RFID tag and tire

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

RFID tags and tires

[0001] The present invention relates generally to RFID (Radio Frequency Identification) tags and tires, and more particularly to an RFID tag with a coupling module and a tire with an RFID tag.

[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] The RFID tag disclosed in Patent Document 1 is formed by inserting a rectangular parallelepiped power supply module that is elongated in the longitudinal direction of the RFID tag into a spring-shaped antenna that is elongated in the longitudinal direction of the RFID tag.

[0004] International Publication No. 2018 / 101315

[0005] RFID tags are required to be lightweight and compact while ensuring a desired communication distance, so it is sometimes desirable to improve the antenna gain of RFID tags 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 that can improve antenna gain.

[0007] An RFID tag according to one aspect of the present invention includes a spring antenna and a coupling module. The coupling module includes a helical antenna and an RFIC element. The RFIC element is connected to the helical antenna. The spring antenna includes a helical coupling portion, a first helical radiating portion, a second helical radiating portion, a first intermediate portion, and a second intermediate portion. The coupling portion has the coupling module disposed therein. The first intermediate portion has less than one turn per 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 less than one turn per 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 includes the RFID tag according to the above aspect and a tire casing in which the RFID tag is embedded.

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

[0010] FIG. 1 is a perspective view of an RFID tag according to a first embodiment. FIG. 2 is an enlarged view of a main portion of the RFID tag. FIG. 3 is a front view of the RFID tag. FIG. 4 is a side view of the coupling portion and coupling module of the RFID tag, viewed from a direction parallel to the winding axis of the coupling portion. FIG. 5 is a perspective view of the coupling module of the RFID tag, seen through the interior of the coupling module. FIG. 6 is a plan view of the coupling module of the RFID tag, seen through the interior of the coupling module. FIG. 7 is an antenna gain-frequency characteristic diagram of the RFID tag according to the first embodiment and RFID tags according to comparative examples 1 and 2. FIG. 8A is a perspective view of a tire equipped with the RFID tag according to the first embodiment. FIG. 8B is a front view of a main portion of the tire equipped with the RFID tag. FIG. 9 is an explanatory diagram of the positional relationship between a first end and a second end of the spring antenna of the RFID tag, when the coupling portion is viewed from a direction parallel to the winding axis of the coupling portion. FIG. 10 is a perspective view of an RFID tag according to a second embodiment. Fig. 11 is a perspective view of an RFID tag according to embodiment 3. Fig. 12 is a front view of the RFID tag according to embodiment 3.

[0011] Hereinafter, embodiments 1 to 3 will be described with reference to the drawings. The drawings referred to in the following embodiments 1 to 3 are schematic diagrams, and the sizes and thicknesses of the components in the drawings do not necessarily reflect the actual dimensions, and the size ratios and thickness ratios between the components do not necessarily reflect the actual dimensional ratios.

[0012] 1 and 2, an RFID tag 1 according to the first embodiment includes 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. In the RFID tag 1, the coupling module 3 and the spring antenna 2 are magnetically coupled.

[0013] 8A and 8B, the RFID tag 1 is embedded in a tire casing 101 of a tire 100. The RFID tag 1 performs communication with, for example, an external reader device.

[0014] 5 and 6, the coupling module 3 has, for example, a rectangular parallelepiped shape that is elongated in a first direction D31. The coupling module 3 has a rectangular parallelepiped shape in which the length in the first direction D31 is longer than the length in a second direction D32 that is perpendicular 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 an element for magnetically coupling with the spring antenna 2, and is also an element for a 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, in the printed wiring board 30, two conductor portions 61a, a plurality (12 in the example of FIG. 5 ) of first connection conductor portions 61b, one intermediate conductor portion 61c, 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, of the 28 metal pins 62, two metal pins 62 are arranged on the two conductor portions 61a, each of the 24 metal pins 62 is arranged on a first end or a second end of one of the plurality of first connection conductor portions 61b, one metal pin 62 is arranged on a first end of the intermediate conductor portion 61c, and one metal pin 62 is arranged on a second end of the intermediate conductor portion 61c. The RFIC element 7 is disposed on, for example, a printed wiring board 30. The resin block 31 is disposed on the printed wiring board 30 and covers the RFIC element 7 and the side surfaces of each of the multiple metal pins 62. Each of the multiple second connection conductors 63 is disposed across two metal pins 62 that are aligned 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 disposed on the resin block 31 and covers the multiple second connection conductors 63.

