JP2015121863A - Article management system, reader antenna and sensor sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which in conventional article management systems, an optimum read condition cannot be maintained without relying on an installation environment of a reader antenna and an RF tag.SOLUTION: An article management system according to the present invention includes: an antenna substrate that has a strip conductor 102a formed in a first face, and has a ground conductor 102g formed in a second face facing the first face; an RFID reader that reads tag information on an RF tag 104 from the RF tag 104 arranged in the vicinity of the strip conductor 102a via the strip conductor 102a; and an adjustment plate 130 that, when viewing the antenna substrate in an upper face view in a state where the RF tag 104 is arranged on the antenna substrate, is arranged at a location overlapping with at least one part of the RF tag 104, and adjusts a resonance frequency of a tag antenna of the RF tag 104.

Description

The present invention relates to an article management system using a RF tag, a reader antenna, and a sensor sheet.

  In an RFID (Radio Frequency IDentification) system that has been spreading in recent years, many article management systems that manage articles using RF tags have been proposed. In this article management system, there are two methods for the positional relationship between the RF tag and the reader antenna that transmits and receives radio signals.

  In the first method, a reader antenna is provided far away from the RF tag, and ID information (for example, tag information) of the RF tag is read from far away to manage presence / absence of an article to be managed. In the first method, since the reader antenna is provided far from the RF tag, there is a problem that erroneous detection occurs when an object or a person enters between the reader antenna and the RF tag.

  On the other hand, in the second method, an RF tag is provided in the vicinity of the reader antenna, and the presence / absence of an article to be managed is managed based on the success or failure of reading the tag information of the RF tag. In the second method, no object or person enters between the reader antenna and the RF tag, and the problem of false detection that occurs in the first method does not occur.

  When this second method is adopted, a transmission line serving as an antenna is formed on a first surface of a printed circuit board or the like (hereinafter referred to as a substrate member) as a reader antenna, and a second antenna facing the first surface is formed. A surface in which a ground conductor is formed can be used. Therefore, Patent Document 1 discloses a technique for forming a tag antenna on a TAB tape used for a non-contact IC card as one form of an antenna. Patent Document 2 discloses a surface on which an auxiliary antenna and an auxiliary antenna are provided. A first spacer having an arrangement surface for arranging the wireless IC tag without connecting the IC chip and the auxiliary antenna included in the wireless IC tag on the surface opposite to the first IC, and the first antenna sandwiching the auxiliary antenna. The second spacer provided on the opposite side of the spacer is laminated, the auxiliary antenna is provided with a hole or a notch, and a resonance part that is omnidirectional with respect to radio waves of the communication frequency is provided. The body is disclosed.

JP 2013-33354 A JP 2011-15099 A

  When the second method is adopted, the distance between the RF tag and the article to be managed greatly affects the reading accuracy. However, in the article management system to which the second method is applied, there are circumstances such as further laying a cover material or the like on the laid RF tag. Therefore, in the article management system to which the second method is applied, the distance between the RF tag caused by the thickness of the cover material and the article to be managed is optimized, and the characteristics of the signal transmitted and received between the reader antenna and the RF tag are optimized. It may not be possible to create an environment that can be set to a simple state. In this regard, Patent Documents 1 and 2 have a problem that the optimum distance between the RF tag and the management target article cannot be set according to the installation environment of the system, and the reading accuracy of the article management system cannot be sufficiently secured.

  An object of the present invention is to provide an article management system, a reader antenna, and a sensor sheet that solve such problems.

  The article management system according to the present invention includes an antenna substrate in which a strip conductor is formed on a first surface and a ground conductor is formed on a second surface opposite to the first surface; When the antenna substrate is viewed from above with an RFID reader that reads out tag information of the RF tag from an RF tag disposed in the vicinity of a strip conductor, and the RF tag is disposed on the antenna substrate, the RF And an adjustment plate that is arranged at a position overlapping at least a part of the tag and adjusts the resonance frequency of the tag antenna of the RF tag.

  The reader antenna according to the present invention includes a ground conductor to which a ground potential is applied, a dielectric layer formed on an upper surface of the ground conductor, and wiring formed on an upper layer of the dielectric layer. When the strip conductor is viewed from above with the strip conductor transmitting and receiving signals transmitted and received between the RF tag placed and the RFID reader, and with the RF tag disposed on the strip conductor, And an adjustment plate that is arranged at a position overlapping at least a part of the tag and adjusts the resonance frequency of the tag antenna of the RF tag.

  In the sensor sheet according to the present invention, an RF tag, a strip conductor wired on a lower portion of the RF tag is formed on a first surface, and a ground conductor is formed on a second surface facing the first surface. When the strip conductor is viewed from above with a plurality of antenna substrates to be formed and the RF tag disposed on the top of the strip conductor, the antenna substrate is disposed at a position overlapping at least a part of the RF tag, And an adjustment plate for adjusting the resonance frequency of the tag antenna of the RF tag.

  According to the present invention, it is possible to realize an installation capable of optimum reading regardless of the installation environment of the reader antenna and the RF tag.

1 is a schematic diagram illustrating a part of an article management system according to a first embodiment. 3 is a top view of the article management system showing the arrangement of articles to be managed and the positional relationship between the RF tag and the reader antenna in the article management system according to the first embodiment. FIG. It is sectional drawing of the front side of the article management system which shows arrangement | positioning of the management object article in the article management system concerning Embodiment 1, and the positional relationship of RF tag and a reader antenna. It is sectional drawing by the side of the goods management system which shows arrangement | positioning of the management object goods in the goods management system concerning Embodiment 1, and the positional relationship of RF tag and a reader antenna. The table | surface which shows the dependence regarding the distance r normalized by wavelength (lambda) about the relative intensity | strength of the quasi-electrostatic field in the electric field E ( _theta) , an induction electric field, and a radiation electric field is shown. It is a figure explaining the simulation conditions of the signal characteristic when not using an adjustment board in the article management system concerning Embodiment 1. FIG. It is a graph explaining the simulation result of the signal characteristic in the article | item management system at the time of setting the metal as a management object article on the conditions shown in FIG. It is a graph explaining the simulation result of the signal characteristic in the goods management system at the time of making the container into which water was put into the management object goods on the conditions shown in FIG. It is a figure explaining the simulation conditions of the signal characteristic at the time of using an adjustment board in the article management system concerning Embodiment 1. FIG. FIG. 10 is a graph for explaining a simulation result of signal characteristics in the article management system when a metal is a managed article under the conditions shown in FIG. 9. FIG. 10 is a graph for explaining a simulation result of signal characteristics in the article management system when a container containing water is used as a management target article under the conditions shown in FIG. 9. It is the figure which showed another form of the installation position of the adjustment board in the article management system concerning Embodiment 1. FIG. It is the figure which showed another form of the installation position of the adjustment board in the article management system concerning Embodiment 1. FIG.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. First, in the article management system according to the first embodiment, an RF tag is installed above the reader antenna (the direction in which the reader antenna faces the article to be managed), and at a position overlapping with at least a part of the RF tag in a top view. An adjustment plate for adjusting the resonance frequency of the reader antenna and the RF tag is installed. In the following, in order to facilitate understanding of the article management system according to the first embodiment, an article management system that does not use the adjustment plate will be described, and then the article management system that uses the adjustment plate will be described. In the following description, an article management system that does not use an adjustment plate is referred to as an article management system 1, and an article management system that uses an adjustment plate is referred to as an article management system 10.

  FIG. 1 is a schematic diagram showing a part of the article management system according to the first embodiment. In the following description, a part of the article management system according to the first embodiment is referred to as an article management system 1. As illustrated in FIG. 1, the article management system 1 according to the first embodiment includes a reader antenna 102, an RFID reader 103, an RF tag 104, and a management target article 105. Here, the reader antenna 102 includes the dielectric layer 101, the strip conductor 102a, the ground conductor 102g, and the matching termination resistor Rt.

  The dielectric layer 101 is, for example, a plate member formed of a dielectric material. In the following description, the surface on which the article to be managed of the dielectric layer 101 is placed is referred to as a surface. Further, in the following description, 102 is used as a symbol for the reader antenna except when the strip conductor and the ground conductor are individually described. The reader antenna 102 is configured by an open transmission line that is matched and terminated, and transmits and receives radio signals to and from the RF tag 104. The reader antenna 102 is a traveling wave near-field antenna for a reader using a microstrip line that is an open transmission line. Also, the reader antenna 102 is open to those that generate an electromagnetic field distribution mainly composed of a quasi-electrostatic magnetic field and an induction electromagnetic field around the transmission line, such as a coplanar line, a grounded coplanar line, a slot line, and a balanced two-wire transmission line. It can be used as a transmission line. Note that the coaxial cable or waveguide that shields the periphery of the transmission line is a shielded transmission line that does not generate such an electromagnetic field around the transmission line. Cannot be used.

