RFID inlay
The RFID inlay utilizes a single series or parallel circuit configuration with substrate-based capacitors and inductors to overcome size limitations, achieving miniaturization and omnidirectional radiation, improving space efficiency and frequency compatibility.
Patent Information
- Application Number
- JP2023222726
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-12-28
- Publication Date
- 2025-07-10
AI Technical Summary
Conventional RFID inlays using metamaterial antennas are limited in miniaturization due to the arrangement of inductors and capacitors, leading to increased antenna width and restricted size reduction.
The RFID inlay is designed with a single series or parallel circuit configuration, incorporating a capacitor and inductor formed by conductor patterns on a substrate, connected to a pair of power supply portions and an IC chip, resonating at a predetermined frequency, allowing for miniaturization and omnidirectional radiation characteristics.
The design achieves miniaturization of the RFID inlay while maintaining effective communication distance and omnidirectional radiation, enhancing space efficiency and frequency band compatibility.
Smart Images
Figure 2025104718000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to an RFID inlay.
Background Art
[0002] Conventionally, a metamaterial antenna having a microwave resonator using a metamaterial has been known. In a metamaterial antenna, a composite right- and left-handed (CRLH) transmission line is configured. Here, the "right-handed system" refers to a propagation state of an electromagnetic wave in which the electric field vector, magnetic field vector, and wave number vector of the electromagnetic wave have a right-handed relationship. The "left-handed system" refers to a propagation state of an electromagnetic wave in which the electric field vector, magnetic field vector, and wave number vector have a left-handed relationship. Usually, in a parallel transmission line, there are a parasitic inductor component of a series branch of the line and a parasitic capacitor component of a branch between the lines, and these components become right-handed system elements. On the other hand, a CRLH transmission line is configured by arranging a capacitor of a series branch of the line and an inductor of a branch between the lines as left-handed system elements. In a metamaterial antenna configured by a CRLH transmission line, since the phase constant becomes zero (the current distribution becomes uniform) at a specific resonance frequency and a zero-order resonance in which the wavelength of the transmitted wave becomes substantially infinite can be realized, it is expected to contribute to miniaturization of the antenna as compared with an antenna (such as a dipole antenna or a one-wavelength loop antenna) in which the wavelength at resonance depends on the antenna size. A proposal has been made to apply this metamaterial antenna as an antenna of an RFID inlay (hereinafter, simply referred to as "inlay" as appropriate) (see Non-Patent Document 1).
Prior Art Documents
Non-Patent Documents
[0003]
Non-Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In Non-Patent Document 1, two capacitors are connected in series to the nodes at both ends from a pair of power supply points where an IC chip is arranged, and two inductors are connected in parallel to the nodes at both ends, and an inlay composed of two series circuits as a whole when viewed from the power supply points is proposed (see FIG. 23 of Non-Patent Document 1; an inlay with the same configuration is described in FIG. 3). In this proposed inlay, since two inductors are arranged sandwiching a plurality of capacitors connected in series, the antenna width becomes large, and there is a limit to the miniaturization of the inlay.
[0005] Therefore, an object of the present invention is to miniaturize an RFID inlay applying a metamaterial antenna more than before.
Means for Solving the Problems
[0006] One aspect of the present invention is an RFID inlay arranged on a substrate and operating by receiving radio waves in a predetermined frequency band from a reader, a capacitor portion formed with a predetermined conductor pattern on the substrate, an inductor portion formed with a predetermined conductor pattern on the substrate, a pair of power supply portions, and an IC chip connected to the pair of power supply portions. The capacitor section, the inductor section, the pair of power supply sections, and the IC chip form a single series circuit, and the single series circuit is configured to resonate at a predetermined frequency included in the frequency band. This is an RFID inlay.
Advantages of the Invention
[0007] According to an aspect of the present invention, miniaturization can be achieved for an RFID inlay to which a metamaterial antenna is applied, as compared with the prior art.
Brief Description of the Drawings
[0008]
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Figure 24
Figure 25
Figure 26
Figure 27
Figure 28
Figure 29
[0009] The embodiments described below are not limited to the drawings described by a brief explanation of the drawings.
[0010] A first aspect of an aspect of the present invention is an RFID inlay disposed on a substrate and operating by receiving radio waves in a predetermined frequency band from a reader, a capacitor portion formed on the substrate with a predetermined conductor pattern, an inductor portion formed on the substrate with a predetermined conductor pattern, a pair of power supply portions, and an IC chip connected to the pair of power supply portions, and a single series circuit is formed by the capacitor portion, the inductor portion, the pair of power supply portions, and the IC chip, and the single series circuit is configured to resonate at a predetermined frequency included in the frequency band, the RFID inlay.
[0011] According to the first aspect of an aspect of the present invention, miniaturization can be achieved more than conventionally for an RFID inlay to which a metamaterial antenna is applied.
[0012] A second aspect of an aspect of the present invention is an RFID inlay disposed on a substrate and operating by receiving radio waves in a predetermined frequency band from a reader, a capacitor portion formed on the substrate with a predetermined conductor pattern, an inductor portion formed on the substrate with a predetermined conductor pattern, a pair of power supply portions, and an IC chip connected to the pair of power supply portions, and The capacitor section, the inductor section, the pair of power supply sections, and the IC chip form a parallel circuit, and the parallel circuit is configured to resonate at a predetermined frequency included in the frequency band, and is an RFID inlay.