[0017] The two conductors 61 a, the first connecting conductors 61 b, and the intermediate conductor 61 c are each made of, for example, copper. The metal pins 62 are each made of, for example, copper or a copper alloy. The second connecting conductors 63 are each made of, for example, copper.

[0018] The material of the resin block 31 includes a resin (for example, an epoxy resin), and the material of the protective layer 32 includes, for example, a resin (for example, an epoxy resin, a polyimide, or the like).

[0019] The coupling module 3 includes a printed wiring board 30, a resin block 31, and a protective layer 32. The outer shape of the coupling module 3 is rectangular when viewed from a first direction D31 parallel to the winding axis A6 of the helical antenna 6 (see FIGS. 4 and 5 ). In the RFID tag 1, the magnetic field coupling between the helical antenna 6 and the spring antenna 2 may be strengthened by shortening the diagonal length of the outer shape of the coupling module 3 when viewed from the first direction D31 and further narrowing the gap between the helical antenna 6 and the spring antenna 2. Specifically, to shorten the diagonal length, the corners of only the resin block 31 may be ground to form a hexagonal outer shape when viewed from the first direction D31, or the printed wiring board 30 may also be ground to form an octagonal shape, further narrowing the gap between the helical antenna 6 and the spring antenna 2. To shorten the diagonal length of the outer shape of the coupling module 3 when viewed from the first direction D31, the entire coupling module 3 may be chamfered, for example, by barrel polishing.

[0020] As described above, the helical antenna 6 of the coupling module 3 includes two conductor portions 61 a, a plurality of first connecting conductor portions 61 b, one intermediate conductor portion 61 c, a plurality of metal pins 62, and a plurality of second connecting conductor portions 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 wiring board 30. The second input / output terminal of the RFIC element 7 is connected to the second land electrode 34 of the printed wiring 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 portion 35 of the printed wiring board 30, and is connected to the second end 612 of the helical antenna 6 via the second wiring portion 36 of the printed wiring board 30. Therefore, in the coupling module 3, an inductor formed by the helical antenna 6 is 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 now be described with reference to FIGS.

[0023] The spring antenna 2 is an antenna that functions as a radio wave radiator from the RFID tag 1 and 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 communicated by the RFID tag 1. The communication frequency band of the RFID tag 1 is, for example, the UHF band, e.g., 860 MHz to 920 MHz. The length of the spring antenna 2 is, for example, 60 mm.

[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 coupling portion 20, the winding axis A21 of the first radiating portion 21, and the winding axis A22 of the second radiating portion 22 are aligned on a straight line. In a direction D1 parallel to the winding axis A20 of the coupling portion 20, the length H20 of the coupling portion 20, the length H21 of the first radiating portion 21, and the length H22 of the second radiating portion 22 are each a free length.

[0027] The coupling module 3 is disposed on the inside of the coupling unit 20. That is, in the spring antenna 2, the coupling module 3 is disposed on the inside of the coupling unit 20. In the spring antenna 2, the coupling module 3 is disposed on the winding axis A20 of the coupling unit 20. The winding axis A20 of the coupling unit 20 is parallel to the winding axis A6 of the helical antenna 6 (see FIGS. 5 and 6 ). The phrase "the winding axis A20 of the coupling unit 20 is parallel to the winding axis A6 of the helical antenna 6" does not necessarily mean that they are strictly parallel, but also includes the case where the acute angle formed between the winding axis A20 of the coupling unit 20 and the winding axis A6 of the helical antenna 6 is 10 degrees or less.

