Patent Publication Number: US-2020279686-A1

Title: Coil, wireless charging receiving apparatus, wireless charging transmission apparatus, and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2018/116329, filed on Nov. 20, 2018, which claims priority to Chinese Patent Application No. 201711483128.8, filed on Dec. 29, 2017, Chinese Patent Application No. 201711161042.3, filed on Nov. 20, 2017. All of the aforementioned patent applications are hereby incorporated by reference in their entireties 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate to the field of wireless charging, and more specifically, to a coil and a wireless charging apparatus and system. 
     BACKGROUND 
     As mobile terminals are widely used, there is an increasingly growing need for wireless charging. When all mobile terminals including smartphones support wireless charging in the future, users no longer need to waste time or efforts in searching for chargers, charging USB cables, or sockets. A mobile phone can be charged without a need to be physically connected to any power supply, and there is no need to worry that the mobile phone cannot be powered on because a battery runs out. 
     However, in a current mobile phone, wireless charging using maximum power cannot be implemented due to heat dissipation, and a charging current is limited. To further improve a charging speed, wireless charging efficiency needs to be improved. During wireless charging, energy is transmitted mainly based on a magnetic coupling principle of a transmission coil and a receiving coil. Therefore, there is a very strong alternating current magnetic field between the transmission coil and the receiving coil. As shown in  FIG. 1 a   , a metal coil is placed in an alternating current magnetic field, and the alternating current magnetic field cuts through a metal conductor and induces an eddy current, leading to an eddy current loss. A magnitude of the eddy current is directly proportional to a size of a metal area. Therefore, a larger area of a coil indicates a larger eddy current loss in the coil in the same magnetic field, and if a transmission coil and a receiving coil have very large eddy current losses, wireless charging efficiency is low. If a coil is merely made thinner, charging efficiency is very low, and even is lower than 50%. This is because an alternating current passes through the coil, a loss in the coil is obtained by multiplying a current by alternating current resistance, and the alternating current resistance includes direct current resistance (in a coil in some approaches, alternating current resistance is approximately 1.5 to 2 times as large as direct current resistance). If the coil is made thinner, the direct current resistance is greatly increased. Consequently, a final alternating current resistance is greatly increased, the loss in the coil is increased, and charging efficiency is reduced. As shown in  FIG. 1 b   , in particular, in a charging status in which a mobile phone does not exactly face a wireless charger, very large eddy current losses are caused in a wireless charging coil of the wireless charger and a wireless charging receiving coil of the mobile phone by a magnetic field in a wireless charging process. 
     SUMMARY 
     Embodiments of this application provide a coil structure. A slot is disposed on the coil, so that a loss in the coil in a wireless charging process can be effectively reduced, and wireless charging efficiency can be improved. 
     Technical solutions according to embodiments discussed herein are as follows: 
     According to a first aspect, a coil is provided. The coil includes an output terminal, an input terminal, and a wire-winding part that is connected between the output terminal and the input terminal. A slot is disposed on at least a part of the wire-winding part, and a depth of the slot in any direction of a cross section of the wire-winding part is less than or equal to a distance between two points that are the farthest away from each other on the cross section of the wire-winding part, to reduce an eddy current loss caused in the coil by a magnetic field. The wire-winding part is a metal conductor made through spiral winding. The input terminal and the output terminal are configured to connect the wire-winding part to an external circuit. 
     When the coil in this application is applied to a wireless charging scenario, under the action of an alternating current magnetic field, the slot is disposed on the coil, so that a closed-loop path generated by an eddy current that is generated by the alternating current magnetic field in a wire-winding metal conductor of the coil is cut off, and resistance caused by the eddy current in the winding of the coil is greatly reduced. In addition, a decrease amplitude of the resistance caused by the eddy current is greater than an increase amplitude of direct current resistance in the wire-winding metal conductor of the coil, so that alternating current resistance in the winding of the coil in the wireless charging scenario is reduced on the whole. 
     In embodiments of this application, a ratio of the alternating current resistance to the direct current resistance in the coil is approximately 1.3, so that a percentage of the resistance generated by the eddy current in the coil is greatly reduced, a loss in the coil is reduced, and charging efficiency is improved. In particular, in a charging status in which a mobile phone does not exactly face a wireless charger, the slot is disposed to partially cut off an eddy current path generated by magnetic lines in the alternating current magnetic field in the winding of the coil, where an angle between a plane of the coil and the magnetic lines is relatively large. This can greatly reduce an eddy current loss generated by the wireless charging magnetic field in the winding of the coil. 
     Optionally, the slot extends in a winding length direction of the wire-winding part, and a length of the slot is equal to a length of the wire-winding part; or the slot is disposed in segments in a winding length direction of the wire-winding part, and a length of the slot is less than a length of the wire-winding part. 
     Optionally, a width of at least one turn of winding of the wire-winding part is not equal to a width of other winding. 
     Optionally, a width of the wire-winding part increases as a winding radius increases, so that a width of an inner ring of the wire-winding part is less than a width of an outer ring. The width of the wire-winding part increases as the winding radius increases on the whole, but it is not excluded that there is an exceptional case for a particular turn of the coil. 
     Optionally, when the slot cuts through the wire-winding part in any direction of the cross section of the wire-winding part, the slot enables at least a part of the wire-winding part to form at least two conductive paths that are connected in parallel, and a parallel connection point of the at least two conductive paths that are connected in parallel is disposed on an uncut part of the wire-winding part, or is disposed on the input terminal and the output terminal, or is directly disposed on a connection terminal of the external circuit. 
     Optionally, when the coil is a two-layer coil, the slot is disposed on at least one layer of the coil. 
     Optionally, when the coil is a two-layer coil, the wire-winding part of the coil includes a first-layer wire-winding part and a second-layer wire-winding part, and the input terminal or the output terminal is located at a first layer of the coil or a second layer of the coil; 
     the output terminal includes a first part of the output terminal and a second part of the output terminal; 
     one end of the first part of the output terminal is connected to an innermost-turn coil of the first-layer wire-winding part, and the first part of the output terminal and the first-layer wire-winding part are located on a same plane; and 
     the second part of the output terminal and the second-layer wire-winding part are located on a same plane, one end of the second part of the output terminal is used as an output end of the coil and is connected to the external circuit, and the other end of the second part of the output terminal and the other end of the first part of the output terminal are connected in series via a through hole disposed between the first-layer wire-winding part and the second-layer wire-winding part. 