  The RFID reader 103 transmits a transmission signal to the reader antenna 102 and receives a response signal generated by the tag antenna of the RF tag 104 via the reader antenna 102. More specifically, one end of the reader antenna 102 is connected to the RFID reader 103. Then, the RFID reader 103 sends the generated transmission signal to the reader antenna 102 and transmits the transmission signal to the tag antenna of the RF tag 104 that is electromagnetically coupled to the reader antenna 102. On the other hand, the RFID reader 103 receives a response signal generated by the RF tag 104 transmitted to the reader antenna 102 by wireless communication. A matching termination resistor Rt is connected to the other end of the strip conductor of the reader antenna 102.

  The RF tag 104 is located at a position where the management target article can be seen from the reader antenna 102 in a state where the article to be managed is placed nearby, and is coupled to the reader antenna 102 by electromagnetic field coupling. Although an example in which a passive tag is used as the RF tag 104 is described in this embodiment, an active tag can also be used as the RF tag 104. When the passive tag receives a signal for inquiring an ID (hereinafter referred to as tag information) from the reader antenna 102, the passive tag automatically uses a power circuit (not shown) in the chip by a part of the signal obtained via the tag antenna. Generates power to operate the chip. Further, the passive tag decodes a part of the received signal and generates reception data. The passive tag refers to the tag information stored in the memory circuit in the chip, operates a modulation circuit (not shown) to generate a modulation signal, and operates using the modulation signal as an antenna via the tag antenna. To the strip conductor 102a.

  The article to be managed 105 is disposed at a position where it is electromagnetically coupled to the tag antenna of the RF tag 104. Hereinafter, the position where the management target article 105 is placed is referred to as a management target article placement area 110. The management target article 105 preferably includes a material having a high dielectric constant such as moisture or a metal, but is not limited thereto. More specifically, in addition to PET bottle drinks, can drinks, snack foods packed in aluminum packages, bundles of thick paper such as books, rice balls, bread, side dishes in plastic packs, human bodies with hands and feet, and shoes It can be an article. The correspondence to various articles such as an article having a lot of moisture is caused by using an RFID system in a UHF band or a microwave band. In an RFID system used in a frequency band of 13.56 MHz or lower, first, the skin thickness becomes thick, so the reaction to moisture becomes extremely weak. In these frequency bands, electromagnetic induction is used for coupling between the reader and the tag. Since electromagnetic induction is a coupling by a magnetic field, it is sensitive to a difference in relative permeability, but is not sensitive to a difference in relative permittivity. Therefore, even if the relative dielectric constant of water is as high as 80, the operation of the tag antenna does not react sensitively to moisture in the case of electromagnetic induction. In general, the relative permeability takes a value in the vicinity of 1 unless many of the substances are magnetic materials. On the other hand, the dielectric constant is often very different from 1. Furthermore, unlike the RFID system that relies only on electromagnetic induction, the present invention uses the electromagnetic field components of the quasi-electrostatic magnetic field, the induction electromagnetic field, and the radiated electromagnetic field. Get higher. For example, as in an RFID system using electromagnetic induction, it is not necessary to perform alignment so that the magnetic flux generated by the reader antenna penetrates the coiled antenna of the tag, or the alignment conditions are relaxed. In addition, as the frequency band used is high, the data rate is also higher than in the case of an RFID system using electromagnetic induction. Therefore, it is desirable to use UHF band or microwave band RFID systems. Note that the RF tag 104 may be covered with a plastic plate or the like. Thereby, durability of a tag can be mentioned. The surface of the RF tag may get a small amount of moisture such as condensation. In such a case, the influence of the minute amount of water is eliminated by adjusting the coupling coefficient between the tag antenna and the managed product. It is also possible to do.

  Here, the operation of the article management system 1 according to the first embodiment will be described. The article management system 1 detects the presence / absence of an article to be managed based on the response signal generated by the RF tag 104. In performing this detection operation, the article management system 1 first sends a tag information read command from the RFID reader 103 via the reader antenna 102 as a transmission signal.

  Subsequently, the RF tag 104 receives a transmission signal. Then, the RF tag 104 generates power using a part of the received signal and starts operation. Thereafter, the RF tag 104 decodes the received signal and reproduces the received data included in the received signal. The RF tag 104 refers to the received data and the tag information included in the built-in storage circuit, and when it should respond by judging from the tag information and the received data, the modulation signal generated based on the tag signal Is sent to the reader antenna 102 as a response signal.

  At this time, the RFID reader 103 determines the presence / absence of an article to be managed based on the intensity or phase change of the response signal from the RF tag 104 corresponding to the transmitted tag information read command. As a more specific example, the RFID reader 103 determines that there is no article to be managed if the signal strength of the response signal from the RF tag 104 is strong, and manages if the signal strength of the response signal from the RF tag 104 is weak. Judge that there is an article. For example, in the example shown in FIG. 1, since there is no managed article on the RF tag 104 arranged on the rightmost side of the drawing, the RF tag 104 has a stronger signal strength than when there is a managed article. The RFID reader 103 determines that there is no management target article 105 at the position of the RF tag 104 based on the strength of the signal intensity. On the other hand, since the management target article 105 is placed on the other three RF tags 104 in FIG. 1, the signal intensity of the response signal transmitted by the other three RF tags 104 does not exist for the management target article. It becomes weaker than the case. Therefore, the RFID reader 103 determines that there is a management target article 105 at the position of the other three RF tags 104. An example of the case where the signal strength of the response signal is weak includes a case where the response signal is below the reception sensitivity of the RFID reader 103 and the response signal cannot be detected. The RFID reader 103 is connected to a computer or functions as a part of the computer, and it is assumed that the presence / absence of the management target article 105 is determined by the computer.

  Here, the signal intensity of the response signal changes as described above because the managed object 105 and the tag antenna of the RF tag 104 are electromagnetically coupled. Therefore, in the following, the positional relationship among the management target article 105, the RF tag 104, and the reader antenna 102 will be described in more detail.

  First, FIG. 2 shows a top view of the article management system 1 according to the first embodiment. In FIG. 2, the figure which expanded the area | region where one management object 105 is placed was shown as a top view. As shown in FIG. 2, in the article management system 1, the strip conductor 102 a of the reader antenna 102 is formed on the dielectric layer 101. The RF tag 104 is installed above the strip conductor 102a. Further, a management target article placement area 110 is set in which the management target article is placed at a position above the RF tag 104 and covered with the RF tag 104. Here, the position where the RF tag 104 is covered is described. However, since the RF tag 104 and the management target article need only be close enough to be electromagnetically coupled, the arrangement of the RF tag 104 and the management target article placement region 110 is as follows. It is not limited to this. The RF tag 104 includes an RFID chip 111 and a tag antenna 112.

  Next, FIG. 3 shows a cross-sectional view of the front side of the article management system 1 according to the first embodiment. FIG. 3 shows an enlarged view of a region where one managed object 105 is placed as in FIG. As shown in FIG. 3, in the article management system 1, the strip conductor 102 a is provided on the front surface side of the dielectric layer 101, and the ground conductor 102 g is provided on the back surface of the dielectric layer 101 to form the reader antenna 102. A microstrip line which is a kind of transmission line is formed. One end of the strip conductor 102a and the ground conductor 102g are connected via a matching termination resistor Rt. The RFID reader 103 is connected to the other end of the strip conductor 102a. With this connection, the strip conductor 102a is terminated with matching. Note that a cover mainly for improving durability may be disposed above the strip conductor 102a and below the ground conductor 102g.

  Further, as shown in FIG. 3, the management target article 105 is disposed at a position where the distance between the RF tag 104 and the tag antenna 112 is the first distance L1. The tag antenna 112 of the RF tag 104 is disposed at a position where the distance from the reader antenna 102 is the second distance L2. The first distance L1 and the second distance L2 are preferably set to have a relationship of L1 <L2. This facilitates the relationship between coupling coefficients k1 and k2, which will be described later, to be k1 <k2. Note that FIG. 3 shows only the distance relationship between the management target article 105, the tag antenna 112, and the reader antenna 102. However, in order to satisfy the above distance relationship, for example, the RF tag 104 is covered with a plastic plate or the like. In addition, the thickness of the plastic plate can be used. That is, the relationship between the first distance L1 and the second distance L2 can be ensured by incorporating the RF tag 104 in a plastic plate and forming a sheet in which the RF tag is incorporated by the plastic plate. Note that the method of forming a sheet with a plastic plate is one form for securing the relationship between the first distance L1 and the second distance L2, and other methods can be used. The distance here is more preferably an electrical length considering the wavelength shortening rate. Further, the distance here is preferably a line-of-sight distance.