[0028] As shown in FIG. 2 , the coupling unit 20 has a first end 201 and a second end 202. In this embodiment, as shown in FIG. 4 , the second end 202 of the coupling unit 20 overlaps the coupling module 3 when viewed from a direction D1 parallel to the winding axis A20 of the coupling unit 20. By overlapping at least one of the first end 201 and the second end 202 of the coupling unit 20 with the coupling module 3 as shown in FIG. 4 , the coupling module 3 can be easily fixed within the coupling unit 20 when inserted into the coupling unit 20. For example, the RFID tag 1 of this embodiment may be configured by inserting the coupling module 3 into the coupling unit 20 from the first end 201 of the coupling unit 20 and fixing the coupling module 3 to the coupling unit 20 with an adhesive (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, but the first end 201, rather than the second end 202, may overlap 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 FIG. 1, the winding direction D20 of the coupling portion 20 is clockwise when viewed from a direction D1 parallel to the winding axis A20, and is the same as the winding direction (clockwise direction) of the helical antenna 6.

[0030] As shown in FIG. 3, in a 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 may be shorter than or equal to the length H3 of the coupling module 3.

[0031] In the present 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 each of the length H21 of the first radiating portion 21 and the length H22 of the second radiating portion 22, but may be the same as each of 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 each determined based on half the wavelength of the radio waves communicated by the RFID tag 1.

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

[0033] 1 , when viewed from a direction D1 parallel to the winding axis A20 of the coupling portion 20, the winding direction D21 of the first radiating portion 21 is opposite to the winding direction D20 of the coupling portion 20. Also, when viewed from the direction D1 parallel to the winding axis A20 of the coupling portion 20, the winding direction D22 of the second radiating portion 22 is opposite to the winding direction D20 of the coupling portion 20.

[0034] 3 , in a direction D1 parallel to the winding axis A20 of the coupling unit 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 one turn per length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling unit 20, and is located between the coupling unit 20 and the first radiating portion 21. The phrase "the first intermediate portion 23 has less than one turn per length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling unit 20" means that the number of turns in the first intermediate portion 23 is less than one within a range of the length that is the same as the length H3 of the coupling module 3. Even if the first intermediate portion 23 has a twisted shape within a range of the length that is the same as the length H3 of the coupling module 3, the number of turns is less than one. In the first embodiment, the first intermediate portion 23 has a linear shape and has zero turns per length H3 of the coupling module 3 in a direction D1 parallel to the winding axis A20 of the coupling portion 20. The first intermediate portion 23 is located on the winding axis A20 of the coupling portion 20. In the first embodiment, the first intermediate portion 23 constitutes a first connection portion that connects the coupling portion 20 and the first radiating portion 21.

[0035] In the direction D1 parallel to the winding axis A20 of the coupling unit 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 one turn per length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling unit 20, and is located between the coupling unit 20 and the second radiating portion 22. "The second intermediate portion 24 has less than one turn per length H3 of the coupling module 3 in the direction D1 parallel to the winding axis A20 of the coupling unit 20" means that the number of turns in the second intermediate portion 24 is less than one within a length range that is the same as the length H3 of the coupling module 3. Even if the second intermediate portion 24 has a twisted shape within a length range that is the same as the length H3 of the coupling module 3, the number of turns is less than one. In the first embodiment, the second intermediate portion 24 has a linear shape and has zero turns per length H3 of the coupling module 3 in a direction D1 parallel to the winding axis A20 of the coupling portion 20. The second intermediate portion 24 is located on the winding axis A20 of the coupling portion 20. In the first embodiment, the second intermediate portion 24 constitutes a second connection portion that connects the coupling portion 20 and the second radiating portion 22.

