RFID tag

Abstract

An RFID tag, wherein a first distance from an IC chip to both ends in the tag longitudinal direction of a pair of rectangular conductors, a second distance from the IC chip to the tip of a pair of first strip parts, and a third distance from the IC chip to the tip of a pair of second strip parts are formed in different lengths. At least one of the first distance, the second distance, and the third distance is set to be an electrical length of a multiple of 1 / 4 of the wavelength of the use frequency of the RFID tag, and the remainder is set to have an electrical length different from the electrical length of a multiple of 1 / 4 of the wavelength of the use frequency of the RFID tag.

Description

RFID tag

[0001] The present disclosure relates to RFID tags.

[0002] 2. Description of the Related Art A method is known for managing items with high accuracy and ease by attaching an RFID (Radio Frequency Identification) tag to the item to be managed and reading and writing information about the item to and from the tag.

[0003] For example, Patent Document 1 describes a configuration in which an RFID tag is attached to a cover or the like during bookbinding and used for book management.

[0004] JP 2002-326474

[0005] When RFID tags are used to manage goods, it is desirable to reduce the tag size to improve versatility. However, reducing the tag size also reduces the inlay size, which can lead to a decrease in the tag's communication performance.

[0006] An object of the present disclosure is to provide an RFID tag that can suppress a decrease in communication performance even when the tag size is reduced, and can improve versatility.

[0007] An RFID tag according to one aspect of an embodiment of the present invention includes an IC chip on which identification information is recorded, a loop-shaped conductor formed in a ring and connected to the IC chip, a pair of rectangular conductors extending from the loop-shaped conductor on both sides in a first direction and formed in a rectangular shape, a pair of first protrusions in each of the pair of rectangular conductors protruding from one side in a second direction perpendicular to the first direction to the outside of the rectangular conductor in the second direction, a pair of second protrusions in each of the pair of rectangular conductors protruding from the other side in the second direction to the outside of the rectangular conductor in the second direction, a pair of first strips formed in a strip and protruding from the pair of first protrusions along the first direction toward the center of the first direction from the pair of first protrusions, and a pair of second strip portions formed in a strip shape and protruding from the second protrusion toward the center of the first direction along the first direction, wherein a first distance from the IC chip to both ends of the pair of rectangular conductors in the first direction, a second distance from the IC chip to the tips of the pair of first strip portions, and a third distance from the IC chip to the tips of the pair of second strip portions are formed to be different lengths, at least one of the first distance, the second distance, and the third distance is set to be an electrical length that is a multiple of 1 / 4 of the wavelength of the operating frequency of the RFID tag, and the remaining of the first distance, the second distance, and the third distance are set to be an electrical length that is different from the electrical length that is a multiple of 1 / 4 of the wavelength of the operating frequency of the RFID tag.

[0008] According to this aspect, by providing the inlay antenna pattern as described above, it is possible to form multiple current paths of different lengths, which allows for a wider range of frequencies to be used, thereby preventing a decline in communication performance even when the tag size is reduced, and improving versatility.

[0009] In an RFID tag according to another aspect of an embodiment of the present invention, the IC chip may be positioned at the center in the first direction and shifted to one side from the center in the second direction, and the length in the first direction of the pair of first strip portions and the pair of second strip portions may be the same.

[0010] According to this aspect, in an antenna pattern in which the IC chip is positioned offset to one side from the center in the second direction, the second distance and the third distance can be reliably made different lengths, thereby reliably increasing the variety of frequencies in use.

[0011] In an RFID tag according to another aspect of an embodiment of the present invention, the IC chip may be positioned in the center of the first direction and the second direction, and the pair of first strip portions and the pair of second strip portions may be formed so as to have different lengths in the first direction.

[0012] According to this aspect, in an antenna pattern in which the IC chip is positioned in the center of the first direction and the second direction, the second distance and the third distance can be reliably made different lengths, thereby reliably increasing the variety of frequencies in use.

[0013] According to the present disclosure, it is possible to provide an RFID tag that can suppress a decrease in communication performance even when the tag size is reduced, and that can improve versatility.

[0014] FIG. 1 is a plan view of the RFID tag shown in FIG. 1 viewed from above; FIG. 2 is a diagram showing an example of dimensions of each part of the conductor pattern of the inlay shown in FIG. 2; FIG. 3 is a diagram showing an example of a configuration for attaching the RFID tag according to the first embodiment to a book as an object to be attached; FIG. 4 is a diagram showing an example of a method for reading information from an RFID tag attached to a plurality of books as objects to be attached; FIG. 5 is a diagram explaining the effect of the first embodiment;

[0015] Hereinafter, embodiments will be described with reference to the accompanying drawings. To facilitate understanding of the description, the same components in the drawings will be denoted by the same reference numerals as much as possible, and duplicated descriptions will be omitted.

[0016] First Embodiment A first embodiment will be described with reference to FIGS.

[0017] In the following description, the X, Y, and Z directions are perpendicular to one another. The X direction is the longitudinal direction of each component of the RFID tag 1, such as the inlay 2. The Y direction is the lateral direction of each component of the RFID tag 1, such as the inlay 2. The Z direction is the stacking direction of each component of the RFID tag, such as the inlay 2. For ease of explanation, the positive side of the Z axis may be referred to as the front side or upper side, and the negative side of the Z axis may be referred to as the back side or lower side.

[0018] <Structure of RFID tag 1> Fig. 1 is a cross-sectional view of the layers of the RFID tag 1 according to the first embodiment. Fig. 2 is a plan view of the RFID tag 1 shown in Fig. 1 as viewed from above. Fig. 2 focuses on the elements related to the inlay 2 in Fig. 1. The RFID tag 1 is a substantially planar device that is attached to an object to which it is attached. As shown in Figs. 1 and 2, the RFID tag 1 has an inlay 2 built in.

[0019] The object to be affixed includes a book 30 such as a book or a magazine, as will be described later with reference to Fig. 4. The object to be affixed is not limited to the book 30, but may be an item that is stacked vertically or horizontally during storage, an item formed by stacking a large amount of paper like the book 30, or an item formed from a moisture-containing material such as paper like the book 30. Examples of such items include cards such as trading cards, stationery such as clear files and notebooks, food such as sweets, newspapers, tickets, and stamps.

[0020] The RFID tag 1 of the first embodiment is preferably flexible and can be attached to an adherend even if the surface of the adherend is curved. Even when bent, the RFID tag 1 of the first embodiment can exhibit good communication performance, and can be used to identify curved objects, thereby diversifying its applications. The RFID tag 1 of the first embodiment is formed in a rectangular shape with the X direction as the longitudinal direction (first direction) and the Y direction as the lateral direction (second direction perpendicular to the first direction) in a plan view seen from the Z direction, as shown in FIG. 2 .

[0021] The inlay 2 is a part that includes elements related to the function of the RFID tag 1, and as shown in Fig. 2, it has an IC chip 21 in which identification information is recorded, a loop conductor 22 connected to the IC chip 21, and a pair of rectangular conductors 23A and 23B. In the following description, the pair of rectangular conductors 23A and 23B may be collectively referred to as "rectangular conductors 23," and is labeled as such in Fig. 1.