     Optionally, one end of the input terminal is connected to an outermost turn of the first-layer wire-winding part or the second-layer wire-winding part, and the other end is connected to the external circuit. 
     Optionally, the first-layer wire-winding part and the second-layer wire-winding part are separately cut off at the input terminal or the output terminal, and the first-layer wire-winding part and the second-layer wire-winding part are connected in parallel via the through hole. 
     Optionally, there are one or more slots, and a projection shape of the slot on a plane of the coil includes one or more of a strip shape, a hole shape, an arc shape, a wavy shape, and a comb shape. A shape of the slot is not limited to the foregoing listed shapes. 
     Optionally, a projection shape of the wire-winding part on the plane of the coil is a ring shape, an elliptical ring shape, or an irregular ring shape. A shape of the coil is not limited to the foregoing listed shapes. 
     According to a second aspect, a wireless charging receiving apparatus of a mobile terminal is provided, includes a matching circuit, an AC/DC conversion module, and a control unit, and further includes the coil in the first aspect and various optional implementations of the first aspect. 
     The matching circuit is connected between the coil and the AC/DC conversion module, and is configured to generate resonance with the coil, so that alternating current energy received by a receiving coil is efficiently transmitted to a to-be-charged device. 
     The control unit is configured to control the AC/DC conversion module to convert an alternating current signal received by the coil into a direct current signal, to supply power to a load in the mobile terminal. 
     In embodiments of this application, the coil is applied to a wireless charging scenario, and for the receiving coil in the wireless charging receiving apparatus, for example, a mobile phone, a slot is disposed on the receiving coil in the wireless charging receiving apparatus, for example, the mobile phone, so that an induced current generated in the receiving coil under the action of an alternating current magnetic field is the same as a current generated in the receiving coil when the receiving coil is not cut through, in other words, energy received by the receiving coil is the same as energy received when the receiving coil is not cut through, but alternating current resistance in the receiving coil is reduced, reducing an energy loss in the receiving coil. 
     Optionally, the wireless charging receiving apparatus of the mobile terminal further includes a magnetic conductive sheet, and the magnetic conductive sheet is disposed on a side, away from a transmission apparatus, of a plane of the coil, and is configured to prevent leakage of a magnetic field generated by the wire-winding part. The transmission apparatus is configured to charge the wireless charging receiving apparatus of the mobile terminal. 
     Optionally, there are one or more coils. 
     According to a third aspect, a wireless charging transmission apparatus of a mobile terminal is provided, and includes a direct current power supply, a DC/AC conversion module, a matching circuit, a transmission coil, and a control unit. The transmission coil is the coil in the first aspect and various optional implementations of the first aspect. 
     the control unit is configured to control the DC/AC conversion module to convert a signal of the direct current power supply into an alternating current signal, and control the alternating current signal to pass through the matching circuit and the transmission coil, so that the transmission coil transmits alternating current energy. 
     In the solution of this application, the slot is disposed on the transmission coil of the wireless charging transmission apparatus, and a wire-winding part of the transmission coil is cut or partially cut, so that when the wireless charging transmission apparatus works in a wireless charging alternating current magnetic field, under the action of the wireless charging alternating current magnetic field, alternating current resistance in the transmission coil is reduced, reducing an energy loss in the transmission coil. 
     According to a fourth aspect, a wireless charging system of a mobile terminal is provided, and includes the wireless charging receiving apparatus of the mobile terminal in the second aspect and various optional implementations of the second aspect and the wireless charging transmission apparatus of the mobile terminal in the third aspect. The wireless charging transmission apparatus of the mobile terminal is configured to charge the wireless charging receiving apparatus of the mobile terminal. 
     Specifically, in embodiments of this application, the slot is disposed on the receiving coil, so that thickness of the receiving coil is reduced or a cross-sectional area is reduced, and the direct current resistance in the coil is increased to some extent. However, in the wireless charging scenario, approximately at least 30% of the alternating current resistance in the coil is not caused by the direct current resistance in the coil, and this part of resistance is actually an equivalent resistance, namely, an eddy current resistance, that is lost because a current is generated in a metal conductor of the coil when a magnetic field generated in a wireless charging process cuts through the metal conductor. When the metal conductor of the coil is cut through by the wireless charging magnetic field, an eddy current closed-loop path is generated in the metal conductor of the coil, and this part of eddy current cannot form an effective output current in the coil, and increases an energy loss in the coil. The coil is cut or partially cut, so that the eddy current closed-loop path that is generated when the metal conductor of the coil is cut through by the wireless charging magnetic field can be cut off, reducing an eddy current loss in the receiving coil. In addition, in this application, the coil is cut, so that a decrease amplitude of the energy loss generated by the eddy current in the receiving coil is greater than a loss caused by an increase in the direct current resistance in the coil, reducing a loss of the alternating current resistance in the coil on the whole. 
     In short, the slot is disposed on the receiving coil, so that the closed-loop path generated by the eddy current in the metal conductor of the coil is cut off, and resistance caused by the eddy current in the receiving coil is greatly reduced. In addition, a decrease amplitude of the resistance caused by the eddy current is greater than an increase amplitude of the direct current resistance, so that the alternating current resistance in the coil in the wireless charging scenario is reduced on the whole. In embodiments of this application, the ratio of the alternating current resistance to the direct current resistance in the coil is approximately 1.3, so that the percentage of the resistance generated by the eddy current in the coil is greatly reduced, the loss in the coil is reduced, and charging efficiency is improved. In particular, in a charging status in which the mobile phone does not exactly face the wireless charger, the eddy current path generated by the magnetic lines in the coil in the wireless charging process is cut off, where the angle between the plane of the coil and the magnetic lines is relatively large, so that the eddy current loss generated by the wireless charging magnetic field in the coil can be greatly reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1 a    is a schematic diagram of a magnetic circuit of a wireless charging system of a mobile terminal; 
         FIG. 1 b    is a schematic diagram of a magnetic circuit of a wireless charging system of a mobile terminal; 
         FIG. 2  is a schematic diagram of a wireless charging receiving apparatus of a mobile terminal according to an embodiment of this application; 
         FIG. 3 a    is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 3 b    is a schematic structural diagram of a cross section of a coil according to another embodiment of the present invention; 
