JP2010050844A - Loop antenna and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a loop antenna and a communication device capable of reducing trouble caused by excessive magnetic coupling while transmitting amplitude and energy required for achieving communication. <P>SOLUTION: The loop antenna 100 have a plurality of coils 10a and 10b which can perform contactless communication with other devices based on magnetic induction, and the plurality of coils 10a and 10b are mutually and electrically connected to each other in parallel. With this structure, the plurality of coils 10a and 10b, which are electrically connected in parallel, operate as one antenna. In this case, the sum total value L2 of inductance values of the plurality of coils 10a and 10b can be reduced as compared with a case where one coil is used. Accordingly, the mutual inductance with the antenna of the other party of communication can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a loop antenna and a communication device.

  In non-contact communication systems that are rapidly spreading in recent years, magnetic induction type non-contact communication using magnetic induction is widely used. According to this magnetic induction method, for example, an antenna such as a loop antenna is used, and a magnetic field is generated by passing a current through the antenna, or an induced electromotive force generated by a magnetic field crossing or linking the antenna is used. It is possible to perform non-contact communication.

  In the loop antenna and communication device used in such a non-contact communication system, it is desirable that the strength of magnetic field coupling is set to an appropriate value in designing the antenna and the communication circuit. For example, if the magnetic field coupling is too weak, sufficient signals and power cannot be supplied, and it may be difficult to perform non-contact communication. However, even if the magnetic field coupling is too strong, the opposing device is adversely affected, and it may not be possible to appropriately perform non-contact communication. In other words, when performing non-contact communication, it is not necessary to simply strengthen the magnetic field coupling, but it is important to maintain an appropriate value.

However, it is difficult to maintain the strength of magnetic field coupling at an appropriate value.
For example, to reduce the coupling with the opposing antenna by reducing the antenna opening area or reducing the number of turns of the antenna coil so that the magnetic field coupling strength does not become too strong. Can be considered. However, since the magnetic field distribution at an arbitrary distance is not constant in the near field, if the aperture area is made too small or the number of turns is excessively reduced with respect to the opposing antenna, sufficient amplitude necessary for communication to be established Or energy may not be obtained.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to reduce problems caused by excessive magnetic coupling while transmitting amplitude and energy necessary for establishment of communication. It is an object of the present invention to provide a new and improved loop antenna and communication apparatus capable of performing the above.

  In order to solve the above-described problem, according to one aspect of the present invention, a plurality of coils capable of non-contact communication with other devices by magnetic induction are provided, and the plurality of coils are electrically connected to each other in parallel. A loop antenna is provided.

  According to this configuration, a plurality of coils electrically connected in parallel operate as one antenna. At this time, the total value of the inductances of the plurality of coils can be reduced as compared with the case of one coil. Therefore, the mutual inductance with the communication partner antenna can be reduced. Further, for example, the opening area (coil surface area) of each coil and the number of turns of each coil are arbitrary, so that the opening area and the number of turns can be set so that the amplitude and energy necessary for establishing communication can be transmitted. .

  The plurality of coils may be arranged on the same plane so that the coil surfaces do not overlap each other.

  The area where the plurality of coils are arranged on the plane may be equal to or larger than the area of the coil surface of the one coil in the loop antenna formed by one coil.

  Further, at least one inductance of the plurality of coils may be equal to an inductance of the one coil in a loop antenna formed by one coil.

  The inductances of the plurality of coils may be the same.

  The plurality of coils may be formed by a single conducting wire.

  In order to solve the above-mentioned problem, according to another aspect of the present invention, there is provided a loop antenna formed by a plurality of coils capable of non-contact communication with other devices by magnetic induction, and the plurality of coils are A communication device is provided that is electrically connected in parallel to each other.

