JP2008131116A - Antenna coil - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna coil which operates normally between a metal-adaptive tag brought into contact with a metallic article and a reader writer. <P>SOLUTION: A magnetic member 4 is stacked on a substrate 3, provided with a hollow core coil 2, in parallel and stored in a case 5. The hollow core coil 2 is a coil formed in a plane to transmit and receive radio waves, and electrically connected to a circuit for radio frequency identification. The substrate 3 is an insulating member where the hollow core coil 2 is arranged. The magnetic member 4 is a flat plate type member made of a material functioning as a magnetic core. The case 5 is a thin type housing formed of an insulating material. The hollow core coil 2 forms a gap between the substrate 3 and magnetic member 4 stored in the case 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an antenna coil used for, for example, an IC card, an identification tag and the like using RFID (Radio Frequency Identification) technology.

  In recent years, an IC chip that can store information electronically, and a system using a card or a tag that includes an interface for exchanging information between the IC chip and the outside, has attracted attention because of its various possibilities. Collecting. Such a system is generally called an RFID system, and is used for solid-state authentication and data transmission / reception in various situations by combining a small recording medium (card or tag) with a reader / writer for reading and writing to the medium. can do.

  As for a small-sized recording medium, there are various names such as an RFID card, an IC card, a wireless card, an RFID tag, and an IC tag. Hereinafter, it is referred to as a tag, but is not intended to be limited to a specific type, and is a broad concept including all the various cards and tags as described above. Such a tag can store a large amount of information in the memory of the IC chip and can prevent counterfeiting as compared with the magnetic recording type used in conventional cards. Widely used as cards, electronic money, electronic tickets, telephone cards, ID cards, cargo management tags, and the like.

  As a method for transmitting and receiving information to and from the reader / writer, a contact type in which an electrode contact provided on the surface of the tag and a contact terminal provided on the reader / writer are brought into contact with each other, provided on the tag and the reader / writer. There is a non-contact type that is performed wirelessly through an antenna coil. In particular, non-contact type tags have high durability and convenience because they do not wear due to contact, do not require a mechanism to move the tag to the reader / writer, and have a high degree of freedom in direction during transmission and reception. It is expected that it will be widely used.

  By the way, in the non-contact type RFID system that performs transmission / reception via the antenna coil as described above, when there is metal on the back surface of the tag, the communication distance is significantly reduced. In order to cope with this, a structure in which a flat magnetic member and a metal shield member are arranged in parallel with the antenna coil has been proposed (see Patent Documents 1 to 3). This is called a metal-compatible tag. The metal-compatible tag that is in close contact with the metal article prevents the antenna coil from operating normally due to the eddy current that occurs because the magnetic flux generated by the tag penetrates the metal. .

JP 2004-304370 A JP 2005-340759 A JP 2006-13976 A JP 2002-344226 A

  By the way, since the metal articles (metal articles) as described above are generally larger than metal-compatible tags, there are portions that are not covered by the metal-compatible tags. On the other hand, in order to increase the communication distance, it is necessary to increase the antenna coil on the reader / writer side.

  For this reason, for example, as shown in FIG. 7, when the metal-compatible tag Y closely attached to the metal article X is brought close to the antenna coil for the reader / writer (R / W), the portion not covered with the metal-compatible tag Y , An eddy current is generated by the magnetic flux from the R / W antenna coil, and an opposite magnetic field (demagnetizing field) is generated.

  Due to the influence of the demagnetizing field, the L value of the R / W antenna coil decreases and the resonance frequency shifts to the high frequency side. As a result, the impedance Z of the antenna circuit increases and communication becomes impossible. Such a problem is pointed out in Patent Document 4, but the solution is different from the present invention.

  The present invention has been proposed in order to solve the above-described problems of the prior art, and the purpose of the present invention is normally between a metal-compatible tag closely attached to a metal article and a reader / writer. It is to provide an antenna coil that operates.

