Abstract:
Geometrically complimentary magnetic field structures are adapted for efficient power transfer by induction from a planar power delivery surface to a power receiving device. Planar surface electro-magnetic coil pole areas for power delivery and receiver coil assemblies as well as several would coil apparatus and configurations are included.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application is a nonprovisional application of provisional application No. 61/238,066 filed Aug. 28, 2009, and is also a nonprovisional application of provisional application 61/254,531, filed Oct. 23, 2009, both of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to electronic systems and methods for providing electrical power and/or data in a wire-free manner to one or more electronic or electrically powered devices with a power delivery surface, and more specifically to such systems and methods wherein the wire-free power transfer is implemented by magnetic induction. 
         [0004]    2. State of the Prior Art 
         [0005]    A variety of electronic or electrically powered devices, cell phones, laptop computers, personal digital assistants, cameras, toys, game devices, tools, medical devices, navigation devices, and many others, have been developed along with ways for powering them. Mobile electronic devices typically include and are powered by batteries that are rechargeable by connecting them through power cord units, which include transformers and/or power converters, to a power source, such as an electric wall outlet or power grid, an automobile or other vehicle accessory electric outlet plug receptacle, or the like, either during use of the electronic device or between uses. A non-mobile electronic device is generally one that is powered through a power cord unit and is not intended to be moved during use any farther than the reach of the power cord, so it generally does not have or need batteries for powering the device between plug-ins. 
         [0006]    In a typical set-up for a mobile device, the power cord unit includes an outlet connector or plug for connecting it to the power source and a battery connector for connecting it to a corresponding battery power receptacle of the battery. The outlet connector or plug and battery connectors are in communication with each other so electrical signals flow between them. In this way, the power source charges the battery through the power cord unit. 
         [0007]    In some setups, the power cord unit may include a power adapter, transformer, or converter connected to the outlet and battery connectors through AC input and DC output cords, respectively. The power adapter adapts an AC input voltage received from the power source through the outlet connector and AC input cord to output a DC voltage through the DC output cord. Others include adapters, transformers, or converters connected to the outlet and battery connectors through DC input and DC output cords. The DC output current flows through the receptacle and is used to charge the battery. 
         [0008]    In some cases, it is more convenient to provide power to these devices without having to connect or plug in wires, so docking stations are provided, wherein a power delivery device is configured to dock a particular portable electronic or electrically-powered device or battery pack in a manner that connects a set of electrical contacts for delivering power from the docking station to the portable device or battery pack. However, typical docking stations are configured in a manner that is unique to one or a few electronic or electrically-powered device models of a particular manufacturer, thus not useable to charge other devices or battery packs. 
         [0009]    To alleviate that problem, several recent innovations have introduced power delivery pads with substantially flat power delivery surfaces on which one or more electronic or electrically powered devices with appropriate power receiver apparatus can be positioned on the power delivery surface to receive electric power. There exist a number of technologies for transferring electric power wire-free to portable electronic or electrically powered devices in this manner. 
         [0010]    The foregoing examples of related art and limitations related therewith are intended to be illustrative, but not exclusive or exhaustive, of the subject matter. Other aspects and limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate example implementations of the present invention, but not the only ways the invention can be implemented, and together with the written description and claims, serve to explain the principles of the invention. 
           [0012]    In the drawings: 
           [0013]      FIG. 1  is a perspective view of an example inductive power delivery pad, which includes a power delivery surface, and an enabled device with power receiver apparatus positioned on the power delivery surface for receiving electric power, wherein a portion of the top skin of the power delivery surface is cut away to reveal the electro-magnetic coil assembly, and wherein a portion of the shell of the electronic or electrically powered device is cut away to reveal the power receiver coil assembly (for clarity and to avoid unnecessary clutter, the other electronic components normally comprised in an electronic or electrically powered device are not show in this figure); 
           [0014]      FIG. 2  is a perspective view of the electro-magnetic coil assembly of the power delivery pad without the housing and surface skin and the receiver coil assembly without the power receiving device shell; 
           [0015]      FIG. 3  is a partial cross-sectional view of the core plate and wire coil of the electro-magnetic coil assembly taken substantially along section line  3 - 3  in  FIG. 2 ; 
           [0016]      FIG. 4  is a diagrammatic plan view of the electro-magnetic coil array of the power delivery pad of  FIG. 1 , showing the example array in alternating north (N) and south (S) elongated strips, along with diagrammatic views of a plurality of example power receivers with respective receiver coil pole constellations positioned in various locations and orientations on the power delivery pad magnetic coil array; 
           [0017]      FIG. 5  is a perspective view of the receiver coil assembly turned up-side down to illustrate the structure of the assembly, including the individual coil spools and poles; 
           [0018]      FIG. 6  is a cross-sectional view similar to  FIG. 3 , but with the power receiver coil assembly positioned on the power delivery surface to receive power; 
           [0019]      FIG. 7  is a diagrammatic view of four coils showing how they can be electrically connected together; 
           [0020]      FIG. 8  is a circuit diagram of the bridge rectifier circuit; 
           [0021]      FIG. 9  is a diagram showing the spatial relationship of the pole pieces for an arrangement of four coils; 
           [0022]      FIG. 10  is a diagram in plan view of a portion of several strip electro-magnetic pole areas in conjunction with receiver coil pole pieces in a geometrically limiting arrangement; 
           [0023]      FIG. 11  is a view similar to  FIG. 10 , but in a different limiting arrangement; 
           [0024]      FIG. 12  is a perspective view of another power delivery surface configuration with rectangular pole areas; 
           [0025]      FIG. 13  is a perspective view of a smaller sized power delivery coil assembly; 
           [0026]      FIG. 14  is a top plan view of the smaller sized power delivery coil assembly of  FIG. 13 ; 
           [0027]      FIG. 15  is a perspective view from the bottom of a power receiver coil assembly; 
           [0028]      FIG. 16  is an enlarged isometric view of a portion of the power delivery coil assembly of  FIGS. 12-14 ; 
           [0029]      FIG. 17  is a partial cross-sectional view of the power delivery coil assembly taken substantially along section line  17 - 17  of  FIG. 16 ; 
           [0030]      FIG. 18  is a cross-sectional view similar to  FIG. 17 , but showing the magnetic fields diagrammatically; 
