COIL TOPOLOGIES, AND COILS

RELATED CASES

[0001] This application claims priority to United States Provisional Appln. No. 63/084,021, filed September 28, 2020, which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to litz wires with ferromagnetic covers, coil topologies, and coils.

BACKGROUND

[0003] This section provides background information related to the present disclosure which is not necessarily prior art.

[0004] Litz wire consists of multiple individually insulated strands (e.g., copper wire strands insulated with silk, other electrical conductors and insulators, etc.) that are twisted or woven together forming a bundle. Litz wire is generally configured to reduce the skin effect and proximity effect losses in conductors. For the litz wire as a whole, the skin effect and associated power losses are reduced as compared to a solid electrical conductor. Litz wire may also increase the ratio of distributed inductance to distributed resistance as compared to a solid conductor, thereby resulting in a higher Q factor.

[0005] Given the higher Q factor achievable with litz wire, conventional wireless charging coils may include litz wire. The Q factor of a wireless charging coil is an important consideration due to its effect on charging efficiency as a higher Q factor corresponds to a lower rate of power loss. The Q factor of the wireless charging coil is related to the wireless charging coil’s resistance and reactance. For example, the Q factor of a wireless charging coil may be increased by decreasing the resistance of the wireless charging coil and increasing reactance of the wireless charging coil. [0006] Inductive power transfer and wireless charging has seen significant growth in consumer electronics, automotive vehicles, industrial devices, biomedical implants and home appliances over the past decade. But designing a complete inductive power transfer system (IPTS) is challenging due to various constraints possible (e.g., cost, efficiency, size, weight, safety, temperature, etc.).

[0007] A general inductive power transfer system consists of a power source, inverter, resonant tank, rectifier, and load. The system efficiency is a product of the inverter, coil-coil , and rectifier efficiency. A high efficiency is important for an inductive power transfer system as this would result in an improved charging area, lower charging time, and low/no cooling requirements. While the inverter and rectifier are capable of operating at high efficiencies with state of the art technology, a majority of the losses occur at the wireless charging coils. And, the inventor hereof has recognized that high efficiencies in an inductive power transfer system may be achieved by optimizing coil design. Coil-coil efficiency is influenced by both the quality factor and coupling factor of the coils. Accordingly, high performance system requirements include having a high quality factor/coupling factor.

[0008] The coupling factor, k, indicates how much magnetic flux reaches from the transmitter coil to the receiver coil. The magnetic flux interaction takes place in the air gap between the coils. The value of 'k' could be between 0 and 1. The value 1 refers to perfect coupling where all the flux from the transmitter penetrates to the receiver coil. On the other hand, the value 0 refers to decoupled coils. This parameter is influenced by the positioning and geometry (shape, coil diameter and wire diameter) of the coils. The coils could be misaligned vertically, laterally or at an angle to each other.

[0009] In a wireless charging application, at least a coil pair is used to transmit energy from the source to the load. The receiver coil position could be free or fixed depending on the application. For free positioning applications, the coupling factor gets poorer as the receiver coil moves away from the center to the edge of the charging area. Moreover, the quality factor of the coils could be poor in applications where the space to place the coils is restricted and small coils are used. The low coupling factor and/or Q-factor results in reducing the charging area, charging time and lowering the coil-coil efficiency. At low coil-coil efficiency charging time, heat dissipation is increased. This could result in requiring a fan to cool down the devices which adds more cost to the system. Accordingly, the challenge of achieving a high performance inductive power transfer system is to have a high Q-factor/coupling factor. SUMMARY

[0010] A coil is formed with a conductor that includes a first side, a second side, a third side and a fourth side and a ferromagnetic cover is provided on the first side of the conductor. The conductor can be formed of litz wire. The ferromagnetic cover may also be provided on a second side where the first side and second side can be on opposite sides or on adjacent sides. The ferromagnetic cover may further be provided on a third side. In an embodiment the coil can be part of a wireless charging system.

[0011] In an embodiment the coil can be two or more layers. The coil can have an open middle section that is devoid of the ferromagnetic cover or the middle section can include the ferromagnetic cover. The ferromagnetic cover can be preformed with a groove and the conductor can be positioned in the groove. The ferromagnetic cover can be provided by inserting an appropriate material between the coils after the coils are formed.

DRAWINGS

[0012] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0013] FIG. 1 is a perspective view of a litz wire with a ferromagnetic cover along only one side of the litz wire according to a first exemplary embodiment.

[0014] FIG. 2 is a cross-sectional view of the litz wire and ferromagnetic cover shown in FIG. 1 , and also illustrating multiple strands of the litz wire.

[0015] FIG. 3 is a perspective view of a litz wire with a ferromagnetic cover disposed along two sides of the litz wire according to a second exemplary embodiment.

