Wireless system and wireless device

Abstract

The present disclosure provides a wireless system, including a first coil, a second coil, and a capacitance adjustment unit. The second coil is configured to inductively couple with the first coil. The capacitance adjustment unit is connected to the first coil, and the capacitance adjustment unit includes at least one closed loop and a connecting wire, and the connecting wire is connected between the first coil and the closed loop. The present disclosure also provides a wireless device.

Description

Technical Field

[0001] The present disclosure relates to a wireless system, and particularly to a wireless system that can reduce electromagnetic interference. Background Art

[0002] With the development of technology, many electronic devices (such as tablet computers or smart phones) nowadays have the function of wireless charging. Users can place the electronic device on a wireless charging transmitter so that the wireless charging receiver in the electronic device generates current by electromagnetic induction or electromagnetic resonance to charge the battery. Due to the convenience of wireless charging, electronic devices with wireless charging modules are gradually favored by the public.

[0003] Generally, a wireless charging device includes a magnetic substrate that carries a coil. Among them, when the coil is energized and operates in a wireless charging mode or a wireless communication mode, the magnetic substrate can make the magnetic lines of force emitted by the coil more concentrated to obtain better performance. However, existing wireless devices generate electromagnetic waves during operation, which in turn cause electromagnetic interference to other electronic devices around the wireless device.

[0004] Therefore, how to design a wireless device that can reduce electromagnetic interference and maintain the same operating performance is a topic worthy of discussion and solution today. Summary of the Invention

[0005] In view of this, the present disclosure proposes a wireless system to solve the above problems.

[0006] Embodiments of the present disclosure provide a wireless system, including a first coil, a second coil, and a capacitance adjustment unit. The second coil is configured to induct the first coil. The capacitance adjustment unit is connected to the first coil. The capacitance adjustment unit includes at least one closed loop and a connecting wire, and the connecting wire is connected between the first coil and the closed loop.

[0007] According to some embodiments of the present disclosure, the closed loop has only one connection end point, which is configured to connect the connecting wire.

[0008] According to some embodiments of the present disclosure, the first coil includes a spiral structure, and the spiral structure forms a hollow region, and the closed loop is disposed within the hollow region.

[0009] According to some embodiments of the present disclosure, the first coil includes a spiral structure, and the spiral structure forms a hollow region, and the closed loop is disposed outside the hollow region.

[0010] According to some embodiments of the present disclosure, the first coil has a signal transmitting coil.

[0011] According to some embodiments of the present disclosure, the second coil has a signal receiving coil.

[0012] According to some embodiments of the present disclosure, the closed loop includes a first closed winding and a second closed winding. The second closed winding is located inside the first closed winding and is not connected to the first closed winding.

[0013] Embodiments of the present disclosure provide a wireless system, including a first coil, a second coil, and a capacitance adjustment unit. The second coil is configured to induct the first coil. The capacitance adjustment unit is connected to the first coil. The capacitance adjustment unit includes a variable capacitor and a connecting wire. The connecting wire is connected between the first coil and the variable capacitor, and one end of the variable capacitor is electrically grounded.

[0014] Embodiments of the present disclosure provide a wireless system, including a first coil, a second coil, and a capacitance adjustment unit. The second coil is configured to induct the first coil. The capacitance adjustment unit surrounds the first coil. The capacitance adjustment unit includes at least one closed loop and is electrically independent of the first coil.

[0015] Embodiments of the present disclosure provide a wireless device, including a first coil and a capacitance adjustment unit. The first coil includes a first metal wire and a second metal wire. The first metal wire is disposed on a first plane and has a first spiral structure. The second metal wire is disposed on a second plane and has a second spiral structure, and the second metal wire is electrically connected to the first metal wire. The capacitance adjustment unit is connected to the first coil. The capacitance adjustment unit includes at least one closed loop and a connecting wire, and the connecting wire is connected between the first coil and the closed loop.

[0016] The present disclosure provides a wireless system, including a first coil and a second coil. When the first coil is powered on, the second coil is configured to induct the first coil to generate electricity. In various embodiments of the present disclosure, the wireless system may include a capacitance adjustment unit configured to be electrically connected to the first coil (or the second coil) to change the interlayer capacitance value of the first coil, so as to reduce the electromagnetic interference of the electromagnetic wave generated by the transmitting-end device to other electronic devices.