  In order to achieve the above object, the present invention is characterized in that a flat magnetic member is disposed on the communication surface side of an antenna coil having a coil portion wound spirally in a plane. And

As another desirable mode, the following antenna coil can be considered.
(1) A gap is provided on the upper surface of the magnetic member.
(2) A flat magnetic member is provided on the side opposite to the communication surface.
(3) Provide a metal shield member on the opposite side of the communication surface.
(4) The thickness of the magnetic member on the communication surface side is 2 mm or less.
(5) The magnetic member on the communication surface side is made of soft magnetic metal, amorphous or ferrite.
(6) Larger than the antenna coil of the communication partner tag.

  As described above, in the present invention, by arranging a flat magnetic member on the communication surface side, an antenna coil that operates normally between a metal-compatible tag closely attached to a metal article and a reader / writer is provided. Can be provided.

  The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described. In addition, although this embodiment is an antenna coil applied to an RFID reader / writer, for example, the specific structure of the reader / writer and the RFID tag that communicates with the reader / writer is not limited to a specific one. Omitted.

  Moreover, in the following description, the structure of each embodiment is demonstrated and the effect of each embodiment is demonstrated by the measurement result based on the Example produced corresponding to each.

[First Embodiment]
[Constitution]
First, the configuration of the first embodiment will be described with reference to FIGS. 1 and 2. That is, the antenna coil 1 (for a reader / writer) according to the present embodiment is configured by stacking magnetic members 4 in parallel on a substrate 3 on which an air-core coil 2 is provided, and housing the case in a case 5. Yes.

  The air-core coil 2 is a coil for transmitting and receiving radio waves formed in a plane, and is electrically connected to an RFID circuit (not shown). The air core coil 2 may be made of, for example, copper or aluminum, but is not limited thereto.

  The substrate 3 is an insulating member on which the air-core coil 2 is disposed. The material of the substrate 3 may be formed of, for example, polyimide, but is not limited to this. The magnetic member 4 is a flat plate member made of a material that functions as a magnetic core. The material of the magnetic member 4 may be, for example, a composite material of soft magnetic metal, amorphous or ferrite powder (or flakes) and plastic or rubber, but is not limited thereto.

  The case 5 is a thin casing formed of an insulating material. A gap is formed by the air-core coil 2 between the substrate 3 accommodated in the case 5 and the magnetic member 4. The space may be a blank space, or a nonmagnetic material and an insulating material may be provided or filled.

  In FIG. 1, a gap is provided between the magnetic member 4 and the case 5 in order to ensure that communication is possible outside the case 5 by including a non-communication area close to the magnetic member 4 in the case 5. Is. This gap may also be a space, a nonmagnetic material, and an insulating material. Further, FIG. 2 eliminates a region where communication cannot be performed by increasing the thickness of the magnetic member 4 and reduces the gap between the magnetic member 4 and the case 5 to reduce the thickness.

[Function and effect]
The operational effects of the present embodiment as described above will be described based on a plurality of actually produced examples and comparative examples.
[Examples with different thicknesses of magnetic members]
First, a plurality of examples with different thicknesses of the magnetic member 4 were produced. The size of the substrate 3 used for the antenna coil 1 is 75 × 70 mm, and the size of the antenna by the air-core coil 2 and the cross-sectional area of the coil are as shown in Table 1 below.

And as shown in Table 2, the magnitude | size of the magnetic sheet used as the magnetic member 4 was 75x70 mm, and Examples 1-7 different about thickness were produced. In Examples 1 to 7, the thicknesses were 0.4, 0.8, 1.0, 1.5, 2.0, 2.5, and 3.0 mm, respectively.

  As Comparative Example 1, as shown in FIG. 3, the same ones as in Examples 1 to 7 were produced except that the magnetic member 4 was not present (magnetic sheet thickness 0.0 mm) and the case 5 was not present.

