RFID tags

Abstract

To provide an omnidirectional RFID tag for infrastructure monitoring that has a sensor function capable of acquiring temperature data, is water-resistant, insulating, heat-resistant, and weather-resistant, and does not cause communication failure even when installed on a metal structure. [Solution] An omnidirectional RFID tag for measuring temperature via wireless communication, which has a first dipole antenna and a second dipole antenna extending parallel to and facing a first direction and a second direction opposite to the first direction from a ring-shaped conductor having an opening with an IC chip, and further has a third dipole antenna extending in a third direction from the first dipole antenna and a fourth dipole antenna extending in a fourth direction opposite to the third direction, and is covered with an elastomer having a roughened or approximately zigzag conductor layer, giving it water resistance, insulation, heat resistance, weather resistance, etc., and which does not cause communication problems even when installed on a metal surface.

Description

[Technical Field]

[0001] The present disclosure relates to an RFID tag, and more particularly to an RFID tag that has a wireless sensing function and is water-resistant, insulating, weather-resistant, durable, and suitable for installation in infrastructure facilities and for long-term monitoring and safety management. [Background technology]

[0002] A well-known conventional technology is RFID (Radio Frequency Identification), which uses electromagnetic fields or radio waves to read and write data wirelessly and then authenticates the items using that data. RFID technology has been widely used in recent years for the purpose of improving efficiency and reducing labor in inventory management, receipt and shipment management, product management, logistics, etc.

[0003] Recently, UHF band RFID ICs and tags using these have been developed that not only have authentication functions but also have sensor functions that can obtain temperature data from the object to which they are attached.

[0004] By installing UHF band RFID tags with sensor functions that can acquire temperature data wirelessly in infrastructure facilities such as energy supply facilities, roads, railways, flood control facilities, and parks, and taking advantage of the ability to read dozens or more tags simultaneously using a single set of RFID reader / writer and antenna connected to a communication network, it will be possible to monitor the temperature distribution of infrastructure facilities in real time from remote locations and perform maintenance and safety management.

[0005] RFID reader / writers used to acquire data from UHF band RFID tags with temperature sensor functions like those mentioned above come in two types: 250mW output types for specified low-power radio stations that do not require license registration, and 1W output types that require license registration for indoor radio stations, etc. While 1W output RFID reader / writers have the advantage of being able to read data from RFID tags installed in greater distances, there are concerns that they may cause interference or damage to other nearby RFID tags and RFID reader / writers.

[0006] In the case of RFID readers and writers with a 250mW output, specific low-power radio station type, there is an advantage in that they do not require license registration, allowing for efficient implementation and widespread use in infrastructure facilities. However, there is an issue in that the communication distance to the RFID tag from which data can be acquired is short, and there is a limit to the distance at which RFID tags can be installed.

[0007] Antennas for 250mW output RFID reader / writers include linearly polarized (horizontally and vertically polarized) and circularly polarized. Linearly polarized waves can extend the communication distance compared to circularly polarized waves for the same power communication (see, for example, Patent Documents 1 and 2). However, because most RFID tag antennas are linearly polarized, when a linearly polarized RFID reader / writer antenna is used, the direction of the linear polarization (direction of the electric field plane) of the RFID tag antenna and the RFID reader / writer antenna must match, and mismatching of these two can result in a reduced communication distance or communication failure. This places restrictions on the installation direction of the RFID tag antenna.

[0008] When using a linearly polarized RFID reader / writer antenna, to eliminate restrictions on the installation direction of the RFID tag, it is necessary to use an RFID tag with an omnidirectional antenna structure. As an omnidirectional RFID tag antenna structure, an antenna structure that spreads isotropically in all directions from an IC chip has been disclosed (see, for example, Patent Document 3), but in that case, it is necessary to use an IC chip with four power feed points. However, an IC chip with a temperature sensor function has only two power feed points.

[0009] Furthermore, RFID tags with sensor functions for installation in infrastructure facilities and long-term monitoring and safety management must have water resistance, insulation, weather resistance, durability, etc. In order to improve the water resistance and durability of RFID tags, RFID tags have been disclosed in which the front and back surfaces are covered with silicone rubber or the like (see, for example, Patent Documents 4 and 5). [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-167145 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-122941 [Patent Document 3] U.S. Design Patent No. 769228 [Patent Document 4] Japanese Patent Application Laid-Open No. 2007-42087 [Patent Document 5] Japanese Patent Application Publication No. 2017-162463 Summary of the Invention [Problem to be solved by the invention]

[0011] In infrastructure monitoring using RFID tags with sensor functions that can acquire temperature data wirelessly, when using a 250mW output RFID reader / writer of a specified low-power radio station type and a linearly polarized RFID reader / writer antenna that can achieve a longer communication distance than a circularly polarized antenna, the linear polarization direction (direction of the electric field plane) of the RFID tag antenna and the RFID reader / writer antenna must match, and a mismatch will reduce the communication distance or cause communication failure. This places restrictions on the installation direction of the RFID tag antenna. To eliminate such restrictions, it is necessary to use RFID tags with an omnidirectional antenna structure.

[0012] In the case of an IC chip with four power supply points, an omnidirectional RFID tag has been disclosed that has an antenna structure that spreads isotropically in all directions from the IC chip, but an RFID IC chip with a sensor function that can acquire temperature data has only two power supply points, and an antenna structure that spreads isotropically in all directions from the IC chip cannot be applied.

[0013] Furthermore, RFID tags with sensor functions for implementation in infrastructure facilities and long-term monitoring and maintenance safety management must have water resistance, insulation, weather resistance, durability, etc. At energy supply facilities, the equipment to be measured for temperature may be hot, so RFID tags for infrastructure monitoring must also be heat resistant. When considering monitoring outdoor infrastructure facilities, flood control facilities, and parks, water resistance, insulation, weather resistance, and durability are required. Furthermore, RFID tags for infrastructure monitoring must be flexible so that they can be attached to objects of various shapes.

[0014] As a flexible RFID tag with improved water resistance and durability, an RFID tag with its front and back surfaces covered with silicone rubber has been disclosed. However, because silicone rubber is a dielectric, covering an RFID tag with silicone rubber can cause communication failure or a reduction in communication distance.

[0015] Furthermore, most infrastructure facilities are made of metal structures, and in the case of RFID tags that use the UHF band, placing an RFID tag on a metal surface can cause communication problems due to interference between the electromagnetic waves entering the RFID tag and those reflected from the metal surface.

[0016] The present disclosure has been made in consideration of the above-mentioned problems, and an object of the present disclosure is to provide an RFID tag for infrastructure monitoring with a sensor function, which has an antenna structure for making the RFID tag omnidirectional, and which is equipped with an RFID IC chip with a sensor function capable of acquiring temperature data, and which has little communication failure or reduction in communication distance even when covered with an elastomer such as silicone rubber to obtain flexibility, water resistance, insulation, heat resistance, weather resistance, durability, etc., and which can prevent communication failure and suppress reduction in communication distance when the RFID tag is attached even if the object to which it is attached is a metal structure. [Means for solving the problem]

[0017] In one aspect of the present disclosure, an annular conductor having an opening on a surface of the insulating substrate; an IC chip having a sensor function capable of acquiring temperature data connected to the annular conductor by a power supply section provided near the opening; a first radiation conductor extending from the annular conductor in a first direction and a second direction opposite to the first direction and connected to the annular conductor; a second radiation conductor extending from the annular conductor in the first direction and connected to the annular conductor; and a third radiation conductor extending from the annular conductor in the second direction and connected to the annular conductor, wherein the first radiation conductor, the second radiation conductor, or the third radiation conductor has a substantially rectangular, meander, or zigzag shape in a planar view; a first dipole antenna formed by the first radiation conductor and a second dipole antenna formed by the second radiation conductor and the third radiation conductor extend parallel to and facing the first direction and the second direction; and an RFID tag having a function of measuring temperature by wireless communication is provided.

[0018] In one aspect of the present disclosure, An RFID tag is provided, comprising: a third dipole antenna consisting of a fourth radiation conductor extending from the first radiation conductor in a third direction and connected to the first radiation conductor; and a fourth dipole antenna consisting of a fifth radiation conductor extending from the third radiation conductor in a fourth direction opposite to the third direction and connected to the third radiation conductor, wherein the fourth radiation conductor or the fifth radiation conductor has a substantially rectangular, meander, or zigzag shape in a planar view.

[0019] The RFID tag according to claim 1 or 2 is provided with a first elastomer layer having at least one uneven structure on a surface of the RFID tag that contacts an object to which the RFID tag is attached. Note that the uneven structure here includes recesses or protrusions.

[0020] In one aspect of the present disclosure, The RFID tag has a first elastomer layer having at least one uneven structure on the surface of the RFID tag that contacts the object to which it is attached, and a second elastomer layer on the other surface of the RFID tag, the RFID tag having a structure in which it is sandwiched and covered between the first elastomer layer and the second elastomer layer, and a gap is formed between the object to which it is attached and the RFID tag, thereby preventing communication failure.

[0021] In one aspect of the present disclosure, The RFID tag is provided in which the uneven structure is a uneven structure consisting of hemispherical recesses, and the diameter of the hemispherical recesses is 5 mm to 20 mm. Note that the uneven structure here includes recesses and protrusions.

[0022] In one aspect of the present disclosure, An RFID tag is provided, characterized in that when the thickness D2 of the second elastomer layer is smaller than a certain value in the range of 0.7 mm or more and less than 1 mm, the communication distance over which temperature data can be received increases as the thickness D2 of the second elastomer layer decreases.

[0023] In one aspect of the present disclosure, The RFID tag has a third elastomer layer, which has at least one conductor layer that is roughly zigzag in cross section, on the surface of the RFID tag that contacts the object to which it is attached, and a fourth elastomer layer on the other surface of the RFID tag, and the RFID tag has a structure in which it is sandwiched and covered by the third elastomer layer and the fourth elastomer layer, and the reflection direction of electromagnetic waves is changed between the object to which it is attached and the RFID tag, thereby preventing communication failure.

[0024] In one aspect of the present disclosure, An RFID tag is provided, characterized in that when the thickness D4 of the fourth elastomer layer is smaller than a certain value in the range of 0.7 mm or more and less than 1 mm, the communication distance over which temperature data can be received increases as the thickness D4 of the fourth elastomer layer decreases.

[0025] In one aspect of the present disclosure, Provided is an RFID tag comprising an insulating substrate, an annular conductor having an opening provided on the surface of the insulating substrate, an IC chip having a sensor function capable of acquiring temperature data and connected to the annular conductor by a power supply section provided near the opening, and an antenna consisting of a radiating conductor, wherein the RFID tag has a first elastomer layer having at least one uneven structure on the surface that contacts the object to which the RFID tag is attached, and a second elastomer layer on the other surface of the RFID tag, the RFID tag having a structure in which the RFID tag is sandwiched and covered between the first elastomer layer and the second elastomer layer, and a gap is formed between the object to which the RFID tag is attached and the RFID tag, thereby preventing communication failure.

[0026] Provided is an RFID tag comprising: an insulating substrate; an annular conductor having an opening provided on the surface of the insulating substrate; an IC chip having a sensor function capable of acquiring temperature data, connected to the annular conductor by a power supply section provided near the opening; and an antenna consisting of a radiating conductor; wherein, in a cross-sectional view, a third elastomer layer having at least one substantially zigzag conductor layer is provided on the surface of the RFID tag that contacts an object to which the RFID tag is attached; and a fourth elastomer layer is provided on the other surface of the RFID tag; the RFID tag has a structure in which the RFID tag is sandwiched and covered by the third elastomer layer and the fourth elastomer layer; and the RFID tag changes the reflection direction of electromagnetic waves between the object to which the RFID tag is attached and the RFID tag, thereby preventing communication failures.

[0027] The term "substantially" in the above-mentioned radiation conductor having a substantially rectangular, meandering, or zigzag shape in plan view and the above-mentioned conductor layer having a substantially zigzag shape in cross section means that the corners or sides may be rounded. Note that the above-mentioned uneven structure includes recesses or protrusions. [Effects of the Invention]

[0028] According to one aspect of the present disclosure, it is possible to provide an RFID tag for infrastructure monitoring with a sensor function, which has an antenna structure that makes the RFID tag omnidirectional, and which is equipped with an RFID IC chip with a sensor function that can acquire temperature data, and which is covered with an elastomer such as silicone rubber to provide flexibility, water resistance, insulation, heat resistance, weather resistance, durability, etc., so that communication failures and reductions in communication distance are minimal, and which can prevent communication failures and reduce reductions in communication distance even when the object to which it is attached is a metal structure. [Brief explanation of the drawings]

