PATENT DOCUMENT

Publication Number: US-10910862-B2
Application Number: US-201715701224-A
Country: US
Kind Code: B2

Title: Electromagnetic shielding for wireless power transfer systems

Abstract:
Embodiments describe electromagnetic shielding for wireless charging systems. A wireless charging system includes a transmitter coil configured to generate a magnetic flux, a receiver coil positioned coaxial with the transmitter coil to receive the generated magnetic flux, where electrical interaction between the transmitter coil and the receiver coil generates electric fields, a transmitter shield positioned between the transmitter coil and the receiver coil to intercept some of the electric fields directed away from the transmitter coil and allow the magnetic flux to pass through the transmitter shield, and a receiver shield positioned between the transmitter shield and the receiver coil to intercept some of the electric fields directed away from the receiver coil and allow the magnetic flux to pass through the receiver shield.

Claims:
What is claimed is: 
     
       1. A wireless charging system, comprising:
 a transmitter coil configured to generate a magnetic flux; 
 a receiver coil positioned coaxial with the transmitter coil to receive the generated magnetic flux, wherein electrical interaction between the transmitter coil and the receiver coil generates electric fields; 
 a transmitter shield positioned between the transmitter coil and the receiver coil to intercept some of the electric fields directed away from the transmitter coil and allow the magnetic flux to pass through the transmitter shield; and 
 a receiver shield positioned between the transmitter shield and the receiver coil to intercept some of the electric fields directed away from the receiver coil and allow the magnetic flux to pass through the receiver shield, the receiver shield comprising an annular layer of conductive material having a gap and a cut positioned opposite to and separate from the gap, wherein the gap and the cut each extend completely across the receiver shield from an inner diameter of the receiver shield to an outer diameter of the receiver shield to electrically separate the receiver shield into a first half and a second half, and wherein one or more connection terminals for the receiver shield are positioned in the gap. 
 
     
     
       2. The wireless charging system of  claim 1 , wherein the transmitter shield and the receiver shield are each grounded to discharge voltage generated by the electric fields. 
     
     
       3. The wireless charging system of  claim 1 , wherein the transmitter shield is positioned along a direction of the magnetic flux. 
     
     
       4. The wireless charging system of  claim 1 , wherein the transmitter shield is formed of a conductive material. 
     
     
       5. The wireless charging system of  claim 4 , wherein the conductive material is NiV. 
     
     
       6. The wireless charging system of  claim 1 , wherein the transmitter shield has a thickness between 20-30 um. 
     
     
       7. A wireless charging device configured to generate magnetic flux to perform wireless power transfer, the wireless charging device comprising:
 a driver board; 
 a plurality of transmitter coils disposed above the driver board and configured to generate the magnetic flux upward; 
 an electromagnetic shield disposed above the plurality of transmitter coils, and configured to be transparent to magnetic flux and opaque to electric fields, the electromagnetic shield comprising: 
 a substrate comprising a stiff material; and 
 a conductive layer disposed on a bottom surface of the substrate, the conductive layer having an annular shape and including a gap and a cut positioned opposite to and separate from the gap, wherein the gap and the cut each extend completely across the conductive layer from an inner diameter of the conductive layer to an outer diameter of the conductive layer to electrically separate the electromagnetic shield into a first half and a second half, and wherein one or more connection terminals for the electromagnetic shield are positioned in the gap; and 
 an adhesive layer disposed between the plurality of transmitter coils and the electromagnetic shield, the adhesive layer configured to attach the electromagnetic shield to the plurality of transmitter coils. 
 
     
     
       8. The wireless charging device of  claim 7 , wherein the electromagnetic shield further includes conductive traces embedded within the conductive layer. 
     
     
       9. The wireless charging device of  claim 8 , wherein the traces are grounded. 
     
     
       10. The wireless charging device of  claim 9 , wherein the traces are positioned perpendicular to coils of wire of the plurality of transmitter coils. 
     
     
       11. The wireless charging device of  claim 7 , wherein the conductive layer is NiV. 
     
     
       12. The wireless charging device of  claim 7 , wherein the conductive layer has a thickness between 25 to 100 nm. 
     
     
       13. The wireless charging device of  claim 7 , further comprising a ferrite layer disposed between the driver board and the plurality of transmitter coils. 
     
     
       14. An electronic device configured to receive magnetic flux for wireless power transfer, the electronic device comprising:
 a ferrite layer; 
 a receiver coil disposed below the ferrite layer, 
 an electromagnetic shield disposed below the receiver coil, the electromagnetic shield configured to be transparent to magnetic flux and opaque to electric fields, the electromagnetic shield comprising an annular layer of conductive material having a gap and a cut positioned opposite to and separate from the gap, wherein the gap and the cut each extend completely across the electromagnetic shield from an inner diameter of the electromagnetic shield to an outer diameter of the electromagnetic shield to electrically separate the electromagnetic shield into a first half and a second half, and wherein one or more connection terminals for the electromagnetic shield are positioned in the gap; 
 a conductive adhesive layer disposed between the receiver coil and the electromagnetic shield, wherein the conductive adhesive layer attaches the electromagnetic shield to the receiver coil; and 
 a protection layer disposed on a bottom surface of the electromagnetic shield. 
 
     
     
       15. The electronic device of  claim 14 , wherein the receiver coil comprises:
 a coil of wire; and 
 an insulating material attached to the coil of wire. 
 