[0013] According to a second aspect of an embodiment of the present invention, miniaturization can be achieved for an RFID inlay to which a metamaterial antenna is applied, as compared with the prior art.
[0014] A third aspect of an embodiment of the present invention is the RFID inlay according to the first or second aspect, wherein the capacitor section is formed of one or more interdigital capacitors.
[0015] According to a third aspect of an embodiment of the present invention, the capacitance can be increased while maintaining a planar structure.
[0016] A fourth aspect of an embodiment of the present invention is the RFID inlay according to any one of the first and second aspects, wherein the capacitor section includes one or more capacitors in which a pair of opposing conductor patterns are formed on the front surface side and the back surface side of the base material, respectively.
[0017] According to a fourth aspect of an embodiment of the present invention, a capacitor can be configured by utilizing the thickness of the base material.
[0018] A fifth aspect of an embodiment of the present invention is the RFID inlay according to any one of the first to fourth aspects, wherein the inductor section is formed of a linear or meandering conductor pattern.
[0019] According to a fifth aspect of an embodiment of the present invention, a conductor pattern having a desired inductance can be set.
[0020] A sixth aspect of an embodiment of the present invention is that the capacitor section has one or more capacitors arranged along a first direction between a first node and a second node. The inductor part is formed of a conductor pattern connecting the first node and the second node. The conductor pattern on which the inductor part is formed extends in a second direction orthogonal to the first direction from each of the first node and the second node, and the length of the conductor pattern in the second direction is substantially the same as the distance between the first node and the second node or longer than the distance, which is the RFID inlay according to any one of the first to fifth aspects.
[0021] According to a sixth aspect of an aspect of the present invention, the communication distance in the first direction can be extended with a reader.
[0022] A seventh aspect of an aspect of the present invention is the RFID inlay according to any one of the first to third and fifth to sixth aspects, wherein the capacitor part is formed on one of the front surface side or the back surface side of the base material, and the inductor part is formed on the other of the front surface side or the back surface side of the base material.
[0023] According to a seventh aspect of an aspect of the present invention, a small antenna with excellent space efficiency can be formed by using both sides of the base material.
[0024] An eighth aspect of an aspect of the present invention is the RFID inlay according to any one of the first to seventh aspects, wherein the frequency band is 860 to 960 MHz.
[0025] According to an eighth aspect of an aspect of the present invention, communication with a reader is possible in the UHF band.
[0026] Hereinafter, embodiments will be described in detail with reference to the drawings.
[0027] Hereinafter, as some embodiments, an inlay including a series resonance circuit type metamaterial antenna is disclosed, and as some embodiments, an inlay including a parallel resonance circuit type metamaterial antenna is disclosed. Fig. 1 shows the equivalent circuits of a series-resonant circuit type metamaterial antenna and a parallel-resonant circuit type metamaterial antenna. In each equivalent circuit, a simplified one containing only one capacitor and one inductor is adopted. For the capacitor C and inductor L included in each equivalent circuit, the subscript R indicates that it is a right-handed element in the metamaterial antenna, and the subscript L indicates that it is a left-handed element in the metamaterial antenna.
[0028] In the series-resonant circuit type metamaterial antenna, the capacitor C L and the inductor L R are connected in series with respect to the IC chip CH, forming a parallel transmission line with a short-circuited end, and constituting a CRLH transmission line as a whole. The negative permittivity and negative permeability are realized by the left-handed elements. The resonant frequency f of the series-resonant circuit type metamaterial antenna is expressed by the following formula (1). In the metamaterial antenna which is a zero-order resonator, it functions as an antenna by LC resonance regardless of the size of the antenna.
Equation
[0029] On the other hand, in the parallel-resonant circuit type metamaterial antenna, the capacitor C R and the inductor L L are connected in parallel with respect to the IC chip CH, forming a parallel transmission line with an open-ended end, and constituting a CRLH transmission line as a whole. Also in this case, the negative permittivity and negative permeability are realized by the left-handed elements. The resonant frequency f of the parallel-resonant circuit type metamaterial antenna is expressed by the following formula (2). Similarly in the case of the parallel-resonant circuit type, it functions as an antenna by LC resonance regardless of the size of the antenna.
Equation
[0030] In both series resonance circuit type and parallel resonance circuit type metamaterial antennas, by adjusting the capacitor C R , C L and the inductor L R , L L , it is possible to fabricate a metamaterial antenna with desired frequency characteristics. In one embodiment, the left-handed elements (capacitor C L and inductor L L that are not parasitic components) are realized by forming a conductor pattern of a desired form, and the right-handed elements (parasitic capacitor component C R and parasitic inductor component L R ) can be adjusted by the size (width and length) and path of the transmission line.
[0031] In the simplified equivalent circuit of FIG. 1, only one capacitor and one inductor are included each, but two or more capacitors and / or inductors may be arranged along the transmission line. In the following description, the minimum unit configuration shown in FIG. 1 is referred to as a "cell". When there are two or more capacitors and / or inductors, a metamaterial antenna is configured by continuously connecting a plurality of cells along the transmission line.
