JP4927665B2 - Auxiliary antenna for RFID tag and its mounting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an auxiliary antenna (adapter) for an RFID tag which can be used even in an object to be identified including metal or the like in a radio wave type RFID tag. <P>SOLUTION: The auxiliary antenna (10) for RFID tag used in a radio wave type RFID tag (20) mainly receives a magnetic field component in a received radio wave to generate a high frequency current, and supplies the high frequency current to an IC (22) of the RFID tag through capacitive coupling or contact conduction with the RFID tag (10). Thus, the radio wave type RFID tag is made to function as a magnetic field reception type RFID tag. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an RFID (wireless identification) tag, and more particularly to an auxiliary antenna for an RFID tag that allows a radio wave (electromagnetic wave) reception type radio frequency RFID tag to function as a magnetic field reception type RFID tag.

  RFID tags are used for logistics management and entrance / exit management. An RFID tag is a combination of an IC chip capable of writing and reading digital information and an antenna. The RFID tag is irradiated with radio waves from a position separated from several centimeters to several meters by a reader / writer to generate power supply energy for the IC chip and to perform data communication to exchange identification information and the like.

  RFID tags are roughly classified into an electromagnetic induction method and a radio wave method. The electromagnetic induction method is a method for transmitting energy and signals by directly magnetically coupling a coil of an RFID tag and an antenna coil of a reader / writer. Because of electromagnetic induction, the maximum communicable distance is about 1 m at the maximum. This method can transmit energy more efficiently than the radio wave method. Moreover, it can be used also for the container etc. which stored the water which influences transmission / reception of an electromagnetic wave. The radio wave system is a system in which radio waves are exchanged between the RFID tag antenna and the reader / writer antenna to transmit energy and signals. Since energy and signals are transmitted by radiating radio waves into the space, communication with an RFID tag farther away than in the electromagnetic induction method becomes possible. For example, it is 3 to 5 m for a passive RFID tag without a built-in power source. In this method, the energy received by the RFID tag is extremely weak. Further, if water, metal, or the like is present near the RFID tag, the radio wave is attenuated thereby, and the RFID tag does not function. Therefore, the radio frequency type RFID tag is used for an object that does not affect the radio wave. Many radio frequency RFID tags use antennas that receive (transmit) mainly electric field components in radio waves (electromagnetic waves) such as dipoles. Radio wave type RFID tags have a wider communication range (distance) than the electromagnetic induction type, are mass-produced, and are less expensive. Therefore, radio wave type RFID tags are the mainstream in logistics management.

When it is necessary to attach an RFID tag to metal in logistics management, it is possible to use a metal-compatible RFID tag specially designed for metal, for example, an RFID tag having a patch antenna structure (for example, Patent Document 1). it can.
Japanese Patent Laying-Open No. 2005-210676

  As described above, the radio frequency RFID tag is widely used for logistics management, etc., but if the metal box or the like (conductor) is included in the packing box to which the RFID tag is attached, the radio frequency RFID tag functions. May not.

  Therefore, in such a case, it is necessary to use a metal-compatible RFID tag. However, it is necessary to attach a metal-compatible RFID tag directly to a metal surface or to employ a patch antenna structure.

  However, for example, a metal body (for example, metal paper for individual packaging (individual packaging) such as cosmetics, a metal thin film shield for moisture prevention inside the packaging box, etc.) is accommodated inside a master packaging box using corrugated cardboard. In this case, it is not possible to use an RFID tag for directly attaching a metal surface. Further, when an RFID tag having a patch antenna structure is attached to the master packing box, a protrusion is formed, and when a plurality of packing boxes are stacked, a gap must be provided between the boxes. In addition, it is conceivable that the protruding RFID tag is damaged due to contact with others. Further, the RFID tag for metal attachment is more expensive than the radio wave type RFID tag (of the popular electric field reception type).

  Therefore, an object of the present application is to provide an auxiliary antenna (adapter) for an RFID tag that makes it possible to use a widely used radio frequency RFID tag even for an object to be identified including metal.

