JP2015142224A - Antenna device and electronic apparatus - Google Patents

Abstract

An antenna device that realizes the close arrangement of an antenna and a conductor at a low cost without reducing the conductor area.
An antenna device includes an antenna that performs communication or power transmission by electromagnetic inductive coupling, and a conductor plate that is disposed in proximity to the antenna. The conductive plate has an electromagnetic band gap structure, and the electromagnetic band gap structure has an electromagnetic band gap in the frequency band of the RF magnetic field transmitted or received by the antenna.
[Selection] Figure 1

Description

  The present invention relates to an antenna device and an electronic apparatus including the antenna device.

  In recent years, near field communication called NFC (Near Field Communication) has begun to be used, mainly for smartphones and home appliances. The NFC terminal is provided with a magnetic antenna such as a loop type or a spiral type, and communication is performed by electromagnetic induction coupling between the antennas.

  In NFC, communication is performed between a terminal (reader / writer) that issues polling and a terminal (tag) that responds to polling. As a typical operation, the reader / writer generates an RF magnetic field, and the tag obtains power necessary for the communication operation from the RF magnetic field generated by the reader / writer or an internal power source, and communicates with the reader / writer.

  In particular, in a mobile terminal such as a smartphone, an antenna may be disposed in the vicinity of a conductor such as a housing due to restrictions such as size and design. When the magnetic field antenna and the conductor are arranged close to each other, many of the RF magnetic fields link the conductors, so that an induced current having the same frequency as the RF magnetic field is generated on the conductor surface. This induced current generates a demagnetizing field that cancels the RF magnetic field. As a result, the RF magnetic field is weakened, resulting in problems such as communication distance deterioration and communication inability. That is, when the magnetic field antenna and the conductor are arranged close to each other, electromagnetic induction coupling occurs between the antenna and the conductor, and the antenna characteristics are deteriorated.

  As a method for solving the above problems, a method using a magnetic material and a method for devising a conductor shape have been proposed. For example, Patent Document 1 discloses a method of reducing interference between an antenna and a conductor and suppressing deterioration of antenna characteristics by disposing a magnetic body between the antenna and the conductor. Patent Document 2 discloses a method of suppressing a demagnetizing field and suppressing deterioration of antenna characteristics by providing one or more notches in a conductor and changing the flow of an induced current.

  On the other hand, research on artificial materials called metamaterials has been actively conducted in recent years. A metamaterial is an artificial material that behaves in a way that cannot exist in nature, and has a characteristic called a left-handed system in which both the dielectric constant and permeability are “negative”, and either the dielectric constant or the permeability. It shows a characteristic called “negative” electromagnetic band gap. Patent Document 3 proposes a method of causing an electromagnetic band gap to act as a magnetic wall that reflects electromagnetic waves in the same phase, and using this action to realize the close arrangement of the antenna and the conductor (for example, Patent Document 3).

JP 2003-108966 A JP 2009-004857 A JP 2011-217028 A

  However, the method of Patent Document 1 has a problem that it cannot be realized at low cost because it costs the material cost of the magnetic material and also causes processing costs for attaching the magnetic material to the antenna. On the other hand, the method of Patent Document 2 can be realized at low cost because it does not use a magnetic material. However, since it is necessary to provide a notch in a conductor such as a housing, EMC, heat dissipation problems associated with reduction of the conductor area, mechanical strength, etc. Problems such as deterioration occur. Patent Document 3 is effective for an electric field antenna that mainly communicates using high-frequency electromagnetic waves, but does not consider the influence of induced currents, and therefore mainly communicates using low-frequency electromagnetic induction. It is not effective for magnetic field antennas.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an antenna device that realizes a close arrangement of an antenna and a conductor.

In order to achieve the above object, an antenna device according to an aspect of the present invention has the following arrangement. That is,
An antenna for communication or power transmission by electromagnetic inductive coupling;
A conductor plate disposed close to the antenna, and an antenna device comprising:
The conductor plate has an electromagnetic band gap structure;
The electromagnetic band gap structure has an electromagnetic band gap in a frequency band of an RF magnetic field transmitted or received by the antenna.

  ADVANTAGE OF THE INVENTION According to this invention, the antenna apparatus which implement | achieves proximity | contact arrangement | positioning of an antenna and a conductor can be provided.

