RFID tag

Abstract

An RFID tag according to the present disclosure includes: a substrate; a first surface-type conductor that is provided on one surface of the substrate; an IC chip connected to the first surface-type conductor; a second surface-type conductor that is provided on the other surface of the first surface-type conductor and spaced apart from and facing the first surface-type conductor; an inverted-F antenna having a conductive portion that penetrates the substrate and connects the first surface-type conductor and the second surface-type conductor, and a planar parasitic element that is provided in the same plane as that of the second surface-type conductor and spaced apart therefrom, and at least one side of the second surface-type conductor and one side of the parasitic element are arranged so as to be able to be electromagnetically coupled to each other.

Description

RFID tag

[0001] The present disclosure relates to RFID tags.

[0002] 2. Description of the Related Art RFID (Radio-Frequency Identification) tags are known that are attached to products and used to manage product information.

[0003] As a technology relating to RFID tags, for example, it is known that by employing an inverted F antenna, communication is possible in accordance with a plurality of frequency bands defined by each country (Patent Document 1).

[0004] Patent No. 4990858

[0005] For example, when an RFID tag is attached to a product for use, it is required to be manufactured with a size and thickness suitable for attachment. In other words, it is desirable for the RFID tag to have a structure that provides sufficient communication distance performance regardless of the manufacturing method or usage method.

[0006] Therefore, the present disclosure proposes an RFID tag that improves the communication distance of RFID.

[0007] In order to solve the above-mentioned problems, the RFID tag of the present disclosure is characterized in that it comprises a substrate, a first surface-type conductor provided on one side of the substrate, an IC chip connected to the first surface-type conductor, a second surface-type conductor provided on the other side of the first surface-type conductor and facing the first surface-type conductor at a distance, an inverted-F antenna having a conductive portion that penetrates the substrate and connects the first surface-type conductor and the second surface-type conductor, and a planar parasitic element provided at a distance on the same plane as the second surface-type conductor, and is arranged so that at least one side of the second surface-type conductor and one side of the parasitic element can be electromagnetically coupled.

[0008] According to one aspect of the embodiment, an RFID tag that improves the communication distance of the RFID tag can be provided.

[0009] 1 is a perspective view of an RFID tag according to an embodiment; FIG. 2 is a schematic perspective view of an RFID tag according to an embodiment; FIG. 3 is a diagram illustrating an example of a configuration according to an embodiment of an RFID tag; FIG. 4 is a diagram illustrating an example of an RFID tag in which an RFID tag is covered with an exterior material and a protective member is attached; FIG. 5 is a diagram illustrating an example of an exterior view of an RFID tag according to an embodiment; FIG. 6 is a perspective view of an inverted-F antenna and a parasitic element; FIG. 7 is a diagram illustrating an example comparing an RFID tag provided with a parasitic element and an RFID configured with an inverted-F antenna; FIG. 8 is a diagram illustrating an example showing the frequency characteristics of the communication distance in the opposing direction in an RFID tag; FIG. 9 is a diagram illustrating an example of the current path length of an RFID tag; FIG. 10 is a graph illustrating the relationship between gain and frequency when the element length of the parasitic element is changed; FIG. 11 is a diagram illustrating the directivity of an inverted-F antenna; FIG. 12 is a diagram illustrating an example of current flow in an inverted-F antenna and a parasitic element; FIG. 13 is a diagram illustrating an example of a current path of a parasitic element; FIG. 14 is a graph illustrating resonant frequencies; FIG. 15 is a diagram illustrating an example of the arrangement of parasitic elements relative to an inverted-F antenna; FIG. 16 is a diagram illustrating an example in which a recess is formed toward the inside of a substrate; and FIG. 17 is a diagram illustrating an example in which wire-shaped antennas of various shapes are arranged instead of parasitic elements.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following embodiments, the same components are designated by the same reference numerals, and redundant description will be omitted.

[0011] (1. Introduction) An inverted-F antenna included in an RFID tag typically has a flat radiating conductor on one side of a substrate, a flat ground conductor on the other side of the radiating conductor, and a through-hole as a short-circuiting conductor for connecting the radiating conductor and the ground conductor. The communication distance of an inverted-F antenna can be improved by extending the through-hole in a direction increasing the distance between the radiating conductor and the ground conductor. The communication distance of an inverted-F antenna can also be improved by increasing the size of the radiating conductor and increasing the area that contributes to radiation.