           [0031]      FIG. 19  is an isometric view of an embodiment of the power receiver coil assembly poised in a position above the power delivery coil assembly; 
           [0032]      FIG. 20  is a circuit diagram of a rectifying regulator circuit for output from the receiver coil assembly; 
           [0033]      FIG. 21  is a side elevation view of an embodiment of the power receiver coil assembly poised in a position above the power delivery coil assembly; 
           [0034]      FIG. 22  is a side elevation view similar to  FIG. 21 , but also showing the magnetic fields; 
           [0035]      FIG. 23  is an isometric view of two halves of a pot core adapted for use in the power delivery and power receiver coil assemblies; and 
           [0036]      FIG. 24  is a cross-sectional view of the two halves of the pot core of  FIG. 23 , but positioned in alignment with each other for transferring power. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    An example power delivery pad  10  and enabled power receiving device  20  are shown in  FIG. 1 . The power delivery pad  10  transfers power wirelessly or wire-free, i.e., without a charging adapter cord, to one or more devices  20  positioned on it. In this context, the terms “wireless”, “wirelessly”, and “wire-free” are used interchangeably to indicate that charging of the device is achieved without a cord-type electric charging unit or adapter between the power delivery surface  12  of the power delivery pad  10  and the power receiving device, and in the example of  FIG. 1 , is achieved by magnetic induction with geometrically complimentary magnetic field structures, as will be described in more detail below. Also, the term “enabled” device is used for convenience to mean an electronic or electrically powered device, for example, cell phones, laptop computers, personal digital assistants, cameras, toys, game devices, tools, medical devices, navigation devices, or just about any other portable device, that is equipped with inductive receiver coils and associated electronic circuitry to enable the device to be electrically charged by the power delivery pad  10 . 
         [0038]    The example power delivery pad  10  and enabled power receiving device  20  in  FIG. 1  are shown as one example implementation, but not the only implementation, that demonstrates a number of features and principles used as part of this invention to achieve efficient and reliable wire-free power transfer to power and/or charge a power receiving device. Therefore, this description will proceed with reference to the example shown in  FIG. 1 , but with the understanding that the invention recited in the claims below can also be implemented in myriad other ways, once the principles are understood from the descriptions and explanations herein, and that some, but not all, of such other implementations and enhancements are also described or mentioned below. 
         [0039]    The drawing views of the examples in the accompanying figures of drawings are diagrammatic, not necessarily exact illustrations, and various component sizes and proportions are exaggerated or not true to scale because of the impracticality of illustrating thin layer or component thicknesses and other dimensions in true scale or proportionate sizes, as is understood by persons skilled in the art, but persons skilled in the art can understand the principles and information being illustrated and how to implement them. 
         [0040]    Magnetic induction has been employed to implement wire-free power transfer before this invention, but such previous implementations of magnetic induction power transfer have been either inherently low in efficiency, or they require costly electronics. The example implementations described herein provide more efficient, cost effective improvements in wire-free power transfer by magnetic induction. 
         [0041]    In the example of  FIG. 1 , the power receiving device is shown positioned somewhat randomly on the power delivery surface  12  of the power delivery pad  10  to receive electric power, which is provided by magnetic induction from alternating magnetic fields generated by the plurality of strip electro-magnet pole areas or regions  14  in the substantially planar surface  56  a core plate  52  of power delivery pad  10 . The strip electro-magnet pole areas  14  are powered to create the alternating magnetic fields, which will be explained in more detail below, by electric power from some electric power source (not shown), such as a wall plug to public utility or grid power, an automobile, boat, airplane, or other vehicle electric power system, a solar electric power generator, or any other source of electric power. The power delivery pad  10  can be connected electrically to any such electric power source by any standard cord  16  or other custom wire connection, as is understood by and within the capabilities of persons skilled in the art, and a magnet driver circuit (not shown in  FIG. 1 , but described in more detail below) for driving the strip electro-magnet pole areas  14  to produce the magnetic fields can be provided in a suitable housing  18  of the power delivery pad  10  or can be external to the power delivery pad  10 . The strip electro-magnet pole areas  14  can be covered by a thin, protective skin or covering material  22 , part of which is shown cut away in  FIG. 1  to reveal the strip electro-magnets  12 , or they can be left exposed, if desired. The skin  22  should be electrically non-conductive and for best power transfer performance, but it might be desirable and feasible to have a magnetic material skin  22 . The example power receiving device  20  in  FIG. 1  is shown with a portion of its shell or casing  24  cut away to reveal the magnetic pick-up or receiver coil assembly  30 , which comprises a plurality of individual receiver coils  32 ,  34 ,  36 ,  38  mounted on a yoke  40 . To avoid unnecessary clutter, the other electronic circuits and components typically housed in the shell or casing  24 , which would typically include a rechargeable battery pack or storage capacitor and other electronic circuits and components to condition the received power and to operate the device  20  for its intended purpose, are not shown in  FIG. 1 . 
         [0042]    The electro-magnetic coil assembly  50  of the example power delivery pad  10  without the housing and surface skin, and the receiver coil assembly  30  without the shell  24  of the example power receiving device  20  are shown in  FIG. 2 . As mentioned above, the electro-magnetic coil assembly  50  comprises a plurality of strip electro-magnet pole areas  14  formed side-by-side on the surface  56  of a magnet core plate  52 . While the strip electro-magnet pole areas  14  can be formed in myriad ways, the example strip electro-magnet pole areas  14  shown in  FIGS. 1 and 2  are formed on a solid plate  52  of soft ferromagnetic material with a plurality of grooves or troughs  54  milled, routed, molded, or otherwise formed in parallel, spaced-apart relation to each other in the upper surface of the plate  52 , as shown in  FIGS. 2 and 3 . One or more coil wire  60  is routed through the troughs  54  around the circumference or perimeter of the individual strip electro-magnet pole areas  14 , as illustrated in  FIG. 2 , so that a current flowing through the coil wire  60  flows around adjacent strip electro-magnets  14  in opposite directions on opposite sides of each strip electro-magnet pole area  14 , as illustrated diagrammatically in  FIG. 4  by the current flow arrows  62 , to generate opposite magnetic polarities in adjacent strip electro-magnet pole areas  14 , as also illustrated in  FIGS. 3 and 4 . In  FIG. 4 , the plus sign “+” in the wire  60  indicates current flowing in the direction into the paper, and the dot “•” in the wire  60  indicates current flowing in the direction out of the paper, in the conventional manner. In practice, the current flow in the direction of the arrows  62  and the opposite north N and south S polarities in the adjacent strip electro-magnet pole areas  14  are instantaneous indications, because the current is driven as alternating current (AC). Consequently, the current flow direction alternates to opposite directions, and the resulting N and S polarities in adjacent strip electro-magnet pole areas  14  also alternate to opposite polarities, at whatever frequency the AC current is driven, as will be understood by persons skilled in the art. The wire  60  can be insulated, and the ends  64 ,  66  of the wire  60  ( FIG. 2 ) terminate in the coil driver circuit (not shown in  FIG. 2 ), which can be located in the housing  18  ( FIG. 1 ) or at any other convenient location. The ferromagnetic material of the core plate  52  is preferably, but not necessarily, an electrically non-conductive material to avoid inducing eddy currents in the core plate  52  by the magnetic field, which would decrease efficiency. 
