RFID tag for rubber products

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

Technical Field

[0001] The present invention relates to an RFID tag for rubber products that is small-sized and excellent in mass productivity and durability.

Background Art

[0002] An RFID tag used in an RFID (Radio Frequency Identification) system stores an antenna and an RF chip. It receives a carrier wave transmitted from the antenna of a reader / writer with the antenna, and rides identification data and the like recorded in the RF chip on a reflected wave and returns it to the reader / writer, thereby enabling a non-contact communication mechanism. By attaching or embedding an RFID tag to, for example, a tire of a vehicle such as an automobile, it is possible to manage the unique information of the tire and manage the history of the manufacture, distribution, and maintenance of the tire. Naturally, when an RFID tag is attached or embedded in a rubber product other than a tire, it can also be used for the management of the product.

[0003] The RFID tag built-in tire of Patent Document 1 includes a first antenna connected to an IC chip and a second antenna electromagnetically coupled to the first antenna, and discloses a technique of electromagnetically coupling the second antenna with a conductive carcass ply cord. Patent Document 2 discloses an RFID tag for rubber products developed by the inventor of the present application. This RFID tag for rubber products includes a coil part as an antenna, a first element extending from one end of the coil part, and a second element extending from the other end of the coil part shorter than the first element and parallel to the first element, and holds a printed circuit board in the gap between the strands of the coil part. This RFID tag for rubber products constitutes a coupling transformer by holding a printed circuit board in the gap of the coil part. Therefore, the mass productivity of the RFID tag for rubber products can be increased.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-132291 [Patent Document 2] Japanese Patent No. 7016200 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] When an RFID tag is attached to a tire, there is a problem that the RFID tag may be damaged due to the deformation of the tire during driving. In addition, free electrons of carbon black contained in the tire receive radio waves, causing a charge to move from minus to plus, and accordingly, a current flows from plus to minus, resulting in a change in impedance and relative permittivity. In Patent Document 1, the first antenna and the second antenna are electromagnetically coupled. Since the signal source impedance of the second antenna is high, there is a problem that it is easily affected by changes in impedance and relative permittivity due to the influence of carbon black. In addition, since the second antenna has a pair of extension portions extending in the left-right direction from the electromagnetic coupling portion, when the tire is deformed, the left and right extension portions are pulled in the left-right direction around the electromagnetic coupling portion, and there is a risk of damage.

[0006] In addition, an RFID tag using a conventional half-wavelength dipole antenna has a problem of large size, and even if a meander line antenna in which the elements of the antenna are bent to reduce the size is used, it is difficult to determine the effective meander length due to the influence of carbon black. In Patent Document 2, since the first element and the second element extend in parallel, the RFID tag is less likely to be damaged and has excellent durability, and a smaller RFID tag can be obtained compared to a conventional half-wavelength dipole antenna. However, there is a demand for an RFID tag with even better durability. Such problems can also occur when the RFID tag is used in rubber products other than tires, particularly rubber products containing materials that affect the communication performance of the RFID tag, such as carbon black.

[0007] The present invention aims to provide an RFID tag for rubber products that is small-sized, excellent in mass productivity and durability in consideration of such problems.

Means for Solving the Problems

[0008] The RFID tag for rubber products of the present invention includes 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 includes a coil portion, a first element extending from one end of the coil portion, and a second element extending from the other end of the coil portion, shorter than the first element and parallel to the first element. The number of turns of the coil portion is less than the number of turns of the secondary side of the coupling transformer, and the coil portion constitutes the primary side of the coupling transformer by holding the printed circuit board in the gap between the strands of the coil portion. At least one of the first element and the second element is provided with a telescopic portion that expands and contracts in its longitudinal direction. Further, it is characterized by being for rubber products containing carbon black. Further, it is characterized by having insulating layers on both the front and back surfaces of the printed circuit board. Further, the coil portion, the first element, and the second element are characterized by being composed of a single wire. Further, it is characterized in that the axis of the coil on the secondary side of the coupling transformer coincides with the axis of the coil portion. Further, when the wavelength of the radio wave at the communication frequency is λ, the electrical length of the portion composed of the first element, the second element, and the coil portion is characterized by being λ / 4.