     
     
       16. The electronic device of  claim 15 , wherein the insulating material is PI. 
     
     
       17. The electronic device of  claim 14 , wherein the electromagnetic shield comprises a conductive layer. 
     
     
       18. The electronic device of  claim 17 , wherein the conductive layer is formed of silver. 
     
     
       19. The electronic device of  claim 14 , wherein the electromagnetic shield has a thickness between 0.05 and 0.15 μm. 
     
     
       20. The electronic device of  claim 14 , wherein the conductive adhesive layer is conductive pressure sensitive adhesive.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a non-provisional patent application of and claims the benefit to U.S. Provisional Patent Application No. 62/399,082, filed Sep. 23, 2016 and titled “Electromagnetic Shielding for Wireless Power Transfer Systems,” and U.S. Provisional Patent Application No. 62/542,210, filed Aug. 7, 2017 titled “Electromagnetic shielding for Wireless Power Transfer Systems” and is related to concurrently filed and commonly assigned U.S. patent application Ser. No. 15/701,237 entitled “INDUCTIVE MODULE”, the disclosures of which are herein incorporated by reference in their entirety for all purposes. 
    
    
     BACKGROUND 
     Electronic devices (e.g., mobile phones, media players, electronic watches, and the like) operate when there is charge stored in their batteries. Some electronic devices include a rechargeable battery that can be recharged by coupling the electronic device to a power source through a physical connection, such as through a charging cord. Using a charging cord to charge a battery in an electronic device, however, requires the electronic device to be physically tethered to a power outlet. Additionally, using a charging cord requires the mobile device to have a connector, typically a receptacle connector, configured to mate with a connector, typically a plug connector, of the charging cord. The receptacle connector typically includes a cavity in the electronic device that provides an avenue within which dust and moisture can intrude and damage the device. Furthermore, a user of the electronic device has to physically connect the charging cable to the receptacle connector in order to charge the battery. 
     To avoid such shortcomings, wireless charging devices have been developed to wirelessly charge electronic devices without the need for a charging cord. For example, some electronic devices can be recharged by merely resting the device on a charging surface of a wireless charging device. A transmitter coil disposed below the charging surface may produce a time-varying magnetic flux that induces a current in a corresponding receiving coil in the electronic device. The induced current can be used by the electronic device to charge its internal battery. 
     Some existing wireless charging devices and electronic devices configured for wireless charging have a number of disadvantages. For instance, some wireless charging devices generate an unintended voltage on a receiving coil. The unintended voltage can create noise in the electronic device within which the receiving coil is housed. The noise can cause disturbance of sensitive electronic components in the electronic device, such as touch-sensitive components like a touch-sensitive display. Additionally, the electronic devices also generate an unintended voltage on a transmitter coil in a wireless charging device. The unintended voltage can cause inefficiencies in wireless power transfer. 
     SUMMARY 
     Some embodiments of the disclosure provide shielding components for a wireless charging system to avoid the generation of detrimental voltages on a receiver coil and/or a transmitter coil of a wireless charging system during wireless power transfer. In some embodiments, a transmitter shield and a receiver shield are implemented in a wireless charging system to intercept electric fields generated between the transmitter coil and the receiver coil during wireless power transfer. By intercepting the electric fields, detrimental voltages are prevented from being generated on the receiver coil by the transmitter coil, and vice versa, during wireless power transfer. 
     In some embodiments, a wireless charging system includes a transmitter coil configured to generate a magnetic flux; a receiver coil positioned coaxial with the transmitter coil to receive the generated magnetic flux, where electrical interaction between the transmitter coil and the receiver coil generates electric fields; a transmitter shield positioned between the transmitter coil and the receiver coil to intercept some of the electric fields directed away from the transmitter coil and allow the magnetic flux to pass through the transmitter shield; and a receiver shield positioned between the transmitter shield and the receiver coil to intercept some of the electric fields directed away from the receiver coil and allow the magnetic flux to pass through the receiver shield. 
     The transmitter shield and receiver shield can each be grounded to discharge voltage generated by the electric field. The transmitter shield can be positioned along the direction of the magnetic flux. The transmitter shield can be formed of a conductive material. In some embodiments, the conductive material can be NiV. The transmitter shield can have a thickness between 20-30 um. 
     In some embodiments, a wireless charging device configured to generate magnetic flux to perform wireless power transfer can include a driver board; a plurality of transmitter coils disposed above the driver board and configured to generate the magnetic flux upward; an electromagnetic shield disposed above the plurality of transmitter coils, and configured to be transparent to magnetic flux and opaque to electric fields, the electromagnetic shield including: a substrate comprising a stiff material; and a conductive layer disposed on a bottom surface of the substrate; and an adhesive layer disposed between the plurality of transmitter coils and the electromagnetic shield, the adhesive layer configured to attach the electromagnetic shield to the plurality of transmitter coils. 
     The electromagnetic shield can further include conductive traces embedded within the conductive layer. The traces can be grounded. The traces can be positioned perpendicular to coils of wire of the plurality of transmitter coils. The conductive material can be NiV. The conductive material can have a thickness between 25 to 100 nm. The wireless charging device can further include a ferrite layer disposed between the driver board and the plurality of transmitter coils. 
     In some embodiments, an electronic device configured to receive magnetic flux for wireless power transfer can include a ferrite layer; a receiver coil disposed below the ferrite layer, an electromagnetic shield disposed below the receiver coil, the electromagnetic shield configured to be transparent to magnetic flux and opaque to electric fields; a conductive adhesive layer disposed between the receiver coil and the electromagnetic shield, where the conductive adhesive layer attaches the electromagnetic shield to the receiver coil; and a protection layer disposed on a bottom surface of the electromagnetic shield. 
     The transmitter coil can include a coil of wire and an insulating material attached to the coil of wire. The insulating material can be PI. The electromagnetic shield can include a conductive layer. The conductive layer can be formed of silver. The electromagnetic shield can have a thickness between 0.05 and 0.15 μm. The conductive adhesive layer can be conductive pressure sensitive adhesive. 
     A better understanding of the nature and advantages of embodiments of the present invention may be gained with reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified diagram illustrating electrical interactions between a transmitter coil and a receiver coil of a wireless charging system during wireless power transfer. 
         FIG. 2  is a simplified diagram illustrating an exemplary wireless charging system including a transmitter shield and a receiver shield, according to some embodiments of the present disclosure. 
         FIG. 3  is a graph representing a measure of mutual inductance achieved between a transmitter coil and a receiver coil when a shielding layer is disposed between the transmitter and receiver coils during wireless power transfer, according to some embodiments of the present disclosure. 
         FIG. 4  is a graph representing an alternating current resistance (ACR) of a material based on its thickness, according to some embodiments of the present disclosure. 
         FIG. 5  illustrates an exploded view of an exemplary wireless charging system including a wireless charging device and an electronic device, each having electromagnetic shielding according to some embodiments of the present disclosure 
         FIG. 6  illustrates a top-down view of an exemplary transmitter shield, according to some embodiments of the present disclosure. 
         FIG. 7  illustrates a transmitter shield positioned over an array of transmitter coils, according to some embodiments of the present disclosure. 
         FIG. 8  illustrates a cross-section of a transmitter shield positioned over an array of transmitter coils, according to some embodiments of the present disclosure. 
         FIG. 9  illustrates a top-down view of an exemplary receiver shield, according to some embodiments of the present disclosure 
         FIG. 10  illustrates a receiver shield positioned over a receiver coil, according to some embodiments of the present disclosure 
         FIG. 11  illustrates a cross-section of a receiver shield positioned over a receiver coil, according to some embodiments of the present disclosure 
     