         [0043]    The surface  56  of the core plate  52  is preferably, but not necessarily, substantially planar, so the strip electro-magnetic pole areas  14  formed on the surface  56 , as described above, result in a substantially planar pattern or array of substantially planar magnetic pole areas or regions  14 , separated by the troughs  54 , on which the power receiving device  20  can be positioned, with or without the protective skin  22 , to receive power inductively. The troughs  54  in the example illustrated in  FIGS. 1-3  are not deep enough to completely separate the strip electro-magnetic pole areas  14  so that a portion  58  of the core plate  52  is left under each trough  54  to provide a magnetic flux F path under each trough  54  to complete the magnetic circuit between adjacent strip electro-magnetic pole areas  14 , as illustrated in  FIG. 3 . In general, the magnetic field lines F created by the excitation current flowing through the wire  60  extend from a strip electro-magnetic pole area  14  into the immediate vicinity above the pole area  14  and over to an adjacent pole area  14 , which by design is of opposite polarity, as illustrated in  FIG. 3 . The field lines F continue within the ferromagnetic core plate  52  and through the material path  58  under the trough  54  and back through the ferromagnetic material to form continuous lines of flux F. 
         [0044]    In this regard, it should be noted that the troughs  54  are not required. The coil current carrier function provided by the wire  60  in the trough  54  could be provided in other ways, for example, but not for limitation, a planar conductor strip (not shown), such as a copper tape, could be adhered to the surface  58  of the core plate  52  around the peripheries or perimeters of respective surface areas  14  to form and create the strip electro-magnetic pole areas  14 . In another example implementation (not shown), no ferromagnetic material is used for the core plate  52  (or otherwise), and the wire windings  60  themselves create and define the geometry to satisfy the basic principles of operation of the power delivery pad  10 , although, without the ferromagnetic plate  52 , the magnetic field flux lines  12  would not concentrate in paths through the core plate, but, instead, would extend below the wires  60  in a similar manner to the flux lines F above the core plate  52  illustrated in  FIG. 3 . It is appropriate to also note that in the implementation shown in  FIGS. 1-3  as well as in implementations in which no ferromagnetic material is used, when no receiver device  20  is nearby, a large portion of any one field F does not pass through ferromagnetic material. 
         [0045]    As shown in  FIGS. 1 and 2  and explained above, the power receiving device  20  is equipped with a the receiver coil assembly  30 . As best seen in  FIG. 5 , in conjunction with  FIGS. 1 and 2 , the receiver coil assembly comprises a plurality of receiver coils  32 ,  24 ,  36 ,  38 . Each receiver coil  32 ,  34 ,  36 ,  38  in the example implementation illustrated in  FIGS. 1 ,  2 , and  5  comprises a wire winding  33 ,  35 ,  37 ,  39 , respectively, wound onto a bobbin or spool  43 ,  45 ,  47 ,  49 , respectively. The wire windings  33 ,  35 ,  37 ,  39  can be insulated copper wire or other wire suitable for windings as is known in the art. Each bobbin or spool  43 ,  45 ,  47 ,  49  is mounted on a pole piece  42 ,  44 ,  46 ,  48 , respectively, that extends from the yoke core  40 . The yoke core  40  and the pole pieces  42 ,  44 ,  46 ,  48  comprise a soft ferromagnetic material. 
         [0046]    When a power receiving device  20  is positioned on the power delivery surface  12  of the power delivery pad  10 , as shown in  FIG. 1  in a manner in which at least one of the receiver pole pieces  42 ,  44 ,  46 ,  48  is aligned with a strip electro-magnetic pole area  14  of one polarity (e.g., N) and at least a different one of the receiver pole pieces  42 ,  44 ,  46 ,  48  is aligned with a different strip electro-magnetic pole area  14  of the opposite polarity (e.g., S), as illustrated in the cross-sectional  FIG. 6 , a magnetic circuit indicated by magnetic flux lines F is formed between the electro-magnetic pole areas  14  of the surface  56  of the core plate  52  and the pole pieces (e.g., pole pieces  42 ,  48  in  FIG. 6 ) of the power receiver coil assembly  30 . In this manner, the electromagnetic coil assembly  50  of the power delivery pad  10  and the receiver coil assembly  30  of the power receiving device  20  essentially form a transformer with the magnetic flux F generated by the excitation windings formed by the wire  60  of the core plate surface  56  pass through the ferromagnetic material of the pole pieces  42 ,  48  and yoke core  40  of the power receiver coil assembly  30 . This magnetic flux F induces a voltage in the windings  33 ,  39  of the receiver coil assembly  30 , which can be used to charge and/or operate the power receiving device  20 , as will be explained in more detail below. 
         [0047]    In a practical implementation, as shown in the example of  FIGS. 1 and 6 , a gap formed by the non-ferromagnetic material of skin  22  on the power delivery surface  12  of the power delivery pad  10  separates the electro-magnetic pole areas  14  of the core plate  56  from the receiver pole pieces (e.g., pole pieces  42 ,  48  in  FIG. 6 ). The non-ferromagnetic material of the shell  24  of the power receiving device  10  (shown in  FIG. 1 , but not in  FIG. 6 ) can also provide part of this gap, if the power receiving device  10  is constructed with the receiver pole pieces  42 ,  44 ,  46 ,  48  inside the shell  24  and not protruding through the shell  24 . The non-ferromagnetic material of the skin  22  can be a protective covering that hides and otherwise secures the inner components of the electro-magnetic coil assembly  40 . This gap becomes part of the overall magnetic circuit F as shown in  FIG. 6 , when the power receiving device  20  is positioned on the power delivery surface  12 . 
         [0048]    As mentioned above, power is transferred from the power delivery surface  12  to the power receiving device  20  through the changing (alternating) magnetic flux F induced in the magnetic circuit. This flux F is induced by exciting an AC current in the power deliver surface windings formed by the wire(s)  60 . The AC frequency can be chosen as a matter of design to balance trade-offs between efficiency and losses. 