[0032] Hereinafter, an inlay including a series resonance circuit type or parallel resonance circuit type metamaterial antenna will be specifically described. In the description, as appropriate, as shown in FIG. 2, the radiation direction of the radio wave is defined, and a display example of the radiation characteristics of the radio wave when an electromagnetic field simulator is applied to each inlay is shown. For the convenience of explaining the drawings, an xyz coordinate system is defined, and it is assumed that the inlay IL is arranged on the xy plane. In the following description, when referring to the x direction and the y direction in relation to the shape of the inlay, they mean directions parallel to the x axis and the y axis, respectively. In addition, direction A (a direction parallel to the z-axis), direction B (a direction parallel to the x-axis), direction C (a direction parallel to the y-axis), and direction D (a direction opposite to direction C) are defined as the radiation directions of radio waves, and the radiation characteristics of the radio waves are expressed. The radiation characteristics of the radio waves shown in FIG. 2 are in the display mode by Sonnet, which is well known to those skilled in the art as an electromagnetic field simulator. All the simulation results in the present disclosure are the results obtained by using Sonnet as the electromagnetic field simulator.
[0033] (I) An inlay including a series resonance circuit type metamaterial antenna The inlay including the series resonance circuit type metamaterial antenna will be specifically described. First, before describing the inlay according to the embodiment, the inlay described in FIG. 23 of Non-Patent Document 1 will be described as an inlay of a reference example.
[0034] Referring to FIG. 3, the outer shape (antenna width L1, antenna length L2) of the inlay IL of the reference example is shown. As shown in FIG. 3, the inlay IL of the reference example REF has two capacitors C each connected in series between the nodes N1 and N2 at both ends from each of a pair of feeding points where the IC chip CH is arranged. REF L Two inductors L (widths t1 and t2 respectively) are connected in parallel between the nodes N1 and N2. As a result, the inlay IL R is composed of two series circuits SC1 and SC2 as a whole when viewed from the IC chip CH (refer to the equivalent circuit). REF
[0035] Each capacitor C L has a configuration of an interdigital capacitor. The interdigital capacitor is a capacitor having a configuration in which a pair of comb-shaped (or rake-shaped) elements face each other in order to increase the capacitance while maintaining a planar structure. The inlay IL REF is provided with a 4-cell configuration metamaterial antenna. In this case, the unit cell is one interdigital capacitor C Land an inductor L R can be considered to include a part of the conductor pattern constituting the capacitor C, and the pitch p of the cells is equal to the length in the x direction of the capacitor C L In the inlay IL of this reference example REF There are a plurality of capacitors C L With two inductors L sandwiching them R Since they are arranged in the y direction, the antenna width L1 inevitably becomes large.
[0036] Fig. 4 shows the simulation results of the inlay IL of the reference example REF These simulation results include the radiation characteristics of radio waves and the communication distance (Read Range) in different directions. Here, the antenna width L1 is 44.8 mm, the antenna length L2 is 58 mm, the inductor widths t1 and t2 are both 5.8 mm, the pitch p is 12 mm, the width in the y direction of the teeth of the interdigital capacitor (hereinafter referred to as the "line width") t3 is 2.2 mm, and the interval in the y direction between adjacent teeth (hereinafter referred to as the "gap width") t4 is 0.4 mm. Note that all the simulation results in the present disclosure represent, in dimensionless form, the distance at which communication with the inlay is possible when the reader emits radio waves with a predetermined transmission power. As shown in Fig. 4, in the inlay IL of the reference example REF it can be seen that for directions A and C, a certain communication distance is ensured in the UHF band (860 - 960 MHz), but almost no communication is possible in direction B. This is also shown in the radiation characteristics of Fig. 4 (NULL in direction B).
[0037] The reason why the inlay IL REF becomes null in direction B is due to the antenna configuration of the inlay IL REF having two series circuits. Fig. 5 shows the current distribution at the resonance of the antenna of the inlay IL REF In Fig. 5, the direction of the current flow is indicated by arrows. As shown in Fig. 5, a pair of inductors L R and a capacitor C LWhen the currents flowing through the strip portions s1 and s2 to be connected are I1 and I2 respectively, the currents I1 and I2 are in opposite directions with respect to the node N1. Therefore, the radio waves radiated by the currents flowing through the strip portions s1 and s2 are canceled out and become null in the direction B.
[0038] Next, as an embodiment, an inlay 10 of an improved example obtained by improving the inlay IL of the reference example will be described. REF will be described. The outer shape and radiation characteristics of the inlay 10 are shown in FIG. 6. As shown in FIG. 6, the inlay 10 is composed of a single series circuit by removing one inductor L from the inlay IL of the reference example in FIG. 3. In the inlay 10, since the radio waves radiated by the current flowing through the strip portion connecting the inductor L and the capacitor C are not canceled out, as shown in the radiation characteristics, it does not become null in the direction B and becomes omnidirectional. REF from R by removing one inductor L. In the inlay 10, the inductor L R and the capacitor C L are not canceled out by the current flowing through the strip portion connecting them, so as shown in the radiation characteristics, it does not become null in the direction B and becomes omnidirectional.
[0039] The inlay IL shown in FIG. 3 REF is designed to resonate at a resonance frequency of 930 to 940 MHz in the UHF band. If one inductor L is simply removed from the inlay IL REF to form the inlay 10, the resonance frequency of the inlay 10 will deviate from the UHF band (for example, it will be about 670 to 680 MHz). That is, the inductance of a single inductor L R is larger than the combined inductance of the two inductors L R connected in parallel as in the inlay IL REF . Therefore, when the inlay 10 is designed by simply removing one inductor L from the inlay IL R , the resonance frequency of the inlay 10 is lower than that of the inlay IL REF (see Equation (1)). R (see Equation (1)). REF (see Equation (1)).
