PRIORITY/CROSS-REFERENCE TO RELATED APPLICATIONS [oooi] This application claims the benefit of U.S. Provisional Application No. 63/046,328, filed June 30, 2020, the disclosures of which are incorporated by reference.

BACKGROUND

[0002] The use of wireless charging for mobile phones is growing rapidly. The market for other consumer electronics, such as wireless electronic devices with small form factors, is also growing. One of the fastest-growing markets is wearable technology, which includes smartwatches, smart glasses, wireless earbuds, and so forth. These mobile devices have a small form factor, which may restrict the size of an inductive coil that can be implemented for wireless charging. Further, existing transmitter coils may have sizing fixed by various standards, such as the Qi standard established by the Wireless Power Consortium (WPC). Efficiency is highest when a wireless charger has a transmitting inductive coil that substantially matches the size of a receiving inductive coil at the mobile device and the coils are aligned.

[0003] Existing wireless-charging coils (transmitter coils and receiver coils) can have unwanted eddy currents that form within the coils. These eddy currents reduce the performance efficiency of the wireless charging by consuming useful energy, referred to as alternating current (AC) loss and direct current (DC) loss. [0004] One challenge with improving performance of wireless-charging coils is coil thickness. Generally, a thicker coil provides better performance. To maintain a sleek and thin form factor for a mobile device, however, a reduction in the coil thickness may be desired. Yet, a thinner coil reduces power efficiency of the wireless charging because of the high resistance of the coil. Some wireless-charging devices use printed circuit board (PCB) trace for the windings of the coil. However, PCB trace may have higher eddy current loss due to the wider trace area facing the magnetic field ( e.g B field). Although PCB trace is more flexible, the width of each turn and the thickness of the trace is limited by the manufacture ability of the provider of the flexible printed circuit (FPC). Some mobile devices may use multi-stranded trace for the coil winding. Although a multi- stranded trace may lower eddy current loss because of the much smaller trace area facing the B field, the gauge of the wire has discrete values, resulting in a fixed width and a fixed thickness of the winding for each turn. This presents a challenge to improving performance of wireless-charging coils without changing the size of the coil, either by decreasing an inner diameter (ID) of the coil or increasing an outer diameter (OD) of the coil, or both. Changing the size of the coil may result in a mismatch of sizing with existing wireless chargers, which may reduce the efficiency of the wireless charging.

SUMMARY

[0005] This document describes a multi-gauge stranded coil for wireless charging and associated methods and systems. The multi-gauge stranded coil includes multiple sections connected together with different gauges or number of strands relative to one another. Inner turns of the coil have a thinner gauge or fewer strands of wire than outer turns of the coil. The thinner gauge or fewer strands in the inner turns reduce AC resistance in the inner turns. Thicker gauge or more strands in the outer turns reduce DC resistance in the outer turns. The differing gauges or number of strands in the different sections of the coil optimize a tradeoff between AC and DC resistances throughout the coil. Also, a shielding material may include a non-uniform thickness to correspond to different thicknesses of the inner and outer turns and provide a uniform thickness for the combination of the shielding material and the coil.

[0006] The multi-gauge stranded coil solves the problem of reducing eddy current losses in the winding of a wireless-charging coil without changing a geometry (inner diameter and/or outer diameter of the coil in an xy-plane, or an overall height of the coil in a z-plane) of an existing coil design. Further, the multi-gauge stranded coil described herein improves wireless charging performance (e.g., wireless-charging efficiency) without impacting an overall thickness of the product. In comparison to existing coil designs for wireless charging of handheld mobile devices, the multi-gauge stranded coil can reduce the AC resistance by approximately 30% to approximately 40%, decrease the DC resistance by approximately 3% to approximately 5%, and increase a DC-DC wireless charging efficiency by approximately 3% to approximately 5%.

[0007] This summary is provided to introduce simplified concepts concerning a multi-gauge stranded coil for wireless charging, which is further described below in the Detailed Description and Drawings. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The details of one or more aspects of a multi-gauge stranded coil for wireless charging are described in this document with reference to the following drawings. The same numbers are used throughout the drawings to reference like features and components:

Fig. 1 illustrates a perspective view and a top plan view of an example multi-gauge stranded coil.

