JP2025083930A - RFID tags for rubber products - Google Patents

Abstract

To provide an RFID tag for rubber products which is small-sized and improved in mass productivity and durability.SOLUTION: An RFID tag 1 for rubber products comprises: a coupling transformer 40; a RF chip 10 connected to the secondary side of the coupling transformer; a printed circuit board 20 on which the RF chip is loaded; and an antenna 30. The antenna includes: a coil part 31; a first element 32 extending from one end of the coil part; and a second element 33 which extends from the other end shorter than the first element and in parallel with the first element. The number of windings of the coil part is less than the number of windings at the secondary side of the coupling transformer and the printed circuit board is held in a clearance between element wires of the coil part, such that the coil part constitutes the primary side of the coupling transformer. At least one of the first element and the second element includes an extension/contraction part 31 which extends/contracts in its own length direction. The extension/contraction part is appropriately deformed with respect to external force, such that the first element and the second element are hard to be broken or deformed, thereby improving durability of the RFID tag.SELECTED DRAWING: Figure 1

Description

The present invention relates to an RFID tag for rubber products that is small, easy to mass-produce, and durable.

The RFID tags used in RFID (Radio Frequency Identification) systems contain an antenna and an RF chip, which receives the carrier wave transmitted from the antenna of the reader/writer and transmits the identification data recorded on the RF chip on a reflected wave back to the reader/writer, thus enabling contactless communication.
By attaching or embedding an RFID tag in the tires of a vehicle such as an automobile, it is possible to manage the tire's unique information and the tire's history of manufacture, distribution, maintenance, etc. Of course, when an RFID tag is attached or embedded in a rubber product other than a tire, it can also be used to manage the product.

The tire with an embedded RFID tag in Patent Document 1 has a first antenna connected to an IC chip and a second antenna electromagnetically coupled to the first antenna, and discloses a technology for electromagnetically coupling the second antenna to a conductive carcass ply cord.
Patent Document 2 discloses an RFID tag for rubber products developed by the present inventor. This RFID tag for rubber products has a coil section as an antenna, a first element extending from one end of the coil section, and a second element that is shorter than the first element and extends parallel to the first element from the other end of the coil section, and holds a printed circuit board in the gaps between the wires of the coil section. This RFID tag for rubber products forms a coupling transformer by holding the printed circuit board in the gaps of the coil section. Therefore, it is possible to increase the mass productivity of RFID tags for rubber products.

JP 2017-132291 A Patent No. 7016200

When attaching an RFID tag to a tire, there is a problem that the RFID tag can be damaged by deformation of the tire while driving. In addition, when the free electrons of the carbon black contained in the tire receive radio waves, the charge moves from negative to positive, and as a result, the electric current flows from positive to negative, which causes changes in impedance and relative dielectric constant.
In Patent Document 1, the first antenna and the second antenna are electromagnetically coupled, and since the signal source impedance of the second antenna is high, there is a problem that it is susceptible to changes in impedance and relative dielectric constant due to the influence of carbon black.
In addition, since the second antenna has a pair of extensions extending in the left and right directions from the electromagnetic field coupling part, when the tire deforms, the left and right extensions are pulled in the left and right directions around the electromagnetic field coupling part, which may result in damage.

In addition, RFID tags using conventional half-wavelength dipole antennas have the problem of being large in size, and even if a meander line antenna, in which the antenna elements are folded to make it smaller, is used, it is difficult to determine the effective meander length due to the influence of carbon black.
In Patent Document 2, the first element and the second element extend parallel to each other, making the RFID tag less susceptible to damage and more durable. In addition, the RFID tag is smaller than a conventional half-wavelength dipole antenna. However, there is a demand for an RFID tag that is even more durable.
Such problems can also occur when RFID tags are used in rubber products other than tires, particularly rubber products that contain materials such as carbon black that affect the communication performance of RFID tags.

Taking these problems into consideration, the present invention aims to provide an RFID tag for rubber products that is small, easy to mass-produce, and durable.