         FIG. 3 c    is a schematic diagram of a coil and a magnetic conductive sheet according to another embodiment of this application; 
         FIG. 3 d    is a schematic structural diagram of cross sections of a coil and a magnetic conductive sheet according to another embodiment of this application; 
         FIG. 4  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 5  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 6  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 7 a    is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 7 b    is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 8  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 9  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 10  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 11  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 12  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 13  is a schematic diagram of a coil according to another embodiment of this application; 
         FIG. 14  is a schematic diagram of a wireless charging transmission apparatus according to another embodiment of this application; 
         FIG. 15 a    and  FIG. 15 b    are a schematic diagram of a wireless charging system according to another embodiment of this application; 
         FIG. 16 a    and  FIG. 16 b    are schematic diagrams of a coil according to another embodiment of this application; and 
         FIG. 17 a    and  FIG. 17 b    are schematic diagrams of a coil according to another embodiment of this application. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following clearly describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. 
     It should be understood that the embodiments of the present invention may be applied to various charging scenarios, and a mobile terminal is not limited to a smartphone, a tablet computer, or a wearable device, and is not limited to various mobile terminal devices such as an electric automobile. This is not limited in the embodiments of the present invention. 
       FIG. 2  shows a wireless charging receiving apparatus of a mobile terminal in some embodiments of the present invention. The wireless charging receiving apparatus of the mobile terminal is disposed inside the mobile terminal, for example, inside a mobile phone. The wireless charging receiving apparatus of the mobile terminal is configured to receive energy transmitted by a wireless charging transmission apparatus, and the wireless charging transmission apparatus is a wireless charger or the like, and is configured to charge the mobile terminal. The wireless charging receiving apparatus of the mobile terminal includes a wireless charging receiving coil, a matching circuit  20 , an AC/DC conversion module, a control unit, and a load output. The wireless charging receiving coil is at least one of coils shown in  FIG. 3 a   ,  FIG. 3 b   , and  FIG. 4  to  FIG. 13 . For example, the coil is the coil shown in  FIG. 3 a   . The coil includes an output terminal  304 , an input terminal  303 , and a wire-winding part  302  that is connected between the output terminal  304  and the input terminal  303 . A slot  305  is disposed on at least a part of the wire-winding part  302 , and a depth of the slot  305  in any direction of a cross section of the wire-winding part is less than or equal to a distance between two points that are the farthest away from each other on the cross section of the wire-winding part, to reduce an eddy current loss caused in the coil by a magnetic field. The wire-winding part  302  is a metal conductor made through spiral winding. The input terminal  303  and the output terminal  304  are configured to connect the wire-winding part  302  to an external circuit. The wire-winding part  302  is configured to cut through the magnetic field in a wireless charging scenario, to generate an induced current. The wire-winding part  302  is a metal conductor made through spiral winding. The input terminal  303  and the output terminal  304  are configured to connect the wire-winding part to the external circuit, to supply the induced current to a load of the external circuit for use. When the wireless charging receiving apparatus of the mobile terminal receives the energy transmitted by the wireless charging transmission apparatus, the wireless charging receiving coil is configured to receive an alternating current signal transmitted by a transmission coil of the wireless charging transmission apparatus. The alternating current signal is transmitted to the AC/DC conversion module by using the receiving coil and the matching circuit  20 . The AC/DC conversion module converts the received alternating current signal into a direct current signal, to charge load in the mobile terminal. The control unit of the wireless charging receiving apparatus of the mobile terminal controls working of the wireless charging receiving coil, the matching circuit  20 , and the AC/DC conversion module. 
     Further, as shown in  FIG. 3 c   , the wireless charging receiving apparatus further includes a magnetic conductive sheet  301 , the magnetic conductive sheet is disposed on a side, away from the transmission apparatus, of a plane of the coil, and is configured to prevent leakage of a magnetic field generated by the wire-winding part. The transmission apparatus is configured to charge the wireless charging receiving apparatus of the mobile terminal. The magnetic conductive sheet  301  plays a magnetic conductive role, so that an inductance value of the wire-winding part  302  can be increased. In addition, the magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield a component below the magnetic conductive sheet. The magnetic conductive sheet  301  may be made of a magnetic material such as ferrite or amorphous-nanocrystalline.  FIG. 3 d    is a schematic structural diagram of cross sections of the coil and the magnetic conductive sheet that are shown in  FIG. 3   c.    
     In this application, the coil is applied to the wireless charging scenario, and for the receiving coil in the wireless charging receiving apparatus, for example, a mobile phone, the slot is disposed on a part of the receiving coil in the wireless charging receiving apparatus, for example, the mobile phone, so that an induced current generated in the receiving coil under the action of an alternating current magnetic field is the same as a current generated in the receiving coil when the receiving coil is not cut through, in other words, energy received by the receiving coil is the same as energy received when the receiving coil is not cut through, but alternating current resistance in the receiving coil is reduced, reducing an energy loss in the receiving coil. 
       FIG. 3 a    is a schematic diagram of a coil according to an embodiment of this application. The coil includes an output terminal  304 , an input terminal  303 , and a wire-winding part  302  that is connected between the output terminal  304  and the input terminal  303 . A slot  305  is disposed on at least a part of the wire-winding part  302 , and a depth of the slot  305  in any direction of a cross section of the wire-winding part is less than or equal to a distance between two points that are the farthest away from each other on the cross section of the wire-winding part, to reduce an eddy current loss caused in the coil by a magnetic field. The wire-winding part  302  is a metal conductor made through spiral winding. The input terminal  303  and the output terminal  304  are configured to connect the wire-winding part  302  to an external circuit. 
     When the coil in this application is applied to a wireless charging scenario, under the action of an alternating current magnetic field, the slot is disposed on the coil, so that a closed-loop path generated by an eddy current that is generated by the alternating current magnetic field in a wire-winding metal conductor of the coil is cut off, and resistance caused by the eddy current in the winding of the coil is greatly reduced. In addition, a decrease amplitude of the resistance caused by the eddy current is greater than an increase amplitude of direct current resistance in the wire-winding metal conductor of the coil, so that alternating current resistance in the winding of the coil in the wireless charging scenario is reduced on the whole. 