The top view of the antenna device which concerns on 1st embodiment. The side view of the antenna device which concerns on 1st embodiment. The figure explaining the principle of an electromagnetic band gap and a magnetic wall. The figure which shows the modification of the antenna device which concerns on 1st embodiment. The top view of the antenna device which concerns on 2nd embodiment. The side view of the antenna device which concerns on 2nd embodiment.

  Hereinafter, some preferred embodiments of the present invention will be described with reference to the accompanying drawings.

<First embodiment>
FIG. 1 is a top view of the antenna device 1 according to the present embodiment, and FIG. 2 is a side view of the antenna device 1. In addition, although the antenna apparatus in this embodiment is demonstrated supposing the antenna applied to an NFC terminal, application of the antenna apparatus of this embodiment is not limited to an NFC terminal. That is, the present invention can be applied to any antenna device including an antenna that performs communication or power transmission by electromagnetic inductive coupling.

  In the antenna device 1, the magnetic field antenna 10 transmits or receives an RF magnetic field for carrying out short-range wireless communication defined by, for example, the NFC standard with an external device. The magnetic field antenna 10 is connected to an NFC communication control IC (hereinafter referred to as an NFC chip) which is a communication circuit for executing communication defined by the NFC standard. In FIG. 1, the magnetic field antenna 10 is a spiral type, but is not limited thereto, and may be a loop type or a helical type.

  The antenna device 1 has a conductor 11 as a conductor plate disposed in the vicinity of the magnetic field antenna 10, and the conductor 11 has an electromagnetic band gap structure 100. The electromagnetic band gap structure 100 includes a conductor 11, a patch conductor 12, a connection conductor 13, and a dielectric layer 14, and has an electromagnetic band gap at least in the frequency band of the RF magnetic field. A structure in which unit cell structures 101 having patch conductors 12 and connecting conductors 13 are periodically arranged in a two-dimensional manner as shown in FIGS. 1 and 2 is called a mushroom structure, and is one of typical structures having an electromagnetic band gap. Known as one. In the present embodiment, at least a part of the conductor of the magnetic field antenna 10 is disposed on a surface that is parallel to the surface of the conductor 11 having the electromagnetic band gap structure 100 and faces the conductor 11.

  Next, the principle of the electromagnetic band gap will be described with reference to FIG. In the mushroom structure, as shown in FIG. 3A, a series capacitor CL is formed between adjacent patch conductors, and a parallel inductor LL is formed by a connection conductor, which are left-handed elements. A series inductor LR is formed by the patch conductor, and a parallel capacitor CR is formed between the patch conductor and the conductor layer. An electromagnetic band gap is formed between the parallel resonance frequency ωsh (= 1 / sqrt (LL × CR)) and the series resonance frequency ωse (= 1 / sqrt (LR × CL)). Theoretically, current propagation can be cut off in the frequency band of the electromagnetic band gap.

  Further, as shown in FIG. 3B, the mushroom structure has an electromagnetic wave incident at a resonance frequency ωm (= 1 / sqrt (L × CL)) between the series capacitor CL and L formed between the cells. Also acts as a magnetic wall that reflects in phase.

  As is clear from the above description, the frequency that becomes the electromagnetic band gap and the frequency that becomes the magnetic wall are different even in the same structure. In the magnetic field antenna, when the conductors are arranged close to each other, the factor that degrades the characteristics of the antenna is the presence of an induced current generated on the conductor surface. In other words, in the case of a magnetic field antenna, it is more effective to use the characteristics of an electromagnetic bandgap that blocks current propagation rather than the characteristics of a magnetic wall that reflects electromagnetic waves in the same phase.

  The electromagnetic band gap structure 100 has an electromagnetic band gap in the frequency band of the RF magnetic field. For example, since the frequency of the RF magnetic field in NFC is 13.56 MHz, the electromagnetic band gap structure 100 is configured to have an electromagnetic band gap in a frequency band including 13.56 MHz. More specifically, the electromagnetic bandgap structure 100 has a parallel resonance frequency ωsh <13.56 MHz, a series resonance frequency ωse> 13.56 MHz, or a parallel resonance frequency ωsh> 13.56 MHz, and a series resonance frequency ωse <13.56 MHz. Has characteristics.