[0012] However, improving the communication distance of an inverted-F antenna using the above-described method results in an increase in size. For example, if the through-hole portion of an inverted-F antenna is extended in a direction increasing the distance between the radiating conductor and the ground conductor, the antenna's thickness increases to the extent that the through-hole is extended. Increasing the thickness of an inverted-F antenna increases the thickness of the RFID tag's substrate. There is a concern that increasing the RFID tag's substrate thickness increases manufacturing costs. Furthermore, an RFID tag with a thicker inverted-F antenna may protrude when attached to an object with the ground side facing the object. Increasing the area of ​​the radiating conductor makes it difficult to adjust the frequency and gain of the inverted-F antenna. Therefore, the present disclosure proposes an RFID tag that improves the communication distance of the RFID tag while suppressing its size increase.

[0013] In this disclosure, an RFID tag having an operating frequency of 920 MHz will be described as an example. Also, in this disclosure, an RFID tag attached to a metal or the like will be described as an example of an object. Note that in this disclosure, the operating frequency and the object are not limited to the above examples.

[0014] 2. Embodiment Fig. 1 is a perspective view showing the appearance of an embodiment of an RFID tag. As shown in Fig. 1, the RFID tag 1 has a substrate 11, an inverted F antenna 12, a parasitic element 13, and an IC chip (see IC chip 18 in Fig. 2).

[0015] Fig. 2 is a schematic perspective view showing an embodiment of the RFID tag 1. As shown in Fig. 2, the substrate 11 has a rectangular outer shape. The substrate 11 has a first plate surface 11a that faces the surface of the object to which the RFID tag 1 is attached, and a second plate surface 11b that is located on the opposite side of the first plate surface 11a and on which the parasitic element 13 is disposed. The substrate 11 is electrically insulating. For example, the substrate 11 is a substrate such as an FR-4 substrate, which is made by impregnating glass fiber with epoxy resin or the like and subjecting it to a heat curing process.

[0016] The inverted-F antenna 12 has a first surface-type conductor 14, a second surface-type conductor 15, and a conductive portion forming a short-circuit line 16 and a feeder line 17. The inverted-F antenna 12 has the first surface-type conductor 14 provided on one surface of the substrate 11, the second surface-type conductor 15 provided on the other surface of the first surface-type conductor 14 and facing the first surface-type conductor 14 with a gap between them, and a conductive portion that penetrates the substrate 11 and connects the first surface-type conductor 14 and the second surface-type conductor 15.

[0017] The first planar conductor 14 is made of a conductor having a rectangular outer shape and is disposed on the first plate surface 11a of the substrate 11 with its long sides aligned along the longitudinal direction of the substrate 11. For example, the first planar conductor 14 may function as a ground conductor. The first planar conductor 14 is electrically connected to the first connection portion 18a and the second connection portion 18b of the IC chip 18.

[0018] The second surface conductor 15 is made of a conductor having a rectangular outer shape and is arranged on the second plate surface 11b of the substrate 11 so that its long sides are aligned along the longitudinal direction of the substrate 11. The second surface conductor 15 functions as a radiation conductor in the present disclosure. The first surface conductor 14 and the second surface conductor 15 are arranged opposite each other with a gap between them via the substrate 11.

[0019] The short-circuiting line 16 penetrates the substrate 11 in the thickness direction and electrically connects the first plane-type conductor 14 and the second plane-type conductor 15. The power supply line 17 penetrates the substrate 11 in the thickness direction and electrically connects the first plane-type conductor 14 and the second plane-type conductor 15.

[0020] The parasitic element 13 is an element that is not fed with power. The parasitic element 13 is planar. The parasitic element 13 is spaced apart on the same plane of the second planar conductor 15. The parasitic element 13 is disposed on the second plate surface 11b. For example, the parasitic element 13 has a U-shaped cutout formed therein, and the cutout is formed so that one of the three sides of the second planar conductor 15 is adjacent to one side of the parasitic element 13, and one side of the second planar conductor 15 is an open portion.