[0040] Therefore, in the inlay 10 of the improved example, by adjusting the size of the antenna, the inductor L RThe inductance, and / or the capacitance of each capacitor C L is reduced, and thus it is configured to resonate at the resonance frequency in the UHF band (for example, the above 930 to 940 MHz). The adjustment of the size of the antenna includes the antenna width L1, the antenna length L2, the dimensions (such as line width and gap width) of the capacitor C L including the pitch p, and the width t2 etc. of the inductor L R etc. This adjustment of the size of the antenna is designed in the direction of reducing the value of the dimensions of each part, so in addition to removing one inductor L REF compared with the inlay IL R it will contribute to further miniaturization of the entire inlay.
[0041] Next, some embodiments of an inlay including a series resonance circuit type metamaterial antenna will be described with reference to FIGS. 7 to 20. This metamaterial antenna includes a capacitor part including one or more capacitors, an inductor part including one or more inductors, a pair of feeding parts, and an IC chip to form a single series circuit, and the single series circuit is configured to resonate at a predetermined resonance frequency. In one embodiment, the resonance frequency is a frequency included in the UHF band (860 to 960 MHz).
[0042] FIG. 7 shows the outer shape of the inlay 11 having a rectangular shape as a whole and a 2-cell configuration and its equivalent circuit. The inlay 11 has a pair of feeding parts F1, F2, and an IC chip CH (shown by a virtual line in the enlarged view of FIG. 7) is arranged on the pair of feeding parts F1, F2. Interdigital capacitors C L are respectively connected to each feeding part, and a linear inductor L L is connected in series to the capacitor C R . As shown in the equivalent circuit, the inlay 11 is configured to include a series resonance circuit type metamaterial antenna. In the inlay 11, the dimensions of each part can be set as appropriate, but the antenna width L1 is 5.7 mm, the antenna length L2 is 48 mm, and the interdigital capacitor C RThe simulation results when the line width t3 is 0.3 mm and the gap width t4 is 0.5 mm are shown in FIG. 8. Also in this example, as in the case of FIG. 6, the communication distance is ensured in the direction B, and it is confirmed that it is omnidirectional. Also, although not shown, when the antenna width L1 was further reduced (5.7 mm → 2.6 mm), it was confirmed that the communication distance in each direction became shorter, but the omnidirectionality was maintained.
[0043] FIG. 9 is square as a whole and shows the outer shape of the inlay 12 having a two-cell configuration and its equivalent circuit. Although not shown, for the inlay 12 as well, the IC chip CH is arranged in a pair of power supply parts in the same manner as the inlay 11. An interdigital capacitor C L is connected to each power supply part. As shown in the equivalent circuit, the inlay 12 is configured to include a series resonance circuit type metamaterial antenna. In the inlay 12, setting the current path so as to be square as a whole is a major difference in the antenna configuration when compared with the inlay 11 of FIG. 7.
[0044] In the inlay 12, the dimensions of each part can be set as appropriate, but when the antenna width L1 is 22 mm, the antenna length L2 is 22 mm, the line width t3 of the interdigital capacitor C L is 0.3 mm, and the gap width t4 is 0.3 mm, the simulation results are shown in FIG. 10. As shown in FIG. 10, by extending the antenna width L1, that is, the length in the y direction of the loop part of the antenna, it can be seen that the communication distance in the direction B is greatly improved in the inlay 11 compared with the case of the inlay 10 (FIG. 8). From this, it is considered that the radio wave radiated from the conductor pattern extending along the y direction contributes to the extension of the communication distance in the direction B.
[0045] Referring again to FIG. 9 in relation to this point, in the inlay 12, two capacitors C LA capacitor section including [it] is arranged along the x direction (an example of the first direction) between nodes n1 and n2 at both ends. Also, in the inlay 12, between nodes n1 and n2, two capacitors C L A loop-shaped inductor L formed of a conductor pattern connected in series with [it] R has an inductor section including [it]. The inductor L R The conductor pattern in which [it] is formed extends from each of nodes n1 and n2 in the y direction (an example of the second direction) orthogonal to the x direction, and the length in the y direction of the conductor pattern (that is, the antenna width L1) is substantially the same as the distance between nodes n1 and n2 (that is, the antenna length L2). In FIG. 9, in the strip portion 121 extending in the y direction from node n1 and the strip portion 122 extending in the y direction from node n2, currents flow in opposite directions. However, since the strip portion 121 and the strip portion 122 are separated by the antenna length L2, the phases of the radio waves radiated in the direction B from the respective currents are shifted, so that the radio waves in the direction B can be prevented from canceling each other out. Note that in the inlay 12 shown in FIG. 9, the antenna width L1 and the antenna length L2 are substantially the same, but that is not the limit. The antenna width L1 may be longer than the antenna length L2. Thereby, since the strip portions extending from nodes n1 and n2 respectively become longer, it becomes possible to further extend the communication distance in the direction B. The loop-shaped inductor L shown in FIG. 9 R is constituted by a straight line, but the form of the inductor L R is not limited to that, and it may be circular or elliptical.
