RFID tags and tires

Abstract

The present invention improves antenna gain. An RFID tag (1) comprises a spring antenna (2) and a coupling module (3). The coupling module (3) includes a helical antenna and an RFIC element. The spring antenna (2) includes a helical coupling part (20), a helical first radiation part (21), a helical second radiation part (22), a first intermediate part (23), and a second intermediate part (24). The coupling part (20) is provided inside the coupling module (3). The first intermediate part (23) is positioned between the coupling part (20) and the first radiation part (21) and has fewer than 1 turn per unit length of the coupling module (3) in the direction (D1) parallel to the winding axis (A20) of the coupling part (20). The second intermediate part (24) is positioned between the coupling part (20) and the second radiation part (22) and has fewer than 1 turn per unit length of the coupling module (3) in the direction (D1) parallel to the winding axis (A20) of the coupling part (20).

Description

Technical Field

[0001] The present invention generally relates to RFID (Radio frequency Identification) tags and tires, and more particularly to RFID tags including a coupling module and tires including RFID tags.

Background Art

[0002] Patent Document 1 discloses an RFID tag including a spring-shaped antenna and a power supply module disposed inside the spring-shaped antenna.

[0003] In the RFID tag disclosed in Patent Document 1, a rectangular parallelepiped-shaped power supply module elongated in the longitudinal direction of the RFID tag is inserted into a spring-shaped antenna elongated in the longitudinal direction of the RFID tag to form the RFID tag.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In RFID tags, it is required to reduce the weight and size while ensuring a desired communication distance. For this reason, in RFID tags, it may be desirable to improve the antenna gain without increasing the inner diameter of the entire spring antenna.

[0006] An object of the present invention is to provide an RFID tag and a tire capable of improving the antenna gain.

Means for Solving the Problems

[0007] An RFID tag according to one aspect of the present invention comprises a spring antenna and a coupling module. The coupling module has a helical antenna and an RFIC element. The RFIC element is connected to the helical antenna. The spring antenna has a helical coupling portion, a helical first radiating portion, a helical second radiating portion, a first intermediate portion, and a second intermediate portion. The coupling portion is positioned with the coupling module on the inside. The first intermediate portion has a number of turns per unit length of the coupling module in a direction parallel to the winding axis of the coupling portion and is located between the coupling portion and the first radiating portion. The second intermediate portion has a number of turns per unit length of the coupling module in the direction parallel to the winding axis of the coupling portion and is located between the coupling portion and the second radiating portion.

[0008] A tire according to one aspect of the present invention comprises an RFID tag according to the above-described aspect and a tire casing in which the RFID tag is embedded. [Effects of the Invention]

[0009] The RFID tag and tire according to the above embodiment of the present invention can improve antenna gain. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a perspective view of an RFID tag according to Embodiment 1. [Figure 2] Figure 2 is a magnified view of the main parts of the RFID tag shown above. [Figure 3] Figure 3 is a front view of the RFID tag shown above. [Figure 4] Figure 4 is a side view of the coupling section and coupling module in the RFID tag shown above, viewed from a direction parallel to the winding axis of the coupling section. [Figure 5] Figure 5 is a perspective view of the coupling module in the RFID tag mentioned above, showing the inside of the coupling module. [Figure 6]Figure 6 is a plan view showing the inside of the coupling module in the RFID tag described above. [Figure 7] Figure 7 shows the antenna gain-frequency characteristics of the RFID tag according to Embodiment 1 and the RFID tags according to Comparative Examples 1 and 2. [Figure 8] Figure 8A is a perspective view of a tire equipped with an RFID tag according to Embodiment 1. Figure 8B is a front view of the main part of the tire equipped with the same RFID tag. [Figure 9] Figure 9 is an explanatory diagram illustrating the positional relationship between the first and second ends of the spring antenna in the RFID tag described above, when the joint is viewed from a direction parallel to the winding axis of the joint. [Figure 10] Figure 10 is a perspective view of an RFID tag according to Embodiment 2. [Figure 11] Figure 11 is a perspective view of an RFID tag according to Embodiment 3. [Figure 12] Figure 12 is a front view of the RFID tag shown above. [Modes for carrying out the invention]

[0011] Embodiments 1 to 3, etc., will be described below with reference to the drawings. The drawings referenced in Embodiments 1 to 3, etc., are schematic diagrams, and the size and thickness of the components shown in the drawings do not necessarily reflect the actual dimensions, nor do the size ratios and thickness ratios between components necessarily reflect the actual dimensional ratios.

[0012] (Embodiment 1) (1) Structure of an RFID tag As shown in Figures 1 and 2, the RFID tag 1 according to Embodiment 1 comprises a spring antenna 2 and a coupling module 3. The coupling module 3 is, for example, a module that magnetically couples with the spring antenna 2. The RFID tag 1 is magnetically coupled with the coupling module 3 and the spring antenna 2.

[0013] The RFID tag 1 is built into the tire casing 101 of the tire 100, for example, as shown in FIGS. 8A and 8B. The RFID tag 1 communicates with, for example, an external reader device.