[0021] For example, the parasitic element 13 is configured to have an element length that resonates at the operating frequency of the inverted F antenna 12 .

[0022] The RFID tag 1 is arranged so that at least one side of the second plane-type conductor 15 and one side of the parasitic element 13 can be electromagnetically coupled. For example, the RFID tag 1 is held by a substrate 11 or the like so that at least one side of the second plane-type conductor 15 and one side of the parasitic element 13 can be electromagnetically coupled.

[0023] The IC chip 18 is disposed on the first surface 11a of the substrate 11. The IC chip 18 is connected to the first surface conductor 14. For example, the IC chip 18 may have a temperature sensor. Note that the IC chip 18 may be disposed on a surface other than the first surface 11a of the substrate 11.

[0024] Furthermore, the RFID tag 1 may have either or both of an exterior material 21 that covers the substrate 11 and a protective member 31 that bonds the first surface conductor 14 side of the substrate 11 to the target object.

[0025] FIG. 3 is a diagram showing an example of the configuration of an RFID tag 1 according to an embodiment. FIG. 3 is a diagram showing an RFID tag 10 (hereinafter also referred to as RFID tag 10) configured by adding an exterior material 21 and a protective member 31 to the RFID tag 1 shown in FIG. 1 . Note that FIG. 3 omits, for example, the first connecting portion 18a and the second connecting portion 18b. The exterior material 21 has a rectangular outer shape. For example, the exterior material 21 is made of polypropylene or polyphenylene sulfide. When the first surface conductor 14 side of the substrate 11 is attached to an object via the exterior material 21, the IC chip 18 is separated from the object by the exterior material 21.

[0026] The protective member 31 is disposed on a surface facing the first plate surface 11a and facing the object to which the RFID tag 10 is to be attached. The protective member 31 is, for example, double-sided tape. The protective member 31 is used to bond the RFID tag 10 to the object to which the RFID tag 10 is to be attached. When the first surface conductor 14 side of the substrate 11 is attached to the object across the protective member 31, the IC chip 18 is separated from the object by the protective member 31.

[0027] Fig. 4 is a diagram showing an example of an RFID tag 10 in which the RFID tag 1 is covered with an exterior material 21 and a protective member 31 is attached. Note that Fig. 4 omits, for example, the first connecting portion 18a and the second connecting portion 18b. As shown in Fig. 4, the substrate 11 is covered with the exterior material 21. The protective member 31 is disposed on a surface facing the first plate surface 11a and facing an object to which the RFID tag 10 is attached.

[0028] FIG. 5 is a diagram showing an example of the appearance of an RFID tag 10 according to an embodiment. FIG. 5 shows an example of an RFID tag 10 in which the RFID tag 1 is covered with an exterior material 21 and a protective member 31 is attached. Note that some reference numerals are omitted in FIG. 5 . FIG. 5(A) is a plan view of the appearance of the RFID tag 10 according to an embodiment. For example, as shown in FIG. 5(A), the exterior material 21 may have holes at both ends for fastening the RFID tag 10 to an object. FIG. 5(B) is a side view of the appearance of the RFID tag 10 according to an embodiment, viewed from the longitudinal direction. FIG. 5(C) is a side view of the appearance of the RFID tag 10 according to an embodiment, viewed from the lateral direction. For example, the protective member 31 may be adhered to the object.

[0029] 6 is a perspective view showing the inverted-F antenna 12 and the parasitic element 13. As shown in FIG. 6, the inverted-F antenna 12 has a first surface-type conductor 14, a second surface-type conductor 15, a short-circuiting line 16, a feeder line 17, an IC chip 18, a first connecting portion 18a, and a second connecting portion 18b. The inverted-F antenna 12 and the parasitic element 13 are arranged so as to be electromagnetically coupled and to have a gap therebetween (see the left diagram of the RFID tag 50a in FIG. 7). In other words, the inverted-F antenna 12 and the parasitic element 13 are connected in terms of the electromagnetic field but not in terms of the current path length.