[0046] FIG. 11 is rectangular as a whole and shows the outer shape of the inlay 13 having a one-cell configuration and its equivalent circuit. In the inlay 13, the IC chip CH is arranged on a linear conductor pattern and powered. A pair of inductors L R are connected to each of a pair of power supply portions where the IC chip CH is arranged, and one interdigital capacitor C R is connected in series to each inductor L LIt is a circuit configuration of a series resonance circuit type that is connected. Although not shown, when the simulation results were confirmed with the inlay of this 1-cell configuration, it was confirmed that although the communication distance becomes shorter compared to the case of 2 cells or more, it functions as an antenna.
[0047] FIG. 12 is rectangular as a whole and shows the outer shape of the 4-cell inlay 14 and its equivalent circuit. In the inlay 14, an IC chip CH is arranged in a pair of power supply parts, and two interdigital capacitors C are provided in each power supply part L are connected in series. For the capacitor C L a linear inductor L R is connected in series. As shown in the equivalent circuit, the inlay 14 is configured to include a series resonance circuit type metamaterial antenna.
[0048] FIG. 13 is square as a whole and shows the outer shape of the 2-cell inlay 15 and its equivalent circuit. In the inlay 15, an IC chip CH (shown by a virtual line in the enlarged view of FIG. 13) is arranged in a pair of power supply parts F1, F2. A linear inductor L is connected to each power supply part R and two interdigital capacitors C are connected in series to each inductor L R . As shown in the equivalent circuit, the inlay 15 is configured to include a series resonance circuit type metamaterial antenna. The inlay 15 in FIG. 13 has the same square 2-cell configuration as the inlay 12 in FIG. 9, but is different from the inlay 12 powered by the capacitor in that it is powered by the inductor. L In the inlay 15, the dimensions of each part can be set as appropriate. However, the antenna width L1 is 20 mm, the antenna length L2 is 20 mm, and the interdigital capacitor C
[0049] In the inlay 15, the dimensions of each part can be set as appropriate. However, the antenna width L1 is 20 mm, the antenna length L2 is 20 mm, and the interdigital capacitor C LThe simulation results when the line width t3 is 0.3 mm and the gap width t4 is 0.3 mm are shown in FIG. 14. The characteristic property shown by the simulation results in FIG. 14 is that, although sufficient communication distances are ensured in directions B and C, the communication distance in direction A is short. That is, in the inlay 15, communication can be performed only within the plane of the antenna. To exhibit such properties, when the adherends each incorporating the inlay 15 are stacked, there is an effect of suppressing radio wave interference between the inlays in the direction in which the adherends are stacked.
[0050] FIG. 15 is rectangular as a whole and shows the outer shape of the inlay 16 having a two-cell configuration and its equivalent circuit. The inlay 16 has a pair of power supply parts F1 and F2, and an IC chip CH is arranged on the pair of power supply parts F1 and F2. An interdigital capacitor C L is connected to each power supply part, and a meander-shaped inductor L L is connected in series to the capacitor C R . As shown in the equivalent circuit, the inlay 16 is configured to include a series resonance circuit type metamaterial antenna. The inlay 16 shown in FIG. 15 has a configuration different from that of the inlay 11 shown in FIG. 7 in that the inductor L R is meander-shaped. By forming the inductor L R into a meander shape, the inductance can be increased as compared with the case of a straight line shape, so that the entire antenna can be miniaturized while ensuring a desired inductance. In FIG. 15, the higher the meander height Mh, the larger the inductance of the inductor L R .
[0051] FIG. 16 is square as a whole and shows the outer shape of the inlay 17 having a two-cell configuration and its equivalent circuit. In the inlay 17, power is supplied to the interdigital capacitor C L , and a loop-shaped inductor L L is connected in series to the interdigital capacitor C R .
[0052] In all of the above-described inlays 11 (FIG. 7), 12 (FIG. 9), 13 (FIG. 11), 14 (FIG. 12), 15 (FIG. 13), 16 (FIG. 15), and 17 (FIG. 16), the comb teeth forming the interdigital capacitor extend in the x direction, but this is not the only case. The interdigital capacitor can also be configured such that the comb teeth extend in the y direction. For example, in FIG. 17, an inlay 18 having a two-cell configuration in which the comb teeth of an interdigital capacitor C L extend in the y direction is disclosed. In the inlay 18, a linear inductor L L is provided in a direction orthogonal to the direction in which the comb teeth of the interdigital capacitor C R extend, but this is not the only case, and the inductor L R may be formed in a meandering shape.
[0053] In the above-described inlay 16 (FIG. 15), the case of having a meandering inductor L R that meanders in the y direction is shown, but this is not the only case. When forming an inductor with a meandering conductor pattern, the meandering direction can be arbitrarily set. For example, in FIG. 17, an inlay 19 having a meandering inductor L R that meanders in the x direction is disclosed. In the inlay 19, the comb teeth forming the interdigital capacitor C L extend in the x direction, but this is not the only case, and it may be configured such that the comb teeth extend in the y direction as in the inlay 18. The direction in which the comb teeth of the interdigital capacitor extend and the meandering direction of the inductor can be set independently.
[0054] In an inlay having a two-cell or more configuration, the directions in which the comb teeth of the plurality of interdigital capacitors extend do not have to be the same, and an inductor may be formed by a plurality of strip portions having different meandering directions when forming the inductor. For example, FIG. 18 shows the outer shape and its equivalent circuit of an inlay 20 having a two-cell configuration and having a square shape as a whole. In the inlay 20, a pair of interdigital capacitors C are connected to a pair of power supply parts where the IC chip CH is arranged. L However, the extending directions of the comb teeth of each interdigital capacitor C L are different (one is in the x direction and the other is in the y direction). An inductor L L is connected in series to the interdigital capacitor C. R This inductor L R includes a meander-shaped strip portion 131 and a meander-shaped strip portion 132, but the meandering directions of the strip portion 131 and the strip portion 132 are different.