Fig. 2 illustrates a top plan view of an example implementation of the multi-gauge stranded coil from Fig. 1.

Fig. 3-1 illustrates a layer stack representing a section view of the multi-gauge stranded coil from Fig. 1, taken along line A — A, with an example implementation of the shielding material.

Fig. 3-2 illustrates a layer stack representing a section view of the multi-gauge stranded coil from Fig. 1, taken along line A — A, with an alternative example implementation of the shielding material.

Fig. 3-3 illustrates a layer stack representing a section view of the multi-gauge stranded coil from Fig. 1, taken along line A — A, with another example implementation of the shielding material.

Figs. 4-1, 4-2, and 4-3 illustrate example implementations for connecting different sections of the multi-gauge stranded coil from Fig. 1. Fig. 5 illustrates a layer stack representing an example system for inductive wireless charging of an electronic device, using the multi-gauge stranded coil from Fig. 1.

Fig. 6 illustrates a block diagram illustrating an example system using the multi-gauge stranded coil from Fig. 1 for wireless charging of a load.

DETAILED DESCRIPTION

Overview

[0009] Aspects of a multi-gauge stranded coil for wireless charging are described. A stranded coil refers to a coil having many fine strands of conducting wires. In aspects, the multi-gauge stranded coil includes a coil with multiple sections serially connected together, which have different gauges or number of strands relative to one another. A first section of the coil, which is connected to a second section of the coil, has a lesser number of strands or a smaller gauge than a second section. Optionally, a third section of the coil is connected to the second section opposite the first section and has a greater number of strands or a larger gauge than the second section. Accordingly, the coil increases gradually, by degrees, or stepwise in thickness and/or number of strands from one end (e.g, the first section) to its opposite end (e.g., third section or final outer section).

[0010] In particular, the coil is wound to have the first section forming one or more inner turns, which define an opening through which a magnetic field (e.g, B field) can pass. The coil is wound to have the second section forming one or more additional turns (e.g, middle turns) of the coil, which are larger than, and share a common center point with, the one or more inner turns. The coil can also be wound to have the third section forming one or more outer turns, which are larger than, and share the common center point with, the additional tum(s) formed by the second section.

[ooii] By using a multi-gauge stranded coil, the coil can be designed to optimize a tradeoff between AC resistance and DC resistance in the coil. The AC resistance is dominant along the inner diameter of the coil because the AC field, which causes AC loss (e.g., heat), is more concentrated along the inner diameter of the coil. The AC resistance is based, at least in part, on turn length and wire gauge. The AC field gradually decreases from the inner diameter toward the outer diameter of the coil, which results in the DC resistance being dominant along the outer diameter of the coil. The DC resistance is based, at least in part, on a cross-section area of the coil. The thinner gauge and/or fewer strands of the inner turns reduces the AC resistance, which reduces the AC losses, and the thicker gauge and/or greater number of strands used in the outer turns reduces the DC resistance. In this way, the inner turns have a shorter length and face a stronger portion of the magnetic field, allowing the trace width to be narrower; the outer windings have a longer length and thicker gauge and interact with a weaker portion of the magnetic field.

[0012] By using thinner strands for the inner turns, more inner turns can be used to reduce the AC resistance, compared to existing coils that use a uniform number of turns and a uniform gauge of wires throughout the coil. Further, these addition inner turns (and middle turns) can be added without changing the inner diameter or the outer diameter of the coil, which enables the coil to be size-matched to existing wireless-charging transmitter coils for high-efficiency wireless-power transfer. Thus, without adjusting the inner diameter or the outer diameter of the coil, the coil can be formed to optimize AC loss in the inner turns and optimize DC loss in the outer turns. In comparison to existing wireless charging coils that have a uniform number of turns and a uniform wire gauge, the multi gauge stranded coil can reduce AC resistance from approximately 30 % to approximately 40 % and increase direct current DC-DC wireless-charging efficiency from approximately 3 % to approximately 5 %.

[0013] These are but a few examples of how the described techniques and devices may be used to enable a multi-gauge stranded coil for wireless charging. Other examples and implementations are described throughout this document. The document now turns to an example device, after which example systems are described.