[0036] In the first embodiment, the length H23 of the first intermediate portion 23 and the length H24 of the second intermediate portion 24 are the same 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 the same" means that the length H23 of the first intermediate portion 23 and the length H24 of the second intermediate portion 24 do not have to be exactly the same. "The length H23 of the first intermediate portion 23 and the length H24 of the second intermediate portion 24 are the same" includes cases where the length H23 of the first intermediate portion 23 is 80% or more and 120% or less of the length H24 of the second intermediate portion 24.

[0037] (2) Method for Manufacturing RFID Tag In the method for manufacturing the RFID tag 1, a first step of preparing the spring antenna 2 and a second step of arranging the coupling module 3 inside the coupling portion 20 of the spring antenna 2 are carried out in sequence.

[0038] In the first step, for example, a spring antenna 2 is prepared by forming a steel wire (for example, a piano wire or a stainless steel wire) and then heat-treating it at a predetermined temperature (for example, 400°C). In the spring antenna 2 that has been heat-treated at the predetermined temperature after forming, the stress that occurred during the spring deformation process of the steel wire is released, so the dimensional accuracy of each of the coupling portion 20, the first radiating portion 21, the second radiating portion 22, the first intermediate portion 23, and the second intermediate portion 24 is improved, and Fe is formed on the surface of the steel wire. ３ O ４ An oxide film containing

[0039] In a second step, the coupling module 3 is inserted into the inside of the coupling portion 20 of the spring antenna 2, which has the coupling portion 20, first radiating portion 21, second radiating portion 22, first intermediate portion 23, and second intermediate portion 24, in a direction (direction D1) along the winding axis A20 of the coupling portion 20, from the first intermediate portion 23 side (or the second intermediate portion 24 side), to fix 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 an adhesive. Alternatively, a portion of the spring antenna 2 may be bent to prevent the coupling module 3 from coming off the coupling portion 20.

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

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

[0042] The spring antenna 2 in the RFID tag 1 of embodiment 1 has a first intermediate portion 23 between the connecting portion 20 and the first radiating portion 21, and a second intermediate portion 24 between the connecting portion 20 and the second radiating portion 22, and therefore functions in the same way as an antenna with a dipole structure.

[0043] (4) Antenna Gain-Frequency Characteristics of RFID Tags Fig. 7 shows the antenna gain-frequency characteristics of the RFID tag 1 of one example of embodiment 1, the RFID tag of comparative example 1, and the RFID tag of comparative example 2. "G1" in Fig. 7 shows the antenna gain-frequency characteristics of the RFID tag 1 of one example, "R1" in Fig. 7 shows the antenna gain-frequency characteristics of the RFID tag of comparative example 1, and "R2" in Fig. 7 shows the antenna gain-frequency characteristics of the RFID tag of comparative example 2.

[0044] In the RFID tag of Comparative Example 1, the total length (free length) of the spring antenna is 60 mm, and the pitch of the springs that make up the spring antenna is larger than the pitch of the helical-shaped coupling portion 20 of the embodiment. In the RFID tag of Comparative Example 2, the total length (free length) of the spring antenna is 37 mm, and the pitch of the springs that make up the spring antenna is larger than the pitch of the helical-shaped coupling portion 20 of the embodiment. In the RFID tag of Comparative Example 1, the pitch of the springs that make up the spring antenna is the same as the inner diameter of the springs that make up the spring antenna. In the RFID tag of Comparative Example 2, the pitch of the springs that make up the spring antenna is also the same as the pitch of the springs that make up the spring antenna in the RFID tag of Comparative Example 1. The inner diameter of the spring-shaped coupling portion 20 of spring antenna 2 is the same as the inner diameter of the springs that make up the spring antenna of Comparative Example 1 and the inner diameter of the springs that make up the spring antenna of Comparative Example 2.

[0045] As can be seen from Figure 7, the RFID tag of Comparative Example 1 has an 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 near 0.90 GHz, while the peak of the spring antenna appears at a frequency higher than 1.10 GHz (near 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 near 0.90 GHz, while the resonance peak of the spring antenna appears near 1.2 GHz (not shown).