[0055] In each of the above-described embodiments, the conductor pattern constituting the antenna included in the inlay is provided on one plane (for example, the surface side of the substrate on which the inlay is mounted). However, it is not limited thereto, and conductor patterns may be arranged on both the surface side and the back side of the substrate on which the inlay is mounted to constitute an antenna. Thereby, a small antenna with excellent space efficiency can be formed by using both the surface side and the back side of the substrate. When incorporating an inlay into a label having a plurality of layers laminated on a substrate, "arranging a conductor pattern on the surface side of the substrate" does not mean that the conductor pattern is formed on the surface of the substrate, but may be formed on any layer on the surface side of the substrate. Similarly, "arranging a conductor pattern on the back side of the substrate" does not mean that the conductor pattern is formed on the back surface of the substrate, but may be formed on any layer on the back side of the substrate.
[0056] As an example, FIG. 19 shows the outer shape (perspective view) of an inlay 21 having a two-cell configuration including an antenna in which conductor patterns are arranged on the surface side and the back side of a substrate (not shown) and its equivalent circuit. In the inlay 21, on the surface side of the substrate, a pair of power supply parts F1, F2 where the IC chip CH is arranged and a pair of interdigital capacitors C L connected to each power supply part are arranged, and on the back side of the substrate, a meander-shaped inductor L Ris arranged. The conductor patterns on the front side and the back side are connected via a pair of vias 211 and 212 that penetrate the base material, and together they form a series resonance circuit. The inlay 21 forms an inductor L with a meandering conductor pattern, R but a linear inductor may be formed instead.
[0057] In a series resonance circuit type metamaterial antenna, the capacitor does not necessarily have to be constituted by an interdigital capacitor. For each of one or more capacitors, a pair of opposing conductor patterns may be formed on the front side and the back side of the base material on which the inlay is mounted, respectively. Thereby, a capacitor can be constituted using the thickness of the base material.
[0058] Fig. 20 shows an example of the outer shape (perspective view) of an inlay provided with a parallel plate capacitor formed by conductor patterns on the front side and the back side of a base material. Fig. 20 shows an inlay 22 in the case where vias are provided to connect the conductor pattern formed on the front side of a substrate (not shown) and the conductor pattern formed on the back side of the substrate (with vias), and an inlay 23 in the case where no vias are provided (without vias), but the equivalent circuits of both are the same.
[0059] In the inlay 22, on the front side of the base material, a pair of power supply parts F1 and F2 where an IC chip CH is arranged, plate-like patterns 101 and 103 which are conductor patterns integrally formed with each power supply part, and a linear strip part 105 R constituting the inductor L are arranged. In the inlay 22, on the back side of the base material, plate-like patterns 102 and 104 formed by conductor patterns are arranged. The strip part 105 and the plate-like patterns 102 and 104 are connected via vias 106 and 107 that penetrate the base material, respectively. In the inlay 22, a parallel plate capacitor C L is constituted by the plate-like pattern 101 and the plate-like pattern 102, and a parallel plate capacitor C LSince it is configured, as shown in the equivalent circuit, it forms a series resonance circuit as a whole. When the plate-shaped patterns constituting each capacitor are formed on the front and back surfaces of the base material, the capacitance of each capacitor is determined by the area of the plate-shaped pattern, the thickness of the base material, and the dielectric constant.
[0060] The inlay 23 is different from the inlay 22 in that the linear strip portion constituting the inductor L R is provided on the back surface side of the base material (not shown). In the inlay 23, a plate-shaped pattern 102a and a plate-shaped pattern 104a are provided on the back surface side of the base material, and the linear strip portion 108 constituting the inductor L R is provided so as to connect the two.
[0061] (II) Inlay including a parallel resonance circuit type metamaterial antenna Next, some embodiments of an inlay including a parallel resonance circuit type metamaterial antenna will be described with reference to FIGS. 21 to 28. This metamaterial antenna is configured such that a parallel circuit is formed by a capacitor portion, an inductor portion, a pair of feeding portions, and an IC chip, and this parallel circuit resonates at a predetermined resonance frequency. In one embodiment, the resonance frequency is a frequency included in the UHF band (860 to 960 MHz).
[0062] FIG. 21 shows the outer shape and the equivalent circuit of an inlay 24 having a rectangular shape as a whole and a two-cell configuration. The inlay 24 has a pair of feeding portions, and an IC chip CH is arranged on the pair of feeding portions. Each feeding portion is connected in parallel with two interdigital capacitors C R and a linear inductor L L Therefore, as shown in the equivalent circuit, the inlay 24 is configured to include a parallel resonance circuit type metamaterial antenna. In the inlay 24, the dimensions of each part can be set as appropriate. However, the antenna width L1 is 6.9 mm, the antenna length L2 is 56 mm, and the interdigital capacitor C RThe simulation results when the line width t3 is 0.3 mm and the gap width t4 is 0.3 mm are shown in FIG. 22. As shown in FIG. 22, it was confirmed that the inlay 24 including the parallel resonance circuit type antenna also has omnidirectionality rather than a null in the direction B.