Example Device

[0014] Fig. 1 illustrates a perspective view 100 and a top plan view 102 of an example multi-gauge stranded coil 104 (coil 104). The coil 104 may be implemented in an electronic device for wireless charging. The coil 104 may be positioned proximate or adjacent to a layer of highly-permeable material, such as a shielding material 106, to provide a path for magnetic flux of a magnetic field ( e.g AC field 108, B field).

[0015] The coil 104 may be an inductive coil wound in a shape that substantially matches a geometry of an inductive transmitter coil of an existing wireless-charging device, such as those used to wirelessly charge a smartphone. The geometry of the coil 104 and of the inductive transmitter coil may be any suitable geometry, including a disk like shape, a ring-like shape, a rectangular shape with rounded corners, and so forth. In some implementations, the geometry may be cylindrical to enable inductive and/or resonance wireless charging.

[0016] The coil 104 is wound to have an inner diameter 110 and an outer diameter 112. The coil 104 includes multiple sections (lengths) of stranded wire (e.g, Litz wire, flexible PCB trace), which differ in thickness (gauge) and/or number of strands. As illustrated, the coil 104 may have a first section 114, a second section 116, and a third section 118. The first section 114 may form one or more inner turns of the coil 104. The second section 116 may form one or more additional turns in a middle region of the coil 104. The third section 118 may form one or more outer turns of the coil 104. Although the coil 104 is illustrated in Fig. 1 with a single turn for each section, any suitable number of turns can be implemented in each section. One section may have more turns than another section. Although the coil 104 is described having three sections, any suitable number of sections may be implemented in the coil 104, including two sections, four sections, five sections, and so forth.

[0017] The first section 114 has a first gauge 120, the second section has a second gauge 122, and the third section has a third gauge 124. The first gauge 120 of the inner tum(s) (e.g., the first section 114) is thinner than the second and third gauges 122, 124. The third gauge 124 of the outer tum(s) (e.g., the third section 118) is thicker than the first and second gauges 120, 122.

[0018] Further, although the coil 104 is illustrated as having a full turn for each section, each section can be formed with any suitable length, including a length that is less than an integer-number of turns. Accordingly, the coil 104 can transition from one section to the next section at any location along a turn, and the coil 104 is not limited by the illustrated examples described herein.

[0019] The coil 104 also includes a first wire 126 and a second wire 128, which connect each end of the coil 104 to circuitry 130. In an example, the first wire 126 may connect the most-inner turn of the first section 114 to the circuitry 130, and the second wire 128 may connect the most-outer turn of the third section 118 to the circuitry 130. The first wire 126 may have substantially the same gauge and/or number of strands as the inner section 114. The second wire 128 may have substantially the same gauge and/or number of strands as the third section 118.

[0020] In some aspects, the circuitry 130 is external to the coil 104 but internal to an electronic device carrying the coil 104. For example, the circuitry 130 may be positioned behind the shielding material 106 (as shown in the top plan view 102) such that the shielding material 106 is between the coil 104 and the circuitry 130. The coil 104 is positioned proximate to a first surface 132 of the shielding material 106. The circuitry 130 may be positioned proximate to a second surface 134, which is opposite the first surface 132. With the circuitry 130 and the coil 104 positioned on opposing sides of the shielding material 106, comparatively, the shielding material 130 can shield the circuitry 130 from the magnetic field 108.

[0021] Fig. 2 illustrates a top plan view 200 of an example implementation of the multi-gauge stranded coil 104 from Fig. 1. As illustrated, the various sections of the coil 104 can each include multiple turns. In the example shown, the first section 114 of the coil 104 may include three turns, the second section 116 may include three turns, and the third section 118 may include four turns. Any suitable number of turns may be used for any individual section of the coil 104. Two or more of the sections may share a common number of turns. Two or more of the sections may have a different number of turns, comparatively. The number of turns in each section may be based on the amount of power desired to wirelessly transmit or receive. Each section, or each turn, may be designed to optimize for the tradeoff between AC resistance and DC resistance. For example, less strands or thinner gauge may be used for the inner tum(s) (along the inner diameter 110 or within a predefined distance from the inner diameter 110) to reduce the AC resistance. As the AC field decreases in an outward direction from the inner diameter 110 toward the outer diameter 112, more strands or thicker gauge may be used. Accordingly, the second section 116 is shown with a thicker gauge than the first section, and the third section 118 is shown with a thicker gauge than the second section 116. In some aspects, each turn, sequentially from the inner diameter 110 to the outer diameter 112, may increase in thickness or number of strands relative to the previous adjacent turn (a neighboring turn positioned on an ID-side of the turn).