         [0049]    As also mentioned above, the receiver pole pieces  42 ,  44 ,  46 ,  48 , when placed on the power delivery surface  12 , will efficiently link flux F from the electro-magnetic pole areas  14  of the core place surface  56 , and, as long as at least one receiver pole piece links to a pole area  14  of N polarity and at least one other pole piece links to a pole area  14  of S polarity, power can in principle be extracted from the power delivery surface  12  and delivered to the power receiving device  20 . To illustrated this principle, the plurality of receiver coils  32 ,  34 ,  36 ,  38  are illustrated diagrammatically in  FIG. 7 , with one end of each respective coil wire  33 ,  35 ,  37 ,  39  connected together at a common node as indicated by A, B, C, D, respectively, and the other end of each respective coil wire  33 ,  35 ,  37 ,  39  terminating at A dot, B dot, C dot, and D dot, respectively. The receiver coil  32  is illustrated for example with its pole piece  42  linked to a magnetic N polarity pole area  14  (not shown in  FIG. 7 ), and the receiver coil  38  is illustrated in this example with its pole piece  48  linked to a magnetic S polarity pole area  14  (not shown in  FIG. 7 ). The other two receiver pole pieces  44 ,  46  of receiver coils  34 ,  36  are shown in this example with no polarity link, such as if they were aligned over a trough  54 . In this example, the A dot end of the coil wire  33  of receiver coil  32  would be of one electrical polarity, e.g., positive (+), and the D dot end of the coil wire  39  of receiver coil  38  would be of the opposite electrical polarity, e.g., negative (−), so electric current would flow through the wires  33 ,  39 , as indicated by arrows  64 . Since the pole pieces  44 ,  46  of the other two receiver coils  34 ,  36  are not linked to any polarity pole area in this example, no electric current is flowing through their wires  35 ,  37 . Any other combination of at least one receiver pole piece linked to one magnetic polarity (e.g., N) and at least one other receiver pole piece linked to the opposite magnetic polarity (e.g., S) will result in current flow in one direction or another. 
         [0050]    A bridge rectifier circuit  66  as shown, for example, in  FIG. 8  can be used to rectify any combination of current flows of either electrical polarity, e.g., positive (+) or negative (−), from the wire ends A dot, B dot, C dot, and/or D dot of the coil wires  33 ,  35 ,  37 ,  39  in  FIG. 7  as explained above. A pair of diodes  68  in a parallel circuit for each coil wire  33 ,  35 ,  37 ,  39  (A dot, B dot, C dot, D dot, respectively) with the wires  33 ,  35 ,  37 ,  39  connected into the parallel diode rectifier circuit between the two diodes  68  is sufficient to extract usable electric power whenever at least one receiver pole piece is linked to one magnetic polarity (e.g., N) and at least one other receiver pole piece is linked to the opposite magnetic polarity (e.g., S), as explained above. The rectifier output, as indicated in  FIG. 8 , is a direct current on two terminals  70 ,  72 , one always positive and the other always negative, which can be conditioned and regulated for use by the power receiving device  20 . 
         [0051]    In the example implementation shown in  FIGS. 1-4 , there are four receiver pole pieces  32 ,  34 ,  36 ,  38  shown in a pattern wherein three of the pole pieces  32 ,  34 ,  36  are positioned at the vertices of an equilateral triangle and the fourth pole piece  38  is positioned in the center of the equilateral triangle. This arrangement is sometimes called a tetrahedron pattern, because the positions of the four pole pieces are at locations that match the appearance of the vertices of a top plan view of a tetrahedron. Other numbers and arrangements of receiver pole pieces can also be used. 
         [0052]    When the pole pieces  32 ,  34 ,  36 ,  38  in the tetrahedron pattern as explained above are appropriately spaced apart from each other in relation to the width of the strip electro-magnetic pole areas  14  of the power delivery pad  10 , as will be explained below, there can be one hundred percent assurance that any location and any orientation of the power receiving device  10  on the power delivery surface  12  of the power delivery pad  10  will result in at least one receiver pole piece is linked to one magnetic polarity (e.g., N) and at least one other receiver pole piece is linked to the opposite magnetic polarity (e.g., S), thus power transfer to the power receiving device  10 . Six example placements of the tetrahedron pattern of receiver pole pieces  32 ,  34 ,  36 ,  38  with appropriate spacing in relation to the strip electro-magnetic pole areas  14  are illustrated in  FIG. 4 . The example  74  has two receiver pole pieces linked to a N polarity pole area  14 , one receiver pole piece linked to a S polarity pole area  14 , and one receiver pole piece not linked to any pole area  14 , e.g., positioned over a trough  54 . The example  76  has two receiver pole pieces linked to a S polarity pole area  14 , one receiver pole piece linked to a N polarity pole area  14 , and one receiver pole piece not linked to any pole area  14 , e.g., positioned over a trough  54 . The example  78  has one receiver pole piece linked to a N polarity pole area  14 , one receiver pole piece linked to a S polarity pole area  14 , and two receiver pole pieces not linked to any pole area  14 , e.g., positioned over a trough  54 , which is the same as the example shown in  FIG. 7  and described above. The example  80  also has two receiver pole pieces linked to a N polarity pole area  14 , one receiver pole piece linked to a S polarity pole area  14 , and one receiver pole piece not linked to any pole area  14 , e.g., positioned over a trough  54 . The example  82  also has one receiver pole piece linked to a N polarity pole area  14 , one receiver pole piece linked to a S polarity pole area  14 , and two receiver pole pieces not linked to any pole area  14 , e.g., positioned over a trough  54 , which is the same as the example shown in  FIG. 7 . The example  84  has two receiver pole pieces linked to a S polarity pole area  14 , one receiver pole piece linked to a N polarity pole area  14 , and one receiver pole piece not linked to any pole area  14 , e.g., positioned over a trough  54 . 
         [0053]    A central principle of the present invention is the relationship between the geometry of the pole areas  14  of the power delivery surface  12  and the geometry of the receiver pole pieces  32 ,  34 ,  36 ,  38  of the power receiver  10 , as explained above. The term “power transfer probability” is used to indicate the statistical probability that a given position and orientation of the power receiving device  10  in proximity with and relative to the power delivery surface  12  will allow for power delivery. Power transfer probability is a function of the geometry of the system, and refers to the probability that at least one receiver pole piece  32 ,  34 ,  36 ,  38  is well coupled to a pole area  14  and of polarity North, and at least one other receiver pole piece  32 ,  34 ,  36 ,  38  is well coupled to another pole area  14  of polarity South. Since magnetic induction link or coupling probability is a function of the system geometry, it is invariant under geometrical scaling. The example implementation shown in  FIGS. 1-4  is capable of maintaining a 100% power transfer probability. Further, the geometry can be chosen through appropriate selection of parameters (defined below) to guarantee a minimum degree of coupling that the relevant poles of the receiver will afford for all positions and orientations of the power receiving device  20  on the power delivery surface  12 . 
         [0054]    The following derivation guarantees that at least two receiver pole pieces of the receiver coil assembly  30  that are engaged in transferring power are fully positioned above pole areas  14  of the power delivery surface  12 . That is to say that the relevant receiver pole pieces of the receiver coil assembly  30  are not partially extending beyond the boundary of the pole areas  14  of the power delivery surface  12 , which they are engaging. For purposes of this derivation, the geometry of the receiver pole pieces  32 ,  34 ,  36 ,  38  are defined as shown in  FIG. 9 , and the first limiting case is shown in  FIG. 10 . In this case, defined by the positioning of the center receiver pole piece  38  and an outer receiver pole piece  32 ,  34 , or  36  resting across width W of the strip electro-magnetic pole area  14 , the parameter R cannot be larger than W−D, where D is the diameter of the receiver pole pieces  32 ,  34 ,  36 ,  38 . If so, a position could be found where neither is fully over the pole area  14 , in violation of the limiting assumption above. Simply, 
         [0000]    
       