[0030] In the following explanation, an RFID tag 50a composed of the above-mentioned inverted F antenna 12 and parasitic element 13, an RFID tag 50b having only the inverted F antenna 12, and an RFID tag 50c in which the area of ​​the second surface conductor of the inverted F antenna 12 is enlarged will be compared.

[0031] FIG. 7 is a diagram illustrating an example comparing an RFID tag provided with a parasitic element and an RFID tag configured with an inverted-F antenna 12. Note that in FIG. 7, the IC chip 18 and other components are omitted as appropriate. As shown in FIG. 7, RFID tag 50a is an RFID tag configured without installing parasitic element 13 or enlarging the area of ​​second-surface conductor 15 (hereinafter also referred to as RFID tag 50a). That is, it is an RFID tag configured without installing parasitic element 13 from RFID tag 50b described below. RFID tag 50b is an RFID tag configured with an inverted-F antenna 12 and parasitic element 13 (hereinafter also referred to as RFID tag 50b). That is, RFID tag 50b has a shape in which parasitic element 13 is installed in RFID tag 50a. RFID tag 50c is an RFID tag configured with an enlarged area of ​​second-surface conductor 15c of inverted-F antenna 12 (hereinafter also referred to as RFID tag 50c). That is, the RFID tag 50 c is an RFID tag in which the area of ​​the second surface conductor 15 c of the RFID tag 50 b is enlarged in the long side direction of the substrate 11 .

[0032] The left view of RFID tag 50a, the left view of RFID tag 50b, and the left view of RFID tag 50c shown in Fig. 7 are top views showing examples of RFID tags covered with exterior material 21. The center view of RFID tag 50a and the center view of RFID tag 50c shown in Fig. 7 are perspective views showing examples of inverted F antenna 12. The center view of RFID tag 50b shown in Fig. 7 is a perspective view showing examples of inverted F antenna 12 and parasitic element 13. The right view of RFID tag 50a, the right view of RFID tag 50b, and the right view of RFID tag 50c shown in Fig. 7 are perspective views showing examples of RFID tags covered with exterior material 21.

[0033] For example, the dimensions of the RFID tag shown in Figure 7 are "58.5 mm x 14 mm" in the "longitudinal direction 51a of the RFID tag (excluding the exterior material) x "shortitudinal direction 51b of the RFID tag (excluding the exterior material)." The "longitudinal direction 51c of the inverted-F antenna 12 x shortitudinal direction 51d of the inverted-F antenna 12" of RFID tag 50a and RFID tag 50b are "22 mm x 8 mm." Furthermore, the "gap 51e between the inverted-F antenna 12 and the parasitic element 13" of RFID tag 50b is "0.5 mm." Furthermore, the "thickness 51f of the substrate 11" is "3.2 mm."

[0034] FIG. 8 is a diagram illustrating an example of the frequency characteristics of the communication distance in the facing direction of an RFID tag. As shown in FIG. 8, the peak value of the facing communication distance between RFID tag 50b and RFID tag 50c is approximately 4 m. The peak value of the facing communication distance for RFID tag 50a is approximately 3 m. Therefore, the facing communication distances for RFID tag 50b and RFID tag 50c are approximately 1.4 times greater than the facing communication distance for RFID tag 50a. By disposing a parasitic element or enlarging the second-surface conductor, the RFID tag increases the current density and the electric field, thereby extending the communication distance. The peak value of the communication distance is the resonant frequency.

[0035] The resonant frequency of an RFID tag shifts to a lower frequency when a booster antenna is installed. For example, the resonant frequency of an RFID tag shifts to a lower frequency when a parasitic element is installed or the area of ​​the second-surface conductor is increased. For example, in this disclosure, the operating frequency of the RFID tag is set to 920 MHz. The frequency of RFID tag 50a reaches a peak value of the communication distance at approximately 920 MHz. The frequency of RFID tag 50b reaches a peak value of the communication distance at approximately 900 MHz, which is shifted approximately 20 MHz lower than that of RFID tag 50a. Furthermore, the frequency of RFID tag 50c reaches a peak value of the communication distance at approximately 880 MHz, which is shifted approximately 40 MHz lower than that of RFID tag 50a. Therefore, RFID tag 50b has a smaller frequency deviation than RFID tag 50c, making it easier to adjust the impedance.

