JP5479226B2 - RFID antenna - Google Patents

Description

  The present invention relates to an RFID antenna used for reading an IC tag.

  As an antenna used when reading data from an IC tag using technology related to RFID (solid identification by radio waves) or writing data to an IC tag, for example, a patch antenna described in Patent Document 1 below is used. Are known.

  This patch antenna is provided with a film-like electrode on the surface of a dielectric substrate, and a ground electrode on the back surface of the dielectric substrate. The feed pin inserted into the inside from the back surface side of the dielectric substrate and the above-mentioned Electric power is supplied to the film-like electrode by capacitively coupling the film-like electrode via the dielectric substrate.

  However, in this type of antenna, an electromagnetic wave propagates in the vicinity of the peripheral edge of the membrane electrode, and therefore there is a region (insensitive region) where the intensity of the electromagnetic field is extremely weak in the portion directly above the center of the antenna body. Therefore, when the IC tag is placed in this insensitive area, there is a problem that the IC tag cannot be recognized because the reflected wave from the IC tag is weak.

  Patent Document 1 describes a patch antenna in which a film electrode for a 2.5 GHz band and a film electrode for a 1.5 GHz band are combined. A feeding point is provided for each of the film electrodes. Since the configuration is provided, a configuration associated with each of the two feeding points is required, and there is a problem that the structure is complicated in both hardware and software of the apparatus.

JP 2004-032014 A

  The problem to be solved by the present invention is to provide an RFID antenna capable of recognizing an IC tag in a wide range without an insensitive area and capable of simplifying the structure in both hardware and software of the apparatus. Is to provide.

  In order to solve the above problems, the present invention provides a first dielectric substrate, a film electrode provided on the surface of the first dielectric substrate, a ground electrode provided on the back surface of the first dielectric substrate, and the film shape. A second dielectric substrate provided in contact with the surface of the electrode; and a loop electrode provided on the surface of the second dielectric substrate; a feeding point provided at one end of the loop electrode; A connection line that electrically connects an end and the film-like electrode or the ground electrode, and the ground electrode that is not connected to the loop-like electrode by the connection line and the film-like electrode are capacitively coupled, or Provided is an RFID antenna characterized by capacitively coupling the film electrode and the loop electrode that are not connected to the loop electrode by a connection line.

In the RFID antenna according to the present invention, since the loop electrode is provided on the surface of the second dielectric substrate provided in contact with the surface of the film electrode, the loop electrode is provided by supplying power to the loop electrode. A magnetic field from the bottom to the top is generated, and it is possible to supply magnetic field energy that can be reflected by the IC tag to an IC tag placed in this region (that is, a portion directly above the center of the antenna body). Become. In addition, the power supplied to the loop electrode is supplied to the film electrode or the ground electrode through the connection line, and the ground electrode and the film electrode that are not connected to the loop electrode by the connection line are capacitively coupled. Alternatively, since the film electrode that is not connected to the loop electrode by the connection line and the loop electrode are capacitively coupled, the electromagnetic wave propagates in the vicinity of the periphery of the film electrode. Therefore, even when an IC tag is placed around the antenna body, the IC tag can be recognized.
The RFID antenna of the present invention has a configuration in which a feeding point is provided only at one end of the loop electrode, and only one feeding point is sufficient. Accordingly, since only a configuration associated with one feeding point is required, the structure can be simplified in both hardware and software of the apparatus.
Furthermore, since the RFID antenna of the present invention has both a feeding electrode and a loop electrode and a membrane electrode, the electrodes should be set to be suitable for the corresponding frequency band. Therefore, it can be applied to different frequency bands.

1A and 1B are diagrams illustrating an RFID antenna according to a first embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is a cross-sectional view taken along line AA in FIG. 2A and 2B are diagrams schematically showing the operating state of the RFID antenna according to the first embodiment of the present invention. FIG. 2A is a conceptual diagram showing the direction of current flowing through the loop electrode, and FIG. It is a conceptual diagram which shows the magnetic field generated when electric power is supplied. FIG. 3 is a diagram for explaining an experiment using the RFID antenna according to Example 1 of the present invention. 4A and 4B are diagrams illustrating an RFID antenna according to a second embodiment of the present invention, in which FIG. 4A is a plan view and FIG. 4B is a cross-sectional view taken along line AA in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments described below.