  By forming the electromagnetic band gap structure 100 described above on the conductor 11, it is possible to suppress the propagation of the induced current generated on the surface of the conductor 11. That is, the proximity arrangement of the magnetic field antenna 10 and the conductor 11 can be realized while suppressing the deterioration of the antenna characteristics of the magnetic field antenna 10.

  In addition, an electromagnetic bandgap structure such as a mushroom structure can be formed on a printed circuit board, and can be realized at a lower cost than the conventional technique using a magnetic material. Further, since it is not necessary to provide a cut in the conductor, the conductor area is not reduced. As a result, problems such as EMC, heat dissipation, and mechanical strength deterioration associated with the reduction of the conductor area do not occur.

  Although the antenna device is an NFC terminal in the present embodiment, the present invention is not limited to this, and the configuration of the present embodiment is applicable to any system that uses a magnetic field antenna such as a wireless power transmission system. In the case of performing power transmission, a power circuit for generating power from the acquired RF magnetic field or transmitting power using the RF magnetic field is provided instead of or in addition to the communication circuit described above. Furthermore, in this embodiment, the electromagnetic band gap structure is a mushroom structure, but the structure is not limited to this, and any structure having an electromagnetic band gap may be used.

  Further, in the present embodiment, the magnetic field antenna 10, the patch conductor 12, the dielectric layer 14, and the conductor 11 are arranged from the top. However, the present invention is not limited thereto, and for example, as shown in FIG. The dielectric layer 14 and the patch conductor 12 may be disposed. Moreover, as shown in FIG.4 (b), the structure which forms not the conductor 11 but the electromagnetic band gap structure 100 directly under the conductor 11 may be sufficient (In this case, 15 is a conductor). In this case, the unit cell structure 101 includes the conductor 11, the conductor 15, the patch conductor 12, and the connection conductor 13, and the electromagnetic band gap structure has an electromagnetic band gap in the frequency band of the RF magnetic field described above. Will be designed. 4B, the space between the conductor 11 and the dielectric layer 14 may be filled with the same dielectric layer or different dielectric layers.

  Moreover, in the said embodiment, although short-distance wireless communication or wireless power transmission was performed via the magnetic field antenna 10, it was good also as a structure which uses these communication and power transmission also using the magnetic field antenna 10. FIG. In this case, when the frequency of the RF magnetic field is different between communication and power transmission, the electromagnetic band gap structure 100 may be configured to obtain an electromagnetic band gap including these frequencies.

<Second embodiment>
In the first embodiment, the antenna device in which the magnetic field antenna and the conductor are arranged on different planes has been described. In the second embodiment, an antenna device will be described in which the magnetic field antenna is arranged so as to be substantially flush with the surface of the conductor plate and surround the conductor plate.

  FIG. 5 is a top view of the antenna device 2 described in the second embodiment, and FIG. 6 is a side view thereof. In addition, although the antenna apparatus 2 in 2nd embodiment is demonstrated supposing an NFC terminal, it is applicable not only to this but the system of another communication system similarly to 1st embodiment.

  The magnetic field antenna 20 transmits or receives an RF magnetic field for performing communication defined by the NFC standard with an external device. The electromagnetic band gap structure 200 includes a conductor 21, a patch conductor 22, a connection conductor 23, and a dielectric layer 24, and has an electromagnetic band gap at least in the frequency band of the RF magnetic field. As shown in FIGS. 5 and 6, the magnetic field antenna 20 is formed on the edge of the conductor 21. In this embodiment, the conductor 21 is formed inside the magnetic field antenna 20, and the conductor 21 and the magnetic field antenna 20 are formed on the same plane.

  The NFC chip 25 is a communication circuit that performs communication processing for performing short-range wireless communication defined by, for example, the NFC standard with an external device. As shown in the figure, the NFC chip 25 is installed in a region within the dotted line 201 (the central portion of the conductor 21) where the electromagnetic bandgap structure 200 does not exist, and is connected to the magnetic field antenna 20. The conductor 21 also functions as a ground for the NFC chip 25. As described above, the antenna device 2 has a configuration in which the magnetic field antenna 20 is disposed so as to surround the circuit board on which the NFC chip 25 is mounted.