      
       R≦W−D  
      
     
         [0055]    The second limiting case is shown in  FIG. 11 . In this case, defined by all of the outer receiver pole pieces  32 ,  34 ,  36  being positioned over like-polarized pole areas  14 , R is bounded by: 
         [0000]    
       
         
           
             R 
             ≥ 
             
               
                 2 
                 3 
               
                
               
                 ( 
                 
                   W 
                   + 
                   
                     2 
                      
                     G 
                   
                   + 
                   D 
                 
                 ) 
               
             
           
         
       
     
         [0056]    A space of solutions exists between these two limits. However, given the following considerations, there exists an optimum within this space. It is assumed to be preferred that the diameter of the contacts be smaller than the width of the insulating gap such that the contacts cannot “short circuit” the fields between adjacent pole areas  14 . It is also assumed to be preferred that the diameter of the receiver pole pieces  32 ,  34 ,  36 ,  38  be as large as possible to maximize transformer coupling. Therefore, it is preferred that the diameter D of the receiver pole pieces  32 ,  34 ,  36 ,  38  be slightly smaller than the width G of the troughs  54 . The diameter D can be expressed as a fraction K of the trough  58  width G: 
         [0000]      D=KG 
         [0000]      Where 
         [0000]      0         K≦1
 
         [0057]    Substituting into the above equations gives 
         [0000]    
       
         
           
             R 
             ≤ 
             
               W 
               - 
               KG 
             
           
         
       
       
         
           and 
         
       
       
         
           
             
               R 
               ≥ 
             
             = 
             
               
                 2 
                 3 
               
                
               
                 ( 
                 
                   W 
                   + 
                   
                     2 
                      
                     G 
                   
                   + 
                   KG 
                 
                 ) 
               
             
           
         
       
     
         [0058]    Combining equations, therefore 
         [0000]              W   -   KG     =       2   3          (     W   +     2      G     +   KG     )             so 
         [0000]        W =(4+5 K ) G    
         [0000]      or 
         [0000]        S =(5+5 K ) G    
         [0059]    In summary, given a grid spacing S, 
         [0000]    
       
         
           
             G 
             = 
             
               
                 1 
                 
                   5 
                   + 
                   
                     5 
                      
                     K 
                   
                 
               
                
               S 
             
           
         
       
       
         
           
             W 
             = 
             
               
                 
                   4 
                   + 
                   
                     5 
                      
                     K 
                   
                 
                 
                   5 
                   + 
                   
                     5 
                      
                     K 
                   
                 
               
                
               S 
             
           
         
       
       
         
           
             R 
             = 
             
               0.8 
                
               S 
             
           
         
       
       
         
           
             D 
             = 
             
               
                 K 
                 
                   5 
                   + 
                   
                     5 
                      
                     K 
                   
                 
               
                
               S 
             
           
         
       
     
         [0060]    If K=0.9, then:
       G=0.10526 S   W=0.89472 S   R=0.80000 S   D=0.09474 S       
 