    
    
     DETAILED DESCRIPTION 
     During wireless power transfer in a wireless charging system, numerous electrical interactions can occur between a transmitter coil and a receiver coil in the wireless charging system. Some of the electrical interactions are intended interactions between the transmitter and receiver coil, while other electrical interactions are unintended interactions that can cause inefficiencies in power transfer and create issues in the electronic device. For example,  FIG. 1  is a simplified diagram illustrating electrical interactions between a transmitter coil  102  and a receiver coil  104  of an exemplary wireless charging system  100  during wireless power transfer. Transmitter coil  102  may be disposed within a wireless charging device, such as a wireless charging mat, and receiver coil  104  may be disposed within a consumer electronic device, such as a smart phone, smart watch, tablet, laptop, and the like. The electronic device may rest on the wireless charging device at interface  112  to enable power transfer. 
     Transmitter coil  102  and receiver coil  104  can be positioned substantially concentric to one another to enable efficient power transfer by means of magnetic induction. During wireless power transfer, transmitter coil  102  can generate time-varying magnetic flux  106 , which can propagate through both device housings at interface  112  and be received by receiver coil  104 . Time-varying magnetic flux  106  interacts with receiver coil  104  to generate a corresponding current in receiver coil  104 . The generated current can be used to charge a battery for operating the electronic device. 
     In addition to time-varying magnetic flux  106 , however, electric fields  108  and  110  can be unintentionally generated between transmitter and receiver coils  102  and  104  during wireless power transfer. For instance, when transmitter coil  102  generates magnetic flux  106 , a large voltage difference can exist between transmitter coil  102  and receive coil  104 . The voltage on transmitter coil  102  in some cases can be larger than the voltage on receiver coil  104 , thereby orienting some electric fields  108  toward receiver coil  104  and causing unintended voltage to be generated in receiver coil  104 . In some additional cases, voltage existing on receiver coil  104  may also orient some electric fields  110  toward transmitter coil  102  and cause detrimental voltage to be generated on transmitter coil  102 . Detrimental voltages generated on receiver coil  104  may disturb and/or disrupt the operation of sensitive components disposed proximate to receiver coil  104 , such as touch-sensitive devices like a touch-sensitive display. And, detrimental voltages generated on transmitter coil  102  may cause inefficiencies in power transfer. 
     I. Wireless Charging System with Electromagnetic Shielding 
     Embodiments of the disclosure describe a wireless charging system that mitigates the unintentional generation of detrimental voltage on a receiver and/or a transmitter coil during wireless power transfer. One or more electromagnetic shielding components may be incorporated in the wireless charging system to prevent electric fields from generating detrimental voltages on the receiver and/or transmitter coils, while allowing time-varying magnetic flux to freely propagate between the transmitter and receiver coils to perform wireless power transfer. 
     In some embodiments, a transmitter shield can be implemented in a wireless charging device to prevent detrimental voltage from being generated on a receiver coil in an electronic device. The transmitter shield can be positioned in the wireless charging device to intercept electric fields generated by the transmitter coil to prevent the electric fields from exposing on the receiver coil. As a result, the intercepted electric fields may generate voltage on the transmitter shield instead of on the receiver coil. This voltage can then be discharged by routing the voltage to ground, thereby disposing of the detrimental voltage and preventing it from affecting sensitive electronic components in the electronic device. In addition to the transmitter shield, a receiver shield can also be implemented in the wireless charging system to prevent detrimental voltage from being generated on the transmitter coil in the wireless charging device. Similar to the transmitter shield, the receiver shield can also be positioned in the electronic device to intercept electric fields generated by the receiver coil so that the electric fields are not exposed to the transmitter coil. Voltage generated in the receiver shield can be discharged to ground to prevent detrimental voltage from being generated on the transmitter coil. Aspects and features of embodiments of such a wireless charging system are discussed in further detail herein. 
       FIG. 2  is a simplified diagram illustrating an exemplary wireless charging system  200  including a transmitter shield  202  and a receiver shield  204 , according to some embodiments of the present disclosure. Transmitter shield  202  may be positioned in front of transmitter coil  102  so that magnetic flux  106  is directed toward transmitter shield  202 . For instance, transmitter shield  202  is positioned between transmitter coil  102  and receiver coil  104  during wireless power transfer so that magnetic flux  106  first passes through transmitter shield  202  before reaching receiver coil  104 . In some embodiments, transmitter shield  202  can be positioned between interface  112  and transmitter coil  102  when an electronic device rests on the wireless charging device to perform wireless power transfer. Accordingly, transmitter shield  202  and transmitter coil  102  can both be positioned within the wireless charging device. Transmitter shield  202  can be substantially transparent to magnetic flux  106  so that a substantial percentage of magnetic flux  106  generated by transmitter coil  102  is received by receiver  104 . 
     While transmitter shield  202  can be substantially transparent to magnetic flux  106 , transmitter shield  202  can, on the other hand, be substantially opaque to electric field  108  such that electric field  108  is substantially blocked by transmitter shield  202 . This prevents electric field  108  from exposing on receiver coil  104  and generating an detrimental voltage on receiver coil  104 . Because transmitter shield  202  substantially blocks electric field  108  before it can reach receiver coil  104 , electric field  108  may generate voltage on transmitter shield  202  instead of receiver coil  104 . The amount of voltage generated on transmitter shield  202  may correspond to the amount of voltage that would have been generated on transmitter coil  104  had transmitter shield  202  not been present. 