[0046] As can be seen from Figure 7, the RFID tag 1 of the embodiment has an improved antenna gain compared to Comparative Example 1. Furthermore, in "G1," which shows the antenna gain-frequency characteristics of the RFID tag 1 of the embodiment, 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, Figure 7 shows that, compared to Comparative Example 1, the coupling coefficient between the coupling module 3 and the spring antenna 2 can be reduced in the embodiment 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 the embodiment can improve the antenna gain in the communication frequency band used by the RFID tag 1.

[0047] (5) Tire Structure As shown in Fig. 8A and Fig. 8B , the tire 100 according to the first embodiment includes an RFID tag 1 and a tire casing 101 incorporating the RFID tag 1. The tire 100 also includes 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. An elastomer is a polymeric substance that has rubber-like elasticity at room temperature. Examples of "elastomer" include thermoplastic elastomers such as diene polymers, i.e., polymers containing diene units, silicone, polyurethane, and polyolefin. 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 radially arranged in the sidewall 103. Therefore, to reduce degradation of antenna radiation characteristics due to the influence of the metal fibers, the RFID tag 1 is positioned perpendicular to the metal fibers. The RFID tag 1 may be embedded, for example, between two layers of electrically insulating rubber that has a high affinity with the elastomer in the sidewall 103, or between two layers of elastomer.

[0049] (6) Effects In the RFID tag 1 according to the first embodiment, the spring antenna 2 has a helical coupling portion 20, a first helical radiating portion 21, a second helical radiating portion 22, a first intermediate portion 23, and a second intermediate portion 24. The first intermediate portion 23 has less than one turn 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 less than one turn 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 the first embodiment, the current generated in the coupling portion 20 due to the magnetic field coupling between the coupling portion 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 portion 23 and the second intermediate portion 24, and is instead efficiently transmitted to the first helical radiating portion 21 and the second helical radiating portion 22, thereby making it possible to improve the antenna radiation efficiency and the antenna gain.

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

[0052] According to the above configuration, when the coupling portion 20, the first radiating portion 21, and the second radiating portion 22 are magnetized and the inductance of the spring antenna 2 changes, causing a wavelength shortening phenomenon, it may be possible to reduce the influence of magnetization. When the influence 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 the first embodiment includes an RFID tag 1 and a tire casing 101 in which the RFID tag 1 is embedded.

[0054] According to the above configuration, it is possible to improve the antenna gain.

[0055] (Variant of embodiment 1) In a variant of embodiment 1, when viewed from a direction D1 (see FIG. 1) parallel to the winding axis A20 of the coupling portion 20, as shown in FIG. 9, the angle θ1 formed between a straight line SL1 passing through the winding axis A20 of the coupling portion 20 and the first end 201 of the coupling portion 20 and a straight line SL2 passing through the winding axis A20 of the coupling portion 20 and the second end 202 of the coupling portion 20 is 90 degrees or less.

[0056] According to the above configuration, when manufacturing the RFID tag 1, the spring antenna 2 can be stably positioned on the 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 to position the coupling module 3 relative to the coupling portion 20.

[0057] The modified example of the first embodiment can improve the antenna gain, similarly to the RFID tag 1 according to the first embodiment.

[0058] (Embodiment 2) An RFID tag 1A according to embodiment 2 will be described with reference to Fig. 10. Regarding the RFID tag 1A according to embodiment 2, the same components as those of the RFID tag 1 according to embodiment 1 (see Figs. 1 to 7, 8A and 8B) are denoted by the same reference numerals and description thereof will be omitted.

