Wireless communication device

Abstract

This wireless communication device comprises: an RFIC chip; an antenna having a first electrode and a second electrode facing each other; and wiring having one end connected to one side of the first electrode and the other end connected to one side of the second electrode. The wiring is disposed between the first electrode and the second electrode. The wiring has: a first wiring portion extending from the one side of the first electrode to the other side; and a second wiring portion folded back from an end of the first wiring portion and extending from the other side of the second electrode to the one side. The first wiring portion and the second wiring portion are disposed adjacent to each other in at least respective parts thereof. The directions of currents flowing in the first wiring portion and the second wiring portion are opposite to each other. The wiring is longer than the total length of the first electrode and the second electrode, and the RFIC chip and the wiring are electrically or magnetically coupled.

Description

wireless communication devices

[0001] The present invention relates to a wireless communication device equipped with an antenna, and more particularly to a wireless communication device that utilizes RFID (Radio-Frequency Identification) technology.

[0002] Conventionally, an "RFID tag," which is a wireless communication device, has been attached to an article. The RFID tag may include an RFID inlay therein, which is an antenna wiring disposed on a film substrate. As shown in FIG. 14 , the IC tag in Patent Document 1 includes a radiating element portion 101 that functions as a dipole antenna, and an RFIC (Radio-Frequency Integrated Circuit) 105 mounted on a matching loop circuit 103 that can be magnetically coupled to the radiating element portion 101.

[0003] JP 2010-268023 A

[0004] However, for example, when an IC tag 100 with a dipole antenna is wrapped around a cylindrical article 110 as shown in FIG. 15, a null point occurs in the horizontal direction where the communication distance is significantly reduced.

[0005] The present invention aims to provide a wireless communication device with improved omnidirectionality.

[0006] A wireless communication device according to one aspect of the present invention includes an RFIC chip, an antenna having a first electrode and a second electrode facing each other, and a wiring having one end connected to one side of the first electrode and the other end connected to one side of the second electrode. The wiring is disposed between the first electrode and the second electrode. The wiring has a first wiring portion extending from one side of the first electrode to the other side, and a second wiring portion folding back from an end of the first wiring portion and extending from the other side of the second electrode to one side. The first wiring portion and the second wiring portion are disposed adjacent to each other at least in part. The directions of current flowing through the first wiring portion and the second wiring portion are opposite. The wiring is longer than the combined length of the first electrode and the second electrode, and the RFIC chip and the wiring are electrically or magnetically coupled.

[0007] According to the present invention, it is possible to provide a wireless communication device with improved omnidirectionality.

[0008] FIG. 1 is a plan view showing the schematic configuration of an RFID inlay according to the first embodiment; FIG. 2 is an explanatory diagram showing an equivalent circuit of wiring; FIG. 3 is an explanatory diagram showing the electric field and magnetic field distribution of an RFID inlay; FIG. 4 is an explanatory diagram showing the electric field strength and magnetic field strength of an RFID inlay; FIG. 5 is an explanatory diagram showing the electric field strength of an RFID inlay; 20 is a diagram showing the antenna gain; Plan view showing the schematic configuration of an RFID inlay of embodiment 4; Plan view showing the schematic configuration of an RFID inlay in a comparative example; Explanatory diagram showing the use form of an RFID inlay in a comparative example; Plan view showing the schematic configuration of an RFID inlay of embodiment 5; Explanatory diagram showing the electric field distribution of an RFID inlay of embodiment 5; Explanatory diagram showing the components of the electric field direction of an RFID inlay of embodiment 5; Explanatory diagram showing the directivity of an RFID inlay of embodiment 5; Explanatory diagram showing the electric field distribution when an RFID inlay of embodiment 5 is wound cylindrically around the Z axis; Explanatory diagram showing the direction of the electric field generated in the RFID inlay in the YZ plane in FIG. 20; Figure showing the antenna gain of an RFID inlay in a cylindrically wound state in embodiment 5; Plan view showing the schematic configuration of an RFID inlay of embodiment 6

[0009] Each of the embodiments described below shows a specific example of the present invention, and the present invention is not limited to this configuration. Furthermore, the numerical values, shapes, configurations, steps, and step orders specifically shown in the following embodiments are examples and do not limit the present invention. Among the components in the following embodiments, components that are not described in the independent claims that represent the highest concepts are described as optional components. Furthermore, in all embodiments, the configurations in each modification are the same, and the configurations described in each modification may be combined with each other.

[0010] (Embodiment 1) Next, a schematic configuration of an RFID inlay 1, which is a wireless communication device according to embodiment 1 of the present invention, will be described with reference to Fig. 1. Fig. 1 is a perspective plan view showing a schematic configuration of the RFID inlay 1 according to embodiment 1. Note that the longitudinal direction of the RFID inlay 1 is defined as the X-axis direction, the width direction of the RFID inlay 1 is defined as the Z-axis direction, and the direction perpendicular to the XZ plane is defined as the Y-axis direction.

[0011] In the first embodiment, the RFID inlay 1 includes a substrate 3 , an antenna 5 , a wiring 13 , a matching circuit section 17 , and an RFIC chip 19 .

[0012] The substrate 3 is a flexible substrate having insulating properties and flexibility, and is made of a resin such as PI (polyimide), PET (polyethylene terephthalate), or PEN (polyethylene naphthalate). The substrate 3 has a first main surface 31 and a second main surface 33, which face each other in the Y-axis direction. The antenna 5, wiring 13, matching circuit unit 17, and RFIC chip 19 are all arranged on the first main surface 31 side.