         [0065]    The following table lists coefficients of S for various other values of K. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 K 
               
             
          
           
               
                   
                 0 
                 0.4 
                 0.6 
                 0.7 
                 0.8 
                 0.9 
                 1 
               
               
                   
                   
               
             
          
           
               
                 G 
                 0.20000 
                 0.14286 
                 0.12500 
                 0.11765 
                 0.11111 
                 0.10526 
                 0.10000 
               
               
                 W 
                 0.80000 
                 0.85714 
                 0.87500 
                 0.88235 
                 0.88889 
                 0.89474 
                 0.90000 
               
               
                 R 
                 0.80000 
                 0.80000 
                 0.80000 
                 0.80000 
                 0.80000 
                 0.80000 
                 0.80000 
               
               
                 D 
                 0.00000 
                 0.05714 
                 0.07500 
                 0.08235 
                 0.08889 
                 0.09474 
                 0.10000 
               
               
                   
               
             
          
         
       
     
         [0066]    Various engineering requirements may define the selection of K—the ratio of the size of the each receiver pole piece  32 ,  34 ,  36 ,  38  compared to the width of the troughs  54  of the surface  56  of the core plate  52  of the power delivery pad  10 . Since field lines F fringe in the area of discontinuities and since, in practice, there will always be an air gap between coupled poles, K may not be simply chosen to be 1.0 as simple assumptions may imply. 
         [0067]    An example variation of the example electro-magnetic coil assembly  50  described above does not use ferromagnetic materials, but rather uses air-wound coils. In this example variation, the coils are held in place by a non-ferromagnetic material such as plastic or epoxy-fiberglass arranged in the same shape as the example implementation described above. The magnetic fields on the power delivery surface have alternating polarities from coil to coil at any single instant in time, and the field structure is defined by the placement of the conductors. Likewise, the power receiver can also contain no ferromagnetic material, and its response to external fields is defined by the placement of its conductors. Analogous to the principles used in the case of a ferromagnetic material-based implementation, the non-ferromagnetic-material-based implementation benefits from the geometry described above. In this case, flux linkage is significantly enhanced by the geometry. If this non-ferromagnetic optional implementation is used, applications requiring significant power transfer would preferably make use of resonant coupling to increase the efficiency of the power transfer. 
         [0068]    While the example implementation described above provides one hundred percent assurance of power transfer, regardless of the location and orientation of the power receiving device  20  on the power delivery surface  12  of the power delivery pad  10 , there may also be applications in which a requirement for placement of a power receiving device  20  at one discrete location and/or orientation on the power transfer surface  12  or placement at one of a plurality of discrete locations and discrete orientations is desirable or at least tolerable. Therefore, another example embodiment of the invention is illustrated in  FIGS. 12-22  to accommodate efficient power transfer under these circumstances. 
         [0069]    To provide this kind of alternative embodiment, an alternative core plate  152  with the grooves or troughs  154  milled, routed, or otherwise formed into the surface  156  of the core plate  152  in a grid pattern along parallel and perpendicular lines is provided form an electro-magnetic coil assembly  150  with a two-dimensional array of rectangular pole areas  114  in the core plate surface  156 , as shown in  FIG. 12 . In this example, the rectangular pole areas  114  are shown as squares, although square rectangles are not required. A power receiving device  120  is shown in  FIG. 12  positioned on the core plate surface  156  of the electro-magnetic coil assembly  150  in lateral and rotational alignment with the rectangular pole areas  114 , although it may be desirable to provide a skin or cover over the core plate surface, as shown by the skin  22  in  FIG. 1  for the first example power delivery pad  10 . 
         [0070]    As best seen in  FIG. 13  in conjunction with  FIG. 12 , this example implementation comprises a substantially planar pattern or array of electro-magnetic pole areas  114  to form a power delivery surface  112  with or without a protective skin or covering (not shown). The enlarged example electro-magnetic coil assembly  150  is shown in  FIG. 13  in a small version or configuration comprising only nine electro-magnetic pole areas  114  for convenience and to accommodate the enlargement in order to illustrate more clearly the structural details. In one example implementation, the core plate  152 , including the core plate surface  156 , comprises ferromagnetic material, although ferromagnetic material for the core plate is not essential. Wire conductors  160  are positioned in the grooves or troughs  154  to extend along adjacent the sides or edges  153  of the electro-magnetic core areas  114  and then extend downwardly through holes  155  at the intersections the troughs  154  adjacent the corners of the electro-magnetic pole areas  114 . Therefore, each electro-magnetic core area  114  is surrounded on all of its perimeter edges  153  by at least one wire  160 . The wires  160  extend through the holes  155  to a printed circuit board  190  under the core plate  152 , which energizes and drives wires  160  to generate the alternating magnetic field in the electro-magnetic pole areas  114 . 
         [0071]    The resulting magnetic polarities of alternating magnetic fields in the electro-magnetic pole areas  114  are illustrated diagrammatically in  FIG. 14 , which is a plan view of the small version depiction of the electro-magnetic coil assembly  150  in  FIG. 13 . The arrows in  FIG. 14  represent the instantaneous direction of current flow around each substantially planar pole region or area  114  at a single moment in time, which reverses and alternates based on the frequency of the driving AC voltage. Inductive power transfer requires a changing magnetic field which, in this embodiment, is provided by an alternating electrical current supplied to the conductive wires  160  surrounding each electro-magnetic pole area  114 . The arrows represent the direction of the alternating current at a single moment in time to demonstrate the principle of operation. Each pole area  114  is labeled N or S indicating North or South magnetic polarity respectively at a single instant in time, which, of course, alternates as the electric current in the wires  160  alternates. This polarity labeling is intended to aid in demonstrating the principle, since in operation the polarity of each pole  155  region would be alternating as prescribed by the alternating current in their respective circumferential windings  160 . 