[0022] The inlay 2 has a loop-shaped conductor 22 and a rectangular conductor 23 formed by dry laminating an aluminum sheet on a substrate 24 such as a synthetic resin film, such as polyethylene terephthalate or polypropylene, and an IC chip 21 mounted at a specified position.

[0023] In the RFID tag 1 of the first embodiment, the shape of the inlay 2, particularly the shape of the antenna pattern including the loop-shaped conductor 22 and the pair of rectangular conductors 23A, 23B, is formed in a rectangular shape with the X direction as the longitudinal direction (first direction) and the Y direction as the short direction (second direction) in a plan view seen from the Z direction as shown in Figure 2, similar to the RFID tag 1.

[0024] The IC chip 21 has an internal capacitance, and the inductance of the rectangular conductor 23 and the internal capacitance of the IC chip 21 form a matching circuit.

[0025] The loop-shaped conductor 22 is a conductive wiring pattern having a loop shape (annular) of one turn or less when viewed in a plan view from the Z direction. In the first embodiment, the loop-shaped conductor 22 is configured to extend at least in the short-side direction (Y direction) of the RFID tag 1 and to be formed in an annular shape having a pair of opposite sides arranged opposite to each other at both ends in the longitudinal direction (X direction). In the first embodiment, the loop-shaped conductor 22 is formed in a rectangular annular shape having a pair of short sides 221A, 221B and a pair of long sides 222A, 222B, as shown in FIG. 2 . In this embodiment, the pair of short sides 221A, 221B function as the above-mentioned "pair of opposite sides."

[0026] In the first embodiment, the pair of long sides 222A, 222B extend in the longitudinal direction (X direction) and function as a "pair of second opposite sides" that are arranged opposite both ends in the lateral direction (Y direction). Of the pair of short sides 221A, 221B, one short side 221A is arranged on the X negative side (left side in FIG. 2 ), and the other short side 221B is arranged on the X positive side (right side in FIG. 2 ). Of the pair of long sides 222A, 222B, one long side 222A is arranged on the Y positive side (upper side in FIG. 2 ), and the other long side 222B is arranged on the Y negative side (lower side in FIG. 2 ).

[0027] The loop conductor 22 is electrically connected to the IC chip 21 and the rectangular conductor 23. When the identification information recorded on the IC chip 21 is read using an RFID reader 40 (see FIG. 5 , etc.), when the rectangular conductor 23 of the inlay 2 receives UHF radio waves, for example, radio waves around 920 MHz, a current flows through the loop conductor 22 due to resonance. This generates an electromotive force that operates the IC chip 21. When the IC chip 21 operates, the identification information recorded on the IC chip 21 is encoded by the IC chip 21, and the encoded data is wirelessly transmitted to a communication device such as the RFID reader 40 using radio waves around 920 MHz as a carrier wave. The RFID reader 40 receives this signal, decodes it, and transfers it to an external device. As such, the RFID tag 1 of this embodiment is a passive radio wave-based wireless tag that does not have a power source (battery) for storing and transmitting identification information. Therefore, compared to active wireless tags that require a battery, the lack of a battery allows for smaller size and lower cost.

[0028] The loop-shaped conductor 22 is disposed, for example, in the approximate center of the inlay 2 as shown in Fig. 2. The IC chip 21 is disposed above and superimposed on the loop-shaped conductor 22 and is electrically connected to the loop-shaped conductor 22. In the first embodiment, a connection position with the IC chip 21 is provided at the approximate center in the X direction of one long side portion 222A of the loop-shaped conductor 22. As a result, when the IC chip 21 is connected to the loop-shaped conductor 22, the IC chip 21 is disposed in the center in the longitudinal direction of the RFID tag 1 and is shifted to one side (the positive Y direction side in the example of Fig. 2) from the center in the lateral direction of the RFID tag 1.

[0029] The pair of rectangular conductors 23A, 23B are formed in a rectangular shape and extend from a pair of short sides 221A, 221B of the loop conductor 22 to both sides in the longitudinal direction (X direction) of the tag. Note that the term "rectangular" used in this embodiment includes a substantially rectangular shape, and also includes cases where the lengths of two adjacent sides are slightly different or adjacent corners are not exactly right angles.

[0030] Each of the pair of rectangular conductors 23A, 23B is provided with a pair of protrusions 231 that protrude outward in the short-side direction (Y direction) from the loop conductor 22 at both ends of the short-side direction of the tag. One rectangular conductor 23A has a pair of protrusions 231A, 231B, with one protrusion 231A protruding in the Y-positive direction and the other protrusion 231B protruding in the Y-negative direction. The other rectangular conductor 23B has a pair of protrusions 231C, 231D, with one protrusion 231C protruding in the Y-positive direction and the other protrusion 231D protruding in the Y-negative direction. In the following description, in each of the pair of rectangular conductors 23A, 23B, the protrusions 231A, 231C that protrude from one side of the rectangular short side of the RFID tag 1 (the Y-positive side in the example of FIG. 2) toward the outside in the short side direction from the loop conductor 22 are also referred to as a "pair of first protrusions 231A, 231C." Similarly, in each of the pair of rectangular conductors 23A, 23B, the protrusions 231B, 231D that protrude from the other side of the rectangular short side of the RFID tag 1 (the Y-negative side in the example of FIG. 2) toward the outside in the short side direction from the loop conductor 22 are also referred to as a "pair of second protrusions 231B, 231D."

[0031] 2, the outer edge in the X direction of each protrusion 231 is arranged to be in the same position as the outer edge in the X direction of the rectangular conductor 23. For convenience of explanation, in FIG. 2, the boundary line on the Y direction center side (the side of the second imaginary line VS) of the pair of protrusions 231A and 231B of one rectangular conductor 23A and the boundary line on the Y direction center side of the pair of protrusions 231C and 231D of the other rectangular conductor 23B are illustrated by dotted lines, but in reality, each of the protrusions 231A to 231D is formed integrally with the rectangular conductors 23A and 23B.

[0032] Furthermore, the pair of rectangular conductors 23A, 23B are provided with strip portions 232 that protrude from the protrusion 231 along the longitudinal direction (X direction) toward the center of the tag and are formed in a strip shape. In one rectangular conductor 23A, strip portions 232A, 232B are formed so as to protrude along the X direction from the pair of protrusions 231A, 231B toward the X positive direction. In the other rectangular conductor 23B, strip portions 232C, 232D are formed so as to protrude along the X direction from the pair of protrusions 231C, 231D toward the X negative direction. In the example of FIG. 2 , the outer edge of each strip portion 232 in the Y direction is positioned at the same position as the outer edge of the protrusion 231 in the Y direction. In the following description, the strip portions 232A, 232C that protrude from the pair of first protrusions 231A, 231C along the longitudinal direction toward the center of the rectangular shape of the RFID tag 1 (the X direction in the example of FIG. 2) will also be referred to as a "pair of first strip portions 232A, 232C." Similarly, the strip portions 232B, 232D that protrude from the pair of second protrusions 231B, 231D along the longitudinal direction toward the center of the rectangular shape of the RFID tag 1 will also be referred to as a "pair of second strip portions 232B, 232D."