[0059] (1) Configuration The RFID tag 1A according to the second embodiment differs from the RFID tag 1 according to the first embodiment in that the winding axis A21 of the first radiating portion 21 and the winding axis A22 of the second radiating portion 22 are misaligned with the winding axis A20 of the coupling portion 20 in a direction perpendicular to the direction D1 parallel to the winding axis A20 of the coupling portion 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 radiating 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 radiating portion 21 are opposite directions, and the winding direction D20 of the coupling portion 20 and the winding direction D22 of the second radiating portion 22 are opposite directions.

[0061] (2) Effects The RFID tag 1A according to the second embodiment, like the RFID tag 1 according to the first embodiment, has a spring antenna 2 including a helical coupling portion 20, a first helical radiating portion 21, a second helical radiating portion 22, a first intermediate portion 23, and a second intermediate portion 24, thereby improving antenna gain. Furthermore, the RFID tag 1A according to the second embodiment makes it easier to arrange the coupling module 3 inside the coupling portion 20.

[0062] In addition, in the RFID tag 1A according to the second embodiment, the winding axis A21 of the first radiating portion 21 and the winding axis A22 of the second radiating portion 22 are misaligned with the winding axis A20 of the coupling portion 20 in a direction perpendicular to the direction D1 parallel to the winding axis A20 of the coupling portion 20.

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

[0064] In the RFID tag 1A according to the second embodiment, the winding direction D21 of the first radiating portion 21 and the winding direction D22 of the second radiating portion 22 are opposite to the winding direction D20 of the coupling portion 20.

[0065] According to the above configuration, when the coupling portion 20, the first radiating portion 21, and the second radiating portion 22 are magnetized and the inductance of the spring antenna 2 changes, causing a wavelength shortening phenomenon, it may be possible to reduce the influence of magnetization. When the influence 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) An RFID tag 1B according to embodiment 3 will be described with reference to Figures 11 and 12. Regarding the RFID tag 1B according to embodiment 3, the same components as those of the RFID tag 1 according to embodiment 1 (see Figures 1 to 7, 8A and 8B) are denoted by the same reference numerals and description thereof will be omitted.

[0067] (1) Configuration The RFID tag 1B of the third embodiment differs from the RFID tag 1 of the first embodiment in that the length H21 of the first radiating portion 21 is different from the length H22 of the second radiating portion 22, and the length H21 of the first radiating portion 21 is longer than the length H22 of the second radiating portion 22.

[0068] (2) Effects The RFID tag 1B according to the third embodiment can improve the antenna gain, similar to the RFID tag 1 according to the first embodiment. Furthermore, in the RFID tag 1B according to the third embodiment, 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 between the length H21 of the first radiating portion 21 and the length H22 of the second radiating portion 22.

[0069] The above-described first to third embodiments are merely examples of various embodiments of the present invention. The above-described first to third embodiments can be modified in various ways depending on the design and the like, and may be combined as appropriate, as long as the object of the present invention can be achieved.

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

[0071] The product to which the RFID tag 1 is applied is not limited to the tire 100, but may also include, for example, clothing, linens, etc.

[0072] (Aspects) The present specification discloses the following aspects.

[0073] An RFID tag (1; 1A; 1B) according to a first aspect includes 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 disposed inside the coupling portion (20). The first intermediate portion (23) has less than one turn 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 less than one turn 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).

[0074] According to this aspect, it is possible to improve the antenna gain.

[0075] In the RFID tag (1; 1A; 1B) according to the second aspect, in the first aspect, in a 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 aspect, during manufacturing, it is possible to easily position the coupling module (3) 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 aspect, in the first or second aspect, the winding axis (A21) of the first radiating portion (21) and the winding axis (A22) of the second radiating portion (22) are misaligned with the winding axis (A20) of the connecting portion (20) in a direction perpendicular to a direction (D1) parallel to the winding axis (A20) of the connecting portion (20).

[0078] According to this aspect, it becomes easier to insert the coupling module (3) inside the coupling portion (20) during manufacturing.