The RFID tag for rubber products of the present invention comprises a coupling transformer, an RF chip connected to the secondary side of the coupling transformer, a printed circuit board on which the RF chip is mounted, and an antenna, the antenna comprising a coil portion, a first element extending from one end of the coil portion, and a second element which is shorter than the first element and extends parallel to the first element from the other end of the coil portion, the number of windings of the coil portion is less than the number of windings of the secondary side of the coupling transformer, the coil portion forms the primary side of the coupling transformer by holding the printed circuit board in the gaps between the wires of the coil portion, and at least one of the first element and the second element comprises an expansion portion which expands and contracts in its longitudinal direction.
The present invention is also characterized in that it is for use in rubber products containing carbon black.
The printed circuit board is also characterized in that it has insulating layers on both the front and back surfaces.
The coil portion, the first element and the second element are each made of a single conducting wire.
The present invention is also characterized in that the axis of the secondary coil of the coupling transformer coincides with the axis of the coil portion.
In addition, when the wavelength of radio waves at a communication frequency is λ, the electrical length of a portion consisting of the first element, the second element and the coil portion is λ/4.

In the RFID tag for rubber products of the present invention, at least one of the first element and the second element has an elastic part that deforms appropriately in response to an external force, making the first element and the second element less susceptible to breakage or deformation and improving the durability of the RFID tag.
In the RFID tag for rubber products of the present invention, a printed circuit board is held in the gap of the coil to form a coupling transformer, which makes it possible to increase the mass productivity of RFID tags for rubber products.
In addition, in the present invention, the first and second elements that function as antennas extend in parallel, making the RFID tag less susceptible to damage and more durable, while also providing a smaller RFID tag than a conventional half-wavelength dipole antenna.
In addition, in this invention, the number of windings in the primary coil is made less than that of the secondary coil, making the input impedance of the primary low, and the secondary high impedance is converted by a coupling transformer to match the input impedance of the RF chip. By lowering the impedance of the primary, for example, even if the RFID tag is used in a rubber product that contains carbon black, the effects of carbon black can be suppressed.

By providing insulating layers on both sides of the printed circuit board, it is possible to prevent the coil section and the secondary coil from being electrically connected.
If the coil portion, the first element, and the second element are formed by bending a single conducting wire, the antenna can be manufactured easily and the reliability of the electrical connection between the coil portion, the first element, and the second element can be increased.
The efficiency of the coupling transformer can be increased by aligning the axis of the secondary coil of the coupling transformer with the axis of the coil section.
If the electrical length of the portion consisting of the first element, second element, and coil portion is set to λ/4, the length of the antenna will be minimized, enabling RFID tags for rubber products to be further miniaturized.

Plan view (a), bottom view (b), side view (c), modified example (d) and modified example (e) of the antenna (a) is a plan view showing the state in which the RF chip and secondary coil are mounted on the printed circuit board, (b) is a plan view showing the state in which the RF chip and connection points are sealed, (c) is a bottom view, and (d) is a side view. (a) is a plan view, (b) is a bottom view, and (c) is a side view showing the state before the printed circuit board is inserted into the gap of the coil part. (a) is a plan view, (b) is a bottom view, and (c) is a side view showing the state after the printed circuit board is inserted into the gap of the coil part. Enlarged views (a) to (d) of the circled areas in Figure 1(a) Equivalent circuit diagram of RFID tag for rubber products A vertical cross-sectional view showing an RFID tag for rubber products covered on both sides with a rubber sheet A vertical cross-sectional view showing an RFID tag for rubber products attached to a tire Plan views (a) to (c) showing the manufacturing method of RFID tags for rubber products 1A and 1B are plan views showing a manufacturing method of an RFID tag for rubber products. Plan views (a) and (b) showing modified examples of the antenna, and enlarged views (c) to (e) of the circled area in FIG. 11(b). FIG. 11 is a plan view showing a modified example of the antenna; 13(a) is a plan view showing a modified example of the antenna, and (b) to (d) are enlarged views of the circled area in FIG. 13(a) 1A and 1B are plan views showing modified examples of the antenna;

The RFID tag for rubber products of the present invention will be described with reference to the drawings.
1 to 4, the RFID tag 1 for rubber products includes an RF chip 10, a printed circuit board 20, an antenna 30, and a coupling transformer 40. In the following description, the RFID tag 1 for rubber products may be simply referred to as the "RFID tag 1."