In order to solve the above problem, an auxiliary planar antenna for an RFID tag of the present invention, an auxiliary planar antenna for RFID tags used in the RFID tag of a radio wave type, mainly receives a magnetic field component of the received radio wave A planar antenna that generates a high-frequency current and supplies the high-frequency current to the IC of the RFID tag through capacitive coupling or contact conduction (electrical connection) with the RFID tag. Is an annular planar conductor having an opening, the outer peripheral length of the planar conductor is determined corresponding to the wavelength of the radio wave used by the RFID tag, and the inner peripheral length corresponds to the internal impedance of the IC of the RFID tag. It is characterized by being defined .

  With this configuration, the magnetic field component of the radio wave (electromagnetic wave) received by the auxiliary antenna is converted into a high frequency current, and this high frequency current is supplied to the RFID tag. As a result, the RFID tag functions as a magnetic field receiving RFID tag. Since the electric field of the electromagnetic wave is reduced around the metal, the sensitivity of the radio frequency RFID tag is reduced. However, the magnetic field of the electromagnetic wave is hardly reduced, and the electromagnetic wave can be received even in the vicinity of the metal. Therefore, for example, a radio wave type (electric field receiving type) RFID tag that is a combination product of a dipole antenna and an IC can be used as the RFID tag.

  Preferably, the RFID tag is attached to an identification target object including a conductive member therein via the auxiliary antenna. By using a combination of an RFID tag and an auxiliary antenna for an identification target including a conductor such as metal or water, the radio wave type RFID tag can be made to function, so that the condition is good.

  Preferably, the shape of the auxiliary antenna is annular, and the outer perimeter is formed to be about 1.2 to 2 wavelengths of the wavelength of the used radio wave, and the inner perimeter is about 0.2 to 1 wavelength. If the shape of the auxiliary antenna is annular, for example, if the antenna shape is a loop shape or a donut shape, a high-frequency current flows in an annular shape and functions as a magnetic field antenna. Further, when the annular shape of the auxiliary antenna is formed so that the outer peripheral length is about 1.2 to 2 wavelengths of the wavelength of the used radio wave and the inner peripheral length is about 0.2 to 1 wavelength, the antenna gain characteristics are improved. It was confirmed that it was good.

  Preferably, two points facing each other on the inner peripheral side of the annular shape of the auxiliary antenna are used as connection points with the IC of the RFID tag. Since the geometrically targeted position on the auxiliary antenna is in electrical balance, it can be easily matched with the IC circuit.

  Preferably, the RFID tag and the auxiliary antenna function as one conductor surface of the patch antenna, and the conductive member inside the identification target object functions as the other conductor surface of the patch antenna. The RFID tag and the auxiliary antenna are integrated to form one conductor surface, and the conductive member inside the identification target object forms the other conductor surface, and an insulating (dielectric material) is formed between these two conductors. ), The structure is similar to a patch antenna (or microstrip antenna), and can thus function as a magnetic field receiving antenna. With such a structure, it is possible to receive the magnetic field component of electromagnetic waves (radio waves), and it is possible to ensure the reception sensitivity of the RFID tag even if the electric field component of the electromagnetic waves decreases due to the presence of metal or the like (depending on the nearby conductor) Can reduce the impact.).

  Preferably, the object to be identified and the conductive member are a box and a packaging material accommodated in the box, the auxiliary antenna is attached to an outer surface of the box, and the RFID tag is the auxiliary antenna. Mounted on top. Since only the RFID tag and the auxiliary antenna are attached to the outer surface of the box, the thickness as in the patch antenna is not required. There is no protrusion on the outer surface of the box (or the thickness is small even if it occurs).

  Preferably, a high-frequency current generated by the IC of the radio wave type RFID tag is supplied to the auxiliary antenna of the magnetic field type antenna through the capacitive coupling or contact conduction, and a radio wave (magnetic field) is emitted from the auxiliary antenna. The reception and transmission of the RFID tag are performed reversibly according to the same principle.

  Preferably, the attachment position of the RFID tag corresponding to the object to be identified is indicated on the auxiliary antenna. Assembling and mounting can be simplified by previously finding a pasting position at which desired performance can be obtained for each identification target object by experiments or the like, and indicating this position on the auxiliary antenna or the identification target object. The display (marker) of the attachment position of each identification object can be performed by printing, etching, or the like.