  FIG. 1 is a diagram showing an RFID antenna according to this embodiment. As shown in FIG. 1, the RFID antenna according to this embodiment includes a first dielectric substrate 1, a film electrode 2, and a ground electrode. 3, a second dielectric substrate 4, a loop electrode 5, and a connection line 6.

  The first dielectric substrate 1 and the second dielectric substrate 4 are substrates formed from a dielectric material. In the present embodiment, a substrate made of a glass epoxy material is used as the first dielectric substrate 1, and the thickness thereof is 3 mm. On the other hand, a substrate made of the same material as the first dielectric substrate 1 is used as the second dielectric substrate 4, and the thickness thereof is 1 mm.

  The film electrode 2 is made of metal and is provided on the surface of the first dielectric substrate 1 (see FIGS. 1A and 1B). In this embodiment, a rectangular electrode having a size of 35 mm × 25 mm is used as the membrane electrode 2, but the shape and size can be set as appropriate.

  The ground electrode 3 is made of metal and is provided on the back surface of the first dielectric substrate 1 (see FIG. 1B). As the ground electrode 3, one having a surface area approximately the same as that of the back surface of the first dielectric substrate 1 and a size larger than that of the film electrode 2 is used.

  The loop electrode 5 is made of metal, and is provided on the surface of the second dielectric substrate 4 provided in contact with the surface of the film electrode 2 (see FIGS. 1A and 1B). The shape of the loop electrode 5 is not limited as long as it has two end portions that do not contact each other. In this embodiment, a substantially circular one is used as the loop electrode 5, but a spiral one may be used, for example. The loop electrode 5 can generate a stronger magnetic field as the number of turns thereof increases.

  One of the two end portions of the loop electrode 5 that do not contact each other, that is, one end of the loop electrode 5 is provided with a feeding point 7 for supplying power to the loop electrode 5 (FIG. 1 ( a)). The feeding point 7 is provided only at one end of the loop electrode 5 and is not provided on the other electrodes. That is, the RFID antenna according to the present embodiment has only one feeding point 7.

  The other of the two end portions of the loop electrode 5 that are not in contact with each other, that is, the other end of the loop electrode 5 is made of a metal for electrically connecting the loop electrode 5 and the film electrode 2. A connecting line 6 is provided (see FIGS. 1A and 1B).

  In the RFID antenna configured as described above, when power is supplied from the feeding point 7 to the loop electrode 5, the power flows from one end of the loop electrode 5 to the other end. It flows through the connecting line 6 and is supplied to the membrane electrode 2. Then, when electric power is supplied to the film electrode 2, the film electrode 2 and the ground electrode 3 are capacitively coupled CC via the first dielectric substrate 1 (FIGS. 2A and 2B). reference).

  When electric power flows from one end of the loop electrode 5 to the other end in this way, a loop current LC as shown in FIG. 2A is generated, and thereby a magnetic field directed from the bottom to the top of the loop electrode 5 is generated. MF occurs (see FIG. 2B). For this reason, a strong electromagnetic field is generated in the portion directly above the center of the antenna body, which is a dead area in the conventional patch antenna. At the same time, since electromagnetic waves propagate near the periphery of the membrane electrode 2, an electromagnetic field EF is also generated around the antenna body (see FIG. 2B). Therefore, according to the RFID antenna according to the present embodiment, it is possible to recognize the IC tag in a wide range without a dead area.

  FIG. 3 is a perspective view of the antenna body 8 on which the RFID antenna according to the present embodiment is mounted. Tables 1 and 2 show the results of a reading experiment of an IC tag (21 mm in diameter) in the UHF band (952 to 955 MHz) using the antenna body 8.