  As described above, according to the present invention, it is possible to reduce problems caused by excessive magnetic coupling while transmitting amplitude and energy necessary for establishing communication.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

  A loop antenna and a communication apparatus including the loop antenna according to each embodiment of the present invention have a plurality of coils connected in parallel as an antenna for one communication system that performs non-contact communication by electromagnetic induction. The number of the plurality of coils is not particularly limited. In the following, the case where there are two coils in the first embodiment will be described, and the basics of such a loop antenna will be described through the first embodiment. A general configuration, effect, principle and the like will be described. Thereafter, in the second embodiment, a modification of the first embodiment will be described by taking as an example a case where the number of the plurality of coils is four, and other modifications and effects thereof will be described. In addition, before describing these first and second embodiments, the present inventors have clarified related technologies and the state of non-contact communication in order to facilitate understanding of each embodiment. Will be explained. That is, below, it demonstrates in the following order.

<1. Related Technology>
[1-1. Related Technology Configuration]
[1-2. State of non-contact communication]
<2. First Embodiment>
[2-1. Composition]
[2-2. Examples of effects]
<3. Second Embodiment>
[3-1. About the number of coils and the like]
[3-2. About transmission / reception area]
[3-3. About coil inductance]
[3-4. Coil placement position, etc.]

<1. Related Technology>
[1-1. Related Technology Configuration]
FIG. 3A is an explanatory diagram illustrating a configuration of a loop antenna according to related technology. FIG. 3B is an explanatory diagram illustrating an equivalent circuit of the loop antenna according to the related art.

  As shown in FIG. 3A, the loop antenna 10 according to the related art has one coil 10x. A terminal A is provided at one end of the coil 10x. A terminal B is provided at the other end. These terminals A and B serve as input / output terminals of the loop antenna 10. 3A shows a case where the coil surface of the coil 10x of the loop antenna 10 (surface on which one turn of the coil is formed) is substantially square, but the shape of the coil including the following embodiments is It is not limited to this example. However, here, the area of the coil surface of the coil 10x is Sx, and the transmission / reception area of the loop antenna 10 (for example, the area where communication is possible by the passage of magnetic flux from the communication partner device) is S2. That is, in this related technique, “S2 = Sx”. In addition, the number of turns of the coil 10x is Nx times (for example, 3 times) here. And let the value of the inductance of this coil 10x be Lx [H]. This loop antenna 10 is represented by an equivalent circuit as shown in FIG. 3B.

[1-2. State of non-contact communication]
Next, referring to FIG. 4A and FIG. 4B, the state of non-contact communication by electromagnetic induction will be described by taking as an example a case where the loop antenna 10 according to the related technology is used. FIG. 4A is an explanatory diagram illustrating non-contact communication using a loop antenna. FIG. 4B is an explanatory diagram illustrating an equivalent circuit of contactless communication using a loop antenna.

  As shown in FIG. 4A, the loop antenna 10 is connected to a communication circuit 11 via terminals A and B to form a communication device 1. On the other hand, the communication device 2 which is an example of another device of the communication partner includes an antenna 20 and a communication circuit 21 connected to the antenna 20 in order to generate or receive a magnetic field used for non-contact communication. Here, the case where the antenna 20 is a loop antenna smaller than the area Sx of the coil surface of the loop antenna 10 is illustrated, but in each embodiment of the present invention described below, the antenna on the communication partner side is illustrated. The shape is not limited to this example. Here, the inductance of the antenna 20 (primary coil) is L1 [H]. Also, let L2 (= Lx) [H] be the inductance of the loop antenna 100 (secondary coil).

  Each of the communication circuits 11 and 21 has at least one of a transmission circuit and a reception circuit, and each circuit has a resistance component and a capacitance component (hereinafter also referred to as “capacitance”). Here, the resistance component and the capacitance of the communication circuit 11 are R2 [Ω] and C2 [F], and the resistance component and the capacitance of the communication circuit 21 are R1 [Ω] and C1 [F]. However, these resistance components and capacitances may include not only the communication circuits 11 and 21 but also antenna components.