[0014] (1.1) Structure of the coupling module As shown in FIGS. 5 and 6, the coupling module 3 is, for example, in the shape of an elongated rectangular parallelepiped in the first direction D31. The coupling module 3 is in the shape of a rectangular parallelepiped whose length in the first direction D31 is longer than the length in the second direction D32 orthogonal to the first direction D31.

[0015] The coupling module 3 has a helical antenna 6 and an RFIC element 7 connected to the helical antenna 6. The helical antenna 6 is an antenna that magnetically couples with the spring antenna 2. The helical antenna 6 is a magnetic coupling element with the spring antenna 2 and an element for the matching circuit of the RFIC element 7 in the coupling module 3.

[0016] The coupling module 3 includes a printed wiring board 30, a resin block 31, and a protective layer 32. The helical antenna 6 of the coupling module 3 includes two conductor portions 61a, a plurality (12 in the example of FIG. 5) of first connection conductor portions 61b, and one intermediate conductor portion 61c included in the printed wiring board 30, a plurality (28 in the example of FIG. 5) of metal pins 62, and a plurality (14 in the example of FIG. 5) of second connection conductor portions 63. The plurality of metal pins 62 are arranged on the printed wiring board 30. More specifically, two of the 28 metal pins 62 are arranged on the two conductor portions 61a, each of the 24 metal pins 62 is arranged on either the first end or the second end of any one of the plurality of first connection conductor portions 61b, one metal pin 62 is arranged on the first end of the intermediate conductor portion 61c, and one metal pin 62 is arranged on the second end of the intermediate conductor portion 61c. The RFIC element 7 is arranged, for example, on the printed wiring board 30. The resin block 31 is arranged on the printed wiring board 30 and covers the side surfaces of each of the plurality of metal pins 62 and the RFIC element 7. Each of the plurality of second connection conductor portions 63 is arranged across two metal pins 62 arranged side by side along a second direction D32 orthogonal to the first direction D31 in a plan view from the thickness direction D30 of the printed wiring board 30. The protective layer 32 is arranged on the resin block 31 and covers the plurality of second connection conductor portions 63.

[0017] The material of each of the two conductor portions 61a, the plurality of first connection conductor portions 61b, and the intermediate conductor portion 61c includes, for example, copper. The material of each of the plurality of metal pins 62 includes, for example, copper or a copper alloy. Also, the material of each of the plurality of second connection conductor portions 63 includes, for example, copper.

[0018] The material of the resin block 31 includes resin (for example, epoxy resin). Also, the material of the protective layer 32 includes, for example, resin (for example, epoxy resin, polyimide, etc.).

[0019] Furthermore, the external shape of the coupling module 3 is composed of a printed circuit board 30, a resin block 31, and a protective layer 32, and is rectangular when viewed from a first direction D31 parallel to the winding axis A6 of the helical antenna 6 (see Figures 4 and 5). In the RFID tag 1, the length of the diagonal of the external shape of the coupling module 3 as viewed from the first direction D31 may be shortened, and the magnetic field coupling between the helical antenna 6 and the spring antenna 2 may be narrowed to strengthen the magnetic field coupling between the helical antenna 6 and the spring antenna 2. Specifically, in order to shorten the length of the diagonal, the external shape of the coupling module 3 as viewed from the first direction D31 may be made hexagonal by grinding down only the corners of the resin block 31, or the printed circuit board 30 may also be ground down to make it octagonal, further narrowing the gap between the helical antenna 6 and the spring antenna 2. In addition, when shortening the length of the diagonal of the external shape of the coupling module 3 as viewed from the first direction D31, chamfering may be performed on the entire coupling module 3, for example, by barrel polishing.

[0020] The helical antenna 6 of the coupling module 3 includes, as described above, two conductor sections 61a, a plurality of first connecting conductor sections 61b, one intermediate conductor section 61c, a plurality of metal pins 62, and a plurality of second connecting conductor sections 63. The winding axis A6 of the helical antenna 6 is parallel to the first direction D31.

[0021] The RFIC element 7 is connected between the first end 611 and the second end 612 of the helical antenna 6. The RFIC element 7 is, for example, an RFIC chip. In this embodiment, the RFIC element 7 has a first input / output terminal (not shown) and a second input / output terminal (not shown). The first input / output terminal of the RFIC element 7 is connected to the first land electrode 33 of the printed circuit board 30. The second input / output terminal of the RFIC element 7 is connected to the second land electrode 34 of the printed circuit board 30. As a result, the RFIC element 7 is connected to the first end 611 of the helical antenna 6 via the first wiring section 35 of the printed circuit board 30, and to the second end 612 of the helical antenna 6 via the second wiring section 36 of the printed circuit board 30. Therefore, the coupling module 3 has an inductor, which is formed by the helical antenna 6, connected between the first input / output terminal and the second input / output terminal of the RFIC element 7.

[0022] (1.2) Spring antenna The spring antenna 2 will be described below with reference to Figures 1 to 4.