[0013] The antenna 5 includes a first electrode 7, a second electrode 10, and wiring 13. The first electrode 7 and the second electrode 10 are arranged opposite each other in the width direction (Z-axis direction) of the substrate 3. The first electrode 7 and the second electrode 10 each have a substantially rectangular shape extending in the longitudinal direction of the substrate 3 and extend in the same direction. The first electrode 7 and the second electrode 10 each function as a radiating element, and the entire first electrode 7 and the entire second electrode 10 each function as an open end of the antenna 5. The first electrode 7 has a first end 8 and a second end 9, and the second electrode 10 has a third end 11 and a fourth end 12.

[0014] The wiring 13 is disposed between the first electrode 7 and the second electrode 10, with one end connected to the second end 9 on one side of the first electrode 7 and the other end connected to the fourth end 12 on one side of the second electrode 10. The wiring 13 has a first wiring portion 14 extending from the second end 9 on one side of the first electrode 7 toward the first end 8 on the other side, and a second wiring portion 15 folding back from an end 16 of the first wiring portion 14 and extending from the third end 11 on the other side of the second electrode 10 toward the fourth end 12 on one side.

[0015] First wiring portion 14 and second wiring portion 15 are arranged to face each other at least in part, and the direction of current flowing through first wiring portion 14 is opposite to the direction of current flowing through second wiring portion 15, so first wiring portion 14 and second wiring portion 15 function as differential lines. First wiring portion 14 and second wiring portion 15 each have a portion having, for example, a meandering shape, which allows the electrical length to be increased within a limited area, and wiring 13 can be made to be more than twice the combined length of first electrode 7 and second electrode 10.

[0016] The matching circuit unit 17 matches the impedance between the antenna 5 and the RFIC chip 19. The matching circuit unit 17 includes, for example, a loop pattern wiring. The first wiring portion 14 of the antenna 5 has a straight portion 21 along the first electrode 7 in the longitudinal center of the substrate 3, and the second wiring portion 15 has a straight portion 23 along the second electrode 10 in the longitudinal center of the substrate 3.

[0017] The matching circuit section 17 electrically connected to the RFIC chip 19 is disposed between the straight portion 21 of the first wiring section 14 and the straight portion 23 of the second wiring section 15. This magnetically couples the first wiring section 14 and the matching circuit section 17, and magnetically couples the second wiring section 15 and the matching circuit section 17. This allows a current to flow in the RFIC chip 19 using, as an energy source, a current flowing through the antenna 5 due to a radio signal at a communication frequency.

[0018] The first electrode 7, the second electrode 10, the wiring 13, and the matching circuit section 17 of the antenna 5 are configured by conductor patterns made of a conductive material such as aluminum foil or copper foil.

[0019] 2 is an explanatory diagram showing an equivalent circuit of the wiring 13. There are output (internal) capacitance C1 of the RFIC chip 19, inductance L1 of the matching circuit unit 17, inductances L3, L5, ..., Lm of the first wiring portion 14, inductances L4, L6, ..., Ln of the second wiring portion 15, and line capacitances C2 to Cn of the opposing regions of the meander between the first wiring portion 14 and the second wiring portion. The line capacitances C2 to Cn make it possible to shorten the electrical length, thereby reducing the longitudinal size of the substrate 3.

[0020] The electric field and magnetic field generated by the antenna 5 will be described with reference to Figures 3 to 5. Figure 3 is an explanatory diagram showing the electric field and magnetic field distribution of the RFID inlay 1. Figure 4 is an explanatory diagram showing the electric field strength and magnetic field strength of the RFID inlay. Figure 5 is an explanatory diagram showing the electric field strength of the RFID inlay.

[0021] Since the dipole antenna 5 has wiring 13 as a differential line at the center of its electrical length, the current of the antenna 5 is concentrated in the wiring 13. This reduces the current flowing through the first electrode 7 and the second electrode 10, thereby reducing the bias of the electric field distribution at the first electrode 7 and the second electrode 10. Since the first electrode 7 and the second electrode 10 are arranged opposite each other, one of them is a positive pole and the other is a negative pole, an electric field of approximately uniform strength is generated perpendicular to the first electrode 7 and the second electrode 10. In this way, the electric field distribution generated between the first electrode 7 and the second electrode 10 arranged opposite each other is approximately uniform along the extension direction of the first electrode 7 and the second electrode 10, i.e., along the longitudinal direction of the substrate 3.

[0022] A magnetic field is generated perpendicular to the direction of the electric field generated by the antenna 5. Because the electric field distribution is uniform, a substantially uniform magnetic field is generated horizontally and uniformly along the direction in which the first electrode 7 and the second electrode 10 extend. Therefore, the radiation characteristics of the antenna 5 are omnidirectional in a plane perpendicular to the horizontal plane (first main surface 31).

[0023] 4 and 5 , if the electrical length of the antenna 5 is λ / 2 relative to the resonant frequency (communication frequency) of the antenna 5, the electrical length of the wiring 13 is λ / 4 or more relative to the resonant frequency. That is, the electrical length of each of the first electrode 7 and the second electrode 10 is λ / 8 or less relative to the resonant frequency.

[0024] By making the electrical length of the wiring 13 λ / 4 or more, the current flowing through the antenna 5 is concentrated in the wiring 13, and the gradient of the voltage distribution in the opposing first electrode 7 and second electrode 10 becomes almost constant, thereby making the electric field strength between the first electrode 7 and second electrode 10 uniform.