The RF chip 10 is connected to the secondary side of a coupling transformer 40, which will be described later. Although a commercially available product can be used as the RF chip 10, it is preferable to use one that is resistant to a vulcanization temperature of about 120°C.
As shown in FIG. 2(a), an RF chip 10 is mounted on the surface of a printed circuit board 20 using an adhesive such as an epoxy die-bonding material.

Furthermore, a secondary coil 41 of the coupling transformer 40 is formed on the surface of the printed circuit board 20. One of the two terminals of the secondary coil 41 is connected to a terminal of the RF chip 10 by wire bonding. The other terminal of the secondary coil 41 reaches the rear surface of the printed circuit board 20 through a through hole 21 as shown in Figs. 2(a) and (c), and further reaches the surface of the printed circuit board 20 through a through hole 22, and is connected to a terminal of the RF chip 10 by wire bonding. In this embodiment, the number of turns of the secondary coil 41 is about 4 (actually 3.96). The secondary coil 41 is not limited to a planar coil formed by deposition or the like, and may be a coil made of a conductor. As shown in Fig. 2(b), it is preferable to seal the RF chip 10 and the connection points with an insulating layer 27.
2(d), the front surface of the printed circuit board 20, i.e., the front surface of the RF chip 10 and the secondary coil 41, is sealed with an insulating layer 23. The rear surface of the printed circuit board 20 is also sealed with an insulating layer 23. As the insulating layer 23, an insulating resin such as an epoxy resin, an acrylic resin (a resin whose main components are acrylic resin and derivatives), or a urethane resin can be used.

The antenna 30 is provided for receiving a carrier wave from the reader/writer and for transmitting a reflected wave back to the reader/writer.
The antenna 30 includes a coil portion 31, a first element 32, and a second element 33. The material of the wire of the antenna 30 may be a metal wire such as a copper wire, an iron wire, or a brass wire.

The coil section 31 functions as the primary side of the coupling transformer 40. The number of turns of the coil section 31 must be less than the number of turns of the secondary side. In this embodiment, the number of turns of the wire constituting the coil section 31 is 1.5, and gaps 31a are formed between the wires. Note that the wires naturally open when no external force is applied to the coil section 31, and this open portion may be the gap 31a, or, as shown in FIG. 1(d), the wires are almost in close contact when no external force is applied to the coil section 31, and the wires elastically open when an external force is applied to the coil section 31 in the vertical direction (axial direction), and this open portion may be the gap 31a. It is preferable that the diameter of the coil section 31 when viewed in a plane is the same as or slightly larger than the outer diameter of the secondary coil 41.

The first element 32 is a member extending from one end of the coil portion 31 .
The second element 33 is a member that extends from the other end of the coil portion 31 in parallel to the first element 32 and is shorter than the first element 32 .
Both the first element 32 and the second element 33 have an expandable portion 34 .
The expansion and contraction portion 34 is a portion that expands and contracts in the longitudinal direction of the first element 32 and the second element 33. In this embodiment, the expansion and contraction portion 34 is made up of a compression coil spring, and extends over almost the entire longitudinal area of the first element 32 and the second element 33. A tension coil spring may be used as the expansion and contraction portion 34 instead of a compression coil spring.

When the wavelength of the radio waves at the communication frequency of the RFID tag 1 is λ, the electrical length of the first element 32 is set to approximately 0.185λ of the wavelength, the electrical length of the second element 33 is set to approximately 0.046λ of the wavelength, and the total length of the first element 32, the second element 33 and the coil portion 31 is set to approximately λ/4, thereby making it possible to make the antenna 30 approximately as short as possible.
In addition, the electrical length of the first element 32 refers to the straight-line distance from the starting end of the first element 32 (one end of the coil portion 31) to the end of the first element 32, and the electrical length of the second element 33 refers to the straight-line distance from the starting end of the second element 33 (the other end of the coil portion 31) to the end of the second element 33, and the expanded length of the compression coil spring that constitutes the expansion and contraction portion 34 is not taken into consideration.