     In this application, a ratio of the alternating current resistance to the direct current resistance in the coil is approximately 1.3, so that a percentage of the resistance generated by the eddy current in the coil is greatly reduced, a loss in the coil is reduced, and charging efficiency is improved. In particular, in a charging status in which a mobile phone does not exactly face a wireless charger, the slot is disposed to partially cut off an eddy current path generated by magnetic lines in the alternating current magnetic field in the winding of the coil, where an angle between a plane of the coil and the magnetic lines is relatively large. This can greatly reduce an eddy current loss generated by the wireless charging magnetic field in the winding of the coil. 
     Further, the slot extends in a winding length direction of the wire-winding part, and a length of the slot is equal to a length of the wire-winding part; or the slot is disposed in segments in a winding length direction of the wire-winding part, and a length of the slot is less than a length of the wire-winding part. 
     Further, a width of at least one turn of winding of the wire-winding part is not equal to a width of other winding(s). 
     Further, a width of the wire-winding part increases as a winding radius increases, so that a width of an inner ring of the wire-winding part is less than a width of an outer ring. The width of the wire-winding part increases as the winding radius increases on the whole, but it is not excluded that there is an exceptional case for a particular turn of the coil. 
     Optionally, when the slot cuts through the wire-winding part in any direction of the cross section of the wire-winding part, the slot enables at least a part of the wire-winding part to form at least two conductive paths that are connected in parallel, and a parallel connection point of the at least two conductive paths that are connected in parallel is disposed on an uncut part of the wire-winding part, or is disposed on the input terminal and the output terminal, or is directly disposed on a connection terminal of the external circuit. 
     Further, when the coil is a two-layer coil, the slot is disposed on at least one layer of the coil. 
     Further, when the coil is a two-layer coil, the wire-winding part of the coil includes a first-layer wire-winding part and a second-layer wire-winding part, and the input terminal or the output terminal is located at a first layer of the coil or a second layer of the coil. 
     The output terminal includes a first part of the output terminal and a second part of the output terminal. 
     One end of the first part of the output terminal is connected to an innermost-turn coil of the first-layer wire-winding part, and the first part of the output terminal and the first-layer wire-winding part are located on a same plane. 
     The second part of the output terminal and the second-layer wire-winding part are located on a same plane, one end of the second part of the output terminal is used as an output end of the coil and is connected to the external circuit, and the other end of the second part of the output terminal and the other end of the first part of the output terminal are connected in series via a through hole disposed between the first-layer wire-winding part and the second-layer wire-winding part. 
     Further, one end of the input terminal is connected to an outermost turn of the first-layer wire-winding part or the second-layer wire-winding part, and the other end is connected to the external circuit. 
     Further, the first-layer wire-winding part and the second-layer wire-winding part are separately cut off at the input terminal or the output terminal, and the first-layer wire-winding part and the second-layer wire-winding part are connected in parallel via the through hole. 
     Further, there are one or more slots, and a projection shape of the slot on a plane of the coil includes one or more of a strip shape, a hole shape, an arc shape, a wavy shape, and a comb shape. A shape of the slot is not limited to the foregoing listed shapes. 
     Further, a projection shape of the wire-winding part on the plane of the coil is a ring shape, an elliptical ring shape, or an irregular ring shape. A shape of the coil is not limited to the foregoing listed shapes. 
     Further, as shown in  FIG. 3 c   , the wireless charging receiving apparatus further includes a magnetic conductive sheet  301 , the magnetic conductive sheet is disposed on a side, away from a transmission apparatus, of the plane of the coil, and is configured to prevent leakage of a magnetic field generated by the wire-winding part. The transmission apparatus is configured to charge the wireless charging receiving apparatus of the mobile terminal. The magnetic conductive sheet  301  plays a magnetic conductive role, so that an inductance value of the wire-winding part  302  can be increased. In addition, the magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield a component below the magnetic conductive sheet. The magnetic conductive sheet  301  may be made of a magnetic material such as ferrite or amorphous-nanocrystalline. 
     In the solution of this application, the slot is disposed on the coil, so that the direct current resistance in the coil is increased to some extent, and the alternating current resistance in the coil is also increased. However, in the wireless charging scenario, approximately 50% to 100% of the alternating current resistance in the coil is not caused by the direct current resistance in the coil, and this part of resistance is actually caused by cutting through the magnetic field in the wireless charging scenario by the metal conductor of the coil. The coil of the wireless charging coil is cut or partially cut in the winding length direction, and an eddy current that is generated in the metal conductor of the wire-winding part  302  of the coil because the coil cuts through the magnetic field in the wireless charging scenario can be cut off, so that a final alternating current resistance in the coil is reduced. In short, the coil is cut, so that resistance caused by the eddy current that is generated by the alternating current magnetic field in the coil is greatly reduced, and finally, the alternating current resistance is greatly reduced. In this application, a ratio of the alternating current resistance to the direct current resistance is approximately 1.3 after optimization, greatly reducing a percentage of an eddy current resistance. 
     In conclusion, the slot is disposed on the coil in the wireless charging receiving apparatus, so that an eddy current closed loop generated by the wireless charging magnetic field in the coil is cut off, and the eddy current resistance is reduced. In addition, the decrease amplitude of the eddy current resistance is greater than the increase amplitude of the direct current resistance in the coil, so that the alternating current resistance in the coil in the wireless charging receiving apparatus is reduced, an energy loss in the charging process is reduced, and charging efficiency is improved. 
     Further, a total length of all slots on the wireless charging receiving coil having the slot accounts for at least 10% of a length of this turn of the wire-winding part. Further, a ratio of a width of the slot to a width of the wire-winding part  302  is less than or equal to 70%. 