[0025] The first electrode 7 and the second electrode 10 are arranged parallel to each other. Here, "parallel" does not only mean that the first electrode 7 and the second electrode 10 are completely parallel to each other, but also means that the angle between the first electrode 7 and the X-axis is between -15 degrees and 15 degrees and the angle between the second electrode 10 and the X-axis is between -15 degrees and 15 degrees. By arranging the first electrode 7 and the second electrode 10 parallel to each other in this way, the direction of the electric field generated between the first electrode 7 and the second electrode 10 can be made uniform. Furthermore, the line width of the first electrode 7 and the line width of the second electrode 10 are larger than the line width of the wiring 13. This makes it possible to make the charge density in the first electrode 7 and the second electrode 10 more uniform, and to generate a more uniform electric field.

[0026] Next, refer to FIG. 6A . FIG. 6A is a partially enlarged view of the periphery of the wiring 13 in FIG. 1 . Because currents flow in opposite directions between the adjacent first wiring portion 14 and second wiring portion, the magnetic field radiated from the wiring 13 is canceled out. This allows a differential line (wiring 13) to be arranged between the radiating elements (first electrode 7 and second electrode 10) without interfering with the magnetic field generated by the electric field between the radiating elements, thereby enabling the RFID inlay 1 to be miniaturized. Refer to FIGS. 6B and 6C . FIG. 6B is an explanatory diagram showing the directivity of the RFID inlay 1 in embodiment 1. FIG. 6C is a diagram showing the antenna gain of the RFID inlay 1 in embodiment 1 wound into a cylindrical shape. As shown in FIG. 6B , the RFID inlay 1 has electric field directivity in the X-axis and Z-axis directions, and also has magnetic field directivity in the Y-axis direction (horizontal plane direction). In FIG. 6C , the RFID inlay 1 is used in a cylindrically wound state in the X-axis direction, with the Z-axis as the central axis. The antenna 5 of the RFID inlay 1 has directivity in both the Z-axis direction and the X-axis direction, improving omnidirectionality.

[0027] As described above, the RFID inlay 1 of the first embodiment includes the RFIC chip 19, the antenna 5 having the first electrode 7 and the second electrode 10 facing each other, and the wiring 13 having one end connected to one side of the first electrode 7 and the other end connected to one side of the second electrode 10. The wiring 13 is disposed between the first electrode 7 and the second electrode 10. The wiring 13 has a first wiring portion 14 extending from one side of the first electrode 7 to the other side, and a second wiring portion 15 folding back from an end 16 of the first wiring portion 14 and extending from the other side of the second electrode 10 to one side. The first wiring portion 14 and the second wiring portion 15 are disposed so as to face each other at least in part, and the directions of currents flowing through the first wiring portion 14 and the second wiring portion 15 are opposite. The wiring 13 is longer than the combined length of the first electrode 7 and the second electrode 10, and the RFIC chip 19 and the wiring 13 are electrically or magnetically coupled.

[0028] With the RFID inlay 1 having this configuration, the current flowing through the antenna 5 can be concentrated in the wiring 13, thereby making the strength of the electric field generated between the opposing first electrode 7 and second electrode 10 more uniform. Therefore, the strength of the magnetic field generated in a direction perpendicular to the electric field can also be made more uniform, improving the omnidirectionality of the antenna 5. The RFID inlay 1 is not limited to being used on cylindrical objects, and may be attached across multiple surfaces of a rectangular object.

[0029] Furthermore, the RFIC chip and the differential line are magnetically coupled via a matching circuit, which allows two resonance points to be provided, enabling the antenna 5 to be used over a wide communication band.

[0030] Furthermore, because the first wiring portion 14 and the second wiring portion 15 run parallel to each other, the magnetic fields generated by the currents flowing in the opposite directions cancel each other out, thereby reducing the effect of the magnetic field generated from the wiring 13 on the magnetic fields radiated from the first electrode 7 and the second electrode 10.

[0031] (Embodiment 2) Next, an RFID inlay 1A of embodiment 2 will be described with reference to Fig. 7. Fig. 7 is a plan view showing a schematic configuration of the RFID inlay 1A of embodiment 2. The RFID inlay 1A of embodiment 2 will be described, focusing on the differences from the RFID inlay 1 of embodiment 1. In the description of embodiment 2, elements having the same configuration, action, and function as those of embodiment 1 will be given the same reference numerals, and descriptions thereof will be omitted to avoid duplication.

[0032] The first wiring portion 14 and the second wiring portion 15 in the RFID inlay 1 of the first embodiment have a meander shape, whereas the first wiring portion 14A and the second wiring portion 15A in the RFID inlay 1A of the second embodiment have a comb-tooth shape.

[0033] 7, the first wiring portion 14A has a base line 41 extending from one side of the first electrode 7A along the first electrode 7A toward the other side, and a plurality of first branch wirings 42 protruding from the base line 41 toward the second electrode 10A. The second wiring portion 15A has a base line 43 that folds back from an end 16A of the base line 41 of the first wiring portion 14A and extends from the other side of the second electrode 10A along the second electrode 10A to one side, and a plurality of second branch wirings 44 protruding from the base line 43 toward the first electrode 7A.

[0034] The second branch wiring 44 of the second wiring portion 15A is disposed between adjacent first branch wirings 42 of the first wiring portion 14A, and the first branch wiring 42 of the first wiring portion 14A is disposed between adjacent second branch wirings 44 of the second wiring portion 15A. Therefore, the first wiring portion 14A and the second wiring portion 15A form a comb-tooth electrode.