  Next, FIG. 4 shows a side sectional view of the article management system 1 according to the first embodiment. FIG. 4 shows an enlarged view of a region where one managed object 105 is placed as in FIG. As shown in FIG. 4, in the first embodiment, the strip conductor 102 a is installed at a part of the lower portion of the RF tag 104. In the article management system 1, the RF tag 104 and the management target article 105 are installed so that the relationship between the first distance L1 and the second distance L2 satisfies the condition of L1 <L2 also in a side view.

  Here, with reference to FIGS. 2 to 4 described above, the effect of the relationship between the components of the article management system 1 will be described in more detail.

  First, as shown in FIG. 2, in the article management system 1, the article to be managed 105 is arranged above the tag antenna 112 of the RF tag 104 and at a position where the distance is the first distance L1. Further, the reader antenna 102 connected to the RFID reader 103 is disposed below the RF tag 104 and the line-of-sight distance between the reader antenna 102 and the tag antenna 112 is separated by the second distance L2. As described above, in the article management system 1, the management target article 105 is disposed outside the region sandwiched between the reader antenna 102 and the RF tag 104. Therefore, the line of sight between the reader antenna 102 and the RF tag 104 is not blocked by the management target article 105. In the article management system 1, the distance between the reader antenna 102 and the tag antenna 112 is set as the second distance L2.

  As described above, in the article management system 1, the first distance L1 between the article to be managed 105 and the tag antenna 112 and the second distance L2 that is the line-of-sight distance between the tag antenna 112 and the reader antenna 102 are adjusted. To do. In the article management system 1, the coupling coefficient k2 between the article to be managed 105 and the tag antenna 112 and the coupling coefficient between the tag antenna 112 and the reader antenna 102 are adjusted by adjusting the first distance L1 and the second distance L2. Adjust k1. In the article management system 1, the signal intensity between the tag antenna 112 and the reader antenna 102 is changed according to the coupling coefficient k2 that changes depending on the presence or absence of the article to be managed 105, and the article to be managed 105 is changed by the change in the signal intensity. Determine the presence or absence.

  Therefore, the relationship between the first distance L1, the second distance L2, the coupling coefficients k1 and k2, and the effect of the article management system 1 according to the first embodiment based on the setting will be described below. First, in the present invention, electromagnetic coupling is used, but the coupling coefficient indicating the strength of this electromagnetic coupling can be evaluated relatively easily by an electromagnetic simulator. In the description of the electromagnetic field coupling, when the wavelength of the radio signal between the tag antenna 112 and the reader antenna 102 is λ, the distance from the wave source (for example, the antenna) is λ / 2π (π is the pi). The near region is reactive near-field, the distance is longer than λ / 2π, and the region closer to λ is the radiative near-field, and these two regions are combined to produce the near field ( near-field region).

In this near field, the electromagnetic field has a complex aspect, and there exists a non-negligible intensity ratio between the quasi-electrostatic magnetic field, the induction electromagnetic field, and the radiated electromagnetic field, and the resultant electromagnetic field vector is also spatial. , Changes in time variously. As an example, when the wave source is a minute dipole antenna, the electric field E [V / m] and the magnetic field H [A / m] formed by this antenna are indicated by a spherical coordinate system (r, θ, φ) and a phasor display. It can show by Formula (1)-Formula (4).

Here, in the above formulas (1) to (4), the charge stored in the minute dipole antenna is q [C], the length of the antenna is l [m], the wavelength is λ [m], and from the wave source to the observation point Was set to r [m]. Further, π is a circular constant, ε is a dielectric constant, and μ is a magnetic permeability. In the formulas (1) to (4), a term proportional to 1 / r ³ is a quasi-electrostatic magnetic field, a term proportional to 1 / r ² is an induction electromagnetic field, and a term proportional to 1 / r is radiated. The electromagnetic field is shown. Since these electromagnetic field components have different dependencies on the distance r, the relative strength changes depending on the distance r.

Subsequently, it shows a table illustrating the quasi-electrostatic field in FIG. 5 in a field E _theta, induced electric field, the dependence on the distance r normalized by the wavelength λ for the relative intensity of the radiation field. The second row of the table shown in FIG. 5 shows the distance converted with a free space wavelength of 950 MHz which is almost the same as the frequency of UHF (Ultra High Frequency) band RFID permitted by the domestic radio law.

  As can be seen from the table shown in FIG. 5, as the distance r increases, each electric field strength decreases, and each component ratio also changes. For example, in the region of r <λ / 2π, the electric field strength increases in the order of quasi-electrostatic field, induction field, and radiation field, and in the region of r> λ / 2π, the field strength decreases in order of quasi-electrostatic field, induction field, and radiation field. . Further, the contribution of the quasi-electrostatic field and the induced electric field is extremely small in the region where r> λ, and only the radiated electric field component is present in the far field where r> 2λ. On the other hand, the contribution of the quasi-electrostatic field and the induced electric field remains sufficiently in the region of r <λ, and the quasi-electrostatic field and the induced electric field make a large contribution in the reactive near field of r <λ / 2π. Further, as seen in the equations (1) to (4), compared to the radiated electric field, the quasi-electrostatic magnetic field and the induction electromagnetic field have an r-direction component and a φ-direction component in addition to the θ-direction component, It has components in various directions.

  In general, compared to the radiated electromagnetic field radiated from the antenna into space, the quasi-electrostatic field and the induced electromagnetic field that remain in the vicinity of the antenna are dominant in the reactive near field. Strong electromagnetic field strength. In the near field of radiation, in general, the absolute electromagnetic field strength becomes weaker as the distance from the wave source becomes longer. In addition, the relative strength of the quasi-electrostatic magnetic field and the induction electromagnetic field is weakened, and the relative strength of the radiated electromagnetic field is increased. As described above, a quasi-electrostatic magnetic field and an induction electromagnetic field exist in the near field, and the coupling between the reader antenna 102 and the tag antenna 112 and the coupling between the tag antenna 112 and the managed article 105 are performed by these electromagnetic fields. Arise.

  In a passive RFID system using a normal UHF band or microwave band, the distance r between the reader antenna 102 and the tag antenna 112 satisfies the relationship r> λ, and a radiated electromagnetic field is used for communication. In order to efficiently generate the radiated electromagnetic field, the reader antenna 102 is a resonant antenna typified by a patch antenna. When such a resonant antenna is used in the near field of r <λ, the electromagnetic field strength varies greatly depending on the location along the antenna due to the standing wave in the resonant antenna. For example, the amplitude is the largest near the top of the standing wave, and the amplitude is 0 at the midpoint of the standing wave. Therefore, when the distance r between the reader antenna 102 and the tag antenna 112 using such a resonant antenna satisfies the relationship r <λ, the portion near the midpoint of the standing wave in the reader antenna is separated from the reader antenna. The signal cannot be received by the tag antenna, or the received signal strength becomes extremely weak. That is, an insensitive area is created, which hinders use.

  For this reason, in the system adopting the first method described in the background art section, the RFID reader is sufficiently separated from the shelf on which the article is placed, the article 105, and the RF tag, so that it is more than the shelf. Radio waves are radiated from a small reader antenna, and there is no choice but to take a wide cover area. Therefore, a system employing the first method requires a large space between the RFID reader and the RF tag. In addition, depending on the material of the shelf, especially in the case of a metal shelf, a multipath phenomenon occurs, and the tag reading becomes unstable due to radio wave interference, and the tag information cannot be read regardless of whether or not there is an article to be managed. There is. Also, if a person or object enters between the reader antenna and the place where the article is placed, the tag cannot be read in the same way as there is an article, and it is falsely detected that there is no article. Produce.

  On the other hand, a coupling circuit can be formed by electromagnetic coupling between antennas through a quasi-electrostatic magnetic field and an induction electromagnetic field that exist in the near field of r <λ, and more preferably in the reactive near field of r <λ / 2π. . In this case, a large space is not required between the RFID reader and the RF tag according to the conditions. However, if a resonant antenna is simply used as the reader antenna 102, a dead area is formed, which hinders use. In addition, the standing wave antenna is generally about λ in size, and when used in proximity to the tag, the cover area becomes extremely narrow.

  Therefore, in the article management system 1 according to the first exemplary embodiment, the reader antenna 102 connected to the RFID reader 103 is configured with an open transmission line that is matched and terminated, and the tag transmission antenna 112 of the RF tag 104 and the open transmission line. The RF tag 104 is arranged so that and are electromagnetically coupled. In the article management system 1, an open transmission line with less radio wave emission is used as the reader antenna 102 of the RFID reader 103, so that the reader antenna 102 passes through a quasi-electrostatic magnetic field and an induction electromagnetic field generated around the open transmission line. And the tag antenna 112 are electromagnetically coupled to form a coupling circuit. That is, an open transmission line is used as a traveling wave antenna that operates in the near field. With this configuration, a large space is not required between the reader antenna 102 and the RF tag 104. In addition, since communication between the reader antenna 102 and the tag antenna 112 is performed at a short distance through the coupling circuit, there is no human or the like between the occurrence of the multipath phenomenon and the place where the reader antenna 102 and the managed article 105 are disposed. It is possible to suppress erroneous detection due to a thing entering. Furthermore, since an open transmission line terminated with matching is used as the reader antenna 102, the main component of the electromagnetic wave propagating through the antenna does not generate a standing wave but propagates as a traveling wave to the matching end. Here, strictly speaking, the fact that a standing wave does not occur means that the standing wave is sufficiently small. Usually, the standing wave ratio is 2 or less, preferably 1.2 or less. means.