       FIG. 3 b    is a sectional view of the coil in  FIG. 3 a    in an AA′ direction.  FIG. 3 d    is a schematic structural diagram of a cross section of the coil and shows a distribution status of magnetic fields near the coil in the solution of this application in a wireless charging process. Lines shown by  306  are alternating current magnetic lines generated by an alternating current in the wireless charging process. When the alternating current magnetic lines  306  pass through the wire-winding part  302 , an induced voltage V ac  may be induced, and the induced voltage V ac  is directly proportional to the width of the wire-winding part  302 . A larger width of wire-winding part  302  leads to a larger induced voltage V ac . Because the wire-winding part  302  is a conductor, the induced voltage V ac  generates an induced current I ac  in the wire-winding part  302 , the induced current I ac  causes a loss in the wire-winding part  302 , and the loss is directly proportional to the square of the induced voltage V ac  or the square of the induced current I ac . In a prior-art solution, the wire-winding part  302  is relatively wide, and consequently an eddy current loss is very large. In the solution of the present invention, the slot  305  is disposed on the coil in the wireless charging receiving apparatus, and two cases are specifically included. In one case, the slot  305  cuts through the coil. In the other case, the slot  305  having a preset depth is disposed on the coil, but the slot does not cut through the coil. Therefore, the eddy current loss in the wire-winding part  302  can be greatly reduced, and wireless charging efficiency can be improved. An adhesive layer  307  in the figure is configured to connect the wire-winding part  302  to the magnetic conductive sheet  701 , and the adhesive layer  307  includes an adhesive such as glue. 
       FIG. 4  is a schematic diagram of a coil according to an embodiment of this application. The coil includes a magnetic conductive sheet  401 , an output terminal  404 , an input terminal  403 , and a wire-winding part  402  that is connected between the output terminal  404  and the input terminal  403 . A slot  405  is disposed on the wire-winding part  402 , and the slot  405  cuts a part of the wire-winding part  402  into a structure including at least two conductive paths connected in parallel. The wire-winding part  402  is configured to cut through a magnetic field to generate an induced current. The input terminal  403  and the output terminal  404  are configured to connect the wire-winding part  402  to an external circuit, to supply the induced current to the external circuit for use. The wire-winding part  402  is made by spirally winding a metal conductor, and turns of the metal conductor are insulated from each other. At a winding start end and a winding termination end, the wireless charging wire-winding part  402  is connected to the external circuit by the input terminal  403  and the output terminal  404 , so that a current passes through the wireless charging coil and forms a magnetic field. The magnetic conductive sheet  401  plays a magnetic conductive role, so that an inductance value of the wire-winding part  402  can be increased. In addition, the magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield the space below the magnetic conductive sheet. The magnetic conductive sheet  401  may be made of a magnetic material such as ferrite or amorphous-nanocrystalline. The magnetic conductive sheet  401  is insulated from the wire-winding part  402 . In this embodiment of the present invention, a plurality of slots  405  are further included. The slot  405  cuts a part of the metal conductor of the wire-winding part  402  into two small windings having relatively small conductor widths, reducing an eddy current loss in the wire-winding part  402 . In particular, there may be a plurality of slots  405  in a width direction of the metal conductor of the wire-winding part  402 , and only one slot is shown in this embodiment. 
       FIG. 5  shows an electric coil in some embodiments of this application. The electric coil includes a magnetic conductive sheet  501 , a wire-winding part  502 , an input terminal  503 , an output terminal  504 , and a slot  505 . The wire-winding part  502  is made by spirally winding a metal conductor by a plurality of turns, and the turns of the metal conductor are insulated from each other. At a winding start end and a winding termination end, the wireless charging wire-winding part  502  is connected to an external circuit by the input terminal  503  and the output terminal  504 , so that a current passes through a wireless charging coil and forms a magnetic field. The magnetic conductive sheet  501  plays a magnetic conductive role, so that an inductance value of the wire-winding part  502  can be increased. In addition, the magnetic field is prevented from leaking to space below the magnetic conductive sheet  501 , to better shield the space below the magnetic conductive sheet  501 . The magnetic conductive sheet  501  may be made of a magnetic material such as ferrite or amorphous-nanocrystalline. The magnetic conductive sheet  501  is insulated from the winding  502 . In this embodiment of the present invention, a plurality of slots  505  in an irregular shape are further included, and the slots may be in various shapes such as a wavy shape, a jagged shape, and an oblique line shape. The slots shown in this embodiment are in the wavy shape. The slot  505  divides a part of a wound wire of the wire-winding part  502  into two small windings having relatively small conductor widths, reducing an eddy current loss in the wire-winding part  502 . Parts that are not cut by the slot  505  and that are of the wire-winding part  502  have relatively large conductor widths, and therefore direct current resistance is relatively small. In this solution, an eddy current loss and a direct current loss can be balanced based on a specific application scenario. 
       FIG. 6  shows a coil in some embodiments of this application. The coil includes a magnetic conductive sheet  601 , a wire-winding part  602 , an input terminal  603 , an output terminal  604 , and a slot  605 . The wire-winding part  602  is made by winding a plurality of turns of metal having unequal widths, and the turns of the metal are insulated from each other. At a winding start end and a winding termination end, the wireless charging wire-winding part  602  is connected to an external circuit by the input terminal  603  and the output terminal  604 , so that a current passes through the wireless charging coil and forms a magnetic field. The magnetic conductive sheet  601  plays a magnetic conductive role, so that an inductance value of the wire-winding part  602  can be increased. In addition, the magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield the space below the magnetic conductive sheet. The magnetic conductive sheet  601  may be made of one or more magnetic materials such as ferrite or amorphous-nanocrystalline. The magnetic conductive sheet  601  is insulated from the wire-winding part  602 . The slot  605  divides the wire-winding part  602  into two windings of relatively small widths at a location, having a relatively large conductor width, of the wire-winding part  602 , effectively reducing an eddy current loss in the wire-winding part  602 . In addition, in this embodiment, the wire-winding part  602  is made through winding by using windings having unequal widths. Compared with a winding manner using equal widths, in this embodiment, alternating current resistance in the wire-winding part  602  can be effectively reduced, and wireless charging efficiency can be improved. 
       FIG. 7 a    shows a coil in some embodiments of this application. The coil includes a magnetic conductive sheet  701 , a wire-winding part  702 , an input terminal  703 , an output terminal  704 , and a slot  705 . The wire-winding part  702  is made through parallel winding of a first-layer winding  702   a  and a second-layer winding  702   b , and the wire-winding part  702  is connected to an external circuit by using the input terminal  703  and the output terminal  704 . The magnetic conductive sheet  701  is located below the second-layer winding  702   b , and is insulated from the wire-winding part  702 . The magnetic conductive sheet  701  plays a magnetic conductive role, so that an inductance value of the wire-winding part  702  can be increased. In addition, a magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield the space below the magnetic conductive sheet  701 . The magnetic conductive sheet  701  may be made of one or more magnetic materials such as ferrite or amorphous-nanocrystalline. The second-layer winding  702   b  and the magnetic conductive sheet  701  are connected by using an adhesive, for example, by using glue. 
