JP2011035493A - Antenna device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna device for an RFID tag which can be installed on various subjects regardless of the material of an installation subject. <P>SOLUTION: The antenna device for the RFID tag is constituted in which an antenna element having a substrate and a conductor pattern installed on the substrate is disposed on a first dielectric layer, and characteristically includes a second dielectric layer, an artificial medium, and a ground plane, wherein the first dielectric layer has the antenna element installed on its one side and the artificial medium installed on its another side, the second dielectric layer has the artificial medium installed on its one side and the ground plane installed on its another side, and a total length of the ground plane is substantially equal to or shorter than the total length of the second dielectric layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an antenna device, and more particularly to an antenna device that can be used for an RFID tag or the like.

  In recent years, RFID (Radio Frequency Identification) technology has attracted attention as contactless authentication technology using electromagnetic fields and radio waves. In the RFID technology, an RFID tag (general name of a medium in which information is exchanged using the RFID technology, such as an IC tag and a non-contact IC card) having an antenna element on which an IC chip processed into a tag or a label is mounted. Object authentication or the like can be performed by reading the contained information with a device called a reader. Currently, the radio frequency RFID mainly uses the UHF band and the 2.45 GHz band.

  Generally, an RFID tag cannot be attached to a metal object. This is because the original performance cannot be maintained in such a state because the RFID tag is bonded to metal. In order to solve this problem, metal-compatible RFID tags have been developed. The configuration is configured by installing an antenna element configured by installing a conductor pattern and an IC chip on an antenna substrate on a dielectric layer. Such a metal-compatible RFID tag functions as an antenna device by installing the dielectric layer side on a metal object and using the metal object as a ground plane. The operation can be performed.

International Publication No. WO2008 / 136530 Pamphlet

  However, the conventional RFID tag for metal is designed so that the performance can be exhibited for the first time when it is installed on metal. Of course, it can be installed on a non-metallic object such as ceramic. Since it does not operate, there is a problem that the installation object is limited to a metal object. In addition, even if the conventional RFID tag is made of metal, it may not operate properly depending on environmental conditions such as when the surface is wet with moisture, such as a frozen product. . Therefore, there is a demand for an RFID tag that operates properly on various installation targets without being affected by the material of the installation target and the surrounding environment.

  The present invention has been made under such a background, and an object of the present invention is to provide an antenna device for an RFID tag that can be installed on various objects regardless of the material of the installation object. To do.

In the present invention, an antenna device for an RFID tag configured by arranging a substrate and an antenna element having a conductor pattern placed on the substrate on the first dielectric layer,
And a second dielectric layer, an artificial medium, and a ground plane.
In the first dielectric layer, the antenna element is installed on one side, and the artificial medium is installed on the other side.
In the second dielectric layer, the artificial medium is installed on one side, and the ground plane is installed on the other side.
An antenna device is provided wherein the ground plane has a total length substantially equal to or shorter than a total length of the second dielectric layer.

  Here, in the antenna device according to the present invention, the ground plane may have a width substantially equal to or shorter than a width of the second dielectric layer.

  In the antenna device according to the present invention, the first and second dielectric layers may have substantially the same overall length.

  In the antenna device according to the present invention, the first and second dielectric layers may have substantially the same width.

  Furthermore, in the antenna device according to the present invention, the artificial medium may be composed of two conductor layers and a third dielectric layer between the conductor layers.

  In the antenna device according to the present invention, the artificial medium may be installed so as to overlap with a feeding point of the antenna element when the antenna device is viewed from the thickness direction.

  In this application, the “total length” of a certain element means the longer dimension of the vertical and horizontal dimensions of the element, and the “width” of a certain element means the vertical and horizontal dimensions of the element. The shorter dimension is meant. However, when the vertical and horizontal dimensions are substantially equal, either the vertical or horizontal dimension is the “full length” and the other is the “width”.

  The present invention provides an antenna device for an RFID tag that can be installed on various objects regardless of the material of the installation object.