[0035] The first wiring portion 14A of the antenna 5A has a straight portion 21 along the first electrode 7A at its other end, and the second wiring portion 15A has a straight portion 23 along the second electrode 10A at its other end. A matching circuit unit 17 electrically connected to the RFIC chip 19 is disposed between the straight portion 21 of the first wiring portion 14A and the straight portion 23 of the second wiring portion 15A.

[0036] The base line 41 of the first wiring portion 14A and the base line 43 of the second wiring portion 15A have currents flowing in opposite directions, and function as differential lines. Most of the current flowing in the wiring 13A flows through the base lines 41 and 43, so little current flows through the first branch wiring 42 and the second branch wiring 44.

[0037] The first electrode 7A has an electrode 45 that protrudes from the vicinity of the first end 8 on the other side of the first electrode 7A toward the second electrode 10A, and the second electrode 10A has an electrode 46 that protrudes from the vicinity of the third end 11 on the other side of the second electrode 10A toward the first electrode 7A. Because the electrodes 45 and 46 face each other, a capacitance is generated, which allows the resonant frequency to be lowered and the RFID inlay 1A to be further miniaturized. Since the potential difference is greatest near the open ends between the radiating elements, a significant effect can be obtained by loading a capacitance there.

[0038] The electrodes 45 and 46 are not limited to having a comb-tooth shape as shown in FIG. 7, but may simply be arranged facing each other.

[0039] According to the RFID inlay 1A of the second embodiment, in addition to the effects of the RFID inlay 1 of the first embodiment, it is possible to increase the capacitive coupling between the first wiring portion 14A and the second wiring portion 15A because capacitance occurs between the first branch wiring 42 and the second branch wiring 44. When the capacitive coupling is increased, the inductance component in the electrical length of the wiring 13A can be reduced, which has the effect of reducing loss.

[0040] Furthermore, the resonant frequency can be lowered by capacitive loading using the comb-tooth electrodes, and the RFID inlay 1A can be made smaller.

[0041] (Embodiment 3) Next, an RFID inlay 1B of embodiment 3 will be described with reference to Fig. 8. Fig. 8 is a plan view showing a schematic configuration of the RFID inlay 1B of embodiment 3. The RFID inlay 1B of embodiment 3 will be described mainly with respect to differences from the RFID inlay 1 of embodiment 1. In the description of embodiment 3, elements having the same configuration, action, and function as those of embodiment 1 will be given the same reference numerals, and descriptions thereof will be omitted to avoid duplication.

[0042] In the RFID inlay 1 of embodiment 1, the antenna 5 and the RFIC chip 19 are arranged on the same substrate 3, but in the RFID inlay 1B of embodiment 3, the RFIC chip 19 and the antenna 5B are arranged on different substrates.

[0043] The resonant circuit unit 51 is disposed between the straight portion 21 of the first wiring portion 14B and the straight portion 23 of the second wiring portion 15B. The resonant circuit unit 51 includes a substrate 52, an RFIC chip 19, and a coil 53.

[0044] The configuration of the resonant circuit section 51 will be described with reference to Fig. 9 and Fig. 10. Fig. 9 is a longitudinal sectional view showing a schematic configuration of the resonant circuit section 51 of embodiment 3. Fig. 10 is an exploded plan view showing each layer of the resonant circuit section 51 of embodiment 3. Fig. 10(a) is a plan view of the lower layer of the substrate 52, Fig. 10(b) is a plan view of the top of the substrate 52, and Fig. 10(c) is a plan view of the uppermost layer.

[0045] The substrate 52 is an insulating and flexible substrate, and is made of a resin such as PI (polyimide), PET (polyethylene terephthalate), or PEN (polyethylene naphthalate). A loop-shaped electrode 54 is disposed on the lower surface of the substrate 52.

[0046] A loop-shaped electrode 57 and an electrode 60 connected to one end of the RFIC chip are arranged on the upper surface of the substrate 52. The loop-shaped electrode 57 has, for example, a loop of multiple turns, and an inner end 58 of the electrode 57 is connected to the other end of the RFIC chip 19. An outer end 59 of the electrode 57 is connected to an outer end 56 of the electrode 54 on the lower surface of the substrate 52 by an interlayer connection such as a through-hole conductor. Furthermore, the electrode 60 is connected to an inner end 55 of the electrode 54 on the lower surface of the substrate 52 by an interlayer connection such as a through-hole conductor. In this way, the electrode 54 and the electrode 57 form the coil 53.

[0047] The upper and lower surfaces of the substrate 52 are protected by resist layers 61, 63, respectively. The resist layer 61 has an opening 62 in the center that is larger than the RFIC chip 19 in a plan view, allowing the RFIC chip 19 to be mounted on the inner end 58 of the electrode 57 and the electrode 60. For example, double-sided tape is attached to the lower surface of the resist layer 63 of the substrate 52, and the substrate 52 is fixed to the region on the substrate 3 between the straight portion 21 of the first wiring portion 14B and the straight portion 23 of the second wiring portion 15B.

[0048] The RFID inlay 1B of embodiment 3 has the same effects as the RFID inlay 1 of embodiment 1. Furthermore, even if the specifications of the RFIC chip 19 change, the RFID inlay 1B can be accommodated by changing the design of only the circuit provided on the substrate 52 separate from the substrate 3. Since there is no need to redesign the entire RFID inlay 1B, the directivity of the antenna 5 does not change.