  Communication devices 1 and 2 perform magnetic contact coupling with each other to perform non-contact communication. That is, the communication device 1 having the loop antenna 10 is brought close to the communication device 2 having the antenna 20 which is a communication partner device. Then, the magnetic field generated by the antenna 20 passes through the coil surface of the loop antenna 10 or is linked to the coil axis, so that an induced electromotive force is generated in the loop antenna 10. As a result, power and signals are supplied to the communication device 1 side. When power or a signal is transmitted from the communication device 1 to the communication device 2, conversely, the communication device 1 generates a magnetic field, and the magnetic field passes through the antenna 20 of the communication device 2 or is linked to the coil axis. become.

  In this way, when the communication device 1 and the communication device 2 are magnetically coupled to perform non-contact communication by electrostatic induction, the coil 10x of the loop antenna 10 of the communication device 1 and the antenna 20 of the communication device 2 are connected. Let M [H] be the mutual inductance. The state of the non-contact communication system in this case is represented by an equivalent circuit model as shown in FIG. 4B. The coil of the antenna 20 of the communication device 2 is also referred to as “primary coil”, and the coil 10x of the communication device 1 is also referred to as “secondary coil”.

  At this time, the mutual inductance M between the primary side coil and the secondary side coil is expressed by the following formula 1 when the coupling coefficient of both is k.

…（式１）

... (Formula 1)

  That is, the mutual inductance M is proportional to the root of the product of the inductances L1 and L2 of each coil as shown in Equation 2 below.

…（式２）

... (Formula 2)

  On the other hand, in a non-contact communication system, each antenna and communication circuit is designed to perform non-contact communication with a predetermined optimum coupling degree, although there are some errors and tolerances. It is determined by the size of the mutual inductance M or the like. In addition, when the degree of coupling is not appropriate, the inventors of the present invention may adversely affect the communication circuit on the transmission side (for example, the communication circuit 21, reading device), the communication circuit on the reception side (for example, the communication circuit 11), or the like. I found. That is, when the degree of coupling is out of the desired range in the non-contact communication system, for example, the circuit on the transmission side or the reception side may satisfy the oscillation condition. If the transmission side or the reception side satisfies the oscillation condition, unnecessary noise may be generated in the signal radiated as a magnetic field from the transmission side, and the signal transmitted on the reception side may not be demodulated normally. Even if the operation on the receiving side is performed normally, if the noise due to oscillation affects the receiving circuit on the transmitting side, the signal returned from the receiving side on the transmitting side is normal. There is also a possibility that it cannot be demodulated. Therefore, the inventors of the present invention have come up with the idea of improving such a problem by reducing the degree of coupling.

In order to reduce the degree of engagement, that is, the mutual inductance M, it is conceivable to reduce at least one of the inductances L1 and L2 as can be seen from Equation 2. The inventors of the present invention have conceived the following three as examples of methods for reducing the inductance.
(1) The opening area of the coil (that is, the area of the coil surface) is reduced.
(2) Reduce the number of coil turns (also called the number of turns).
(3) Connect two or more coils in parallel.

  However, according to the method (1), there is a limit in reducing the opening area of the coil. For example, in FIG. 4A, as described above, non-contact communication is established by the magnetic field generated by the antenna 20 interlinking within the coil surface or crossing the coil wire. However, when the area of the coil surface of the loop antenna 10 is reduced, it becomes difficult for the loop antenna 10 to receive the magnetic field generated by the antenna 20. That is, it is difficult to communicate when the loop antenna 10 and the antenna 20 are in an offset positional relationship. Therefore, the allowable range of the positional relationship between the loop antenna 10 and the antenna 20 is narrowed, and it is difficult to combine the two, and the communication opportunity is reduced. As a result, user convenience is also reduced.

  On the other hand, for example, in FIG. 4A, when the antenna 20 and the loop antenna 10 form a pseudo-transformer and power is supplied from the antenna 20 to the loop antenna 10, the power supplied to the communication device 1 side is It is proportional to the number of turns of the antenna 10. Therefore, according to the method (2) in which the number of turns of the coil is reduced, it becomes difficult to transmit necessary amplitude and energy. That is, a non-contact communication state is compared to a transformer, and the number of turns and voltage of the primary side coil are N1 and V1, and the number of turns and voltage of the secondary side coil are N2 and V2. Then, V1 / V2 = N1 / N2 is established in the relationship between the voltage and the number of turns. Therefore, if the number of turns is simply reduced, the voltage generated in the secondary coil is reduced. This also qualitatively explains that it is difficult to transmit the necessary amplitude and energy. However, this qualitative explanation does not limit the reason why it is difficult to transmit the amplitude and energy.