[0033] In Figure 2, for the sake of convenience, the boundary lines between the base ends of the pair of strip portions 232A and 232B of one rectangular conductor 23A on the negative X-direction side and each of the protrusions 231A and 231B, and the boundary lines between the base ends of the pair of strip portions 232C and 232D of the other rectangular conductor 23B on the positive X-direction side and each of the protrusions 231C and 231D are shown with dotted lines, but in reality, each of the strip portions 232A to 232D is formed integrally with the rectangular conductors 23A and 23B.

[0034] In other words, the strip portion 232 includes a pair of first strip portions 232A, 232C provided to protrude from the protruding portions 231A, 231C of the pair of rectangular conductors 23A, 23B at one long side 222A of the pair of long sides 222A, 222B of the loop-shaped conductor 22. Similarly, the strip portion 232 includes a pair of second strip portions 232B, 232D provided to protrude from the protruding portions 231B, 231D of the pair of rectangular conductors 23A, 23B at the other long side 222B.

[0035] 2, it is preferable that each strip portion 232 is formed so as not to overlap the portion of the loop conductor 22 where the IC chip 21 is installed when viewed from the short side direction (Y direction) of the tag. This prevents the conductor pattern from being interposed outside the IC chip 21 in the Y direction, which is thought to improve the wireless transmission performance of the IC chip 21, particularly in the Y direction, and further suppresses degradation of communication performance due to the influence of moisture contained in the object to be affixed and the influence of RFID tags being close to each other when affixed to multiple objects to be affixed.

[0036] The width of each strip portion 232 (dimension in the Y direction, LB in FIG. 3 ) is smaller than the amount of protrusion of each protrusion 231 in the Y direction from the rectangular conductor 23. As a result, a gap (LC in FIG. 3 ) is formed between each strip portion 232 and the rectangular conductor 23 or between each strip portion 232 and the loop conductor 22.

[0037] The pair of rectangular conductors 23A, 23B function as a dipole antenna configured to exhibit resonance characteristics with the IC chip 21 for radio wave frequencies for wireless communication (e.g., UHF band frequencies). The rectangular conductors 23A, 23B as dipole antennas have an overall electrical length equivalent to approximately λ / 2 (λ is the communication wavelength). The pair of rectangular conductors 23A, 23B have a structure that achieves impedance conjugate matching with the IC chip 21 for radio waves with frequencies, for example, around 920 MHz (e.g., 860 MHz to 960 MHz, more preferably 915 MHz to 935 MHz).

[0038] The conductive wiring pattern of the inlay 2, including the loop-shaped conductor 22 and the rectangular conductor 23, can be formed by existing methods such as pressing or etching copper foil or aluminum foil, plating, silkscreen printing of metal paste, or metal wire, but here it was formed by etching aluminum.

[0039] As shown in Fig. 2, the conductive wiring pattern of the inlay 2, including the loop conductor 22 and the rectangular conductor 23, is preferably formed symmetrically with respect to a first imaginary line VL that passes through approximately the longitudinal center of the RFID tag 1 in a plan view (the position where the IC chip 21 in Fig. 2 is located). The first imaginary line VL is a line that is parallel to the XY plane and extends in the Y direction. The first imaginary line VL also divides the RFID tag 1 into approximately two equal regions in the X direction. In Fig. 2, the first imaginary line VL is indicated by a dashed line extending along the Y direction.

[0040] Similarly, as shown in Fig. 2, the conductive wiring pattern of the inlay 2, including the loop conductor 22 and the rectangular conductor 23, is preferably formed symmetrically with respect to a second imaginary line VS that passes through approximately the center of the RFID tag 1 in the short direction in a plan view. The second imaginary line VS is a line that is parallel to the XY plane and extends in the X direction. The second imaginary line VS also divides the RFID tag 1 into approximately two equal regions in the Y direction. In Fig. 2, the second imaginary line VS is indicated by a dashed line extending along the X direction.

[0041] That is, in this embodiment, the conductive wiring pattern of the inlay 2 including the loop conductor 22 and the rectangular conductor 23 is formed so as to be line symmetrical with respect to both the X direction and the Y direction.

[0042] 2, the pair of rectangular conductors 23A, 23B are preferably formed so as to protrude in the X direction from the entire area extending in the direction of extension (Y direction) of the pair of short sides 221A, 221B. In other words, it is preferable that the left short side 221A in Fig. 2 and the rectangular conductor 23A are integrally formed, and the right short side 221B in Fig. 2 and the rectangular conductor 23B are integrally formed.

[0043] 2, for convenience of explanation, the boundary line between one rectangular conductor 23A and one short side portion 221A and the boundary line between the other rectangular conductor 23B and the other short side portion 221B are shown by dotted lines, but in reality, the pair of rectangular conductors 23A, 23B are formed integrally with the loop conductor 22. In other words, the boundary line between the pair of rectangular conductors 23A, 23B and the pair of short side portions 221A, 221B, the boundary line between the pair of rectangular conductors 23A, 23B and the four protrusions 231A to 231D, and the boundary line between the four protrusions 231A to 231D and the four strip portions 232A to 232D, which are shown by dotted lines in FIG.

[0044] Furthermore, the pair of rectangular conductors 23A, 23B may be formed so as to protrude in the X direction from the pair of short side portions 221A, 221B, or may be configured so as to protrude in the X direction from only a portion of the extension direction (Y direction) of the pair of short side portions 221A, 221B.

[0045] Fig. 3 is a diagram showing an example of dimensions of each part of the conductor pattern of the inlay 2 shown in Fig. 2. In the example of dimensions shown in Fig. 3, all of the conditions regarding the shapes of the loop conductor 22 and rectangular conductor 23 described above are satisfied.

[0046] Here, in the RFID tag 1 of the first embodiment, the dimension of the inlay 2 in the longitudinal direction (X direction) is 70 mm, and the dimension of the inlay 2 in the lateral direction (Y direction) is 14 mm.

[0047] 3, the longitudinal (X-direction) dimension LA of each of the strips 232A-232D is, for example, 14.6 mm, preferably in the range of 4.6 mm to 19.6 mm. The Y-direction width dimension LB of each of the strips 232A-232D is, for example, 0.5 mm, preferably in the range of 0.5 mm to 1.5 mm. The Y-direction gap dimension LC between each of the strips 232A-232D and the rectangular conductors 23A, 23B is, for example, 1.0 mm, preferably in the range of 1.0 mm to 2.0 mm.

[0048] The dimension LD from the negative X-direction end of rectangular conductor 23A to the base of strip portions 232A and 232B and the dimension LD from the positive X-direction end of rectangular conductor 23B to the base of strip portions 232C and 232D are, for example, 15.0 mm. The dimension LE from the installation position of IC chip 21 on loop conductor 22 to both ends of the pair of rectangular conductors 23A and 23B in the longitudinal direction (X direction) is, for example, 34.0 mm. In this example, based on the dimensions LD and LE, the dimension LF from the installation position of IC chip 21 on loop conductor 22 to the base of first strip portions 232A and 232C is 19.0 mm.

[0049] As described above, the RFID tag 1 according to the first embodiment is configured to include the loop conductor 22 and the rectangular conductor 23 formed by the conductive pattern shown in FIG. 2, thereby making it possible to suppress a decrease in communication performance due to the influence of moisture contained in the object to which the tag is attached, the influence of RFID tags being in close proximity to each other when the RFID tags are attached to multiple objects to which the tag is attached, and so on.