Effects of the Invention

[0009] In the RFID tag for rubber products of the present invention, at least one of the first element and the second element is provided with a telescopic portion, and the telescopic portion deforms appropriately with respect to an external force. As a result, the first element and the second element are less likely to break or deform, and the durability of the RFID tag can be improved. In the RFID tag for rubber products of the present invention, a coupling transformer is configured by holding a printed circuit board in the gap of the coil portion. Therefore, the mass productivity of the RFID tag for rubber products can be improved. Further, in the present invention, since the first element and the second element that function as an antenna extend in parallel, the RFID tag is less likely to be damaged, has excellent durability, and a smaller RFID tag can be obtained compared to a conventional half-wavelength dipole antenna. Further, in the present invention, by making the number of turns of the coil portion on the primary side less than the number of turns of the coil on the secondary side, the input on the primary side is made to have a low impedance, and the secondary side is converted to a high impedance by a coupling transformer to match the input impedance of the RF chip. By lowering the impedance on the primary side, for example, even when the RFID tag is used for a rubber product containing carbon black or the like, the influence of carbon black or the like can be suppressed.

[0010] By providing insulating layers on both the front and back surfaces of the printed circuit board, it is possible to prevent a situation where the coil portion and the secondary coil are electrically connected. If the coil portion, the first element, and the second element are formed by bending a single wire, the manufacture of the antenna becomes easy, and the reliability of the electrical connection between the coil portion, the first element, and the second element is enhanced. By aligning the axis of the secondary coil of the coupling transformer with the axis of the coil portion, the efficiency of the coupling transformer can be increased. If the electrical length of the portion composed of the first element, the second element, and the coil portion is set to λ / 4, the length of the antenna becomes the shortest, and the RFID tag for rubber products can be further miniaturized.

Brief Description of the Drawings

[0011]

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Embodiments for Carrying Out the Invention

[0012] The RFID tag for rubber products of the present invention will be described with reference to the drawings. As shown in FIGS. 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 sometimes be simply referred to as "RFID tag 1".

[0013] The RF chip 10 is connected to the secondary side of the coupling transformer 40 described later. As the RF chip 10, a commercially available product can be used, but it is preferable to use one having resistance to a vulcanization temperature of about 120°C. As shown in FIG. 2(a), the RF chip 10 is mounted on the surface of the printed circuit board 20 using an adhesive such as an epoxy-based die bonding material.

[0014] Furthermore, the 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 the terminal of the RF chip 10 by wire bonding. The other terminal of the secondary coil 41 reaches the back surface of the printed circuit board 20 through the through hole 21 as shown in FIGS. 2(a) and (c), and further reaches the surface of the printed circuit board 20 through the through hole 22 and is connected to the terminal of the RF chip 10 by wire bonding. In the present 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 vapor deposition or the like, and may be a coil made of a conductive wire. As shown in FIG. 2(b), it is preferable to seal the RF chip 10 and the connection portion with an insulating layer 27. As shown in FIG. 2(d), the surface of the printed circuit board 20, that is, the surface of the RF chip 10 and the secondary coil 41 is sealed with an insulating layer 23. Also, the back surface of the printed circuit board 20 is sealed with the insulating layer 23. As the insulating layer 23, an insulating resin such as an epoxy resin, an acrylic resin (a resin mainly composed of an acrylic resin and derivatives), or a urethane resin can be used.

[0015] The antenna 30 is provided to receive a carrier wave from a reader / writer and also to return a reflected wave to the reader / writer. The antenna 30 includes a coil portion 31, a first element 32, and a second element 33. As the material of the antenna 30's wire, a metal wire such as a copper wire, an iron wire, or a brass wire may be used.