[0017] In addition, setting the capacitance adjustment unit does not change the inductance value and impedance value of the first coil, so it does not affect the performance of the transmitting-end device during wireless charging. In some embodiments, the capacitance adjustment unit may include a closed loop and a connecting wire. The closed loop is formed by a wire winding, and the closed loop has only one connection end connected to the aforementioned connecting wire. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present disclosure can be clearly understood through the following detailed description and in conjunction with the drawings. It should be emphasized that, in accordance with industry standard practices, the various features are not drawn to scale and are for illustrative purposes only. In fact, for the sake of clarity, the dimensions of the various features may be arbitrarily enlarged or reduced.

[0019] Figure 1 It is a schematic diagram of a wireless system according to an embodiment of the present disclosure.

[0020] Figure 2 It is an exploded view of a first coil module according to an embodiment of the present disclosure.

[0021] Figure 3 It is a top view schematic diagram of a coil assembly according to an embodiment of the present disclosure.

[0022] Figure 4 It is a structural schematic diagram of a coil assembly in a first plane according to an embodiment of the present disclosure.

[0023] Figure 5 It is a structural schematic diagram of a coil assembly in a third plane according to this embodiment of the present disclosure.

[0024] Figure 6 It is a structural schematic diagram of a coil assembly in a second plane according to this embodiment of the present disclosure.

[0025] Figure 7 It is a structural schematic diagram of a coil assembly in a second plane according to another embodiment of the present disclosure.

[0026] Figure 8 It is a top view schematic diagram of a coil assembly of a wireless device according to another embodiment of the present disclosure.

[0027] Figure 9 It is a schematic diagram of the upper layer structure of a coil assembly in a first plane according to an embodiment of the present disclosure.

[0028] Figure 10 It is a schematic diagram of the lower layer structure of a coil assembly in a second plane according to this embodiment of the present disclosure.

[0029] Figure 11 It is a top view schematic diagram of a coil assembly of a wireless device according to another embodiment of the present disclosure.

[0030] Figure 12 It is a schematic diagram of the upper layer structure of a coil assembly in a first plane according to an embodiment of the present disclosure.

[0031] Figure 13 It is a schematic diagram of the lower layer structure of a coil assembly in a second plane according to this embodiment of the present disclosure.

[0032] Figure 14 Structural schematic diagram of a coil assembly in a first plane according to another embodiment of the present disclosure.

[0033] Description of reference numerals:

[0034] 1 Wireless system

[0035] 10 Transmitting end device

[0036] 20 Receiving end device

[0037] 100 First coil module

[0038] 102 Coil assembly

[0039] 102A Coil assembly

[0040] 102B Coil assembly

[0041] 1021 First plane

[0042] 1022 Second plane

[0043] 1023 Third plane

[0044] 103 First terminal contact

[0045] 1031 Extension wire

[0046] 104 Adhesive layer

[0047] 105 Second terminal contact

[0048] 106 Magnetic conductive plate

[0049] 108 Substrate

[0050] 110 Coil structure

[0051] 111 First metal wire

[0052] 1111 First end

[0053] 1112 Second end

[0054] 112 Second metal wire

[0055] 1121 First end

[0056] 1122 Second end

[0057] 1124 Hollow area

[0058] 114 Connecting piece

[0059] 150, 150A, 150B Capacitance adjustment unit

[0060] 152 Closed loop

[0061] 1521 Connection end point

[0062] 1522 First closed winding

[0063] 1523 Second closed winding

[0064] 153 Variable capacitor

[0065] 154 Connecting wire

[0066] 200 Second coil module

[0067] 302 Coil assembly

[0068] 302A Coil assembly

[0069] 3021 First plane

[0070] 3022 Second plane

[0071] 304 First metal wire

[0072] 3041 First end

[0073] 3043 Second end

[0074] 306 Second metal wire

[0075] 3061 First end

[0076] 3063 Second end

[0077] MC, MC1, MC2, MC3, MC5, MC6 Metal connectors Detailed implementation manner

[0078] In order to make the objectives, features, and advantages of the present disclosure more obvious and understandable, specific embodiments are hereinafter given and detailed descriptions are provided in conjunction with the accompanying drawings. Among them, the configurations of the components in the embodiments are for illustrative purposes only and are not intended to limit the present disclosure. And the partial repetition of the reference numerals in the embodiments is for the purpose of simplifying the description and does not mean the relevance between different embodiments. The directional terms mentioned in the following embodiments, such as: up, down, left, right, front or back, etc., are only with reference to the directions of the attached drawings. Therefore, the directional terms used are for illustration and not for limiting the present disclosure.