The compression coil spring that constitutes the expandable portion 34 is a spring that utilizes a repulsive force when compressed, and a gap 35 is formed between adjacent wires as shown in FIG. 5(a). Therefore, the expandable portion 34 shortens when subjected to a compressive force as shown in FIG. 5(b), lengthens when subjected to a tensile force as shown in FIG. 5(c), and can bend when subjected to a lateral force as shown in FIG. 5(d). In this way, the first element 32 and the second element 33 are provided with the expandable portion 34, and by the expandable portion 34 appropriately deforming in response to an external force, the first element 32 and the second element 33 become less likely to break or deform, and the durability of the RFID tag 1 can be improved.

In this embodiment, the coil portion 31, the first element 32, and the second element 33 are formed by bending a single conductor wire. This makes it easier to manufacture the antenna 30 and increases the reliability of the electrical connection between the coil portion 31, the first element 32, and the second element 33, but is not limited to this and the antenna 30 may be formed by joining ends of multiple conductor wires together.
By folding back the ends of the first element 32 and the second element 33 as shown in FIG. 1(e), when the RFID tag 1 is attached to a rubber product, it is possible to prevent the ends of both elements 32, 33 from piercing or tearing the rubber product, and it is also possible to prevent damage to the RFID tag 1.

As shown in Figures 3 and 4, the printed circuit board 20 is held in place by inserting it into the gaps 31a between the wires of the coil section 31, and the coil section 31 forms the primary side of the coupling transformer 40. It is preferable to align the axis of the coil section 31 with the axis of the secondary coil 41. Both the front and back sides of the printed circuit board 20 are sealed with an insulating layer 23, so the coil section 31 and the secondary coil 41 are not electrically connected. In addition, the wires of the coil section 31 in the part where the printed circuit board 20 is not inserted are naturally insulated to maintain the electrical coil function.

6 is an equivalent circuit diagram when the RFID tag 1 is attached to a rubber product such as a tire. During reception, radio waves received by the first element 32 and the second element 33 are transmitted to the RF chip 10 via the coupling transformer 40. Specifically, a current with an inverted phase to the radio waves flows through the first element 32 and the second element 33, causing a current to flow through the coil section 31 on the primary side, and inducing an AC voltage in the coil 41 on the secondary side.
Here, while the impedance of the RF chip 10 is several kΩ to 10 kΩ, the impedance between the first element 32 and the second element 33 is small, about 100Ω. The impedance between the first element 32 and the second element 33 is small due to the impedance of the antenna 30 itself as well as the influence of resistance components such as carbon black contained in rubber products. Some types of vulcanized rubber tires have a resistivity of about several tens of kΩ·cm. If the RFID tag 1 of the present invention is embedded in a vulcanized rubber tire and both terminals of the RF chip 10 are directly connected to the first element 32 and the second element 33, the received radio waves cannot be efficiently guided to the RF chip 10.

Therefore, in the RFID tag 1 of the present invention, the ratio n (n=N2/N1) of the number of windings N2 on the secondary side of the coupling transformer 40 to the number of windings N1 on the primary side is adjusted. Specifically, when the RF chip 10 with an input impedance Z is connected to the first element 32 and the second element 33 via the coupling transformer 40, the impedance on the primary side of the coupling transformer 40 is Z/ ⁿ² . Therefore, by making the number of windings N1 of the coil part 31 on the primary side smaller than the number of windings N2 of the coil 41 on the secondary side, n is increased to make the input on the primary side low impedance, and the secondary side is converted to high impedance by the coupling transformer 40 to match the input impedance Z of the RF chip 10. By lowering the impedance on the primary side, for example, even if the RFID tag 1 is used in a rubber product containing carbon black, the influence of carbon black, etc. can be suppressed.
However, increasing the number of windings N2 on the secondary side is restricted by the area of the coupling transformer 40 and the like, and the ratio n of the number of windings on the secondary side to the number of windings on the primary side must be appropriately adjusted depending on the specifications of the RF chip 10, the material of the rubber product, the amount of carbon black, etc., and the like.