[0016] The coil portion 31 functions as the primary side of the coupling transformer 40. The number of turns of the coil portion 31 needs to be less than that of the secondary side. In this embodiment, the number of turns of the wire constituting the coil portion 31 is 1.5, and a gap 31a is formed between the wires. Note that the wires are naturally open without an external force applied to the coil portion 31, and this open portion may be the gap 31a. Alternatively, as shown in Fig. 1(d), the wires are almost in close contact without an external force applied to the coil portion 31, and by applying an external force in the vertical direction (axial direction) to the coil portion 31, the wires are elastically opened, and this opened portion may be the gap 31a. The diameter of the coil portion 31 in plan view is preferably the same as or slightly larger than the outer diameter of the secondary coil 41.

[0017] The first element 32 is a member extending from one end of the coil portion 31. The second element 33 is a member extending from the other end of the coil portion 31, shorter than the first element 32 and parallel to the first element 32. Both the first element 32 and the second element 33 are provided with a telescopic portion 34. The telescopic portion 34 is a portion that expands and contracts in the longitudinal direction of the first element 32 itself and the second element 33 itself. In this embodiment, the telescopic portion 34 is composed of a compression coil spring and extends over almost the entire longitudinal direction of the first element 32 and the second element 33. A tension coil spring may be used instead of the compression coil spring as the telescopic portion 34.

[0018] When the wavelength of the radio wave at the communication frequency of the RFID tag 1 is λ, by setting the electrical length of the first element 32 to approximately 0.185λ of the wavelength, the electrical length of the second element 33 to approximately 0.046λ of the wavelength, and the total extension of the first element 32, the second element 33, and the coil portion 31 to approximately λ / 4, the antenna 30 can be made generally the shortest. Note that the electrical length of the first element 32 refers to the straight-line distance from the start end (one end of the coil part 31) of the first element 32 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 start end (the other end of the coil part 31) of the second element 33 to the end of the second element 33. The developed length of the compression coil spring constituting the telescopic part 34 is not considered.

[0019] The compression coil spring constituting the telescopic part 34 is a spring that utilizes the repulsive force generated by being compressed. As shown in Fig. 5(a), a gap 35 is formed between adjacent wire strands. Therefore, as shown in Fig. 5(b), the telescopic part 34 shortens when subjected to a compressive force, becomes longer when subjected to a tensile force as shown in Fig. 5(c), and can bend when subjected to a force from the lateral direction as shown in Fig. 5(d). In this way, the first element 32 and the second element 33 are provided with the telescopic part 34, and by appropriately deforming the telescopic part 34 with respect to an external force, it becomes difficult for the first element 32 and the second element 33 to break or deform, and the durability of the RFID tag 1 can be improved.

[0020] In this embodiment, the coil part 31, the first element 32, and the second element 33 are formed by bending a single wire. This simplifies the manufacture of the antenna 30 and increases the reliability of the electrical connection between the coil part 31, the first element 32, and the second element 33. However, it is not limited to this, and the antenna 30 may also be formed by joining the ends of a plurality of wires. As shown in Fig. 1(e), if the ends of the first element 32 and the second element 33 are folded back, 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 the rubber product or cutting the rubber product, and further prevent the RFID tag 1 from being damaged.

[0021] As shown in FIGS. 3 and 4, the printed circuit board 20 is held by inserting the printed circuit board 20 into the gap 31a between the strands of the coil portion 31, and the coil portion 31 constitutes the primary side of the coupling transformer 40. It is preferable that the axis of the coil portion 31 coincides with the axis of the secondary coil 41. Since both the front and back surfaces of the printed circuit board 20 are sealed with the insulating layer 23, the coil portion 31 and the secondary coil 41 are not electrically connected. Further, between the strands of the coil portion 31 where the printed circuit board 20 is not inserted, it is naturally insulated in order to maintain the electrical coil function.

[0022] FIG. 6 is an equivalent circuit diagram when the RFID tag 1 is attached to a rubber product such as a tire. At the time of reception, the 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, currents of inverted phases of radio waves flow through the first element 32 and the second element 33, a current flows through the primary coil portion 31, and an alternating voltage is induced in the secondary coil 41. Here, while the impedance of the RF chip 10 is about several kΩ to 10 kΩ, the impedance between the first element 32 and the second element 33 is as small as about 100 Ω. The reason why the impedance between the first element 32 and the second element 33 is small is that, in addition to the impedance of the antenna 30 itself, the influence of resistance components such as carbon black contained in the rubber product is large. The vulcanized rubber tire has a resistivity of about several tens of kΩ·cm depending on the type. 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.