[0022] Fig. 3-1 illustrates a layer stack representing a section view 300 of the multigauge stranded coil 104 from Fig. 1, taken along line A — A, with an example implementation of the shielding material 106. The various sections 114, 116, 118 of the coil 104 may be substantially aligned along one surface (e.g., a top surface), which is opposite another surface (e.g., a bottom surface) adjacent to the second surface 134 of the shielding material 106. In aspects, the substantially-aligned surface (e.g, the top surface) of the sections 114, 116, 118 of the coil 104 faces a housing of an electronic device carrying the coil 104. Because the sections 114, 116, and 118 have different thicknesses (e.g., gauge and/or number of strands) in a direction of the z-axis, the sections 114, 116, and 118 may not be aligned along the other surface (e.g., the bottom surface adjacent to the shielding material 106). As above, the first surface 132 of the shielding material 106 shields circuitry (e.g, the circuitry 130 from Fig. 1 or other circuitry) against magnetic fields (magnetic field 108 from Fig. 1) associated with wireless charging from interfering with the circuitry.

[0023] The shielding material 106 may have a non-uniform thickness. For example, the shielding material 106 can be formed with a stepwise increase in thickness, from a perimeter of the shielding material 106 toward a center point corresponding to a center of the coil 104, to correspond to the differences in thickness of adjacent sections of the coil and without impacting a total z-thickness of the combination of the shielding material 106 and the coil 104. Put another way, the shielding material 106 may have a stepwise decrease in z-height from a center point to a perimeter of the shielding material 106 (or a perimeter of the coil 104), where each z-direction decrease corresponds to a change in thickness of the coil 104. This stepwise change (increase or decrease) allows the combination of the shielding material 106 and the coil 104 to have a uniform total thickness (z-height).

[0024] For example, the shielding material 106 may have a first region 302 having a first thickness 304, a second region 306 having a second thickness 308, and a third region 310 having a third thickness 312. The difference between the first thickness 304 of the first region 302 of the shielding material 106 and the second thickness 308 of the second region 306 of the shielding material 106 may correspond to the difference in thickness between the first section 114 and the second section 116 of the coil 104. Although three regions of the shielding material 106 are described herein, any suitable number of regions can be implemented for the shielding material 106, which correspond to the differences in thickness throughout the coil 104.

[0025] The shielding material 106 may be any suitable material that has a high permeability, such as a ferrite material or nanocrystalline sheets. A greater thickness of the shielding material 106 can provide higher permeability. A higher-permeability and/or high-saturation flux density (B _sat ) material region is positioned under the inner turns (e.g, the first section 114) of the coil 104, which have a thinner gauge and fewer turns, where the AC field is strongest. Comparatively, a lower-permeability region is positioned under the outer turns (e.g., the third section 118) of the coil 104, which have a thicker gauge and/or more turns, where the AC field is weaker.

[0026] In aspects, the coil 104 is positioned between the shielding material 106 and a housing of an electronic device carrying the coil 104. Further, the shielding material 106 is positioned between the coil 104 and circuitry (e.g., the circuitry 130 from Fig. 1 or other circuitry) of the electronic device. As above, the shielding material 106 shields the circuitry from magnetic fields associated with wireless charging of the electronic device housing the coil 104.

[0027] Fig. 3-2 illustrates a layer stack representing a section view 320 of the multi gauge stranded coil from Fig. 1, taken along line A — A, with an alternative example implementation of the shielding material. The shielding material 106 may be formed in separate sections that have different thicknesses one to another. [0028] Nanocrystalline layers are thin (e.g., approximately 25 micrometers) and are stackable. In an example, the first region 302 of the shielding material 106 may be formed with ten layers (250 micrometers), the second region 306 of the shielding material 106 may be formed with fewer layers (e.g., eight layers (200 micrometers)), which provides a slightly lower permeability material than the first region 302. Continuing, the third region 310 of the shielding material 106 may be formed with even fewer layers (e.g, six layers (150 micrometers)) of nanocrystalline sheets, which provides a material with a lower permeability than the first and second regions 302, 306. Accordingly, the shielding material 106 is formed with varying permeability, which varies in relation to a varying thickness of the adjacent coil 104.

