RFID tags

Abstract

This invention provides an RFID tag that can communicate while in contact with a conductor and has excellent shock resistance. [Solution] The RFID tag 1 of the present invention comprises a first waveguide section 20, a resonant section 30 directly coupled to the first waveguide section, a second waveguide section 40 positioned with a gap 61 between it and the resonant section and electromagnetically or electrostatically coupled to it, an RF chip 50 directly coupled to the resonant section, and an insulating material 10 to which the first waveguide section, the resonant section, and the second waveguide section are fixed. The resonant section is positioned between the first waveguide section and the second waveguide section. By bringing a conductor into contact with the waveguide section and electrically connecting the conductor and the waveguide section, the same effect as increasing the area of ​​the waveguide section can be obtained, and radio waves can be received from a wider area.

Description

Technical Field

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

Background Art

[0002] An RFID tag used in an RFID (Radio Frequency Identification) system generally stores an antenna and an RF chip. It receives a carrier wave transmitted from 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 non-contact communication.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The RFID tag described in Patent Document 1 has several problems: it requires adjusting the length of the side of each waveguide element that makes up the plate-shaped inverted F antenna, which makes the design process time-consuming and limits the degree of design freedom. In addition, the components of the RFID tag are easily damaged when subjected to impact from external forces, etc.

[0006] The present invention aims to provide an RFID tag that can communicate while in contact with a conductor and has excellent shock resistance, taking these problems into consideration. [Means for solving the problem]

[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 gap is characterized by being filled with the insulating material. Furthermore, 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. Furthermore, the insulating material is characterized by being insulating rubber. Furthermore, the RF chip and the resonant portion are mounted on a printed circuit board. [Effects of the Invention]

[0008] In the RFID tag of the present invention, when the first waveguide and / or the second waveguide come 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 area. Thus, the RFID tag of the present invention can communicate with a reader / writer even when the first waveguide and / or the second waveguide come into contact with a conductor. Furthermore, since RFID tags do not have antennas, there is no need to adjust the antenna dimensions to match the radio waves, thus eliminating problems such as the time-consuming design process and the limitation of design flexibility. Furthermore, by filling the gap between the second waveguide and the resonant section with an insulating material, the second waveguide and the resonant section will not come into contact and be damaged even when subjected to external forces or vibrations, resulting in an RFID tag with excellent impact resistance. Furthermore, by forming the first waveguide, resonant section, and second waveguide section on a flexible and insulating sheet, RFID tags 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. By mounting the RF chip and resonant element on a printed circuit board, rigidity can be increased. [Brief explanation of the drawing]

[0009] [Figure 1] 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. [Figure 2] Plan views (a) to (d) showing variations in the mounting positions of the coil and RF chip. [Figure 3] Equivalent circuit diagram of an RFID tag [Figure 4] Side views (a) to (d) showing the state in which conductors are in contact with the top and bottom of the RFID tag. [Figure 5] Side view showing conductors placed before and after the RFID tag. [Figure 6] A plan view (a) and a side view (b) showing an RFID tag formed on a sheet, side views (c) and (d) showing a method for manufacturing an RFID tag, and a side view (e) of a modified example of an RFID tag. [Modes for carrying out the invention]

[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 section 20, the resonant section 30, and the second waveguide section 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 from materials such as expanded polystyrene, polyethylene, polyimide, or insulating rubber.

[0011] The first waveguide section 20 is the part that receives radio waves transmitted from the reader / writer. The first waveguide portion 20 is provided on the back surface 12 of the insulating material 10. In this embodiment, the first waveguide portion 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 first waveguide section 20 is not designed with a length or shape that matches the wavelength of the radio waves transmitted from the reader / writer. In other words, the first waveguide section 20 simply guides the radio waves transmitted from the reader / writer, and communication is possible when the guided radio waves resonate with the resonant section 30 facing the first waveguide section 20. Specifically, when the first waveguide section 20 receives a radio wave, the resonant section 30 resonates strongly if the radio wave corresponds to the resonant frequency of the resonant section 30.

[0012] The resonant section 30 is the part that is directly coupled to the first waveguide section 20. The resonant portion 30 in this embodiment is a substantially 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 integrally. By folding along lines A1 and A2 shown in Figure 1(a), the resonant section 30 is positioned parallel to the first waveguide section 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 section 20 and the resonant section 30 will not come into contact even when subjected to external forces or vibrations. The coil portion 31 has a cut portion 32 in a 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 as shown in FIG. 2 may be used.