[0023] Therefore, in the RFID tag 1 of the present invention, the ratio n (n = N2 / N1) of the number of turns N2 of the secondary side to the number of turns N1 of the primary side of the coupling transformer 40 is adjusted. Specifically, when the RF chip 10 with the input impedance Z and the first element 32 and the second element 33 are connected via the coupling transformer 40, the impedance of the primary side of the coupling transformer 40 is Z / n 2Thus, by making the number of turns N1 of the coil portion 31 on the primary side less than the number of turns N2 of the coil 41 on the secondary side, n is increased to make the input on the primary side have a low impedance, and the secondary side is converted to a 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 when the RFID tag 1 is used for a rubber product containing carbon black or the like, the influence of carbon black or the like can be suppressed. However, increasing the number of turns N2 on the secondary side is restricted by factors such as the area of the coupling transformer 40, and the ratio n of the number of turns between the secondary side and the primary side needs to be appropriately adjusted according to the specifications of the RF chip 10, the material of the rubber product, the content of carbon black or the like.

[0024] The antenna 30 of the RFID tag 1 operates in a manner similar to that of 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 to or embedded in a vulcanized rubber product, there is an advantage that the ground plane is further strengthened by the second element 33 being electrically connected to the vulcanized rubber product. Also, in a conventional dipole antenna type RFID tag, two antenna elements with an electrical length of λ / 4 extend in the left and right directions from a printed circuit board on which an RF chip is mounted. In this configuration, if the rubber product is deformed and reverse forces are applied to the two antenna elements respectively, there is a risk that the connection points between the antenna elements and the printed circuit board will be damaged. On the other hand, in the RFID tag 1 of the present invention, since the first element 32 and the second element 33 extend parallel in the same direction, there are advantages such as the connection points between the base of the first element 32 or the second element 33 and the printed circuit board 20 being less likely to be damaged and the RFID tag 1 being able to be miniaturized. Further, vulcanized rubber enters and cures in the gap 35 of the expansion and contraction portion 34, and the RFID tag 1 is integrated with a vulcanized rubber product such as a tire. Therefore, by appropriately deforming the expansion and contraction portion 34 following the deformation of the tire or the like, the first element 32 and the second element 33 are less likely to be damaged, and the durability of the RFID tag 1 can be improved.

[0025] As shown in FIG. 7, both the front and back surfaces of the RFID tag 1 for rubber products may be covered with rubber sheets 50 and 51. Specifically, the RFID tag 1 is disposed between the first rubber sheet 50 and the second rubber sheet 51, and the first rubber sheet 50 and the second rubber sheet 51 are pressure-bonded to manufacture the RFID tag 1 covered with rubber. As the materials of the rubber sheets 50 and 51, general natural rubber or various synthetic rubbers can be used, and further, a material having adhesiveness such as a butyl rubber sheet may be used. By covering the RFID tag 1 with the rubber sheets 50 and 51, even when the rubber product is deformed, it is possible to prevent the components constituting the RFID tag 1 from being damaged or the positional relationship between the components from being displaced. Also, waterproofness and dustproofness can be imparted to the RFID tag 1.

[0026] FIG. 8 shows a state in which the RFID tag 1 covered with rubber is attached to the inside of a tire 60 as an example of a rubber product. The position where 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 embedded in the rubber of the tire 60. Also, an RFID tag 1 not covered with rubber may be attached to or embedded in 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 a ground for 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.

[0027] Next, a method for manufacturing the RFID tag 1 for rubber products will be described. As shown in FIG. 9(a), first, a plurality of coils 41 on the secondary side of the coupling transformer 40 are arranged in the left-right direction on the printed circuit board 20 (step A). Next, as shown in FIG. 9(b), openings 24 and 25 are provided in front of and behind a plurality of secondary coils 41 (step B). It is necessary to make the distance from the front opening 24 to the rear opening 25 match the length of the RFID tag 1 in the front-rear direction. Next, as shown in FIG. 9(c), a cut 26 is made between a plurality of secondary coils 41 (step C). The interval at which the cut 26 is made needs to match the length of the RFID tag 1 in the left-right direction. Steps A to C can be performed in any order, and 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 the insulating layer 27.