[0029] Fig. 3-3 illustrates a layer stack representing a section view 330 of the multi gauge stranded coil from Fig. 1, taken along line A — A, with another example implementation of the shielding material. In Fig. 3-3, the different regions 302, 306, 310 of the shielding material 106 are formed by stacking additional layers (e.g, nanocrystalline layers), which are shorter in width (x-direction, y-direction). For example, a first set of nanocrystalline layers are stacked to form first layer 332. A second set of nanocrystalline layers, which are smaller in the xy-plane than the first set of nanocrystalline layers, are stacked in the center of the shielding material 106 to form second layer 334, such that the second set is positioned between the first layer 332 and the first and second sections 114, 116 of the coil 104. In addition, a third set of nanocrystalline layers, which are smaller in the xy-plane than the second set of nanocrystalline layers, are stacked in the center of the shielding material 106 to form third layer 336, such that the third layer 336 is positioned between the second layer 334 and the first section 114 of the coil 104. Further, the third layer faces the opening defined by the coil 104. In this way, the regions 302, 306, 310 have the appropriate z-height, as described above.

[0030] Figs. 4-1, 4-2, and 4-3 illustrate example implementations 400, 410, 420, and 430 for connecting different sections of the multi-gauge stranded coil from Fig. 1. The different sections 114, 116, 118 can be connected to one another in any suitable way. In the example illustrated in Fig. 4-1, the first section 114 of the coil 104 can be soldered to the second section 116 of the coil 104, which may form a first soldering point 402 (soldering ball). The second section 116 may be soldered to the third section 118, forming a second soldering point 404.

[0031] In Fig. 4-2, the coil 104 is formed by adding strands (e.g., copper strands) at specific locations along the length of the coil 104 to increase the thickness of the coil 104. For example, the first section 114 may include a first set of strands that run the full length of the coil 104 (e.g., through the center of the coil 104). To form the second section 116, a second set of strands are added to the first set of strands, beginning at location 412, to increase the thickness of the coil 104 throughout the second section 116. Then, at location 414, a third set of strands are added to the outside of the second set of strands to increase the thickness of the coil 104 throughout the third section 118. Individual sets of strands may have any suitable number of strands to increase the thickness of the coil 104 by a predefined amount.

[0032] Alternatively, as illustrated in implementation 420, additional strands of wire can be added to the coil 104 in a manner that provides a more-gradual increase in thickness. For example, a small number of strands (e.g., 10 or less) may be added to the coil 104 at more frequent locations (e.g., locations 422) to create the more-gradual increase in thickness. In this way, the second section 116 (e.g., middle turns) may be formed from multiple subsections 116-1, 116-2, 116-3, 116-4, 116-5, serially increasing in thickness from the subsection 116-1, connected to the first section 114, to the subsection 116-5, connected to the third section 118.

[0033] Fig. 4-3 illustrates yet another example implementation 430 in which the coil 104 is formed from a single material that is formed (pressed, rolled, stretched, etc.) into the multiple sections 114, 116, 118, without separating the sections 114, 116, 118. In this way, connection points 432, 434 may be already formed and may provide a solid, smooth contour from one section to the next. In some aspects, by forming the coil 104 in this way, the coil 104 may have a gradual increase in size, without defined sections, sufficient to balance the AC loss against the DC loss throughout the coil 104.

[0034] Fig. 5 illustrates an example implementation 500 of a system for magnetic inductive wireless charging of an electronic device. A wireless-power transmitter 502 is illustrated as a charger base 502-1. However, any suitable wireless-power transmitter can be used to wirelessly transfer power via magnetic inductive wireless charging of a battery of a receiving device. The wireless-power transmitter 502 can also include other devices capable of implementing wireless charging, such as desktop computers, gaming systems or consoles, audio systems, automobiles, track pads, drawing pads, tablets, laptops, smartphones, netbooks, e-readers, and some home appliances. [0035] A wireless-power receiver 504 is illustrated with a variety of example devices, including a computing watch 504-1 (e.g., smartwatch), computing spectacles 504-2 (e.g., smart glasses), an electronic earbuds case 504-3, a portable audio player 504-4 (e.g, mp3 player), and a security camera 504-5. The wireless-power receiver 504 can also include other devices with a small form factor, such as small wireless phones, electronic toothbrushes, electronic razors, drones, wireless gaming controllers, remote controls, digital cameras, and other small battery-powered devices.