[0016] FIG. 4 is a cross-sectional view of the litz wire and ferromagnetic cover shown in FIG. 3, and also illustrating multiple strands of the litz wire.

[0017] FIG. 5 is a perspective view of a litz wire with a ferromagnetic cover disposed along three sides of the litz wire according to a third exemplary embodiment.

[0018] FIG. 6 is a cross-sectional view of the litz wire and ferromagnetic cover shown in FIG. 5, and also illustrating multiple strands of the litz wire. [0019] FIG. 7 is a perspective view of a litz wire with a ferromagnetic cover disposed along two sides of the litz wire according to a fourth exemplary embodiment.

[0020] FIG. 8 is a cross-sectional view of the litz wire and ferromagnetic cover shown in FIG. 7, and also illustrating multiple strands of the litz wire.

[0021] FIG. 9 is a perspective view of a litz wire with a ferromagnetic cover curved around a portion of the litz wire according to a fifth exemplary embodiment.

[0022] FIG. 10 is a cross-sectional view of the litz wire and curved ferromagnetic cover shown in FIG. 9, and also illustrating multiple strands of the litz wire.

[0023] FIG. 11 is a cross-sectional view of a multilayered coil topology according to a sixth exemplary embodiment.

[0024] FIG. 12 is a perspective view of a multilayered coil according to a seventh exemplary embodiment.

[0025] FIG. 13 is a perspective view of a multilayered coil according to an eighth exemplary embodiment.

[0026] FIG. 14 is a perspective view of a multilayered coil according to a ninth exemplary embodiment.

[0027] FIG. 15 is a perspective view of a multilayered coil according to a tenth exemplary embodiment.

[0028] FIG. 16 illustrates a perspective view of a ferromagnetic cover prior to installation of a conductor.

[0029] FIG. 17 illustrates a perspective view of the embodiment depicted in FIG. 16 with a conductor installed.

[0030] FIG. 18 illustrates a perspective view of the embodiment depicted in FIG. 17 with ferromagnetic cover added to a side of the conductor.

[0031] FIG. 19 illustrates a schematic representation of a wireless charger with a coil assembly.

[0032] FIG. 20 illustrates a graph showing inductance versus cover thickness for a range of permeability values.

[0033] FIG. 21 illustrates a graph showing coupling factor versus cover thickness for a range of permeability values at a 2 mm vertical distance. [0034] FIG. 22 illustrates a graph showing coupling factor versus cover thickness for a range of permeability values at a 4 mm vertical distance.

[0035] FIG. 23 illustrates a chart showing AC resistance with a ferrite cover of 0.1 mm thickness.

[0036] FIG. 24 illustrates a chart showing AC resistance with a ferrite cover of 0.5 mm thickness.

[0037] FIG. 25 illustrates a chart showing Q-factor with a ferrite cover of 0.1 mm thickness.

[0038] FIG. 26 illustrates a chart showing Q-factor with a ferrite cover of 0.3 mm thickness.

[0039] FIG. 27 illustrates a chart showing Q-factor with a ferrite cover of 0.5 mm thickness.

[0040] FIG. 28 illustrates a chart show figure of merit values for a coil with varying distances between two layers.

[0041] FIG. 29 illustrates a chart show figure of merit values for a coil with a ferrite cover with varying thickness of the ferrite cover.

[0042] Corresponding reference numerals may indicate corresponding (although not necessarily identical) parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0043] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0044] Conventionally, litz wire has been used for wireless charging coils given the higher Q factors achievable with litz wires as compared to solid electrical conductors and the fact that litza wire has lower AC resistance. But as recognized by the inventor hereof, conventional products with litz wire charging coils tend to have deficient performance. Although the use of conventional litz wire helps to reduce and thereby improve internal proximity effect and skin effect losses, conventional litz wire is unable to reduce and improve external proximity effect losses that degrade performance at high frequencies. The inventor hereof has also recognized the difficulty of achieving high inductances and quality factors for wireless charging coils with current state of the art products in a given size constraint. [0045] As noted above in the background, the inventor hereof has recognized that high efficiencies in an IPTS may be achieved by optimizing coil design as a majority of the losses occur at the wireless charging coils. The inventor hereof has also recognized that the use of litz wire with a ferromagnetic cover can improve both the coupling factor and the Q-factor of the coils, thereby enabling high coil-coil efficiency. Accordingly, disclosed herein are exemplary embodiments of litz wires with ferromagnetic covers that can improve the coil-coil efficiency of inductive power transfer systems.

[0046] The inventor hereof has also recognized that using multilayered coils may increase the Q-factor in a given area as compared to single layered coils. Accordingly, disclosed herein are exemplary embodiments of multilayered coil topologies that allow for improvements to the Q- factor and coupling factor when compared to conventional coil design and/or that that can achieve high Q-factor and inductance in a given area, thereby improving coil-coil efficiency.