[0023] The spring antenna 2 is an antenna that functions as a radio wave emitter from the RFID tag 1 and also functions as an antenna booster. The spring antenna 2 is elastically deformable. The spring antenna 2 includes a steel wire (e.g., piano wire or stainless steel wire). The material of the spring antenna 2 includes, for example, steel (e.g., stainless steel).

[0024] The free length of the spring antenna 2 is determined based on half the wavelength of the radio waves transmitted by the RFID tag 1. The communication frequency band used by the RFID tag 1 is, for example, the UHF band, specifically 860MHz to 920MHz. The length of the spring antenna 2 is, for example, 60mm.

[0025] As shown in Figures 1 and 3, the spring antenna 2 has a helical coupling portion 20, a helical first radiating portion 21, a helical second radiating portion 22, a first intermediate portion 23, and a second intermediate portion 24.

[0026] When the spring antenna 2 is not elastically deformed, the winding axis A20 of the joint 20, the winding axis A21 of the first radiating section 21, and the winding axis A22 of the second radiating section 22 are all on the same straight line. The lengths H20 of the joint 20, H21 of the first radiating section 21, and H22 of the second radiating section 22 in the direction D1 parallel to the winding axis A20 of the joint 20 are all free lengths.

[0027] The coupling module 3 is positioned on the inside of the coupling section 20. In other words, in the spring antenna 2, the coupling module 3 is positioned inside the coupling section 20. In the spring antenna 2, the coupling module 3 is positioned on the winding axis A20 of the coupling section 20. The winding axis A20 of the coupling section 20 is parallel to the winding axis A6 of the helical antenna 6 (see Figures 5 and 6). The statement "the winding axis A20 of the coupling section 20 is parallel to the winding axis A6 of the helical antenna 6" is not limited to cases where they are strictly parallel, but also includes cases where the acute angle between the winding axis A20 of the coupling section 20 and the winding axis A6 of the helical antenna 6 is 10 degrees or less.

[0028] As shown in Figure 2, the coupling portion 20 has a first end 201 and a second end 202. In this embodiment, as shown in Figure 4, the second end 202 of the coupling portion 20 overlaps the coupling module 3 when viewed from a direction D1 parallel to the winding axis A20 of the coupling portion 20. By overlapping at least one of the first end 201 and the second end 202 of the coupling portion 20 with the coupling module 3 as shown in Figure 4, it becomes easier to fix the coupling module 3 within the coupling portion 20 when the coupling module 3 is inserted into the coupling portion 20. For example, the RFID tag 1 of this embodiment may be constructed by inserting the coupling module 3 into the coupling portion 20 from the first end 201 of the coupling portion 20 and fixing the coupling module 3 to the coupling portion 20 with an adhesive portion (not shown) made of a flexible resin material, such as a silicone rubber-based resin material. In this embodiment, the second end 202 of the coupling portion 20 overlaps the coupling module 3 when viewed from a direction D1 parallel to the winding axis A20 of the coupling portion 20. However, it is also possible that the first end 201, rather than the second end 202, overlaps the coupling module 3 when viewed from a direction D1 parallel to the winding axis A20 of the coupling portion 20.

[0029] As shown in Figure 1, the winding direction D20 of the coupling portion 20 is clockwise when viewed from the direction D1 parallel to the winding axis A20, and is the same as the winding direction (clockwise) of the helical antenna 6.

[0030] As shown in Figure 3, in the direction D1 parallel to the winding axis A20 of the coupling portion 20, the length H20 of the coupling portion 20 is longer than the length H3 of the coupling module 3, but it may be less than or equal to the length H3 of the coupling module 3.

[0031] Furthermore, in this embodiment, in the direction D1 parallel to the winding axis A20 of the coupling portion 20, the length H20 of the coupling portion 20 is shorter than the length H21 of the first radiating portion 21 and the length H22 of the second radiating portion 22, but may be the same length as the length H21 of the first radiating portion 21 and the length H22 of the second radiating portion 22. The electrical length of the helical first radiating portion 21 and the electrical length of the helical second radiating portion 22 are determined based on half the wavelength of the radio waves transmitted by the RFID tag 1.

[0032] In Embodiment 1, the length H21 of the first radial portion 21 and the length H22 of the second radial portion 22 are the same in the direction D1 parallel to the winding axis A20 of the joint portion 20. "The length H21 of the first radial portion 21 and the length H22 of the second radial portion 22 are the same" means that the length H21 of the first radial portion 21 and the length H22 of the second radial portion 22 do not have to be exactly the same length. "The length H21 of the first radial portion 21 and the length H22 of the second radial portion 22 are the same" includes the case where the length H21 of the first radial portion 21 is 90% or more and 110% or less of the length H22 of the second radial portion 22.

[0033] In this embodiment, as shown in Figure 1, when viewed from a direction D1 parallel to the winding axis A20 of the connecting portion 20, the winding direction D21 of the first radial portion 21 is in the opposite direction to the winding direction D20 of the connecting portion 20. Also, when viewed from a direction D1 parallel to the winding axis A20 of the connecting portion 20, the winding direction D22 of the second radial portion 22 is in the opposite direction to the winding direction D20 of the connecting portion 20.