  Preferably, the radio wave type RFID tag includes an antenna that converts an electric field component of the received radio wave into a high frequency current. For example, a dipole antenna that receives an electric field in electromagnetic waves (radio waves) can be obtained relatively inexpensively.

  The method of attaching an auxiliary antenna for an RFID tag according to the present invention is a process of attaching an auxiliary antenna that mainly receives a magnetic field component of a radio wave and generates a high-frequency current on the surface of an identification target object including a conductive member therein. And attaching a radio frequency RFID tag to a predetermined position on or near the auxiliary antenna corresponding to the object to be identified, and the radio frequency RFID tag at the predetermined position Impedance matching with the auxiliary antenna is achieved (a desired characteristic is obtained). An optimum attachment position of the auxiliary antenna and the RFID tag is obtained in advance for each identification target object, and the pasting operation to the identification target object is shortened.

  Preferably, a plurality of positions where the radio frequency RFID tag is attached in advance corresponding to a plurality of types of the identification target objects. One set of the RFID tag and the auxiliary antenna can be used for a plurality of types of the objects to be identified, and the assembly of the auxiliary antenna and the RFID tag is speeded up.

  Preferably, the mounting position of the radio frequency type RFID tag is indicated in advance on the surface of the identification target object on or near the auxiliary antenna by printing or etching. Since an RFID tag may be attached to the auxiliary antenna or the mark on the identification target object, it is simple.

  In addition, the RFID tag of the present invention is cut out in a circular or polygonal shape with a peripheral length of about 0.5 to 1 wavelength in the approximate center of a circular or polygonal metal foil (plate) with a peripheral length of about 1.5 to 2 wavelengths. Two points on the inner periphery of the shape that are substantially opposite to each other are used as connection points with the IC. Thereby, a magnetic field reception type RFID tag can be easily obtained.

  In addition, the RFID tag of the present invention is cut out in a circular or polygonal shape with a peripheral length of about 0.5 to 1 wavelength in the approximate center of a circular or polygonal metal foil (plate) with a peripheral length of about 1.5 to 2 wavelengths. An IC tag is connected to two substantially opposite points on the inner circumference of the shape, and an RFID tag having electrode surfaces at both ends is capacitively coupled or brought into contact conduction by bonding or the like. As the RFID tag, a radio frequency type RFID tag can be used. Accordingly, the RFID tag can function as a magnetic field reception type RFID tag.

  Examples of the present invention will be described below. First, points of interest of the present invention will be described.

  The present invention utilizes a phenomenon in which the electric field component of radio waves (electromagnetic waves) is weakened and the magnetic field component is increased around a metal that is a conductor. Widely used radio frequency type RFID tags (popular products) receive mainly electric field components (electric fields) of radio waves with a dipole antenna or the like, so that the electric field decreases around metal and reception (transmission) sensitivity decreases. . On the other hand, since loop antennas and some planar antennas (magnetic field receiving antennas) mainly receive magnetic field components (magnetic fields) of radio waves, radio waves can be received even near metal.

  The auxiliary antenna of the present invention is configured as a magnetic field receiving antenna, and mainly receives a magnetic field component in radio waves to generate a high frequency current and functions as a high frequency signal source. By electrically coupling the RFID tag to the auxiliary antenna, a high frequency current is induced in the RFID tag, and the IC of the RFID tag is activated. Therefore, even if the RFID tag is a radio wave type RFID tag that receives an electric field, it can be used near a conductor such as metal. When the RFID tag is a radio wave type RFID tag that receives a magnetic field, it is possible to improve reception sensitivity by using an auxiliary antenna having a larger gain.

  The response from the RFID tag is performed in the reverse route described above. That is, the RFID tag IC activated by receiving the supply of the high frequency current modulates the high frequency current supplied with the digital information. When the RFID tag is electrically coupled to the magnetic field type auxiliary antenna, a radio wave (radiated magnetic field) is radiated and output from the auxiliary antenna as a response wave.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a composite RFID tag 1 that combines an auxiliary antenna and an RFID tag according to the present invention. In the figure, an auxiliary antenna 10 indicated by hatching is an annular planar antenna ( a planar antenna in which a central portion of a rectangular planar conductor is opened in a quadrilateral shape) , and has a rectangular outer periphery and a rectangular inner periphery. Various shapes of the auxiliary antenna 10 can be used according to the application as described later. An RFID tag 20 is attached to the auxiliary antenna 10. On the surface of the auxiliary antenna 10, a mark 11 indicating a position to attach the RFID tag 20 is shown by printing or pattern etching.