[Metal tags for communication partners]
The metal corresponding | compatible tag used as a communicating party with said comparative example 1 and Examples 1-7 is demonstrated. As shown in FIGS. 1 to 3, the basic configuration is obtained by laminating a magnetic member 40 and a metal article 60 in parallel on a substrate 30 provided with an air-core coil 20. As shown in Table 3, the actual test was made by attaching four types of tags A to D in the center of a 120 × 120 mm aluminum plate (thickness 2.0 mm). Using.

  Note that these tags A to D actually used are commercially available products from different manufacturers, and the materials and the like of the magnetic member 40 are different. Therefore, the difference in characteristics between the tags does not depend only on the difference in size, area, and the like.

[Communication characteristics]
Tables 4 to 7 show the results of the above-described comparative example 1 and examples 1 to 7 and the measurement of the availability of communication by changing the distance corresponding to the metal. In these tables, communication is indicated by ◯, and communication is impossible by ×.

これによると、タグＡ，Ｃ，Ｄが近づいた場合には、金属の影響を受けて、通信不可能な距離（１２ｍｍ〜２６ｍｍ程度）が存在することが分かる。 First, Table 4 shows communication results between Comparative Example 1 and tags A to D.

According to this, when the tags A, C, and D are approaching, it is understood that there is a distance (about 12 mm to 26 mm) where communication is impossible due to the influence of metal.

Next, communication results between Examples 1 to 4 and tags A to D are shown in Tables 5 to 8.

  According to this, by disposing the magnetic member 4 on the communication surface of the antenna coil 1, it is possible to greatly reduce or eliminate the distance in the vicinity of which communication with the tags A to D is impossible. This is because when the tags A to D are brought into close contact with a metal article 60 larger than this and brought close to the antenna coil 1, magnetic flux due to eddy current generated in a portion not covered by the tags A to D is generated by the magnetic member 4. As a result, the antenna coil 1 operates normally.

  The range in which this communication is impossible varies depending on the area ratio between the antenna coil 1 and the tags A to D (tag side antenna coils). For this reason, as shown in FIG. 1, if a gap is provided between the magnetic member 4 and the case 5 in accordance with the characteristics of the worst antenna coil 1 expected to be used, the range that does not operate normally is absorbed. be able to. For example, when communicating with the tag A in Table 5, a gap of 12 mm or more is provided between the magnetic member 4 and the case 5 to cover a portion where communication is impossible, and outside the case 5 If there is, it can be configured to communicate.

Furthermore, Tables 9 to 11 show communication results between Examples 5 to 7 and tags A to D.

  Thus, when the magnetic member 4 is thickened (2.0, 2.5, 3.0 mm), there is no distance that cannot be communicated in the vicinity. For this reason, as shown in FIG. 2, it is not necessary to provide a gap between the magnetic member 4 and the case 5, and the overall thickness can be reduced.

  On the other hand, in Tables 4 to 11, the maximum communicable distance is summarized in the graph of FIG. As is apparent from FIG. 4, when the magnetic member 4 is thickened, the magnetic flux from the antenna coil 1 also decreases, and the communication distance tends to decrease. As in the case of Example 7 and tag D, communication may not be possible. To do. For this reason, it is necessary to select an appropriate thickness of the magnetic member 4 according to the application so that the maximum communicable distance can be sufficiently obtained while ensuring communication in the vicinity.

[Second Embodiment]
[Constitution]
The configuration of the second embodiment of the present invention will be described with reference to FIG. That is, the present embodiment is basically the same configuration as the first embodiment (no gap between the magnetic member 4 and the case 5). However, in the present embodiment, even if the antenna coil 1 on the reader / writer side is also in contact with the metal article (conductor plate 8), in order to increase the communication distance, the side opposite to the communication surface of the substrate 3 is used. It is characterized in that a magnetic member 4a and a shield member 6 are laminated on the surface via a spacer 7.