[0063] FIG. 23 shows the outer shape of the inlay 25 and its equivalent circuit. The inlay 25 is the same as the inlay 24 (FIG. 21) in terms of the basic antenna form, but is different from the inlay 24 in that it is square as a whole. In the inlay 25, a capacitor part including two capacitors C R is arranged along the x direction (an example of the first direction) between the nodes n1 and n2 at both ends. Also, in the inlay 25, a loop-shaped inductor L R formed by a conductor pattern connected to one end of each of the two capacitors C L is included. The conductor pattern in which the inductor L L is formed extends in the y direction (an example of the second direction) orthogonal to the x direction from each of the nodes n1 and n2, and the length in the y direction of the conductor pattern (that is, the antenna width L1) is substantially the same as the distance between the nodes n1 and n2 (that is, the antenna length L2). In FIG. 23, in the strip portion 251 extending in the y direction from the node n1 and the strip portion 252 extending in the y direction from the node n2, currents flow in opposite directions, but since the strip portion 251 and the strip portion 252 are separated by the antenna length L2, the phases of the radio waves radiated in the direction B from the respective currents are shifted, so that the radio waves in the direction B can be prevented from being canceled out. In the inlay 25 shown in FIG. 23, the antenna width L1 and the antenna length L2 are substantially the same, but it is not limited to this, and the antenna width L1 may be longer than the antenna length L2. Thereby, since the strip portions extending from the nodes n1 and n2 respectively become longer, it becomes possible to further extend the communication distance in the direction B. The loop-shaped inductor L L shown in FIG. 23 is composed of straight lines, but the inductor L RThe form is not limited thereto, and it may be circular or elliptical.
[0064] In the inlay 25, the dimensions of each part can be set as appropriate. However, when the antenna width L1 is 30 mm, the antenna length L2 is 30 mm, the line width t3 of the interdigital capacitor C R is 0.3 mm, and the gap width t4 is 0.3 mm, the simulation results are shown in FIG. 24. As shown in FIG. 24, in the inlay 25, by extending the antenna width L1, that is, the length in the y direction of the loop portion of the antenna, it can be seen that the communication distance in the direction B is greatly improved compared with the case of the inlay 24 (FIG. 22). Similar to the case of the series resonance circuit type, it is considered that the radio wave radiated from the conductor pattern extending along the y direction contributes to the extension of the communication distance in the direction B.
[0065] FIG. 25 is rectangular as a whole and shows the outer shape of the inlay 26 having a 1-cell configuration and its equivalent circuit. In the inlay 26, the IC chip CH is arranged on the linear conductor pattern and is powered. As seen from the IC chip CH, one interdigital capacitor C R and the linear inductor L L are connected in parallel. When the simulation results were confirmed for this inlay with a 1-cell configuration, although the communication distance was shorter compared with the case of 2 cells or more, it was confirmed that it functions as an antenna.
[0066] FIG. 26 is rectangular as a whole and shows the outer shape of the inlay 27 having a 2-cell configuration and its equivalent circuit. In the inlay 27, the IC chip CH is arranged on the linear conductor pattern and is powered. As seen from the IC chip CH, two interdigital capacitors C R and the meander-shaped inductor L L are connected in parallel. By making the inductor L L meander-shaped, the inductance can be increased compared with the linear case, so that the entire antenna can be miniaturized while ensuring the desired inductance. Although not shown, in the parallel resonance circuit type metamaterial antenna, as illustrated in FIG. 17, the interdigital capacitor may be configured such that the comb teeth extend in the y direction, or the meander-shaped inductor may be configured to meander in the x direction.
[0067] Conductor patterns can be arranged on both the front and back sides of the substrate on which the inlay is mounted to form a parallel resonance circuit type metamaterial antenna. Thereby, a small antenna with excellent space efficiency can be formed using both sides of the substrate. As an example, FIG. 27 shows the outer shape (perspective view) and the equivalent circuit of an inlay 28 with a two-cell configuration including an antenna in which conductor patterns are arranged on the front and back sides of a substrate (not shown). In the inlay 28, on the front side of the substrate, a pair of linear conductor patterns 281 and 282 on which an IC chip CH is arranged, and two interdigital capacitors C R are arranged. On the back side of the substrate, a meander-shaped inductor L L is arranged. The conductor patterns on the front and back sides are connected via a pair of vias 283 and 284 that penetrate the substrate, whereby the two interdigital capacitors C R and the inductor L L are connected in parallel. The inlay 28 forms the inductor L R with a meander-shaped conductor pattern, but a linear inductor may be formed instead.
[0068] FIG. 28 shows an inlay 29 including a parallel plate capacitor formed by conductor patterns formed on the front and back sides of a substrate and its equivalent circuit. In the inlay 29, on the front side of the substrate, a pair of power supply parts F1 and F2 on which an IC chip CH is arranged, plate-shaped patterns 201 and 203 that are conductor patterns integrally formed with each power supply part, and an inductor L LA linear strip portion 205 that constitutes [the relevant component] is disposed. The strip portion 205 is connected to the plate-shaped pattern 201 and the plate-shaped pattern 203. In the inlay 29, plate-shaped patterns 202 and 204 formed by conductor patterns are disposed on the back surface side of the base material. In the inlay 29, a parallel-plate capacitor C is formed by the plate-shaped pattern 201 and the plate-shaped pattern 202. R is formed, and a parallel-plate capacitor C is formed by the plate-shaped pattern 203 and the plate-shaped pattern 204. R is formed. The inductor L L The strip portion 205 that constitutes [the inductor L] is connected in parallel to the parallel-plate capacitor C. R Therefore, as shown in the equivalent circuit, a parallel resonance circuit is constituted as a whole. When the plate-shaped patterns that constitute each capacitor are formed on the front and back surfaces of the base material, the capacitance of each capacitor is determined by the area of the plate-shaped pattern, the thickness of the base material, and the dielectric constant.