  This attachment position is determined in accordance with the type of the identification target object (the structure, material, accommodation contents, etc. of the identification target object) to be described later to which the composite RFID tag 1 is attached. Specifically, an RFID tag attachment position (alignment position) that can obtain the optimum sensitivity of the composite RFID tag 1 is obtained in advance by calculation or experiment, and the attachment position corresponding to the type of the object to be identified is determined. . This is made into a database, and the attachment mark 11 is formed by pattern printing or etching when the auxiliary antenna 10 is manufactured. Further, if the name or number of the object to be identified is indicated in the vicinity of the mark 21, it is easy to assemble.

  As described above, the auxiliary antenna 10 converts the magnetic field component of the received radio wave into a high frequency current and supplies it to the RFID tag 20. The auxiliary antenna 10 and the RFID tag 20 are electrically coupled by a capacitive component or contact conduction. The contact conduction can be performed, for example, by partially exposing the metal corresponding to each other of the auxiliary antenna 10 and the RFID tag 20. Alternatively, the adhesive between the auxiliary antenna 10 and the RFID tag 20 may be electrically coupled partially using a conductive adhesive or the like. The IC of the RFID tag 20 obtains a power source from a high-frequency current, and performs a reaction according to a received signal, for example, writing and reading of a product number.

  FIG. 2 shows the auxiliary antenna and the RFID tag individually. FIG. 2A shows the auxiliary antenna 10. In the embodiment, the annular conductor of the auxiliary antenna is a square, and the outer peripheral length is set to 1.2 to 2λ and the inner peripheral length is set to about 0.2 to 1λ, where λ is the wavelength of the high frequency signal used. . These sizes are tuned to a more preferable size according to the use object, the use environment, and the like.

  For example, when the frequency of the radio wave used in the physical distribution management system is 953 MHz, the length of one side of the outer circumference of the auxiliary antenna is about 12.5 cm, and the length of one side of the inner circumference is about 5.0 cm. The auxiliary antenna has a thickness of about 0.1 mm, and the annular antenna pattern is formed on one side-attached paper by metal vapor deposition.

  FIG. 2B shows an example of the RFID tag used in the embodiment. In this example, the RFID tag 20 is an electric field receiving type with a frequency of a used radio wave of 953 MHz, an IC 22 is disposed in the center, and a folded dipole antenna is connected to the upper and lower feeding points.

  For example, the RFID tag 20 has a length of about 8 cm, a width of about 2 cm, and a thickness of about 0.1 mm. The RFID tag 20 has an antenna pattern formed on a base material such as a PET film by metal vapor deposition or metal foil pasting. An adhesive layer is formed on the metal film, and a non-sticky release paper is bonded thereto.

  FIG. 3 schematically shows the assembly of the composite RFID tag 1. The auxiliary antenna 10 has a metal film 13 such as an aluminum foil formed as an antenna pattern on a substrate 12 such as a PET film, a weak adhesive layer 14 is formed on the lower surface of the substrate 12, and a release paper 15 is attached. It is matched. The RFID tag 20 is bonded to an appropriate position (for example, a marker position not shown) of the metal film 13. Further, the composite RFID tag 1 is configured by covering the whole with protective paper.

  As described above, when the auxiliary antenna 10 and the RFID tag 20 are brought into contact and conduction, the adhesive on the back surface of the RFID tag 20 is partially peeled (metal exposure) or the conductive adhesive is partially applied to the part. The auxiliary antenna 10 and the RFID tag 20 are bonded together in a state where the antenna is used, and the IC feeding terminal (or antenna) of the RFID tag 20 is electrically connected to the feeding point on the metal film 13 of the auxiliary antenna 10.

  FIG. 4 is a diagram for explaining a case where the composite RFID tag 1 is used in a master carton (outer box) for medicines and cosmetics. The individual packaging boxes 51 for chemicals and cosmetics are packed with metal foil or the like, and a plurality of containers 51 are stored in a master carton 50 made of corrugated paper having a thickness of about 3 to 5 mm. The composite RFID tag 1 of the present application is attached to the surface of the master carton 50.