[0034] As shown in Figure 3, in the direction D1 parallel to the winding axis A20 of the coupling portion 20, the length H23 of the first intermediate portion 23 is longer than the length H3 of the coupling module 3, but may be the same as the length H3 of the coupling module 3. The first intermediate portion 23 has less than 1 turn per unit length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling portion 20, and is located between the coupling portion 20 and the first radial portion 21. "The first intermediate portion 23 has less than 1 turn per unit length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling portion 20" means that the number of turns of the first intermediate portion 23 is less than 1 in the range of the first intermediate portion 23 that is the same length as the length H3 of the coupling module 3. Even if the first intermediate portion 23 has a twisted shape in the range of the first intermediate portion 23 that is the same length as the length H3 of the coupling module 3, the number of turns is still less than 1. In Embodiment 1, the first intermediate section 23 has a linear shape, and the number of turns per unit length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling section 20 is zero. The first intermediate section 23 is located on the winding axis A20 of the coupling section 20. In Embodiment 1, the first intermediate section 23 constitutes a first connecting section that connects the coupling section 20 and the first radial section 21.

[0035] In the direction D1 parallel to the winding axis A20 of the coupling portion 20, the length H24 of the second intermediate portion 24 is longer than the length H3 of the coupling module 3, but may be the same as the length H3 of the coupling module 3. The second intermediate portion 24 has less than 1 turn per unit length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling portion 20, and is located between the coupling portion 20 and the second radial portion 22. "The second intermediate portion 24 has less than 1 turn per unit length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling portion 20" means that the number of turns of the second intermediate portion 24 is less than 1 in the range of the second intermediate portion 24 that is the same length as the length H3 of the coupling module 3. Even if the second intermediate portion 24 has a twisted shape in the range of the second intermediate portion 24 that is the same length as the length H3 of the coupling module 3, the number of turns is still less than 1. In Embodiment 1, the second intermediate section 24 has a linear shape, and the number of turns per unit length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling section 20 is zero. The second intermediate section 24 is located on the winding axis A20 of the coupling section 20. In Embodiment 1, the second intermediate section 24 constitutes a second connecting section that connects the coupling section 20 and the second radial section 22.

[0036] In Embodiment 1, the length H23 of the first intermediate section 23 and the length H24 of the second intermediate section 24 are the same in the direction D1 parallel to the winding axis A20 of the joint section 20. "The length H23 of the first intermediate section 23 and the length H24 of the second intermediate section 24 are the same" means that the length H23 of the first intermediate section 23 and the length H24 of the second intermediate section 24 do not have to be exactly the same length. "The length H23 of the first intermediate section 23 and the length H24 of the second intermediate section 24 are the same" includes the case where the length H23 of the first intermediate section 23 is 80% or more and 120% or less of the length H24 of the second intermediate section 24.

[0037] (2) Method of manufacturing RFID tags The manufacturing method for the RFID tag 1 involves, in order, a first step of preparing the spring antenna 2 and a second step of placing the coupling module 3 inside the coupling portion 20 of the spring antenna 2.

[0038] In the first step, a spring antenna 2 is prepared by forming a steel wire (e.g., piano wire or stainless steel wire) and then heat-treating it at a predetermined temperature (e.g., 400°C). In the spring antenna 2 that has been heat-treated at the predetermined temperature after forming, the stress from the spring deformation process of the steel wire is released, improving the dimensional accuracy of each of the joint portion 20, the first radiating portion 21, the second radiating portion 22, the first intermediate portion 23, and the second intermediate portion 24, and also forming an oxide film containing Fe3O4 on the surface of the steel wire.

[0039] In the second step, the coupling module 3 is inserted into the inside of the coupling portion 20 of the spring antenna 2, which has a coupling portion 20, a first radiating portion 21, a second radiating portion 22, a first intermediate portion 23, and a second intermediate portion 24, from the first intermediate portion 23 side (or the second intermediate portion 24 side) in the direction along the winding axis A20 of the coupling portion 20 (direction D1), thereby fixing the coupling module 3 to the spring antenna 2. When coupling the coupling module 3 to the spring antenna 2, for example, the coupling portion 20 and the coupling module 3 may be molded with resin or rubber, or the spring antenna 2 and the coupling module 3 may be fixed with adhesive. Alternatively, a part of the spring antenna 2 may be bent to prevent the coupling module 3 from coming out of the coupling portion 20.

[0040] In the manufacturing method of the RFID tag 1 of this embodiment, the first and second steps can be performed separately. Compared to a manufacturing method in which the coupling module is placed during the spring-forming process of the steel wire and a spring is formed around the coupling module, the dimensional accuracy of the spring antenna 2 is improved, and it becomes possible to prevent load from being applied to the coupling module 3 when it is inserted. As a result, the coupling module 3 is less likely to be damaged, and the manufacturing quality can be improved.