[0029] [Figure 1] 1A and 1B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape A) according to the first embodiment. [Figure 2] 10A and 10B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape B) according to comparative example 1. FIG. [Figure 3]10A and 10B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape C) according to comparative embodiment 2. FIG. [Figure 4] 10 is an example of a plan view of an RFID tag (antenna shape D) according to the second embodiment. [Figure 5] 13 is an example of a plan view of an RFID tag (antenna shape E) according to comparative example 3. FIG. [Figure 6] This is a conceptual diagram of the arrangement of an RFID tag and an antenna of an RFID reader / writer when measuring the communication distance CL at which temperature data can be received in free space, which is a parameter that represents the characteristics of an RFID tag. [Figure 7] FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape A) of embodiment 1. [Figure 8] FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape B) of comparative form 1. [Figure 9] FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in an RFID tag (antenna shape C) according to comparative form 2. [Figure 10] FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in an RFID tag (antenna shape D) according to embodiment 2. [Figure 11]FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in an RFID tag (antenna shape E) of comparative form 3. [Figure 12] 10A and 10B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape F) according to a third embodiment. [Figure 13] FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance over which temperature data can be received, in an RFID tag (antenna shape F) according to embodiment 3. [Figure 14] 10A and 10B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape G) according to a fourth embodiment. [Figure 15] FIG. 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance over which temperature data can be received, in an RFID tag (antenna shape G) according to embodiment 4. [Figure 16] 10A and 10B are examples of (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an RFID tag covered with a first elastomer layer and a second elastomer layer having an uneven structure according to embodiment 5. [Figure 17] 1A and 1B are a plan view and a cross-sectional view, respectively, of an example of a mold for molding a first elastomer layer, which has an uneven structure consisting of hemispherical recesses. [Figure 18] 10A and 10B are examples of (a) a plan view (second elastomer layer), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an RFID tag covered with a first elastomer layer and a second elastomer layer having an uneven structure (diameter approximately 12 mm) consisting of hemispherical recesses according to embodiment 5. [Figure 19]10A and 10B are examples of (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an RFID tag covered with a first elastomer layer and a second elastomer layer having an uneven structure (diameter approximately 8 mm) consisting of hemispherical recesses according to embodiment 5. [Figure 20] 10A and 10B are examples of (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an RFID tag covered with a first elastomer layer and a second elastomer layer having an uneven structure (diameter approximately 5 mm) consisting of hemispherical recesses according to embodiment 5. [Figure 21] 10A and 10B are examples of (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an RFID tag according to a fifth embodiment, which is covered with a first elastomer layer and a second elastomer layer and has only one rectangular recess of approximately the same size as the antenna of the RFID tag. [Figure 22] 1A and 1B are examples of a plan view (second elastomer layer side), a cross-sectional view, and a plan view (first elastomer layer side) of an RFID tag covered with a first elastomer layer and a second elastomer layer made of silicone rubber that do not have a concave-convex structure according to comparative embodiment 4. [Figure 23] 10A and 10B are examples of (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an RFID tag covered with a first elastomer layer and a second elastomer layer having an uneven structure (diameter approximately 12 mm) consisting of hemispherical recesses according to embodiment 6. [Figure 24] 10A and 10B are examples of (a) a plan view (fourth elastomer layer side), (b) a cross-sectional view, and (c) a plan view (third elastomer layer side) of an RFID tag covered with a third elastomer layer and a fourth elastomer layer having a substantially zigzag conductor layer according to embodiment 7. [Figure 25] 10 is a table showing an example of communication distances over which temperature data can be received when RFID tags of various structures are placed on a metal plate. [Figure 26]This is an example of the change in the communication distance at which temperature data can be received when an elastomer-coated RFID tag (antenna shape G) consisting of a first elastomer layer (thickness approximately 6.5 mm) with an uneven structure (diameter approximately 12 mm) consisting of hemispherical recesses according to embodiment 5 is placed on a metal plate and the thickness D2 of the second elastomer layer is changed. [Figure 27] 10 is a table showing an example of communication distances over which temperature data can be received when elastomer-coated RFID tags having various uneven structures according to the fifth embodiment are placed on a metal plate. [Figure 28] This is an example of the change in the communication distance at which temperature data can be received when an elastomer-coated RFID tag (antenna shape A) consisting of a first elastomer layer (thickness approximately 6.5 mm) with an uneven structure (diameter approximately 12 mm) consisting of hemispherical recesses according to embodiment 5 is placed on a metal plate and the thickness D2 of the second elastomer layer is changed. [Figure 29] 13 is a table showing an example of communication distances over which temperature data can be received when elastomer-coated RFID tags having various uneven structures according to the sixth embodiment are placed on a metal plate. [Figure 30] This is an example of the change in the communication distance at which temperature data can be received when an elastomer-coated RFID tag (antenna shape G) covered with a third elastomer layer and a fourth elastomer layer having an approximately zigzag conductor layer according to embodiment 7 is placed on a metal plate and the thickness D4 of the fourth elastomer layer is changed. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the embodiments described below, identical or common parts are denoted by the same reference numerals in the drawings, and their description will not be repeated. For ease of understanding, the scale of each part in the drawings may differ from the actual scale. Directions such as parallel, right angle, orthogonal, horizontal, vertical, up / down, left / right, and terms such as identical and equal are permitted to be deviated to the extent that they do not impair the functions and effects of the embodiments. The X-axis, Y-axis, and Z-axis directions represent directions parallel to the X-axis, Y-axis, and Z-axis, respectively. The X-axis, Y-axis, and Z-axis directions are perpendicular to each other.

[0031] Next, each element of the RFID tag according to this embodiment will be described in detail.

[0032] (Embodiment 1) [RFID tag (antenna shape A)] 1A and 1B are a plan view and a cross-sectional view, respectively, of an example of an RFID tag (antenna shape A) 101 according to embodiment 1. The RFID tag 101 according to embodiment 1 will be described with reference to Fig. 1. The RFID tag 101 according to embodiment 1 includes an insulating substrate 10, a conductor layer 11, an IC chip 20, a power supply portion 21, an opening 22, an impedance matching portion (annular conductor) 30, and first to third radiation conductors (31 to 33).

[0033] The insulating substrate 10 is a plate-like or film-like member. The material of the insulating substrate 10 is not particularly limited, and examples thereof include resin substrates such as polyethylene terephthalate (PET), polyurethane (PU), polyimide (PI), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), fluorinated resin copolymer, triacetyl cellulose (TAC), polyethylene naphthalate (PEN), syndiotactic polystyrene, polyphenylene sulfide, polycarbonate, polyarylate, polysulfone, polyester sulfone, polyetherimide, cyclic polyolefin, brominated phenoxy resin, norbornene resin, cycloolefin polymer, cycloolefin copolymer, and polyacetal; and composite substrates such as paper substrates, paper-phenol substrates, paper-epoxy substrates, glass composite substrates, and glass-epoxy substrates. From the viewpoint of flexibility, resin substrates and paper substrates are preferred. The thickness of the insulating substrate 10 is preferably 8 to 1000 μm, more preferably 8 to 150 μm, from the viewpoint of flexibility and strength of the substrate.

[0034] The conductor layer 11 is a conductor layer formed in a planar shape on the insulating substrate 10 by a predetermined known method. The material of the conductor layer 11 is not particularly limited, and the conductor layer 11 is formed from a conductive conductor. For example, the conductor layer 11 may be made of a metal such as aluminum, copper, gold, platinum, silver, nickel, chromium, zinc, lead, tungsten, or iron. The conductor layer 11 may be made of a metal oxide such as tin oxide or ITO (indium tin oxide), a conductive film using metal nanowires such as gold, silver, or copper, a conductive resin mixture in which resin is mixed with the above metal powder or a conductive carbon material, or a conductive resin film. The thickness of the conductor layer 11 is preferably 0.01 to 1000 μm, and more preferably 1 to 100 μm, from the viewpoints of flexibility and strength.

[0035] The first to third radiation conductors (31 to 33) are made of a conductor layer 11 formed in a planar shape on an insulating substrate 10 by a predetermined known method, and function as antennas, enabling transmission and reception of predetermined information between the IC chip 20 of the RFID tag 101 and an external communication device such as a reader. The first radiation conductor 31, which serves as a first dipole antenna, and the second dipole antenna consisting of the second radiation conductor 32 and the third radiation conductor 33 are structured to extend in parallel and face each other from the impedance matching section (annular conductor) 30 in a first direction and a second direction opposite to the first direction.

[0036] The distance from the end of the impedance matching section (annular conductor) 30 in the first direction to the end of the first dipole antenna in the first direction and the distance from the end of the impedance matching section (annular conductor) 30 in the second direction to the end of the first dipole antenna in the second direction may be the same or different. Furthermore, the distance from the end of the impedance matching section (annular conductor) 30 in the first direction to the end of the second dipole antenna in the first direction and the distance from the end of the impedance matching section (annular conductor) 30 in the second direction to the end of the second dipole antenna in the second direction may be the same or different.

[0037] In Fig. 1, the antenna pattern of the first to third radiation conductors (31 to 33) is a substantially rectangular dipole antenna, but from the viewpoint of reducing the antenna size, it may be a substantially meander-shaped dipole antenna or a substantially zigzag dipole antenna having a multiple folded structure. Here, the "substantially" in the substantially rectangular, substantially meander-shaped, or substantially zigzag dipole antenna means that the corners or sides may be rounded.

[0038] The impedance matching section (annular conductor) 30 and the first to third radiation conductors (31 to 33) may have a structure consisting of a continuous conductor layer, or may have a structure in which the impedance matching section (annular conductor) 30 and the first to third radiation conductors (31 to 33) are electrically connected by another conductor layer, or may have a structure in which they are fixed and connected at a close distance so that electromagnetic coupling is formed at ultra-high frequencies in the UHF band.

[0039] The IC chip 20 is a semiconductor component electrically connected to the impedance matching section (annular conductor) 30 at the power supply section 21 near the opening 22. The IC chip 20 may have a sensor function that detects the state of an object with which the RFID tag 101 comes into contact. The IC chip 20 has a sensor function that can acquire temperature data, and transmits information indicating the temperature detected by the sensor via an antenna consisting of the first to third radiation conductors (31 to 33). Note that the physical quantity detected by the sensor is not limited to temperature, and may be, for example, humidity, current, voltage, resistance, pressure, airflow, or dielectric constant. In infrastructure monitoring, detecting changes in these physical quantities can be used to sense wetness or water leakage, or to sense distortion or displacement of infrastructure facilities.

[0040] The IC chip 20 may be arranged in the same layer as the impedance matching section (annular conductor) 30, or in a different layer. The IC chip 20 may be arranged so as to straddle the power supply section 21, which is formed by a slit or a notch formed in the impedance matching section (annular conductor) 30.

[0041] The impedance matching section (annular conductor) 30 is an annular conductor that forms a substantially quadrilateral opening 22 near which the power supply section 21 is provided. The opening 22 has a pair of sides parallel to the X-axis direction and a pair of sides parallel to the Y-axis direction. The impedance matching section (annular conductor) 30 forms a loop circuit that surrounds the opening 22 in a region that includes the power supply section 21. The impedance matching section (annular conductor) 30 matches impedance between the IC chip 20 and the antenna formed by the first to third radiation conductors (31 to 33) by the action of this loop circuit.

[0042] In the illustrated embodiment, the shape of the opening 22 is a substantially quadrilateral having a pair of long sides parallel to the X-axis direction and a pair of short sides parallel to the Y-axis direction. However, the shape of the opening 22 is not limited to the illustrated embodiment and may be, for example, a substantially quadrilateral having a pair of short sides parallel to the X-axis direction and a pair of long sides parallel to the Y-axis direction. The substantially quadrilateral shape of the opening 22 may include a perfect quadrilateral. Here, "substantially" means that the corners or sides may be rounded. The quadrilateral may include a rectangle, a rhombus, a parallelogram, and a square. The shape of the opening 22 may be a polygon other than a quadrilateral, a circle, or an ellipse.

[0043] If impedance matching is not achieved between the IC chip 20 and the antenna consisting of the first to third radiation conductors (31 to 33), signal reflection occurs, reducing the communication distance of the RFID tag 101. The impedance of IC chips 20 for UHF band RFID tags ranges from several tens to several hundred ohms and is not standardized. Impedance matching with the IC chip 20 can be achieved by controlling the imaginary part (reactance) of the complex impedance depending on the size and shape of the loop structure of the impedance matching section (annular conductor) 30.

[0044] The RFID tag 101 may include an insulating layer that covers the IC chip 20, the power supply portion 21, the opening 22, the impedance matching portion (annular conductor) 30, and the first to third radiating conductors (31 to 33). The IC chip 20, the power supply portion 21, the opening 22, the impedance matching portion (annular conductor) 30, and the first to third radiating conductors (31 to 33) are sandwiched between the insulating base material 10 and the insulating layer, and the insulating layer functions as a protective film. Examples of the material and thickness of the insulating layer may be the same as those of the insulating base material 10 described above.

[0045] 7 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader-writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape A) 101 according to the first embodiment. A conceptual diagram of the arrangement of the RFID tag and the antenna of the RFID reader-writer in measuring the communication distance CL at which temperature data can be received is shown in FIG. 6. The angle 0° is defined as the case where the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader-writer are parallel to the floor surface. The angle when the RFID tag reader / writer antenna is rotated clockwise and the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the RFID tag reader / writer antenna is orthogonal is defined as 90°, and the angle when the RFID tag reader / writer antenna is rotated counterclockwise and the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the RFID tag reader / writer antenna is defined as -90°. In the graph of the angle dependency of communication distance shown in Figure 7, the longest communication distance CL at which temperature data can be received at each angle is plotted against the angle as communication distance (cm).

[0046] In Figure 7, an RFID tag (antenna shape A) 101 has a structure in which a first dipole antenna consisting of the first radiation conductor 31 and a second dipole antenna consisting of the second radiation conductor 32 and the third radiation conductor 33 extend parallel to face each other in a first direction and a second direction. This RFID tag exhibits approximately omnidirectional characteristics in the angle range of -40° to 40° with respect to the linearly polarized wave from the antenna of the RFID tag reader / writer.

[0047] Regardless of whether the insulating substrate side or the annular conductor side of the RFID tag faces the antenna surface of the RFID tag reader / writer, the communication distance over which temperature data can be received is the same as long as the RFID tag antenna is positioned in the same way relative to the antenna of the RFID tag reader / writer.

[0048] The dimensions of the radiating conductor forming the dipole antenna, such as its length and width, are not limited to the shape shown in Figure 1, and can be optimized for the environment in which infrastructure facilities are monitored.

[0049] Next, a comparative example (comparison example) to be compared with this embodiment will be described.

[0050] (Comparative form 1) 2A and 2B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape B) 102 according to comparative embodiment 1. The difference between the RFID tag (antenna shape A) 101 according to embodiment 1 and the RFID tag (antenna shape B) 102 according to comparative embodiment 1 is that the RFID tag (antenna shape A) has a structure in which the first dipole antenna and the second dipole antenna extend parallel to each other while facing each other, whereas the RFID tag (antenna shape B) 102 has a structure in which only the first dipole antenna is included.

[0051] 8 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in an RFID tag (antenna shape B) 102 according to comparative example 1. The communication distance at which temperature data can be received for RFID tag (antenna shape B) 102 at an angle of 0° is reduced to approximately half that of RFID tag (antenna shape A) 101, and further, the communication distance changes significantly depending on the angle. In FIG. 8, the dashed curve represents a simulation of the angle dependency of the communication distance at which temperature data can be received, using a Gaussian function.

[0052] (Comparative form 2) 3A and 3B are an example of a plan view and a cross-sectional view of an RFID tag (antenna shape C) 103 according to comparative embodiment 2. The difference between the RFID tag (antenna shape A) 101 according to embodiment 1 and the RFID tag (antenna shape C) 103 according to comparative embodiment 2 is that the RFID tag (antenna shape A) has a structure in which the first dipole antenna and the second dipole antenna extend parallel to each other, whereas the RFID tag (antenna shape C) 103 has a structure in which only the second dipole antenna is included.

[0053] 9 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in an RFID tag (antenna shape C) 103 according to comparative example 1. The communication distance at which temperature data can be received for RFID tag (antenna shape C) 103 at an angle of 0° is reduced to approximately 75% of that of RFID tag (antenna shape A) 101, and further, the communication distance at which temperature data can be received changes significantly depending on the angle. In FIG. 9, the dashed curve represents a simulation of the angle dependency of the communication distance at which temperature data can be received, using a Gaussian function.