[0049] 8, in the RFID inlay 1B of the third embodiment, the first electrode 7B has an electrode 47 that protrudes from the vicinity of the second end 9 on one side of the first electrode 7B toward the second electrode 10B, and the second electrode 10B has an electrode 48 that protrudes from the vicinity of the fourth end 12 on one side of the second electrode 10B toward the first electrode 7B. Since the electrodes 47 and 48 face each other, a capacitance is generated, which allows the resonant frequency to be lowered and the RFID inlay 1B to be further miniaturized. Since the potential difference is greatest near the open ends between the radiating elements, a significant effect can be obtained by loading a capacitance there.

[0050] The electrodes 47 and 48 are not limited to having a comb-tooth shape as shown in FIG. 8, but may simply be arranged facing each other.

[0051] Please refer to Fig. 11. Fig. 11 is a diagram showing the antenna gain of the RFID inlay 1B in embodiment 3. As shown in Fig. 11, the RFID inlay 1B can provide omnidirectional antenna gain in the XY plane. That is, omnidirectional antenna gain can be obtained on a plane perpendicular to the main surface of the substrate 3. Therefore, when the XZ plane of the RFID inlay 1B is wrapped around a cylindrical article, omnidirectional antenna gain can be obtained in the horizontal direction from the cylindrical surface, enabling wireless communication without the occurrence of null points.

[0052] In contrast, the antenna gain of an RFID inlay having a conventional dipole antenna will be described with reference to Fig. 12. Fig. 12 is a diagram showing the antenna gain of an RFID inlay in a comparative example. As shown in Fig. 12, with a conventional dipole antenna, a null point occurs in the X-axis direction. Therefore, when the XZ plane of the RFID inlay is wrapped around a cylindrical object, a direction in which wireless communication is not possible occurs horizontally from the cylindrical surface. This may hinder smooth wireless communication and may lead a user to mistakenly believe that the RFID inlay is damaged.

[0053] (Fourth Embodiment) Next, an RFID inlay 1C of a fourth embodiment will be described with reference to Fig. 13. Fig. 13 is a plan view showing a schematic configuration of the RFID inlay 1C of the fourth embodiment. The RFID inlay 1C of the fourth embodiment will be described, focusing on the differences from the RFID inlay 1 of the first embodiment. In the description of the fourth embodiment, elements having the same configuration, action, and function as those of the first embodiment will be given the same reference numerals, and descriptions thereof will be omitted to avoid duplication.

[0054] In the RFID inlay 1 of embodiment 1, the antenna 5 and the RFIC chip 19 are electrically connected via the matching circuit section 17 by magnetic field coupling, but in embodiment 4, the RFIC chip 19 is directly connected to the wiring 13 of the antenna 5.

[0055] One end of the RFIC chip 19 and the first wiring portion 14 are electrically and directly connected at a connection point 82 near a connection portion 81 between the first electrode 7 and the first wiring portion 14, and the other end of the RFIC chip 19 and the second wiring portion 15 are electrically and directly connected at a connection point 84 near a connection portion 83 between the second electrode 10 and the second wiring portion 15. A conductive bonding material such as solder or anisotropic conductive paste is used for this connection.

[0056] In the RFID inlay 1C of embodiment 4, when the inductance components of the first wiring portion 14 and the second wiring portion 15 and the output capacitance C1 of the RFIC chip 19 resonate at the communication frequency, the potential difference becomes maximum between the connection point 82 of the first wiring portion 14 and the connection point 84 of the second wiring portion 15. Because the point where the potential difference becomes maximum is connected to the radiating element, the potential difference between the radiating elements also becomes maximum, and electromagnetic waves are efficiently radiated from the first electrode 7 and the second electrode 10, which are the radiating elements.

[0057] (Embodiment 5) Next, an RFID inlay 1D of embodiment 5 will be described with reference to Fig. 16. Fig. 16 is a plan view showing a schematic configuration of the RFID inlay 1D of embodiment 5. The RFID inlay 1D of embodiment 5 will be described mainly with respect to differences from the RFID inlay 1 of embodiment 1. In the description of embodiment 5, elements having the same configuration, action, and function as those of embodiment 1 will be given the same reference numerals, and descriptions thereof will be omitted to avoid duplication.

[0058] In the RFID inlay 1 of embodiment 1, the first electrode 7 and the second electrode 10 have the same length, but in the RFID inlay 1D of embodiment 5, the first electrode 7 and the second electrode 10 have different lengths, with the second electrode 10 being longer than the first electrode 7. A third end portion 11D, which is the open end of the longer second electrode (radiating electrode), extends along the outer periphery of the insulating substrate 3 toward a first end portion 8, which is the open end of the shorter first electrode (radiating electrode) 7.

[0059] The substrate 3 has, for example, a substantially rectangular shape with two long sides and two short sides. The substrate 3 has a first long side 34 and a second long side 35 that face each other, and a first short side 36 and a second short side 37 that face each other.

[0060] The straight portion 21 of the first electrode 7D and the straight portion 23 of the second electrode 10D each extend in the same longitudinal direction of the substrate 3. The straight portion 21 of the first electrode 7D extends along the first long side 34 of the substrate 3, and the straight portion 23 of the second electrode 10D extends along the second long side 35 of the substrate 3.