  When the end of the transmission line is matched with sufficient accuracy, or when the electromagnetic wave propagating in the transmission line is sufficiently attenuated near the end of the transmission line, a traveling wave is generated without generating a large standing wave in the transmission line. Becomes the main component. A traveling wave antenna can be formed by utilizing the electromagnetic field distribution in such a transmission line. Further, the electromagnetic field formed in the space around the line has a relatively small radiated electromagnetic field, and an electrostatic magnetic field and an induction electromagnetic field are main components. The electromagnetic field intensity of the electrostatic magnetic field and the induction electromagnetic field is stronger than that of the radiated electromagnetic field, and the electromagnetic field intensity obtained from the RF tag 104 is increased even when the reader is operating with the same output. In other words, it is possible to form an environment in which the radiation electromagnetic field is not scattered around while guaranteeing the operation of the tag.

  In a standing wave type antenna such as a patch antenna that is normally used, the electromagnetic field distribution in the vicinity of the antenna is extremely non-uniform according to the standing wave inside the antenna. The area where 105 can be managed is limited. On the other hand, in the case of a traveling wave antenna composed of an open transmission line described in the present embodiment, there is no portion that does not change like a node in the electromagnetic field distribution even in the vicinity of the antenna, and it always changes everywhere. Therefore, even in the near field, the electromagnetic field associated with the standing wave along the antenna becomes uniform, so that there is no area where the tag information of the RF tag 104 cannot be read. That is, the degree of freedom of arrangement of the reader antenna 102 and the tag antenna 112 is improved.

  Further, in the article management system 1, since this traveling wave is used as a signal to communicate through electromagnetic coupling between the reader antenna 102 and the tag antenna 112, unlike the resonance type antenna, there is no insensitive area, which hinders use. It does not occur. Therefore, the article management system 1 extends the transmission line regardless of the wavelength within a range in which the strength of the quasi-electrostatic magnetic field and the induction electromagnetic field generated around the open transmission line is sufficiently large to operate the RF tag 104, A large cover area can be taken. That is, in the article management system 1 according to the first embodiment, by using the above-described open transmission line, the radiation loss of power is suppressed and the cover area can be easily expanded.

  The open transmission line here is basically a transmission line for the purpose of transmitting electromagnetic waves in the longitudinal direction of the line while suppressing radiation, and indicates an open type. Examples include balanced two-wire transmission lines and similar transmission lines, transmission lines such as microstrip lines, coplanar lines, and slot lines, and grounded coplanar lines and triplate lines that are modifications of these transmission lines. In addition, an antenna that spreads in a plane that transmits signals by changing the electromagnetic field in the gap region sandwiched between the mesh-like conductor portion and the sheet-like conductor portion and the leaching region on the outer side of the mesh-like conductor portion depends on the conditions. It is possible to use. This planar antenna has a standing wave mixed therein and operates as a traveling wave antenna although it is incomplete, and can be used if the non-uniformity of the electromagnetic field distribution caused by the standing wave can be ignored. On the other hand, a shielded transmission line that does not generate such an electromagnetic field around the transmission line, such as a coaxial cable or a waveguide that shields the periphery of the transmission line, cannot be used without special measures for leaking the electromagnetic field.

  In addition, an electromagnetic field exists in a region between the opposing conductive sheet bodies, and the electromagnetic field is changed by changing the voltage between the two conductive sheet bodies. There is an electromagnetic wave transmission sheet that changes the voltage between them to advance the electromagnetic field in a desired direction. In a broader sense, this electromagnetic wave transmission sheet may be regarded as a kind of the open transmission line of the present invention when viewed in the longitudinal direction of the sheet. However, the electromagnetic wave transmission sheet is not necessarily optimal for the implementation of the present invention due to the standing wave in the sheet. In the case of the electromagnetic wave transmission sheet, the upper surface of the waveguide becomes a metal mesh sufficiently finer than the wavelength, and the evanescent wave can be regarded as leaking from the upper surface. Such a transmission line having a plurality of slots in which electromagnetic fields leak with an interval, width and length generally less than 1/10 of the wavelength is an open transmission line of the article management system 1 according to the first embodiment. Can be regarded as a kind of

  On the other hand, so-called crankline antennas and meanders are designed to obtain a certain radiated electromagnetic field strength by designing a crank shape with the intention of radiating strongly from an open transmission line or by actively using higher-order modes. A traveling wave antenna for electromagnetic radiation in the far field using a line antenna, a leaky coaxial cable, etc. is different from an open transmission line of the article management system 1 according to the first embodiment. These are preferentially radiated from a crank shape or slot periodically provided with a size of about the wavelength, generally 1/10 or more of the wavelength. The intensity varies greatly depending on the location. Therefore, when using in the near field, the reading of tag information may become unstable, or the tag may not be read depending on the location. Furthermore, in the UHF band RFID system, the allocated frequency is different in each country in the world, and is distributed in a band of approximately 860 to 960 MHz. This has a wide range of about 10% as a specific band, and requires a significant change in the design of the resonance point of the resonance antenna and the cycle of the crank, meander, and slot. On the other hand, since the article management system 1 according to the first embodiment uses an open transmission line with an extremely wide band from the beginning, the same antenna can be used as the reader antenna 102 without any particular change.

  Further, according to the article management system 1 according to the first exemplary embodiment, the management target article 105 is placed apart from the RF tag 104 so that the management target article 105 and the tag antenna 112 of the RF tag 104 are electromagnetically coupled. A managed article placement area 110 is provided. Therefore, when the management target article 105 is present, the management target article 105 and the tag antenna 112 form a coupling circuit, so that the resonance frequency of the tag antenna 112 changes compared to the case where the management target article 105 is not present, The feeding point impedance of the antenna 112 changes. The tag antenna 112 generally resonates at the frequency of the signal used for communication in free space, the feed point impedance is adjusted, and the reception sensitivity is maximized. The reception sensitivity is lowered, and the operation of the tag antenna 112 when a reflected signal is sent to the RFID reader 103 is also adversely affected. As a result, the power reception sensitivity with respect to the signal used for communication falls. Further, the transmission output of the signal reflected by the RF tag 104 is also reduced. Therefore, the RF tag 104 cannot receive a signal from the RFID reader 103, or the received power of the signal is low, so that the operation power of the tag cannot be secured, or the tag cannot generate a reflected electromagnetic field with sufficient strength. As a result, the RFID reader 103 cannot read the tag information of the RF tag 104. Alternatively, the intensity and phase of the reflected electromagnetic field that reaches the RFID reader 103 change greatly with changes in the resonance frequency of the tag. That is, when the management target article 105 is in the management target article placement area 110, the tag information cannot be read, or the intensity or phase of the reflected electromagnetic field from the RF tag 104 is smaller than when there is no management target article 105. Since it changes greatly, the RFID reader 103 can detect that there is an article to be managed 105. That is, as a result of the change in the operational characteristics of the tag antenna 112 due to the presence / absence of the management target article 105, the RFID reader 103 can detect the intensity and phase change of the reflected signal from the RF tag 104, and manage from the detection result. The presence or absence of the target article can be detected.

  As described above, in the article management system 1 according to the first embodiment, it is not always necessary for the management target article 105 to block the prospects of the RF tag 104 and the RFID reader 103 to detect the presence or absence of the management target article 105. Since it is only necessary to provide a place to place the management target article 105 away from the tag antenna 112 (or the RF tag 104) so that the tag 105 is electromagnetically coupled to the tag antenna 112, the arrangement of the articles to be managed is not necessarily RFID. The arrangement is not limited between the reader 103 and the RF tag 104, and a free arrangement is possible.

  In addition, the article management system 1 according to the first exemplary embodiment does not look at the fact that the article is arranged in the vicinity of the reader antenna 102 to which power is supplied, from the change of the operating characteristics of the reader antenna 102, A change in operating characteristics is determined based on a change in a read signal of tag information in the RFID reader 103 via the reader antenna 102. Thus, by interposing the RF tag 104, the degree of freedom of the relative position of the place where the reader antenna 102 and the management target article 105 are arranged can be improved. In addition, even with one reader antenna 102 or RFID reader 103, the presence or absence of a plurality of management target articles 105 can be detected by arranging a plurality of RF tags 104. Furthermore, the electromagnetic field formed in the place where the tag antenna 112 places the management target article 105 includes components of a quasi-electrostatic magnetic field and an induction electromagnetic field in addition to the radiated electromagnetic field. Therefore, the electromagnetic field component spreads in various directions as compared with a normal far-field radiation electromagnetic field component. Therefore, the article management system 1 according to the first embodiment can improve the degree of freedom of the relative position between the article to be managed and the tag.