  The present inventors also elucidated these points and conducted further research. As a result, the present inventors can transmit the amplitude and energy necessary for communication without reducing communication opportunities, and reduce the mutual inductance to reduce problems due to excessive magnetic coupling. The method (3) has been conceived. The inventors of the present invention have completed each embodiment of the present invention using the method (3) and the like.

<2. First Embodiment>
The loop antenna according to the first embodiment of the present invention will be described below with reference to FIGS. 1A and 1B. The communication device according to each embodiment of the present invention includes the loop antenna according to each embodiment connected to the communication circuit 11 as illustrated in FIG. 4A. That is, the communication apparatus according to each embodiment is configured by replacing the loop antenna 10 or the antenna 20 of one or both communication apparatuses illustrated in FIG. 4A with the loop antenna described in each embodiment. Therefore, hereinafter, the loop antenna will be mainly described.

[2-1. Composition]
FIG. 1A is an explanatory diagram illustrating a configuration of a loop antenna according to the first embodiment of the present invention. FIG. 1B is an explanatory diagram illustrating an equivalent circuit of the loop antenna according to the present embodiment.

  As shown in FIG. 1A, the loop antenna 100 according to the present embodiment includes two coils 10a and 10b as a plurality of coils. In the present embodiment, as shown in FIG. 1A, the coils 10a and 10b are arranged on the same plane so that the coil surfaces of the coils (surfaces on which one turn of the coil is formed) do not overlap each other. It is done.

  The coil 10a is formed such that the number of turns is Na, the area of the coil surface is set to Sa, and the inductance is La. The coil 10b is formed such that the number of turns is Nb, the area of the coil surface is set to Sb, and the inductance is Lb. In this case, the transmission / reception area S2 of the loop antenna 100 is “S2≈Sa + Sb”. In the present embodiment, the transmission / reception area S2 is an example of an area where the coil 10a and the coil 10b are arranged on a plane.

  At this time, the winding direction of the coil 10a and the winding direction of the coil 10b are set to be the same direction. That is, when a transmission signal is input from the terminals A and B, the direction of the magnetic field generated by the coil 10a is the same as the direction of the magnetic field generated by the coil 10b (for example, the direction toward the front or the back of the paper). 10a and 10b are formed.

  As described above, the coil 10a and the coil 10b are electrically connected to each other in parallel via the terminals A and B which are input / output terminals. However, “connected in parallel” here means that a plurality of coils are electrically connected in parallel when connected to a communication circuit or the like, and at the stage of forming the loop antenna 100. There is no need to already be connected in parallel. Further, the coil 10a and the coil 10b may be formed by a single conductor, although the terminals A and B are arranged in the middle. That is, as shown in FIG. 1A, the loop antenna 100 according to the present embodiment can form two coils 10a and 10b with a single conductive wire as in a single stroke. In this case, the loop antenna 100 can be easily formed. Furthermore, although the terminals A and B are provided between the coil 10a and the coil 10b, the positions of the terminals A and B are not limited.

  The inductance of the loop antenna 100 will be described with reference to FIG. 1B. That is, as shown in FIG. 1B, an equivalent circuit of the two coils 10a and 10b is represented by two coils 10a and 10b connected in parallel. In this case, the total inductance value L2 is expressed by the following Expression 3.

…（式３）

... (Formula 3)

[2-2. Examples of effects]
Here, in order to facilitate understanding of the effects and the like of the loop antenna 100 according to the present embodiment, it is assumed that the coils 10a and 10b of the loop antenna 100 are equal to the coil 10x shown in FIG. 3A and the like. That is, “Na = Nx, Sa = Sx, La = Lx” is set for the coil 10a, and “Nb = Nx, Sb = Sx, Lb = Lx” is set for the coil 10b. Then, the transmission / reception area S2 of the loop antenna 100 is “S2 = Sx + Sx = 2 · Sx”. Further, the inductance of the loop antenna 100 is expressed by the following formula 4.