  More specifically, the composite RFID tag is attached by receiving mainly the magnetic field component of the radio wave on the surface of the master carton 50 that is the object to be identified including the conductive member inside as described above to generate the high frequency current. The generated auxiliary antenna 10 is attached. Corresponding to the master carton 50, the radio wave type RFID tag 20 is attached at a predetermined position on or near the auxiliary antenna. As described above, impedance matching between the radio frequency RFID tag 20 and the auxiliary antenna 10 side is achieved at a predetermined position.

  The optimum attachment position of the auxiliary antenna 10 and the RFID tag 20 is obtained in advance for each type of the master carton 50, and the pasting work on the identification target object is shortened.

  Since the composite RFID tag 1 attached in this way is thin as a whole, it does not become a protrusion on the surface of the master carton 50.

  5 to 7 are explanatory diagrams for explaining the characteristics of the composite RFID tag 1 using the auxiliary antenna of the present invention.

  FIG. 5 is a diagram for explaining the measurement conditions, in which the composite RFID tag 1 of the above-described embodiment is disposed on the surface of the corrugated cardboard corresponding to the outer box 50 as a separate object to be recognized. A metal film is attached to the back of the corrugated paper. The reader / writer 60 was disposed at a position 2.5 m away from the metal film directly facing the composite RFID tag 1, and the reception sensitivity of the composite RFID tag 1 was measured at a predetermined frequency (for example, 953 MHz). Since the limit reading distance of the RFID tag 20 was about 5 m in free space, the difference in performance due to the distance from the metal to the metal due to the difference in the RF tag was observed at a distance of 2.5 m, which is half of that.

  Further, as shown in FIG. 6A, the thickness of the corrugated paper corresponding to the outer box 50 is 5 mm, and a metal film (aluminum foil) 52 is bonded to the back surface thereof. The distance L from the position of the metal film 52 to the composite RFID tag 1 was changed, and the reception sensitivity of the composite RFID tag 1 was measured by the received signal intensity display (RSSI) of the reader / writer 60.

  As a comparative example, as shown in FIG. 6B, only the RFID tag 20 (without an auxiliary antenna) is attached to cardboard paper. For the RFID tag 20 as well, the reception sensitivity of the RFID tag 20 was measured by changing the distance L from the position of the metal film 52 to the RFID tag 20 under the same conditions as in the above example.

  FIG. 7 is a graph showing the measurement results, and the solid line in the figure indicates the sensitivity characteristic of the composite RFID tag 1. Moreover, the dotted line in the figure shows the sensitivity characteristic of a standard RFID tag of a comparative example.

  As shown in the figure, the composite RFID tag 1 using the auxiliary antenna of the present application has a good reception sensitivity of about −55 dBm even on the surface of corrugated paper (corresponding to a position 5 mm from the metal foil). Have. It can also be seen that even at a position about 2 cm away from the metal foil, there is a sensitivity of about -64 dBm, and it can be used for thick items such as cardboard boxes, wooden boxes, and plastic cases. However, when it is separated from the metal foil by about 2.5 cm, reading becomes impossible.

  On the other hand, the radio wave type RFID tag 20 of the comparative example is −60 dBm at a distance of 6 cm from the metal surface and −68 dBm at a distance of 4 cm. When the RFID tag 20 is brought close to about 3.6 cm from the metal surface, reading becomes impossible.

  As described above, when the radio frequency type RFID tag 20 is brought close to a metal plate to about 4 cm, reading becomes impossible. On the other hand, the composite RFID tag 1 has the best reading ability at 5 mm assuming a cardboard box, and becomes unreadable when separated by about 3 cm. This means that the radio wave type RFID tag 20 shows good performance in free space, and the composite RFID tag 1 shows good performance when approaching metal.

  The above measurement was performed with a distance of 2.5 m between the metal-bonded corrugated cardboard 50 and the reader / writer 60, but the composite RFID tag 1 was readable even at a position separated to about 7 m. This is presumably because the antenna gain was improved because the spread of radio waves converged in one direction by the metal plate.

  8 and 9 are graphs for explaining examples of sensitivity characteristics of the annular auxiliary antenna.