  The article management system 1 according to the first embodiment is based on the RFID system, and the RF tag 104 has a unique ID (tag information), and multiple access is possible based on the tag information. Therefore, if the tag information of the RF tag 104 and the location where the management target article 105 is arranged are linked, the location where the management target article 105 is located can be identified from the tag information of the RF tag 104 that cannot be read. On the other hand, when there is no management target article 105, the RF tag 104 responds to a signal from the RFID reader 103, and the RFID reader 103 can read the tag information of the RF tag 104. Therefore, when there is no management target article 105, the tag information of the RF tag 104 can be read with the intensity of the normal reflected electromagnetic field, so that it can be detected that there is no management target article 105. Further, the location where the management target article 105 is not present can be identified from the tag information of the read RF tag 104. Also, when managing a plurality of management target articles 105, the tag information attached to the location where the management target article 105 is arranged is different, so that the location can be specified and the article management can be performed. Since the presence / absence of the management target article 105 can be detected as described above, the article management system 1 according to the first embodiment can manage the presence / absence of the management target article 105 without having to attach the RF tag 104 to the management article.

  In the article management system 1 according to the first embodiment, a place for placing the management target article 105 away from the RF tag 104 is provided so that the management target article 105 is electromagnetically coupled to the tag antenna 112 of the RF tag 104. Since the RF tag 104 is not attached to the management target article 105 and the RF tag 104 can be used repeatedly, the tag cost per article is substantially divided by the number of times the tag is used. . That is, it goes without saying that the problem of the high cost of the RF tag 104 can be solved by repeating a sufficient number of times of use.

  Further, in the article management system 1 according to the first embodiment, since the RF tag 104 is not attached to the management target article 105, privacy infringement or information caused by illegally reading the RF tag 104 attached to the management target article 105. Does not cause security problems. That is, the article management system 1 according to the first embodiment does not cause a problem of illegal reading of tag information by a third party.

  Further, the article management system 1 according to the first exemplary embodiment is configured such that the wavelength of the signal used for communication between the RFID reader 103 and the RF tag 104 is λ, and the first management between the management target article 105 and the tag antenna 112 is performed. A managed article placement area 110 is provided in which the managed article 105 is placed so that the distance L1 satisfies the relationship of L1 ≦ λ. In the article management system 1 according to the first embodiment, the second distance L2 that is the line-of-sight distance between the reader antenna 102 of the RFID reader 103 and the tag antenna 112 of the RF tag 104 satisfies the relationship L2 ≦ λ. . In addition, the distance in the article management system 1 according to the first embodiment is a distance in radio wave propagation, and substantially coincides with the shortest geometric distance.

  If the distance L1 between the management target article placement area 110 where the management target article 105 is placed and the tag antenna 112 of the RF tag 104 satisfies the relationship L1 ≦ λ, the place where the article is placed when viewed from the RF tag 104 Is in the range of the near field. Therefore, the contribution of the quasi-electrostatic field and the induction electric field is sufficient, and the managed article 105 includes a material having a high dielectric constant such as moisture or a metal, and the managed article 105 is placed in the managed article placement area 110. If there is, the tag antenna 112 and the management target article 105 can be electromagnetically coupled through a quasi-electrostatic magnetic field or an induction electromagnetic field. Since the human body also contains a large amount of moisture as the management target article 105, it can be detected and used for human flow line management.

  By setting the first distance L1 to a value satisfying L1 ≦ λ, the components of the quasi-electrostatic magnetic field and the induction electromagnetic field exist in the near field of the tag antenna 112 with non-negligible intensities. The component causes electromagnetic field coupling between the tag antenna 112 and the managed article 105 via mutual inductance, capacitance, or the like. Therefore, the circuit constant of the tag antenna 112 changes depending on the presence / absence of the management target article 105, and the operating characteristics of the tag antenna 112 change. Further, the resonance frequency of the tag antenna 112 changes as a more easily understandable change depending on the presence or absence of the management target article 105. If a commercially available RF tag is used as the RF tag 104 for system cost reduction, the tag antenna 112 is a standing wave antenna based on a dipole antenna. In such an RF tag 104, high sensitivity is realized by setting the resonance frequency of the tag antenna 112 according to the frequency of wireless communication. Thus, the state where the resonance frequency of the tag antenna 112 resonates at the set frequency corresponds to the state where there is no managed object 105.

  Next, when the management target article 105 is placed on the RF tag 104, the tag antenna 112 is coupled to the management target article 105, so that the resonance frequency generally decreases. Therefore, the sensitivity of the tag antenna 112 at the radio communication frequency is greatly reduced. For example, when the operating power of the RFID chip 111 cannot be provided due to a decrease in reception sensitivity, the RF tag 104 does not respond to an inquiry from the RFID reader 103. Alternatively, even when operating power can be covered, the tag antenna 112 cannot cause an electromagnetic field change in a sufficiently strong space due to the modulation signal generated by the RFID chip 111.

  As a result, the RF tag 104 does not respond to the inquiry from the RFID reader 103 when the management target article 105 is present, or the reflected electromagnetic field from the RF tag 104 is smaller than when the management target article 105 is not present. The intensity changes greatly. By detecting the change in the intensity of the reflected electromagnetic field with the RFID reader 103, it can be determined that there is no managed object 105. This determination process can be performed by, for example, a computer. As described above, the article management system 1 according to the first embodiment detects the presence / absence of the management target article 105 without attaching the RF tag 104 to the management target article 105, and manages the presence / absence of the management target article 105. be able to.

  Further, in the article management system 1 according to the first embodiment, in order to cause a change in the response of the RF tag 104 depending on the presence / absence of the management target article 105, a first distance between the RF tag 104 and the management target article 105 is used. L1 only needs to satisfy the relationship of L1 ≦ λ, and the prospect of the RF tag 104 and the reader antenna 102 does not need to be blocked by the management target article 105. That is, the arrangement of the management target article 105 is not limited between the tag antenna 112 and the RF tag 104 of the RFID reader 103, and the degree of freedom of arrangement is improved. For example, when detecting the presence / absence of a product on a product display shelf, the reader antenna 102 and the RF tag 104 can be incorporated into the shelf board, and the antenna is hidden, so that the appearance is extremely excellent.

  Note that although a method for detecting a change in signal strength due to a shift in the resonance frequency of the tag antenna 112 from the radio communication frequency has been described here, the present invention is not limited to this. If the resonance frequency is shifted, the presence / absence of the article may be detected by sweeping the wireless communication frequency within a range legally permitted by the reader and detecting the deviation of the resonance frequency. Also, the phase changes greatly before and after the resonance frequency. Therefore, it goes without saying that the presence / absence of an article can also be detected by observing the phase change.

  Similarly to the first distance L1, if the line-of-sight distance L2 between the tag antenna 112 and the reader antenna 102 satisfies the relationship L2 ≦ λ, the reader antenna 102 and the tag antenna 112 are within the range of the near field. Be inside. Here, the line-of-sight distance L <b> 2 means the distance between the strip conductor 102 a that is a particularly strong wave source in the reader antenna 102 and the tag antenna 112. By setting the line-of-sight distance L2 to be λ or less, the contribution of the quasi-electrostatic field and the induction field is sufficient, and the reader antenna 102 and the tag antenna 112 can be electromagnetically coupled. In particular, in the article management system 1 according to the first embodiment, since the presence or absence of an article is determined based on an analog quantity, that is, the intensity of the reflected electromagnetic field from the RF tag 104, a change in the reflected electromagnetic field intensity due to radio wave interference causes erroneous detection. Cheap. However, with this configuration, in the article management system 1 according to the first embodiment, the radio communication between the reader antenna 102 and the tag antenna 112 is centered on direct waves, and radio wave interference due to the multipath phenomenon hardly occurs. Therefore, erroneous detection can be suppressed. Further, the electromagnetic field formed by each antenna of the RFID reader 103 and the RF tag 104 includes a quasi-electrostatic magnetic field and an induction electromagnetic field component in addition to the radiated electromagnetic field. Therefore, the electromagnetic field component spreads in various directions as compared with the case of only a normal far-field radiation electromagnetic field component. Therefore, in the article management system 1 according to the first embodiment, the degree of freedom of the relative position between the reader antenna 102 and the RF tag 104 can be improved.