[0036] FIG. 9 is a diagram showing an example of the current path length of an RFID tag. RFID tag 50a is a side view of the inverted-F antenna 12. RFID tag 50b is a side view of the inverted-F antenna 12 and the parasitic element 13. RFID tag 50c is a side view of the inverted-F antenna 12 in which the area of ​​the second surface conductor 15c of the inverted-F antenna 12 has been increased. As shown in FIG. 9 , the current path length 53b of the RFID tag 50b in FIG. 9 and the current path length 53c of the RFID tag 50c in FIG. 9 are shifted to a lower frequency side compared to the current path length 53a of the RFID tag 50a in FIG. 9 . However, in RFID tag 50b, the current path between the inverted-F antenna 12 and the parasitic element 13 is not connected. Therefore, the RFID tag 50b does not shift to a lower frequency side than the RFID tag 50c.

[0037] 10 is a graph illustrating the relationship between gain and frequency when the element length of the parasitic element 13 is changed. When the impedance of the inverted-F antenna 12 is matched, the communication distance increases as the gain increases. The gain is maximized at the frequency at which the parasitic element resonates. The resonant frequency is determined primarily by the element length and the effective relative dielectric constant, which is determined by the dielectric around the parasitic element.

[0038] As shown in FIG. 10 , the resonant frequency of RFID tag 50b is approximately 1.1 GHz. When the element length of parasitic element 13 is 73 mm, the resonant frequency of parasitic element 13 is approximately 0.9 GHz. When the element length of parasitic element 13 is 113 mm, the resonant frequency of parasitic element 13 is approximately 0.6 GHz. In other words, increasing the element length of parasitic element 13 shifts the frequency toward lower frequencies. On the other hand, the resonant frequency of RFID tag 50c is 1.5 GHz or higher. Therefore, the element length of RFID tag 50c must be longer than that of RFID tag 50b. Therefore, the element length of parasitic element 13 can be made shorter than that of RFID tag 50c to adjust the frequency. In other words, the RFID tag can be made smaller than RFID tag 50c. Note that increasing the element length of parasitic element 13 in an RFID tag can increase heat loss in the conductor and reduce gain.

[0039] FIG. 11 is a diagram illustrating the directivity of the inverted-F antenna 12. FIG. 11 shows the directivity of the inverted-F antenna 12. That is, the inverted-F antenna 12 has directivity such that the maximum distance is in the center of the front in both the XZ plane (solid line shown in FIG. 11 ) and the YZ plane (dashed line shown in FIG. 11 ). In other words, the RFID tag 1 having the inverted-F antenna 12 has directivity such that the maximum distance is in the direction of the second surface conductor 15, with the first surface conductor 14 as the reference. For example, radiation is not possible in the direction opposite the Z direction, due to the presence of an object such as metal. Note that the inverted-F antenna 12 is oriented in the direction of the second surface conductor 15, with the first surface conductor 14 as the reference. Furthermore, the longitudinal direction of the inverted-F antenna 12 is the X direction, and the lateral direction of the inverted-F antenna 12 is the Y direction.

[0040] Figure 12 is a diagram showing an example of current flow in the inverted-F antenna 12 and the parasitic element 13. As shown in Figure 12, the current density in the inverted-F antenna 12 and the parasitic element 13 increases as the color becomes lighter, and decreases as the color becomes darker. In other words, the current density in the inverted-F antenna 12 and the parasitic element 13 is maximum at the center and minimum at both ends. The element length of the parasitic element 13 is the length indicated by λe / 2.

[0041] The following describes a method for adjusting the frequency of the RFID tag 1 of the present disclosure. The frequency can be adjusted by narrowing or widening the distance between the conductive portion (through hole) formed by the short-circuit line 16 and the power supply line 17. The through hole has a high current density because it is located near the IC chip 18. Therefore, adjusting the distance between the through holes affects the length of the current path, and therefore the frequency can be adjusted. Specifically, narrowing the distance between the short-circuit line 16 and the power supply line 17 increases the frequency, while widening the distance between the short-circuit line 16 and the power supply line 17 decreases the frequency.