[0054] Compared to comparative form 1 and comparative form 2, the RFID tag (antenna shape A) 101 of embodiment 1 exhibits approximately omnidirectional characteristics in the angle range of -40° to 40°. This is thought to be because the first dipole antenna and the second dipole antenna are configured to extend parallel to each other from the impedance matching section (annular conductor) 30 in the first and second directions, making the distribution of the electromagnetic field formed by the two dipole antennas broader.

[0055] (Embodiment 2) 4 is an example of a plan view of an RFID tag (antenna shape D) 104 according to embodiment 2. The RFID tag 101 according to embodiment 2 includes an insulating substrate 10, a conductor layer 11, an IC chip 20, a power supply portion 21, an opening 22, an impedance matching portion (annular conductor) 30, and first to fifth radiating conductors (31 to 35).

[0056] The material and thickness of the insulating substrate 10 may be the same as those exemplified in the first embodiment. The conductor layer 11 is a conductor layer formed in a planar shape on the insulating substrate 10 by a predetermined known method, and the material and thickness may be the same as those exemplified in the first embodiment. The IC chip 20 is a semiconductor component electrically connected to an impedance matching section (annular conductor) 30 at a power supply section 21 near the opening 22, as in the example of the first embodiment, and may have a sensor function for detecting the state of an object with which the RFID tag 104 comes into contact. The impedance matching section (annular conductor) 30 is a ring conductor that forms the opening 22, as in the example of the first embodiment, and matches impedance between the IC chip 20 and an antenna composed of the first to fifth radiating conductors (31 to 35).

[0057] The first to fifth radiating conductors (31 to 35) are made of a conductor layer 11 formed in a planar shape on the insulating substrate 10 by a predetermined known method. They function as antennas, enabling transmission and reception of predetermined information between the IC chip 20 of the RFID tag 104 and an external communication device such as a reader. The first radiating conductor 31, which serves as a first dipole antenna, and the second dipole antenna, which consists of the second radiating conductor 32 and the third radiating conductor 33, are configured to extend in parallel and face each other from the impedance matching section (annular conductor) 30. The RFID tag (antenna shape D) 104 further includes a third dipole antenna, which extends in a third direction that is approximately perpendicular to the extension direction of the first radiating conductor 31 and is made of a fourth radiating conductor 34 connected to the first radiating conductor 31, and a fourth dipole antenna, which extends from the third radiating conductor 33 in a fourth direction opposite to the third direction and is made of a fifth radiating conductor 35 connected to the third radiating conductor 33.

[0058] The distance from the end of the impedance matching section (annular conductor) 30 in the third direction to the end of the third dipole antenna in the third direction and the distance from the end of the impedance matching section (annular conductor) 30 in the fourth direction to the end of the fourth dipole antenna in the fourth direction may be the same or different.

[0059] In Fig. 4, the antenna patterns of the first to fifth radiation conductors (31 to 35) are substantially rectangular dipole antennas, but from the viewpoint of reducing the antenna size, they may be substantially meander-shaped dipole antennas or substantially zigzag dipole antennas having multiple folded structures. Here, the word "substantially" in the substantially rectangular, substantially meander-shaped, or substantially zigzag dipole antennas means that the corners or sides may be rounded.

[0060] The impedance matching section (annular conductor) 30 and the first to fifth radiating conductors (31 to 35) may have a structure consisting of a continuous conductor layer, or may have a structure in which the impedance matching section (annular conductor) 30 and the first to fifth radiating conductors (31 to 35) are electrically connected by another conductor layer, or may have a structure in which they are fixed and connected at a close distance so that electromagnetic coupling is formed at ultra-high frequencies in the UHF band.

[0061] The RFID tag (antenna shape D) 104 according to embodiment 2 has a different structure from the RFID tag (antenna shape A) 101 according to embodiment 1 in that, in addition to a first dipole antenna and a second dipole antenna extending parallel to each other from the impedance matching section (annular conductor) 30, the RFID tag (antenna shape D) 104 also has a third dipole antenna extending in a third direction that is approximately perpendicular to the first dipole antenna and a fourth dipole antenna extending in a fourth direction.

[0062] 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in RFID tag (antenna shape D) 104 according to embodiment 2. In the case of RFID tag 101, 102, or 103, when the angle at which the direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer intersect at right angles of 90° or −90°, the communication distance at which temperature data can be received is close to zero, whereas in RFID tag (antenna shape D) 104, it exceeds 90 cm.

[0063] In the RFID tag (antenna shape D) 104 according to embodiment 2, the ratio of the communication distance at which temperature data can be received when the extension direction of the first dipole antenna or the second dipole antenna is perpendicular to the linear polarization direction from the antenna of the RFID tag reader / writer by 90° to the communication distance at which temperature data can be received when the extension direction of the first dipole antenna or the second dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer is 0.7 or more, and a communication distance at which good temperature data can be received is obtained in all angle ranges, demonstrating an improvement in the omnidirectionality of the RFID tag.

[0064] The dimensions of the radiating conductor forming the dipole antenna, such as its length and width, are not limited to the shape shown in FIG. 4, and can be optimized for the environment in which infrastructure facilities are monitored.

[0065] (Comparative form 3) 5 is an example of a plan view of an RFID tag (antenna shape E) 105 according to comparative embodiment 3. The differences between the RFID tag (antenna shape D) 104 according to embodiment 2 and the RFID tag (antenna shape E) 105 according to comparative embodiment 3 are described below. The RFID tag (antenna shape D) 104 has a first radiation conductor 31 serving as a first dipole antenna, and a second dipole antenna consisting of a second radiation conductor 32 and a third radiation conductor 33, which extend parallel to each other in the first and second directions from an impedance matching section (annular conductor) 30. The RFID tag (antenna shape D) 104 also has a third dipole antenna consisting of a fourth radiation conductor 34 connected to the first radiation conductor 31, and a fourth dipole antenna consisting of a fifth radiation conductor 35 connected to the third radiation conductor 33, which extends from the third radiation conductor 33 in a fourth direction opposite to the third direction. In contrast, the RFID tag (antenna shape E) 105 according to comparative embodiment 3 has a sixth radiation conductor 36 extending in the second direction instead of the first radiation conductor 31 extending in the first and second directions from the impedance matching section (annular conductor) 30, and does not have the third radiation conductor 33. Therefore, the first dipole antenna formed by the sixth radiation conductor 36 and the second dipole antenna formed by the second radiation conductor 32 do not have a structure in which they extend parallel to each other in the first and second directions.

[0066] 11 is a diagram showing the relationship between the angle between the extending direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape E) 105 according to comparative embodiment 3. Compared to the case of the RFID tag (antenna shape D) 104 according to embodiment 2 (FIG. 10), the decrease in the communication distance at which temperature data can be received is greater in the angle range of 10° to 90°.

[0067] (Embodiment 3) 12 is a plan view of an RFID tag (antenna shape F) 106 according to embodiment 3. The difference from the RFID tag (antenna shape A) 101 (FIG. 1) according to embodiment 1 is that the first radiating conductor 31, the second radiating conductor 32, or the third radiating conductor 33 in the RFID tag 101 is substantially rectangular, whereas the first radiating conductor 31, the second radiating conductor 32, or the third radiating conductor 33 in the RFID tag 106 is substantially meander-shaped.

[0068] The impedance matching section (annular conductor) 30 and the first to third radiation conductors (31 to 33) may have a structure consisting of a continuous conductor layer, or may have a structure in which the impedance matching section (annular conductor) 30 and the first to third radiation conductors (31 to 33) are electrically connected by another conductor layer, or may have a structure in which they are fixed and connected at a close distance so that electromagnetic coupling is formed at ultra-high frequencies in the UHF band.

[0069] 13 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape F) 106 according to the third embodiment. Compared to comparative embodiment 1 (FIGS. 2 and 8) and comparative embodiment 2 (FIGS. 3 and 9), which have only one dipole antenna, the RFID tag (antenna shape F) 106 has a substantially omnidirectional characteristic in the angle range of -40° to 40°. For example, in the RFID tag (antenna shape F) 106, the ratio of the communication distance at which temperature data can be received when the angle between the extension direction of the first dipole antenna or the second dipole antenna and the linear polarization direction from the antenna of the RFID tag reader / writer is -40° to the communication distance at which temperature data can be received when the orientation of the first dipole antenna or the second dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer is 0.9 or more.

[0070] The dimensions such as the length and width of the radiating conductor forming the dipole antenna and the structure such as the approximate meander shape are not limited to the shape shown in Fig. 12 and can be optimized for the environment in which infrastructure facilities are monitored. Furthermore, the "approximately meander shape" in the above-mentioned approximate meander shape means that the corners or sides may be rounded.

[0071] (Fourth embodiment) 14 is a plan view of an RFID tag (antenna shape G) 107 according to embodiment 4. The difference from the RFID tag (antenna shape D) 104 (FIG. 4) according to embodiment 2 is that while the first radiating conductor 31, the second radiating conductor 32, the third radiating conductor 33, the fourth radiating conductor 34, or the fifth radiating conductor 35 in the RFID tag 107 are substantially rectangular, the first radiating conductor 31, the second radiating conductor 32, the third radiating conductor 33, the fourth radiating conductor 34, or the fifth radiating conductor 35 in the RFID tag 107 are substantially meander-shaped.

[0072] The impedance matching section (annular conductor) 30 and the first to fifth radiating conductors (31 to 35) may have a structure consisting of a continuous conductor layer, or may have a structure in which the impedance matching section (annular conductor) 30 and the first to fifth radiating conductors (31 to 35) are electrically connected by another conductor layer, or may have a structure in which they are fixed and connected at a close distance so that electromagnetic coupling is formed at ultra-high frequencies in the UHF band.

[0073] 15 is a diagram showing the relationship between the angle between the extending direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance over which temperature data can be received, in the RFID tag (antenna shape G) 107 according to embodiment 4. The RFID tag has a nearly omnidirectional characteristic within an angle range of -60° to 50°.

[0074] The dimensions such as the length and width of the radiating conductor forming the dipole antenna and the meandering structure are not limited to the shape shown in Fig. 14 and can be optimized for the environment in which infrastructure facilities are monitored. The term "approximately meandering" means that the corners or sides may be rounded.

[0075] (Embodiment 5) FIG. 16 shows (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side) of an elastomer-coated RFID tag (antenna shape G) 108 according to embodiment 5. The elastomer-coated RFID tag is covered with a first elastomer layer 60 and a second elastomer layer 61. The first elastomer layer side is the surface that contacts the object to which the tag is attached, and the second elastomer layer side is the surface that faces the antenna of the RFID tag reader / writer. Covering and sealing the tag with elastomer improves water resistance, insulation, heat resistance, and weather resistance. Furthermore, the gaps in the first elastomer layer 60 with the uneven structure act as spacers, preventing communication failures and minimizing a reduction in communication distance even when the RFID tag is attached to the surface of a metal structure. Note that the uneven structure here includes both uneven and uneven portions.

[0076] When an RFID tag is attached to a metal structure, placing the tag directly on the surface of the metal structure can result in communication problems, such as incommunication failure or a significant reduction in communication distance. For this reason, RFID tags are sometimes attached to the target object via a spacer made of a foam with a low dielectric constant to ensure communication distance. Since the smaller the dielectric constant, the more effective the spacer, so foams with a high porosity are often used. For example, polystyrene foam, which is often used for the above-mentioned applications, has a relative dielectric constant of approximately 1.02 (depending on the degree of foaming), making it a material with a particularly low dielectric constant among various resins. In the UHF band, the thickness of a foam spacer required to adequately prevent communication problems when attaching an RFID tag to the surface of a metal object requires a thickness of at least 1 cm, depending on the shape of the RFID tag. In contrast, the relative dielectric constant of elastomers, such as silicone rubber, is 3.0 to 3.5, which is higher than that of polystyrene foam. Therefore, in the present disclosure, in the elastomer layer having the uneven structure, voids are generated by the uneven structure in the elastomer on the side that contacts the metal object to be attached, forming voids between the object to be attached and the RFID tag, thereby creating an air gap, thereby making the elastomer layer low-dielectric. By using such an RFID tag with a sealed structure made of elastomer in which voids are generated by the unevenness in the elastomer on the side that contacts the object to be attached, the RFID tag has flexibility, water resistance, insulation, heat resistance, weather resistance, durability, etc., and further makes it possible to prevent communication failures and suppress a reduction in communication distance in infrastructure monitoring, even if the object to be attached is a metal structure.

[0077] The materials for the first elastomer layer and the second elastomer layer are not particularly limited and include, for example, thermosetting elastomers such as silicone rubber, urethane rubber, fluororubber, styrene-butadiene rubber, isoprene rubber, butadiene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, non-diene rubbers such as butyl rubber (e.g., isobutylene-isoprene rubber), ethylene-propylene rubber, ethylene-propylene-diene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, acrylic rubber, polysulfide rubber, and epichlorohydrin rubber. Thermoplastic elastomers include polystyrene-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, vinyl chloride-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, butadiene-based thermoplastic elastomers, and silicone-based thermoplastic elastomers. Furthermore, inorganic fine particles may be dispersed in these elastomers.

[0078] In one example of an elastomer-coated RFID tag (antenna shape G) 108 shown in Figure 16, the elastomer is covered with an elastomer having a concave-convex structure in the form of a grid-like arrangement of cross-shaped recesses of rectangular grooves. First, a silicone resin tray with a concave-convex structure in the form of a grid-like arrangement of cross-shaped protrusions of rectangular grooves is cut to a size larger than the RFID tag and placed at the bottom of a rectangular container or the like. A liquid prepared by mixing and stirring a first component (base) and a second component (curing agent) of a two-component silicone RTV rubber in a 1:1 weight ratio is poured onto the tray and allowed to harden at room temperature. After approximately three hours, when the surface of the thermosetting elastomer has solidified and become tacky, an RFID tag is placed on the surface of the thermosetting elastomer. A liquid prepared by mixing and stirring a first component (base) and a second component (curing agent) of a two-component silicone RTV rubber in a 1:1 weight ratio is poured onto the tray and allowed to harden at room temperature for approximately eight hours. The method for producing the elastomer-coated RFID tag 108 is not limited to the above.

[0079] In one example of the first elastomer having the uneven structure shown in Figure 16, the unevenness is approximately 1 mm deep, and recesses formed by crossing rectangular grooves, each approximately 1 mm wide and 7 mm long, are arranged in a grid pattern. The thickness D1 of the first elastomer layer is approximately 2 mm, and the thickness D2 of the second elastomer layer is approximately 0.5 mm. The thicknesses of the first elastomer layer and the second elastomer layer and the shape of the uneven structure are not limited to those shown in Figure 16 and can be optimized for the environment in which infrastructure monitoring is performed.