[0036] The wireless-power transmitter 502 may include a transmitter coil 506, which may be any suitable coil used to generate an electromagnetic field for magnetic inductive wireless-power transmission, including existing coils. In some aspects, the multi-gauge stranded coil 104 may be implemented as the transmitter coil 506.

[0037] The wireless-power receiver 504 may include the multi-gauge stranded coil 104, implemented as a receiver coil to generate an electric current, based on exposure to the electromagnetic field, to charge a battery of the wireless-power receiver 504. Efficiency of the power transfer is greatest when the multi-gauge stranded coil 104 is not only aligned with the transmitter coil 506 but also substantially size-matched to the transmitter coil 506. Using the techniques described herein, the multi-gauge stranded coil 104 may improve wireless-charging performance without requiring a change to the size of the multi-gauge stranded coil 104, enabling the multi-gauge stranded coil 104 to continue to be size-matched to existing transmitter coils 506.

[0038] Fig. 6 illustrates a block diagram illustrating an example system 600 using a multi-gauge stranded coil 104 for wireless charging of a load. The wireless-power transmitter 502 includes a microcontroller unit (MCU) 602 connected to a transmitter power management integrated circuit (PMIC) 604, which is connected to an inverter circuit 606 ( e.g ., full-bridge inverter circuit, half-bridge inverter circuit). The inverter circuit 606 is connected to one or more capacitors, such as capacitor Ctx 608. The capacitor Ctx 608 is connected to a transmitter coil L _tx , such as the transmitter coil 506. The system 600 includes an AC adapter 610 that provides an input voltage V,„, which is usable by the transmitter PMIC 604 and the MCU 602 to manage power driven to the transmitter coil 506. The inverter circuit 606 converts a DC input supply voltage (e.g., input voltage V, _n ) into symmetric AC voltage of a desired magnitude and frequency. The resultant AC voltage is output to the capacitor Ctx 608, which passes the energy to the transmitter coil 506.

[0039] The transmitter coil L _tx 506 generates a magnetic field 612 and couples to a receiver coil L _nc 614 (e.g., the multi-gauge stranded coil 104) to transmit energy to the receiver coil L _rx 614. The receiver coil L _r 614 receives the energy from the magnetic field 612 generated by the transmitter coil L _tx 506. This energy induces an electric current in the receiver coil L _rx 614. The receiver coil L _rx 614 passes energy from the electric current to one or more capacitors C _rx 616, which then pass the energy to a receiver PMIC 618. The receiver PMIC 618 uses the energy provided by the one or more capacitors C _rx 616 to provide an output voltage V _ou t to a PMIC for charging 620. Additionally, the receiver PMIC 618 can provide load modulation back to the wireless-power transmitter 502 in accordance with Qi wireless-charging protocol. Load modulation signals can pass through the receiver coil L _rx 614 and on to the wireless-power transmitter 502 via the transmitter coil L _tx 506 to enable the wireless-power transmitter 502 to manage the amount of power being transmitted. Additionally, the wireless-power transmitter 502 may provide signals to the wireless-power receiver 504 by using frequency modulation, such as frequency- shift keying (FSK). These modulated signals may pass through the transmitter coil L _tx 506 and on to the wireless-power receiver 504 via the receiver coil L _rx to enable communication (e.g., control signals or feedback signals) from the wireless-power transmitter 502 to the wireless-power receiver 504. The PMIC for charging 620 provides power management for quick charging of a load, such as load 622 (e.g., battery), by providing a DC current at a voltage level of the load 622.

Conclusion

[0040] Although aspects of the multi-gauge stranded coil for wireless charging have been described in language specific to features and/or methods, the subject of the appended claims is not necessarily limited to the specific features or methods described. Rather, the specific features and methods are disclosed as example implementations of the multi-gauge stranded coil for wireless charging, and other equivalent features and methods are intended to be within the scope of the appended claims. Further, various different aspects are described, and it is to be appreciated that each described aspect can be implemented independently or in connection with one or more other described aspects.