     In some embodiments, voltage generated on transmitter shield  202  can be removed so that the voltage does not permanently remain on transmitter shield  202 . As an example, voltage on transmitter shield  202  can be discharged to ground. Thus, transmitter shield  202  can be coupled to a ground connection  206  to allow voltage on transmitter shield  202  to be discharged to ground. Ground connection  206  can be a ground ring or any other suitable conductive structure coupled to ground that can remove voltage from transmitter shield  202 . 
     Similar to transmitter shield  202 , a receiver shield  204  may also be implemented in wireless charging system  200  to prevent detrimental voltage from being generated on transmitter coil  102  from electric field  110  generated by receiver coil  104 . Receiver shield  204  may be positioned in front of receiver coil  104  so that magnetic flux  106  first passes through receiver shield  204  before exposing on receiver coil  104 . In some embodiments, receiver shield  204  is positioned within a housing of an electronic device within which receiver coil  104  is also disposed. Thus, receiver shield  204  can be positioned between interface  112  and receiver coil  104  when the electronic device rests on a wireless charging device to perform wireless power transfer. 
     Similar to transmitter shield  202 , receiver shield  204  can be substantially transparent to magnetic flux  106  so that a substantial percentage of magnetic flux  106  generated by transmitter coil  102  passes through receiver shield  204  and is received by receiver  104 , while receiver shield  204  can be substantially opaque to electric field  110  such that electric field  110  is substantially blocked by receiver shield  204 . This prevents electric field  110  from being exposed to transmitter coil  102  and generating an detrimental voltage on transmitter coil  102  while enabling wireless power transfer. Like transmitter shield  202 , receiver shield  204  may also be grounded so that voltage generated by electric field  110  may be discharged to a ground connection  208 . Ground connection  208  may be a structure similar to ground connection  206  in some embodiments, or it may be the same structure as ground connection  206  in other embodiments. 
     By incorporating transmitter and receiver shield  202  and  204  into wireless charging system  200 , the wireless charging device and the electronic device within which transmitter and receiver shields  202  and  204  are implemented are exposing their grounds to each other. This mutes any ground noise caused by the electrical interactions between transmitter and receiver coils  102  and  104 . 
     As can be appreciated by disclosures herein, transmitter shield  202  and receiver shield  204  are shielding structures that are able to block the passage of electric fields, yet allow the passage of magnetic flux. These shielding structures may include materials and thicknesses that are suitable for providing such electrical characteristics and functions. Details of the materials that can be used to form transmitter shields and receiver shields are discussed in further detail herein. 
     A. Shielding Material 
     According to some embodiments of the present disclosure, an electromagnetic shield, e.g., transmitter shield  202  and/or receiver shield  204 , can be formed of a material having properties that enable magnetic flux to pass through but prevent electric fields from passing through. In a first example, an electromagnetic shield can be formed of a non-conductive material. Non-conductive materials naturally allow magnetic flux to pass through but prevents electric fields from passing through. In a second example, transmitter shield  202  can be formed of a conductive material that has a plurality of apertures. The conductive nature of the material allows voltage to be discharged to ground and the apertures provide avenues through which magnetic flux may tunnel to expose on transmitter shield  202 . In a third example, transmitter shield  202  can be formed of a very thin conductive material that allows magnetic flux to pass through but prevents electric fields from passing through. The thickness of the conductive material can be thin enough to allow passage of magnetic flux and have low enough resistance to allow voltage to travel through the conductive material in an efficient manner. Materials of various conductive properties and thicknesses are discussed in  FIGS. 3 and 4  herein. 
       FIG. 3  is a graph  300  representing a measure of mutual inductance achieved between a transmitter coil and a receiver coil when a shielding layer, e.g., any one of transmitter shield  202  or receiver shield  204 , is disposed between the transmitter and receiver coils during wireless power transfer. The y-axis represents the percentage of mutual inductance attained between the transmitter and receiver coil increasing upward where 100% indicates that all of the magnetic flux generated by the transmitter coil is received by the receiver coil. The x-axis represents thickness of the shielding layer in a logarithmic scale ranging from 1.0E-05 to 1.0E-00 in millimeters increasing to the right. 
     Various curves are plotted against graph  300  as shown in  FIG. 3 . The various curves represent different conductive materials having different conductivities in terms of percentage of the conductivity of copper (i.e., % IACS, or percentage of the International Annealed Copper Standard). For instance, graph  300  may include curves representing materials having conductivities of 100% IACS, 10% IACS, 1% IACS, 0.1% IACS, 0.01% IACS, 0.001% IACS, and 0.001% IACS at a specific frequency of 10 MHz. Materials having higher conductivity, i.e., higher % IACS, means those materials are better at accommodating the movement of electric charge. The various curves can provide guidance on selecting material of a certain conductivity and thickness to allow a high percentage of mutual inductance between the transmitter and receiver coil. As shown, each curve represents an achievable mutual inductance between the transmitter and receiver coils based on its thickness for different materials having different conductivities. For instance, a transmitter shield formed of a material having a conductivity of 100% IACS may allow a mutual inductance of 100% when its thickness is approximately 1.0E-05 mm. In another example, a transmitter shield formed of a material having a conductivity of 1% IACS may allow a mutual inductance of 100% when its thickness is less than approximately 1.0E-03. Thus, as can be understood by graph  300 , materials having higher conductivity can decrease the mutual inductance between the transmitter and receiver coil, but this decrease in mutual inductance may be compensated by decreasing the thickness of the shield. Allowing higher mutual inductance means that the wireless charging system is transferring power more efficiently and that the shield has less negative impact on wireless power transfer. 