[0061] In addition to the straight line portion 23, the second electrode 10D also has a straight line portion 24 and a straight line portion 25. The straight line portion 23 and the straight line portion 24 are continuously connected, and the straight line portion 24 extends along the second short side 37 of the substrate 3. The straight line portion 24 and the straight line portion 25 are continuously connected, and the straight line portion 25 extends along the first long side 34 of the substrate 3. In this manner, the second electrode 10D extends along three sides of the substrate 3, and the straight line portion 24 and the straight line portion 25 form a folded portion 26. The third end 11D of the second electrode 10D is the tip of the straight line portion 25 and faces the first end 8D of the first electrode 7D. Note that instead of the second electrode 10D having the folded portion 26, the first electrode 7D may have the folded portion 26.

[0062] The total length of the first electrode 7D and the second electrode 10D is equal to or less than λ / 4, where λ is the wavelength corresponding to the resonant frequency of the antenna 5D.

[0063] The electric field generated from the antenna 5D will be described with reference to Fig. 17 and Fig. 18. Fig. 17 is an explanatory diagram showing the electric field distribution when the RFID inlay 1D is resonating. Fig. 18 is an explanatory diagram showing the components in the electric field direction of the antenna 5D of the RFID inlay 1D of the fifth embodiment.

[0064] One of the linear portions 21 of the first electrode 7D and the linear portion 23 of the second electrode 10D, which are arranged opposite to each other, is a positive pole and the other is a negative pole, so that an electric field of approximately uniform strength is generated perpendicular to the first electrode 7 and the second electrode 10. Figure 17 shows an example in which the linear portion 21 of the first electrode 7D is a positive pole and the linear portion 23 of the second electrode 10D is a negative pole.

[0065] In this way, the electric field distribution generated between the first electrode 7 and the second electrode 10 arranged opposite to each other is approximately uniform along the direction in which the first electrode 7 and the second electrode 10 extend, i.e., along the longitudinal direction of the substrate 3. In addition, a magnetic field is generated perpendicular to the direction of the electric field generated by the antenna 5. Because the electric field distribution is uniform, an approximately uniform magnetic field is generated horizontally and uniformly along the direction in which the first electrode 7 and the second electrode 10 extend. Therefore, the radiation characteristics of the antenna 5 are omnidirectional in a plane perpendicular to the horizontal plane (first main surface 31).

[0066] In the fifth embodiment, an electric field is generated from the first end 8D of the first electrode 7D toward the other side of the linear portion 23 of the second electrode 10D, the linear portion 24, and the linear portion 25. That is, in addition to the electric field component Ez generated from the first electrode 7D toward the second electrode 10D, an electric field component Ex is also generated in the direction in which the first electrode 7D extends. As a result, as shown in FIG. 18 , the electric field E generated from the antenna 5D of the RFID inlay 1D is a composite component of the electric field component Ez and the electric field component Ex. Therefore, the electric field E of the RFID inlay 1D of the fifth embodiment is inclined at an angle θ with respect to the Z axis. The angle θ varies depending on the relationship between the magnitudes of the electric field component Ez and the electric field component Ex, for example, depending on the ratio of the lengths of the linear portion 21 of the first electrode 7D and the linear portions 23, 24, and 25 of the second electrode 10D.

[0067] 19 is an explanatory diagram showing the directivity of the antenna 5D of the RFID inlay 1D of embodiment 5. Compared with the directivity of the RFID inlay 1D of embodiment 1 shown in FIG. 6B, the directivity of the RFID inlay 1D of embodiment 5 is inclined at an angle θ with respect to the Z axis as a whole, both in the directivity due to the electric field propagating in the X-axis direction and the Z-axis direction and in the directivity due to the magnetic field propagating in the Y-axis direction. This inclination of the directivity can improve the readability of the RFID inlay 1D from below (negative Z-axis direction).

[0068] Fig. 20 is an explanatory diagram illustrating the electric field distribution when the RFID inlay 1D of embodiment 5 is wound into a cylindrical shape around the Z axis. Note that the substrate 3, matching circuit section 17, and RFIC chip 19 are omitted from Fig. 20 to make it easier to see the main parts. As shown in Fig. 20, even when the RFID inlay 1D is wound into a cylindrical shape around the Z axis, an electric field component Ez is generated in the Z axis direction from the first electrode 7D to the second electrode 10D, and an electric field component Ey is generated in the Y axis direction from the first electrode 7D to the straight portion 25 of the folded portion 26 of the second electrode 10D.

[0069] 21 is an explanatory diagram showing the direction of the electric field E generated in the RFID inlay 1D in the YZ plane in FIG. 20. Even when the RFID inlay 1D is rolled into a cylindrical shape, the electric field E generated from the RFID inlay 1D in the YZ plane is a composite component of the electric field component Ex and the electric field component Ez. Therefore, the direction of the electric field E is tilted at an angle θ with respect to the Z axis. In this way, even when the RFID inlay 1D is rolled into a cylindrical shape, the directivity of the RFID inlay 1D is tilted, thereby improving the read characteristics from the negative direction of the Z axis.

[0070] Fig. 22 is a diagram showing the antenna gain of the RFID inlay 1D in a cylindrically wound state in embodiment 5. Compared with Fig. 6C showing the gain of the RFID inlay 1 in embodiment 1, the RFID inlay 1D in embodiment 5 has almost no change in directivity in the circumferential direction of the Z axis, but has improved directivity in the vertical direction, that is, the Z axis direction.

