RFID tag

Abstract

Provided is an RFID tag capable of communicating while in contact with a conductor and having excellent impact resistance.　The RFID tag 1 of the present invention comprises: a first waveguide part 20; a resonance part 30 directly coupled to the first waveguide part 20; a second waveguide part 40 disposed with a gap 61 from the resonance part 30 and electromagnetically or electrostatically coupled to the resonance part 30; an RF chip 50 directly coupled to the resonance part 30; and an insulating material 10 to which the first waveguide part 20, the resonance part 30, and the second waveguide part 40 are fixed. The resonance part is disposed between the first waveguide part and the second waveguide part. By bringing the conductor into contact with the waveguide part and electrically connecting the conductor to the waveguide part, it is possible to obtain the same effect as that obtained by increasing the area of the waveguide part, and radio waves can be received from a wider range.

Description

RFID tag

[0001] The present invention relates to an RFID tag that can communicate while in contact with a conductor and has excellent impact resistance.

[0002] Generally, an RFID tag used in an RFID (Radio Frequency Identification) system stores an antenna and an RF chip. It receives the carrier wave transmitted from a reader / writer with the antenna, and rides the identification data and the like recorded in the RF chip on the reflected wave and returns it to the reader / writer, thus enabling non-contact communication.

[0003] The inventor of the present application developed an RFID tag provided with a planar inverted-F antenna that can communicate even while in contact with a conductor (metal plate) (Patent Document 1). Specifically, this RFID tag constitutes a planar inverted-F antenna with a first insulating substrate, a first waveguide element, a second waveguide element, a power feeding section, and a short-circuit section. Further, a resonance circuit that resonates in the radio wave frequency band is constituted by an inductor pattern formed by the first waveguide element, the short-circuit section, the second waveguide element, and the power feeding section, and a capacitor formed by the first waveguide element, the second waveguide element, and the first insulating substrate. By adjusting the total length of the sides of the first waveguide element and the second waveguide element that constitute the planar inverted-F antenna to, for example, λ / 4 or λ / 2, the planar inverted-F antenna is matched with the wavelength λ of the radio wave transmitted from the reader / writer.

[0004] Japanese Patent No. 6705116

[0005] In the RFID tag of the above Patent Document 1, since it is necessary to adjust the length of the sides of each waveguide element that constitutes the planar inverted-F antenna, there are problems such as the design being time-consuming and the design freedom being restricted. There is also a problem that the constituent members of the RFID tag are liable to be damaged when impacted by an external force or the like.

[0006] In consideration of such problems, an object of the present invention is to provide an RFID tag that can communicate while in contact with a conductor and has excellent impact resistance.

[0007] The RFID tag of the present invention comprises a first waveguide, a resonant portion directly coupled to the first waveguide, a second waveguide positioned with a gap between it and the resonant portion and electromagnetically or electrostatically coupled to it, an RF chip directly coupled to the resonant portion, and an insulating material to which the first waveguide, the resonant portion, and the second waveguide are fixed, wherein the resonant portion is positioned between the first waveguide and the second waveguide. Furthermore, the insulating material is embedded in the gap. Furthermore, the insulating material is a sheet having flexibility and insulating properties, and the first waveguide, the resonant portion, and the second waveguide are formed on the sheet. Furthermore, the insulating material is insulating rubber. Furthermore, the RF chip and the resonant portion are mounted on a printed circuit board.

[0008] In the RFID tag of the present invention, when the first and / or second waveguide comes into contact with a conductor, the conductor itself can be used as part of the waveguide. In other words, by bringing the conductor into contact with the waveguide and electrically connecting the conductor and the waveguide, the same effect as expanding the area of ​​the waveguide can be obtained, allowing radio waves to be received from a wider range. Thus, the RFID tag of the present invention can communicate with a reader / writer even when the first and / or second waveguide comes into contact with a conductor. Furthermore, since the RFID tag does not have an antenna, there is no need to adjust the dimensions of the antenna to match the radio waves, thus eliminating the problems of time-consuming design and limited design freedom. In addition, if the gap between the second waveguide and the resonant part is filled with an insulating material, the second waveguide and the resonant part will not come into contact and be damaged even when subjected to external force or vibration, resulting in an RFID tag with excellent impact resistance. Moreover, if the first waveguide, resonant part, and second waveguide are formed on a flexible and insulating sheet, the RFID tag can be easily manufactured by folding the sheet. By using insulating rubber as the insulating material, external forces can be absorbed through the elastic deformation of the rubber, resulting in an RFID tag that is resistant to external forces. Mounting the RF chip and resonant section on a printed circuit board can increase rigidity.