[0050] In the first embodiment, for convenience of explanation, the loop-shaped conductor 22 and the rectangular conductor 23 are separate elements and are shown separated by a dotted line in Fig. 2. However, in the present embodiment, as described above, the loop-shaped conductor 22 and the rectangular conductor 23 are actually formed as a single unit, and the separation position between the loop-shaped conductor 22 and the rectangular conductor 23 shown by the dotted line in Fig. 2 is merely an example. In other words, in the first embodiment, not only the rectangular conductor 23 but also at least a portion of the loop-shaped conductor 22 may function as an antenna portion. Similarly, at least a portion of the rectangular conductor 23 may also function as a loop conductor.

[0051] 1, in the RFID tag 1 of the first embodiment, a label paper (film-based tack paper) 3 is further disposed above the inlay 2. The label paper 3 is printable on the surface on the positive side of the Z axis. The material of the label paper 3 can be selected as appropriate, and materials other than paper, such as resin materials, may be used as long as they are printable.

[0052] The label paper 3 is also formed with a larger dimension in the X direction than the inlay 2, with the inlay 2 located in its center and excess portions on both sides in the X direction that do not overlap with the inlay 2. An adhesive portion 4 having adhesiveness is provided on the back surface of this excess portion on the negative side of the Z axis, on the surface that comes into contact with the object to which it is to be affixed (the lower surface in Figure 1). In this way, the inlay 2 and the adhesive portion 4 are arranged so as not to overlap in a plan view. In the example of Figure 1, a pair of adhesive portions 4A, 4B are arranged on the positive and negative sides of the X axis relative to the inlay 2.

[0053] The adhesive portion 4 comes into contact with the object to be affixed and adheres to the object by its adhesive force, thereby affixing the entire RFID tag 1 to the object to be affixed.

[0054] The adhesive portion 4 is preferably formed, for example, from an adhesive hot melt. Hot melt is a thermoplastic adhesive that is solid at room temperature but liquefies when heated and melted, and is applied to an adherend, where it forms a bond by cooling and solidifying. An adhesive hot melt is one that retains adhesive strength on the exposed surface even after cooling and solidifying. The adhesive portion 4 is preferably formed using biological resources (biomass) or biodegradable materials. The biomass content of the adhesive portion 4 is, for example, 25%.

[0055] Additionally, a bonding portion 5 is laminated on the back surface of the label paper 3 on the negative side of the Z axis. The bonding portion 5 is bonded to the top surface of the inlay 2 and the top surface of the adhesive portion 4, thereby covering the inlay 2 and the adhesive portion 4 with the label paper 3. Furthermore, when laminated, the bonding portion 5 can penetrate into the gap formed by the inlay 2 and the label paper 3 above it and fill this gap.

[0056] The joints 5 are preferably formed using, for example, a non-adhesive hot melt adhesive. A non-adhesive hot melt adhesive has no adhesive strength on the exposed surface after cooling and solidifying. As with the adhesive parts 4, the joints 5 are preferably formed using biological resources (biomass) or biodegradable materials.

[0057] Before use, the RFID tag 1 has a release paper 6 disposed below the adhesive portion 4. The release paper 6 is formed, for example, to be the same size as or larger than the label paper 3, and the label paper 3 and the release paper 6 are tightly attached by the adhesive portion 4. This prevents the pair of adhesive portions 4A, 4B on both sides of the label paper 3 in the X direction from being exposed to the outside before being used to attach the RFID tag 1 to an object, thereby maintaining adhesive strength. When the RFID tag 1 is used, the release paper 6 is peeled off from the RFID tag 1, and the exposed adhesive portions 4A, 4B of the label paper 3 allow the RFID tag 1 to be attached to an object.

[0058] 1, and a plurality of RFID tags 1 may be arranged on one sheet of release paper 6. This can improve manufacturing efficiency and transport efficiency.

[0059] The thickness of the RFID tag 1 in the Z direction (excluding the release paper 6) of the first embodiment is 80 μm to 260 μm, preferably 150 to 230 μm. The thickness of the adhesive portion 4 in the Z direction is preferably about 10 μm to 30 μm.

[0060] 1 and 2, a pair of adhesive portions 4A, 4B are arranged on the positive and negative sides of the X axis relative to the inlay 2. With this arrangement, the inlay 2 itself is not directly attached to the object to which it is to be attached, but is indirectly attached to the object via the adhesive portion 4.

[0061] The laminated structure of the RFID tag 1 is not limited to that shown in Fig. 1. For example, the label paper 3 may be formed to be the same size as the inlay 2. In this case, since the outer edge of the label paper 3 cannot come into contact with the object to be affixed, the adhesive portion 4 is provided on the entire lower surface of the base material 24 of the inlay 2 that faces the object to be affixed, and the inlay 2 is directly affixed to the object to be affixed. Furthermore, in the configuration shown in Fig. 1, a continuous adhesive portion may be provided between the pair of adhesive portions 4A, 4B to form a single adhesive layer. In this case, the inlay 2 is also directly affixed to the object to be affixed.

[0062] The RFID tag 1 may also be configured such that elements such as a magnetic sheet, a spacer layer, and a dielectric layer are further laminated on the side of the inlay 2 facing the object to which it is to be affixed (the lower side in FIG. 1 ). The magnetic sheet is a sheet material containing a magnetic material, and is preferably one that has excellent magnetic shielding properties against radio waves in the frequency band (e.g., the UHF band) used to read the IC chip 21. The spacer layer is an element that positions the inlay 2 at a distance of its thickness from the object to which it is to be affixed, and is preferably formed of an insulator such as, for example, cardboard, woven or nonwoven fabric made of fibers such as synthetic resin, or a sheet of inorganic material such as ceramic glass. The dielectric layer is preferably formed of an insulator material with a relative permittivity of approximately 1.2 to 3.0, which increases the communication distance of the RFID tag 1.

[0063] <Application Example of RFID Tag 1> Fig. 4 is a diagram showing an example of a configuration for affixing the RFID tag 1 according to the first embodiment to a book 30 as an object to which the RFID tag is to be affixed. As shown in Fig. 4, when the object to which the RFID tag is to be affixed is a book 30, the RFID tag 1 can be affixed, for example, to the back surface 31A of the back cover 31. Furthermore, when the object to which the RFID tag is to be affixed is a book 30, various bibliographic information about the book 30 to which the RFID tag is affixed can be recorded in the IC chip 21 of the RFID tag 1.

[0064] Furthermore, when the object to be affixed is a book 30, the position at which RFID tag 1 is affixed is not limited to the example in Fig. 4, and may be other positions such as front surface 31B of back cover 31, back surface 32A or back surface 32B of cover 32, spine 33, inside leaf 34, or cover 35. In order to read information from RFID tag 1 with high accuracy, it is preferable that RFID tag 1 be affixed as close to the outer surface of book 30 as possible so as to minimize obstructions between the RFID tag and a reading device such as RFID reader 40 (see Fig. 5).

[0065] 5 is a diagram showing an example of a method for reading information from RFID tags 1-1 to 1-5 affixed to a plurality of books 30-1 to 30-5 as attachment objects. As shown in FIG. 5, RFID tags 1-1 to 1-5 are affixed to a plurality of books 30-1 to 30-5, respectively, and the plurality of books 30-1 to 30-5 are stacked flat in a vertical direction.