         [0072]    In this example, the power receiving device  120  ( FIG. 12 ) derives power from the core plate surface  156  of the power delivery surface  12  by virtue of alternating magnetic flux that passes from the power delivery surface  12  to the power receiving device  120 . In one embodiment the power receiver  120  that is designed to obtain power from the core plate surface  156  shown in  FIG. 14  has a receiver coil assembly  130  as shown in  FIG. 15  with the same number and size of electro-magnetic pole areas  144  as does the power delivery surface  150 . In this way, when the receiver coil assembly  130  of the power receiving device  120  is aligned atop the electro-magnetic coil assembly  150  of a power delivery pad (with their ferromagnetic pole areas  144 ,  114 , respectively, facing each other) they transfer power efficiently from the electro-magnetic core assembly  150  to the receiver core assembly  130 . When a receiver coil assembly  130  of a power receiving device  120  is placed on a core plate surface  156  of a power delivery surface  12 , as explained above, there is necessarily an air gap that dominates the overall reluctance of the paths traced by the coupled lines of magnetic flux. The larger the cross-sectional area of the air gap, the less the reluctance that the air gap causes. An important feature of this example magnetic core assembly  150  and receiver coil assembly  130  is that the cross-sectional area of the air gap between them is very large, approaching the available size of the power receiver  120 . 
         [0073]      FIG. 4  shows a close-up of how power is supplied to the wire windings  160  and how the wire windings  160  are routed from the holes  155  into the troughs  154  to extend along respective edges  153  of the electro-magnetic pole areas  114 . In this example embodiment, a printed circuit board  190  has at least two electrically conductive layers  192 ,  194  separated by a non-conductive or dielectric material  196 , for example, epoxy fiberglass, as illustrated diagrammatically in  FIG. 17 . One of the electrically conductive layers  192 ,  194  has an electrical potential (voltage) A, and another of the two layers  192 ,  194  has an electric potential (voltage) B. The wire conductors  160  are then connected to the printed circuit board  190  with one end connected electrically at  191  to layer  192  at the potential A and the other end connected electrically at  193  to layer  194  at the potential B to produce the current-flow diagram (see arrows) of  FIG. 14 . In this way each wire  160  is being energized by the potential difference of plane A and plane B. These two planes or layers  192 ,  194  form a parallel plate capacitor. Each of the wires  160  provide an inductance connected across the potential AB. The parallel combination of the capacitor formed by the planes A and B of conductive layers  192 ,  194  of printed the circuit board  190 , and the wires  160  thereby form a tank circuit with a resonant frequency. 
         [0074]    In one embodiment, the core plate surface  156  is formed of a ferromagnetic material shaped to provide rectangular pole areas  114 , as seen from above as depicted in  FIGS. 12-14 . Further, in one embodiment, the pole areas  114  are delineated by troughs  154  as can be seen in  FIGS. 13 ,  14 ,  16 , and  17 . Within the troughs  154  are one or more conductors  160  that carry an alternating current.  FIG. 18  shows these conductors  160  in cross section and with the convention that a plus sign indicates current flowing away from the viewer, and a dot indicates current flowing towards the viewer. The polarities of the pole areas  114  and the direction of the currents in the wires  160  shown in  FIG. 16  is intended to illustrate, for the purpose of description, the principle of operation of this example embodiment. The particular polarities and directions shown represent a snapshot in time, as in operation, these polarities and directions are alternating. 
         [0075]    The troughs  154  are not deep enough to separate the pole areas  114 . Rather a path  158  is left under each trough  154  to allow the completion of a magnetic circuit between adjacent pole areas  114 . It should be noted that troughs  154  are not a required feature of this invention but are describes as one particular embodiment. Other means for providing the coil current to define the pole areas  114  can be used, for example, but not for limitation, strips of copper tape (not shown) applied to the surface  156 . 
         [0076]    In general, magnetic field flux lines F created by the excitation current extend from a pole area  114  of the surface  156  into the immediate vicinity above the pole area  114  and over to an adjacent pole area  114 , which by design is of opposite polarity. The field lines F continue within the ferromagnetic material  158  of the core plate  152  under a trough  155  and back through the ferromagnetic material  152  to form continuous lines of flux F. Note that with no devices nearby, a large portion of any one flux line F does not pass through ferromagnetic material  152 . 
         [0077]    In another embodiment (not shown), no ferromagnetic (or otherwise) material is used, and the windings themselves create and define the necessary geometry to satisfy the basic principle of operation herein disclosed. 
         [0078]    The power receiving device  120  comprises a power receiving assembly  130  that includes a set of pole areas  144  with substantially the same size and shape as the pole areas  114  on the core plate surface  156  of the power delivery surface. One difference is that the number of pole areas  144  on the power receiving assembly  130  may be different than the number of pole areas  114  on the power delivery coil assembly  150 . In one embodiment, the pole areas  114  are arranged as a grid with a period of, for example, 10 mm in both orthogonal axes along the surface. In one example embodiment, the number of pole areas  114  on the core plate surface  156  of the power delivery coil assembly  150  is 400. Also in one example embodiment the power receiver assembly  130  intended to extract power from the core plate surface  156  is comprised of nine pole areas  114 . 
         [0079]    In one example embodiment, the construction of the power receiver assembly  200  is identical to the construction of the power delivery magnetic coil assembly  150 . Because of the identical construction, the power receiver assembly  130  resonates at the same frequency as the power delivery magnetic coil assembly  150 . If not, parallel capacitors can be added or adjusted to ensure the resonant frequencies match. 
         [0080]    In one example embodiment, the output of the power receiver assembly  130  is an alternating signal across the parallel plates  192 ,  194  of the printed circuit board  190  as described above. In another example embodiment, an alternating potential is induced in a pair of wires that form windings around the pole areas  144  of the power receiver assembly  130 . In either case, a DC potential can be obtained by rectification. 
         [0081]    In another example embodiment, a pulse width modulated rectifier is used to extract DC power from the alternating potential from the receiver pole area  144  windings. In this case, pulse width modulation is used to adjust the rectified potential derived from the alternating potential to regulate the output voltage.  FIG. 20  shows the means by which an alternating potential can be converted to a regulated DC potential labeled Vo, including, for example, a buck regulator circuit  202  or switch mode power supply. A controller can be used to adjust the pulse width modulation switch  201  shown in  FIG. 20  to the proper operating point to achieve the desired output voltage Vo, as is understood by persons skilled in the art. In another example embodiment, the pulse width modulated switch is combined with the bridge rectifier  203  such that the bridge rectifier  203  conducts for only a portion of the time. In this way, a more cost effective and efficient conversion from alternating potential to output voltage Vo can be obtained. 