  FIG. 8 shows an example of sensitivity characteristics of the auxiliary antenna according to the embodiment. The horizontal axis represents the size of the outer circumference of the annular body, and the right vertical axis represents the relative gain when the peak value of the antenna is 0 dB. The left vertical axis indicates the size of the inner perimeter.

  In this embodiment, the auxiliary antenna is designed to have an outer peripheral length of 1.63λ (wavelength), an inner peripheral length of 0.63λ, and a dimensional difference between the inner peripheral length and the outer peripheral length of about 1λ. The frequency used is 953 MHz.

  In this type of antenna (annular planar antenna), the outer perimeter of the annular shape of the antenna is related to the resonance frequency of the antenna and is represented by 2 wavelengths × 1 / √ε. ε is the dielectric constant of the insulator, which is about 1.5 in the case of cardboard. In this case, the outer peripheral length is 1.63λ (wavelength) (= 2λ × 1 / √1.5). As packaging materials, foams having a low dielectric constant to plastics having a high dielectric constant are used. Considering the dielectric constant of these materials, it is preferable that the outer perimeter of the auxiliary antenna is set to about 1.2 to 2 wavelengths.

  The inner peripheral length of the annular shape of the auxiliary antenna is selected mainly from the viewpoint of matching with the IC. The two symmetrical points on the circumference of the annular body cut out from the center of the metal plate are used as the balanced feeding point of the patch antenna, but the internal impedance differs depending on the type of IC, and the impedance of the antenna changes depending on the dielectric constant and thickness of the insulator. Then, adjust the inner peripheral shape of the antenna so that it matches the IC. For this reason, it is preferable that the inner peripheral length of the annular shape of the auxiliary antenna is 0.2 to 1 wavelength. In FIG. 8, the range of the inner and outer perimeters of the auxiliary antenna is indicated by hatching areas.

  FIG. 9 is a graph for explaining the influence of the inner and outer peripheral lengths of the auxiliary antenna on the sensitivity characteristics. As described above, the reference shape of the auxiliary antenna was designed with the outer peripheral length of the auxiliary antenna being 1.63λ, the inner peripheral length being 0.63λ, and the dimensional difference between the inner peripheral length and the outer peripheral length being approximately 1λ.

  FIG. 6A shows the sensitivity characteristics when the outer peripheral length of the auxiliary antenna is 1.63λ and the inner peripheral length is changed to around 0.63λ. FIG. 5B shows the sensitivity characteristics when the inner peripheral length of the auxiliary antenna is 0.63λ and the outer peripheral length is changed to around 1.6λ. From these characteristics, it can be seen that the outer peripheral length of the auxiliary antenna further affects the gain characteristics. It can also be seen that the change in the inner peripheral length has a relatively small effect on the gain characteristics.

  FIG. 10 shows another embodiment of the auxiliary antenna of the present application. In this example, the RFID tag IC 22 is directly connected to the magnetic field receiving type auxiliary antenna 10 without going through the RFID tag antenna. By connecting the IC 22 between two points at symmetrical positions of the annular shape, the high frequency current induced in the antenna 10 is directly supplied to the IC 22.

  Note that the inner peripheral shape of the auxiliary antenna 10 can be formed into a shape that facilitates impedance matching with the internal circuit of the IC. As described above, the change in the inner peripheral length is less affected than the change in the outer peripheral length.

  FIG. 11 shows another example of the shape of the auxiliary antenna 10. In the above-described embodiment, a quadrangular annular body is used, but the present invention is not limited to this.

  In FIG. 2A, the outer periphery of the annular body 10 is formed in a circle and the inner periphery is formed in a quadrangle. In FIG. 5B, the outer periphery of the annular body 10 is formed in a circular shape, and the inner periphery is also formed in a circular shape. In FIG. 3C, the outer periphery of the annular body 10 is formed in an elliptical shape, and the inner periphery is also formed in an elliptical shape.