[0080] When an RFID tag is attached to a metal structure and the RFID tag is installed on the surface of the metal structure, from the viewpoints of preventing communication failures and minimizing a reduction in communication distance, the concave-convex structure preferably has a deep concave-convex structure, forming a gap between the RFID tag and the attached object to isolate the RFID tag. However, in infrastructure monitoring using RFID tags with sensor functions that can acquire temperature data wirelessly, an excessively deep concave-convex structure may adversely affect the response and accuracy of temperature monitoring due to reduced heat transfer. Therefore, the optimal depth of the concave-convex structure must be determined taking into account the response and accuracy required for temperature monitoring when monitoring infrastructure facilities. Taking these factors into consideration, the thickness of the first elastomer layer 60 is preferably 1 mm to 20 mm, more preferably 1 mm to 12 mm, and even more preferably 1 mm to 7 mm.

[0081] The shape of the uneven structure is preferably one that maximizes the area of ​​the recessed portions of the recesses, since this separates the object to which the RFID tag is attached from the RFID tag by a gap, and is therefore preferable for preventing communication failures and suppressing a reduction in communication distance when the RFID tag is attached to the surface of a metal structure. In the example of the first elastomer having the uneven structure shown in Figure 16, the width of the rectangular grooves that intersect in a crisscross pattern and are approximately 7 mm long is preferably 1 mm to 3 mm, and more preferably 1 mm to 6 mm.

[0082] The shape of the uneven structure is not limited to the above-mentioned shape of rectangular grooves intersecting in a cross shape, and various uneven structure shapes that can form a gap between the attachment object and the RFID tag can be applied, such as an uneven structure with conical or cylindrical protrusions, an uneven structure with prismatic columns such as triangular columns or quadrangular columns, an uneven structure with hemispherical recesses, an uneven structure with hemispherical protrusions, etc. Here, the uneven structure includes recesses and protrusions.

[0083] Figure 17 shows an example of a mold for molding a first elastomer layer having a concave-convex structure with hemispherical depressions. Hemispherical structures 40 (diameter approximately 12 mm), 41 (diameter approximately 8 mm), and 42 (diameter approximately 5 mm) were attached in a grid pattern to the bottom of a plastic container to create a mold for molding a first elastomer layer having a concave-convex structure with hemispherical depressions. A liquid made by mixing and stirring two-component silicone HTV rubber components A (base resin) and B (curing agent) in a 1:1 weight ratio was poured into the mold and cured at room temperature to form a first elastomer layer made of silicone rubber having a concave-convex structure with hemispherical depressions.

[0084] Using the mold for molding the elastomer layer shown in Figure 17, three elastomer layers were fabricated, each having the same thickness: a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) with hemispherical recesses, a first elastomer layer with a concave-convex structure (diameter approximately 8 mm) with hemispherical recesses, a first elastomer layer with a concave-convex structure (diameter approximately 5 mm) with hemispherical recesses, and a first elastomer layer made of silicone rubber without a concave-convex structure. The thickness of each was approximately 6.5 mm.

[0085] 18 to 21 show examples of an elastomer-coated RFID tag 109 (FIG. 18) made of a first elastomer layer having a concave-convex structure (diameter: approximately 12 mm) with hemispherical recesses formed therein, an elastomer-coated RFID tag 110 (FIG. 19) made of a first elastomer layer having a concave-convex structure (diameter: approximately 8 mm) with hemispherical recesses formed therein, an elastomer-coated RFID tag 111 (FIG. 20) made of a first elastomer layer having a concave-convex structure (diameter: approximately 5 mm) with hemispherical recesses formed therein, and an elastomer-coated RFID tag 112 (FIG. 21) having only one rectangular recess of approximately the same size as the antenna of the RFID tag, (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side). 22 shows an elastomer-coated RFID tag 113 according to comparative embodiment 4, which has a first elastomer layer made of silicone rubber without a concave-convex structure. These have a structure in which an RFID tag 107 (antenna shape G) is sandwiched and covered between a first elastomer layer and a second elastomer layer. In the above tag, the first elastomer layer side is the surface that contacts the object to which it is attached, and the second elastomer layer side is the surface that faces the antenna of the RFID tag reader / writer.

[0086] The above-mentioned structure in which the RFID tag 107 (shape G) is sandwiched and covered between the first elastomer layer and the second elastomer layer may be formed by forming the first elastomer layer, then adhering the RFID tag to the first elastomer layer, and pouring a two-component silicone rubber mixture onto it and allowing it to harden; alternatively, the RFID tag may be adhered to the first elastomer layer, and then a second elastomer layer that is separately prepared on a release paper or the like and undergoing a hardening reaction may be attached to the first elastomer layer and allowed to harden; or the RFID tag may be adhered to the first elastomer layer, and then covered with a second elastomer layer that has been prepared in advance; and various methods can be used to form the structure.

[0087] Fig. 25 shows the communication distance at which temperature data can be received when RFID tags of various structures are placed on a metal plate. In the measurement, the angle was set to 0°, which is the angle when the extension direction of the RFID tag antenna coincides with the direction of linear polarization from the antenna of the RFID tag reader / writer. When placed in contact with the surface of a metal plate, neither the existing RFID tag (Temperature Sensor Dogbone) 70 used as a comparative example nor the RFID tag 107 disclosed herein could receive temperature data, and the communication distance was approximately 0 cm.

[0088] 25 shows the communication distance at which temperature data can be received when a silicone sheet (approximately 2 mm thick) is sandwiched as a spacer between an existing RFID tag (Temperature Sensor Dogbone) 70 as a comparative example and an RFID tag 107 of the present disclosure and a metal plate, but in both cases the communication distance was approximately 8 cm, which was not much of an improvement. In contrast, in the case of an elastomer-coated RFID tag 108 covered with a first elastomer layer (silicone, approximately 2 mm thick) and a second elastomer (silicone) layer, which has an uneven structure in which recesses in which rectangular grooves intersect each other are arranged in a grid pattern, the silicone layer separating the RFID tag's IC chip from the metal plate has a thickness of approximately 2 mm, the same as the silicone spacer described above, but the communication distance was improved to approximately 27 cm. The first elastomer (silicone) layer has an uneven structure in which rectangular grooves intersect in a cross shape and are arranged in a grid pattern, and the air gaps of the voids give it lower dielectric constant than a homogeneous silicone sheet without voids, making it more effective as a spacer to prevent communication interference when inserted between a metal surface and an RFID tag. Therefore, introducing a structure with voids into the elastomer layer covering the RFID tag is effective in preventing communication interference and suppressing a reduction in communication distance when an RFID tag with a sensor function for infrastructure monitoring is attached to a metal structure.

[0089] In an RFID tag having a structure in which it is sandwiched and covered between a first elastomer layer and a second elastomer layer, the communication distance over which temperature data can be received is the same regardless of whether the first elastomer layer having an uneven structure is provided on the insulating substrate side or the annular conductor side of the RFID tag, as long as the antenna position of the RFID tag relative to the antenna of the RFID tag reader / writer is the same.

[0090] Figure 26 shows the change in the communication distance at which temperature data can be received when the thickness D2 of the second elastomer layer is changed when the thickness D1 of the first elastomer layer is approximately 6.5 mm in an elastomer-coated RFID tag 109 (see Figure 18, antenna shape G). The elastomer-coated RFID tag 109 is made of a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) formed with hemispherical depressions and is mounted on a metal plate. In the measurement, the angle was defined as 0°, which is the angle when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag is aligned with the linear polarization direction from the antenna of the RFID tag reader / writer. The elastomer-coated RFID tag 109 has a structure in which the RFID tag 107 (shape G) is sandwiched and covered between the first elastomer layer and the second elastomer layer. The second elastomer layer is located on the front surface of the RFID tag facing the antenna of the RFID tag reader / writer, and the communication distance decreases depending on the thickness of the dielectric elastomer. To examine the effect of the thickness D2 of the second elastomer layer, second elastomer layers of various thicknesses D2 were created by mixing and stirring two-component silicone HTV rubber components A and B in a 1:1 weight ratio, pouring the mixture into a plastic container with release paper at the bottom, and curing it at room temperature.

[0091] In Figure 26, a critical phenomenon is observed in the communication distance at which temperature data can be received from the elastomer-coated RFID tag 109. When the thickness D2 of the second elastomer layer is smaller than a certain value in the range of 0.7 mm or more and less than 1 mm, a critical phenomenon is observed in which the communication distance increases as the thickness D2 decreases. Furthermore, when the film thickness is in the range of 1 mm or more, the communication distance remains almost constant. In RFID tags consisting of a first elastomer layer and a second elastomer layer with a concave-convex structure, in order to reduce the decrease in communication distance due to dielectric loss in the elastomer, which is a dielectric, the thickness D2 of the second elastomer layer is preferably less than 1 mm, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. The dashed curve in Figure 26 is a curve fit using a sigmoid function.

[0092] In an elastomer-coated RFID tag 109 (Fig. 18) consisting of a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) formed with hemispherical depressions, when the second elastomer layer made of silicone rubber was replaced with a polypropylene film (thickness 0.03 mm) and the tag was placed on a metal plate, the communication distance at which temperature data could be received was 61 cm. Because polypropylene has a lower dielectric constant of 2.2 to 2.6 compared to silicone rubber (dielectric constant 3.0 to 3.5), the communication distance was approximately the same as the communication distance when RFID tag 107 (shape G) was attached to the first elastomer layer and an air layer was used instead of the second elastomer layer. When the second elastomer layer was made of 0.1 mm thick silicone rubber, the communication distance was 52 cm, approximately 85% of the value when polypropylene film (thickness 0.03 mm) was used. When silicone rubber is used for the second elastomer layer, the thinner the film thickness D2, the longer the communication distance will be, but on the other hand, the weather resistance and durability will be reduced, so the film thickness D2 will be set to suit the environment in which infrastructure monitoring will be performed.

[0093] The decrease in communication distance when a material with a high dielectric constant is in contact with or near an RFID tag is thought to be due to dielectric loss. Dielectric loss occurs when a dielectric material is subjected to an AC electric field, and some of the energy is lost as heat within the dielectric. The higher the dielectric constant, the greater the dielectric loss. The relative dielectric constant of a material is approximately 1 for air, approximately 1.02 for polystyrene foam, 2.2-2.6 for polypropylene, and 3.0-3.5 for silicone rubber. While silicone rubber has a relatively high relative dielectric constant, the reduction in communication distance due to dielectric loss when used as an RFID tag sealant or cover material has not been considered. The relationship between the silicone layer thickness D2 and communication distance exhibits a critical phenomenon, as shown in Figure 26. By keeping the silicone layer thickness D2 below 1 mm, communication distance can be improved.

[0094] 27 shows the communication distances at which temperature data can be received for elastomer-coated RFID tag 109 (FIG. 18), which is installed on a metal plate as an attachment target, and which is made of a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) with hemispherical recesses, RFID tag 110 (FIG. 19), which is made of a first elastomer layer with a concave-convex structure (diameter approximately 8 mm) with hemispherical recesses, RFID tag 111 (FIG. 20), which is made of a first elastomer layer with a concave-convex structure (diameter approximately 5 mm) with hemispherical recesses, and elastomer-coated RFID tag 112 (FIG. 21), which has only one rectangular recess of approximately the same size as the RFID tag antenna. Also shown is elastomer-coated RFID tag 113 (FIG. 22), which is made of a first elastomer layer made of silicone rubber without a concave-convex structure, according to comparative example 4. In the measurement, the angle was defined as 0° when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag coincided with the direction of linear polarization from the antenna of the RFID tag reader / writer. In measuring the communication distance, the first elastomer layer side was the surface that contacted the object to which the RFID tag was attached, and the second elastomer layer side was the surface facing the antenna of the RFID tag reader / writer.

[0095] In an elastomer-coated RFID tag with a concave-convex structure in which hemispherical recesses are formed, mounted on a metal plate, the communication distances were 52 cm, 51 cm, and 28 cm when the diameters of the hemispherical recesses were 12 mm, 8 mm, and 5 mm, respectively. The reason why the communication distance at which temperature data can be received increases as the diameter of the hemispherical recesses increases is because the proportion of voids in the first elastomer layer increases as the diameter of the hemispherical recesses increases. Since the thickness of the first elastomer layer increases with the diameter of the hemispherical recesses, an excessive diameter of the hemispherical recesses reduces heat transfer. In consideration of this, the diameter of the hemispherical recesses is preferably 5 mm to 20 mm, more preferably 5 mm to 16 mm, and even more preferably 5 mm to 12 mm.

[0096] From the perspective of communication distance, replacing the second elastomer layer made of silicone rubber with a resin film with a lower dielectric constant and a thinner film thickness can achieve a longer communication distance. For infrastructure monitoring RFID tags, depending on the infrastructure environment in which they are installed, it may be preferable to increase the communication distance by replacing the second elastomer layer with a thinner resin film. Furthermore, depending on the infrastructure environment in which they are installed, it may be preferable to simplify the structure of the RFID tag by using only the first elastomer layer with a concave-convex structure, without the second elastomer layer.

[0097] In the above-described uneven structure having hemispherical recesses, the diameter of the hemispherical recesses does not have to be uniform; instead, the uneven structure may have hemispherical recesses of multiple diameters. For example, in a mold for molding a first elastomer layer having an uneven structure having hemispherical recesses as shown in FIG. 17, hemispherical structures of smaller diameters can be attached to the gaps in a lattice made of hemispherical structures to form a mold having hemispherical protrusions of multiple diameters. Using the mold having hemispherical protrusions of multiple diameters, a first elastomer layer having an uneven structure having hemispherical recesses of multiple diameters can be produced. In this case, the diameter of the smaller hemispherical structures filling the gaps in the lattice made of hemispherical structures is preferably less than 5 mm. By forming an uneven structure having hemispherical recesses of multiple diameters, the proportion of voids in the first elastomer layer can be further increased.

[0098] In a tag with a structure in which an RFID tag is sandwiched and covered between a first elastomer layer with a concave-convex structure and a second elastomer, the concave portions are positioned so as to contact the metal surface, forming a gap between the metal surface and the first elastomer layer, as shown in Figures 18 to 21. However, even when the concave portions are positioned so as to contact the RFID tag and the flat portion of the first elastomer layer is positioned so as to contact the metal surface, the communication distance over which temperature data can be received is almost the same. This is because the proportion of the gap formed by the concave portions is the same regardless of the position of the concave portions.