[0028] Next, as shown in FIG. 10(a), using the front opening 24, the secondary coil 41 is inserted into the gap 31a between the strands of the coil portion 31. As a result, the coil portion 31 functions as the primary side of the coupling transformer 40. At this time, the first element 32 and the second element 33 can be placed on the side edge portion 28 of the front opening 24, and the coil portion 31 can be moved toward the secondary coil 41 while sliding the surface of the side edge portion 28. Also, since the first element 32 is placed on the side edge portion 28 in a state where the secondary coil 41 is inserted into the gap 31a between the strands, there is no risk of the antenna 30 falling off from the printed circuit board 20. If necessary, the coil portion 31 and the printed circuit board 20 may be adhered. Finally, as shown in FIG. 10(b), by cutting the printed circuit board 20 along the cut 26, the RFID tag 1 for rubber products is completed.

[0029] Next, a modified example of the antenna is shown. The antenna 70 shown in FIGS. 11(a) and (b) forms the telescopic portion 36 by bending a part of the first element 32 and the second element 33. In this case, as shown in FIG. 11(c), the telescopic portion 36 becomes shorter when receiving a compressive force, becomes longer when receiving a tensile force as shown in FIG. 11(d), and can be bent when receiving a force from the lateral direction as shown in FIG. 11(e). The antenna 71 shown in Fig. 12 forms a telescopic part 37 by forming a compression coil spring in a part of the first element 32 and the second element 33. In this case, the telescopic part 37 that receives an external force deforms as shown in Figs. 5(b) to (d).

[0030] The antenna 72 shown in Fig. 13(a) forms a telescopic part 38 in the entire first element 32 and second element 33 by twisting a plurality of element wires (for example, three element wires). In this case, the telescopic part 38 slightly shortens when receiving a compressive force as shown in Fig. 13(b), slightly lengthens when receiving a tensile force as shown in Fig. 13(c), and can bend when receiving a force from the lateral direction as shown in Fig. 13(d). Note that the telescopic parts 36 and 37 do not necessarily have to be provided in both the first element 32 and the second element 33, and it may be arranged such that only the second element 33, which is easily affected by an external force, is provided as shown in Fig. 14.

Industrial Applicability

[0031] The present invention is an RFID tag for rubber products that is small-sized, excellent in mass productivity and durability, and has industrial applicability.

Explanation of Signs

[0032] 1 RFID tag for rubber product 10 RF chip 20 Printed circuit board 21 Through hole 22 Through hole 23 Insulation layer 24 Front opening 25 Rear opening 26 Notch 27 Insulation layer 28 Side edge part 30 Antenna 31 Coil part 31a Gap 32 First element 33 Second 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 Tire

Claims

1. 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 includes a coil portion, a first element extending from one end of the coil portion, and a second element extending from the other end of the coil portion, shorter than the first element and parallel to the first element, The number of turns of the coil portion is less than the number of turns of the secondary side of the coupling transformer, The coil portion constitutes the primary side of the coupling transformer by holding the printed circuit board in the gap between the strands of the coil portion, An RFID tag for rubber products, characterized in that at least one of the first element and the second element includes a telescopic portion that expands and contracts in its longitudinal direction.

2. The RFID tag for rubber products according to claim 1, which is for rubber products containing carbon black.

3. The RFID tag for rubber products according to claim 1 or 2, characterized in that insulating layers are provided on both the front and back surfaces of the printed circuit board.

4. The RFID tag for rubber products according to claim 1, characterized in that the coil portion, the first element, and the second element are composed of a single wire.

5. The RFID tag for rubber products according to claim 1, characterized in that the axis of the coil on the secondary side of the coupling transformer coincides with the axis of the coil portion.

6. The RFID tag for rubber products according to claim 1, characterized in that when the wavelength of the radio wave at the communication frequency is λ, the electrical length of the portion composed of the first element, the second element, and the coil portion is λ / 4.

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