  The magnetic member 4 a is a flat plate made of the same material as the magnetic member 4. The shield member 6 is a metal flat plate. The material of the shield member 6 may be aluminum, for example, but is not limited to this. Further, the spacer 7 is inserted so that a gap is formed between the substrate 3 and the magnetic member 4a.

[Function and effect]
The operational effects of the present embodiment as described above will be described based on a plurality of actually produced examples and comparative examples.
[Example in which a magnetic member is provided on the side opposite to the communication surface]
First, as shown in FIG. 5, Example 8 was obtained by providing a magnetic member 4 a having a thickness of 2.0 mm on the side opposite to the communication surface of the substrate 3. In addition, the thickness of the magnetic member 4 on the communication surface side was 1.0 mm, the thickness of the shield member 6 was 1.0 mm, and the sizes of the magnetic members 4 and 4a and the shield member 6 were 75 × 70 mm. Further, as shown in FIG. 6, Comparative Example 2 was the same as Example 8 except that the magnetic member 4 was not provided on the communication surface side.

[Communication characteristics]
Tables 12 and 13 show the results of measuring the communication distances with the same tags A to D as in the above embodiment for the above Example 8 and Comparative Example 2.

  From Tables 12 and 13, the following can be understood. That is, when there is no magnetic member 4a, there is an incommunicable distance (about 2 mm to 8 mm) when the tags A, C, and D approach, but in the vicinity when the magnetic member 4a is present. There is no distance that cannot be communicated.

  Even in the present embodiment, if the magnetic members 4 and 4a are present, the communication distance tends to decrease. Therefore, the maximum distance for communication can be sufficiently obtained while ensuring communication in the vicinity. Accordingly, it is necessary to select an appropriate thickness of the magnetic members 4 and 4a.

[Other Embodiments]
The present invention is not limited to the embodiment as described above, and the material, size, shape, number, arrangement, and the like of each member can be appropriately changed, and various modes can be used as described below. Is included. For example, in the above embodiment, a plate-shaped member prepared in advance is used as the magnetic member. However, the magnetic member may be formed by printing or applying a resin containing a magnetic material on the shield member. Good. Further, as a part or all of the magnetic material, a flat magnetic powder may be used in order to improve the shielding characteristics.

It is sectional drawing which shows the antenna coil (with a gap) of the 1st Embodiment of this invention. It is sectional drawing which shows the antenna coil (there is no gap) of the 1st Embodiment of this invention. It is sectional drawing which shows the comparative example of embodiment of FIG. It is explanatory drawing which shows the relationship between the magnetic sheet thickness and communication distance in embodiment of FIG. It is sectional drawing which shows the antenna coil of the 2nd Embodiment of this invention. It is sectional drawing which shows the comparative example of embodiment of FIG. It is a figure explaining the problem when affixing an RFID tag on a metal article.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Antenna coil 2, 20 ... Air core coil 3, 30 ... Board | substrate 4, 4a, 40 ... Magnetic member 4a ... Magnetic member 5 ... Case 6 ... Shield member 7 ... Spacer 8 ... Conductor plate 60 ... Metal article

Claims (7)

In an antenna coil provided with a coil portion wound spirally in a plane,
An antenna coil comprising a flat magnetic member disposed on the communication surface side.   The antenna coil according to claim 1, wherein a gap is provided on an upper surface of the magnetic member.   3. The antenna coil according to claim 1, wherein a flat magnetic member is disposed on the side opposite to the communication surface.   The antenna coil according to any one of claims 1 to 3, wherein a metal shield member is disposed on a side opposite to the communication surface.   The antenna coil according to any one of claims 1 to 4, wherein a thickness of the magnetic member on the communication surface side is 2 mm or less.   The antenna coil according to any one of claims 1 to 5, wherein the magnetic member on the communication surface side is made of soft magnetic metal, amorphous or ferrite.   The antenna coil according to claim 1, wherein the antenna coil is larger than an antenna coil of a tag of a communication partner.

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