The antenna 30 of the RFID tag 1 operates similarly to a monopole antenna 30, with the second element 33 as the ground plane and the first element 32 as the antenna wire. When the RFID tag 1 is attached or embedded in a vulcanized rubber product, there is an advantage in that the ground plane is further strengthened by the second element 33 being electrically connected to the vulcanized rubber product.
Furthermore, in a conventional dipole antenna type RFID tag, two antenna elements with an electrical length of λ/4 extend in the left-right direction from a printed circuit board equipped with an RF chip. In this configuration, if the rubber product deforms and forces are applied to the two antenna elements in opposite directions, the connection between the antenna elements and the printed circuit board may be damaged. In contrast, in the RFID tag 1 of the present invention, the first element 32 and the second element 33 extend in parallel in the same direction, which has the advantage that the connection between the base of the first element 32 or the second element 33 and the printed circuit board 20 is less likely to be damaged and that it can be made smaller.
Furthermore, vulcanized rubber enters into the gaps 35 of the stretchable portion 34 and hardens, and the RFID tag 1 becomes integrated with the vulcanized rubber product such as a tire. Therefore, the stretchable portion 34 also deforms appropriately in response to the deformation of the tire or the like, making the first element 32 and the second element 33 less likely to be damaged, and improving the durability of the RFID tag 1.

7, both the front and back sides of the RFID tag 1 for rubber products may be covered with rubber sheets 50, 51. Specifically, the RFID tag 1 is placed between a first rubber sheet 50 and a second rubber sheet 51, and the first rubber sheet 50 and the second rubber sheet 51 are pressure-bonded to each other, thereby manufacturing the RFID tag 1 covered with rubber.
Ordinary natural rubber or various synthetic rubbers can be used as the material for the rubber sheets 50 and 51, and furthermore, adhesive materials such as butyl rubber sheets can be used. By covering the RFID tag 1 with the rubber sheets 50 and 51, even if the rubber product is deformed, the components constituting the RFID tag 1 can be prevented from being damaged or the relative positions of the components can be prevented from being displaced, and the RFID tag 1 can be made waterproof and dustproof.

8 shows a state in which the rubber-covered RFID tag 1 is attached to the inside of a tire 60 as an example of a rubber product. The position to which the RFID tag 1 is attached is not particularly limited. The RFID tag 1 may be attached to the inside of the tire 60, or may be embedded in the rubber of the tire 60. Also, an RFID tag 1 that is not covered with rubber may be attached or embedded to the inside of the tire 60.
By attaching the RFID tag 1 to the tire 60, the second element 33 is electrically connected to the tire 60, and as a result, the tire 60 functions as the ground of the RFID tag 1. Therefore, the RFID tag 1 of the present invention can communicate with high sensitivity even when attached to a rubber product such as the tire 60. The connection between the second element 33 and the tire 60 may be a capacitive connection or a direct connection.

Next, a method for manufacturing the RFID tag 1 for use in rubber products will be described.
As shown in FIG. 9(a), first, a plurality of secondary coils 41 of a coupling transformer 40 are arranged in the left-right direction on a printed circuit board 20 (Step A).
9(b), openings 24, 25 are provided on the front and rear sides of the multiple secondary coils 41 (Step B). The distance from the front opening 24 to the rear opening 25 needs to match the length of the RFID tag 1 in the front-to-rear direction.
9(c), slits 26 are made between the multiple secondary coils 41 (step C). The intervals at which the slits 26 are made must match the length of the RFID tag 1 in the left-right direction.
Steps A to C may be performed in any order. Also, it is necessary to connect the RF chip 10 to the secondary coil 41 at an appropriate timing. After connecting the RF chip 10 to the secondary coil 41, it is preferable to cover its surface with an insulating layer 27.

Next, as shown in FIG. 10(a), the front opening 24 is used to insert the secondary coil 41 into the gap 31a between the wires of the coil section 31. This allows the coil section 31 to function as the primary side of the coupling transformer 40. At this time, the first element 32 and the second element 33 are placed on the side edge 28 of the front opening 24, and the coil section 31 can be moved toward the secondary coil 41 while sliding on the surface of the side edge 28. In addition, since the first element 32 is placed on the side edge 28 with the secondary coil 41 inserted into the gap 31a between the wires, there is no risk of the antenna 30 falling off the printed circuit board 20. The coil section 31 and the printed circuit board 20 may be bonded together as necessary.
Finally, as shown in FIG. 10(b), the printed circuit board 20 is cut at the notches 26, thereby completing the RFID tag 1 for use in rubber products.