[0047] In exemplary embodiments, ferromagnetic material (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) is disposed along at least one side of a litz wire. The ferromagnetic cover may be longitudinally disposed along a length (e.g., along a substantial entire length, etc.) of the litz wire. The ferromagnetic cover may be configured (e.g., shaped, sized, etc.) to cover and shield at least one side of the litz wire.

[0048] Also disclosed are exemplary embodiments of coil topologies and coils. In exemplary embodiments, a coil topology includes ferromagnetic material disposed between at least two of a plurality of coil layers.

[0049] With reference now to the figures, FIGS. 1 and 2 illustrate a litz wire 104 with a ferromagnetic cover 108 disposed along only one side of the litz wire 104 according to a first exemplary embodiment. The ferromagnetic cover 108 is longitudinally disposed along a length (e.g., along a substantial entire length, etc.) of the litz wire 104. The ferromagnetic cover 108 is configured (e.g., sized, shaped, etc.) to cover and shield the one side of the litz wire 104.

[0050] The electrically-conductive material used for the multiple strands 105 (FIG. 2) of the litz wire 104 may comprise copper, aluminum, alloys thereof, and/or other electrical conductor(s). The electrically insulating material used for the wire strands of the litz wire 104 may comprise silk, polyurethane, polyester, polyimide, polytetrafluoroethylene (PTFE) fluorocarbon polymer insulation material, and/or other electrically insulator(s). [0051] The ferromagnetic cover 108 may comprise a relatively thin flexible ferromagnetic tape (e.g., ferrite tape, supermalloy tape, other adhesive ferromagnetic tape, strip, or film, etc.) adhesively attached to the one side of the litz wire 104. The ferromagnetic tape may be applied manually or via an automated process. In this example, the ferromagnetic tape may have a length about equal to the length of the litz wire 104. The ferromagnetic tape may have a width about equal to or greater than a height (e.g., diameter, etc.) of the litz wire 104. The ferromagnetic tape may extend longitudinally along the length of the litz wire 104 to thereby cover and shield the one side of the litz wire 104.

[0052] Alternative embodiments may include other ferromagnetic materials in addition to, or as an alternative, to the ferromagnetic tape, such as a ferromagnetic coating, pre-shaped ferromagnetic cover, etc. For example, the ferromagnetic material 108 may comprise a coating that is coated onto the litz wire 104, which coating may comprise a mixture of adhesive (e.g., glue powder, etc.) and ferromagnetic particles (e.g., ferrite particles, supermalloy particles, nanocrystalline ferromagnetic material, etc.). As another example, the ferromagnetic material 108 may be pre-shaped (e.g., molded, FIGS. 16-18, etc.) into a shape such that the litz wire 104 may be press fit, friction fit, or interference fit manually or via an automated process into the predetermined shape of the pre-shaped ferromagnetic material.

[0053] FIGS. 3 and 4 illustrate a litz wire 204 with a ferromagnetic cover 208 disposed along two sides of the litz wire 204 according to a second exemplary embodiment. The ferromagnetic cover 208 includes first and second ferromagnetic material portions 208a and 208b respectively disposed along two generally opposing first and second sides of the litz wire 204. The first and second ferromagnetic material portions 208a and 208b may be generally parallel with each other and extend longitudinally along a length (e.g., along a substantial entire length, etc.) of the litz wire 204. The ferromagnetic cover 208 is configured (e.g., sized, shaped, etc.) to cover and shield the opposing first and second sides of the litz wire 204. The ferromagnetic cover 208 and the strands 205 (FIG. 8) of the litz wire 204 may be further configured as discussed herein with respect to the ferromagnetic cover 108 and the strands 105 (FIG. 2) of the litz wire 104.

[0054] FIGS. 5 and 6 illustrate a litz wire 304 with and a ferromagnetic cover 308 disposed along two sides and the bottom of the litz wire 304 according to a third exemplary embodiment. . The ferromagnetic cover 308 includes first and second ferromagnetic material portions 308a and 308b respectively disposed along two generally opposing first and second sides of the litz wire 304. The ferromagnetic cover 308 further includes a third ferromagnetic material portion 308c disposed along a bottom of the litz wire 304.

[0055] The third ferromagnetic portion 308c may be generally perpendicular to the first and second ferromagnetic material portions 308a, 308b, such that that the ferromagnetic cover 308 has a generally rectangular U-shaped configuration cooperatively defined by the first, second, and third ferromagnetic material portions 308a, 308b, 308c. By way of example, the ferromagnetic cover 308 may be pre-shaped (e.g., molded, etc.) into the generally rectangular U-shaped configuration, which, in turn, may be sized such that the litz wire 304 may be press fit, friction fit, or interference fit manually or via an automated process into the U-shaped channel defined by the ferromagnetic cover 308. Alternatively, the ferromagnetic cover 308 may comprise a relatively thin flexible ferromagnetic tape (e.g., ferrite tape, supermalloy tape, other adhesive ferromagnetic tape, strip, or film, etc.), a ferromagnetic coating (e.g., a mixture of adhesive and ferromagnetic particles, etc.), etc.