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

[0080] According to this aspect, when each of the coupling portion (20), the first radiation portion (21), and the second radiation portion (22) is magnetized and the magnetic susceptibility increases, the inductance of the spring antenna (2) changes, the resonant frequency of the spring antenna (2) changes, and a wavelength shortening phenomenon occurs, the influence of the magnetization can be offset in some cases.

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

[0082] According to this aspect, it is 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 (1; 1A; 1B) according to the sixth aspect, in any one of the first to fifth aspects, 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 aspect, when the coupling module (3) is easily placed inside the coupling portion (20) of the spring antenna (2) during manufacturing, the positioning of the coupling module (3) becomes easy and it becomes possible to prevent the coupling module (3) from falling off from the coupling portion (20).

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

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

[0087] In the RFID tag (1; 1A; 1B) according to the eighth aspect, the material of the spring antenna (2) in the seventh aspect is Fe ３ O ４ Includes.

[0088] According to this aspect, it is possible to improve reliability.

[0089] A tire (100) according to a ninth aspect includes an RFID tag (1; 1A; 1B) according to any one of the first to eighth aspects, and a tire casing (101) having the RFID tag (1; 1A; 1B) built in.

[0090] According to this aspect, it is possible to improve the antenna gain.

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

[0092] In a tire (100) according to an eleventh aspect, in the tenth aspect, the tire casing (101) has a sidewall (103). The RFID tag (1; 1A; 1B) is embedded in the sidewall (103) of the tire casing (101).

[0093] According to this aspect, the RFID tag (1; 1A; 1B) is less likely to be subjected to external forces while the vehicle equipped with the tire (100) is traveling, thereby making it possible to improve the reliability of the RFID tag (1; 1A; 1B).

[0094] 1, 1A, 1B RFID tag 2 Spring antenna 20 Coupling portion 201 First end 202 Second end 21 First radiation portion 22 Second radiation portion 23 First intermediate portion 24 Second intermediate portion 3 Coupling module 6 Helical antenna 7 RFIC element 100 Tire 101 Tire casing 103 Sidewall A6 Winding axis A20 Winding axis A21 Winding axis A22 Winding axis D1 Direction D20 Winding direction D21 Winding direction D22 Winding direction D31 First direction D32 Second direction H3 Length H20 Length H21 Length H22 Length H23 Length H24 Length

Claims

1. An RFID tag comprising: a spring antenna; and a coupling module, wherein the coupling module has a helical antenna; and an RFIC element connected to the helical antenna, wherein the spring antenna has: a helical coupling portion with the coupling module disposed inside; a first helical radiating portion; a second helical radiating portion; a first intermediate portion having less than one turn per length of the coupling module in a direction parallel to a winding axis of the coupling portion and located between the coupling portion and the first radiating portion; and a second intermediate portion having less than one turn per length of the coupling module in the direction parallel to the winding axis of the coupling portion and located between the coupling portion and the second radiating portion.

2. The RFID tag according to claim 1, wherein 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.

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

4. An RFID tag as described in any one of claims 1 to 3, wherein the winding direction of the first radiating portion and the winding direction of the second radiating portion are opposite to the winding direction of the coupling portion.

5. An RFID tag as described in any one of claims 1 to 4, wherein in the direction parallel to the winding axis of the coupling portion, the length of the coupling portion is shorter than each of the length of the first radiating portion and the length of the second radiating portion.

6. The RFID tag according to any one of claims 1 to 5, wherein the coupling portion has a first end and a second end, and the first end or the second end of the coupling portion overlaps the coupling module when viewed from the direction parallel to the winding axis of the coupling portion.

7. The RFID tag according to any one of claims 1 to 6, wherein the spring antenna includes a piano wire or a stainless steel wire.

8. The material of the spring antenna is Fe. ３ O ４ The RFID tag of claim 7 , comprising:

9. A tire comprising: an RFID tag according to any one of claims 1 to 8; and a tire casing in which the RFID tag is embedded.

10. The tire of claim 9, wherein the tire casing comprises an electrically insulating elastomer.

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

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