     In addition to conductivity and mutual inductance, the resistivity of a material may also be considered when determining a suitable material for forming the shield. This is because the material cannot be so resistive that it is too difficult to route voltage on the shield to ground.  FIG. 4  is a graph  400  representing an alternating current resistance (ACR) of a material based on its thickness. The ACR of a material represents the amount of resistance a material has when an alternating current (AC) voltage is applied. The y-axis represents the amount of resistance of a material in units of ohms increasing upward, and the x-axis represents thickness of the shielding layer in a logarithmic scale in millimeters increasing to the right. 
     Similar to graph  300  in  FIG. 3 , various curves are plotted against graph  400 . The various curves may be curves for conductive materials having different conductivity in terms of % IACS. As shown in  FIG. 4 , the curves represent materials having the same conductivities as those shown in graph  300  of  FIG. 3  for ease of reference and cross comparison. The various curves can provide guidance on selecting material of a certain resistance and thickness to form a shield that can enable the efficient discharge of accumulated voltage from an electric field without generating excessive heat. In  FIG. 4 , each curve may represent an amount of resistance based on its thickness for different materials having different conductivities. For instance, a transmitter shield formed of a material having a conductivity of 100% IACS may have a resistance of approximately 7 ohms when its thickness is approximately 1.0E-04 mm. In another example, a transmitter shield formed of a material having a conductivity of 1% IACS may have a resistance of approximately 10 ohms when its thickness is approximately 1.0E-02 mm. Thus, as can be understood by graph  400 , the ACR of a material can increase as thickness increases, but the ACR can be decreased by using materials with lower conductivity. Having higher resistance means that it is more difficult to discharge voltage accumulated on the shield. Moving voltage through a material having high resistance results in the dissipation of energy in the form of heat, which can decrease efficiency and cause damage to electrical components in excessive degrees. 
     In some embodiments, a transmitter shield and/or a receiver shield can be formed of a material that allows high mutual inductance of between 90-100% and a mutual ACR of less than 10 ohms with a desired thickness determined by device design constraints. Thus, an exemplary material that can be used to form a transmitter shield can include nickel vanadium (NiV) with a thickness ranging between 25 to 100 nm. In a particular embodiment, the transmitter shield is formed of NiV with a thickness of approximately 50 nm. An exemplary material that can be used to form a receiver shield can include silver with a thickness ranging between 0.05 and 0.15 μm. In a particular embodiment, the receiver shield is formed of silver with a thickness of approximately 0.1 μm. 
     Although the shields may be formed of a conductive material, other materials having similar properties can be used instead. For instance, a material including carbon may be used to form the electromagnetic shields. In an example, the transmitter shield may include carbon ink, such as N6X carbon ink. Such an ink can be easily customized to achieve the electrical properties desired to allow passage of magnetic flux while preventing passage of electric fields. As shown in  FIGS. 3 and 4 , carbon ink is represented by a vertical line. This is because the thickness of carbon ink is dictated by the process with which the carbon ink is deposited. For instance, typical printing processes can print carbon ink in thicknesses of approximately 25 μm. 
     B. Exemplary Wireless Charging System with Electromagnetic Shielding 
     As mentioned herein, a transmitter shield can be included in a wireless charging device, such as a wireless charging mat, and a receiver shield can be included in an electronic device configured to rest on the wireless charging device to wirelessly receiver power from the wireless charging mat.  FIG. 5  illustrates an exploded view of an exemplary wireless charging system  500  including a wireless charging device  502  and an electronic device  504 , each having electromagnetic shielding according to some embodiments of the present disclosure. Wireless charging device  502  can generate time-varying magnetic flux to induce a corresponding current in electronic device  504  for performing wireless power transfer. 
     Wireless charging mat  502  can include a housing formed of two shells: a first shell  505  and a second shell  506 . First shell  505  can mate with second shell  506  to form an interior cavity within which internal components may be positioned. First and second shells  505  and  506  can also include notches  508   a  and  508   b , respectively, that form an opening within the housing when first and second shells  505  and  506  are mated. An electrical connector  510 , such as a receptacle connector, can be positioned within the opening so that wireless charging mat  500  can receive power from an external power source through a cable connected to electrical connector  510 . In some embodiments, electrical connector  510  may include a plurality of contact pins and a plurality of terminals electrically coupled to the contact pins so that power can be routed from the external power source to the wireless charging mat  500  to provide power for wireless power transfer. 
     The interior cavity formed between mated first and second shells  505  and  506  can include components that generate the magnetic flux for performing the wireless charging of electronic device  504 . As an example, an array of transmitter coils  509  coupled to a driver board  510  can be housed within the inner cavity. Transmitter coils  509  can be operated to generate time-varying magnetic flux that propagate above the top surface of first shell  505  to induce a current in receiver coil  520  in electronic device  504 . Driver board  510  can be a printed circuit board (PCB) configured to route signals and power for operating transmitter coils  509 . 
     In addition to transmitter coils  509  and driver board  510 , wireless charging device  502  can also include a transmitter shield  512  according to some embodiments of the present disclosure. Transmitter shield  512  can be configured to allow passage of magnetic flux and to prevent passage of electric fields, as discussed herein with respect to transmitter shield  202  in  FIG. 2 . Accordingly, transmitter shield  512  can be positioned within wireless charging device  502  in a suitable location for blocking electric field from exposing on a receiver coil  520  in electronic device  504 . For example, transmitter shield  512  can be positioned in the direction of magnetic flux flow, such as between transmitter coils  509  and first shell  505 . 