       FIG. 7 b    is a schematic diagram of a section of the coil in  FIG. 7 a    at a BB′ location. The slot  705  divides the first-layer winding  702   a  into two windings having relatively small conductor widths, and the second-layer winding  702   b  is a complete winding having a relatively large conductor width. In this embodiment, only  702   a  is cut by the slot  705  into two windings having relatively small conductor widths. In another application, similar to  702   a ,  702   b  may also be cut into two windings having relatively small conductor widths, and the slot  705  may cut only a part of winding of the wire-winding part  702  by using a method similar to the method shown in Embodiment 2. 
       FIG. 8  shows a coil in some embodiments of this application. The coil includes a magnetic conductive sheet  801 , a wire-winding part  802 , an input terminal  803 , an output terminal  804 , and slots  805  and  806 . The wire-winding part  802  is made by spirally winding a metal conductor by a plurality of turns, and the turns of the metal conductor are insulated from each other. At a winding start end and a winding termination end, the wireless charging wire-winding part  802  is connected to an external circuit by the input terminal  803  and the output terminal  804 , so that a current passes through a wireless charging coil and forms a magnetic field. The magnetic conductive sheet  801  plays a magnetic conductive role, so that an inductance value of the wire-winding part  802  can be increased. In addition, the magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield the space below the magnetic conductive sheet. The magnetic conductive sheet  801  may be made of a magnetic material such as ferrite or amorphous-nanocrystalline. In this embodiment of the present invention, a slot in a “comb-shaped” structure formed by the slots  805  and  806  is further included. The slots  805  are arranged in a winding direction and a metal width direction, so that a width of the wire-winding part  802  can be reduced. Cut-line slots of the slots in a width direction of the winding of the wire-winding part  802  can effectively cut off an eddy current path. Therefore, the “comb-shaped” slot can effectively cut off the eddy current path in the wire-winding part  802 , and an eddy current loss can be reduced. The slots may completely cut through the wire-winding part  802  in a metal thickness direction, or may cut only a part in a metal thickness direction. The slots may be implemented in a mechanical etching, laser etching, or chemical reaction corrosion manner. 
       FIG. 9  shows an embodiment of a structure of a comb-shaped slot. There are a plurality of slots  906  in a width direction of a metal winding, and the slots are distributed on two sides of a slot  905 , and respectively point to an outer side of the winding and an inner side of the winding, so that eddy current losses in inner and outer small windings obtained after each turn of the metal winding is cut by the slot  905  can be effectively reduced. 
       FIG. 10  shows an embodiment of a structure of another comb-shaped slot. Slots  1006  in a width direction of a metal winding of a coil and a slot  1005  in a winding direction of the metal winding intersect, so that the entire slot cuts the coil in a shape of “ ”. The slot in the shape of “two connected crosses” is disposed, so that an eddy current loss can be reduced by disposing only a small quantity of slots. 
     As shown in  FIG. 11 , in an embodiment, slots  1015  are through holes. A plurality of slots  1015  are distributed on a wire-winding part  1012 , so that an eddy current loss can be reduced. A through-hole shape of the slot  1015  may be a round shape, a square shape, a “cross” shape, or another polygon shape. A quantity of slots  1015  distributed on each turn of a metal conductor on the wire-winding part  1012  and an arrangement manner may be determined based on a size of a nearby magnetic field. The slot in the round shape, the square shape, the “cross” shape, or another polygon shape is disposed, so that an eddy current loss can be reduced by disposing only a small quantity of slots. 
     As shown in  FIG. 12 , in another embodiment of this application, a width of a wire-winding part  1022  is optimized based on a strength of a magnetic field near a coil in a wireless charging process, to reduce a loss in the coil.  1021  represents a magnetic conductive sheet that may be specifically made of a material such as ferrite or amorphous-nanocrystalline. The wire-winding part  1022  is made by spirally winding a metal conductor by a plurality of turns. In the plurality of turns of the coil, a width of an inner ring of the metal conductor is relatively small, and when a winding outer diameter of the coil increases, a width of the conductor first increases and then decreases. Therefore, an overall characteristic of a width of the coil of the wire-winding part  1022  is as follows: Conductor widths of an inner ring and an outer ring are relatively small, and a conductor width of a conductor at a middle location is relatively large, and a specific value of the width may be designed based on an actual application scenario. An input terminal  1023  and an output terminal  1024  are connected to an external circuit. When a current passes through the coil, a magnetic field is generated to couple the coil to another coil, to wirelessly transmit electric energy. 
     As shown in  FIG. 13 , slots  1025  are added to the wire-winding part  1022 . The slots  1025  each cut a part, having a relatively large conductor width, of the metal conductor of the wire-winding part  1022 , and cut the conductor having the relatively large conductor width into two or more conductors having relatively small conductor widths, to effectively reduce an eddy current loss at this location, and further reduce a loss in the coil. 
       FIG. 14  shows a wireless charging transmission apparatus of a mobile terminal in some embodiments of this application. The wireless charging transmission apparatus includes a direct current power supply, a DC/AC conversion module, a matching circuit, a transmission coil, and a control unit, and the transmission coil is any one of the coils described in the foregoing embodiments. 
     The control unit is configured to control the DC/AC conversion module to convert a signal of the direct current power supply into an alternating current signal, and control the alternating current signal to pass through the matching circuit and the transmission coil, so that the transmission coil transmits alternating current energy. 
     The wireless charging receiving coil is at least one of the coils shown in  FIG. 3 a   ,  FIG. 3 b   , and  FIG. 4  to  FIG. 13 . 
     In the solution of this application, the slot is disposed on the transmission coil of the wireless charging transmission apparatus, and a wire-winding part of the transmission coil is cut or partially cut, so that when the wireless charging transmission apparatus works in a wireless charging alternating current magnetic field, under the action of the wireless charging alternating current magnetic field, alternating current resistance in the transmission coil is reduced, reducing an energy loss in the transmission coil. 
       FIG. 15 a    and  FIG. 15 b    show a wireless charging system of a mobile terminal in some embodiments of this application. The wireless charging system includes a wireless charging receiving apparatus of the mobile terminal and a wireless charging transmission apparatus of the mobile terminal. The wireless charging transmission apparatus of the mobile terminal is configured to charge the wireless charging receiving apparatus of the mobile terminal. 
     The wireless charging transmission apparatus of the mobile terminal includes a direct current power supply, a DC/AC conversion module, a matching circuit  10 , a transmission coil, and a control unit. The wireless charging receiving apparatus of the mobile terminal includes a receiving coil, a matching circuit  20 , an AC/DC conversion module, a control unit, and a load. 