         [0082]    It may be desirable for a variety of reasons, including efficient power transfer, to align the power receiver assembly pole areas  144  with the pole areas  114  of the power delivery coil assembly  150 . An advantage of some of the example embodiments described herein is that many optimum relative alignment positions are available such that means are possible to adjust a randomly placed power receiving device  120  to a nearby optimum position on the power delivery magnetic coil assembly  150 . One example implementation of such alignment includes use of very thin magnetic material, for example, but not for limitation, rubberized magnetic material similar to that used for common refrigerator magnets, but polarized in a way similar to the matrix of pole areas  114  on the core plate surface  156  of the power deliver coil assembly and the pole areas  144  of the power receiver assembly  130 . In this example embodiment, the polarized magnetic material is very thin and is adhered to the pole-side surface of both the power core plate surface  156  and the power receiver assembly  130 . For example, such thin magnetic material could also serve the purpose of the protective cover  22  in  FIG. 1 . With such an arrangement, the magnetic materials of both surfaces tend to align themselves together in a position that is optimum for power transfer. For example, if a power receiver assembly  130  was to be placed randomly on a core plate surface  156  of the power delivery coil assembly  150 , in such a position that the poles were not in good alignment, the magnetic materials adhered to each surface would cause the power receiving device  120  position and orientation to translate on the power delivery surface  12  as a result of opposite magnetic poles pulling together. By design, this kind of alignment correction can bring the power receiving device  120  into proper position in relation to the surface  156  of the power delivery coil assembly  150  such that optimum power transfer can be achieved. 
         [0083]    When a power receiving device  120  rests on a power delivery surface  156 , a magnetic circuit is formed between the pole area  114  of the power delivery surface  156  and the pole areas  144  of the power receiving device  120 . As a result, magnetic flux passes between the power delivery surface  156  and the power receiver assembly  130  as shown for illustration by arrows  205  in  FIG. 22 . 
         [0084]    Flux must pass through the “air” gap separating the surface  156  of power delivery coil assembly  500  and the power receiver assembly  130 . By “air” gap, it is meant a separation  206  between magnetic materials. In these separation areas, the permeability of the medium, whether it is assumed to be of air, plastic, or otherwise, is much smaller than the permeability of typical magnet materials such as ferrite. The cross-sectional area of the “air” gap  206  is where the energy must flow to transfer energy from the surface  156  of the power delivery coil assembly  150  to the power receiver assembly  130 . The larger this area is, the more coupling will exist between the power delivery surface  156  and the power receiver assembly  130 . It is a feature of the present invention that the area used to couple one to another is near the theoretical maximum for a power receiver of a given size. In other words, almost the whole area of power delivery surface  156  and the mating, juxtaposed power receiver surface of the power receiver assembly  130  is filled up with magnetic material, except for small grooves or troughs  154  and a small air gap  206 . If the coupling is very near one, then, in one embodiment, the voltage is transferred from the primary side (the power delivery surface  150  side) to the secondary side (the power receiver  130  side) at nearly a ratio of 1. In this case the system acts very much like a transformer. 
         [0085]    Another example embodiment does not use ferromagnetic materials. In this example embodiment, the windings  160  are held in place by a non-ferromagnetic material such as plastic or epoxy-fiberglass arranged in the same shape as the ferromagnetic-material-based embodiment described herein. 
         [0086]    In another example implementations, each coil in both the power delivery coil assembly and the power receiver coil assembly, can be wound around half of a magnetic pot-core, such as the example half pot core  310  for the power delivery coil assembly and the other half pot core  320  for the power receiver coil assembly illustrated in  FIGS. 23 and 24 . There can be either one or a plurality of the half pot cores  310  in the power delivery coil assembly dispersed under the surface cover  322  ( FIG. 24 ), and there can be one or more of the half pot cores  320  in the power receive coil assembly. As also shown in  FIGS. 23 and 24 , each half pot core  310  comprises a pot-shaped member  311  with a cylindrical side wall  312  and an end wall  313  with a core piece  314  protruding from the end wall  313  for a length that positions the distal end  315  of the cylindrical wall  312  and the distal end  316  of the core piece  314  at about the same distance from the end wall  313 . A bobbin or spool  317  containing the wire coil  318  is positioned on the core piece  314  inside the pot-shaped member  311 . Similarly, each half pot core  320  comprises a pot-shaped member  331  with a cylindrical side wall  332  and an end wall  333  with a core piece  334  protruding from the end wall  333  for a length that positions the distal end  335  of the cylindrical wall  332  and the distal end  336  of the core piece  334  at about the same distance from the end wall  333 . A bobbin or spool  337  containing the wire coil  338  is positioned on the core piece  334  inside the pot-shaped member  331 . When the power receiver device is placed on the power delivery surface in a position to align the two halves  310 ,  320 , as illustrated in Figure the two half pot cores  310 ,  320  form a nearly complete magnetic circuit efficiently coupling the primary (power delivery pad coil  318 ) to the secondary (receiver coil  338 ). This embodiment allows for efficient magnetic coupling from power delivery pad to receiver device when the two halves  310 ,  320  are aligned to form a single pot core with a gap  322 . 
         [0087]    The foregoing description is considered as illustrative of the principles of the invention. Furthermore, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and process shown and described above. Accordingly, resort may be made to all suitable modifications and equivalents that fall within the scope of the invention. The words “comprise,” “comprises,” “comprising,” “include,” “including,” and “includes” when used in this specification are intended to specify the presence of stated features, integers, components, or steps, but they do not preclude the presence or addition of one or more other features, integers, components, steps, or groups thereof. Also, directional words, such as upper, lower, front, back, top, bottom, and the like are used for convenience in describing features in relation the orientation of the item on the sheet of drawings and not intended to limit the orientation in actual use.