     In some embodiments, first shell  505  includes a charging surface  514  upon which electronic device  504  having receiver coil  520  may be placed to receive power from wireless charging mat  502 . Charging surface  514  can be a generally planar region of a top surface of shell  505  where magnetic flux generated by transmitter coils  509  is present to induce a current in receiver coil  520  for charging an internal battery of electronic device  504 . Electronic device  504  may merely rest on charging surface  512  to receive power from wireless charging device  502 . The interface (e.g., interface  112  in  FIG. 1 ) where electronic device  504  makes contact with wireless charging device  502  can be a plane where respective housings of electronic device  504  and wireless charging device  502  make contact with each other. Magnetic flux generated by wireless charging device  502  can be shielded from internal components in electronic device  504  by a ferrite plate  522 . In some embodiments, ferrite plate  522  is positioned above receiver coil  520  so that magnetic flux is first exposed to receiver coil  520  before being blocked by ferrite plate  522 . 
     Electronic device  504  can include a top housing  526  and a bottom housing  528  that can mate to form an inner cavity that houses internal components, such as receiver coil  520  and ferrite plate  522 . According to some embodiments of the present disclosure, electronic device  504  can also include an electromagnetic shield within its inner cavity. For example, electronic device  504  can include a receiver shield  524  that can be configured to allow magnetic flux generated by transmitter coils  509  to be received by receiver coil  520  but prevent electric fields from receiver coil  520  from exposing on transmitter coils  509 , as discussed herein with respect to receiver shield  204  in  FIG. 2 . Receiver shield  524  can be positioned within electronic device  504  in a suitable location for blocking electric field from exposing on transmitter coils  509  in wireless charging device  502 . For example, receiver shield  524  can be positioned between receiver coils  520  and bottom housing  528 . In this position, the magnetic flux first passes through receiver shield  524  before exposing on receiver coil  520 . 
     Implementing transmitter shield  512  and receiver shield  524  allows mutual inductance to exist between transmitter coils  509  and receiver coil  520 , but prevents detrimental voltages from being generated in transmitter coils  509  and receiver coil  520 . Preventing these voltages from being generated improves the operation of both wireless charging device  502  and electronic device by avoiding electrical disturbances. 
     II. Structure of Electromagnetic Shielding 
     The transmitter shield and receiver shield can each be formed to have a specific structure suitable for implementation in a wireless charging system for performing wireless power transfer without generating detrimental voltages on the transmitter and receiver coils. Details of the structure of transmitter and receiver shields will be discussed further herein. 
     A. Transmitter Shield 
       FIG. 6  illustrates a top-down view of an exemplary transmitter shield  600 , according to some embodiments of the present disclosure. Transmitter shield  600  can be housed in a wireless charging device, such as a wireless charging mat, e.g., wireless charging mat  502  having transmitter shield  512  in  FIG. 5 . In some embodiments, transmitter shield  600  can have dimensions that correspond to the dimensions of the wireless charging device. For instance, transmitter shield  600  can be in the shape of a rectangle having a width W and a length L that correspond to the width and length of the wireless charging device. Although transmitter shield  600  can be in the shape of a rectangle, it is to be appreciated that embodiments are not so limited that transmitter shields in other embodiments can have any other shape that corresponds to a wireless charging device, such as a square, rectangle, hexagon, triangle, and the like. In some embodiments, a notch  606  may be formed at an edge of transmitter shield  600  to provide space for other components in a wireless charging mat, such as a receptacle connector for making connection with an external cable to receive power from an external source. 
     Transmitter shield  600  may be coupled to ground at its edges  602  to discharge any voltage on transmitter shield  600 . Voltage existing near the inner regions of transmitter shield  600  may have to travel to edges  602  by traversing across a large portion of transmitter shield  600 , which may cause difficulties in routing the voltage to ground, e.g., by creating larger resistances. Thus, in some embodiments, one or more conductive traces  604  may be embedded within transmitter shield  600  to assist with discharging voltage to ground. The low resistivity and high conductivity of traces  604  provides an avenue through which voltage can quickly travel to edges  602 . Accordingly, transmitter shield  600  may be able to quickly discharge voltage to ground. 
     In some embodiments, transmitter shield  600  can have dimensions that are suitable for shielding an array of transmitter coils disposed within the wireless charging device. For example,  FIG. 7  illustrates an exemplary wireless charging device  600  including transmitter shield  600  positioned over an array of transmitter coils  702 . Transmitter coils  702  may be similar in function and form to transmitter coils  509  in  FIG. 5 . Upper layers of wireless charging device  700  are not illustrated so that transmitter shield  600  and transmitter coils  702  can be seen. Additionally, transmitter coils  702  are illustrated with dotted lines to indicate that transmitter coils are disposed below transmitter shield  600 . Showing transmitter coils  702  helps to understand their relative position with respect to transmitter shield  600 . 
     As shown in  FIG. 7 , transmitter shield  600  is large enough to cover the entire array of transmitter coils  708  so that each transmitter coil is shielded by transmitter shield  600 . During operation, each transmitter coil  708  may generate magnetic flux that pass through transmitter shield  600  to induce a current on a receiver coil. Electric fields generated by the large voltage difference between a transmitter coil and a receiver coil may generate voltage in transmitter shield  600  around each transmitter coil. The generated voltage may flow across transmitter shield  600  to edges  602  and be discharged to ground. 