  Further, in the article management system according to the first embodiment, the presence / absence of an article such as the intensity or phase change of the reflected electromagnetic field from the RF tag 104 or the resonance frequency change of the tag antenna 112 is determined. The accompanying radio wave interference leads to false detection. However, according to the article management system 1 according to the first embodiment, by satisfying the relationship of L2 ≦ λ, the wireless communication between the reader antenna 102 and the tag antenna 112 is centered on the direct wave and reflects the surrounding environment. The radio interference caused by the multipath phenomenon is less likely to occur. Therefore, erroneous detection can be suppressed. In particular, when managing the presence / absence of products on the shelf, the shelf is often made of metal or a metal refrigerated case, but the system can be stably operated even in such an environment.

  Furthermore, in the article management system 1 according to the first embodiment, the line-of-sight distance L2 between the reader antenna 102 and the RF tag 104 is UHF, which is one of the frequencies of the RFID standard, by satisfying the relationship of L2 ≦ λ. The band is about 0.3 m or less, and the 2.4 GHz band is about 0.12 m or less. In addition, since the distance L1 between the managed article placement region 110 and the RF tag 104 also satisfies the relationship of L1 ≦ λ, in the UHF band, which is one of the frequencies of the RFID standard, about 0.3 m or less, 2.4 GHz The band is about 0.12 m or less. Accordingly, the interval between the reader antenna 102 and the managed object placement area 110 is also in this order and becomes narrower. Therefore, by using the article management system 1 according to the first embodiment, by narrowing the interval between the management target article 105 and the RF tag 104 or the reader antenna 102, an object or person different from the management target article 105 may enter. Can be suppressed and erroneous detection can be suppressed.

  Further, in the article management system 1 according to the first embodiment, it is desirable that the first distance L1 satisfies the relationship L1 ≦ λ / 2π when the circumference ratio is π. When the managed object 105 affects the frequency characteristics of the tag antenna 112, when the first distance L1 is located within the reactive near field that satisfies the relationship of L1 ≦ λ / 2π, L1> λ / The intensity of the electromagnetic field formed by the tag antenna 112 is stronger than in the case of the 2π radiation near field. Furthermore, the contribution of the quasi-electrostatic magnetic field and the induction electromagnetic field that remain in the vicinity of the antenna becomes relatively large, and the contribution of the radiated electromagnetic field becomes small. Therefore, in the article management system 1 according to the first embodiment, the coupling between the management target article 105 and the tag antenna 112 becomes strong. As a result, the influence of the presence / absence of the management target article 105 on the operation characteristics of the tag antenna 112 is increased. Therefore, the article management system 1 according to the first embodiment also increases the change in the reflected electromagnetic field transmitted from the RF tag 104 to the RFID reader 103, becomes an article management system that is resistant to disturbances and noise, and can suppress false detection.

  In the article management system 1 according to the first embodiment, it is desirable that the line-of-sight distance L2 satisfies the relationship L2 ≦ λ / 2π. As described above, when the line-of-sight distance L2 satisfies the relationship L2 ≦ λ / 2π, the article management system 1 according to the first embodiment is closer to the antenna than the case where the line-of-sight distance L2 is L2> λ / 2π. The contribution of the remaining quasi-electrostatic magnetic field and induction electromagnetic field is relatively large, and the coupling between the reader antenna 102 and the tag antenna 112 is strengthened. Therefore, in the article management system 1 according to the first embodiment, communication between the RFID reader 103 and the RF tag 104 is also less susceptible to disturbance and noise. Thereby, the article management system 1 according to the first embodiment can realize an article management system that is less susceptible to disturbance and noise. In addition, since the electromagnetic field components of the quasi-electrostatic magnetic field, the induction electromagnetic field, and the radiated electromagnetic field are mixed with sufficient strength, and the vector direction changes with time, the article management system 1 according to the first embodiment. Can improve the degree of freedom of the relative orientation of the reader antenna 102 and the tag antenna 112.

  Furthermore, in the article management system 1 according to the first embodiment, the line-of-sight distance between the reader antenna 102 and the RF tag 104 is one of the frequencies of the RFID standard by satisfying the relationship of L2 ≦ λ / 2π. The band is about 0.05 m or less and the 2.4 GHz band is about 0.02 m or less. Therefore, according to the article management system 1 according to the first embodiment, an article management system that does not require a large space between the reader antenna 102 and the RF tag 104 can be realized. For example, the reader antenna 102, the RF tag 104, and an article to be managed can be stored in a product shelf. In addition, by narrowing the interval, it is possible to further prevent people and objects from entering between them, and to suppress erroneous detection caused by blocking the line of sight.

  On the other hand, in general, when an RF tag is attached to a well-known product on the product shelf for management, the attachment position of the RF tag varies depending on the product to which the tag is attached. Therefore, satisfying the relationship of L2 ≦ λ / 2π described above is not preferable because it restricts the type of product and limits the attachment position of the RF tag. Therefore, when the RF tag is attached to the management target article for management, an antenna using a radiated electromagnetic field that can communicate to the far field is used so that the reader antenna and the RF tag can communicate with each other even if the distance is slightly apart. There is a need. Therefore, it is not suitable for the use of an open transmission line for the purpose of basically suppressing radiation and transmitting electromagnetic waves in the longitudinal direction of the line, and a resonance type antenna or a leaky coaxial cable that is normally used is used. . However, when a reader antenna that generates a radiated electromagnetic field with such high efficiency is used, the intensity of the radiated electromagnetic field is attenuated only at 1 / r with respect to the distance, so that the reading area is expanded. As a result, troubles in product management occur, such as reading RF tags attached to products on other adjacent shelves.

However, according to the article management system 1 according to the first embodiment, since the RF tag 104 is not affixed to a product, for example, the reader antenna 102 is laid on the bottom of the product shelf, and the coupling coefficient is adjusted on the RF tag 104. It is easy to arrange 104 so as to satisfy the relationship of L2 ≦ λ / 2π, and further to arrange a product to be managed thereon. Therefore, in the article management system 1 according to the first embodiment, it is possible to use an open transmission line for the purpose of basically suppressing radiation and transmitting electromagnetic waves in the longitudinal direction of the line. Thus, the reader antenna 102 that suppresses radiation whose intensity is attenuated only at 1 / r and uses a quasi-electrostatic magnetic field attenuated at 1 / r ³ or an induced electromagnetic field attenuated at 1 / r ² as a main electromagnetic field component. By using it, when managing the presence or absence of products on the product shelf, it becomes easy to read the RF tag 104 with one reader antenna 102 and limit the product management area. The problem of reading the RF tag 104 is unlikely to occur. In addition, although the example of merchandise management on the merchandise shelf has been described here, even when managing other shelves and floor-standing items, similarly, the area where the RF tag 104 is read by one reader antenna 102 is limited. Needless to say, it is easy to limit the area for article management.

  In the article management system 1 according to the first embodiment, it is desirable that the first distance L1 and the second distance L2 satisfy the relationship L2> L1. The strength of electromagnetic coupling varies depending on the structure of the antenna and resonator, and the characteristics of the medium between the antennas, but also greatly depends on the distance. According to the article management system 1 according to the first embodiment, by setting L2> L1, the coupling coefficient k2 between the management target article placement area 110 where the management target article 105 is placed and the tag antenna 112 is determined as a reader antenna. The coupling coefficient k1 between 102 and the tag antenna 112 can be made larger. That is, by ensuring the relationship of L2> L1, the change in the reflected wave intensity due to the change in the frequency characteristics of the tag antenna 112 due to the presence or absence of the article becomes larger than the maintenance of the communication between the tag antenna 112 and the reader antenna 102. . That is, since the article management system 1 according to the first embodiment can reliably grasp the presence / absence of the article to be managed 105, erroneous detection can be suppressed.

In the article management system 1 according to the first embodiment, it is desirable that the coupling coefficient k1 between the reader antenna 102 and the tag antenna 112 is set to a value of 10 ⁻⁵ or more. The power receiving sensitivity that gives the operation limit of the current UHF band RF tag is approximately −20 dBm. On the other hand, the output of the high-power UHF band RFID reader is 30 dBm. Therefore, if the coupling coefficient k1 is a value of 10 ⁻⁵ or more, power for operating the UHF band RF tag can be supplied.