[0079] It must be understood that the components specifically described or illustrated may exist in various forms well known to those skilled in the art. In addition, when a layer is "on" another layer or substrate, it may mean "directly" on another layer or substrate, or it may mean that a layer is on another layer or substrate, or there is another layer interposed between other layers or substrates.

[0080] In addition, relative terms such as "lower" or "bottom" and "higher" or "top" may be used in the embodiments to describe the relative relationship of one element in the figure to another element. It can be understood that if the device shown in the figure is turned upside down, the element described on the "lower" side will become the element on the "higher" side.

[0081] Herein, the terms "about" and "approximately" generally mean within 20% of a given value or range, preferably within 10%, and more preferably within 5%. The quantity given herein is an approximate quantity, meaning that the meaning of "about" and "approximately" can still be implied without specific description.

[0082] Please refer to Figure 1 , Figure 1 , which is a schematic diagram of a wireless system 1 according to an embodiment of the present disclosure. In this embodiment, the wireless system 1 includes two wireless devices (a transmitting device 10 and a receiving device 20), and the receiving device 20 can be disposed on the transmitting device 10. Among them, the transmitting device 10 can be, for example, a wireless charging board, including a first coil module 100, and the first coil module 100 can further have a first coil. The receiving device 20 can be, for example, a smart phone or a tablet computer, including a second coil module 200, and the second coil module 200 can further have a second coil.

[0083] In this embodiment, the first coil can be operated as a signal transmitting coil, and the second coil can be operated as a signal receiving coil. When the first coil is energized, the adjacent second coil will be correspondingly induced to generate electricity, thereby charging the battery (not shown in the figure) in the receiving device 20.

[0084] For example, the first coil (or the second coil) can be used as a resonant charging coil based on the standard of the Alliance for Wireless Power (A4WP), but not limited thereto. In addition, the first coil (or the second coil) can also be used as an inductive charging coil based on the standard of the Wireless Power Consortium (WPC), such as the Qi standard. Therefore, this implementation can enable the transmitting device 10 (or the receiving device 20) to simultaneously correspond to different forms of charging methods to increase the applicable range. For example, at a short distance (e.g., less than 1 cm), inductive operation is used; while at a long distance, resonant operation is used.

[0085] Please refer to Figure 2 , Figure 2 , which is an exploded view of a first coil module 100 according to an embodiment of the present disclosure. As Figure 2As shown, the first coil module 100 may include a coil assembly 102, an adhesive layer 104, and a magnetic conductive plate 106. In this embodiment, the coil assembly 102 is disposed on the magnetic conductive plate 106, and the coil assembly 102 is connectable to the magnetic conductive plate 106 by means of the adhesive layer 104. Among them, the adhesive layer 104 may be a tape or any other material that can be used for connection.

[0086] In addition, in this embodiment, the magnetic conductive plate 106 may be a ferrite, but is not limited thereto. For example, in other embodiments, the magnetic conductive plate 106 may also include nanocrystalline materials. The magnetic conductive plate 106 may have a magnetic permeability corresponding to the coil assembly 102, such that the electromagnetic waves of the coil assembly 102 are more concentrated.

[0087] As Figure 2 shown, the coil assembly 102 includes a substrate 108 and a coil structure 110 (first coil), and the coil structure 110 is formed on the substrate 108. In this embodiment, the substrate 108 is a flexible circuit board, but is not limited thereto, as long as any substrate that can be used to form the coil structure 110 falls within the scope of the present disclosure.

[0088] Next, please refer to Figures 3 to 6 , Figure 3 which is a top view schematic diagram of the coil assembly 102 according to an embodiment of the present disclosure, Figure 4 which is a schematic structural diagram of the coil assembly 102 in a first plane 1021 according to an embodiment of the present disclosure, Figure 5 which is a schematic structural diagram of the coil assembly 102 in a third plane 1023 according to this embodiment of the present disclosure, and Figure 6 which is a schematic structural diagram of the coil assembly 102 in a second plane 1022 according to this embodiment of the present disclosure.