     As mentioned above, conductive traces  604  can be embedded in transmitter shield  600  to expedite the discharging of generated voltage on transmitter shield  600 . Conductive trances  604  can be positioned over respective transmitter coils to route these voltages to ground at edges  602 . Additionally, conductive traces  604  can be positioned orthogonal to the windings of each transmitter coil  702  to minimize current generation in conductive traces  604  during operation of transmitter coils  702 . This current can be generated by electrical interaction between conductive traces  604  and magnetic flux generated by transmitter coils  702 . The induced current may impede the ability to discharge voltage on transmitter shield  600 . Thus, arranging conductive traces  604  orthogonal to the winding of transmitter coils  702  may minimize this induced current. 
     In some embodiments, transmitter shield  600  can be formed of a structure that includes more than one layer of material.  FIG. 8  is a simplified diagram illustrating a cross section  800  of a transmitter shield and transmitter coils for a wireless charging device, according to some embodiments of the present disclosure. Specifically,  FIG. 8  illustrates a cross-section of exemplary transmitter coil  702  and transmitter shield  600  shown in  FIG. 6 . Transmitter shield  600  may be disposed above transmitter coils  702  so that magnetic flux generated by transmitter coils  702  may flow upward through transmitter shield  600  toward an interface surface  808 . Interface surface  808  may be a top surface of a housing of the wireless charging device, such as charging surface  514  in  FIG. 5 , that makes contact with a housing of an electrical device to perform wireless charging. Transmitter coils  702  can each be encapsulated by a protective layer such as coil encapsulating layer  810 . Encapsulating layer  810  can be formed of any suitable non-conductive material for protecting transmitter coils  702 , such as polyimide (PI). 
     According to embodiments of the present disclosure, transmitter shield  600  can include a conductive layer  802  for performing the electrical functions of transmitter shield  600 . For instance, conductive layer  802  can be a layer of conductive material having properties that allow magnetic flux to pass through transmitter shield  600  but prevent electric fields from passing through transmitter shield  600 , such as any of the conductive materials discussed herein with respect to  FIGS. 3 and 4 . In a particular embodiment, conductive layer  802  can be formed of NiV having a thickness of approximately 50 nm. 
     As mentioned herein, transmitter shield  600  can include conductive traces  604  for expediting the discharge of accumulated voltage from electric fields. As shown in  FIG. 8 , conductive traces  604  can be embedded within conductive layer  802  so that voltage existing in conductive layer  802  can flow into conductive traces  604  and be quickly routed to edges of transmitter shield  600  and discharged to ground. 
     Conductive layer  802  can be attached to a support structure configured to provide structural support for conductive layer  802 . As an example, conductive layer  802  can be attached to substrate  804 . In some embodiments, substrate  804  can be a base structure upon which conductive layer  802  may be deposited or laminated. Substrate  804  can be formed of a stiff material having a minimum thickness for surviving the deposition or lamination of conductive layer  802 . For instance, substrate  804  may be formed of polyethylene terephthalate (PET) having a thickness ranging between 20 to 30 μm, particularly 26 μm in certain embodiments. Thus, substrate  804  can provide structural support for conductive layer  802 . 
     In some embodiments, an adhesive layer  806  may fix conductive layer  802  over transmitter coils  702  so that conductive layer  802  is positioned to intercept electrical fields associated with transmitter coils  702  during wireless power transfer to prevent detrimental voltage from being generated on the receiver coil. Since transmitter coils  702  may not extend across the entire bottom surface of conductive layer  802 , adhesive layer  806  may not have to extend across the entire bottom surface of conductive layer  802  either. Instead, adhesive layer  806  can just extend far enough to sufficiently couple transmitter coils  702  conductive layer  802 . Accordingly, in some embodiments, adhesive layer  806  does not extend across the entire bottom surface of conductive layer  802 , thereby reducing manufacturing cost. Adhesive layer  806  can be formed of any suitable non-conductive adhesive material. For example, adhesive layer  806  can be formed of pressure sensitive adhesive (PSA). 
     B. Receiver Shield 
       FIG. 9  illustrates a top-down view of an exemplary receiver shield  900 , according to some embodiments of the present disclosure. Receiver shield  900  can be housed in an electronic device, such as a smart phone, smart watch, tablet, laptop, and the like, e.g., electronic device  504  having shield  524  in  FIG. 5 . In some embodiments, receiver shield  900  can have dimensions that correspond to the dimensions of a receiver coil. For instance, receiver shield  900  can be generally circular in shape, or any other shape that corresponds to a receiver coil, such as a square, rectangle, hexagon, triangle, and the like. Receiver shield  900  may have a gap  902  to provide an area where a connection to ground can be routed for discharging voltage generated on receiver shield  900 . Additionally, gap  902  can provide space for other components of the electronic device, such as connection terminals for a receiver coil, as will be discussed further herein. 
     In some embodiments, connection to ground can be established at an end  904  of receiver shield  900  closest to the top of gap  902  so that voltage generated on receiver shield  900  can be discharged to ground. While providing a connection to ground at end  904  helps discharge voltage on receiver shield  900 , performance of receiver shield  900  can be improved by including a cut  908  in receiver shield  900  positioned opposite of gap  902  to electrically separate receiver shield  900  into two halves: first half  910  and second half  912 . A connection to ground can be provided at end  906  closes to the bottom of gap  902  so that both halves  910  and  912  can be coupled to ground to discharge any voltage generated in receiver shield  900 . Without cut  908  in receiver shield  900 , the potential difference between ends  904  and  906  may be based on the voltage captured by the entire surface area of receiver shield  900 . This can cause a large potential difference to build up between ends  904  and  906 , and can be difficult to discharge to ground. By including cut  908 , the potential difference can be substantially decreased, such as by a half, thereby making it easier to discharge the voltage to ground. 