[0069] As described above, various embodiments of the inlay including the series resonance circuit type and parallel resonance circuit type metamaterial antennas have been described. However, the outer shape of the inlay is not limited to the rectangular shape or square shape described above, and can take various forms. As an example, FIG. 29 shows an inlay provided with an antenna having a circular outer shape and an antenna having a triangular shape. In FIG. 29, the inlay 30 includes a series resonance circuit type metamaterial antenna having a circular two-cell configuration. The inlay 31 includes a series resonance circuit type metamaterial antenna having a triangular two-cell configuration. The inlay 32 includes a parallel resonance circuit type metamaterial antenna having a circular two-cell configuration. The inlay 33 includes a parallel resonance circuit type metamaterial antenna having a triangular two-cell configuration. In addition, the outer shape of the inlay can take any polygonal shape.
[0070] As described above, the inlays of some embodiments include a series resonance circuit type metamaterial antenna in which a capacitor section, an inductor section, a pair of power feeding sections, and an IC chip form a single series circuit, and this single series circuit is configured to resonate at a predetermined frequency. Therefore, compared with the case of configuring two series circuits as in the inlay of the reference example (FIG. 3) to resonate at the same frequency, the inductor can function effectively and the entire inlay can be miniaturized. Furthermore, in the configuration of the inlay of the reference example, due to having two series circuits, the radio waves cancel each other out and the radiation characteristics become null in a specific direction, but by adopting the configuration of a single series circuit, the radiation characteristics can be made omnidirectional. As illustrated in FIG. 13, the radiation characteristics can also be set so that the communication distance in a specific direction is extended by appropriately setting the path through which the current flows. Also, the inlays of some embodiments include a parallel resonance circuit type metamaterial antenna in which a capacitor section, an inductor section, a pair of power feeding sections, and an IC chip form a parallel circuit, and this parallel circuit is configured to resonate at a predetermined frequency.
[0071] As described above, various embodiments of the RFID inlay of the present invention have been described, but the present invention is not limited to the above embodiments. Also, within the scope not departing from the gist of the present invention, various improvements, modifications, and combinations of individual technical elements included in the embodiments are possible. For example, it is also possible to configure the series resonance circuit type or parallel resonance circuit type metamaterial antenna to resonate at a frequency in the microwave band (2.45 GHz or higher).
Explanation of Reference Numerals
[0072] IL, 10 to 33... Inlay 101, 102, 102a, 103, 104, 104a, 201, 202, 203, 204... Plate-like pattern 106, 107, 211, 212, 283, 284... Via 105, 108, 121, 122, 131, 132, 205, 251, 252... Strip section 281, 282… conductor patterns L R , L L … inductor C L , C R … capacitor CH… IC chip F1, F2… power supply section N1, N2, n1, n2… nodes
Claims
1. An RFID inlay disposed on a substrate and operating by receiving radio waves in a predetermined frequency band from a reader, comprising: a capacitor portion formed on the substrate with a predetermined conductor pattern; an inductor portion formed on the substrate with a predetermined conductor pattern; a pair of power supply portions; an IC chip connected to the pair of power supply portions; wherein a single series circuit is formed by the capacitor portion, the inductor portion, the pair of power supply portions, and the IC chip, and the single series circuit is configured to resonate at a predetermined frequency included in the frequency band. The RFID inlay.
2. An RFID inlay disposed on a substrate and operating by receiving radio waves in a predetermined frequency band from a reader, comprising: a capacitor portion formed on the substrate with a predetermined conductor pattern; an inductor portion formed on the substrate with a predetermined conductor pattern; a pair of power supply portions; an IC chip connected to the pair of power supply portions; wherein a parallel circuit is formed by the capacitor portion, the inductor portion, the pair of power supply portions, and the IC chip, and the parallel circuit is configured to resonate at a predetermined frequency included in the frequency band. The RFID inlay.
3. The capacitor portion is formed of one or more interdigital capacitors. The RFID inlay according to claim 1 or 2.
4. The capacitor portion includes one or more capacitors in which a pair of opposing conductor patterns are formed on the front surface side and the back surface side of the substrate, respectively. The RFID inlay according to claim 1 or 2.
5. The inductor portion is formed of a linear or meandering conductor pattern. The RFID inlay according to claim 1 or 2.
6. The capacitor portion has one or more capacitors arranged along a first direction between a first node and a second node, the inductor portion is formed of a conductor pattern connecting the first node and the second node, the conductor pattern forming the inductor portion extends in a second direction orthogonal to the first direction from each of the first node and the second node, and a length of the conductor pattern in the second direction is substantially the same as or longer than a distance between the first node and the second node. The RFID inlay according to claim 1 or 2.
7. The capacitor portion is formed on one of the front surface side or the back surface side of the substrate, and the inductor portion is formed on the other of the front surface side or the back surface side of the substrate. The RFID inlay according to claim 1 or 2.
8. The frequency band is 860 to 960 MHz. The RFID inlay according to claim 1 or 2.