[0099] In the case of elastomer-coated RFID tag 112 (FIG. 21), which is made of a first elastomer layer with only one rectangular recess of approximately the same size as the RFID tag antenna, there is a large gap (25 mm long x 90 mm wide x 5.5 mm high) between the metal plate and the RFID tag antenna. If we consider only the effect of the gap in the first elastomer layer, the communication distance should be greater than that of elastomer-coated RFID tags 109, 110, and 111, which have an uneven structure with hemispherical recesses. However, as shown in FIG. 27, the measured value was 8 cm, which is shorter than that of the RFID tag with a hemispherical uneven structure. This is thought to be because, since there is no uneven structure formed in the first elastomer layer between the metal plate and the RFID tag antenna, the electromagnetic waves specularly reflected from the metal plate are reflected toward the RFID tag antenna without being affected by dielectric loss, and interference with the incident waves to the RFID tag antenna reduces the communication distance. In contrast, the uneven structure formed in the first elastomer layer attenuates the electromagnetic waves that are reflected specularly from the metal plate through dielectric loss, preventing communication failures and reducing the communication distance of RFID tags placed on the metal plate.

[0100] In Figure 27, the communication distance at which temperature data can be received in the elastomer-coated RFID tag 113 (Figure 22) according to comparative form 4, in which the first elastomer layer is made of silicone rubber without a concave-convex structure, is 20 cm, which is smaller than that of an RFID tag having a concave-convex structure with hemispherical depressions.

[0101] 28 shows the effect of the thickness D2 of the second elastomer layer on the communication distance over which temperature data can be received when an RFID tag 101 (antenna shape A) is sandwiched and covered between a first elastomer layer and a second elastomer layer, each having an uneven structure (diameter approximately 12 mm) with hemispherical recesses, and the tag is placed on a metal plate. In the measurement, the angle was defined as 0°, which is the angle when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag coincides with the direction of linear polarization from the antenna of the RFID tag reader / writer.

[0102] In Figure 28, similar to the case of the RFID tag 107 (shape G) sandwiched and covered between the first and second elastomer layers (Figure 26), the RFID tag 101 (shape A) sandwiched and covered between the first and second elastomer layers also exhibited a critical phenomenon: when the thickness D2 of the second elastomer layer was less than a certain value in the range of 0.7 mm to less than 1 mm, the communication distance increased as the thickness D2 decreased. Furthermore, when the thickness was 1 mm or more, the communication distance remained almost constant. For RFID tags consisting of the first and second elastomer layers with a concave-convex structure, the thickness D2 of the second elastomer layer is preferably less than 1 mm, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less, to reduce the decrease in communication distance due to dielectric loss in the elastomers, which are dielectrics. The dashed curve in Figure 28 is a curve fit using a sigmoid function.

[0103] (Embodiment 6) 18 to 22 are all tags having a structure in which an RFID tag 107 (antenna shape G) is sandwiched and covered between a first elastomer layer and a second elastomer layer, but instead of RFID tag 107 (antenna shape G), elastomer-coated RFID tags 114 to 119 were created, each having a structure in which an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched and covered between a first elastomer layer and a second elastomer layer. The existing RFID tag (Temperature Sensor Dogbone) 70 is an RFID tag comprising an insulating substrate, an annular conductor with an opening provided on the surface of the insulating substrate, an IC chip with a sensor function capable of acquiring temperature data connected to the annular conductor by a power supply part provided near the opening, and an antenna made of a radiating conductor. FIG. 23 shows an example of an RFID tag 114 (antenna structure of existing RFID tag 70) covered with a first elastomer layer and a second elastomer layer having an uneven structure (diameter: approximately 12 mm) with hemispherical recesses, including (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side).

[0104] In the elastomer-coated RFID tag, an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched and covered between a first elastomer layer and a second elastomer layer. Examples of the elastomer-coated RFID tag include elastomer-coated RFID tag 114 made of a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) with hemispherical recesses, elastomer-coated RFID tag 115 made of a first elastomer layer with a concave-convex structure (diameter approximately 8 mm) with hemispherical recesses, elastomer-coated RFID tag 116 made of a first elastomer layer with a concave-convex structure (diameter approximately 5 mm) with hemispherical recesses, elastomer-coated RFID tag 117 with only one rectangular recess of approximately the same size as the RFID tag antenna, and elastomer-coated RFID tag 118 made of a first elastomer layer of silicone rubber with no concave-convex structure. Figure 29 shows an example of the communication distance over which temperature data can be received when these tags are installed on a metal plate as an attachment target. When measuring the communication distance, the first elastomer layer side is the surface that comes into contact with the object to which it is attached, and the second elastomer layer side is the surface that faces the antenna of the RFID tag reader / writer.

[0105] Even in elastomer-coated RFID tags, in which an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched between a first elastomer layer and a second elastomer layer, the effect of the uneven structure with hemispherical recesses was demonstrated in the communication distance at which temperature data could be received when the tag was placed on a metal plate. When the diameter of the hemispherical recess was 12 mm (elastomer-coated RFID tag 114), 8 mm (elastomer-coated RFID tag 115), and 5 mm (elastomer-coated RFID tag 116), the communication distance was 42 cm, 37 cm, and 26 cm, respectively. The larger the diameter of the hemispherical recess, the longer the communication distance at which temperature data could be received. This is because the proportion of voids in the first elastomer layer increases as the diameter of the hemispherical recess increases. Since the thickness of the first elastomer layer increases as the diameter of the hemispherical recess increases, an excessively large diameter of the hemispherical recess reduces heat transfer, and therefore the diameter of the hemispherical recess is preferably 5 mm or more and 20 mm or less, more preferably 5 mm or more and 16 mm or less, and even more preferably 5 mm or more and 12 mm or less.

[0106] In Figure 29, the communication distance at which temperature data can be received for elastomer-coated RFID tag 118, which has a first elastomer layer made of silicone rubber without a concave-convex structure, when placed on a metal plate is 19 cm, which is smaller than that of an RFID tag with a concave-convex structure formed with hemispherical depressions.

[0107] In an RFID tag having a structure in which it is sandwiched and covered between a first elastomer layer and a second elastomer layer, the communication distance over which temperature data can be received is the same regardless of whether the first elastomer layer having an uneven structure is provided on the insulating substrate side or the annular conductor side of the RFID tag, as long as the antenna position of the RFID tag relative to the antenna of the RFID tag reader / writer is the same.

[0108] In an elastomer-coated RFID tag in which an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched and covered between a first elastomer layer and a second elastomer layer, the effect of the uneven structure was also demonstrated in tag 117, which is made of a first elastomer layer with only one rectangular recess of approximately the same size as the RFID tag antenna, and the communication distance at which temperature data can be received when installed on a metal plate is 30 cm, a greater value than elastomer-coated RFID tag 118, which does not have an uneven structure. It was shown that the antenna structure of the RFID tag, which is sandwiched and covered between the first elastomer layer and the second elastomer layer, has an effect on the prevention of communication failures and the suppression of a reduction in communication distance when an elastomer-coated RFID tag is installed on a metal plate.

[0109] (Embodiment 7) The phenomenon of communication distance being significantly shortened and communication becoming impossible when an RFID tag is attached to a metal object is explained by the generation of eddy currents due to electromagnetic waves incident on the metal object. When this phenomenon is viewed from the perspective of the phase change of electromagnetic waves incident on a metal surface from the air, it results in fixed-end reflection, with a phase shift of π causing phase inversion and weakening the incident and reflected waves. Metal-compatible RFID tags have been devised to address communication problems when attached to metal. For example, (i) a tag that enables reading by creating distance between the RFID tag and the metal surface using a foam separator or similar, and (ii) a tag that enables reading by placing a magnetic sheet made of a soft magnetic material between the tag and the metal surface, changing the reflection direction of the incident magnetic flux.

[0110] In the present disclosure, a conductor layer having a substantially zigzag cross-sectional shape is introduced between the RFID tag and the metal surface to prevent communication failures and minimize a reduction in communication distance when acquiring temperature data via wireless communication, even when the object to which the RFID tag is attached is a metal structure. This changes the direction of reflection of electromagnetic waves that pass through the RFID tag, thereby obtaining an RFID tag that can acquire temperature data via wireless communication, even when the object to which the RFID tag is attached is a metal structure. The word "substantially zigzag" in the term "substantially zigzag conductor layer" means that the corners or sides may be rounded.

[0111] 24 shows an example of (a) a plan view (fourth elastomer layer side), (b) a cross-sectional view, and (c) a plan view (third elastomer layer side) of an elastomer-coated RFID tag 119 according to embodiment 6, which is covered with a third elastomer layer 62 and a fourth elastomer layer 63 each having a substantially zigzag conductor layer in a cross-sectional view. Covering and sealing with elastomer improves water resistance, insulation, heat resistance, weather resistance, durability, and the like. Furthermore, the third elastomer layer having the substantially zigzag conductor layer changes the reflection direction of electromagnetic waves that have passed through the RFID tag relative to the direction of incidence of the electromagnetic waves on the RFID tag, thereby preventing communication failures caused by interference between electromagnetic waves input to the RFID tag and electromagnetic waves specularly reflected from a metal surface. In FIG. 24, the RFID tag 107 (antenna structure G) covered with the third elastomer layer 62 and the fourth elastomer layer 63 is referred to as an elastomer-coated RFID tag 119, but the RFID tag to be covered is not particularly limited.

[0112] The material of the approximately zigzag conductor layer 12 is not particularly limited and is formed from a conductive conductor. For example, it may be metal, such as aluminum, copper, gold, platinum, silver, nickel, chromium, zinc, lead, tungsten, or iron. The material of the approximately zigzag conductor layer 12 may be a metal oxide, such as tin oxide or ITO (indium tin oxide), a conductive film using metal nanowires, such as gold, silver, or copper, a conductive resin mixture in which resin is mixed with the above metal powder or a conductive carbon material, or a conductive resin film. From the viewpoints of flexibility and strength, the thickness of the approximately zigzag conductor layer 12 is preferably 0.01 to 1000 μm, more preferably 1 to 100 μm. Alternatively, the material of the approximately zigzag conductor layer 12 may be a planar conductor layer formed on the insulating substrate 10 using a known method on the material exemplified above.

[0113] The materials of the third elastomer 62 and the fourth elastomer 63 are not particularly limited, and may be the same as the above examples of the first elastomer 60 and the second elastomer 61 .

[0114] Because RFID tags for infrastructure monitoring require water resistance, insulation, heat resistance, weather resistance, and durability, as shown in FIG. 24 , the third elastomer layer 62 includes a generally zigzag conductor layer, and the generally zigzag conductor layer 12 is embedded within the elastomer in a cross-sectional view. The generally zigzag conductor layer 12 does not necessarily have to be embedded within the elastomer. The first elastomer layer may have a generally zigzag conductor structure in a cross-sectional view, and the conductor layer may be formed on the generally zigzag surface of the elastomer that is attached to the metal. Furthermore, the conductor layer may be covered with an insulating layer to improve water resistance, insulation, heat resistance, weather resistance, and durability. The material of the insulating layer is not particularly limited and may be the same as the aforementioned example of the insulating substrate 10.

[0115] The generally zigzag conductor layer 12 preferably has a bending angle of 10° to 85°, more preferably 30° to 60°. The V-groove spacing is preferably 1 mm to 120 mm, more preferably 2 mm to 20 mm. The V-groove spacing does not need to be uniform, and may be comprised of multiple V-groove spacings. The structure of the generally zigzag conductor layer is not particularly limited and is determined taking into consideration the shape and size of the RFID tag, the shape of the object to be fitted with the RFID tag and the required communication distance for wireless temperature measurement in infrastructure monitoring. The thickness of the third elastomer layer 62 is preferably 1 mm to 20 mm, more preferably 1 mm to 12 mm, and even more preferably 1 mm to 7 mm.

[0116] From the viewpoint of preventing communication failures and suppressing a reduction in communication distance caused by interference between the electromagnetic waves incident on the RFID tag and the electromagnetic waves specularly reflected from a metal surface by changing the reflection direction of the electromagnetic waves that have passed through the RFID tag to a different direction relative to the direction of incidence of the electromagnetic waves on the RFID tag, the conductor layer that can change the reflection direction of the electromagnetic waves that have passed through the RFID tag to a different direction is not limited to a conductor layer that is approximately zigzag in cross section, but may also be a conductor layer that is honeycomb in cross section, or a conductor layer that has a curved or spherical surface other than a flat surface.Furthermore, the conductor layer may have a repeated structure of curved or spherical conductor layers, or may have a structure in which flat, curved, or spherical conductor layers are combined.

[0117] 30 shows an example of the change in communication distance at which temperature data can be received when an elastomer-coated RFID tag 119 (antenna shape G) covered with a third elastomer layer and a fourth elastomer layer having a conductor layer with a roughly zigzag shape in cross section is placed on a metal plate to be attached, and the change in thickness D4 of the fourth elastomer layer results in a change in the communication distance at which temperature data can be received. In the measurement, the angle was set to 0° when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag coincided with the direction of linear polarization from the antenna of the RFID tag reader / writer.

[0118] In Figure 30, a critical phenomenon is observed in the communication distance at which temperature data from the elastomer-coated RFID tag 119 can be received. When the thickness D4 of the fourth elastomer layer is smaller than a certain value in the range of 0.7 mm or more and less than 1 mm, a critical phenomenon is observed in which the communication distance increases as the thickness D2 decreases. Furthermore, when the film thickness is 1 mm or more, the communication distance remains almost constant. In an RFID tag consisting of a third elastomer layer and a second elastomer layer with a roughly zigzag conductor layer in cross section, the thickness D4 of the fourth elastomer layer is preferably less than 1 mm, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less, to reduce the decrease in communication distance due to dielectric loss in the dielectric elastomer. The dashed curve in Figure 30 is a curve fit using a sigmoid function.

[0119] In an RFID tag having a structure in which it is sandwiched and covered between a third elastomer layer and a fourth elastomer layer, the communication distance over which temperature data can be received is the same regardless of whether the third elastomer layer having an uneven structure is provided on the insulating substrate side or the annular conductor side of the RFID tag, as long as the antenna position of the RFID tag relative to the antenna of the RFID tag reader / writer is the same.

[0120] (Example) Next, the present embodiment and a comparative embodiment will be specifically described. The present invention is not limited to these specific examples. The materials and devices used in the specific examples are as follows.