[0066] In this case, a user approaches the stacked books 30-1 to 30-5 using a small, lightweight, portable reading device such as the RFID reader 40 shown in Fig. 5, and then operates the RFID reader 40. This allows the information ID1 to ID5 about each of the books 30-1 to 30-5, which is recorded on each of the RFID tags 1-1 to 1-5 attached to each of the books 30-1 to 30-5, to be read all at once.

[0067] The reader may be a stationary type, with the books 30-1 to 30-5 stacked flat within the readable range of the reader, and the information ID1 to ID5 may be read from each of the RFID tags 1-1 to 1-5. Also, even when multiple books 30-1 to 30-5 are closely arranged on a bookshelf, that is, when multiple books are stacked horizontally, the information ID1 to ID5 can be read all at once from each of the RFID tags 1-1 to 1-5 in the same manner as described above.

[0068] A book 30 is made by binding together many sheets of paper. When books are sold or stored in bookstores or libraries, many books 30-1 to 30-5 are often stacked flat, as shown in FIG. 5 . For this reason, if RFID tags 1 are affixed to cover portions such as the front cover 32 and back cover 31, or to endpapers 34 and flap 35 near the cover portions, the RFID tags 1-1 to 1-5 of each stacked book 30-1 to 30-5 may be sandwiched between the books above and below them. For this reason, in the past, the RFID tags affixed to each book 30-1 to 30-5 may be positioned close to each other, or moisture contained in the many sheets of paper forming each book 30-1 to 30-5 may reduce the communication distance of the RFID tags, resulting in poor RFID tag reading accuracy. A similar problem may arise when multiple books 30 are closely spaced on a bookshelf.

[0069] On the other hand, as described above, the RFID tag 1 of the first embodiment is configured with the loop conductor 22 and rectangular conductor 23 formed by the conductive pattern shown in Figure 2, thereby making it possible to suppress degradation of communication performance due to the effects of moisture contained in the object to which it is attached (e.g., book 30) and the effects of RFID tags 1-1 to 1-5 being in close proximity to each other when affixed to multiple objects to which it is attached (e.g., books 30-1 to 30-5). Therefore, when the RFID tag 1 of the first embodiment is applied to an object to which it is attached, such as book 30, which is made by stacking multiple sheets of paper, the effect of suppressing degradation of communication performance can be more pronounced. Furthermore, the same effect can be obtained even when multiple books 30-1 to 30-5 are stacked, making it possible to accurately read information ID1 to ID5 from each tag 1-1 to 1-5.

[0070] <Effects of RFID tag 1> The effects of the RFID tag 1 according to the first embodiment will be further described with reference to Fig. 6. Fig. 6 is a diagram for explaining the effects of the first embodiment, and is a diagram schematically showing that the antenna portion of the RFID tag 1 has current paths with multiple electrical lengths L1, L2, and L3.

[0071] For ease of illustration, FIG. 6 omits the portion of the RFID tag 1 on the positive side (right side) of the center in the X direction. Therefore, FIG. 6 illustrates only one rectangular conductor 23A of the pair of rectangular conductors 23A, 23B located on the negative X direction side. Similarly, only one first rectangular conductor 232A of the pair of first strips 232A, 232C located on the negative X direction side is illustrated, and only one second rectangular conductor 232B of the pair of second strips 232B, 232D located on the negative X direction side is illustrated. In the following description, the effects of the portion including one rectangular conductor 23A, the first strip 232A, and the second strip 232B will be described with reference to FIG. 6 . However, the same effects are also achieved in the portion including the other rectangular conductor 23B, the first strip 232C, and the second strip 232D located on the positive X direction side, which is not illustrated in FIG. 6 .

[0072] As described above, in the RFID tag 1 of the first embodiment, the IC chip 21 is disposed at the center of the RFID tag 1 in the longitudinal direction, and is disposed offset to one side (the positive Y direction in the example of FIG. 2 ) from the center of the RFID tag 1 in the lateral direction. In other words, the IC chip 21 is disposed closer to the pair of first strip portions 232A, 232C than to the pair of second strip portions 232B, 232D. Furthermore, the length in the longitudinal direction (X direction) of the pair of first strip portions 232A, 232C and the pair of second strip portions 232B, 232D, i.e., the dimension LA illustrated in FIG. 3 , is all the same.

[0073] In the RFID tag 1 of the first embodiment, due to the arrangement of the IC chip 21 and the setting of the length of each strip portion 232, the first distance L1 from the IC chip 21 to both ends of the pair of rectangular conductors 23A, 23B in the longitudinal direction (X direction), the second distance L2 from the IC chip 21 to the tips of the pair of first strip portions 232A, 232C, and the third distance L3 from the IC chip 21 to the tips of the pair of second strip portions 232B, 232D are formed to be different lengths, as shown in Fig. 6. In the case of the example dimensions shown in Fig. 3, the magnitude relationship among the distances L1 to L3 shown in Fig. 6 is first distance L1 < second distance L2 < third distance L3.

[0074] At least one of the first distance L1, the second distance L2, and the third distance L3 is set to have an electrical length that is a multiple of ¼ of the wavelength of the operating frequency of the RFID tag 1. The remaining of the first distance L1, the second distance L2, and the third distance L3 are set to have an electrical length that is different from the electrical length that is a multiple of ¼ of the wavelength of the operating frequency of the RFID tag 1.

[0075] Here, the longitudinal dimension (X direction) of the antenna portion of inlay 2, i.e., the dimension from the end of rectangular conductor 23A on the negative X side to the end of rectangular conductor 23B on the positive X side, is formed to be half the wavelength of the highest frequency among the usable frequencies applicable as carrier frequencies in RFID tag 1. Here, if the highest frequency is f1, the relationship between this frequency f1 and wavelength λ1 is λ1 = c (speed of light) / f1. The longitudinal dimension of inlay 2 is then (λ1) / 2.

[0076] As shown by the dashed line in Figure 6, the current I1 flowing into the inlay 2 from the connection with the IC chip 21 travels in a substantially straight line along the X direction, following the shortest distance, toward both ends of the rectangular conductors 23A and 23B. As a result, the length of the current path of the current I1 (i.e., the first distance L1) is approximately (λ1) / 2. Therefore, the antenna portion of the inlay 2 can resonate with radio waves of wavelength λ1 and carrier frequency f1, enabling communication to be established with a reader / writer located at a desired distance.

[0077] As shown by the solid line in Figure 6, the current I2 flowing from the connection portion with the IC chip 21 into the inlay 2 initially travels approximately linearly along the X-axis, following the shortest distance, toward both ends of the rectangular conductors 23A and 23B. Next, upon reaching the end of the protrusions 231A and 231C toward the center in the X-axis direction, the current changes direction toward the Y-axis direction and continues along the end. Then, upon reaching the base of the first strips 232A and 232C, the current changes direction toward the center in the X-axis direction along the first strips 232A and 232C and continues toward the tips of the first strips 232A and 232C. As a result, the length of the current path of the current I2 (i.e., the second distance L2) is longer than the first distance L1 = (λ1) / 2. Therefore, the antenna portion of the inlay 2 can resonate with radio waves at a carrier frequency f2 with a wavelength λ2 longer than the wavelength λ1, enabling communication to be established with a reader / writer located at a desired distance.