[0042] FIG. 13 is a diagram related to frequency adjustment. FIG. 13 is a diagram showing an example of the current path of the parasitic element 13. As shown in FIG. 13, in RFID tag 50b, the parasitic element 13 is separated from the current path 54a, so the amount of change in impedance is small when the tag is enlarged. On the other hand, in RFID tag 50c, the amount of change in impedance is large because the enlarged second surface-type conductor 15 is directly connected to the current path 54b. Comparing RFID tag 50b and RFID tag 50c, the amount of change in impedance of RFID tag 50b is small. A small amount of change in impedance makes adjustment easier. Therefore, RFID tag 50b is advantageous in frequency adjustment.

[0043] The following describes a method for adjusting the gain of an RFID tag according to the present disclosure. This disclosure describes a method for adjusting the gain at a resonant frequency. FIG. 14 is a graph showing resonant frequencies. As shown in FIG. 14, the resonant frequency of RFID tag 50b is approximately 1.1 GHz. On the other hand, the resonant frequency of RFID tag 50c is approximately 1.5 GHz. The peak value of the gain of RFID tag 50b is determined by the resonant frequency, which is adjusted by the element length of parasitic element 13. Comparing RFID tag 50b and RFID tag 50c, the resonant frequency of RFID tag 50b is on the lower frequency side. Therefore, it is easy to adjust the resonant frequency to the operating frequency of 920 MHz according to the present disclosure. Furthermore, the resonant frequency depends on the effective relative dielectric constant of substrate 11 and exterior material 21. The peak value of the gain of RFID tag 50c is determined by the resonant frequency, which is adjusted by the length of second surface conductor 15. However, since the resonant frequency of the second surface-type conductor 15c of the RFID tag 50c is 1.5 GHz, the second surface-type conductor must be made even longer to achieve a resonant frequency of 920 MHz. Therefore, the RFID tag 50b has an advantage in terms of gain adjustment.

[0044] 15 shows an example of the arrangement of the parasitic element relative to the inverted-F antenna 12. The shape of the parasitic element of the RFID tag 1 described above is U-shaped, but is not limited to this. For example, the parasitic element may have a shape described below.

[0045] As shown in Fig. 15(A), the parasitic element 13a may be rectangular. As shown in Fig. 15(B), the parasitic element 13b may be U-shaped as described above. As shown in Fig. 15(C), the parasitic element 13c may be square-shaped so as to surround the inverted-F antenna 12. As shown in Fig. 15(D), the parasitic element 13d may be meander-shaped.

[0046] When the frequency at which the parasitic element resonates and the resonant frequency of the inverted-F antenna 12 match, the communication distances of the shapes shown in Figures 15(A) to 15(D) increase in the following order: rectangular shape (Figure 15(A)), U-shaped shape (Figure 15(B)), square-shaped shape (Figure 15(C)), and meander shape (Figure 15(D)). That is, the rectangular shape (Figure 15(A)) has a longer communication distance than the other shapes. On the other hand, the longitudinal length 57a of the rectangular shape (Figure 15(A)) is longer than the longitudinal length 57b of the U-shaped shape (Figure 15(B)). Therefore, the U-shaped shape (Figure 15(B)) is advantageous in that it can be made smaller.

[0047] (3. Modification of the Embodiment) Next, an RFID tag according to a modification of the present disclosure will be described, focusing mainly on the differences from the RFID tag according to the above embodiment.

[0048] For example, a recess is formed on the surface of the first surface conductor 14 of the substrate 11 facing inward of the substrate 11, and the IC chip 18 is disposed inside the recess. That is, in the RFID tag 1, a recess is formed on the surface of the first plate surface 11a of the substrate 11 facing inward of the substrate 11, and the IC chip is disposed inside the recess.

[0049] FIG. 16 shows an example in which a recess is formed facing inward in the substrate 11. As shown in FIG. 16 , the RFID tag is created by combining two substrates 11. As shown in FIG. 16 (A), the RFID tag is created by bonding a substrate 11 having a first surface-type conductor 14 and a substrate 11 having a second surface-type conductor 15 to each other on the side opposite the side on which the first surface-type conductor 14 and the second surface-type conductor 15 are arranged (see FIG. 16 (B)). Next, the IC chip 18 is placed in the recess formed by combining the two substrates 11. The IC chip 18 may be sealed 32 with resin or the like. Then, the RFID tag may have the substrates with the recess formed and the inverted-F antenna 12 covered with an exterior material 21 (see FIG. 16 (C)).

