. Such terminology may include the words specifically mentioned above, derivatives thereof, and words of similar import. Similarly, the terms “first”, “second” and other such numerical terms referring to structures do not imply a sequence or order unless clearly indicated by the context. 
         [0091]    When introducing elements or features of the present disclosure and the exemplary embodiments, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of such elements or features. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It is further to be understood that the method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed. 
         [0092]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein and the claims should be understood to include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims. All of the publications described herein, including patents and non-patent publications, are hereby incorporated herein by reference in their entireties.