[0056] The first, second, and third ferromagnetic material portions 308a, 308b, 308c extend longitudinally along a length (e.g., along a substantial entire length, etc.) of the litz wire 304. The ferromagnetic cover 308 is configured (e.g., sized, shaped, etc.) to cover and shield the opposing first and second sides and bottom of the litz wire 304. Advantageously, covering the bottom of the litz wire 304 with ferromagnetic material may eliminate the need or necessity of having a bottom ferrite shield that is conventionally used with wireless charging coils. The ferromagnetic cover 308 and the strands 305 (FIG. 6) of the litz wire 304 may be further configured as discussed herein with respect to the ferromagnetic cover 108 and the strands 105 (FIG. 2) of the litz wire 104.

[0057] FIGS. 7 and 8 illustrate a litz wire 404 with a ferromagnetic cover 408 disposed along one side and the bottom of the litz wire 404 according to a fourth exemplary embodiment. The ferromagnetic cover 408 includes first and second ferromagnetic material portions 408a and 408b respectively disposed along one side and the bottom of the litz wire 404. The second ferromagnetic portion 408b may be generally perpendicular to the first ferromagnetic material portion 408a, such that that the ferromagnetic cover 408 has a generally L-shaped configuration cooperatively defined by the first and second ferromagnetic material portions 408a, 408b.

[0058] The first and second ferromagnetic material portions 408a, 408b extend longitudinally along a length (e.g., along a substantial entire length, etc.) of the litz wire 404. The ferromagnetic cover 408 is configured (e.g., sized, shaped, etc.) to cover and shield the opposing first and second sides and bottom of the litz wire 404. Advantageously, covering the bottom of the litz wire 404 with ferromagnetic material may eliminate the need or necessity of having a bottom ferrite shield that is conventionally used with wireless charging coils. The ferromagnetic cover 408 and the strands 405 (FIG. 8) of the litz wire 404 may be further configured as discussed herein with respect to the ferromagnetic cover 108 and the strands 105 (FIG. 2) of the litz wire 104.

[0059] FIGS. 9 and 10 illustrate a litz wire 504 with a ferromagnetic cover 508 curved around the litz wire 504 according to a fifth exemplary embodiment. The ferromagnetic cover 508 has a curved shape (e.g., concave shape, U-shape, etc.) that generally follows the shape of the outer surface of the litz wire 504.

[0060] By way of example, the ferromagnetic cover 508 may be pre-shaped (e.g., molded, etc.) into the curved shape and sized accordingly such that the litz wire 504 may be press fit, friction fit, or interference fit manually or via an automated process into the channel defined by the ferromagnetic cover 508. Alternatively, the ferromagnetic cover 508 may comprise a relatively thin flexible ferromagnetic tape (e.g., ferrite tape, supermalloy tape, other adhesive ferromagnetic tape, strip, or film, etc.), a ferromagnetic coating (e.g., a mixture of adhesive and ferromagnetic particles, etc.), etc.

[0061] The ferromagnetic cover 508 extends longitudinally along a length (e.g., along a substantial entire length, etc.) of the litz wire 504. The ferromagnetic cover 508 is configured (e.g., sized, shaped, etc.) to cover and shield the corresponding curved portion of the litz wire 504. Advantageously, covering the bottom of the litz wire 504 with ferromagnetic material 508 may eliminate the need or necessity of having a bottom ferrite shield that is conventionally used with wireless charging coils. The ferromagnetic cover 508 and the strands 505 (FIG. 10) of the litz wire 504 may be further configured as discussed herein with respect to the ferromagnetic cover 108 and the strands 105 (FIG. 2) of the litz wire 104.

[0062] The litz wire 504 and the ferromagnetic cover 508 may be further configured as discussed herein with respect to the litz wire 104 and ferromagnetic cover 108, respectively.

[0063] FIG. 11 illustrates a multilayered coil topology 602 according to a sixth exemplary embodiment. The multilayered coil topology 602 may include any number of coil layers as indicated by “Layer N”. The multilayered wireless charging coil topology 602 may also include any number of coil turns per layer as indicated by “Turns N”. In this exemplary embodiment, each coil layer includes six coil turns. The coils may wound into various shapes, such as circular, rectangular, square, oval, hexagonal, etc.

[0064] Ferromagnetic material 606 (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) is disposed along a bottom of the lowest coil layer, i.e., Layer 1, to thereby provide a ferromagnetic bottom shield. The ferromagnetic material 606 may comprise a ferrite shield on which the lowest coil layer is mounted.