[0050] For example, in the dimensions shown in FIG. 16 , the "thickness 61a of the substrate having the first surface conductor 14" and the "thickness 61b of the substrate having the second surface conductor 15" are each 1.54 mm, and when bonded together, the "thickness 61a of the substrate having the first surface conductor 14" and the "thickness 61b of the substrate having the second surface conductor 15" are approximately 3 mm (61d). Furthermore, the "surface 61e of the outer covering material 21 facing the first surface conductor 14" is 1.2 mm. The "surface 61f of the outer covering material 21 facing the second surface conductor 15" is 0.5 mm. The "thickness 61c of the outer covering material 21 and the substrate bonded together" is approximately 5 mm. In other words, an RFID tag having a recess formed facing inward in the substrate 11 can be formed with a substrate 11 that is approximately the same thickness as an RFID tag having no recess in the substrate 11.

[0051] Next, RFID tags according to other modifications will be described, focusing mainly on the differences from the RFID tags of the above-described embodiments. Specifically, examples of parasitic element shapes and wire-like antennas of various shapes arranged in place of the parasitic element will be described.

[0052] 17A and 17B are diagrams showing examples of arranging wire-shaped antennas in place of parasitic elements. Fig. 17 illustrates an example of arranging wire-shaped antennas in place of parasitic elements in an RFID tag composed of the inverted-F antenna 12 and parasitic elements described above in Fig. 15 and elsewhere. As shown in Fig. 17A, various wire-shaped antennas can be considered in place of parasitic elements, including a rectangular antenna 1300a (Fig. 17A), a U-shaped antenna 1300b (Fig. 17B), a square-shaped antenna 1300c (Fig. 17C), and a meander-shaped antenna 1300d (Fig. 17D).

[0053] (4. Effects of RFID Tag According to the Present Disclosure) As described above, according to the present embodiment, the RFID tag 1 is an RFID tag 1 having a substrate 11, a first surface-type conductor 14 provided on one surface of the substrate 11, an IC chip 18 connected to the first surface-type conductor 14, a second surface-type conductor 15 provided on the other surface of the first surface-type conductor 14 and facing the first surface-type conductor 14 at a distance, an inverted-F antenna 12 that penetrates the substrate 11 and has a conductive portion that connects the first surface-type conductor 14 and the second surface-type conductor 15, and a planar parasitic element 13 provided on the same plane as the second surface-type conductor 15 but spaced apart, and at least one side of the second surface-type conductor 15 and one side of the parasitic element 13 are arranged so as to be electromagnetically coupled to each other.

[0054] In this way, in the RFID tag according to the present disclosure, by arranging the parasitic element 13 on the same plane as the second surface-type conductor 15, when manufacturing the RFID tag according to the present disclosure, the distance between the second surface-type conductor 15 and the parasitic element 13 can be accurately manufactured. Furthermore, by arranging the parasitic element 13 on the same plane as the second surface-type conductor 15, when manufacturing the RFID tag according to the present disclosure, manufacturing is easier than with a wire antenna. By having the parasitic element 13, the RFID tag can easily adjust the frequency, gain, etc., thereby improving the communication distance. Therefore, an RFID tag that improves the communication distance of the RFID tag can be provided.

[0055] The parasitic element 13 has an element length that resonates at the operating frequency of the inverted F antenna 12 .

[0056] In this way, the RFID tag according to the present disclosure can improve the communication distance by causing the parasitic element 13 to resonate at the operating frequency of the inverted F antenna 12.

[0057] In addition, the parasitic element 13 has a U-shaped cutout formed therein, and the cutout is formed so that each of the three sides of the second surface conductor 15 is adjacent to one side of the parasitic element 13, and one side of the second surface conductor 15 is an open portion.