[0013] The second waveguide portion 40 is a part for receiving radio waves transmitted from the reader / writer. The second waveguide portion 40 is provided on the surface 11 of the insulating material 10. As a result, as shown in FIGS. 1(b) and (d), the first waveguide portion 20 and the second waveguide portion 40 are arranged in parallel via the insulating material 10. The second waveguide portion 40 of the present embodiment has a rectangular shape and is formed by a well-known method such as etching of a metal thin film such as aluminum or pattern printing. Unlike a general antenna, the second waveguide portion 40 does not adapt its length and shape to the wavelength of the radio waves transmitted from the reader / writer. That is, only the radio waves transmitted from the reader / writer are guided to the second waveguide portion 40, and the guided radio waves can communicate by resonating with the resonance portion 30 facing the second waveguide portion 40. That is, when the second waveguide portion 40 receives radio waves, the resonance portion 30 resonates strongly when the radio waves correspond to the resonance frequency of the resonance portion 30. Further, the second waveguide portion 40 is arranged with a gap 61 from the resonance portion 30 and is electromagnetically coupled or electrostatically coupled to the resonance portion 30. Since the gap 61 is filled with the insulating material 10, the second waveguide portion 40 and the resonance portion 30 do not come into contact even when an external force or vibration is applied.

[0014] The resonance portion 30 is arranged at a position sandwiched between the first waveguide portion 20 and the second waveguide portion 40. In this way, the first waveguide portion 20, the resonance portion 30, and the second waveguide portion 40 are fixed to the insulating material 10 so as to be parallel to each other. Then, as shown in the equivalent circuit diagram of FIG. 3, a first capacitor portion C1 is formed by the first waveguide portion 20 and the second waveguide portion 40, and a second capacitor portion C2 is formed by the second waveguide portion 40 and the resonance portion 30. The RF chip 50 is stretched so as to connect both ends of the cut portion 32 and is directly coupled to the coil portion 31. The RF chip 50 has an equivalent capacitance based on its internal components such as on-chip capacitors, and the third capacitor section C3 is formed based on this equivalent capacitance. The 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). Set the value of the resonant frequency f0 so that it falls within the frequency band of the radio waves transmitted from the reader / writer.

number

[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, it is necessary to match the impedance between the resonant section 30 and each waveguide section 20 and 40, and to match 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 radio waves received by the first waveguide 20 and / or the second waveguide 40. Specifically, the RF chip 50 rectifies a portion of the radio waves transmitted from the reader / writer to generate the power supply voltage necessary for operation. The RF chip 50 then uses this 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] The RFID tag 1 of the present invention is characterized by its ability to 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 due to the presence of a metal conductor (lower conductor 80) on the lower side of the RFID tag 1, the lower conductor 80 also functions as part of the first waveguide 20. Therefore, 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, causing the second waveguide 40 and the upper conductor 81 to 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, causing the second waveguide 40 and the first waveguide 20 to come into contact with the upper conductor 81 and the lower conductor 80, respectively, communication is still 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; it may also include, for example, the human body, grass, wood, water, or the ground. Conductive rubber is also included as a "conductor." Furthermore, general tires contain carbon black, 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), a conductor (short-circuit conductor 82) exists between the upper conductor 81 and the lower conductor 80, allowing communication even in the event of a short circuit. If the inductance of the loop section 71 generated by the short circuit is L2, the resonant frequency f1 [Hz] is given by equation (2).

number

[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, if RFID tag 1 is in contact with the lower conductor 80, with a front conductor 83 in front of it and a rear conductor 84 behind it, when the reader / writer RW transmits radio waves W1 from in front of the front conductor 83 towards 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 RFID tag 1. Furthermore, 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 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 wave W1 from the reader / writer RW may be directly reflected by the rear conductor 84 and reach the RFID tag 1 as the reflected wave 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 wavelength λ of the radio wave, 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 through the conductors, the operator can find conditions under 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 sheet 90, the gap 61 between the resonant section 30 and the second waveguide section 40 becomes equal to the thickness of sheet 90. Therefore, even if the RFID tag 1 is subjected to an external force, sheet 90 will not be crushed or thinned, the LC resonant circuit will not deform, and the resonant frequency f0 will not change, thus maintaining a good communication state. 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. [Industrial applicability]

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

[0022] C1 First capacitor section C2 Second Capacitor Section C3 Third capacitor section 1 RFID tag 10 Insulating material 11 Surface 12 Back side 20 First Waveguide 30 Resonance part 31 Coil section 32 Cut section 40 Second Waveguide Section 50 RF chips 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 seats 91 Insulating material

Claims

1. The device comprises a first waveguide, a resonant section directly coupled to the first waveguide, a second waveguide positioned with a gap between it and the resonant section and electromagnetically or electrostatically coupled to it, an RF chip directly coupled to the resonant section, and an insulating material to which the first waveguide, the resonant section, and the second waveguide are fixed. The RFID tag is characterized in that the resonant portion is positioned between the first waveguide portion and the second waveguide portion.

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.

Images