It is an example of schematic sectional drawing of the conventional antenna device. It is an example of the schematic top view of the antenna apparatus by this invention. It is an example of the schematic sectional drawing in the AA line of the antenna apparatus shown in FIG. It is an example of schematic sectional drawing in the BB line of the antenna apparatus shown in FIG. It is the graph which showed the frequency dependence of return loss S11 obtained as a result of analysis in the antenna device by the 1st example. It is the graph which showed the frequency dependence of return loss S11 obtained as a result of analysis in the antenna device by the 2nd example. It is the graph which showed the frequency dependence of the return loss S11 obtained as a result of the analysis in the antenna device by the 3rd example. It is the graph which showed the frequency dependence of the return loss S11 obtained as a result of the analysis in the antenna device by the 4th example.

  Hereinafter, the present invention will be described in more detail.

  As described above, in the conventional RFID tag, the dielectric layer side of the RFID tag is installed on a metal object, and the surface of the metal object functions as a ground plane for the antenna device, so that the RFID tag is connected to the antenna. It works as a device. That is, the RFID tag alone does not operate as an antenna device. For this reason, generally, the RFID tag installation target is limited to a metal object that can function as a ground plane of the antenna device.

  Even when the RFID tag is installed on the surface of a metal object, the RFID tag may not operate properly as an antenna device depending on the influence of the surrounding environment, for example, when the surface is wet. is there.

  In addition, in order to obtain an appropriate operating characteristic as an antenna device, a normal RFID tag needs to be processed with high accuracy such as inserting a fine slit in a device constituent member such as a dielectric layer. Such high-precision processing not only complicates the manufacturing process but can also cause variations in the performance of the obtained product.

  Under such a background, the inventors of the present application have conducted extensive research and development on the structure of the antenna device, and as a result, an artificial medium is used and a ground plane is previously installed on the antenna device, thereby installing the RFID tag. It has been found that the subject is not limited to metal ones. According to this result, an artificial medium is used as a dielectric, a ground plane is set in the antenna device in advance, and the antenna device is configured as an “independently operated unit”. It is expected that an RFID tag that is not easily affected can be realized.

  However, when an independent operation type antenna device in which a ground plane is previously installed is actually designed and manufactured, the antenna device finally obtained is enlarged, and a small antenna device cannot be obtained. There is.

  FIG. 1 schematically shows a cross-sectional view of the antenna device disclosed in Patent Document 1 (International Publication No. WO2008 / 136530 pamphlet). This antenna device 1 includes an antenna element 15 (antenna substrate 12 and conductor pattern 10), a first spacer layer 20, an artificial medium 50 (first conductive layer 52, dielectric layer 54, and second conductive layer). 56), the second spacer layer 60, and the ground plane 70.

  As shown in FIG. 1, conventionally, a ground plane 70 of an antenna device for an RFID tag is generally designed and manufactured in a state as large as possible. This is to suppress the influence of the boundary area of the ground plane 70 as much as possible. That is, generally, when the size of the ground plane 70 is relatively small with respect to the antenna element 15, the influence of the boundary region of the ground plane 70 on the antenna element 15 cannot be ignored, and appropriate characteristics can be obtained for the antenna device 1. It is expected to disappear.

  Therefore, in order to avoid such a problem, the size of the ground plane needs to be larger than that of other components as shown in FIG. 1, for example, but this also increases the size of the entire antenna device. There is a problem of end.

  However, the inventors of the present application have found that in the antenna device provided with the artificial medium, it is difficult to cause the above-described problem in other words, in other words, the size of the ground plane is, for example, It has been found that such an antenna device operates properly even if the size of the second spacer layer 60 is reduced to about the size, and the present invention has been achieved.

That is, according to the present invention, there is provided an antenna device for an RFID tag configured by arranging an antenna element having a substrate and a conductor pattern placed on the substrate on the first dielectric layer,
And a second dielectric layer, an artificial medium, and a ground plane.
In the first dielectric layer, the antenna element is installed on one side, and the artificial medium is installed on the other side.
In the second dielectric layer, the artificial medium is installed on one side, and the ground plane is installed on the other side.
An antenna device is provided wherein the ground plane has a total length substantially equal to or shorter than a total length of the second dielectric layer.