[0058] In this way, in the RFID tag according to the present disclosure, by making the parasitic element 13 U-shaped, the length of the long side of the RFID tag can be made shorter than when the parasitic element 13 is rectangular, etc. Therefore, the RFID tag 1 can be made smaller than when the parasitic element 13 is rectangular.

[0059] The IC chip 18 also has a temperature sensor.

[0060] In this way, the RFID tag 1 according to the present disclosure has an IC chip 18 equipped with a temperature sensor, thereby allowing the circuit board to be simplified.

[0061] Furthermore, a recess is formed on the surface of the first surface conductor 14 of the substrate 11 facing inward of the substrate 11, and the IC chip 18 is disposed inside the recess.

[0062] In this way, the RFID tag 1 according to the present disclosure can protect the IC chip 18 from impact when the RFID tag 1 is attached to an object because the IC chip 18 is not directly attached to the object. Furthermore, when the RFID tag 1 is attached to an object, the IC chip 18 having the temperature sensor is located on the object side, enabling accurate temperature measurement.

[0063] The substrate 11 also has an exterior material 21 that covers it, and when the first surface conductor 14 side of the substrate 11 is attached to an object across the exterior material 21, the IC chip 18 is separated from the object by the exterior material 21.

[0064] In this way, the RFID tag 1 according to the present disclosure has the exterior material 21, which can suppress deterioration of the RFID tag 1 and damage to the IC chip 18. Furthermore, the RFID tag 1 has the exterior material 21, which separates the IC chip 18 from the target object.

[0065] In addition, the substrate 11 has a protective member 31 that bonds the first surface conductor 14 side to the object, and when the first surface conductor 14 side of the substrate 11 is attached to the object across the protective member 31, the IC chip 18 is separated from the object by the protective member 31.

[0066] In this way, the RFID tag 1 according to the present disclosure has the protective member 31, which can suppress deterioration of the RFID tag 1 and damage to the IC chip 18. Furthermore, the RFID tag 1 has the protective member 31, which makes it easier to attach to an object, and the increased adhesion increases thermal conductivity, allowing for accurate temperature measurement.

[0067] The above-described embodiments and modifications can be combined as appropriate within the scope of not causing any contradiction in the processing content.

[0068] Furthermore, the effects described in this specification are merely examples and are not limiting, and other effects may also be present.

[0069] REFERENCE SIGNS LIST 1 RFID tag 11 Substrate 11a First plate surface 11b Second plate surface 12 Inverted F antenna 13 Parasitic element 14 First plane-type conductor 15 Second plane-type conductor 16 Short-circuit line 17 Power supply line 18 IC chip 18a First connection portion 18b Second connection portion 21 Sheath material 31 Protective member 32 Sealing

Claims

1. An RFID tag comprising: a substrate; a first plane conductor provided on one side of the substrate; an IC chip connected to the first plane conductor; a second plane conductor provided on the other side of the first plane conductor and facing the first plane conductor at a distance; an inverted-F antenna having a conductive portion that penetrates the substrate and connects the first plane conductor and the second plane conductor; and a planar parasitic element provided on the same plane as the second plane conductor but spaced apart, wherein at least one side of the second plane conductor and one side of the parasitic element are arranged so as to be electromagnetically coupled.

2. The RFID tag according to claim 1, characterized in that the parasitic element has an element length that resonates at the operating frequency of the inverted F antenna.

3. The RFID tag according to claim 1, characterized in that the parasitic element has a U-shaped cutout formed therein, the cutout being formed so that one of the three sides of the second surface conductor is adjacent to one side of the parasitic element, and one side of the second surface conductor is an open portion.

4. The RFID tag according to claim 1, wherein the IC chip has a temperature sensor.

5. The RFID tag according to claim 4, characterized in that a recess is formed on the surface of the first surface conductor of the substrate facing inward of the substrate, and the IC chip is positioned inside the recess.

6. The RFID tag according to claim 4, further comprising an exterior material covering the substrate, and when the first-surface conductor side of the substrate is attached to an object across the exterior material, the IC chip is separated from the object by the exterior material.

7. The RFID tag according to claim 4, further comprising a protective member that bonds the first surface conductor side of the substrate to the object, and when the first surface conductor side of the substrate is attached to the object across the protective member, the IC chip is separated from the object by the protective member.

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