  When the relative distance in the z direction between the IC tag and the antenna body 8 (that is, the distance from the center of the surface of the antenna body 8 to the IC tag) is 0 mm, by using this antenna body 8, the IC tag and the antenna body 8 are used. The data could be read from the IC tag in the entire range where the relative distance in the x and y directions was -20 to 20 mm (see Table 1). Further, even when the relative distance between the IC tag and the antenna body 8 in the z direction is 10 mm, by using this antenna body 8, the relative distance between the IC tag and the antenna body 8 in the x and y directions is -20 to 20 mm. The data could be read from the IC tag in the entire range (see Table 2).

  The RFID antenna according to the present embodiment has a configuration in which a feeding point 7 is provided only at one end of the loop electrode 5, and only one feeding point 7 is required. Only the configuration associated with point 7 is required. Therefore, there is an advantage that the structure can be simplified in both hardware and software of the apparatus.

  Although the above experiment has demonstrated the adaptation to the UHF band IC tag, the RFID antenna according to the present embodiment can also be applied to a 2.4 GHz IC tag. In the present embodiment, the loop electrode 5 and the membrane electrode 2 suitable for the frequency band are used so that they can be applied to the same frequency band. For example, the loop electrode 5 is suitable for the 953 MHz band. By setting the membrane electrode 2 to be suitable for the 2.45 GHz band, it is possible to recognize IC tags of different frequency bands while having one feeding point 7.

  FIG. 4 is a diagram showing the RFID antenna according to this embodiment. As shown in this figure, the RFID antenna according to this embodiment connects the other end of the loop electrode 5 and the ground electrode 3. It differs from the RFID antenna according to the first embodiment in that the film electrode 2 and the loop electrode 5 that are electrically connected by the line 6 and are not connected to the loop electrode 5 by the connection line 6 are capacitively coupled CC. .

  In the RFID antenna according to the present embodiment, when power is supplied from the feeding point 7 to the loop electrode 5, the power flows from one end of the loop electrode 5 to the other end, and the connection line 6 is supplied to the ground electrode 3. Then, when power is supplied to the loop electrode 5, the loop electrode 5 and the film electrode 2 are capacitively coupled CC via the second dielectric substrate 4 (see FIG. 4B).

  Thus, when electric power flows from one end of the loop electrode 5 to the other end, a magnetic field from the bottom to the top of the loop electrode 5 is generated. A strong electromagnetic field is generated directly above. At the same time, since electromagnetic waves propagate near the periphery of the membrane electrode 2, an electromagnetic field is also generated around the antenna body. Therefore, similarly to the RFID antenna according to the first embodiment, the RFID antenna according to the present embodiment can recognize the IC tag in a wide range without the dead area.

  The RFID antenna according to the present embodiment also has a configuration in which the feeding point 7 is provided only at one end of the loop electrode 5, and only one feeding point 7 is required. Only the configuration associated with point 7 is required. Therefore, there is an advantage that the structure can be simplified in both hardware and software of the apparatus.

  Further, the RFID antenna according to the present embodiment also has both the loop electrode 5 and the film electrode 2 while having one feeding point 7, so that these electrodes are respectively in the corresponding frequency bands. By setting it appropriately, it is possible to recognize IC tags in different frequency bands.

DESCRIPTION OF SYMBOLS 1 1st dielectric substrate 2 Film electrode 3 Ground electrode 4 2nd dielectric substrate 5 Loop electrode 6 Connection line 7 Feeding point 8 Antenna body

Claims (1)

  A first dielectric substrate; a film electrode provided on a surface of the first dielectric substrate; a ground electrode provided on a back surface of the first dielectric substrate; and a second dielectric provided in contact with the surface of the film electrode. A body substrate and a loop electrode provided on the surface of the second dielectric substrate, a feeding point is provided at one end of the loop electrode, the other end of the loop electrode and the film electrode or the ground electrode And connecting the ground electrode not connected to the loop electrode by the connection line and the film electrode, or connecting to the loop electrode by the connection line. An RFID antenna, wherein the film electrode and the loop electrode are not capacitively coupled.

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