[0078] 6, the current I3 flowing from the connection portion with the IC chip 21 to the inlay 2 initially travels in a substantially straight line along the X direction, following the shortest distance, toward both ends of the rectangular conductors 23A and 23B. Next, after passing through the short sides 221A and 221B of the loop conductor 22, the current I3 changes direction toward the negative Y direction and heads toward the negative Y direction ends of the rectangular conductors 23A and 23B. When it reaches the negative Y direction ends of the rectangular conductors 23A and 23B, it changes direction toward the outside in the X direction and continues along these ends. When it reaches the central end of the protrusions 231B and 231D in the X direction, it changes direction toward the negative Y direction and continues along these ends. Furthermore, when the inlay 2 reaches the base of the second strips 232B and 232D, it changes direction of travel along the second strips 232B and 232D toward the center in the X direction and heads toward the tip of the second strips 232B and 232D. As a result, the length of the current path of the current I3 (i.e., the third distance L3) becomes longer than the second distance L2 = (λ2) / 2. Therefore, the antenna portion of the inlay 2 can resonate with radio waves of carrier frequency f3 with wavelength λ3 longer than wavelength λ2, and can establish communication with a reader / writer located at a desired distance.

[0079] That is, the RFID tag 1 according to the first embodiment can resonate with radio waves having carrier frequencies of f1>f2>f3 (wavelengths λ1<λ2<λ3) due to the existence of various current paths as shown by the dashed-dotted line I1, the solid line I2, and the dotted line I3 in Fig. 6, and can establish communication with a reader / writer at a desired distance. In other words, the RFID tag 1 can resonate with radio waves in a wide frequency band from carrier frequencies f1 to f3, and can establish communication at a desired distance.

[0080] In other words, by selecting the operating frequency from multiple frequencies f1, f2, and f3, at least one of the first distance L1 corresponding to frequency f1, the second distance L2 corresponding to frequency f2, and the third distance L3 corresponding to frequency f3 will have an electrical length that is a multiple of 1 / 4 of the wavelength of the operating frequency of the RFID tag 1, thereby ensuring communication performance.

[0081] Furthermore, if the longitudinal (X-direction) dimension of the inlay 2 is standardized to 70 mm and the transverse (Y-direction) dimension to 14 mm, the first distance L1 will be constant, and the highest frequency f1 among the applicable operating frequencies will be a fixed value. On the other hand, by changing the longitudinal (X-direction) lengths of the pair of first strips 232A, 232C and the pair of second strips 232B, 232D, i.e., the dimension LA illustrated in FIG. 3, the second distance L2 and the third distance L3 can be adjusted to any length. Therefore, the magnitudes of the operating frequencies f2 and f3, which are smaller than frequency f1, can be adjusted arbitrarily. Therefore, even if the tag size is standardized, the range of operating frequencies of the RFID tag 1 can be set arbitrarily, improving versatility.

[0082] As described above, the RFID tag 1 according to the first embodiment includes the antenna pattern of the inlay 2 described with reference to Fig. 2 and other figures, thereby forming multiple current paths with different lengths L1, L2, and L3, as described with reference to Fig. 6. This allows for a wider range of frequencies to be used, thereby preventing a decrease in communication performance even when the tag size is reduced, and improving versatility. Furthermore, since the inlay 2 includes multiple current paths with different electrical lengths, the reception strength of radio waves at the antenna section can be increased.

[0083] Furthermore, in the RFID tag 1 according to the first embodiment, the IC chip 21 is disposed at the center of the tag's longitudinal direction (X direction) and offset to one side from the center of the tag's transverse direction (Y direction). In such an arrangement of the IC chip 21, it is preferable that the pair of first strips 232A, 232C and the pair of second strips 232B, 232D have the same longitudinal length (LA in FIG. 3). This configuration ensures that the second distance L2 and the third distance L3 are different lengths in an antenna pattern in which the IC chip 21 is disposed offset to one side from the center of the tag's transverse direction, thereby enabling a greater variety of usable frequencies.

[0084] Second Embodiment A second embodiment will be described with reference to FIGS.

[0085] Fig. 7 is a plan view of an RFID tag 1A according to the second embodiment. Fig. 7 corresponds to Fig. 2 of the first embodiment. As shown in Fig. 7, in the RFID tag 1A according to the second embodiment, one long side portion 222A of the loop-shaped conductor 22 is disposed at the center in the short-side direction (Y direction) of the RFID tag 1, and a connection position with the IC chip 21 is provided at approximately the center in the X direction of the one long side portion 222A. As a result, when the IC chip 21 is connected to the loop-shaped conductor 22, the IC chip 21 is disposed at the center in the long-side and short-side directions of the RFID tag 1.

[0086] In the second embodiment, the portions of the rectangular conductors 23A and 23B that are located on the Y-axis side (upper side in FIG. 7 ) of one of the long sides 222A extend toward the center in the longitudinal direction from the short sides 221A and 221B, respectively, and are formed so as to have a gap between them. The width of this gap in the X-axis direction is greater than the width of the IC chip 21 in the X-axis direction when it is installed on the loop conductor 22, as shown in FIG. 7 , for example.

[0087] In the second embodiment, the IC chip 21 is disposed at the center position in the longitudinal and lateral directions of the RFID tag 1, which is the point where the first imaginary line VL and the second imaginary line VS intersect.

[0088] Furthermore, with this arrangement of the IC chip 21, the pair of short sides 221A, 221B and the pair of long sides 222A, 222B of the loop-shaped conductor 22 are arranged to be symmetrical with respect to the first imaginary line VL and are arranged on the Y-negative side of the second imaginary line VS. That is, the pair of short sides 221A, 221B are formed so that their ends on the Y-positive side in the extension direction (Y direction) are substantially aligned with the second imaginary line VS, and their ends on the Y-negative side are aligned with the Y-negative ends of the rectangular conductors 23A, 23B. The ends on the Y-negative side of the pair of long sides 222B are aligned with the Y-negative ends of the rectangular conductors 23A, 23B. That is, the long sides 222B and the rectangular conductors 23A, 23B are formed so that their ends on the Y-negative side are aligned in a straight line along the X direction. The long side portion 222A is located at the center of the RFID tag 1 in the widthwise direction (Y direction).

[0089] In particular, in the second embodiment, the pair of first strips 232A, 232C and the pair of second strips 232B, 232D are formed to have different lengths in the longitudinal direction, as the IC chip 21 is disposed in the longitudinal direction and at the center of the longitudinal direction of the RFID tag 1. In the example of Fig. 7, the pair of first strips 232A, 232C are formed to be shorter than the pair of second strips 232B, 232D.

[0090] The RFID tag 1A of the second embodiment includes a loop conductor 22 and a rectangular conductor 23 formed by the conductive pattern shown in FIG. 7. As described in the first embodiment with reference to FIGS. 4 and 5, this configuration can suppress degradation of communication performance due to factors such as the effects of moisture contained in the object to which the RFID tag is to be attached (e.g., the book 30 illustrated in FIG. 4) and the effects of RFID tags being placed close to each other when attached to multiple objects to which the RFID tag is to be attached (e.g., the books 30-1 to 30-5 illustrated in FIG. 5). Therefore, when the RFID tag 1A of the second embodiment is applied to an object to which the RFID tag is to be attached, such as the book 30, which is made by stacking multiple sheets of paper, the effect of suppressing degradation of communication performance can be more pronounced. Furthermore, the same effect can be obtained even when multiple books 30-1 to 30-5 are stacked, making it possible to accurately read information from each tag.

