Abstract:
A combination capacitor and inductor employ a common volume for energy-storing electrical and magnetic fields thereby reducing the bulk of these components with respect to separate components of comparable value.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
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     CROSS REFERENCE TO RELATED APPLICATION 
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     BACKGROUND OF THE INVENTION 
     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. 
     Inductors and capacitors are 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 
     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. 
     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 energy 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. 
     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. 
     SUMMARY OF THE INVENTION 
     The present invention provides a conductor and capacitor configured to share an energy storage volume thereby significantly reducing the bulk of the devices. Generally, the capacitor incorporates a high magnetic permeability material into its layers so that it may fit into the coil of the inductor in place of the normal core. 
     Specifically, in one embodiment, the 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 further having a capacitor positioned within the surrounded volume and providing a capacitor structure including opposed conductive plates attached 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 being one or both of a ferromagnetic and ferrimagnetic material. 
     It is thus a feature of at least one embodiment of the invention to provide a compact package including both a capacitor and an inductor by implementing an inductor core with the capacitive element. 
     The high permeability material may be distributed in a plurality of layers in the capacitor structure. 
     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. 
     The high permeability material may be iron or an iron alloy laminated with a nonferrous metal. 
     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 permittivity in the conductive plates of the capacitor. 
     The high magnetic permeability material may be a plurality of granules incorporating inter-granular gaps of low magnetic permeability. 
     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. 
     The capacitor structure and the surrounded volume may be toroids. 
     It is thus a feature of at least one embodiment of the invention to provide a form factor providing a reduced surface to volume. 
     The conductive plates and insulator may be wound in a spiral. 
     It is thus a feature of at least one embodiment of the invention to provide a simple fabrication method for the combined inductor and capacitor. 
     The capacitor plates may extend substantially parallel to an axis of a magnetic field generated by the inductor when current passes through the inductor. 
     It is thus a feature of at least one embodiment of the invention to minimize eddy current conduction in the capacitor plates caused by fluctuating magnetic fields of the inductor. 
     The first and second terminals may be electrically separate from the third and fourth terminal. 
     It is thus a feature of at least one embodiment of the invention to provide an independently accessible capacitor and inductor for maximum flexibility in incorporating the capacitor and the inductor into different circuits. 
     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 
         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; 
         FIG. 2  is a simplified electrical schematic of the electrical equivalent of the embodiment of  FIG. 1  showing an independent inductor and capacitor; 
         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; 
         FIG. 4  is a figure similar to that of  FIG. 3  showing laminated ferrous and nonferrous metals used for the capacitor plates; 
         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; 
         FIG. 6  is a figure similar to that of  FIG. 3  showing nonferrous capacitor plates and a high permeability insulating layer; 
         FIG. 7  is a perspective view of an alternative embodiment to that of  FIG. 1  showing a linear form factor; 
         FIG. 8  is a perspective view of an alternative embodiment to  FIG. 7  showing a spiral capacitor plate configuration; 
         FIG. 9  is a figure similar to that of  FIG. 7  showing an embodiment of the invention producing a combination capacitor and transformer; 
         FIG. 10  is a figure similar to that of  FIG. 2  showing a simplified electrical schematic of the equivalent circuit of  FIG. 7 ; 
         FIG. 11  is a figure similar to that of  FIG. 9  showing in simplified form an alternative winding producing an auto transformer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 . 
     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 . 
     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. 
     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 . 
     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. 
     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. 
     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 . 
     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. 
     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. 
     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. 
     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 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 . 
     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. 
     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 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. 
     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. 
     Referring now to  FIG. 7 , the integrated capacitor inductor  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 . 
     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. 
     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 . 
     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. 
     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. 
     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. 
     Referring now to  FIG. 11 , in one embodiment, the primary winding  50  may share a terminal  56  with the secondary winding  52  in the manner of an auto transformer or variable transformer (where the shared terminal  56  may slide along the windings to change the relative turns ratio between the primary winding  50  and secondary winding  52 ). 
     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. 
     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. 
     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.