[0009] Plan view (a) and perspective view (b) of the components constituting the RFID tag; perspective view (c) and longitudinal section view (d) of the RFID tag; plan views (a) to (d) showing variations in the mounting position of the coil and RF chip; equivalent circuit diagram of the RFID tag; side views (a) to (d) showing the state in which conductors are in contact with the top and bottom of the RFID tag; side view showing the state in which conductors are arranged in front of and behind the RFID tag; plan view (a) and side view (b) showing the state in which the RFID tag is formed on a sheet; side views (c) and (d) showing the manufacturing method of the RFID tag; side view (e) of a modified example of the RFID tag.

[0010] Embodiments of the RFID tag of the present invention will be described with reference to the drawings. As shown in Figure 1, the RFID tag 1 comprises an insulating material 10, a first waveguide 20, a resonant section 30, a second waveguide 40, and an RF chip 50. The insulating material 10 is a member for fixing the first waveguide 20, the resonant section 30, and the second waveguide 40 in predetermined positions. The insulating material 10 in this embodiment is a rectangular parallelepiped having two parallel planes (a front surface 11 and a back surface 12). The insulating material 10 can be made of polystyrene foam, polyethylene, polyimide, insulating rubber, or the like.

[0011] The first waveguide section 20 is the part for receiving radio waves transmitted from the reader / writer. The first waveguide section 20 is provided on the back surface 12 of the insulating material 10. In this embodiment, the first waveguide section 20 is rectangular in shape and is formed by well-known methods such as etching or pattern printing of a thin metal film such as aluminum. Unlike a typical antenna, the length and shape of the first waveguide section 20 are not matched to the wavelength of the radio waves transmitted from the reader / writer. That is, the first waveguide section 20 is simply guided by the radio waves transmitted from the reader / writer, and communication is possible by the guided radio waves resonating with the resonant section 30 facing the first waveguide section 20. In other words, when the first waveguide section 20 receives radio waves, the resonant section 30 resonates strongly if the radio waves correspond to the resonant frequency of the resonant section 30.

[0012] The resonant portion 30 is the part that is directly coupled to the first waveguide portion 20. The resonant portion 30 in this embodiment is a roughly rectangular annular shape and is formed by well-known methods such as etching or pattern printing of a thin metal film such as aluminum. The annular portion of the resonant portion 30 functions as a coil portion 31. It is preferable to form the resonant portion 30 and the first waveguide portion 20 as a single unit. By bending along lines A1 and A2 shown in Figure 1(a), the resonant portion 30 is arranged parallel to the first waveguide portion 20 with a gap 60 between them, as shown in Figures 1(b) and (d). Since the gap 60 is filled with insulating material 10, the first waveguide portion 20 and the resonant portion 30 will not come into contact even when subjected to external forces or vibrations. The coil portion 31 is provided with a cut portion 32 in part thereof. The shape of the coil portion 31 and the position of the cut portion 32 are not particularly limited, and for example, the shape of the coil portion 31 and the position of the cut portion 32 may be as shown in Figure 2.

[0013] The second waveguide section 40 is the part for receiving radio waves transmitted from the reader / writer. The second waveguide section 40 is provided on the surface 11 of the insulating material 10. As a result, as shown in Figures 1(b) and (d), the first waveguide section 20 and the second waveguide section 40 are arranged in parallel with the insulating material 10. The second waveguide section 40 in this embodiment is rectangular in shape and is formed by well-known methods such as etching or pattern printing of a thin metal film such as aluminum. Unlike a typical antenna, the length and shape of the second waveguide section 40 are not matched to the wavelength of the radio waves transmitted from the reader / writer. That is, the second waveguide section 40 is simply guided by the radio waves transmitted from the reader / writer, and the guided radio waves can communicate by resonating with the resonant section 30 facing the second waveguide section 40. In other words, when the second waveguide section 40 receives radio waves, the resonant section 30 resonates strongly if the radio waves correspond to the resonant frequency of the resonant section 30. Furthermore, the second waveguide section 40 is positioned with a gap 61 between it and the resonant section 30, and is electromagnetically or electrostatically coupled to the resonant section 30. Since the gap 61 is filled with insulating material 10, the second waveguide section 40 and the resonant section 30 will not come into contact even when subjected to external forces or vibrations.