[0091] <Effects of RFID tag 1A> The effects of the RFID tag 1A according to the second embodiment will be further described with reference to Fig. 8. Fig. 8 is a diagram for explaining the effects of the second embodiment, and is a diagram schematically showing that the antenna portion of the RFID tag 1A has current paths with multiple electrical lengths L1, L2, and L3.

[0092] As described above, in the RFID tag 1 of the second embodiment, the IC chip 21 is disposed at the center of the RFID tag 1 in both the longitudinal and lateral directions. That is, the IC chip 21 is disposed equidistant from the Y-direction positions of the pair of first strip portions 232A, 232C and the pair of second strip portions 232B, 232D. Furthermore, the pair of first strip portions 232A, 232C and the pair of second strip portions 232B, 232D are formed so that their lengths in the longitudinal direction (X-direction), i.e., the dimension LA illustrated in FIG. 3, are different from each other. In the example of FIGS. 7 and 8, the longitudinal length LA of the pair of first strip portions 232A, 232C is shorter than that of the pair of second strip portions 232B, 232D.

[0093] In the RFID tag 1A of the second embodiment, due to the arrangement of the IC chip 21 and the length of each strip portion 232, as shown in Fig. 8, the first distance L1 from the IC chip 21 to both ends of the pair of rectangular conductors 23A, 23B in the longitudinal direction (X direction), the second distance L2 from the IC chip 21 to the tips of the pair of first strip portions 232A, 232C, and the third distance L3 from the IC chip 21 to the tips of the pair of second strip portions 232B, 232D are formed to be different lengths. In the example of Fig. 8, the magnitude relationship of each distance is first distance L1 < second distance L2 < third distance L3. Furthermore, each distance L1, L2, and L3 is the same as that of the first embodiment.

[0094] At least one of the first distance L1, the second distance L2, and the third distance L3 is set to have an electrical length that is a multiple of ¼ of the wavelength of the operating frequency of the RFID tag 1 A. The remaining of the first distance L1, the second distance L2, and the third distance L3 are set to have an electrical length that is different from the electrical length that is a multiple of ¼ of the wavelength of the operating frequency of the RFID tag 1 A.

[0095] As shown by the dashed-dotted line in Figure 8, current I1A flowing from the connection portion with the IC chip 21 into the inlay 2 travels approximately linearly along the X-direction, following the shortest distance, toward both ends of the rectangular conductors 23A and 23B. As a result, the length of the current path of current I1A (i.e., first distance L1) is approximately (λ1) / 2. Therefore, the antenna portion of the inlay 2 can resonate with radio waves of wavelength λ1 and carrier frequency f1, enabling communication to be established with a reader / writer located at a desired distance. This frequency f1 is the highest frequency available as a carrier frequency in the RFID tag 1A.

[0096] 8, the current I2A flowing from the connection portion with the IC chip 21 to the inlay 2 initially travels in a substantially straight line along the X direction, following the shortest distance, toward both ends of the rectangular conductors 23A and 23B. Next, after passing through the short sides 221A and 221B of the loop conductor 22, the current I2A changes direction toward the Y-positive side and heads toward the Y-positive ends of the rectangular conductors 23A and 23B. When it reaches the Y-positive ends of the rectangular conductors 23A and 23B, it changes direction toward the outside in the X direction and continues along these ends. When it reaches the central ends of the protrusions 231A and 231C in the X direction, it changes direction toward the Y-positive side and continues along these ends. Furthermore, when the inlay 2 reaches the base of the first strips 232A and 232C, it changes direction of travel along the first strips 232A and 232C toward the center in the X direction and heads toward the tip of the first strips 232A and 232C. As a result, the length of the current path of the current I2A (i.e., the second distance L2) becomes longer than the first distance L1 = (λ1) / 2. Therefore, the antenna portion of the inlay 2 can resonate with radio waves of carrier frequency f2 with wavelength λ2 longer than wavelength λ1, and communication can be established with a reader / writer located at a desired distance.

[0097] 6, the current I3A flowing into the inlay 2 from the connection with the IC chip 21 initially travels in a substantially straight line along the X direction, following the shortest distance, toward both ends of the rectangular conductors 23A and 23B. After passing through the short sides 221A and 221B of the loop conductor 22, the current I3A changes direction toward the negative Y direction and travels toward the negative Y ends of the rectangular conductors 23A and 23B. When it reaches the negative Y ends of the rectangular conductors 23A and 23B, it changes direction toward the outside in the X direction and travels along these ends. When it reaches the central ends of the protrusions 231B and 231D in the X direction, it changes direction toward the negative Y direction and travels along these ends. Furthermore, when the inlay 2 reaches the base of the second strips 232B and 232D, it changes direction of travel along the second strips 232B and 232D toward the center in the X direction and heads toward the tip of the second strips 232B and 232D. As a result, the length of the current path of the current I3A (i.e., the third distance L3) becomes longer than the second distance L2 = (λ2) / 2. Therefore, the antenna portion of the inlay 2 can resonate with radio waves of carrier frequency f3 with wavelength λ3, which is longer than wavelength λ2, and can establish communication with a reader / writer located at a desired distance.

[0098] That is, the RFID tag 1A according to the second embodiment can resonate with radio waves having carrier frequencies of f1>f2>f3 (wavelengths λ1<λ2<λ3) due to the existence of various current paths as shown by the dashed-dotted line I1A, the solid line I2A, and the dotted line I3A in Fig. 8, and can establish communication with a reader / writer at a desired distance. In other words, the RFID tag 1A according to the second embodiment can resonate with radio waves in a wide frequency band from carrier frequencies f1 to f3, and can establish communication at a desired distance, just like the first embodiment.

[0099] In other words, in the RFID tag 1A of the second embodiment, as in the first embodiment, by selecting an operating frequency from among multiple frequencies f1, f2, and f3, at least one of the first distance L1 corresponding to frequency f1, the second distance L2 corresponding to frequency f2, and the third distance L3 corresponding to frequency f3 becomes an electrical length that is a multiple of 1 / 4 of the wavelength of the operating frequency of the RFID tag 1, thereby ensuring communication performance.

[0100] Furthermore, if the longitudinal dimension (X direction) of the inlay 2 is standardized to 70 mm and the transverse dimension (Y direction) to 14 mm, the first distance L1 will be constant, and the highest frequency f1 among the applicable operating frequencies will be a fixed value. On the other hand, by changing the longitudinal (X direction) lengths of the pair of first strips 232A, 232C and the pair of second strips 232B, 232D, i.e., the dimension LA illustrated in FIG. 3 , the second distance L2 and the third distance L3 can be adjusted to any length. Therefore, the magnitudes of the operating frequencies f2 and f3, which are smaller than frequency f1, can be adjusted arbitrarily. Therefore, as with the first embodiment, the RFID tag 1A according to the second embodiment can also arbitrarily set the operating frequency range of the RFID tag 1A, even when the tag size is standardized, thereby improving versatility.