(Configuration of antenna device according to the present invention)
Next, a specific configuration of the antenna device according to the present invention will be described with reference to FIGS.

  FIG. 2 shows an example of a schematic top view of the antenna device according to the present invention. 3 shows an example of a schematic cross-sectional view of the antenna device shown in FIG. 2 taken along line AA, and FIG. 4 shows a schematic view of the antenna device shown in FIG. 2 taken along line BB. An example of a simple sectional view is shown.

  As shown in FIGS. 2 to 4, the antenna device 100 according to the present invention includes an antenna element 115, a first spacer layer 120, an artificial medium 150, a second spacer layer 160, and a ground plane 170. It is configured by stacking in this order.

  The antenna element 115 includes an antenna substrate 112 (full length Lb, width Wb, and thickness Tb) such as a flexible resin, and a conductor pattern 110 (full length La, full length La, installed on the antenna substrate 112 and having an IC chip). Width Wa and thickness Ta). In FIG. 2, point P is a feeding point, and an IC chip is disposed here.

  The artificial medium 150 includes a dielectric layer 154 (full length Le, width We, thickness Te), and a first conductive layer 152 and a second conductive layer disposed on each side of the dielectric layer 154. 156 (each of which has a total length Ld1, a width Wd1, a thickness Td1, and a total length Ld2, a width Wd2, and a thickness Td2). Both the conductive layers 152 and 156 are installed so that their positions are aligned along the thickness direction of the artificial medium 150.

  The first and second spacer layers 120 and 160 (full length Lc, width Wc, thickness Tc, and full length Lf, width Wf, thickness Tf, respectively) are made of a general dielectric. The ground plane 170 (full length Lg, width Wg, thickness Tg) is made of metal such as copper, for example.

  For the sake of clarity and simplification, the conductor pattern 110 in FIGS. 3 and 4 is not shown in accordance with the pattern corresponding to the conductor pattern 110 in FIG. 2, that is, the conductor pattern 110 in FIGS. Note that it is shown as a uniform layer. Although not shown in FIGS. 2 to 4, a resin-like adhesive is provided between the first spacer layer 120 and the artificial medium 150 and / or between the second spacer layer 160 and the artificial medium 150. A layer may be installed.

  Thus, in the antenna device 100 according to the present invention, since the ground plane 170 is installed outside the second spacer layer 160, an “independently operated” antenna device can be obtained. Therefore, the antenna device 100 according to the present invention can be installed on an installation target made of various materials such as ceramics regardless of the material of the installation target. In addition, it is possible to provide an RFID tag that is not easily affected by the surrounding environment such as moisture.

  2 to 4, the total length Lg of the ground plane 170 is equal to the total length Lf of the second spacer layer 160. That is, as shown in FIG. 1 described above, only the ground plane 170 is not expanded in the X direction in FIGS. 2 and 3 with respect to the other components of the antenna device 100.

  Therefore, in the present invention, the antenna device 100 can be miniaturized, and an RFID tag with less restrictions on the size of the installation target can be provided.

  The antenna device according to the present invention is configured as an “independently operated unit” as described above. Therefore, an additional advantage is obtained that the product can be previously evaluated or inspected in advance.

  In addition, it is not necessary to install a slit or the like in the constituent member as in the conventional case, and the structure of the antenna device is simplified. As a result, the manufacturing process is simplified, and the advantage that variation in performance between products is suppressed is obtained.

2 to 4, the total length Lg of the ground plane 170 is substantially equal to the total length Lf of the second spacer layer 160. 2 to 4, the antenna substrate 112, the artificial medium 150 (the dielectric layer 154), the first spacer layer 120, and the second spacer layer 160 that constitute the antenna device 100 are all the same. This is because it has a full length. More generally, in the present invention, the total length Lg of the ground plane 170 is substantially equal to the largest total length of the antenna substrate 112, the artificial medium 150, the first spacer layer 120, and the second spacer layer 160. May have dimensions equal to.
Here, the size of the ground plane when the antenna device is viewed from above may be a size including the conductor pattern and the artificial medium that constitute the antenna element. For example, it is assumed that the conductor pattern is long in the horizontal direction, the artificial medium is long in the vertical direction perpendicular to the horizontal direction, and forms a cross character as a whole. In this case, the size of the ground plane is such a size as to include all these ten characters.
On the other hand, the total length Lg of the ground plane 170 may be smaller than the dimension Lf of the second spacer layer 160. For example, the total length Lg of the ground plane 170 may be about the total length La of the conductor pattern 110 of the antenna element 115.