[0041] (3) Operation of RFID tags In RFID tag 1, when the spring antenna 2 receives radio waves (signals) in the UHF communication frequency band, the radio waves are transmitted to the helical antenna 6 which is magnetically coupled to the spring antenna 2, causing a current corresponding to the signal to flow through the RFIC element 7. The RFIC element 7 operates by receiving the current supplied from the helical antenna 6 and outputs a current (signal) corresponding to the information stored in the internal memory unit (not shown) of the RFIC element 7 to the helical antenna 6. Radio waves (signals) corresponding to this current are radiated to the outside from the spring antenna 2 which is magnetically coupled to the helical antenna 6.

[0042] The spring antenna 2 in the RFID tag 1 according to Embodiment 1 has a first intermediate section 23 between the coupling section 20 and the first radiating section 21, and a second intermediate section 24 between the coupling section 20 and the second radiating section 22, so it functions similarly to a dipole antenna.

[0043] (4) Antenna gain-frequency characteristics of RFID tags Figure 7 shows the antenna gain-frequency characteristics of RFID tag 1 of one embodiment of Embodiment 1, RFID tag of Comparative Example 1, and RFID tag of Comparative Example 2. In Figure 7, "G1" represents the antenna gain-frequency characteristics of RFID tag 1 of one embodiment, "R1" represents the antenna gain-frequency characteristics of RFID tag of Comparative Example 1, and "R2" represents the antenna gain-frequency characteristics of RFID tag of Comparative Example 2.

[0044] In Comparative Example 1, the RFID tag has a spring antenna with a total length (free length) of 60 mm, and the pitch of the springs constituting the spring antenna is greater than the pitch of the helical coupling portion 20 in one embodiment. In Comparative Example 2, the RFID tag has a spring antenna with a total length (free length) of 37 mm, and the pitch of the springs constituting the spring antenna is greater than the pitch of the helical coupling portion 20 in one embodiment. In the RFID tag of Comparative Example 1, the pitch of the springs constituting the spring antenna is the same as the inner diameter of the springs constituting the spring antenna. Similarly, in the RFID tag of Comparative Example 2, the pitch of the springs constituting the spring antenna is the same as the pitch of the springs constituting the spring antenna in the RFID tag of Comparative Example 1. The inner diameter of the spring-shaped coupling portion 20 of the spring antenna 2 is the same as the inner diameter of the springs constituting the spring antenna of Comparative Example 1 and the inner diameter of the springs constituting the spring antenna of Comparative Example 2.

[0045] As can be seen from Figure 7, the RFID tag of Comparative Example 1 has improved antenna gain compared to the RFID tag of Comparative Example 2. In Figure 7, "R1," which shows the antenna gain-frequency characteristics of Comparative Example 1, shows a resonance peak of the coupling module around 0.90 GHz, but the spring antenna peak appears at a higher frequency than 1.10 GHz (around 1.3 GHz) (not shown). Regarding "R2," which shows the antenna gain-frequency characteristics of Comparative Example 2, the resonance peak of the coupling module appears around 0.90 GHz, but the spring antenna resonance peak appears around 1.2 GHz (not shown).

[0046] As can be seen from Figure 7, the RFID tag 1 of one embodiment has an even higher antenna gain than comparative example 1. Furthermore, the "G1" which shows the antenna gain-frequency characteristic of the RFID tag 1 of one embodiment shows that the resonance peak of the coupling module 3 appears around 0.90 GHz, and the resonance peak of the spring antenna 2 appears around 0.96 GHz. In other words, from Figure 7, it can be seen that in one embodiment, the coupling coefficient between the coupling module 3 and the spring antenna 2 can be reduced without making the inner diameter of the coupling portion 20 of the spring antenna 2 larger than the inner diameter of the spring antenna of comparative example 1. From the above, it can be seen that the RFID tag 1 of one embodiment can improve the antenna gain in the communication frequency band used by the RFID tag 1.

[0047] (5) Tire structure As shown in Figures 8A and 8B, the tire 100 according to Embodiment 1 comprises an RFID tag 1 and a tire casing 101 in which the RFID tag 1 is built. The tire 100 further comprises a wheel 104. The tire 100 is, for example, a tire used on a vehicle such as an automobile.

[0048] The tire casing 101 contains an electrically insulating elastomer. The elastomer is a polymeric substance that has rubber-like elasticity at room temperature. "Elastomer" includes, for example, diene polymers, i.e., polymers containing diene units, silicones, polyurethanes, and thermoplastic elastomers such as polyolefins. The tire casing 101 has a tread 102 and a sidewall 103. The RFID tag 1 is embedded in the sidewall 103 of the tire casing 101. In particular, when the RFID tag 1 is embedded in the sidewall 103, metal fibers are arranged radially in the sidewall 103, so in order to reduce the deterioration of antenna radiation characteristics due to the influence of the metal fibers, the RFID tag 1 is arranged perpendicular to the metal fibers. The RFID tag 1 may, for example, be encapsulated between two layers containing electrically insulating rubber with high affinity to the elastomer in the sidewall 103, or between two layers containing the elastomer.