     Receiver shield  900  can have dimensions that are suitable for shielding a receiver coil disposed within the electronic device. For example,  FIG. 10  illustrates a top-down view of an exemplary receiver system  1000  for an electronic device. Receiver system  1000  can include receiver shield  900 , a ferrite plate  1002 , and a receiver coil  1004  positioned between receiver shield  900  and ferrite plate  1002 . Receiver coil  1004  is illustrated with dotted lines to indicate that transmitter coils are disposed behind receiver shield  900  as shown from the top-down perspective of  FIG. 10 . Showing receiver coil  1004  helps to understand its relative position with respect to receiver shield  900 . 
     As shown in  FIG. 10 , receiver shield  900  is large enough to cover the entire receiver coil  1004  so that receiver coil  900  is completely shielded by receiver shield  900 . In some embodiments, receiver coil  1004  can have a flat, disc-like shape formed of a winding of coil that is wound from an inner diameter to an outer diameter. Likewise, receiver shield  900  can also have a disk-like shape that has a corresponding inner and outer diameter. During operation, an electric field from receiver coil  900  can generate a voltage in receiver shield  900 . The generated voltage may flow across receiver shield  900  to at least one of ends  904  and  906  and be discharged to ground. 
     In some embodiments, connection terminals  1006  can be positioned in gap  902  of receiver shield  900 . Connection terminals  1006  can provide electrical routes through which current induced in receiver coil  1004  can be routed to provide power to charge a battery in the electronic device. Additionally, connection terminals  1006  can include ground lines for routing voltage in receiver shield  900  to ground. For instance, receiver shield  900  can include a single ground line for routing voltage from the entire receiver shield  900  to ground (e.g., in instances where cut  908  is not present), or it can include two ground lines, one for routing voltage from first half  910  of receiver shield  900  to ground, and another for routing voltage from a second half  912  of receiver shield  900  to ground. Each ground line can be positioned close to the respective end for which it discharges voltage to ground. For example, the ground line for grounding first half  910  can be positioned close to end  904 , while the ground line for grounding second half  912  can be positioned close to end  906 . 
     Ferrite plate  1002  can be positioned on a side of receiver coil  1004  opposite of the side on which receiver shield  900  is positioned. Ferrite plate  1002  can prevent magnetic flux and electrical fields from disturbing sensitive electrical components within the electronic device. In some embodiments, ferrite plate  1002  can be formed of any suitable ferromagnetic material. To better understand the structural layering of receiver system  1000 , a cross-sectional view of receiver system  1000  is shown in  FIG. 11 . 
       FIG. 11  is a simplified diagram illustrating a cross section  1100  of receiver system  1000 , according to some embodiments of the present disclosure. Receiver system  1000  can include receiver shield  900  coupled to receiver coil  1004 , which is coupled to ferrite plate  1002 . Receiver coil  1004  can be positioned below ferrite plate  1002  so that ferrite plate  1002  can protect sensitive electrical components from magnetic flux and electrical fields generated during wireless power transfer. Receiver shield  900  may be disposed below receiver coil  1004  so that magnetic flux generated by a transmitter may flow upward from interface surface  1108  through receiver shield  900  before being received by receiver coil  1004 . Interface surface  1108  may be a bottom surface of a housing of the electronic device that makes contact with a charging surface of a wireless charging device for performing wireless charging. Receiver coil  1004  can be encapsulated by a protective layer, such as coil encapsulating layer  1110 . Encapsulating layer  1110  can be formed of any suitable non-conductive material for protecting receiver coil  1004 , such as polyimide (PI). 
     According to embodiments of the present disclosure, receiver shield  900  can be formed of a layer of conductive material that can perform the electrical functions of a receiver shield discussed herein. For instance, receiver shield  900  can be a layer of conductive material having properties that allow magnetic flux to pass through receiver shield  900  but prevent electric fields from passing through receiver shield  900 , such as any of the conductive materials discussed herein with respect to  FIGS. 3 and 4 . In a particular embodiment, receiver shield  900  can be formed of silver, such as silver flake, having a thickness of approximately 0.1 μm. 
     Receiver shield  900  can be coupled to receiver coil  1004  by an adhesive layer  1102 . Adhesive layer  1102  may fix receiver shield  900  underneath receiver coil  1004  so that receiver shield  900  is positioned to intercept electrical fields associated with receiver shield  900  during wireless power transfer to prevent detrimental voltage from being generated on the transmitter coil. In some embodiments, adhesive layer  1102  can be configured to route voltage to ground by coupling with a connection terminal, such as connection terminal  1006  in  FIG. 10 . Thus, adhesive layer  1102  can be formed of any suitable conductive adhesive material. For example, adhesive layer  1102  can be formed of conductive pressure sensitive adhesive (CPSA). 
     In some embodiments, receiver shield  900  can be covered by a protective layer  1104 . Protective layer  1104  can be positioned below receiver shield  900  to cover any exposed surfaces and prevent receiver shield  900  from oxidizing. Protective layer can be formed of any suitable dielectric material. 
     Spatially relative terms, such as “bottom,” “top,” “upward,” or “downward” and the like may be used to describe an element and/or feature&#39;s relationship to another element(s) and/or feature(s) as, for example, illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use and/or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as a “bottom” surface may then be oriented “above” other elements or features. The device may be otherwise oriented (e.g., rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     Although the invention has been described with respect to specific embodiments, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.

Metadata:
Filing Date: 20170911
Publication Date: 20210202
Grant Date: 20210202
Priority Date: 20160923
Inventors: ELKAYAM, SHIMON
GARBUS, BRANDON R.
GRAHAM, Christopher S.
LARSSON, KARL RUBEN F.
Assignee: APPLE INC
CPC Classifications: [{"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/402", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": true, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/10", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J50/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H02J7/025", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01F38/14", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 61686717