In the article management system 1 according to the first embodiment, the coupling coefficient k1 between the reader antenna 102 and the tag antenna 112 is preferably set to a value of 10 ⁻² or less. When the tag antenna 112 is regarded as a dipole resonator, the reader antenna 102 (for example, an open transmission line) and the tag antenna 112 are electromagnetically coupled. When the open transmission line and the resonator are coupled, a circuit is obtained. Can be interpreted. Therefore, if the coupling coefficient is too strong, the operation of the open transmission line is greatly affected, and as a result, the operation of the other RF tag 104 as a coupled resonator system is also affected. A situation where a plurality of resonators are coupled in parallel to the open transmission line is considered as a circuit of a band rejection filter. In that case, if the tag antenna of the UHF band RF tag uses copper or aluminum at room temperature, since the no-load Q value is approximately 100 or less, if the coupling coefficient k1 that determines the ratio band is 10 ⁻² or less, Almost no influence on the operation of the open transmission line. Therefore, by setting the coupling coefficient k1 to a value of 10 ⁻² or less, the coupling of the tag antenna 112 can be suppressed from affecting the open transmission line, and the RFID reader 103 coupled in parallel to the open transmission line can be suppressed. The mutual influence between them can also be suppressed.

  In addition, the article management system 1 according to the first embodiment includes the management target article 105 and the tag antenna 112 when the management target article 105 exists in the management target article placement area 110 and the coupling coefficient k1 between the reader antenna 102 and the tag antenna 112. It is desirable that the coupling coefficient k2 satisfies the relationship of k1 <k2. According to the present invention, k1 <k2, that is, the coupling coefficient k2 between the managed article placement region 110 and the tag antenna 112 is made larger than the coupling coefficient k1 between the reader antenna 102 and the tag antenna 112. Thus, the change in the reflected signal intensity due to the change in the frequency characteristics of the tag antenna 112 due to the presence or absence of an article becomes larger than the maintenance of the communication between the reader antenna 102 and the tag antenna 112. That is, in the article management system 1 according to the first embodiment, the presence / absence of the article to be managed 105 can be reliably detected, so that erroneous detection can be suppressed.

  In the first embodiment, the arrangement relationship between the reader antenna 102, the RF tag 104, and the management target article 105 has been specifically described. However, the relative positions and orientations of these components are the specific examples shown in FIG. Yes it is not limited to.

  As described above, in the article management system 1 according to the first embodiment, the resonance frequency of the tag antenna 112 varies depending on the distance between the RF tag 104 placed on the upper part of the reader antenna 102 and the article to be managed. The presence / absence of an article to be managed is determined on the basis of a change in signal strength of a radio signal caused by doing so. However, in the article management system 1 described above, the change in the signal intensity due to the change in the resonance frequency of the tag antenna 112 is not a linear change with respect to the distance between the RF tag 104 and the article to be managed. Therefore, in the article management system 1 according to the first embodiment, there arises a problem that erroneous detection occurs depending on the distance between the RF tag 104 and the management target article in a state where the management target article is placed on the RF tag 104. For example, when a cover material or the like is provided in the upper layer of the RF tag 104, erroneous detection may occur if the distance between the RF tag 104 and the management target article generated due to the thickness of the cover material is not appropriate. The above problem will be described in detail below.

  First, a change in signal intensity according to the distance between the RF tag 104 and the management target article 105 is examined by simulation. FIG. 6 is a diagram for explaining the simulation conditions. 6 is a top view of the article management system 1 for explaining the positions of the signal input / output ports P1 and P2 and the observation port P3 for observing the signal intensity. 6 is a cross-sectional view of the article management system 1 for explaining the distance between the strip conductor 102a and the RF tag 104 and the distance between the RF tag 104 and the article to be managed 105.

  As shown in the upper diagram of FIG. 6, in this simulation, a signal is propagated from a port P1 provided at one end of the strip conductor 102a to a port P2 provided at the other end of the strip conductor 102a. Then, the signal strength of the observation port P3 provided in the tag antenna 112 is observed.

  As shown in the lower diagram of FIG. 6, in this simulation, the first insulating member 121 having a thickness T1 is provided on the upper layer of the strip conductor 102a, and the RF tag 104 is arranged on the upper layer of the first insulating member 121. Further, a second insulating member 122 having a thickness of T2 is provided as a cover material on the upper layer of the RF tag 104. Here, the thickness T1 was set to 5 mm, and the thickness T2 was set to 1 mm. Then, the signal intensity at the tag antenna 112 when the distance L1 between the RF tag 104 and the management target article 105 is changed is observed.

  Next, the characteristics of the signal intensity observed at the observation port P3 under the simulation conditions shown in FIG. 6 are shown in FIGS. FIG. 7 is a graph for explaining a simulation result of signal characteristics in the article management system in the case where metal is an article to be managed under the conditions shown in FIG.

  As shown in the upper diagram of FIG. 7, when a metal is used as the management target article 105, the resonance frequency of the tag antenna 112 increases as the distance L1 increases. When the distance L1 exceeds 20 mm, the resonance frequency fluctuates. Is almost gone. Here, in the article management system 1 according to the first embodiment, since the RF tag 104 is read by a 950 MHz signal, a change in signal strength with respect to the distance L1 of the 950 MHz signal is shown in the lower diagram of FIG.

  7, when the signal frequency is 950 MHz, the signal intensity when the distance L1 between the RF tag 104 and the management target article 105 is 5 mm and the management target article 105 is separated by 20 mm or more is shown. Close to. Therefore, for example, when the thickness of the second insulating member 122 is set to about 5 mm, the managed object 105 is not changed even though the managed object 105 is placed on the second insulating member 122. There is a possibility that it will be judged.

  FIG. 8 is a graph for explaining a simulation result of signal characteristics in the article management system when a container filled with water under the conditions shown in FIG. As shown in the upper diagram of FIG. 7, even when a container filled with water is used as the management target article 105, the resonance frequency of the tag antenna 112 increases as the distance L1 increases, and the distance L1 exceeds 20 mm. The fluctuation of the resonance frequency is almost eliminated. Further, when a container filled with water is used as the article to be managed 105, the change in the signal intensity due to the frequency is small in the region where the distance L1 is 3 mm or less. Here, in the article management system 1 according to the first embodiment, since the RF tag 104 is read by a 950 MHz signal, the change in signal strength with respect to the distance L1 of the 950 MHz signal is shown in the lower diagram of FIG.

  As shown in the lower diagram of FIG. 8, when the signal frequency is 950 MHz, the signal intensity is 10 mm when the distance L1 between the RF tag 104 and the management target article 105 is 10 mm, and the signal intensity when the management target article 105 is separated by 20 mm or more. Close to. Therefore, for example, when the thickness of the second insulating member 122 is set to about 10 mm, the managed object 105 is not changed even though the managed object 105 is placed on the second insulating member 122. There is a possibility that it will be judged.

  As described above, when the article management system 1 according to the first embodiment is used as it is, depending on the thickness of the cover material provided as the second insulating member 122, there is a problem that erroneous detection occurs. Therefore, in the article management system 10 according to the first embodiment, an adjustment plate that adjusts the resonance frequency of the tag antenna 112 is used in a portion that overlaps at least a part of the RF tag 104. FIG. 9 is a diagram showing the arrangement of the adjusting plate and the simulation conditions in the article management system 10 according to the first embodiment. In the following description, a substrate formed by the dielectric layer 101, the strip conductor 102a, and the ground conductor 102g is referred to as an antenna substrate.

  As shown in the upper diagram of FIG. 9, in the article management system 10, an adjustment plate (for example, a conductor piece 130) is provided below the RF tag 104 so as to be arranged in parallel with the strip conductor 102 a. As shown in the lower diagram of FIG. 9, the conductor piece 130 is disposed in the same layer as the strip conductor 102a.

  The conductor piece 130 is disposed so as to overlap at least a part of the RF tag 104 in a state where the RF tag 104 is disposed on the strip conductor 102a of the antenna substrate. That is, when the RF tag 104 is not placed on the strip conductor 102a, the RF tag 104 is simply arranged on the strip conductor 102a. In the example shown in FIG. 9, the conductor piece 130 has a length corresponding to the length of the RF tag 104, but may be a length corresponding to the length of the strip conductor 102a, for example. In this case, the conductor piece 130 becomes one conductor tape for the plurality of RF tags 104. In the example shown in FIG. 9, metal is used as the adjustment plate, but a cloth or the like having a relatively high dielectric constant can be used as the adjustment plate.

  Here, the result of verifying the article management system 10 according to the first embodiment by the same simulation as the simulation shown in FIGS. 7 and 8 will be described. The simulation conditions of the article management system 10 according to the first embodiment are the same as the simulation conditions according to the first embodiment shown in FIG. In order to clarify the difference between the article management system 1 according to the first embodiment shown in FIG. 6 and the article management system 10 according to the first embodiment shown in FIG. The simulation results when L1 = 5 mm in FIG. 7 and L1 = 10 mm in FIG. 8 are the most severe reading conditions in FIG. 8 will be described. Therefore, FIGS. 10 and 11 are graphs illustrating signal characteristic simulation results in the article management system 10 according to the first embodiment.