[0089] In this embodiment, the substrate 108 of the coil assembly 102 includes a first layer structure, a second layer structure, and a third layer structure, which are located in the first plane 1021, the second plane 1022, and the third plane 1023 respectively, and the third plane 1023 is located between the first plane 1021 and the second plane 1022. It should be noted that Figure 6 in the coil structure 110 is located below the second plane 1022, but for the sake of clear illustration, Figure 6 the coil structure 110 in is still shown as a solid line.

[0090] As Figures 4 to 6As shown, the coil structure 110 (first coil) of the coil assembly 102 may include a first metal wire 111, a second metal wire 112, and a connecting member 114. The first metal wire 111 is disposed on the first plane 1021, the second metal wire 112 is disposed on the second plane 1022, and the connecting member 114 is disposed on the third plane 1023. Furthermore, as Figure 3 shown, the coil assembly 102 may further have a first terminal contact 103 and a second terminal contact 105, configured to be electrically connected to an external circuit, such as a control chip.

[0091] Next, as Figure 4 shown, the first metal wire 111 is formed with a first spiral structure, having a first end 1111 and a second end 1112. As Figure 5 shown, one end of the connecting member 114 is connected to the first terminal contact 103. Additionally, as Figure 6 shown, the second metal wire 112 is formed with a second spiral structure, having a first end 1121 and a second end 1122.

[0092] Furthermore, the coil assembly 102 may further include a plurality of metal connecting members (also referred to as vias), configured to penetrate the substrate 108 to connect the first metal wire 111 and the second metal wire 112. For example, as Figures 3 to 6 shown, the coil assembly 102 includes a metal connecting member MC1 and a metal connecting member MC2. The metal connecting member MC1 is configured to connect the first end 1111 of the first metal wire 111, the connecting member 114, and the first end 1121 of the second metal wire 112. Furthermore, the second end 1122 of the second metal wire 112 is electrically connected to the first metal wire 111 through the metal connecting member MC2.

[0093] As Figure 4 and Figure 5 shown, the coil assembly 102 further includes a metal connecting member MC3, configured to connect the connecting member 114 and an extension wire 1031. Additionally, the coil assembly 102 further includes a plurality of metal connecting members MC5 and metal connecting members MC6, disposed around the connecting member 114. As Figures 3 to 6 shown, the plurality of metal connecting members MC5 and metal connecting members MC6 are respectively disposed on both sides of the connecting member 114. These metal connecting members MC5 and metal connecting members MC6 are configured to electrically connect the first metal wire 111 and the second metal wire 112, enabling a part of the first spiral structure of the first metal wire 111 to be in parallel with the second spiral structure of the second metal wire 112. Therefore, the effect of reducing the overall impedance of the coil assembly 102 can be achieved, and the number of turns of the coil assembly 102 can also be increased.

[0094] It should be noted that, in this embodiment, the first coil module 100 may further include a capacitance adjustment unit 150, which is connected to the first coil. For example, as Figure 6 shown, the capacitance adjustment unit 150 is disposed on the second plane 1022. The capacitance adjustment unit 150 may include at least one closed loop 152 and a connecting wire 154, and the connecting wire 154 is connected between the second metal wire 112 (the first coil) and the closed loop 152.

[0095] As Figure 6 shown, the closed loop 152 may be formed by a wire, and the closed loop 152 has only one connection end point 1521, configured to be connected to the connecting wire 154, and the capacitance adjustment unit 150 only includes one connecting wire 154. Furthermore, a hollow area 1124 is formed in the second spiral structure of the second metal wire 112, and the closed loop 152 is disposed within the hollow area 1124.

[0096] By providing the capacitance adjustment unit 150 in this embodiment, the interlayer capacitance value of the first coil (or the capacitance value between two adjacent turns of the first coil) can be changed to reduce the electromagnetic interference (EMI) of the electromagnetic waves generated by the transmitting end device 10 to other electronic devices. In addition, providing the capacitance adjustment unit 150 does not change the inductance value and impedance value of the first coil, which means it does not affect the performance of the transmitting end device 10 during wireless charging.