…（式４）

... (Formula 4)

  Therefore, from Equation 4, if two coils 10x are connected in parallel as in the loop antenna 100 according to the present embodiment, the inductance of the loop antenna 100 is reduced as compared with the loop antenna 10 formed by one coil 10x. It can be seen that it can be made smaller. When the loop antenna 100 according to the present embodiment is used instead of the loop antenna 10 shown in FIG. 4A, the mutual inductance M can be reduced as can be seen from Equation 4 and Equation 2. Therefore, according to the loop antenna 100 according to the present embodiment, the mutual inductance M can be reduced, and the load on the communication partner device such as a reading device due to excessive magnetic coupling can be reduced. The occurrence of problems can be prevented by reducing the adverse effects on itself.

  Further, the number of turns Na and Nb of each of the coils 10a and 10b can be set equal to or more than the number of turns Nx of the coil 10x shown in FIG. 3A, for example. Therefore, the mutual inductance M can be reduced without reducing the number of turns Na and Nb. Therefore, according to the loop antenna 100 according to the present embodiment, it is possible to transmit amplitude and energy necessary for communication.

  Furthermore, the transmission / reception area S2 of the loop antenna 100 (that is, an example of the area where the plurality of coils 10a and 10b are arranged in the plane) is S2 = 2 · Sx in the above case, and the loop is formed only by the coil 10x shown in FIG. 3A. It becomes larger than the transmission / reception area of the antenna. Accordingly, the probability that the magnetic flux generated by the communication partner device passes through the loop antenna 100 can be improved, and the communication opportunity can be improved. It is also possible to set the transmission / reception area S2 of the loop antenna 100 to be the same as the transmission / reception area of the loop antenna using only the coil 10x shown in FIG. 3A. In this case, for example, the areas Sa and Sb of the coil surfaces of the coils 10a and 10b are set to be “Sa + Sb≈Sx”. Note that in order for the loop antenna 100 to communicate with the communication partner device, the magnetic flux generated by the communication partner device needs to intersect or link with the winding of the loop antenna 100. In this case, the winding of the coil 10a and the winding of the coil 10b are arranged in the transmission / reception area S2 = Sx. That is, compared to the loop antenna 10 using only the coil 10x shown in FIG. 3A and the like, the loop antenna 100 can arrange the windings of the coils in the transmission / reception area S2 densely. Therefore, according to the loop antenna 100 according to the present embodiment, it is possible to improve the chance of communication by improving the probability that the magnetic flux generated by the communication partner device intersects or links. Such a loop antenna 100 is particularly effective when mounted on a communication device having a limited antenna arrangement area such as a card. In other words, according to the present embodiment, even when the arrangement area is limited, the communication opportunity (that is, the coupling opportunity) is improved by making the windings dense without reducing the area, and the mutual inductance M Can be reduced.