[0065] Ferromagnetic material 610 (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) is disposed between each adjacent pair of coil layers. The ferromagnetic material may comprise contiguous layers of ferrite respectively disposed between each corresponding pair of adjacent coil layers. As depicted in FIG. 11, a first ferrite layer 610A is disposed between Layers 1 and 2, a second ferrite layer 610b is disposed between Layers 2 and 3, and a third ferrite layer 610c is disposed between Layers 3 and 4.

[0066] Ferromagnetic material 608 (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) is disposed between coil turns and along an outside of the outermost coil. Accordingly, the ferromagnetic material 608 is disposed between corresponding adjacent portions of the conductor 604. The conductor 604 may comprise a solid conductor (e.g., solid copper conductor, etc.), litz wire, etc. For example, the conductor 604 and the ferromagnetic material 608 may comprise litz wire with a ferromagnetic cover as discussed herein with respect to the litz wires 104, 204, 304, 404, 504 and ferromagnetic covers 108, 208, 308, 408, 508, respectively. Thus, the discussion of the litz wires and ferromagnetic covers will be abbreviated in this embodiment and subsequent embodiments with the understanding that each different embodiment of the coil topology and coil may use litz wires with ferromagnetic covers as discussed herein, although such is not require for all embodiments.

[0067] Ferromagnetic material 614 (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) is within a center opening defined by the coil layers. Alternatively, the center opening defined by the coil layers may be devoid of ferromagnetic material such that the center opening remains open, e.g., to allow air flow therethrough, etc.

[0068] In exemplary embodiments in which the conductor 604 comprises litz wire, ferromagnetic material may be used as a cover for the litz wire (e.g., in each coil layer, etc.) instead of using silk or other electrically insulating material that is conventionally used to individually insulate the wire strands of the litz wire. Alternatively, silk or other electrically-insulating material may be used such that there ferromagnetic material is not between each coil turn. Ferromagnetic material may be used or provided in only certain areas instead of filling the entire center opening and/or the entire area between adjacent coil layers with ferromagnetic material. Ferromagnetic areas may also be configured or arranged differently, e.g., using ferromagnetic blocks (e.g., ferrite blocks, supermalloy blocks, nanocrystalline ferromagnetic material blocks, etc.) between adjacent coil layers, etc.

[0069] The multilayered coil topology 602 may be used in various applications, including wireless power transfer applications (e.g., devices that wirelessly transmit power or receive wireless power, etc.), wireless charging devices (e.g., automotive wireless chargers, other wireless chargers, etc.), transformers, devices to be charged (e.g., smartphones, tablets, other electronic devices, etc.), etc. Accordingly, the multilayered coil topology 602 disclosed herein should not be limited to use with only one particular type of application, end use, device to charged, wireless charger, wireless power transfer device, etc.

[0070] FIG. 12 illustrates a multilayered coil 700 according to a seventh exemplary embodiment. The multilayered coil 700 includes two coil layers 703a, 703b each having seven coil turns per layer and a generally square shaped configuration. Alternative embodiments may include a multilayered coil with more than two layers, more or less than seven coil turns per layer, and/or in a different shape, e.g., circular, oval, hexagonal, rectangular, other non-square shape, etc.

[0071] Ferromagnetic material 706 is disposed along a bottom of the lower coil layer 703b, to thereby provide a ferromagnetic bottom shield. Ferromagnetic material 710 is disposed between (e.g., defines a single contiguous ferromagnetic layer between, etc.) the upper and lower coil layers 703a, 703b. Ferromagnetic material 708 is disposed between coil turns such that the ferromagnetic material 708 is disposed between corresponding adjacent portions of the conductor 704 (e.g., solid conductor, litz wire, etc.).

[0072] Ferromagnetic material 714 is within a center opening defined by the upper and lower coil layers 703a, 703b. Alternatively, the center opening defined by the coil layers 703a, 703b may be devoid of ferromagnetic material such that the center opening remains open, e.g., to allow air flow therethrough, etc.

[0073] The ferromagnetic materials 706, 708, 710, 714 may comprise ferrite, supermalloy nanocrystalline ferromagnetic material, and/or other ferromagnetic material. The conductor 704 and ferromagnetic materials 706, 708, 710, 714 may comprise a conductor and ferromagnetic material as discussed herein, e.g., conductor 604 and ferromagnetic materials 606, 608, 610, 614, etc. Thus, the discussion of the conductors and ferromagnetic materials will be abbreviated in this embodiment and subsequent embodiments with the understanding that each different embodiment of the coil (e.g., FIGS. 13-15, etc.) may use conductors and ferromagnetic materials as discussed herein, although such is not require for all embodiments.