[0049] (6) Effects The RFID tag 1 according to Embodiment 1 has a spring antenna 2 comprising a helical coupling portion 20, a helical first radiating portion 21, a helical second radiating portion 22, a first intermediate portion 23, and a second intermediate portion 24. The first intermediate portion 23 has fewer than 1 turns per length H3 of the coupling module 3 in a direction D1 parallel to the winding axis A20 of the coupling portion 20, and is located between the coupling portion 20 and the first radiating portion 21. The second intermediate portion 24 has fewer than 1 turns per length H3 of the coupling module 3 in a direction D1 parallel to the winding axis A20 of the coupling portion 20, and is located between the coupling portion 20 and the second radiating portion 22.

[0050] The above configuration makes it possible to improve the antenna gain. More specifically, in the RFID tag 1 according to Embodiment 1, the current generated in the coupling part 20 by the magnetic field coupling between the coupling part 20 and the helical antenna 6 of the coupling module 3 is less likely to be radiated to the outside as magnetic field energy in the first intermediate part 23 and the second intermediate part 24, and is efficiently transmitted to the helical first radiating part 21 and the helical second radiating part 22, thereby increasing the antenna radiation efficiency and improving the antenna gain.

[0051] Furthermore, in the RFID tag 1 according to Embodiment 1, the winding direction D21 of the first radiating portion 21 and the winding direction D22 of the second radiating portion 22 are in the opposite direction to the winding direction D20 of the connecting portion 20.

[0052] With the above configuration, if the coupling portion 20, the first radiating portion 21, and the second radiating portion 22 are each magnetized, the inductance of the spring antenna 2 changes, the resonant frequency of the spring antenna 2 changes, and the phenomenon of wavelength shortening occurs, the effect of magnetization can be reduced in some cases. If the effect of magnetization is not a concern, the winding direction D21 of the first radiating portion 21 and the winding direction D22 of the second radiating portion 22 may be the same as the winding direction D20 of the coupling portion 20.

[0053] The tire 100 according to Embodiment 1 comprises an RFID tag 1 and a tire casing 101 in which the RFID tag 1 is built.

[0054] The above configuration makes it possible to improve the antenna gain.

[0055] (Modified version of Embodiment 1) In a modified example of Embodiment 1, as viewed from a direction D1 parallel to the winding axis A20 of the joint 20 (see Figure 1), the angle θ1 between the straight line SL1 passing through the winding axis A20 of the joint 20 and the first end 201 of the joint 20, and the straight line SL2 passing through the winding axis A20 of the joint 20 and the second end 202 of the joint 20, is 90 degrees or less, as shown in Figure 9.

[0056] According to the above configuration, when manufacturing the RFID tag 1, the spring antenna 2 can be stably positioned on a jig or stage on which the spring antenna 2 is placed, making it easier to insert the coupling module 3 inside the coupling portion 20 of the spring antenna 2 and facilitating the positioning of the coupling module 3 relative to the coupling portion 20.

[0057] A modified version of Embodiment 1, similar to the RFID tag 1 according to Embodiment 1, makes it possible to improve the antenna gain.

[0058] (Embodiment 2) The RFID tag 1A according to Embodiment 2 will be described with reference to Figure 10. With respect to the RFID tag 1A according to Embodiment 2, components similar to those in the RFID tag 1 according to Embodiment 1 (see Figures 1 to 7, 8A, and 8B) are denoted by the same reference numerals and their descriptions are omitted.

[0059] (1) Composition The RFID tag 1A according to Embodiment 2 differs from the RFID tag 1 according to Embodiment 1 in that the winding axis A21 of the first radiating part 21 and the winding axis A22 of the second radiating part 22 are offset from the winding axis A20 of the connecting part 20 in a direction perpendicular to the direction D1 parallel to the winding axis A20 of the connecting part 20.

[0060] In this embodiment, when viewed from a direction D1 parallel to the winding axis A20 of the coupling portion 20, the winding direction (winding direction) D20 of the coupling portion 20 is clockwise (right-handed), and the winding direction D21 of the first radial portion 21 is counterclockwise (left-handed). In this embodiment, the winding direction D20 of the coupling portion 20 and the winding direction D21 of the first radial portion 21 are in opposite directions, and the winding direction D20 of the coupling portion 20 and the winding direction D22 of the second radial portion 22 are in opposite directions.

[0061] (2) Effects The RFID tag 1A according to Embodiment 2, like the RFID tag 1 according to Embodiment 1, has a spring antenna 2 that includes a helical coupling portion 20, a helical first radiating portion 21, a helical second radiating portion 22, a first intermediate portion 23, and a second intermediate portion 24, making it possible to improve the antenna gain. In addition, the RFID tag 1A according to Embodiment 2 makes it easier to place the coupling module 3 inside the coupling portion 20.

[0062] Furthermore, in the RFID tag 1A according to Embodiment 2, the winding axis A21 of the first radiating section 21 and the winding axis A22 of the second radiating section 22 are offset from the winding axis A20 of the connecting section 20 in a direction perpendicular to the direction D1 parallel to the winding axis A20 of the connecting section 20.

[0063] With the above configuration, when manufacturing the RFID tag 1A, the first radiating section 21 and the second radiating section 22 are less likely to get in the way when inserting the coupling module 3 into the coupling section 20, making it easier to insert the coupling module 3 into the coupling section 20.