[0071] According to the RFID inlay 1D of the fifth embodiment, the first electrode 7D and the second electrode 10D have different lengths, and therefore the direction of the electric field generated between the tip of the longer electrode and the tip of the shorter electrode differs from the direction of the electric field generated in the section where the first electrode 7D and the second electrode 10D face each other, and therefore the direction of the electric field generated between the first electrode 7D and the second electrode 10D is tilted from the direction perpendicular to the first electrode 7D and the second electrode 10D, thereby further improving the omnidirectionality of the antenna.

[0072] Furthermore, in the RFID inlay 1D of embodiment 5, the first end 8D, which is the tip of the first electrode 7D, and the third end 11D, which is the tip of the second electrode 10D, face each other in the direction in which the first electrode 7D or the second electrode 10D extends. This generates an electric field component Ex between the tip of the first electrode 7D and the tip of the second electrode 10D in the direction in which the first electrode 7D or the second electrode 10D extends. In this way, an electric field component Ex can be generated in a direction different from the electric field component Ez, which is perpendicular to the portion where the first electrode 7D and the second electrode 10D face each other in the longitudinal direction of the substrate 3. This causes the electric field E of the RFID inlay 1D, which is a combination of the two electric field components Ez and Ex, to be tilted from the direction perpendicular to the first electrode 7D and the second electrode 10D, thereby further improving the omnidirectionality of the antenna.

[0073] (Sixth Embodiment) Next, an RFID inlay 1E of a sixth embodiment will be described with reference to Fig. 23. Fig. 23 is a plan view showing a schematic configuration of the RFID inlay 1E of the sixth embodiment. The RFID inlay 1E of the sixth embodiment will be described mainly with respect to differences from the RFID inlay 1D of the fifth embodiment. In the description of the sixth embodiment, elements having the same configuration, action, and function as those of the fifth embodiment will be given the same reference numerals, and descriptions thereof will be omitted to avoid duplication.

[0074] The RFID inlay 1E of the sixth embodiment is a combination of the RFID inlay 1D of the fifth embodiment and the RFID inlay 1B of the third embodiment. The RFID inlay 1E of the sixth embodiment is similar to the RFID inlay 1D of the fifth embodiment in that it has a folded portion 26, and similar to the RFID inlay 1B of the third embodiment in that it has a comb-tooth electrode portion 71 on one side of each of the first electrode 7E and the second electrode 10E.

[0075] The straight portion 21 of the first electrode 7E and the straight portion 23 of the second electrode 10E in the RFID inlay 1E of embodiment 6 each do not have an open end on one side, and do not have portions corresponding to the second end 9 and the fourth end 12 in the RFID inlay 1B of embodiment 3.

[0076] The comb-tooth electrode portion 71 in the RFID inlay 1E of embodiment 6 comprises a base 72 to which the straight portion 21 of the first electrode 7E is bent inward toward the substrate 3 at a connection portion 81E and then bent to the other side to connect, a plurality of electrodes 74 protruding from the base 72 toward the second electrode 10E, a base 73 to which the straight portion 23 of the second electrode 10E is bent inward toward the substrate 3 at a connection portion 83E and then bent to the other side to connect, and a plurality of electrodes 75 protruding from the base 73 toward the first electrode 7E.

[0077] The plurality of electrodes 74 and the plurality of electrodes 75 are alternately arranged in the longitudinal direction of the substrate 3. This generates capacitance between the electrodes 74 and the electrodes 75. Since the number of electrodes 74 and electrodes 75 included in the comb-tooth electrode portion 71 is greater than that of the RFID inlay 1B of the third embodiment, the resonant frequency can be further lowered, and the RFID inlay 1E can be made smaller.

[0078] The present invention is not limited to the above-described embodiments, but can be modified as follows.

[0079] In the above embodiment, the RFID inlay 1 is used as an example of a wireless communication module, but this is not limiting. The above-described antenna configuration may be configured such that the substrate 3 is made of a rigid material that is not flexible. Furthermore, the wireless communication module may be configured as an RFID tag using the RFID inlay 1.

[0080] Although the present invention has been described in various embodiments with a certain degree of detail, the disclosure of these embodiments may vary in structural details, and variations in the combination and order of elements in the various embodiments may be realized without departing from the scope and spirit of the invention as claimed.

[0081] A first aspect of the present invention provides a wireless communication device comprising an RFIC chip, an antenna having a first electrode and a second electrode facing each other, and a wiring having one end connected to one side of the first electrode and the other end connected to one side of the second electrode. The wiring is disposed between the first electrode and the second electrode. The wiring has a first wiring portion extending from one side of the first electrode to the other side, and a second wiring portion folding back from an end of the first wiring portion and extending from the other side of the second electrode to one side. The first wiring portion and the second wiring portion are disposed adjacent to each other at least in part. The directions of current flowing through the first wiring portion and the second wiring portion are opposite. The wiring is longer than the combined length of the first electrode and the second electrode, and the RFIC chip and the wiring are electrically or magnetically coupled.

[0082] According to this aspect of the wireless communication device, the current flowing through the antenna can be concentrated in the wiring, so that the strength of the electric field generated between the opposing first and second electrodes can be made uniform, and therefore the strength of the magnetic field generated in a direction perpendicular to the electric field can also be made uniform, thereby improving the omnidirectionality of the antenna.

[0083] According to a second aspect, in the wireless communication device of the first aspect, the RFIC chip and the wiring are magnetically coupled via a matching circuit section.

[0084] According to a third aspect, in the wireless communication device of the first or second aspect, the first wiring portion and the second wiring portion run parallel to each other.