[0121] [material] (1) Aluminum foil / PET composite film: PANAC; AL-PET9-100, aluminum foil thickness 9 μm, PET film thickness 100 μm. (2) IC chip 20: AXZON; Magnus-S3, size 1.6BSC x 1.6BSC, thickness 0.35mm, equipped with temperature sensor function. (3) UHF RFID tag: Avery Dennison Smartrac; Temperature Sensor Dogbone, frequency band: UHF 860-960MHz, IC chip: IC chip 20 (Magnus-S3), equipped with temperature sensor function. (4) Adhesive: Bond Ultra Multi-Purpose SU manufactured by Konishi Co., Ltd. (5) Styrofoam block: Made by Daiso; expanded polystyrene, 20x10cm, 5cm thick. (6) Thermosetting elastomer; silicone two-component RTV rubber, EZ Mold, MY Co., Ltd. (7) Thermosetting elastomer: silicone two-component HTV rubber, HTV-4000, Engraving Japan. (8) Silicone tray: Silicone resin tray with uneven structure, Nakajima Kirijiro Shoten. (9) Absolute ethanol; Kenei Pharmaceutical Co., Ltd., ethanol 99.5 vol% or more. (10) Metal plate: Taiho; steel plate, length 100mm, width 200mm, thickness 1mm. (11) Hemispherical structure: manufactured by Motobayashi Co., Ltd., rhinestone seal, material: ABS resin, diameter: approximately 12 mm, approximately 8 mm, approximately 5 mm. (12) Release paper sheet; manufactured by Kyowa Shiko Co., Ltd., size 150mm x 105mm. (13) Plastic case; Sanada Seiko Co., Ltd., clear case S tray, width 79 x depth 220 x height 17 mm (external dimensions). (14) Plastic case; Sanada Seiko Co., Ltd., clear case D tray, width 110 x depth 159 x height 17 mm (external dimensions). (15) Polypropylene sheet; manufactured by Can Do Co., Ltd., thickness 0.03 mm.

[0122] [Device] (16) UHF RFID reader / writer: Takaya Corporation; UTR-S201, specific low-power radio station type, transmission frequency 916.8MHz~923.2MHz (18 channels), transmission output 10dBm (10mW)~24dBm (250mW), interface USB interface board TR3-IF-U1C. (17) UHF band external antenna (linearly polarized): Takaya Co., Ltd.; UTR-UA1709-1 [software] (18) Temperature measurement software for IC chip 20: UTRTempSensor Demo Ver. 1.001 manufactured by Takaya Co., Ltd. (19)Graph processing software: WaveMetrics; Igor Pro.

[0123] [RFID tag creation] The RFID tags 101 to 107 in the first to fourth embodiments and the first to third comparative embodiments were fabricated as follows: An impedance matching section (annular conductor) 30 (length in the X-axis direction: approximately 14 mm, width in the Y-axis direction: approximately 6 mm) having a substantially quadrangular opening 22 in which the IC chip 20 was mounted was cut out from an RFID tag temperature sensor dogbone (IC chip 20), the thin transparent resin film used to protect the IC chip 20 was peeled off, and the surface of the annular conductor was cleaned with ethanol. The conductor layer 11 side of the radiation conductors (30 to 36) fabricated by cutting an aluminum foil / PET composite film was fixed and connected with an adhesive so that the conductor layer 11 side of the impedance matching section (annular conductor) 30 was in contact with the conductor layer 11 side. By appropriately specifying (a thickness of 60 μm or less) the thickness of the insulating layer (thickness of the adhesive layer) that contacts and fixes and connects the annular conductor of the impedance matching section having the IC chip 20 and the conductor layer 11 that forms the antenna consisting of a radiating conductor, electromagnetic coupling is formed between the annular conductor of the impedance matching section and the radiating conductor, and a communication distance between the RFID tag and the antenna of the RFID reader / writer can be obtained that is approximately the same as when the annular conductor of the impedance matching section and the radiating conductor that forms the antenna are continuous conductor layers.

[0124] The impedance matching section (annular conductor) 30 and the first to sixth radiating conductors (31 to 36) may have a structure made up of a continuous conductor layer, or may have a structure in which the impedance matching section (annular conductor) 30 and the first to sixth radiating conductors (31 to 36) are electrically connected by another conductor layer, or may have a structure in which they are fixed and connected at a close distance so that electromagnetic coupling is formed at ultra-high frequencies in the UHF band. The method of producing an RFID tag is not limited to the above.

[0125] [Measurement method] The communication distance CL, a parameter that represents the characteristics of an RFID tag, was measured using the temperature measurement software (UTRTempSensor Demo Ver. 1.001) for IC chip 20, with the RFID reader / writer output set to 24 dBm (250 mW), the reader / writer antenna (linearly polarized) 50 as an external antenna, and the RFID tag temperature measurement distance CL, which is placed in the air, was measured by fixing the RFID tags (101-107) to a polystyrene foam block with tape so that the first dipole antenna or the second dipole antenna was parallel to the floor. The reader / writer antenna (linearly polarized) 50 was held at a certain angle relative to the RFID tags (101-107), and the distance between the RFID tag and the reader / writer antenna (linearly polarized) 50 was changed to measure the communication distance at which the RFID reader / writer could receive temperature data from IC chip 20. The temperature measurement software (UTRTempSensor Demo Ver.1.001) used to measure the communication distance was set to a reader / writer output of 24 dBm and an OnChip RSSI (Received Signal Strength Indicator) with a lower limit of 15 dBm and an upper limit of 23 dBm. When the RFID tag was placed on a metal plate, the lower limit of the OnChip RSSI was set to 5 dBm, and the communication distance was measured. The curve fitting shown as dashed lines in Figures 8, 9, 26, 28, and 30 was obtained using graph processing software (WaveMetrics; Igor Pro).

[0126] Regardless of whether the insulating substrate side or the annular conductor side of the RFID tag faces the antenna surface of the RFID tag reader / writer, the communication distance over which temperature data can be received is the same as long as the RFID tag antenna is positioned in the same way relative to the antenna of the RFID tag reader / writer. [Example]

[0127] FIG. 1 shows an example of an RFID tag (antenna shape A) 101 according to the first embodiment. The RFID tag (antenna shape A) 101 has a shape in which a first dipole antenna composed of a first radiation conductor 31 and a second dipole antenna composed of a second radiation conductor 32 and a third radiation conductor 33 extend in a first direction (the X direction in FIG. 1 ) and a second direction (the −X direction in FIG. 1 ) from an impedance matching section (annular conductor) 30. The fourth-direction (−Y direction in FIG. 1 ) end of the first dipole antenna and the third-direction (the Y direction in FIG. 1 ) end of the second dipole antenna extend parallel to each other and face each other at approximately equal intervals. The distance between the first dipole antenna and the second dipole antenna is set within a range of 0.1 mm to 14 mm inclusive, in accordance with the shape of the impedance matching section (annular conductor) 30.

[0128] 7 shows the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in RFID tag (antenna shape A) 101. When the angle between the extension direction of the first dipole antenna or the second dipole antenna and the linear polarization direction from the antenna of the RFID tag reader / writer is 40°, the communication distance at which temperature data can be received is 218 cm, and when the extension direction of the first dipole antenna or the second dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer (angle 0°), the communication distance at which temperature data can be received is 240 cm, the ratio of which is approximately 0.9.

[0129] The RFID tag (antenna shape A) 101 exhibits nearly omnidirectional characteristics in the angle range of -40° to 40°. This is thought to be because the first dipole antenna and the second dipole antenna are configured to extend parallel to each other from the impedance matching section (annular conductor) 30 in the first and second directions, making the distribution of the electromagnetic field formed by the two dipole antennas broader.

[0130] [Comparative Example 1] 2 shows an example of an RFID tag (antenna shape B) 102 according to comparative embodiment 1. The difference between the RFID tag (antenna shape A) according to embodiment 1 and the RFID tag (antenna shape B) according to comparative embodiment 1 is that the RFID tag (antenna shape A) has a structure in which the first dipole antenna and the second dipole antenna extend parallel to each other, while the RFID tag (antenna shape B) 102 has a structure in which only the first dipole antenna is included.

[0131] 8 shows the relationship between the angle between the extension direction of the first dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape B) 102 according to comparative example 1. When the angle between the extension direction of the first dipole antenna and the linear polarization direction from the antenna of the RFID tag reader / writer is 40°, the communication distance at which temperature data can be received is 50 cm. When the extension direction of the first dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer (angle 0°), the communication distance at which temperature data can be received is 126 cm, the ratio of these values ​​being approximately 0.4. When there is only one dipole antenna, the directivity is high, and the angle dependency of the communication distance at which temperature data can be received becomes significant.

[0132] Comparative Example 2 3 shows an example of an RFID tag (antenna shape C) 103 according to comparative embodiment 2. The difference between the RFID tag (antenna shape A) according to embodiment 1 and the RFID tag (antenna shape C) according to comparative embodiment 2 is that the RFID tag (antenna shape A) has a structure in which the first dipole antenna and the second dipole antenna extend parallel to each other, while the RFID tag (antenna shape C) 102 has a structure in which only the second dipole antenna is included.

[0133] 9 shows the relationship between the angle between the extension direction of the first dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, for an RFID tag (antenna shape C) 103 according to comparative example 2. When the angle between the extension direction of the second dipole antenna and the linear polarization direction from the antenna of the RFID tag reader / writer is 40°, the communication distance at which temperature data can be received is 120 cm. When the extension direction of the first dipole antenna or the second dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer (angle 0°), the communication distance at which temperature data can be received is 190 cm, the ratio of these values ​​being approximately 0.6. When there is only one dipole antenna, the directivity is high, and the angle dependency of the communication distance at which temperature data can be received becomes significant. [Example]

[0134] 4 shows an example of an RFID tag (antenna shape D) 104 according to embodiment 2. In addition to the structure of the RFID tag (antenna shape A) 101 according to embodiment 1, the RFID tag (antenna shape D) 104 includes a third dipole antenna extending from the first radiation conductor 31 in the third direction (a direction substantially perpendicular to the extending direction of the first radiation conductor) and consisting of a fourth radiation conductor 34 connected to the first radiation conductor 31, and a fourth dipole antenna extending from the third radiation conductor 33 in a fourth direction opposite to the third direction and consisting of a fifth radiation conductor 35 connected to the third radiation conductor 33.

[0135] 10 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in RFID tag (antenna shape D) 104 according to embodiment 2. In the case of RFID tags 101, 102, and 103, the communication distance at which temperature data can be received was close to zero when the angle at which the direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer intersected at a right angle of 90°, whereas in RFID tag (antenna shape D) 104 it is 90 cm or more, and the ratio of the communication distance at which temperature data can be received when the direction of the first dipole antenna or the second dipole antenna of the RFID tag is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer (angle 0°) is 0.75. In addition, the ratio of the communication distance at which temperature data can be received when the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer is 60° to the communication distance at which temperature data can be received when the direction of the first dipole antenna or the second dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer is approximately 0.73.

[0136] With the RFID tag (antenna shape D) 104, a communication distance sufficient to receive good temperature data was obtained in all angular regions, demonstrating improved omnidirectionality of the RFID tag. This is thought to be because the first dipole antenna and the second dipole antenna are configured to extend parallel to each other in the first and second directions from the impedance matching section (annular conductor) 30, which broadens the distribution of the electromagnetic field formed by the two dipole antennas, and this is compounded by the effects of the third dipole antenna extending in the third direction and the fourth dipole antenna extending in the fourth direction.

[0137] Comparative Example 3 5 shows an example of an RFID tag (antenna shape E) 105 according to comparative embodiment 3. The difference from the RFID tag (antenna shape D) 104 according to embodiment 2 is that the RFID tag (antenna shape E) 105 according to comparative embodiment 3 has a sixth radiation conductor 36 extending in the second direction instead of the first radiation conductor 31 extending in the first and second directions from the impedance matching section (annular conductor) 30, and does not have the third radiation conductor 33. Therefore, the first dipole antenna formed by the sixth radiation conductor 36 and the second dipole antenna formed by the second radiation conductor 32 do not have a structure in which they extend parallel to each other in the first and second directions.

[0138] 11 is a diagram showing the relationship between the angle between the extending direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape E) 105 according to comparative embodiment 3. Compared to the case of the RFID tag (antenna shape D) 104 according to embodiment 2 (FIG. 10), the decrease in the communication distance at which temperature data can be received is greater in the angle range of 10° to 90°, and at angles around 50° to 70°, the communication distance at which temperature data can be received is reduced to 20 cm or less. [Example]

[0139] 12 shows an example of an RFID tag (antenna shape F) 106 according to embodiment 3. The shape of the RFID tag (antenna shape F) 106 is such that the first radiating conductor 31, which is the radiating conductor forming the first dipole antenna of the RFID tag (antenna shape A) 101 (FIG. 1) according to embodiment 1, and the second radiating conductor 32 and third radiating conductor 33, which are the radiating conductor forming the second dipole antenna, are changed from a substantially rectangular shape to a substantially meandering shape, thereby reducing the size of the RFID tag.

[0140] In the RFID tag (antenna shape F) 106, the fourth direction (-Y direction in FIG. 12) end of the first dipole antenna and the third direction (Y direction in FIG. 12) end of the second dipole antenna extend parallel to each other at approximately equal intervals, similar to the RFID tag (antenna shape A) 101. The interval between the first dipole antenna and the second dipole antenna is set in the range of 0.1 mm to 14 mm inclusive in accordance with the shape of the impedance matching portion (annular conductor) 30.

[0141] 13 is a diagram showing the relationship between the angle between the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance at which temperature data can be received, in the RFID tag (antenna shape F) 106 according to the third embodiment. Compared to the comparative embodiments 1 and 2, which have only one dipole antenna, the RFID tag (antenna shape F) exhibits substantially omnidirectionality in the angle range of -40° to 40°. For example, in the RFID tag (antenna shape F) 106, the ratio of the communication distance at which temperature data can be received when the angle between the extension direction of the first dipole antenna or the second dipole antenna and the linear polarization direction from the antenna of the RFID tag reader / writer is -40° to the communication distance at which temperature data can be received when the orientation of the first dipole antenna or the second dipole antenna is parallel to the linear polarization direction from the antenna of the RFID tag reader / writer (angle 0°) is 0.9 or more. [Example]

[0142] 14 shows an example of an RFID tag (antenna shape G) 107 according to the fourth embodiment. The shape of the RFID tag (antenna shape G) 107 is the same as that of the RFID tag (antenna shape D) 104 according to the second embodiment, except that the first radiation conductor 31 forming the first dipole antenna, the second radiation conductor 32 and the third radiation conductor 33 forming the second dipole antenna, the fourth radiation conductor 34 forming the third dipole antenna, and the fifth radiation conductor 35 forming the fourth dipole antenna are changed from a substantially rectangular shape to a substantially meander shape, thereby reducing the size of the RFID tag. Furthermore, compared to the shape of the RFID tag (antenna shape F) 106, the shape of the RFID tag (antenna shape G) 107 is different from that of the RFID tag (antenna shape F) 106, in that the substantially meander-shaped fourth radiation conductor 34 forming the third dipole antenna and the substantially meander-shaped fifth radiation conductor 35 forming the fourth dipole antenna are added.