  Therefore, in the present invention, the total length Lg of the ground plane 170 is the largest member among the total length La of the conductor pattern 110 to the antenna substrate 112, the artificial medium 150, the first spacer layer 120, and the second spacer layer 160. It is in the range up to the full length.

  Similarly, in the example of FIGS. 2 to 4, the width Wg of the ground plane 170 is substantially equal to the width Wf of the second spacer layer 160. 2 to 4, the antenna substrate 112, the artificial medium 150 (the dielectric layer 154), the first spacer layer 120, and the second spacer layer 160 that constitute the antenna device 100 are all the same. This is because it has a width. More generally, in the present invention, the width Wg of the ground plane 170 is substantially equal to the largest width among the widths of the antenna substrate 112, the artificial medium 150, the first spacer layer 120, and the second spacer layer 160. May have dimensions equal to. On the other hand, the width Wg of the ground plane 170 may be smaller than the dimension Wf of the second spacer layer 160. For example, the width Wg of the ground plane 170 may be about the width Wa of the conductor pattern 110 of the antenna element 115.

  Therefore, in the present invention, the width Wg of the ground plane 170 is the largest member among the width Wa of the conductor pattern 110 to the antenna substrate 112, the artificial medium 150, the first spacer layer 120, and the second spacer layer 160. It is in the range between the width.

(Characteristic evaluation)
Next, the influence of the size of the ground plane on the characteristics of the antenna device will be described using the antenna characteristic evaluation results obtained in the four specific antenna devices.

  For the evaluation of the characteristics of the antenna device, an electromagnetic field simulator Microwave Studio (registered trademark) based on the Finite Integrate method was used, and the frequency dependence of the return loss S11 of the input impedance of the antenna device was measured. Each example below includes a configuration different from the present invention (for example, the first example and the second example). However, in the following description, for the sake of clarity, each member of the antenna device will be described with reference numerals shown in FIGS.

  Table 1 summarizes the dimensions of the ground plane used in the four examples shown below.

（第１の例）
第１の例では、アンテナ装置は、以下の仕様の部材で構成されると仮定した。
（１）アンテナ素子１１５：
導体パターン１１０の寸法は、全長Ｌａが９４ｍｍ、幅Ｗａが１６ｍｍ、厚さＴａが
３８μｍとした。アンテナ基板１１２は、ＰＥＴフィルム製とし、全長Ｌｂが１００ｍｍ、幅Ｗｂが４０ｍｍ、厚さＴｂが０．０３８ｍｍとした。
（２）第１のスペーサ層１２０：
第１のスペーサ層１２０の全長Ｌｃは、１００ｍｍ、幅Ｗｃは、４０ｍｍ、厚さＴｃは、６００μｍとした。比誘電率は、１６とした。
（３）人工媒質１５０：
２つの導電層１５２、１５６の寸法は、いずれも、全長Ｌｄ１、Ｌｄ２が２５ｍｍ、幅Ｗｄ１、Ｗｄ２が４０ｍｍ、厚さＴｄ１、Ｔｄ２が１８μｍとした。２つの導電層１５２、１５６は、銅製とし、導電率σは、５．８×１０^７Ｓ／ｍとした。誘電体層１５４の寸法は、全長Ｌｅが１００ｍｍ、幅Ｗｅが４０ｍｍ、厚さＴｅが３００μｍとした。比誘電率εｒは、９．６とした。両導電層１５２、１５６は、誘電体層１５４の各側の中心部分に、該誘電体層１５４の厚さ方向に沿って位置が揃うように配置した。なお、アンテナ素子１１５の給電点Ｐは、アンテナ装置を厚さ方向から見たとき、導電層１５２、１５６のＸＹ平面の中心部分に配置される。
（４）第２のスペーサ層１６０：
第２のスペーサ層１６０の全長Ｌｆは、１００ｍｍ、幅Ｗｆは、４０ｍｍ、厚さＴｆは、１５μｍとした。比誘電率εｒは、３．３とした。
（５）グラウンドプレーン１７０：
表1に示すように、グラウンドプレーン１７０は、全長Ｌｇが無限長さ、幅Ｗｇが無限長さ、厚さＴｇが１０μｍとした。
（６）その他：
第１のスペーサ層１２０と人工媒質１５０の間、および人工媒質１５０と第２のスペーサ層１６０の間には、接着層を介在させた。接着層は、いずれも、全長が１００ｍｍ、幅が４０ｍｍ、厚さが３０μｍであり、比誘電率は、εｒ＝２．６とした。グラウンドプレーン１７０を除く各構成部材は、厚さ方向に沿って、位置が揃うように配置した。