  Here, the case where the inductances La and Lb of the coils 10a and 10b are equal to the inductance Lx of the coil 10x shown in FIG. In this case, the strength of the magnetic field coupling by the coil 10a and the magnetic field coupling by the coil 10b can be made uniform. However, the inductances La and Lb of the coils 10a and 10b according to the present embodiment are not limited to this example. That is, the inductance La of the coil 10a and the inductance Lb of the coil 10b can be set to different values. For example, the inductance La of the coil 10a is set equal to the inductance Lx of the coil 10x shown in FIG. And the inductance Lb of the coil 10b is arbitrarily set. Then, the inductance L2 of the loop antenna 100 becomes a value where La = Lx in the above equation 3. In this case, the inductance Lb can be adjusted by increasing or decreasing the number of turns Nb of the coil 10b and the area Sb of the coil surface relative to the coil 10a. For example, if “Lx (ie La) << Lb”, “L2≈Lx” can be set, and if “Lx (ie La) >> Lb”, “L2≈Lb” can be set. it can. In this case, for example, when it is not desired to change the condition “L2 = Lx” for the inductance L2 of the loop antenna 100, but it is desired to increase the transmission / reception area S2 of the loop antenna 100, an optimum condition that satisfies “Lx << Lb” is satisfied. It is possible to design the coil 10b. On the other hand, for example, when the inductance L2 of the loop antenna 100 is set to be equal to or less than Lx and the transmission / reception area S2 of the loop antenna 100 is to be increased, an optimum condition that satisfies “Lx <Lb (so that Lx << Lb is not satisfied)” It is possible to design the coil 10b. Note that the actual inductance of each coil and the area of the coil surface described above depend on the shape of the antenna (for example, the antenna 20 shown in FIG. 4A) of the device with which the communication is performed, so that it is optimal by, for example, actual measurement or experiment. It is desirable to set.

  However, here, “Lx << Lb” means that Lx is sufficiently or very small compared to Lb, and “Lx >> Lb” is conversely that Lx is sufficiently or very small compared to Lb. It means a big case. That is, for example, when Lx << Lb, Lx can be set to a level that can be ignored electrically when compared with Lb, and when Lx >> Lb, it is compared with Lx. In this case, Lb can be set to a size that can be ignored electrically.

  As described above, according to the loop antenna 100 according to the present embodiment, the mutual inductance can be reduced, the strength of magnetic field coupling can be reduced, and the burden on the communication partner device can be reduced. Therefore, it is possible to reduce the adverse effect on the communication partner device and the adverse effect on the communication circuit itself connected to the loop antenna 100. At this time, the transmission / reception area S2 (area where the coil is arranged; also referred to as opening area) is not required to be extremely reduced, and conversely, the transmission / reception area S2 is increased or the winding arrangement density is increased. It is possible to Therefore, according to the loop antenna 100 according to the present embodiment, the magnetic field from the communication partner device can be sufficiently linked (or crossed), and sufficient amplitude and energy can be transmitted to establish communication. Can do.

<3. Second Embodiment>
The first embodiment of the present invention has been described above.
Next, a second embodiment of the present invention will be described with reference to FIGS. 2A and 2B. Hereinafter, other modified examples and the like will be described using the configuration of the second embodiment as an example. The second embodiment and other modified examples are basically configured in the same manner as the first embodiment except that the number of coils is different, and the same operational effects can be obtained. Therefore, the following description will focus on differences from the first embodiment. At this time, when describing another modification, not only the second embodiment but also the configuration of the first embodiment are taken as an example as appropriate.

  FIG. 2A is an explanatory diagram illustrating a configuration of a loop antenna according to the second embodiment of the present invention. FIG. 2B is an explanatory diagram illustrating an equivalent circuit of the loop antenna according to the present embodiment.

[3-1. About the number of coils]
As shown in FIG. 2A, the loop antenna 200 according to the present embodiment further includes coils 10c and 10d as a plurality of coils in addition to the two coils 10a and 10b. That is, the loop antenna 200 has four coils 10a to 10d. The coils 10a to 10d are electrically connected in parallel, and are arranged on the same plane so that the coil surfaces of the coils do not overlap each other.

  The coils 10a and 10b are formed in the same manner as in the first embodiment. On the other hand, the coil 10c is formed such that the number of turns is Nc, the area of the coil surface is set to Sc, and the inductance is Lc. The coil 10d is formed such that the number of turns is Nd, the area of the coil surface is set to Sd, and the inductance is Ld. In this case, the transmission / reception area S2 of the loop antenna 200 is “S2≈Sa + Sb + Sc + Sd”. In the present embodiment, the transmission / reception area S2 is an example of an area where the coils 10a to 10d are arranged on a plane. At this time, the winding directions of the coils 10a to 10d are all set to be the same direction. That is, when a transmission signal is input from the terminals A and B, the coils 10a to 10d are formed so that the directions of the magnetic fields generated by the coils 10a to 10d are all the same (for example, the direction toward the front or the back of the page). The

  As in this embodiment, the number of coils that are electrically connected in parallel and constitute one loop antenna may be any number as long as it is two or more. At this time, the coils are desirably arranged in a matrix as shown in FIG. 2A. When arranged in a matrix, the transmission / reception area S2 of the loop antenna can be expanded two-dimensionally, or the arrangement density of the windings in the loop antenna can be increased.