[0143] 15 is a diagram showing the relationship between the angle between the extending direction of the first dipole antenna or the second dipole antenna of the RFID tag and the linear polarization direction from the antenna of the RFID tag reader / writer, and the communication distance over which temperature data can be received, in the RFID tag (antenna shape G) 107 according to embodiment 4. Nearly omnidirectional characteristics are obtained within the angle range of -60° to 50°. [Example]

[0144] FIG. 16 shows an example of an elastomer-coated RFID tag (antenna shape G) 108 according to the fifth embodiment, which is covered with an elastomer having an uneven structure in which rectangular grooves intersect at a cross-shaped pattern and recesses are arranged in a grid pattern. To create the tag, a silicone resin tray having an uneven structure in which rectangular grooves intersect at a cross-shaped pattern and protrusions are arranged in a grid pattern was cut to a size larger than the RFID tag and placed at the bottom of a rectangular container or the like. A liquid prepared by mixing and stirring a first component (base resin) and a second component (curing agent) for a two-component silicone RTV rubber in a 1:1 weight ratio was poured into the tray and allowed to harden at room temperature. After approximately three hours, when the surface of the thermosetting elastomer had solidified and become tacky, an RFID tag was placed on the surface of the thermosetting elastomer. A liquid prepared by mixing and stirring a first component (base resin) and a second component (curing agent) for a two-component silicone RTV rubber in a 1:1 weight ratio was poured into the tray and allowed to harden at room temperature for approximately eight hours. The method of producing the elastomer-coated RFID tag 108 is not limited to the above.

[0145] In one example of the first elastomer having a concave-convex structure in the form of a grid of recesses where rectangular grooves intersect at a cross, as shown in Figure 16, the recesses have a depth of approximately 1 mm, and are formed by rectangular grooves that intersect at a cross, each approximately 1 mm wide and 7 mm long, and are arranged in a grid. The thickness D1 of the first elastomer layer is approximately 2 mm, and the thickness D2 of the second elastomer layer is approximately 0.5 mm. The thickness of the elastomer and the shape of the concave-convex structure are not limited to those shown in Figure 16.

[0146] The RFID tag is covered and sealed with an elastomer to improve its water resistance, insulation, heat resistance, weather resistance, durability, etc., and the introduction of voids due to the uneven structure in the elastomer layer acts as a spacer, preventing communication failures and suppressing a reduction in communication distance when the RFID tag is attached to a metal surface. Even when the object to which the RFID tag is attached is a metal structure, from the viewpoint of preventing communication failures and suppressing a reduction in communication distance, it is preferable that the shape of the uneven structure has as large an area of ​​the recessed portions as possible and a high void ratio. It is also preferable that the height of the unevenness is high, forming a gap between the object to which the RFID tag is attached and the RFID tag, separating them by an air gap.

[0147] However, in infrastructure monitoring using RFID tags with sensor functions capable of wirelessly acquiring temperature data, excessive increases in porosity and asperity height can adversely affect the response and accuracy of temperature monitoring due to reduced heat transfer. Therefore, the optimal porosity and asperity shape and size must be determined taking into account the required temperature monitoring response and accuracy, as well as the required communication distance, when monitoring infrastructure facilities. The depth of the asperity structure is preferably 0.5 mm to 20 mm, more preferably 0.5 mm to 15 mm, and even more preferably 0.5 mm to 10 mm. Taking these factors into consideration, the thickness of the first elastomer layer 60 is preferably 1 mm to 20 mm, more preferably 1 mm to 15 mm, and even more preferably 1 mm to 10 mm.

[0148] The shape of the uneven structure is preferably one that maximizes the area of ​​the recessed portions of the concave portions, since this provides a greater gap between the RFID tag and the object to which it is attached, thereby preventing communication failures and minimizing a reduction in communication distance when the RFID tag is attached to the surface of a metal structure that serves as the object to which it is attached. In the case of an example of the first elastomer having the uneven structure shown in Figure 16, the width of the rectangular grooves that intersect in a crisscross pattern and are approximately 7 mm long is preferably 1 mm to 3 mm, and more preferably 1 mm to 6 mm.

[0149] FIG. 25 shows the communication distances over which temperature data can be received when RFID tags of various structures are installed on a metal plate. A metal plate measuring 100 mm in length, 200 mm in width, and 1 mm in thickness was used. This metal plate was placed on the floor, and various RFID tags were placed on top of it. The communication distances over which temperature data can be received were measured. The extension direction of the RFID tag's dipole antenna and the linear polarization direction from the RFID tag reader / writer antenna were parallel (at an angle of 0°). When installed directly on the surface of a metal plate, neither the existing RFID tag (Temperature Sensor Dogbone) 70 (comparison example) nor the RFID tag 107 of the present disclosure could receive temperature data, resulting in a communication distance of approximately 0 cm. The communication distances over which temperature data can be received were also shown when a silicone sheet (approximately 2 mm thick) was sandwiched between the existing RFID tag (Temperature Sensor Dogbone) 70 (comparison example) and the RFID tag 107 of the present disclosure and the metal plate. In both cases, the communication distance was approximately 8 cm, showing little improvement.

[0150] In contrast, in the case of the elastomer-coated RFID tag 108, which is covered with a first elastomer (silicone) layer and a second elastomer (silicone) layer having an uneven structure in which recesses in the shape of cross-shaped rectangular grooves are arranged in a grid pattern, the communication distance is improved to approximately 27 cm, even though the thickness of the silicone layer isolating the RFID tag's IC chip, annular conductor, and antenna part from the metal plate is approximately 2 mm, as above.

[0151] The shape of the uneven structure is not limited to the above-mentioned shape of rectangular grooves intersecting in a cross shape, and various shapes of uneven structures that can form a gap between the attachment object and the RFID tag can be applied, such as an uneven structure with conical or cylindrical protrusions, an uneven structure with prismatic columns such as triangular columns or quadrangular columns, an uneven structure with hemispherical recesses, an uneven structure with hemispherical protrusions, etc. Here, the uneven structure includes recesses and protrusions.

[0152] 17 shows an example of a mold for molding a first elastomer layer having a concave-convex structure with hemispherical recesses. Plastic hemispherical structures 40 (diameter approximately 12 mm), 41 (diameter approximately 8 mm), and 42 (diameter approximately 5 mm) were attached in a grid pattern to the bottom of a plastic container to form a mold for molding a first elastomer layer having a concave-convex structure with hemispherical recesses. The method and material for producing the mold for molding a first elastomer layer having a concave-convex structure are not limited, and it may be an integrated mold made of resin or metal.

[0153] A liquid prepared by mixing and stirring two-component silicone HTV rubber components A (main component) and B (curing agent) in a 1:1 weight ratio was poured into a mold for molding the first elastomer layer having the above-mentioned uneven structure with hemispherical depressions, and cured at room temperature for approximately 8 hours to form a first elastomer layer made of silicone rubber having an uneven structure with hemispherical depressions.

[0154] Using the mold for molding the elastomer layer shown in Figure 17, three elastomer layers were formed, each having the same thickness: a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) with hemispherical recesses, a first elastomer layer with a concave-convex structure (diameter approximately 8 mm) with hemispherical recesses, a first elastomer layer with a concave-convex structure (diameter approximately 5 mm) with hemispherical recesses, and a first elastomer layer made of silicone rubber without a concave-convex structure. The thickness of each layer was approximately 6.5 mm.

[0155] 18 to 21 show examples of an elastomer-coated RFID tag 109 (FIG. 18) made of a first elastomer layer having a concave-convex structure (diameter: approximately 12 mm) with hemispherical recesses formed therein; an elastomer-coated RFID tag 110 (FIG. 19) made of a first elastomer layer having a concave-convex structure (diameter: approximately 8 mm) with hemispherical recesses formed therein; an elastomer-coated RFID tag 111 (FIG. 20) made of a first elastomer layer having a concave-convex structure (diameter: approximately 5 mm) with hemispherical recesses formed therein; and an elastomer-coated RFID tag 112 (FIG. 21) having only one rectangular recess of approximately the same size as the antenna of the RFID tag, (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side). 22 shows an elastomer-coated RFID tag 113 according to comparative embodiment 4, which has a first elastomer layer made of silicone rubber without a concave-convex structure. These have a structure in which an RFID tag 107 (antenna shape G) is sandwiched and covered between a first elastomer layer and a second elastomer layer.

[0156] In Figures 18 to 22, the surface of the RFID tag facing the insulating substrate is on the first elastomer side, and the surface of the RFID tag facing the annular conductor is on the second elastomer layer side. However, in an RFID tag that is sandwiched and covered between the first elastomer layer and the second elastomer layer, the communication distance over which temperature data can be received is the same regardless of whether the first elastomer layer with a concave-convex structure is provided on the surface of the RFID tag facing the insulating substrate or the annular conductor, as long as the antenna position of the RFID tag relative to the antenna of the RFID tag reader / writer is the same.

[0157] Figure 26 shows the change in the communication distance at which temperature data can be received when the thickness D2 of the second elastomer layer is changed when the thickness D1 of the first elastomer layer is approximately 6.5 mm in an elastomer-coated RFID tag 109 (see Figure 18, antenna shape G). The elastomer-coated RFID tag 109 is made of a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) formed with hemispherical depressions and is mounted on a metal plate. In the measurement, the angle was defined as 0°, which is the angle when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag is aligned with the linear polarization direction from the antenna of the RFID tag reader / writer. The elastomer-coated RFID tag 109 has a structure in which the RFID tag 107 (shape G) is sandwiched and covered between the first elastomer layer and the second elastomer layer. The second elastomer layer is located on the front surface of the RFID tag facing the antenna of the RFID tag reader / writer, and the communication distance decreases depending on the thickness of the dielectric elastomer.

[0158] To examine the effect of the second elastomer layer thickness D2, we mixed and stirred two-component silicone HTV rubber components A and B in a 1:1 weight ratio. The resulting mixture was poured into a plastic container with a release paper at the bottom and allowed to cure at room temperature. Second elastomer layers with various thicknesses D2 were created. Because the effect of the second elastomer layer thickness D2 on communication distance was most pronounced at thicknesses thinner than 1 mm, we measured the thickness of the second elastomer layer peeled from the release paper in advance. An RFID tag was then attached to the first elastomer layer, which had a textured structure (approximately 12 mm in diameter) with hemispherical depressions. This was then covered with a silicone sheet-like second elastomer layer. To improve measurement accuracy, we also performed similar measurements of communication distances when the second elastomer layer thickness D2 was varied as shown in Figures 28 and 30, using second elastomer layers of the same thickness whose thicknesses had been measured beforehand.

[0159] In Figure 26, a critical phenomenon was observed in the communication distance at which temperature data from the elastomer-coated RFID tag 109 can be received. When the thickness D2 of the second elastomer layer is smaller than a certain value in the range of 0.7 mm or more and less than 1 mm, a critical phenomenon was observed in which the communication distance increased as the thickness D2 decreased. Furthermore, when the film thickness was in the range of 1 mm or more, the communication distance remained almost constant. In an RFID tag consisting of a first elastomer layer and a second elastomer layer with a concave-convex structure, in order to reduce a decrease in communication distance due to dielectric loss in the elastomer, which is a dielectric, the thickness D2 of the second elastomer layer is preferably less than 1 mm, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less.

[0160] 27 shows the communication distances at which temperature data can be received for elastomer-coated RFID tag 109 (FIG. 18), which is installed on a metal plate as an attachment target, and which is made of a first elastomer layer with a concave-convex structure (diameter approximately 12 mm) with hemispherical recesses, RFID tag 110 (FIG. 19), which is made of a first elastomer layer with a concave-convex structure (diameter approximately 8 mm) with hemispherical recesses, RFID tag 111 (FIG. 20), which is made of a first elastomer layer with a concave-convex structure (diameter approximately 5 mm) with hemispherical recesses, and elastomer-coated RFID tag 112 (FIG. 21), which has only one rectangular recess of approximately the same size as the RFID tag antenna. Also shown is elastomer-coated RFID tag 113 (FIG. 22), which is made of a first elastomer layer made of silicone rubber without a concave-convex structure, according to comparative example 4. In the measurement, the angle was defined as 0° when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag coincided with the direction of linear polarization from the antenna of the RFID tag reader / writer. In measuring the communication distance, the first elastomer layer side was the surface that contacted the object to which the RFID tag was attached, and the second elastomer layer side was the surface facing the antenna of the RFID tag reader / writer.

[0161] In RFID tags with a concave-convex structure in which hemispherical recesses are formed and installed on a metal plate, the communication distances when the diameter of the hemispherical recesses is 12 mm (elastomer-coated RFID tag 109), 8 mm (elastomer-coated RFID tag 110), and 5 mm (elastomer-coated RFID tag 111) are 52 cm, 51 cm, and 28 cm, respectively.The communication distance is improved for elastomer-coated RFID tags with larger diameter hemispherical recesses and larger gaps, as the gaps increase.

[0162] Figure 27 also shows an elastomer-coated RFID tag 112 (Figure 21) with a single rectangular recess approximately the same size as the RFID tag antenna. This tag has a first elastomer layer between the metal plate and the RFID tag antenna, which has a single recess consisting of a large gap measuring 25 mm long, 90 mm wide, and approximately 5.5 mm high. Considering only the effect of the gap in the first elastomer layer, the communication distance should be greater than that of elastomer-coated RFID tags 109, 110, and 111, which have a concave-convex structure with a hemispherical recess. However, the measured value was only 8 cm. This is because there is no concave-convex structure formed in the first elastomer layer between the metal plate and the RFID tag antenna. Therefore, the light is reflected specularly from the metal plate, but is reflected toward the RFID tag antenna without being affected by dielectric loss. This reduces the communication distance due to interference with the incident wave on the RFID tag antenna.

[0163] Comparative Example 4 Figure 27 also shows the communication distance at which temperature data can be received for elastomer-coated RFID tag 113 (Figure 22) according to comparative embodiment 4, which has a first elastomer layer made of silicone rubber without a concave-convex structure. The communication distance at which temperature data can be received for elastomer-coated RFID tag 113 (Figure 22) having a first elastomer layer made of silicone rubber without a concave-convex structure is 20 cm, which is shorter than that of an RFID tag with a concave-convex structure formed with hemispherical recesses. This result also demonstrates the effect of the voids in the first elastomer layer due to the hemispherical recesses.