(First example)
In the first example, it is assumed that the antenna device is composed of members having the following specifications.
(1) Antenna element 115:
The conductor pattern 110 had a total length La of 94 mm, a width Wa of 16 mm, and a thickness Ta of 38 μm. The antenna substrate 112 is made of a PET film, has a total length Lb of 100 mm, a width Wb of 40 mm, and a thickness Tb of 0.038 mm.
(2) First spacer layer 120:
The total length Lc of the first spacer layer 120 was 100 mm, the width Wc was 40 mm, and the thickness Tc was 600 μm. The relative dielectric constant was 16.
(3) Artificial medium 150:
As for the dimensions of the two conductive layers 152 and 156, the total lengths Ld1 and Ld2 were 25 mm, the widths Wd1 and Wd2 were 40 mm, and the thicknesses Td1 and Td2 were 18 μm. The two conductive layers 152 and 156 were made of copper, and the conductivity σ was 5.8 × 10 ⁷ S / m. Regarding the dimensions of the dielectric layer 154, the total length Le was 100 mm, the width We was 40 mm, and the thickness Te was 300 μm. The relative dielectric constant εr was 9.6. Both the conductive layers 152 and 156 are arranged at the central portion of each side of the dielectric layer 154 so that the positions thereof are aligned along the thickness direction of the dielectric layer 154. Note that the feeding point P of the antenna element 115 is disposed at the center of the XY plane of the conductive layers 152 and 156 when the antenna device is viewed from the thickness direction.
(4) Second spacer layer 160:
The total length Lf of the second spacer layer 160 was 100 mm, the width Wf was 40 mm, and the thickness Tf was 15 μm. The relative dielectric constant εr was 3.3.
(5) Ground plane 170:
As shown in Table 1, the ground plane 170 had an overall length Lg of infinite length, a width Wg of infinite length, and a thickness Tg of 10 μm.
(6) Other:
Adhesive layers were interposed between the first spacer layer 120 and the artificial medium 150 and between the artificial medium 150 and the second spacer layer 160. All of the adhesive layers had a total length of 100 mm, a width of 40 mm, a thickness of 30 μm, and a relative dielectric constant of εr = 2.6. The constituent members other than the ground plane 170 were arranged so that their positions were aligned along the thickness direction.

  FIG. 5 shows the return loss S11 of the antenna device obtained as a result of the analysis. From this figure, it can be seen that in the frequency range of about 0.94 GHz to about 0.96 GHz, the return loss S11 is much lower than −10 dB, and the antenna device exhibits good characteristics. Note that the return loss at this time is normalized by the complex conjugate impedance with respect to the input impedance of the IC chip in order to consider matching with the IC chip.

(Second example)
Also in the second example, the antenna device is configured in substantially the same manner as in the first example. However, in this case, the dimensions of the ground plane 170 are different from those in the first example. As shown in Table 1, the ground plane 170 had an overall length Lg of 200 mm, a width Wg of 200 mm, and a thickness Tg of 10 μm. In the ground plane 170, the other constituent members are the surface of the ground plane 170 along the thickness direction in the full length direction (X direction in FIGS. 2 to 4) and the width direction (Y direction in FIGS. 2 to 4). It installed so that it might be arrange | positioned in the center part.