Next, modified examples of the antenna will be shown.
11(a) and (b), the expandable portion 36 is formed by bending a portion of the first element 32 and the second element 33. In this case, the expandable portion 36 shortens when subjected to a compressive force as shown in Fig. 11(c), lengthens when subjected to a tensile force as shown in Fig. 11(d), and can bend when subjected to a lateral force as shown in Fig. 11(e).
12, the expansion/contraction portion 37 is formed by forming a compression coil spring in a part of the first element 32 and the second element 33. In this case, the expansion/contraction portion 37 that receives an external force is deformed as shown in FIGS.

In the antenna 72 shown in Fig. 13(a), a plurality of strands (e.g., three strands) are twisted together to form an expandable portion 38 throughout the first element 32 and the second element 33. In this case, the expandable portion 38 becomes slightly shorter when subjected to a compressive force as shown in Fig. 13(b), becomes slightly longer when subjected to a tensile force as shown in Fig. 13(c), and can bend when subjected to a lateral force as shown in Fig. 13(d).
It is not necessary that both the first element 32 and the second element 33 have the stretchable portions 36, 37, and as shown in FIG. 14, only the second element 33, which is more susceptible to the effects of external forces, may have them.

The present invention is an RFID tag for rubber products that is small, easy to mass-produce, and durable, and has industrial applicability.

1. RFID tags for rubber products
10 RF Chip
20 Printed Circuit Board
21 Through Hole
22 through hole
23 Insulating layer
24 Front opening
25 Rear opening
26 Cut
27 Insulating layer
28 Side edge
30 Antenna
31 Coil section
31a Gap
32 First Element
33 2nd Element
34 Telescopic part
35 Gap
36 Telescopic part
37 Telescopic part
40 Coupling transformer
41 Secondary coil
50 First rubber sheet
51 Second rubber sheet
60 Tires

The RFID tag for rubber products of the present invention comprises a coupling transformer, an RF chip connected to the secondary side of the coupling transformer, a printed circuit board on which the RF chip is mounted, and an antenna, the antenna comprising a coil portion, a first element extending from one end of the coil portion, and a second element which is shorter than the first element and extends parallel to the first element from the other end of the coil portion, the number of windings of the coil portion being less than the number of windings of the secondary side of the coupling transformer, and the coil portion forms the primary side of the coupling transformer by holding the printed circuit board in the gaps between the wires of the coil portion, and at least one of the first element and the second element has an expansion portion which expands and contracts in its longitudinal direction, and the expansion portion is formed by bending a straight wire in a horizontal plane .
The present invention is also characterized in that it is for use in rubber products containing carbon black.
The printed circuit board is also characterized in that it has insulating layers on both the front and back surfaces.
The coil portion, the first element and the second element are each made of a single conducting wire.
The present invention is also characterized in that the axis of the secondary coil of the coupling transformer coincides with the axis of the coil portion.
In addition, when the wavelength of radio waves at a communication frequency is λ, the electrical length of a portion consisting of the first element, the second element and the coil portion is λ/4.

Claims (6)

The device includes a coupling transformer, an RF chip connected to a secondary side of the coupling transformer, a printed circuit board on which the RF chip is mounted, and an antenna,
the antenna comprises a coil section, a first element extending from one end of the coil section, and a second element extending from the other end of the coil section, the second element being shorter than the first element and extending parallel to the first element;
the number of turns of the coil portion is smaller than the number of turns of the secondary side of the coupling transformer,
the coil portion constitutes a primary side of the coupling transformer by holding the printed circuit board in gaps between wires of the coil portion,
An RFID tag for rubber products, wherein at least one of the first element and the second element has an elastic portion that expands and contracts in its longitudinal direction.
2. The RFID tag for rubber products according to claim 1, characterized in that it is for rubber products containing carbon black.
3. The RFID tag for rubber products according to claim 1, further comprising insulating layers on both sides of the printed circuit board.
2. The RFID tag for rubber products according to claim 1, wherein the coil portion, the first element and the second element are made of a single conducting wire.
2. The RFID tag for use in rubber products according to claim 1, wherein an axial center of a coil on a secondary side of the coupling transformer coincides with an axial center of the coil portion.
The RFID tag for rubber products as described in claim 1, characterized in that, when the wavelength of radio waves at the communication frequency is λ, the electrical length of the portion consisting of the first element, the second element and the coil portion is λ/4.

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