[0164] Figure 28 shows the effect of the thickness D2 of the second elastomer layer on the communication distance over which temperature data can be received when an RFID tag 101 (antenna shape A) is sandwiched between a first elastomer layer and a second elastomer layer with a concave-convex structure (diameter approximately 12 mm) formed with hemispherical recesses and is placed on a metal plate. In the measurement, the angle was defined as 0° when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag coincided with the direction of linear polarization from the antenna of the RFID tag reader / writer. As in the case of the structure in which the RFID tag 107 (shape G) is sandwiched between the first elastomer layer and the second elastomer layer (Figure 26), when the RFID tag 101 (shape A) is sandwiched between the first elastomer layer and the second elastomer layer, a critical phenomenon was observed in which the communication distance increased as the thickness D2 decreased when the thickness D2 of the second elastomer layer was smaller than a certain value in the range of 0.7 mm to 1 mm. Furthermore, when the film thickness was 1 mm or more, the communication distance remained almost constant.

[0165] In the case of antenna shape A (Fig. 28) and antenna shape G (Fig. 26), the communication distance at which temperature data can be received showed similar thickness dependence and critical phenomena with respect to the thickness D2 of the silicone rubber that forms the second elastomer layer, regardless of the antenna shape. In an RFID tag consisting of a first elastomer layer and a second elastomer layer with a concave-convex structure, in order to reduce the decrease in communication distance due to dielectric loss in the elastomer, which is a dielectric, the thickness D2 of the second elastomer layer is preferably less than 1 mm, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. [Example]

[0166] 18 to 22 are all tags having a structure in which an RFID tag 107 (antenna shape G) is sandwiched and covered between a first elastomer layer and a second elastomer layer, but instead of RFID tag 107 (antenna shape G), elastomer-coated RFID tags 114 to 118 were created, each having a structure in which an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched and covered between a first elastomer layer and a second elastomer layer. The existing RFID tag (Temperature Sensor Dogbone) 70 is an RFID tag comprising an insulating substrate, an annular conductor with an opening provided on the surface of the insulating substrate, an IC chip with a sensor function capable of acquiring temperature data connected to the annular conductor by a power supply part provided near the opening, and an antenna made of a radiating conductor. FIG. 23 shows an example of an RFID tag 114 (antenna structure of an existing UHF band RFID tag 70) covered with a first elastomer layer and a second elastomer layer having an uneven structure (diameter approximately 12 mm) with hemispherical recesses, showing (a) a plan view (second elastomer layer side), (b) a cross-sectional view, and (c) a plan view (first elastomer layer side).

[0167] FIG. 29 shows an example of the communication distance over which temperature data can be received when an elastomer-coated RFID tag is placed on a metal plate to which it is attached. The elastomer-coated RFID tag 114 is made of a first elastomer layer having a concave-convex structure (diameter: approximately 12 mm) with hemispherical recesses, the elastomer-coated RFID tag 115 is made of a first elastomer layer having a concave-convex structure (diameter: approximately 8 mm) with hemispherical recesses, the elastomer-coated RFID tag 116 is made of a first elastomer layer having a concave-convex structure (diameter: approximately 5 mm) with hemispherical recesses, the elastomer-coated RFID tag 117 has only one rectangular recess of approximately the same size as the RFID tag antenna, and the elastomer-coated RFID tag 118 is made of a first elastomer layer made of silicone rubber and has no concave-convex structure. When measuring the communication distance, the first elastomer layer side is the surface that comes into contact with the object to which it is attached, and the second elastomer layer side is the surface that faces the antenna of the RFID tag reader / writer.

[0168] Even in elastomer-coated RFID tags, in which an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched between a first elastomer layer and a second elastomer layer, the effect of the uneven structure with hemispherical recesses was demonstrated in the communication distance at which temperature data could be received when the tag was placed on a metal plate. As shown in Figure 29, when the diameter of the hemispherical recess was 12 mm (elastomer-coated RFID tag 114), 8 mm (elastomer-coated RFID tag 115), and 5 mm (elastomer-coated RFID tag 116), the communication distance was 42 cm, 37 cm, and 26 cm, respectively. The larger the diameter of the hemispherical recess, the longer the communication distance at which temperature data could be received. This is because the proportion of voids in the first elastomer layer increases as the diameter of the hemispherical recess increases.

[0169] In FIG. 29, the communication distance at which temperature data can be received in the elastomer-coated RFID tag 118, in which the first elastomer layer is made of silicone rubber without a concave-convex structure, when placed on a metal plate, is 19 cm, which is a smaller value than that of an RFID tag with a concave-convex structure in which hemispherical recesses are formed.

[0170] In an elastomer-coated RFID tag in which an existing RFID tag (Temperature Sensor Dogbone) 70 is sandwiched and covered between a first elastomer layer and a second elastomer layer, the effect of the uneven structure was also demonstrated in tag 117, which is made of a first elastomer layer having only one rectangular recess of approximately the same size as the RFID tag antenna, and the communication distance at which temperature data can be received when placed on a metal plate is 30 cm, which is greater than that of elastomer-coated RFID tag 117 which does not have an uneven structure. [Example]

[0171] FIG. 24 shows an example of an elastomer-coated RFID tag 119 according to the seventh embodiment, which is covered with a third elastomer layer and a fourth elastomer layer having a substantially zigzag conductor layer in a cross-sectional view. The tag was fabricated as follows: First, an aluminum foil / PET composite film was used to fabricate a substantially zigzag conductor layer, consisting of a series of unit structures, each with an isosceles triangle apex angle (90°) on the top and two equal sides each having a length of 5 mm. The unit structure was then placed at the bottom of a rectangular container or the like. A 1:1 mixture of a first component (base) and a second component (curing agent) for a two-component silicone RTV rubber was poured into the elastomer-coated RFID tag and allowed to cure at room temperature. The elastomer-coated RFID tag was allowed to cure for approximately 8 hours. The thickness D3 of the third elastomer layer was approximately 6.5 mm. The size and fabrication of the elastomer-coated RFID tag 119 are not limited to those described above.

[0172] FIG. 30 shows an example of the change in the communication distance at which temperature data can be received when an elastomer-coated RFID tag 119 (antenna shape G) covered with a third elastomer layer and a fourth elastomer layer having a roughly zigzag conductor layer in cross section is placed on a metal plate serving as an attachment target, and the change in the thickness D4 of the fourth elastomer layer results in a change in the communication distance at which temperature data can be received. In the measurement, the angle was defined as 0°, when the extension direction of the first dipole antenna or the second dipole antenna of the RFID tag coincided with the direction of linear polarization from the antenna of the RFID tag reader / writer. In FIG. 30, a critical phenomenon was observed in the communication distance at which temperature data can be received from the elastomer-coated RFID tag 119. When the thickness D4 of the fourth elastomer layer was smaller than a certain value in the range of 0.7 mm or more and less than 1 mm, a critical phenomenon was observed, in which the communication distance increased as the thickness D2 decreased. Furthermore, when the thickness was 1 mm or more, the communication distance remained almost constant. In an RFID tag consisting of a third elastomer layer and a fourth elastomer layer having a conductor layer that is approximately zigzag in cross section, in order to reduce a decrease in communication distance due to dielectric loss in the elastomer, which is a dielectric, the thickness D4 of the fourth elastomer layer is preferably less than 1 mm, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less.

[0173] In the elastomer-coated RFID tag 119 (antenna shape G), which is covered with a third elastomer layer and a fourth elastomer layer having a roughly zigzag conductor layer in a cross-sectional view, when it is installed on a metal plate to which it is attached, it is possible to prevent communication failures and reduce a reduction in communication distance because the third elastomer layer having the roughly zigzag conductor layer changes the reflection of electromagnetic waves that have passed through the RFID tag to a different direction from the direction of incidence of the electromagnetic waves on the RFID tag, thereby reducing interference between the electromagnetic waves input to the RFID tag and the electromagnetic waves that are specularly reflected from the metal surface.

[0174] In Figure 24, the surface of the RFID tag facing the insulating substrate faces the third elastomer, and the surface of the RFID tag facing the annular conductor faces the fourth elastomer layer. However, in an RFID tag that is sandwiched and covered between the third and fourth elastomer layers, the communication distance over which temperature data can be received is the same regardless of whether the third elastomer layer with a concave-convex structure is provided on the surface of the RFID tag facing the insulating substrate or the annular conductor, as long as the antenna position of the RFID tag relative to the antenna of the RFID tag reader / writer is the same. [Industrial Applicability]

[0175] The present disclosure provides an RFID tag having a substantially omnidirectional antenna structure that is required when using a specified low-power radio station type RFID reader / writer with an output of 250 mW and a linearly polarized RFID reader / writer antenna that can achieve a longer communication distance than a circularly polarized antenna. Furthermore, by using an RFID tag covered with an elastomer layer having a concave-convex structure or an elastomer layer having a conductor layer that is substantially zigzag in cross section, it is possible to provide an RFID tag that has flexibility, water resistance, insulation, heat resistance, weather resistance, durability, etc., and that can prevent communication failures and minimize a reduction in communication distance when the RFID tag is attached to the surface of an object, even if the object is a metal structure. This allows RFID tags with sensor functions that can obtain temperature data wirelessly to be installed in infrastructure facilities such as energy supply facilities, roads, railways, flood control facilities, and parks.With the ability to read dozens of tags simultaneously using a single set of RFID reader / writer and antenna connected to a communication network, it is possible to monitor the temperature distribution of infrastructure facilities in real time from remote locations and perform maintenance and safety management.

[0176] Although the embodiments have been described above, the technology of the present disclosure is not limited to the above-described embodiments, and various modifications and improvements are possible, such as combinations with or substitutions for part or all of other embodiments. [Explanation of symbols]

[0177] 10. Insulating substrate 11 Conductor layer 12 Approximately zigzag conductor layer 20 IC chips 21 Power supply unit 22 Aperture 30 Impedance matching section (annular conductor) 31 First radiation conductor 32 Second radiation conductor 33 Third Radiating Conductor 34 Fourth Radiating Conductor 35 5th radiating conductor 36 Sixth Radiating Conductor 40 Hemispherical structure (diameter approximately 12mm) 41 Hemispherical structure (diameter approximately 8mm) 42 Hemispherical structure (diameter approx. 5mm) 50 Reader / writer antenna (linearly polarized) 60 First elastomer layer having a concave-convex structure 61 Second elastomer layer 62 a third elastomer layer having a substantially zigzag conductor layer; 63 Fourth elastomer layer 70 Existing RFID tags 101~107 RFID tags 108~119 Elastomer coated RFID tags

Claims

1. an insulating substrate; a ring-shaped conductor having an opening provided on a surface of the insulating substrate; and an IC chip having a sensor function capable of acquiring temperature data, the IC chip being connected to the ring-shaped conductor by a power supply part provided near the opening; a first radiation conductor extending from the annular conductor in a first direction and a second direction opposite to the first direction and connected to the annular conductor; a second radiation conductor extending from the annular conductor in the first direction and connected to the annular conductor; a third radiation conductor extending from the annular conductor in the second direction and connected to the annular conductor; the first radiation conductor, the second radiation conductor, or the third radiation conductor has a substantially rectangular, meandering, or zigzag shape in plan view; a first dipole antenna formed by the first radiation conductor and a second dipole antenna formed by the second radiation conductor and the third radiation conductor extend in parallel to and opposite to the first direction and the second direction; Equipped with a function to measure temperature via wireless communication, RFID tag.

2. a third dipole antenna including a fourth radiation conductor extending in a third direction from the first radiation conductor and connected to the first radiation conductor; a fourth dipole antenna including a fifth radiation conductor extending from the third radiation conductor in a fourth direction opposite to the third direction and connected to the third radiation conductor, the fourth radiation conductor or the fifth radiation conductor has a substantially rectangular, substantially meandering, or substantially zigzag shape in plan view; The RFID tag of claim 1 .

3. a first elastomer layer having at least one uneven structure on a surface of the RFID tag that contacts the object to which the RFID tag is attached; The RFID tag according to claim 1 or 2.

4. a first elastomer layer having at least one uneven structure on a surface of the RFID tag that contacts the object to which the RFID tag is attached; a second elastomer layer on the other surface of the RFID tag; the RFID tag has a structure in which it is sandwiched and covered between the first elastomer layer and the second elastomer layer, forming a gap between the object and the RFID tag to prevent communication failure; The RFID tag according to claim 1 or 2.

5. the concave-convex structure is a concave-convex structure formed of hemispherical concave portions, The diameter of the hemispherical recess is 5 mm or more and 20 mm or less. The RFID tag according to claim 4.

6. When the thickness D2 of the second elastomer layer is smaller than a certain value in a range of 0.7 mm or more and less than 1 mm, the communication distance over which the temperature data can be received increases with the decrease in the thickness D2 of the second elastomer layer. The RFID tag according to claim 4.

7. a third elastomer layer having at least one conductor layer having a substantially zigzag shape in a cross-sectional view is provided on a surface of the RFID tag that contacts the object to which the RFID tag is attached; a fourth elastomer layer on the other surface of the RFID tag; the RFID tag has a structure in which it is sandwiched and covered between the third elastomer layer and the fourth elastomer layer, The direction of reflection of electromagnetic waves is changed between the RFID tag and the object to be attached, thereby preventing communication failure. The RFID tag according to claim 1 or 2.

8. When the thickness D4 of the fourth elastomer layer is smaller than a certain value in a range of 0.7 mm or more and less than 1 mm, the communication distance over which the temperature data can be received increases with the decrease in the thickness D4 of the fourth elastomer layer. The RFID tag according to claim 7.

9. An RFID tag comprising: an insulating substrate; an annular conductor having an opening provided on a surface of the insulating substrate; an IC chip having a sensor function capable of acquiring temperature data, the IC chip being connected to the annular conductor by a power supply part provided near the opening; and an antenna made of a radiating conductor, a first elastomer layer having at least one uneven structure is provided on a surface of the RFID tag that contacts the object to which the RFID tag is attached; a second elastomer layer on the other surface of the RFID tag; the RFID tag has a structure in which it is sandwiched and covered between the first elastomer layer and the second elastomer layer, forming a gap between the object and the RFID tag to prevent communication failure; RFID tag.

10. An RFID tag comprising: an insulating substrate; an annular conductor having an opening provided on a surface of the insulating substrate; an IC chip having a sensor function capable of acquiring temperature data, the IC chip being connected to the annular conductor by a power supply part provided near the opening; and an antenna made of a radiating conductor, a third elastomer layer having at least one conductor layer that is approximately zigzag in cross section is provided on a surface of the RFID tag that contacts the object to which the RFID tag is attached; a fourth elastomeric layer on the other side of the RFID tag; the RFID tag has a structure in which it is sandwiched and covered between the third elastomer layer and the fourth elastomer layer, The direction of reflection of electromagnetic waves is changed between the RFID tag and the object to be attached, thereby preventing communication failure. RFID tag.

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