[0074] FIG. 13 illustrates a multilayered coil 800 according to an eighth exemplary embodiment. The multilayered coil 800 includes two coil layers 803 a, 803b each having eight coil turns per layer and a generally square shaped configuration. Alternative embodiments may include a multilayered coil with more than two layers, more or less than eight coil turns per layer, and/or in a different shape, e.g., circular, oval, hexagonal, rectangular, other non-square shape, etc.

[0075] Ferromagnetic material 806 is disposed along a bottom of the lower coil layer 803b, to thereby provide a ferromagnetic bottom shield. Ferromagnetic material 808 is disposed between coil turns such that the ferromagnetic material 808 is disposed between corresponding adjacent portions of the conductor 804 (e.g., solid conductor, litz wire, etc.). The center opening 818 defined by the upper and lower coil layers 803a, 803b is devoid of ferromagnetic material such that the center opening 818 remains open, e.g., to allow air flow therethrough, etc.

[0076] Ferromagnetic blocks or elements 816 (e.g., ferrite blocks, supermalloy blocks, nanocrystalline ferromagnetic material blocks, etc.) are disposed between the upper and lower coil layers 803a, 803b. In this example, four ferrite blocks are disposed between the upper and lower coil layers 803a, 803b at predetermined locations or areas, e.g., for improved performance, etc. Accordingly, this exemplary multilayer coil 800 does not include a single contiguous ferrite layer between the upper and lower coil layers 803a, 803b.

[0077] The ferromagnetic materials 806, 808, 816 may comprise ferrite, supermalloy, nanocrystalline ferromagnetic material, and/or other ferromagnetic material. The conductor 804 and ferromagnetic materials 806, 808, 816 may comprise a conductor and ferromagnetic material as discussed herein, e.g., conductor 604 and ferromagnetic materials 606, 608, 610, 614, etc.

[0078] FIG. 14 illustrates a multilayered coil 900 according to a ninth exemplary embodiment. The multilayered coil 900 includes two coil layers 903a, 903b each having eight coil turns per layer and a generally square shaped configuration. Alternative embodiments may include a multilayered coil with more than two layers, more or less than eight coil turns per layer, and/or in a different shape, e.g., circular, oval, hexagonal, rectangular, other non-square shape, etc.

[0079] Ferromagnetic material 906 (e.g., ferrite blocks, supermalloy blocks, nanocrystalline ferromagnetic material blocks, etc.) is disposed along a portion of the bottom of the lower coil layer 903b, to thereby provide a ferromagnetic bottom shield. In this example, four ferrite blocks or elements 906 are disposed along the bottom of the lower coil layer 903b. Accordingly, this exemplary multilayer coil 900 does not include a single contiguous ferromagnetic bottom layer.

[0080] Ferromagnetic material 908 is disposed between coil turns such that the ferromagnetic material 908 is disposed between corresponding adjacent portions of the conductor 904 (e.g., solid conductor, litz wire, etc.). The center opening 918 defined by the upper and lower coil layers 903a, 903b is devoid of ferromagnetic material such that the center opening 918 remains open, e.g., to allow air flow therethrough, etc.

[0081] Ferromagnetic blocks or elements 916 (e.g., ferrite blocks, supermalloy blocks, nanocrystalline ferromagnetic material blocks, etc.) are disposed between the upper and lower coil layers 903a, 903b. In this example, four ferrite blocks or elements 916 are disposed between the upper and lower coil layers 903a, 903b at predetermined locations or areas for improved performance. Accordingly, this exemplary multilayer coil 900 does not include a single contiguous ferromagnetic layer between the upper and lower coil layers 903a, 903b.

[0082] The ferromagnetic materials 906, 908, 916 may comprise ferrite, supermalloy, nanocrystalline ferromagnetic material and/or other ferromagnetic material. The conductor 904 and ferromagnetic materials 906, 908, 916 may comprise a conductor and ferromagnetic material as discussed herein, e.g., conductor 604 and ferromagnetic materials 606, 608, 610, 614, etc.

[0083] FIG. 15 illustrates a multilayered coil 1000 according to a tenth exemplary embodiment. The multilayered coil 1000 includes two coil layers 1003a, 1003b each having eight coil turns per layer and a generally square shaped configuration. Alternative embodiments may include a multilayered coil with more than two layers, more or less than eight coil turns per layer, and/or in a different shape, e.g., circular, oval, hexagonal, rectangular, other non-square shape, etc. [0084] Ferromagnetic material 1006 is disposed along a bottom of the lower coil layer 1003b, to thereby provide a ferromagnetic bottom shield. Ferromagnetic material 1008 is disposed between coil turns such that the ferromagnetic material 1008 is disposed between corresponding adjacent portions of the conductor 1004 (e.g., solid conductor, litz wire, etc.). Ferromagnetic material 1010 is disposed between (e.g., defines a single contiguous ferrite layer between, etc.) the upper and lower coil layers 1003a, 1003b. The center opening 1018 defined by the upper and lower coil layers 1003a, 1003b is devoid of ferromagnetic material such that the center opening 1018 remains open, e.g., to allow air flow therethrough, etc.