  The first embodiment (two coils), the present embodiment (four coils), and the loop antenna having three or more coils include, for example, a winding method, an embedding method, a printing method, It can be formed by an etching method or the like. In addition, as a method of connecting a plurality of coils in parallel, not only directly connecting each coil in parallel as shown in FIG. 1A, but also, for example, a plurality of coils are formed on a substrate and a through formed on the substrate is formed. It is also possible to connect the coils in parallel via a hole (through hole or the like).

[3-2. About coil area]
As described above, the transmission / reception area S2 of the loop antenna 200 is “S2≈Sa + Sb + Sc + Sd”. For example, if “Sa = Sb = Sc = Sd = Sx”, then “S2≈4 · Sx> Sx”. Therefore, it is possible to further increase the area where the magnetic field generated by the communication counterpart device when establishing non-contact communication should be linked (or crossed). Therefore, according to the loop antenna 200 according to the present embodiment, it is possible to increase the probability that the magnetic field generated by the device on the communication partner side will be linked (or crossed) and increase the communication opportunity. Further, similarly to the case of the first embodiment, for example, “S2≈Sx”, that is, “Sa + Sb + Sc + Sd≈Sx” may be set. In this case, similarly to the first embodiment, the arrangement density of the windings in the transmission / reception area S2 can be improved without changing the transmission / reception area S2. Also in this case, as a result, it is possible to increase the probability that the magnetic field generated by the device on the communication partner side will link (or cross) the windings, and increase the communication opportunity.

  As described above, the transmission / reception area S2 of the loop antenna 200, that is, the arrangement area of the plurality of coils, is set to, for example, the coil surface of one coil 10x in the loop antenna 10 formed by one coil 10x as shown in FIG. 3A. It is possible to set more than the area. As a result, the loop antenna 200 in the present embodiment can increase the probability of occurrence of magnetic field coupling due to electromagnetic induction and increase communication opportunities. This also applies to the loop antenna 100 according to the first embodiment.

[3-3. About coil inductance]
FIG. 2B shows an equivalent circuit of the loop antenna 200 shown in FIG. 2A.
As shown in this equivalent circuit, the four coils 10a to 10d are connected in parallel. Therefore, the inductance L2 of the loop antenna 200 according to the present embodiment is expressed as the following Expression 5.

…（式５）

... (Formula 5)

  Here, as in the first embodiment, if “La = Lb = Lc = Ld = Lx” is assumed, “L2 = Lx / 4” is obtained, and the inductance of the loop antenna 200 is also reduced to reduce the communication partner. The mutual inductance M with the device can be reduced. As a result, it is possible to reduce the strength of magnetic field coupling while enabling transmission of necessary amplitude and energy without reducing the number of turns and opening area (coil arrangement area) of each coil. Of course, the inductances La to Ld of the coils 10a to 10d are not necessarily equal. It is possible to adjust the inductance of each coil 10a to 10d by increasing or decreasing the area Sa to Sd of each coil surface 10a to 10d or increasing or decreasing the number of turns Na to Nd. For example, when 5 coils are further added from FIG. 2A (2 × 2 coils) and 3 × 3 coils are connected in parallel, the inductance of the coil at the center is made larger or smaller than other coils. It is also possible. Such adjustment of the inductance enables a new design of the loop antenna. In addition, since the number of coils connected in parallel, the inductance of each coil, and the area of the coil surface of each coil also depend on the shape of the antenna (for example, the antenna 20 shown in FIG. 4A) of the communication partner device, etc. For example, it is desirable that the optimum setting is made by actual measurement or experiment.