[0064] Furthermore, in the RFID tag 1A according to Embodiment 2, the winding direction D21 of the first radiating portion 21 and the winding direction D22 of the second radiating portion 22 are in the opposite direction to the winding direction D20 of the connecting portion 20.

[0065] With the above configuration, if the coupling portion 20, the first radiating portion 21, and the second radiating portion 22 are magnetized, the inductance of the spring antenna 2 changes, the resonant frequency of the spring antenna 2 changes, and the phenomenon of wavelength shortening occurs, the effect of magnetization can be reduced in some cases. If the effect of magnetization is not a concern, the winding direction D21 of the first radiating portion 21 and the winding direction D22 of the second radiating portion 22 may be the same as the winding direction D20 of the coupling portion 20.

[0066] (Embodiment 3) The RFID tag 1B according to Embodiment 3 will be described with reference to Figures 11 and 12. With respect to the RFID tag 1B according to Embodiment 3, components similar to those in the RFID tag 1 according to Embodiment 1 (see Figures 1 to 7, 8A, and 8B) are denoted by the same reference numerals and their descriptions are omitted.

[0067] (1) Composition The RFID tag 1B according to Embodiment 3 differs from the RFID tag 1 according to Embodiment 1 in that the length H21 of the first radiating portion 21 and the length H22 of the second radiating portion 22 are different, with the length H21 of the first radiating portion 21 being longer than the length H22 of the second radiating portion 22.

[0068] (2) Effects The RFID tag 1B according to Embodiment 3, like the RFID tag 1 according to Embodiment 1, is capable of improving antenna gain. Furthermore, in the RFID tag 1B according to Embodiment 3, if the magnetic coupling between the coupling module 3 and the spring antenna 2 is too strong, the coupling value can be adjusted by changing the ratio of the length H21 of the first radiating section 21 to the length H22 of the second radiating section 22.

[0069] The embodiments described above (1 to 3) are merely one of many embodiments of the present invention. The embodiments described above (1 to 3) can be modified in various ways depending on the design, etc., as long as the objectives of the present invention are achieved, and may be combined as appropriate.

[0070] (Other variations) For example, the structure of the coupling module 3 is not limited to the examples shown in Figures 5 and 6, and may have other structures.

[0071] The products to which RFID tags 1 are applied are not limited to tires 100; for example, clothing, linens, etc., may also be included.

[0072] (Aspect) This specification discloses the following aspects:

[0073] An RFID tag according to the first embodiment (1; 1A; 1B) comprises a spring antenna (2) and a coupling module (3). The coupling module (3) has a helical antenna (6) and an RFIC element (7). The RFIC element (7) is connected to the helical antenna (6). The spring antenna (2) has a helical coupling portion (20), a helical first radiating portion (21), a helical second radiating portion (22), a first intermediate portion (23), and a second intermediate portion (24). The coupling module (3) is positioned inside the coupling portion (20). The first intermediate portion (23) has fewer than 1 turn per unit length (H3) of the coupling module (3) in a direction (D1) parallel to the winding axis (A20) of the coupling portion (20), and is located between the coupling portion (20) and the first radiating portion (21). The second intermediate section (24) has fewer than 1 turn per unit length (H3) of the coupling module (3) in a direction (D1) parallel to the winding axis (A20) of the coupling section (20), and is located between the coupling section (20) and the second radial section (22).

[0074] According to this embodiment, it becomes possible to improve the antenna gain.

[0075] In the RFID tag (1;1A;1B) according to the second embodiment, in the first embodiment, in the direction (D1) parallel to the winding axis (A20) of the coupling portion (20), the length (H23) of the first intermediate portion (23) and the length (H24) of the second intermediate portion (24) are each longer than the length (H3) of the coupling module (3).

[0076] According to this embodiment, during manufacturing, the coupling module (3) can be easily placed inside the coupling portion (20) of the spring antenna (2), thereby improving the performance of the spring antenna (2).

[0077] In the RFID tag (1A) according to the third embodiment, in the first or second embodiment, the winding axis (A21) of the first radiating part (21) and the winding axis (A22) of the second radiating part (22) are offset from the winding axis (A20) of the connecting part (20) in a direction perpendicular to the direction (D1) parallel to the winding axis (A20) of the connecting part (20).

[0078] According to this embodiment, the coupling module (3) can be easily inserted into the coupling portion (20) during manufacturing.

[0079] In the RFID tag according to the fourth embodiment (1;1A;1B), in any one of the first to third embodiments, the winding direction (D21) of the first radiating portion (21) and the winding direction (D22) of the second radiating portion (22) are in the opposite direction to the winding direction (D20) of the connecting portion (20).

[0080] According to this embodiment, when the coupling portion (20), the first radiating portion (21), and the second radiating portion (22) are magnetized and their magnetic susceptibility increases, the inductance of the spring antenna (2) changes, the resonant frequency of the spring antenna (2) changes, and the phenomenon of wavelength shortening occurs, the effect of magnetization can be offset.