  The example shown in FIG. 10 is a graph for explaining the simulation result of the signal characteristics in the article management system in the case where metal is the article to be managed under the conditions shown in FIG. 10, the resonance frequency of the article management system 10 having the conductor piece 130 is lower than that of the article management system 1 not having the conductor piece 130. Further, when looking at the point where the frequency of the signal is 950 MHz, in the article management system 10 having the conductor piece 130, the signal intensity when L1 = 5 mm and the signal intensity when the article 105 to be managed is not placed. Is larger than that of the article management system 1 that does not have the conductor piece 130. Specifically, as shown in the lower diagram of FIG. 10, the difference between the signal strength when L1 = 5 mm and the signal strength when the managed article 105 is not placed has a conductor piece 130. It is about 3 dB in the article management system 1 that is not present, whereas it is about 20 dB in the article management system 10 having the conductor piece 130. Further, as shown in the upper diagram of FIG. 10, in the article management system 10 having the conductor piece 130, the peak point where the signal intensity is the highest when the managed article 105 is not placed is located at a position close to 950 MHz. doing. In other words, in the example illustrated in FIG. 10, the signal strength is maximized when the management target article 105 is not placed by adjusting the resonance frequency of the tag antenna 112 by providing the conductor piece 130.

  The example shown in FIG. 11 is a graph for explaining a simulation result of signal characteristics in the article management system when a container filled with water under the conditions shown in FIG. Also in the example shown in the upper diagram of FIG. 11, similarly to the example shown in the upper diagram of FIG. 10, the resonance frequency of the article management system 10 having the conductor piece 130 is The frequency is lower than that of the system 1. Further, when looking at the point where the frequency of the signal is 950 MHz, in the article management system 10 having the conductor piece 130, the signal intensity when L1 = 5 mm and the signal intensity when the article 105 to be managed is not placed. Is larger than that of the article management system 1 that does not have the conductor piece 130. Specifically, as shown in the lower diagram of FIG. 11, the difference between the signal strength when L1 = 5 mm and the signal strength when the managed article 105 is not placed has a conductor piece 130. It is about 2 dB in the article management system 1 that is not present, whereas it is about 8 dB in the article management system 10 having the conductor piece 130. Further, as shown in the upper diagram of FIG. 11, in the article management system 10 having the conductor piece 130, the peak point where the signal intensity is the highest when the managed article 105 is not placed is located at a position close to 950 MHz. doing. That is, in the example shown in FIG. 11 as well, by adjusting the resonance frequency of the tag antenna 112 by providing the conductor piece 130, the signal intensity becomes the highest when the article to be managed 105 is not placed.

  As described above, in the article management system 10 according to the first exemplary embodiment, the adjustment piece (for example, the conductor piece 130) is provided at a position that overlaps at least a part of the RF tag 104 when the reader antenna 102 is viewed from above. The conductor piece 130 is capacitively coupled to the tag antenna 112 of the RF tag 104. Therefore, in the article management system 10 having the conductor piece 130, the resonance frequency of the tag antenna 112 is adjusted by the strength of capacitive coupling between the conductor piece 130 and the tag antenna 112. Then, by adjusting the strength of this capacitive coupling, the resonance frequency of the tag antenna 112 in a state where the management target article 105 is not placed can be set at a position very close to the use frequency.

  Thereby, in the article management system 10 according to the first exemplary embodiment, it is possible to prevent the management target article 105 from being determined not to be present despite being placed on the upper part of the second insulating member 122. . For example, when a metal is placed as the management target article 105 on the second insulating member 122 having a thickness of 5 mm, if there is no conductor piece 130, the difference in signal strength due to the presence or absence of the management target article 105 is 3 dB. There is a risk of misjudgment. On the other hand, by providing the conductor piece 130, even if the thickness of the second insulating member 122 is 5 mm, the signal intensity difference depending on the presence or absence of the management target article 105 is 20 dB, and the risk of erroneous determination is extremely reduced.

  In the article management system 10, a sensor sheet including a dielectric layer 101, a strip conductor 102a, a ground conductor 102g, and an RF tag 104 is spread on a floor or a shelf. In the article management system 10, a cover material such as a flooring may be provided on the upper part of the sensor sheet for durability or aesthetics of the sensor sheet. And various thickness is calculated | required by this use for this cover material. Therefore, the article management system 10 is required to prevent erroneous detection regardless of the thickness of the cover material. In such a situation, the article management system 10 having the conductor piece 130 that can prevent erroneous detection even when the thickness of the cover material is about 5 mm to 10 mm is particularly effective.

  In the description of the above embodiment, the adjustment plate is formed in the same layer as the strip conductor 102a. In this case, the adjustment plate can be formed on the dielectric layer 101 such as a printed board in the same process as the strip conductor 102a.

  In the description of the above embodiment, the adjustment plate is formed in the same layer as the strip conductor 102a. However, the adjustment plate may be formed at a position overlapping at least a part of the RF tag 104. For example, the RF tag It may be formed in the same layer as 104. Then, the figure which shows another form of the installation position of an adjustment board is shown in FIG.12 and FIG.13.

  In the article management system 20 shown in FIG. 12, an adjustment plate (for example, a conductor piece 131) is provided in the same layer as the RF tag 104 and is provided below the RF tag 104. In the article management system 30 illustrated in FIG. 13, an adjustment plate (for example, a conductor piece 132) is the same layer as the RF tag 104 and is provided on the upper part of the RF tag 104. The installation method shown in FIGS. 12 and 13 can be realized by using an adjustment plate as a conductor seal, for example, and attaching the conductor seal to the RF tag 104.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

1, 10, 20, 30 Item management system 11 Antenna substrate 12 Antenna substrate 13 Conductor sheet 14a, 14b Distributor 16 Spacer 101 Dielectric layer 102 Reader antenna 102a Strip conductor 102g Ground conductor 103 RFID reader 104 RF tag 105 Management object 110 Managed object arrangement area 111 RFID chip 112 Tag antenna 121 First insulating member 122 Second insulating member 130, 131, 132 Conductor piece Rt Matching termination resistance

Claims (13)

An antenna substrate having a strip conductor formed on a first surface and a ground conductor formed on a second surface facing the first surface;
An RFID reader that reads tag information of the RF tag from an RF tag disposed in the vicinity of the strip conductor via the strip conductor;
When the antenna substrate is viewed from above with the RF tag disposed on the antenna substrate, the RF tag is disposed at a position overlapping at least a part of the RF tag, and the resonance frequency of the tag antenna of the RF tag is adjusted. An adjustment plate to be
An article management system. A first insulating member laminated on the layer where the strip conductor is formed;
The RF tag is disposed so as to be close to the strip conductor via the first insulating member,
The article management system according to claim 1, wherein the adjustment plate is formed in the same layer as the layer in which the strip conductor is formed.   2. The article management system according to claim 1, wherein when the direction from the ground conductor toward the strip conductor is an upward direction, the adjustment plate is formed above or below the RF tag.   The article management system according to claim 1, wherein the adjustment plate is a conductor.   The article management system according to claim 1, wherein the adjustment plate is provided for each of the RF tags. A ground conductor to which a ground potential is applied;
A dielectric layer formed on the top surface of the ground conductor;
A strip conductor that is formed in an upper layer of the dielectric layer, and that transmits and receives signals transmitted and received between the RF tag placed on the dielectric layer and the RFID reader;
When the strip conductor is viewed from above with the RF tag disposed on the top of the strip conductor, the RF tag is disposed at a position overlapping at least a part of the RF tag, and the resonance frequency of the tag antenna of the RF tag is set. An adjustment plate to be adjusted;
A reader antenna. A first insulating member laminated on the layer where the strip conductor is formed;
The RF tag is disposed so as to be close to the strip conductor via the first insulating member,
The reader antenna according to claim 6, wherein the adjustment plate is formed on the same layer as the layer on which the strip conductor is formed.   The reader antenna according to claim 6, wherein the adjustment plate is formed above or below the RF tag when a direction from the ground conductor toward the strip conductor is an upward direction.   The reader antenna according to claim 6, wherein the adjustment plate is a conductor. An RF tag;
A plurality of antenna substrates on which a strip conductor is formed on the first surface and is wired below the RF tag, and a ground conductor is formed on a second surface opposite to the first surface;
When the strip conductor is viewed from above in a state where the RF tag is disposed on the upper portion of the strip conductor, the RF tag is disposed at a position overlapping at least a part of the RF tag, and resonance between the tag antennas of the RF tag An adjustment plate for adjusting the frequency,
A sensor sheet. A first insulating member laminated on the layer where the strip conductor is formed;
The RF tag is disposed so as to be close to the strip conductor via the first insulating member,
The sensor sheet according to claim 10, wherein the adjustment plate is formed in the same layer as the layer in which the strip conductor is formed.   The sensor sheet according to claim 10, wherein the adjustment plate is formed above or below the RF tag when a direction from the ground conductor toward the strip conductor is an upward direction.   The sensor sheet according to claim 10, wherein the adjustment plate is a conductor.

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