[0085] According to a fourth aspect, in the wireless communication device of any one of the first to third aspects, the first wiring portion has a first branch wiring branching toward the second wiring portion, and the second wiring portion has a second branch wiring branching toward the first wiring portion. The second branch wiring is disposed between adjacent first branch wirings, and the first branch wiring is disposed between adjacent second branch wirings.

[0086] According to a fifth aspect, in the wireless communication device of any one of the first to fourth aspects, the wiring is at least twice the total length of the first electrode and the second electrode.

[0087] According to a sixth aspect, in the wireless communication device of any one of the first to fifth aspects, the length of each of the first electrode and the second electrode is λ / 8 or less, where λ is a wavelength corresponding to the resonant frequency of the antenna.

[0088] According to a seventh aspect, the wireless communication device of any one of the first to sixth aspects further comprises a flexible first substrate on which an antenna and wiring are arranged.

[0089] According to an eighth aspect, the wireless communication device of the seventh aspect further comprises a second substrate on which an RFIC chip is arranged, and the second substrate is fixed to the first substrate.

[0090] According to a ninth aspect, in the wireless communication device of any one of the first to eighth aspects, the line width of the first electrode and the line width of the second electrode are larger than the line width of the wiring.

[0091] According to a tenth aspect, in the wireless communication device of any one of the first to ninth aspects, the first electrode and the second electrode have different lengths.

[0092] According to an eleventh aspect, in a wireless communication device of any one of the first to tenth aspects, the sum of the lengths of the first electrode and the second electrode is λ / 4 or less, where λ is the wavelength corresponding to the resonant frequency of the antenna.

[0093] According to a twelfth aspect, in the wireless communication device of the tenth aspect, a tip of the first electrode and a tip of the second electrode face each other in the direction in which the first electrode or the second electrode extends.

[0094] REFERENCE SIGNS LIST 1, 1A, 1B, 1C, 1D, 1E RFID inlay 3 Substrate 5, 5A, 5B, 5C, 5D, 5E Antenna 7, 7D, 7E First electrode 8, 8D First end 9 Second end 10, 10D, 10E Second electrode 11, 11D Third end 12 Fourth end 13 Wiring 14 First wiring portion 15 Second wiring portion 16 End 17 Matching circuit portion 19 RFIC chip 21 Straight portion 23, 24, 25 Straight portion 26 Folded portion 31 First main surface 33 Second main surface 34 First long side 35 Second long side 36 First short side 37 Second short side 41 Base line 42 First branch wiring 43 Base line 44 Second branch wiring 45, 46, 47, 48 Electrode 51 Resonant circuit section 52 Substrate 53 Coil 54 Electrode 55, 56 End section 57 Electrode 58, 59 End section 60 Electrode 61 Resist layer 62 Opening 71 Comb-shaped electrode section 72 Base section 73 Base section 74, 75 Electrodes 81 Connection section 82 Connection point 83 Connection section 84 Connection point

Claims

1. A wireless communication device comprising: an RFIC chip; an antenna having a first electrode and a second electrode facing each other; and wiring having one end connected to one side of the first electrode and the other end connected to one side of the second electrode, the wiring being arranged between the first electrode and the second electrode, the wiring having a first wiring portion extending from one side of the first electrode to the other side, and a second wiring portion folding back from an end of the first wiring portion and extending from the other side of the second electrode to one side, the first wiring portion and the second wiring portion being arranged adjacent to each other in at least a portion thereof, the directions of current flowing in the first wiring portion and the second wiring portion being opposite, the wiring being longer than the combined length of the first electrode and the second electrode, and the RFIC chip and the wiring being electrically or magnetically coupled.

2. The wireless communication device according to claim 1, wherein the RFIC chip and the wiring are magnetically coupled via a matching circuit section.

3. The wireless communication device according to claim 1 or 2, wherein the first wiring portion and the second wiring portion run parallel to each other.

4. A wireless communication device according to any one of claims 1 to 3, wherein the first wiring portion has a first branch wiring that branches toward the second wiring portion, the second wiring portion has a second branch wiring that branches toward the first wiring portion, the second branch wiring is arranged between adjacent first branch wirings, and the first branch wiring is arranged between adjacent second branch wirings.

5. The wireless communication device according to any one of claims 1 to 4, wherein the wiring has a length at least twice the total length of the first electrode and the second electrode.

6. A wireless communication device according to any one of claims 1 to 5, wherein the length of each of the first electrode and the second electrode is λ / 8 or less, where λ is a wavelength corresponding to the resonant frequency of the antenna.

7. The wireless communication device according to any one of claims 1 to 6, comprising a flexible first substrate on which the antenna and the wiring are arranged.

8. The wireless communication device according to claim 7, further comprising a second substrate on which the RFIC chip is disposed, the second substrate being fixed to the first substrate.

9. The wireless communication device according to any one of claims 1 to 8, wherein the line width of the first electrode and the line width of the second electrode are larger than the line width of the wiring.

10. A wireless communication device according to any one of claims 1 to 9, wherein the first electrode and the second electrode have different lengths.

11. A wireless communication device according to any one of claims 1 to 10, wherein the total length of the first electrode and the second electrode is λ / 4 or less, where λ is a wavelength corresponding to the resonant frequency of the antenna.

12. The wireless communication device according to claim 10, wherein the tip of the first electrode and the tip of the second electrode face each other in the direction in which the first electrode or the second electrode extends.

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