[0085] The ferromagnetic materials 1006, 1008, 1010 may comprise ferrite, supermalloy, nanocrystalline ferromagnetic material, and/or other ferromagnetic material. The conductor 1004 and ferromagnetic materials 1006, 1008, 1010 may comprise a conductor and ferromagnetic material as discussed herein, e.g., conductor 604 and ferromagnetic materials 606, 608, 610, 614, etc.

[0086] FIGS. 16, 17, and 18 illustrate a coil 1100 at different stages of assembly according to an eleventh embodiment. In this exemplary embodiment, ferromagnetic material (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) is molded into a predetermined shape. As shown in FIG. 16, the molded ferromagnetic material includes a lower ferromagnetic shielding layer 1106, a center portion 1114, and winding grooves 1122. The grooves 1122 extend circumferentially around the center portion 1114 along the lower ferromagnetic shielding layer 1106. The grooves 1122 may be configured (e.g., shaped, sized, etc.) to frictionally receive a conductor 1104 (FIG. 17) (e.g., conductor having a 1 millimeter (mm) wire diameter, etc.).

[0087] As depicted in FIG. 17, the conductor 1104 is adhesively attached (e.g., glued, etc.) to the lower ferromagnetic shielding layer 1106. The conductor 1104 is press fit, friction fit, or interference fit within the grooves 1122 to thereby define a plurality of coil turns (e.g., twelve coil turns, etc.).

[0088] As depicted in FIG. 18, the spacing between adjacent coil turns is filled with ferromagnetic material 1108. For example, a ferromagnetic mixture including adhesive (e.g., glue, etc.) and ferromagnetic particles (e.g., ferrite particles, supermalloy particles, nanocrystalline ferromagnetic material, etc.) may be dispensed onto the coil 1100 to fill the spacing between adjacent coil turns with the ferromagnetic mixture.

[0089] Accordingly, the coil 1100 (FIG. 18) may therefore include ferromagnetic material(s) (e.g., ferrite, supermalloy, nanocrystalline ferromagnetic material, other ferromagnetic material, etc.) defining the lower ferromagnetic shielding layer 1106, the center portion 1114, the grooves 1122, and filling the spacing between adjacent coil turns. The conductor 1104 and ferromagnetic materials 1106, 1108, 1114 may comprise a conductor (e.g., litz wire, solid conductor, etc.) and ferromagnetic material as discussed herein, e.g., conductor 604 and ferromagnetic materials 606, 608, 610, 614, etc.

[0090] In this exemplary embodiment, the ferromagnetic material is molded such that the coil 1100 (FIG. 18) defined by the conductor 1104 (FIG. 17) within the grooves 1122 has twelve turns and a generally circular configuration. Alternative embodiments may be configured differently such as with more or less than twelve turns, with a different shape, e.g., oval, hexagonal, rectangular, square, other non-circular shape, etc., and/or with grooves configured for frictionally receiving a conductor having a wire diameter different than 1 mm, etc.

[0091] In another exemplary embodiment, a method includes molding a ferromagnetic material into a predetermined shape that includes a lower ferromagnetic shielding layer and winding grooves along the lower ferromagnetic shielding layer. The method further includes adhesively attaching a conductor to the lower ferromagnetic shielding layer and press fitting, friction fitting, or interference fitting the conductor within the grooves to thereby define a plurality of coil turns of a coil. The method also includes dispensing ferromagnetic material onto the coil to thereby fill the spacing between adjacent coil turns with the dispensed ferromagnetic material. The conductor may comprises litz wire including a ferromagnetic cover along at least one side of the litz wire. The dispensed ferromagnetic material may comprise a mixture including adhesive (e.g., glue, etc.) and ferromagnetic particles (e.g., ferrite particles, supermalloy particles, nanocrystalline ferromagnetic material, etc.).

[0092] The litz wires with ferromagnetic covers (e.g., FIGS. 1-10, etc.), coil topologies (e.g., FIG. 11, etc.), and coils (e.g., FIGS. 12-18, etc.) disclosed herein may be used in various applications, including wireless power transfer applications (e.g., devices that transmit or receive wireless power, etc.) wireless charging devices (e.g., automotive wireless chargers, other wireless chargers, etc.), transformers, devices to be charged (e.g., smartphones, tablets, other portable electronic devices, etc.), etc. Accordingly, the litz wires with ferromagnetic covers, coil topologies, and coils disclosed herein should not be limited to use with only one particular type of application, end use, device to charged, wireless charger, wireless power transfer device, etc.