[0081] In the RFID tag according to the fifth embodiment (1;1A;1B), in any one of the first to fourth embodiments, in the direction (D1) parallel to the winding axis (A20) of the coupling portion (20), the length (H20) of the coupling portion (20) is shorter than the length (H21) of the first radiating portion (21) and the length (H22) of the second radiating portion (22).

[0082] According to this embodiment, it becomes possible to reduce the coupling coefficient between the coupling portion (20) and the helical antenna (6), thereby weakening the magnetic coupling.

[0083] In the RFID tag according to the sixth embodiment (1;1A;1B), in any one of the first to fifth embodiments, the coupling portion (20) has a first end (201) and a second end (202). The first end (201) or the second end (202) of the coupling portion (20) overlaps the coupling module (3) when viewed from a direction (D1) parallel to the winding axis (A20) of the coupling portion (20).

[0084] According to this embodiment, when the coupling module (3) is easily positioned inside the coupling portion (20) of the spring antenna (2) during manufacturing, it becomes easier to position the coupling module (3) and prevents the coupling module (3) from falling off the coupling portion (20).

[0085] In the RFID tag according to the seventh embodiment (1;1A;1B), in any one of the first to sixth embodiments, the spring antenna (2) includes piano wire or stainless steel wire.

[0086] According to this embodiment, it is possible to improve the durability of the spring antenna (2).

[0087] In the RFID tag (1;1A;1B) according to the eighth embodiment, the material of the spring antenna (2) includes Fe3O4, as in the seventh embodiment.

[0088] This embodiment makes it possible to improve reliability.

[0089] The tire (100) according to the ninth embodiment comprises an RFID tag (1;1A;1B) from any one of the first to eighth embodiments, and a tire casing (101) in which the RFID tag (1;1A;1B) is embedded.

[0090] According to this embodiment, it becomes possible to improve the antenna gain.

[0091] In the tire (100) according to the tenth embodiment, the tire casing (101) includes an electrically insulating elastomer, as in the ninth embodiment.

[0092] In the tire (100) according to the eleventh embodiment, as in the tenth embodiment, the tire casing (101) has a sidewall (103). The RFID tags (1; 1A; 1B) are embedded in the sidewall (103) of the tire casing (101).

[0093] According to this embodiment, the RFID tags (1;1A;1B) are less susceptible to external forces while the vehicle equipped with tires (100) is in motion, thereby improving the reliability of the RFID tags (1;1A;1B). [Explanation of Symbols]

[0094] 1, 1A, 1B RFID tags 2. Spring antenna 20 Joint 201 1st end 202 2nd end 21 First Radiation Section 22 Second Radiation Section 23. First Intermediate Section 24. Second Intermediate Section 3. Combination Module 6. Helical antenna 7 RFIC elements 100 tires 101 Tire Casing 103 Sidewall A6 Winding shaft A20 Winding shaft A21 Winding shaft A22 Winding shaft D1 direction D20 Winding direction D21 Winding direction D22 Winding direction D31 1st direction D32 2nd direction H3 Length H20 Length H21 Length H22 Length H23 Length H24 Length

Claims

1. Spring antenna and Equipped with a coupling module, The aforementioned coupling module is Helical antenna and The RFIC element is connected to the helical antenna, The aforementioned spring antenna is The coupling module is located on the inside of a helical coupling portion, A helical first radial section, A helical second radial section, The number of turns per unit length of the coupling module in a direction parallel to the winding axis of the coupling portion is less than 1, and a first intermediate portion is located between the coupling portion and the first radial portion, The number of turns per unit length of the coupling module in the direction parallel to the winding axis of the coupling portion is less than 1, and the coupling portion has a second intermediate portion located between the coupling portion and the second radial portion, RFID tags.

2. In the direction parallel to the winding axis of the coupling portion, the length of the first intermediate portion and the length of the second intermediate portion are each longer than the length of the coupling module. The RFID tag according to claim 1.

3. The winding axis of the first radial section and the winding axis of the second radial section are offset from the winding axis of the connecting section in a direction perpendicular to the direction parallel to the winding axis of the connecting section. The RFID tag according to claim 1 or 2.

4. The winding direction of the first radial portion and the winding direction of the second radial portion are opposite to the winding direction of the connecting portion. The RFID tag according to claim 1 or 2.

5. In the direction parallel to the winding axis of the joint, the length of the joint is shorter than the length of the first radial portion and the length of the second radial portion, The RFID tag according to claim 1 or 2.

6. The aforementioned joint has a first end and a second end, The first or second end of the coupling portion overlaps the coupling module when viewed from the direction parallel to the winding axis of the coupling portion. The RFID tag according to claim 1 or 2.

7. The spring antenna includes piano wire or stainless steel wire. The RFID tag according to claim 1 or 2.

8. The material of the spring antenna is Fe ３ O ４ including, The RFID tag according to claim 7.

9. The RFID tag according to claim 1 or 2, A tire casing having the aforementioned RFID tag built in, tire.

10. The tire casing includes an electrically insulating elastomer. The tire according to claim 9.

11. The tire casing has a sidewall, The RFID tag is embedded in the sidewall of the tire casing. The tire according to claim 10.

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