     The DC/AC conversion module converts the direct current power supply into an alternating current signal. The alternating current signal flows through the matching circuit  10  and the transmission coil. The transmission coil sends the alternating current signal to the receiving coil in the wireless charging receiving apparatus of the mobile terminal. The alternating current signal received by the receiving coil is transmitted to the AC/DC conversion module through the receiving coil and the matching circuit  20 . The AC/DC conversion module converts the received alternating current signal into a direct current signal, to supply power to the load. The control unit of the wireless charging transmission apparatus of the mobile terminal controls working of the transmission coil, and the control unit of the wireless charging receiving apparatus of the mobile terminal controls working of the receiving coil. 
     At least one of the transmission coil and the receiving coil is at least one of the coils shown in  FIG. 3 a   ,  FIG. 3 b   , and  FIG. 4  to  FIG. 13 . 
     Specifically, in this application, a slot is disposed on the receiving coil, so that thickness of the receiving coil is reduced or a cross-sectional area is reduced, and direct current resistance in the coil is increased to some extent. However, in a wireless charging scenario, approximately 50% to 100% of alternating current resistance in the coil is not caused by the direct current resistance in the coil, and this part of resistance is actually an equivalent resistance, namely, an eddy current resistance, that is lost because a current is generated in a metal conductor of the coil when a magnetic field generated in a wireless charging process cuts through the metal conductor. When the metal conductor of the coil is cut through by the wireless charging magnetic field, an eddy current closed-loop path is generated in the metal conductor of the coil, and this part of eddy current cannot form an effective output current in the coil, and increases an energy loss in the coil. The coil is cut or partially cut, so that the eddy current closed-loop path that is generated when the metal conductor of the coil is cut through by the wireless charging magnetic field can be cut off, reducing an eddy current loss in the receiving coil. In addition, in this application, the coil is cut, so that a decrease amplitude of the energy loss generated by the eddy current in the receiving coil is greater than a loss caused by an increase in the direct current resistance in the coil, reducing a loss of the alternating current resistance in the coil on the whole. 
     In short, the slot is disposed on the receiving coil, so that the closed-loop path generated by the eddy current in the metal conductor of the coil is cut off, and resistance caused by the eddy current in the receiving coil is greatly reduced. In addition, a decrease amplitude of the resistance caused by the eddy current is greater than an increase amplitude of the direct current resistance, so that the alternating current resistance in the coil in the wireless charging scenario is reduced on the whole. In this application, a ratio of the alternating current resistance to the direct current resistance in the coil is approximately 1.3, so that a percentage of the resistance generated by the eddy current in the coil is greatly reduced, a loss in the coil is reduced, and charging efficiency is improved. In particular, in a charging status in which a mobile phone does not exactly face a wireless charger, an eddy current path generated by magnetic lines in the coil in the wireless charging process is cut off, where an angle between a plane of the coil and the magnetic lines is relatively large, so that an eddy current loss generated by a wireless charging magnetic field in the coil can be greatly reduced. 
     At least one of the transmission coil and the receiving coil shown in  FIG. 15 a    and  FIG. 15 b    is used as the coil in this application, improving wireless charging efficiency. In this solution, the slot is disposed on the receiving coil in the wireless charging receiving apparatus of the mobile terminal or the transmission coil of the wireless charging transmission apparatus of the mobile terminal, so that the direct current resistance in the coil is increased to some extent, and the alternating current resistance in the coil is also increased. However, in the wireless charging scenario, approximately 50% to 100% of the alternating current resistance in the coil is not caused by the direct current resistance in the coil, and this part of resistance is actually caused by cutting the coil by the wireless charging magnetic field. When a wire-winding part of the receiving coil or the transmission coil is cut or partially cut, an eddy current generated when the coil is cut by the wireless charging magnetic field can be cut off, to reduce a final alternating current resistance in the receiving coil or the transmission coil. In short, the slot is disposed on the coil, so that impact caused by the eddy current on the resistance in the coil is greatly reduced, and finally, the alternating current resistance in the coil is greatly reduced. In this application, a ratio of the alternating current resistance to the direct current resistance in the coil is approximately 1.3 after optimization, greatly reducing a percentage of the eddy current resistance. In conclusion, the slot is disposed, so that the eddy current resistance is reduced. In addition, a decrease amplitude of the eddy current resistance is greater than an increase amplitude of the direct current resistance, so that the alternating current resistance in the wireless charging receiving coil or the transmission coil is reduced, and charging efficiency is improved. 
     Further, when the transmission coil and the receiving coil horizontally deviate from each other by a particular distance, most magnetic lines are perpendicular to a plane of the transmission coil or the receiving coil, or an eddy current loss in the transmission coil or the receiving coil is increased rapidly because an angle between most magnetic lines and a plane of the coil is relatively large. Consequently, when the transmission coil and the receiving coil deviate from each other during wireless charging, overall wireless charging efficiency is reduced, and is obviously lower than that when the two coils do not deviate from each other horizontally. In addition, when the transmission coil and the receiving coil horizontally deviate from each other by a long distance, to keep a same output power, a current larger than a current generated when the transmission coil and the receiving coil do not deviate from each other needs to pass through the transmission coil on a transmit side. Consequently, an alternating current magnetic field is stronger, and a loss in the coil is greater. In prior approaches, a problem of a loss in a case of deviation cannot be resolved by optimizing a conductor width. Consequently, in an existing technical solution of wireless charging, charging efficiency obtained when the transmission coil and the receiving coil deviate from each other is obviously lower than charging efficiency obtained when the two coils exactly face each other. In the technical solution of this application, a technical solution is proposed for low charging efficiency obtained when the transmission coil and the receiving coil horizontally deviate from each other by a long distance during wireless charging, to effectively reduce losses in the coils caused when there is a large horizontal deviation, increase a degree of freedom in horizontal space during wireless charging, and improve charging experience of a user. 
     Specifically, analysis of charging efficiency is verified through simulation. For example, in this solution, a slot is disposed to cut off an eddy current path in a coil having a relatively large width, to effectively reduce a loss generated in the coil in a wireless charging process, and improve wireless charging efficiency. The following table shows wireless charging efficiency obtained when a wireless charging receiving coil uses an existing technical solution of a coil having unequal widths and charging efficiency obtained when the wireless charging receiving coil uses a solution of a coil having unequal widths in the technology in the present invention. A test result indicates that the technology in the embodiments of the present invention effectively improve the wireless charging efficiency. When winding center locations of two coils horizontally deviate from each other by 10 mm, efficiency is improved by 5.19%. 
     