[0093] For example, FIG. 19 illustrates a schematic representation of a wireless charger with a coil assembly 1200 that can be any embodiment of the coils discussed above or some other configuration that includes the litz wire with the ferromagnetic cover. The coil assembly is controlled by a controller 1240 that can be one or more circuits and/or integrated circuits that powers the coil in a desired manner so as to allow for power transfer to a receiving coil. Both the coil assembly 1200 and the controller 1240 are provided in and/or supported by a housing 1250 that collectively defines a wireless charger 1260.

[0094] Exemplary embodiments including ferromagnetic material along at least one side of litz wire as disclosed herein may provide or include one or more (but not necessarily any or all) of the following advantages or features. The ferromagnetic material may improve the coupling factor with a receiver/transmitter coil. The ferromagnetic material may reduce and improve the external proximity effect enhancing the quality factor of the coil. The ferromagnetic material may improve the relative permeability of the medium, thereby enhancing the inductance of the coil. The improvement in the quality factor and coupling factor may enable high wireless charging system efficiencies. The ferromagnetic material may also reduce resistance and reduce heat.

[0095] Exemplary embodiments including a coil topology and/or a coil as disclosed herein may provide or include one or more (but not necessarily any or all) of the following advantages or features. The coil topology may improve the coupling factor with a transmitter/receiver coil. The coil topology may have the capability of achieving very high quality factors. A given quality factor can be achieved for a given size restriction by using a specific litz wire type, increasing the number of layers, and/or changing the permeability of the ferromagnetic material used. The coil topology may also have the capability of achieving a large or specific inductance in a small area by using a specific litz wire type, increasing the number of layers, and/or changing the permeability of the ferromagnetic material. The improvement in the quality factor and coupling factor may enable high wireless charging system efficiencies. Ferromagnetic areas/middle openings may be provided that enable airflow paths. This, in turn, may allow fans to be used for providing active cooling for the transmitter coil and/or receiver coil if deemed necessary or desirable for certain applications.

[0096] Turning to Figs. 20-29, simulated experimental data is shown for embodiments of the coils discussed. More particularly, a coil was simulated where the wire has an outer diameter of 0.82 mm and the ferrite cover between the coils ranges from 0.1 mm to 1.0 mm thick and has a height of 1.33 mm. The ferrite material could be made up of either MnZn or NiZn. The lower shielding ferrite has a thickness of at least 1mm. The coil has 12 number of turns with an outer length ranging from 44.08 mm up to 65.68 mm depending on the ferrite cover thickness and an inner length of 22 mm.

[0097] Fig. 20 illustrates that increased inductance can be obtained with a cover that ranges from 0.1 to 1.0 mm thick. Fig. 21 shows how that for a vertical distance of 2 mm, the ferrite material can provide a substantial increase in coupling but the benefits are reduced as the cover thickness increases. Fig. 22 illustrates the point that at greater distances (such as the 4 mm of vertical distance used for the data in Fig. 22) the benefits are further reduced as the cover thickness approaches 1.0 mm. Thus, it may often be beneficial to have a thinner ferrite cover.

[0098] Fig. 23 illustrates the fact that a substantial reduction in AC resistance is possible with a ferrite cover having a thickness of 0.1 mm. As can be appreciated, the reduction in AC resistance is substantial. Fig. 24 illustrates that AC resistance is comparable when the ferrite cover has a thickness of 0.5 mm but the percentage improvement is less as AC resistance for a conventional design goes down, in part due to the increased spacing.

[0099] Figs. 25-27 illustrate that as the ferrite cover thickness increases from 0.1 mm to 0.3 mm to 0.5 mm, respectively, the quality factor (or Q-factor) can be substantially improved.

[00100] Figs. 28-29 illustrate results for an exemplary embodiment having 2 identical layers with circular shape. The wire used has a total outer diameter of 0.92 mm. Moreover, it has a ferrite cover having a thickness of 0.1 mm, a height of 1.33 mm and an initial permeability of 230. There is a ferrite between layers which could have a thickness up to 1 mm. It could have an initial permeability up to 10000. The ferrite material could be made up of either MnZn or NiZn. The lowest shielding ferrite has a thickness of at least 1mm. The coil has 6 number of turns per layer with an outer length of 38 mm and an inner length of 20 mm. The height of the wireless charging coil could be up to 4.82 mm and the frequency is 115 kHz. The receiving coil is Qi receiver example 3.

[00101] As can be appreciated from the above discussion, one way to determine the effectiveness of a coil system is to determine a figure of merit (FOM). Mathematically, this can defined as:

FOM = kQ where k is the coupling factor and Q is the quality factor. Naturally, the higher the FOM, the better the coil performance one can expect. As can be appreciated from Figs. 28-29, even the worse case for the version with ferrite cover (Fig. 29) is substantially better than the best-case version without the ferrite cover (as shown in Fig. 28). Thus there is evidence of substantial improvement with the disclosed designs.

[00102] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements, intended or stated uses, or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.