[3-4. Coil placement position, etc.]
Heretofore, the first embodiment and the second embodiment of the present invention have been described. In the loop antenna 100 according to the first embodiment and the loop antenna 200 according to the second embodiment, the case where the plurality of coils 10a to 10d are arranged on the same plane has been described. However, the arrangement positions of the plurality of coils 10a to 10d are not limited to the same plane.

  For example, in the case of the loop antenna 100 according to the first embodiment, the surface on which the coil 10a is disposed and the surface on which the coil 10b is disposed may have a predetermined angle. Moreover, each coil 10a, 10b may have a coil surface that is bent or curved. In these cases, since the loop antenna 100 can be magnetically coupled to a communication partner device using either the coil 10a or the coil 10b, the loop antenna 100 can be mounted on various types of communication devices.

  Further, for example, in the loop antenna 100 shown in FIG. 1, the interval d between the coils 10a and 10b is extended so that the winding part l1 of the coil 10a and the winding part l2 of the coil 10b overlap each other. The coil 10b or the coil 10a can be folded back. In this case, a part l1 of the winding of the coil 10a and a part l2 of the winding of the coil 10b overlap each other, but the part l1 and the part l2 have the same direction (for example, the lower side of the drawing). (Or upward) current flows, so that communication with each other is not hindered. In this manner, by arranging a part of the plurality of coils so as to be overlapped, it is possible to reduce the coil arrangement area S2.

  However, when the plurality of coils 10a to 10d are arranged on the same plane as in the first embodiment and the second embodiment, the transmission / reception area S2 of the loop antennas 100 and 200 (that is, the arrangement area of the coils 10a to 10d). Can be increased. Usually, for example, when the loop antennas 100 and 200 are mounted on a communication device such as a card, there is a high possibility that the card is held substantially in parallel with a communication partner device. In this case, the convenience of the user is improved when the transmission / reception area S2 of the loop antennas 100 and 200 is expanded on the plane of the card. Therefore, it is desirable to arrange the plurality of coils 10a to 10d on the same plane as in the first and second embodiments.

  As mentioned above, although preferred embodiment of this invention was described in detail, referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

It is explanatory drawing explaining the structure of the loop antenna which concerns on 1st Embodiment of this invention. It is explanatory drawing explaining the equivalent circuit of the loop antenna which concerns on the same embodiment. It is explanatory drawing explaining the structure of the loop antenna which concerns on 2nd Embodiment of this invention. It is explanatory drawing explaining the equivalent circuit of the loop antenna which concerns on the same embodiment. It is explanatory drawing explaining the structure of the loop antenna which concerns on related technology. It is explanatory drawing explaining the equivalent circuit of the loop antenna which concerns on related technology. It is explanatory drawing explaining the non-contact communication by a loop antenna. It is explanatory drawing explaining the equivalent circuit of non-contact communication by a loop antenna.

Explanation of symbols

1, 2 Communication device 10, 100, 200 Loop antenna 10a, 10b, 10c, 10d, 10x Coil 11, 21 Communication circuit A, B terminal

Claims (7)

It has a plurality of coils that can contactlessly communicate with other devices by magnetic induction,
The plurality of coils are loop antennas that are electrically connected to each other in parallel.   The loop antenna according to claim 1, wherein the plurality of coils are arranged on the same plane so that the coil surfaces do not overlap each other.   3. The loop antenna according to claim 2, wherein an area where the plurality of coils is arranged on the plane is equal to or larger than an area of a coil surface of the one coil in the loop antenna formed by one coil.   The loop antenna according to any one of claims 1 to 3, wherein at least one inductance of the plurality of coils is equal to an inductance of the one coil in a loop antenna formed by one coil.   The loop antenna according to claim 4, wherein the inductance of each of the plurality of coils is the same.   The loop antenna according to claim 1, wherein the plurality of coils are formed by a single conducting wire. Having a loop antenna formed by a plurality of coils capable of non-contact communication with other devices by magnetic induction;
The communication device, wherein the plurality of coils are electrically connected to each other in parallel.

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