       
         
           
               
               
               
               
               
             
               
                   
                   
               
               
                   
                 Charging  
                 Prior 
                 Prior 
                 Solution of  
               
               
                   
                 efficiency  
                 approach  
                 approach  
                 embodiments in  
               
               
                   
                 comparison 
                 1 
                 2 
                 this application 
               
               
                   
                   
               
             
            
               
                   
                 A receiving coil  
                 86.00% 
                 86.50% 
                 87.00% 
               
               
                   
                 exactly faces a  
                   
                   
                   
               
               
                   
                 transmission coil. 
                   
                   
                   
               
               
                   
                 A receiving coil  
                 72.80% 
                 75.70% 
                 80.51% 
               
               
                   
                 horizontally  
                   
                   
                   
               
               
                   
                 deviates from  
                   
                   
                   
               
               
                   
                 a transmission  
                   
                   
                   
               
               
                   
                 coil by 10 mm. 
               
               
                   
                   
               
            
           
         
       
     
       FIG. 16 a    and  FIG. 16 b    are schematic diagrams of a coil according to another embodiment of this application. This embodiment includes a first conductive layer  1601 , a second conductive layer  1602 , a plurality of metal through holes  1603 , and a magnetic conductive sheet  1611 . Specifically,  FIG. 16 a    is a top view in a direction of the first conductive layer  1601 , and  FIG. 16 b    is a top view in a direction of the second conductive layer  1602 . The first conductive layer includes a first-layer wire-winding part  01  and a first part  02  of an output terminal, and the second conductive layer includes a second-layer wire-winding part  11 , a second part  12  of the output terminal, and an input terminal  13 . One end of the second part  12  of the output terminal is connected to an innermost ring of the second-layer wire-winding part  11 , and extends towards an outer ring to a location between an innermost coil and an outermost coil of the second-layer wire-winding part  11 . The other end of the second part  12  of the output terminal is connected to one end of the first part  02  of the output terminal in the first conductive layer via the metal through hole  1603 . The first part  02  of the output terminal and the second part  12  of the output terminal are connected in series to form the output terminal of the coil, and the other end of the first part  02  of the output terminal is connected to an external circuit. The first-layer wire-winding part  01  and the second-layer wire-winding part  11  are respectively cut off at a junction between the first-layer wire-winding part  01  and the output terminal and a junction between the second-layer wire-winding part  11  and the output terminal. In addition, the first-layer wire-winding part  01  and the second-layer wire-winding part  11  are connected in parallel on cut parts via the metal through holes  1603 . Any one of the foregoing cut slots may be disposed on the first-layer wire-winding part  01  and the second-layer wire-winding part  11 . One end of the input terminal  13  is connected to an outer ring of the second-layer wire-winding part  11 , and the other end is connected to the external circuit. The magnetic conductive sheet  1611  is located below the second conductive layer, and is insulated from the second conductive layer. The magnetic conductive sheet  1611  plays a magnetic conductive role, so that an inductance value of the coil can be increased. In addition, a magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield the space below the magnetic conductive sheet  1611 . The magnetic conductive sheet  1611  may be made of one or more magnetic materials such as ferrite or amorphous-nanocrystalline. 
       FIG. 17 a    and  FIG. 17 b    are schematic diagrams of a coil according to another embodiment of this application. This embodiment includes a first conductive layer  1701 , a second conductive layer  1702 , a plurality of metal through holes  1703 , and a magnetic conductive sheet  1711 . Specifically,  FIG. 17 a    is a top view in a direction of the first conductive layer  1701 , and  FIG. 17 b    is a top view in a direction of the second conductive layer  1702 . The first conductive layer includes a first-layer wire-winding part  001 , a first part  002  of an output terminal, and an input terminal  003 , and the second conductive layer includes a second-layer wire-winding part  011  and a second part  012  of the output terminal. One end of the second part  012  of the output terminal is connected to an innermost ring of the second-layer wire-winding part  011 , and extends towards an outer ring to a location between an innermost coil and an outermost coil of the second-layer wire-winding part  011 . The other end of the second part  012  of the output terminal is connected to one end of the first part  002  of the output terminal in the first conductive layer via the metal through hole  1703 . The first part  002  of the output terminal and the second part  012  of the output terminal are connected in series to form the output terminal of the coil, and the other end of the first part  002  of the output terminal is connected to an external circuit. The first-layer wire-winding part  001  and the second-layer wire-winding part  011  are respectively cut off at a junction between the first-layer wire-winding part  001  and the output terminal and a junction between the second-layer wire-winding part  011  and the output terminal. In addition, the first-layer wire-winding part  001  and the second-layer wire-winding part  011  are connected in parallel on cut parts via the metal through holes  1703 . Any one of the foregoing cut slots may be disposed on the first-layer wire-winding part  001  and the second-layer wire-winding part  011 . One end of the input terminal  003  is connected to a terminal of an outer ring of the first-layer wire-winding part  001 , and the other end is connected to the external circuit. The magnetic conductive sheet  1711  is located below the second conductive layer, and is insulated from the second conductive layer. The magnetic conductive sheet  1711  plays a magnetic conductive role, so that an inductance value of the coil can be increased. In addition, a magnetic field is prevented from leaking to space below the magnetic conductive sheet, to better shield the space below the magnetic conductive sheet  1711 . The magnetic conductive sheet  1711  may be made of one or more magnetic materials such as ferrite or amorphous-nanocrystalline. 
     The foregoing descriptions are merely specific implementations of embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.