[0097] Please refer to Figure 7 , Figure 7 which is a schematic structural diagram of a coil assembly 102A on the second plane 1022 according to another embodiment of the present disclosure. The coil assembly 102A in this embodiment is similar to the coil assembly 102, except that the capacitance adjustment unit 150 in this embodiment only includes the closed loop 152, which surrounds the second metal wire 112 (the first coil), and the capacitance adjustment unit 150 is electrically independent of the first coil.

[0098] Please refer to Figures 8 to 10 , Figure 8 which is a top view schematic diagram of a coil assembly 102B of a wireless device according to another embodiment of the present disclosure, Figure 9 which is a schematic diagram of the upper layer structure of the coil assembly 102B on the first plane 1021 according to an embodiment of the present disclosure, and Figure 10 which is a schematic diagram of the lower layer structure of the coil assembly 102B on the second plane 1022 according to this embodiment of the present disclosure.

[0099] In this embodiment, as Figure 9 and Figure 10As shown, the winding directions of the first metal wire 111 and the second metal wire 112 are opposite, and they are connected in series with each other through the metal connector MC in the hollow region 1124. Among them, the first end 1111 of the first metal wire 111 is electrically connected to the first end 1121 of the second metal wire 112 through the aforementioned metal connector MC. In this embodiment, the first metal wire 111 has a first spiral structure, and the second metal wire 112 has a second spiral structure.

[0100] In addition, as Figure 8 shown in Figure 10 , the coil assembly 102B further has an extension wire 1031, and the second end 1122 of the second metal wire 112 is electrically connected to the extension wire 1031 and the first terminal contact 103 through the metal connector MC. Furthermore, as Figure 8 shown in Figure 9 , the second end 1112 of the first metal wire 111 is connected to the second terminal contact 105.

[0101] It should be noted that the second spiral structure formed by the second metal wire 112 has a hollow region 1124, and the capacitance adjustment unit 150 is disposed outside the hollow region 1124. Specifically, the closed loop 152 is adjacent to the first terminal contact 103, and the closed loop 152 is connected to the second end 1122 of the second metal wire 112 through the connection wire 154. Among them, the number of turns of the closed loop 152 is more than 2 turns, but not limited thereto. The number of turns of the closed loop 152 can be determined according to the capacitance value to be adjusted.

[0102] From the foregoing embodiments, it can be seen that regardless of whether the first metal wire 111 and the second metal wire 112 are connected in series or in parallel, the capacitance adjustment unit 150 can be used to adjust the capacitance value of the first coil to reduce the problem of electromagnetic interference generated by the wireless device (such as the transmitting end device 10).

[0103] Please refer to Figures 11 to 13 , Figure 11 , which is a top view schematic diagram of a coil assembly 302 of a wireless device according to another embodiment of the present disclosure. Figure 12 is a schematic diagram of the upper structure of the coil assembly 302 in the first plane 3021 according to the embodiment of the present disclosure, and Figure 13 is a schematic diagram of the lower structure of the coil assembly 302 in the second plane 3022 according to this embodiment of the present disclosure.

[0104] As Figure 12 shown, the first metal wire 304 has a first end 3041 and a second end 3043, which are respectively connected to the first terminal contact 103 and the second terminal contact 105. Furthermore, as Figure 13As shown, the second metal wire 306 has a first end 3061 and a second end 3063. The first end 3061 is connected to the first metal wire 304 through the metal connector MC1, and the second end 3063 is connected to the second end 3043 of the first metal wire 304 through the metal connector MC2.

[0105] It should be noted that the capacitance value adjustment unit 150A of this embodiment is disposed on the first plane 3021 and is connected to the first end 3041 of the first metal wire 304 through the connecting wire 154. Among them, the closed loop 152 includes a first closed winding 1522 and a second closed winding 1523. The first closed winding 1522 is connected to the connecting wire 154, and the second closed winding 1523 is located inside the first closed winding 1522 and is not connected to the first closed winding 1522.

[0106] Based on the structural design of the capacitance value adjustment unit 150A of this embodiment, the effect of the capacitance value adjustment unit adjusting the capacitance value of the first coil (formed by the first metal wire 304 and the second metal wire 306) can be further improved.

[0107] Please refer to Figure 14 , Figure 14 FIG. 302A is a schematic structural diagram of a coil assembly 302A in the first plane 3021 according to another embodiment of the present disclosure. The coil assembly 302A of this embodiment is similar to the coil assembly 302, except that the capacitance value adjustment unit 150B in this embodiment includes a variable capacitor 153, one end of which is connected to the connecting wire 154 and the other end is electrically grounded.