As described above, in the embodiment of the present invention, the auxiliary antenna and the radio frequency type RFID tag are combined to form one metal plate of the patch antenna, and the stored item (conductor) in the cardboard box is used as the other metal of the patch antenna. Since it is a plate and corrugated paper is similar to the patch antenna structure as an insulator between both metal plates, it functions as an RFID tag that can receive radio waves even near metal. Since only the auxiliary antenna and the radio frequency type RFID tag exist on the surface of the cardboard box, the thickness can be smaller than that of a patch antenna as a general metal-compatible tag.
(The invention's effect)
According to the present invention, an auxiliary antenna is combined with an inexpensive radio frequency RFID tag that is widely used as a standard product for physical distribution management, etc., and functions as a magnetic field reception type RFID tag, so that it can be operated near metal. It becomes. In addition, since the metal inside the cardboard box or the like can be used as an antenna plate, the RFID tag can be thin, and even if affixed to the surface of the cardboard box or the like, it does not become a protruding portion, so that it is good. In addition, since it operates at a longer distance than in the case of a single RFID tag, the condition is good.

It is explanatory drawing explaining the state which attached the RFID tag to the auxiliary antenna of this application. It is explanatory drawing explaining an auxiliary antenna and an RFID tag. It is explanatory drawing explaining the assembly of an auxiliary antenna and an RFID tag. It is explanatory drawing explaining the example which affixes and uses a composite RFID tag on the cardboard box using the metal packing material. It is explanatory drawing explaining the characteristic measurement of a composite RFID tag. It is explanatory drawing explaining the separation distance L of a composite RFID tag, and the separation distance L of the RFID tag for comparison. It is a graph explaining the receiving sensitivity characteristic by the separation distance L from a metal surface. It is a graph explaining the example of a characteristic of an auxiliary antenna. It is a graph explaining the sensitivity characteristic change by the change of outer periphery length and inner periphery length. It is explanatory drawing explaining another Example. It is explanatory drawing explaining the other example of a shape of an auxiliary antenna.

Explanation of symbols

  10 Auxiliary antenna, 11 Marker, 12 Base material, 13 Metal (aluminum) foil, 20 RFID tag, 22 IC, 30 Protective paper

Claims (9)

An auxiliary planar antenna for an RFID tag used for a radio frequency RFID tag,
A planar antenna that mainly receives a magnetic field component of a radio wave and generates a high-frequency current, and supplies the high-frequency current to the RFID tag IC through capacitive coupling or contact conduction with the RFID tag;
The planar antenna is an annular planar conductor having an opening at the center, the outer peripheral length of the planar conductor is determined corresponding to the wavelength of the radio wave used by the RFID tag, and the inner peripheral length of the IC of the RFID tag An auxiliary planar antenna for an RFID tag, characterized in that it is determined in accordance with an internal impedance.   The auxiliary planar antenna for an RFID tag according to claim 1, wherein the RFID tag is attached to an object to be identified including a conductive member therein via the auxiliary planar antenna.   The outer peripheral length of the planar conductor having an opening at the center is about 1.2 to 2 wavelengths of the wavelength of the used radio wave, and the inner circumference is about 0. 0 of the wavelength of the used radio wave corresponding to the IC type of the RFID tag. The auxiliary planar antenna for an RFID tag according to claim 1 or 2, which is formed within a range of 2 to 1 wavelength.   4. The auxiliary planar antenna for an RFID tag according to claim 3, wherein two points facing each other on the inner peripheral side of the annular shape are connection points with the IC. 5. The RFID tag and said auxiliary planar antenna functions as one of the conductor surface of the patch antenna, the to function electrically conductive member of the identification target body part as the other conductive surface of the patch antenna, according to claim 2 Auxiliary planar antenna for RFID tags. The object to be identified and the conductive member are a box and a packaging material accommodated in the box, the auxiliary planar antenna is attached to the outer surface of the box, and the RFID tag is on the auxiliary planar antenna. The auxiliary planar antenna for an RFID tag according to claim 2, which is attached to the RFID tag.   The RFID tag according to claim 1, wherein a high-frequency current generated by an IC of the RFID tag is supplied to the planar antenna through the capacitive coupling or contact conduction, and radio waves are emitted from the planar antenna. Auxiliary planar antenna for use. The auxiliary planar antenna for an RFID tag according to claim 2 , wherein a position where the RFID tag is attached corresponding to the object to be identified is indicated on the auxiliary planar antenna. The auxiliary planar antenna for an RFID tag according to any one of claims 1 to 8, wherein the RFID tag includes an antenna that converts an electric field component of a received radio wave into a high-frequency current.

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