  FIG. 6 shows the return loss S11 of the antenna device obtained as a result of the analysis. In the second example, the obtained return loss S11 was substantially the same as the result in the first example.

(Third example)
Also in the third example, the antenna device is configured in substantially the same manner as in the first example. However, in this case, the dimensions of the ground plane are different from those in the first example. As shown in Table 1, the ground plane had an overall length Lg of 100 mm (same dimensions as the second spacer layer 160), a width Wg of 100 mm, and a thickness Tg of 10 μm. Each component member was arranged so that the positions were aligned along the thickness direction. However, in the width direction (the Y direction in FIGS. 2 to 4), the ground plane 170 is installed along the thickness direction so that other constituent members are arranged at the center of the surface of the ground plane 170. did.

  FIG. 7 shows the return loss S11 of the antenna device obtained as a result of the analysis. In the third example, the obtained return loss S11 was substantially the same as the results in the first and second examples. From this, it was found that the antenna device 100 operates properly even when the total length Lg of the ground plane 170 is the same as that of the second spacer layer 160.

(Fourth example)
Also in the fourth example, the antenna device is configured in substantially the same manner as in the first example. However, in this case, the dimensions of the ground plane are different from those in the first example. As shown in Table 1, the ground plane 170 has the same dimensions as the second spacer layer 160. That is, the total length Lg of the ground plane 170 is 100 mm, and the width Wg is 40 mm. The thickness Tg was 10 μm. The constituent members are arranged so that their positions are aligned along the thickness direction in both the full length direction (X direction in FIGS. 2 to 4) and the width direction (Y direction in FIGS. 2 to 4) (that is, FIG. 2). -Arrangement as shown in FIG.

  FIG. 8 shows the return loss S11 of the antenna device obtained as a result of the analysis. The return loss S11 obtained in the fourth example was substantially the same as the results in the above three examples. From this, it was found that the antenna device 100 operates properly even if the ground plane 170 has the same dimensions as the second spacer layer 160.

  As described above, it has been confirmed that the characteristics of the antenna device are not significantly affected even when the size of the ground plane changes from an infinite length to a size substantially equal to the second spacer layer.

  The present invention can be used for an RFID tag using RFID technology.

DESCRIPTION OF SYMBOLS 1 Conventional antenna apparatus 10 Conductor pattern 12 Antenna board | substrate 15 Antenna element 20 1st spacer layer 50 Artificial medium 52 1st conductive layer 54 Dielectric layer 56 2nd conductive layer 60 2nd spacer layer 70 Ground plane 100 Antenna device according to invention 110 conductor pattern 112 antenna substrate 115 antenna element 120 first spacer layer 150 artificial medium 152 first conductive layer 154 dielectric layer 156 second conductive layer 160 second spacer layer 170 ground plane

Claims (6)

An antenna device for an RFID tag configured by arranging an antenna element having a substrate and a conductor pattern placed on the substrate on a first dielectric layer,
And a second dielectric layer, an artificial medium, and a ground plane.
In the first dielectric layer, the antenna element is installed on one side, and the artificial medium is installed on the other side.
In the second dielectric layer, the artificial medium is installed on one side, and the ground plane is installed on the other side.
The antenna device according to claim 1, wherein a total length of the ground plane is substantially equal to or shorter than a total length of the second dielectric layer.   The antenna device according to claim 1, wherein the ground plane has a width substantially equal to or shorter than a width of the second dielectric layer.   The antenna device according to claim 1 or 2, wherein the first and second dielectric layers have substantially the same overall length.   4. The antenna device according to claim 1, wherein the first and second dielectric layers have substantially the same width. 5.   The antenna device according to any one of claims 1 to 4, wherein the artificial medium includes two conductor layers and a third dielectric layer between the conductor layers.   The antenna device according to claim 1, wherein the artificial medium is installed so as to overlap a feeding point of the antenna element when the antenna device is viewed from a thickness direction.

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