[0108] Through the configuration of the capacitance value adjustment unit 150B in this embodiment, the capacitance value of the first coil of the coil assembly 302A can be adjusted in real time to further reduce the problem of electromagnetic interference generated by the coil assembly 302A.

[0109] It should be noted that in the foregoing embodiments, the capacitance value adjustment unit 150 is disposed in the transmitting end device 10, but in other embodiments, it may also be disposed in the receiving end device 20. The setting position of the capacitance value adjustment unit 150 can be determined according to actual needs. For example, when the capacitance value adjustment unit 150 is disposed in the transmitting end device 10, the purpose of miniaturizing the receiving end device 20 can be achieved. In addition, when the capacitance value adjustment unit 150 is disposed in the receiving end device 20, the receiving end device 20 can be matched with various types of transmitting end devices (for example, a transmitting end device without a capacitance value adjustment unit).

[0110] The present disclosure provides a wireless system, including a first coil and a second coil. When the first coil is powered on, the second coil is configured to induce the first coil to generate electricity. In various embodiments of the present disclosure, the wireless system may include a capacitance adjustment unit 150, configured to be electrically connected to the first coil (or the second coil) to change the interlayer capacitance value of the first coil, so as to reduce the electromagnetic interference of the electromagnetic waves generated by the transmitting end device 10 to other electronic devices.

[0111] In addition, setting the capacitance adjustment unit 150 does not change the inductance value and impedance value of the first coil, so it does not affect the performance of the transmitting end device 10 during wireless charging. In some embodiments, the capacitance adjustment unit 150 may include a closed loop and a connecting wire. The closed loop is formed by a wire winding, and the closed loop has only one connection end point, which is connected to the aforementioned connecting wire.

[0112] Although the embodiments of the present disclosure and their advantages have been disclosed as above, it should be understood that any person skilled in the art can make changes, substitutions and modifications without departing from the concept and scope of the present disclosure. In addition, the protection scope of the present disclosure is not limited to the processes, machines, manufactures, compositions of matter, devices, methods and steps in the specific embodiments described in the specification. Any person skilled in the art can understand the processes, machines, manufactures, compositions of matter, devices, methods and steps developed currently or in the future from the disclosure content of the present disclosure. As long as they can perform substantially the same functions or obtain substantially the same results in the embodiments described herein, they can be used according to the present disclosure. Therefore, the protection scope of the present disclosure includes the above-mentioned processes, machines, manufactures, compositions of matter, devices, methods and steps. In addition, each claim constitutes an individual embodiment, and the protection scope of the present disclosure also includes the combination of each claim and embodiment.

Claims

1. A wireless system, comprising: A first coil: A second coil configured to sense the first coil; and A capacitance adjustment unit connected to the first coil, the capacitance adjustment unit comprising at least one closed loop and a connecting wire, and the connecting wire is connected between the first coil and the closed loop; Wherein the closed loop comprises a first closed winding and a second closed winding, the second closed winding is located within the first closed winding and is not connected to the first closed winding, and the first closed winding is connected to the connecting wire.

2. The wireless system according to claim 1, wherein the closed loop has only one connection end configured to connect the connecting wire.

3. The wireless system according to claim 1, wherein the first coil comprises a spiral structure, and the spiral structure forms a hollow region, and the closed loop is disposed within the hollow region.

4. The wireless system according to claim 1, wherein the first coil comprises a spiral structure, and the spiral structure forms a hollow region, and the closed loop is disposed outside the hollow region.

5. The wireless system according to claim 1, wherein the first coil has a signal transmitting coil.

6. The wireless system according to claim 1, wherein the second coil has a signal receiving coil.

7. A wireless device, comprising: A first coil, comprising: A first metal wire disposed on a first plane and having a first spiral structure; And A second metal wire disposed on a second plane and having a second spiral structure, and the second metal wire is electrically connected to the first metal wire; And A capacitance adjustment unit connected to the first coil, the capacitance adjustment unit comprising at least one closed loop and a connecting wire, and the connecting wire is connected between the first coil and the closed loop; Wherein the closed loop comprises a first closed winding and a second closed winding, the second closed winding is located within the first closed winding and is not connected to the first closed winding.

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