[0014] The resonant section 30 is positioned between the first waveguide section 20 and the second waveguide section 40. In this way, the first waveguide section 20, the resonant section 30, and the second waveguide section 40 are fixed to the insulating material 10 so that they are parallel to each other. As shown in the equivalent circuit diagram of Figure 3, the first waveguide section 20 and the second waveguide section 40 form the first capacitor section C1, and the second waveguide section 40 and the resonant section 30 form the second capacitor section C2. The RF chip 50 is stretched across both ends of the cut section 32 and directly coupled to the coil section 31. The RF chip 50 has an equivalent capacitance based on its internal components such as on-chip capacitors, and a third capacitor section C3 is formed based on this equivalent capacitance. Rigidity may be increased by mounting the RF chip 50 and the resonant section 30 on a single printed circuit board.

[0015] The LC resonant circuit 70 is composed of a coil section 31 and first to third capacitor sections C1 to C3. When setting the resonant frequency of this LC resonant circuit 70, the inductance of the coil section 31 and the capacitance of the first to third capacitor sections C1 to C3 are taken into consideration. The resonant frequency f0 [Hz] is given by equation (1). The value of the resonant frequency f0 is set so that it falls within the frequency band of the radio waves transmitted from the reader / writer. Here, L1 is the inductance of the coil section 31, C1 is the capacitance of the first capacitor section C1, C2 is the capacitance of the second capacitor section C2, and C3 is the capacitance of the third capacitor section C3. Note that when calculating C3, the capacitance value published as one of the specifications of the RF chip 50 can be used.

[0016] The design ensures that a potential difference exists between the coil section 31 and the first waveguide section 20, and between the resonant section 30 and the second waveguide section 40. Specifically, impedance matching between the resonant section 30 and each waveguide section 20 and 40 is necessary, as is matching the resonant frequency of the LC resonant circuit 70 with the frequency of the radio waves transmitted from each waveguide section 20 and 40. For example, the inductance can be adjusted by adjusting the shape of the coil section 31, or the resonant frequency can be adjusted by providing through holes in the first waveguide section 20 and the second waveguide section 40. The RF chip 50 operates based on the radio waves received by the first waveguide section 20 and / or the second waveguide section 40. Specifically, the RF chip 50 rectifies a portion of the radio waves transmitted from the reader / writer and generates the power supply voltage necessary for operation. The RF chip 50 then uses the generated power supply voltage to operate control logic circuits and non-volatile memory containing product-specific information, and to operate communication circuits for sending and receiving data with the reader / writer.

[0017] A key feature of the RFID tag 1 of the present invention is that it can communicate with a reader / writer even when in contact with a conductor. For example, as shown in Figure 4(a), when the first waveguide 20 and the lower conductor 80 come into contact, the lower conductor 80 also functions as part of the first waveguide 20, so that the radio waves transmitted from the reader / writer pass through the lower conductor 80 and the first waveguide 20 and are converted into electrical signals in the LC resonant circuit 70. Similarly, as shown in Figure 4(b), when multiple metals (upper conductors 81) are stacked on the upper side of the RFID tag 1 and the second waveguide 40 and the upper conductor 81 come into contact, or as shown in Figure 4(c), when the upper conductor 81 and lower conductor 80 are located on both the upper and lower sides of the RFID tag 1 and the second waveguide 40 and the first waveguide 20 come into contact with the upper conductor 81 and the lower conductor 80, respectively, communication is possible.

[0018] In this application, "conductor" is a general term for "a substance with relatively high electrical conductivity," similar to its general dictionary definition, with metal being a typical example. However, "conductor" is not limited to metal; for example, it may be the human body, grass, wood, water, or the ground. Conductive rubber is also included as a "conductor." Furthermore, general tires have carbon black added to them, and if the carbon black content is high, the tire itself may be conductive. Therefore, tires with added carbon black are also included as "conductors" in this application. Communication is possible even when the RFID tag 1 of the present invention is attached to the surface or inside of a tire, or embedded in a tire. Furthermore, as shown in the area enclosed by the ellipse in Figure 4(d), communication is possible even when a conductor (short-circuit conductor 82) exists between the upper conductor 81 and the lower conductor 80, causing a short circuit. If the inductance of the loop portion 71 generated by the short circuit is L2, the resonant frequency f1 [Hz] is given by equation (2). Here, assuming that the inductance L2 is about 10 times greater than the inductance L1 of the coil section 31, the fluctuation of f1 will be limited to a small range, indicating that communication is possible without any changes to the design of the LC resonant circuit 70.