  Such a configuration has an advantage that the board area can be reduced compared to a configuration in which a circuit board is provided outside (for example, laterally) the magnetic field antenna because the space inside the magnetic field antenna can be used effectively. However, since the electromagnetic induction coupling is likely to occur between the magnetic field antenna and the conductor (such as the ground of the circuit board), the antenna characteristics are likely to deteriorate.

  A large amount of the induced current generated on the conductor surface flows in a portion where the interlinking magnetic field is strong. That is, in the antenna device 2, an induced current flows along the edge of the conductor 21 close to the magnetic field antenna 20. In the second embodiment, as described above, the electromagnetic band gap structure 200 is formed on the edge of the conductor 21. Therefore, it is possible to effectively suppress the propagation of the induced current generated at the edge of the conductor 21 and suppress the deterioration of the antenna characteristics.

  The components mounted on the conductor 21 are not limited to the NFC chip. For example, as described in the first embodiment, a power circuit for generating power from an externally supplied RF magnetic field or outputting an RF magnetic field for supplying power to the outside via the magnetic field antenna 20 May be installed separately. Alternatively, such a power circuit may be mounted together with an NFC chip that is a communication circuit. Further, instead of or in addition to the communication circuit and the power circuit, a connector for connecting to another substrate may be mounted.

  In the present embodiment, the configuration in which the magnetic field antenna 20 and the conductor 21 are formed on the same plane has been described. However, the present invention is not limited to this. For example, the magnetic field antenna 20 and the patch conductor 22 are formed on the same plane. It does not matter. In this case, in FIG. 6, the magnetic field antenna 20 is disposed on the side of the patch conductor 22 of the dielectric layer 24.

  As described above, according to each of the embodiments described above, the induction current generated in the conductor is suppressed by forming the electromagnetic bandgap structure on the conductor disposed close to the magnetic field antenna. Therefore, an antenna device that realizes the close arrangement of the magnetic field antenna and the conductor can be provided at a low cost without reducing the conductor area. Moreover, if the magnetic field antenna and the circuit configuration of the above embodiment are applied to various communication devices and electronic devices such as mobile phones and PDAs, an electronic device that is inexpensive and has good antenna performance in NFC communication or wireless power transmission can be obtained. Can be provided.

DESCRIPTION OF SYMBOLS 1 Antenna apparatus 10 Magnetic field antenna 11 Conductor 12 Patch conductor 13 Connection conductor 14 Dielectric layer 100 Electromagnetic band gap structure

Claims (10)

An antenna for communication or power transmission by electromagnetic inductive coupling;
A conductor plate disposed close to the antenna, and an antenna device comprising:
The conductor plate has an electromagnetic band gap structure;
The antenna device according to claim 1, wherein the electromagnetic band gap structure has an electromagnetic band gap in a frequency band of an RF magnetic field transmitted or received by the antenna.   The antenna device according to claim 1, wherein at least a part of the conductor of the antenna is disposed on a plane parallel to a plane of the conductor plate having the electromagnetic band gap structure.   The antenna device according to claim 1, wherein at least a part of the conductor of the antenna is disposed on the same surface as the surface of the conductor plate having the electromagnetic band gap structure.   The antenna device according to any one of claims 1 to 3, further comprising a communication circuit that is connected to the antenna and that performs short-range wireless communication using the RF magnetic field having the frequency band.   The antenna device according to claim 4, wherein the conductor plate functions as a ground of the communication circuit.   The antenna device according to claim 4, wherein the communication circuit is disposed so as to face the conductor plate.   The power supply circuit according to claim 1, further comprising: a power circuit that is connected to the antenna and that generates power based on the RF magnetic field having the frequency band supplied from an external device and acquired through the antenna. The antenna device according to any one of 6.   8. The power supply circuit according to claim 1, further comprising a power circuit connected to the antenna and outputting the RF magnetic field having the frequency band from the antenna for generating power by an external device. The antenna device according to 1. The antenna device according to any one of claims 1 to 3,
An electronic device comprising: a circuit connected to the antenna and processing the RF magnetic field in the frequency band obtained from the antenna.   The circuit performs a short-range wireless communication by the RF magnetic field having the frequency band using the antenna and wireless power transmission using the RF magnetic field having the frequency band via the antenna. The electronic device according to claim 9, comprising at least one of a power circuit.

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