[0019] Furthermore, as shown in Figure 5, communication is possible even when the conductor is not in contact with the RFID tag 1. For example, when the RFID tag 1 is in contact with the lower conductor 80, and the front conductor 83 is located in front of it and the rear conductor 84 is located behind it, when the reader / writer RW transmits radio waves W1 from in front of the front conductor 83 towards the RFID tag 1, the front conductor 83 functions as a director. Therefore, the radio waves W1 are radiated from the front conductor 83 as radiated waves W2 and reach the RFID tag 1. When these radiated waves W2 reach the lower conductor 80, they are also radiated as radiated waves W3 from the lower conductor 80, which is functioning as a director, and reach the rear conductor 84. These radiated waves W3 are then reflected by the rear conductor 84 and reach the RFID tag 1 as reflected waves W4. In this way, the presence of the front conductor 83 and rear conductor 84 enables highly efficient communication. This is the same principle as a Yagi antenna. Alternatively, the radio waves W1 from the reader / writer RW may be directly reflected by the rear conductor 84 and reach the RFID tag 1 as reflected waves W5. The distance D from the RFID tag 1 to the front conductor 83 or rear conductor 84 is generally suitable to be about 1 / 4 of the radio wave wavelength λ, but the preferred distance D varies depending on the environment in which the RFID tag 1 is placed. Therefore, by changing the wavelength and incident angle of the radio waves reaching the RFID tag 1 via the conductors, the operator can find a situation in which communication is possible by moving the reader / writer up and down and left and right, or by changing the radiation angle of the radio waves.

[0020] As shown in Figures 6(a) and (b), the first waveguide section 20, the resonant section 30, and the second waveguide section 40 may be formed on a flexible and insulating sheet 90. In this case, as shown in Figure 6(c), the sheet 90 functions as an insulating material 10 by folding and bonding it in the order of (1) and (2) at the positions of lines A3 and A4, so that the RFID tag 1 can be easily manufactured as shown in Figure 6(d). For ease of understanding, the sheet 90 is shown with a dashed line. The material of the sheet 90 is not particularly limited as long as it is flexible and insulating, but for example, PET, polyimide, vinyl, etc. can be used. The thickness of the sheet 90 is not particularly limited, but is generally around several tens of micrometers. By using the sheet 90, the gap 61 between the resonant section 30 and the second waveguide section 40 becomes equal to the thickness of the sheet 90. Therefore, even if the RFID tag 1 is subjected to an external force, the sheet 90 will not be crushed and thinned, the LC resonant circuit will not be deformed, and the resonant frequency f0 will not change, so a good communication state can be maintained. Furthermore, as shown in Figure 6(e), the rigidity of the RFID tag may be increased by wrapping a sheet around a thin insulating material 91 in the vertical direction.

[0021] The present invention relates to an RFID tag that can communicate while in contact with a conductor and has excellent shock resistance, and has industrial applicability.

[0022] C1 First capacitor section C2 Second capacitor section C3 Third capacitor section 1 RFID tag 10 Insulating material 11 Front surface 12 Back surface 20 First waveguide section 30 Resonant section 31 Coil section 32 Cut section 40 Second waveguide section 50 RF chip 60 Gap 61 Gap 70 LC resonant circuit 71 Loop section 80 Lower conductor 81 Upper conductor 82 Short circuit conductor 83 Front conductor 84 Rear conductor 90 Sheet 91 Insulating material

Claims

1. An RFID tag comprising: a first waveguide; a resonant portion directly coupled to the first waveguide; a second waveguide portion positioned with a gap between it and the resonant portion and electromagnetically or electrostatically coupled to it; an RF chip directly coupled to the resonant portion; and an insulating material to which the first waveguide, the resonant portion, and the second waveguide are fixed, wherein the resonant portion is positioned between the first waveguide and the second waveguide.

2. The RFID tag according to claim 1, characterized in that the insulating material is embedded in the gap.

3. The RFID tag according to claim 1, characterized in that the insulating material is a sheet having flexibility and insulating properties, and the first waveguide portion, the resonant portion, and the second waveguide portion are formed on the sheet.

4. The RFID tag according to claim 1, characterized in that the insulating material is insulating rubber.

5. The RFID tag according to claim 1, characterized in that the RF chip and the resonant portion are mounted on a printed circuit board.

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