[0101] As described above, the RFID tag 1A according to the second embodiment includes the antenna pattern of the inlay 2 described with reference to Fig. 7 and other figures, thereby forming multiple current paths with different lengths L1, L2, and L3, as described with reference to Fig. 8. This allows for a wider range of frequencies to be used, thereby preventing a decrease in communication performance even when the tag size is reduced, and improving versatility. Furthermore, since the inlay 2 includes multiple current paths with different electrical lengths, the reception strength of radio waves at the antenna unit can be increased.

[0102] Furthermore, in the RFID tag 1A according to the second embodiment, the IC chip 21 is disposed at the center of the tag's longitudinal direction (X direction) and transverse direction (Y direction). When the IC chip 21 is disposed in this manner, it is preferable that the pair of first strip portions 232A, 232C and the pair of second strip portions 232B, 232D have different longitudinal lengths (LA in FIG. 3). This configuration ensures that the second distance L2 and the third distance L3 are different lengths in an antenna pattern in which the IC chip 21 is disposed at the center of the tag's longitudinal direction and transverse direction, thereby increasing the variety of frequencies available.

[0103] Next, examples of the present invention will be described in detail.

[0104] <Settings for First Test> Example 1 and Comparative Example 1 were set as follows, and a first test was conducted to verify the influence of the conductor pattern of the inlay 2 on the performance quality of the RFID tag.

[0105] Example 1 Two RFID tags 1 shown in Figures 1 and 2 were created with the dimensions of each part shown in Figure 3. In the following explanation, these two tags will be distinguished and referred to as RFID tag 1-1 and RFID tag 1-2. The created RFID tag 1-1 was affixed to a 110 kg, 46-size coated paper sheet (108.00 mm x 151.00 mm). The tag was attached in the lower right corner in a plan view with the longitudinal direction of the paper as the up-down direction, so that the long and short sides of tag 1-1 were each 13.00 mm from the outer edge of the paper.

[0106] A paperback comic book (113 mm wide x 176 mm high) was selected as the book 30 to be affixed to. The paper with the RFID tag 1-1 affixed was inserted between the back cover 31 and the last page of the book, with the tag affixed side facing the last page, similar to the state where the RFID tag 1-1 was affixed to the back surface 31A of the back cover 31.

[0107] Using a book 30 with such an RFID tag 1 attached, we tested the reading performance of the RFID tag 1-1 based on the TIPP (Tagged-Item Performance Protocol) Tagged Item Grading, a guideline for measuring and evaluating the performance quality of RFID tags (https: / / www.gs1.org / sites / default / files / docs / epc / Tagged_Item_Test_Methodology.pdf). This guideline was standardized by an international organization called GS1.

[0108] Fig. 9 is a schematic diagram of the measurement environment for the first test according to Example 1. As shown in Fig. 9, four RFID antennas, namely, a first antenna 51, a second antenna 52, a third antenna 53, and a fourth antenna 54, were installed in an anechoic chamber 50. The measurement environment shown in Fig. 9 is based on the provisions of the above-mentioned guidelines. C50 was applied to the anechoic chamber 50. A Tagformance Pro manufactured by Voyantic was used as the measuring device including the first to fourth antennas 51 to 54.

[0109] In the following description, the X1 direction, Y1 direction, and Z1 direction are set as being orthogonal to each other. The Z1 direction is the vertical direction of the anechoic chamber 50. The X1 direction and the Y1 direction are the horizontal directions of the anechoic chamber 50, and are the 0-degree and 270-degree directions of the mounting table 55, respectively (see FIG. 10 ). For ease of explanation, the positive side of the Z1 axis may also be referred to as the upper side, and the negative side of the Z1 axis may also be referred to as the lower side.

[0110] 9, the first antenna 51, the second antenna 52, the third antenna 53, and the fourth antenna 54 are arranged so as to face a predetermined point in the anechoic chamber 50, and are arranged at positions such that the directions facing the predetermined point are at angles of 0 degrees, 30 degrees, 60 degrees, and 90 degrees, respectively, from the horizontal, as shown by the dotted lines in Fig. 9. Furthermore, the first to fourth antennas 51 to 54 are arranged along the same X1Z1 plane.

[0111] One book 30 with an RFID tag 1-1 affixed was prepared and placed on the top surface of the mounting table 55 inside the anechoic chamber 50. The book 30 was placed with the cover 32 facing up and the back cover 31 facing down, i.e., with the RFID tag 1-1 positioned at the bottom of the book 30. Therefore, the books 30 were stacked flat, with one book's worth of pages above the RFID tag 1-1. As shown by the dotted line in FIG. 9 , the height of the mounting table 55 was adjusted so that the RFID tag 1-1 was positioned at a predetermined point where the opposing directions of the first to fourth antennas 51 to 54 intersect. The first to fourth antennas 51 to 54 were all installed so that the distance from the RFID tag 1-1 at the predetermined point was 1 meter.

[0112] 9, another RFID tag 1-2 was placed above the book 30 placed on the table 55, that is, on the cover 32 of the book 30, as an element for preventing the antennas 51 to 54 from reading information from the RFID tag 1-1. The RFID tag 1-2 was placed in a position overlapping the RFID tag 1-1 when viewed in the Z1 direction.

[0113] FIG. 10 is a plan view of the measurement environment shown in FIG. 9 . For convenience of illustration, FIG. 10 shows only the first antenna 51, which is horizontally arranged among the first to fourth antennas 51 to 54. However, the same applies to the other second, third, and fourth antennas 52, 53, and 54, and the orientations of the RFID tag 1-1 and the book 30. Although not shown in FIG. 10 , an object 60 and an RFID tag 1-2 are stacked on the Z1 positive side of the RFID tag 1-1. As shown in FIG. 10 , the state in which the long side of the RFID tag 1-1 and the spine 33 of the book 30 are placed on the mounting base 55 so that they directly face the first to fourth antennas 51 to 54 is defined as the 0-degree direction. The angle is set so that the angle increases as the orientation of the long side of the RFID tag 1-1 and the spine 33 of the book 30 rotates clockwise in FIG. 10 around the predetermined point where the RFID tag 1-1 is placed. The mounting base 55 is rotatable around a rotation axis along the Z1 direction passing through a predetermined upper point, and the book 30 placed on the mounting base 55 is configured so that the orientation of the spine 33 can be changed by rotating the mounting base 55.

[0114] Under these conditions, the sensitivity (average output for reading information from the RFID tag 1-1) of the first to fourth antennas 51 to 54 was measured when the long side of the RFID tag 1-1 and the spine 33 of the book 30 were oriented in 10 directions: 0 degrees, 30 degrees, 60 degrees, 120 degrees, 150 degrees, 180 degrees, 210 degrees, 240 degrees, 300 degrees, and 330 degrees. In addition, the backscatter (strength of the response wave from the RFID tag 1-1) of the first to fourth antennas 51 to 54 was measured in two directions: 0 degrees and 180 degrees.

[0115] Using the above measured values, it was determined whether the grade conditions set by TIPP were met. Grades are evaluation standards related to the quality of the reading performance of the RFID tag 1, and multiple types are set. For each grade, a standard value is set for each of the above measured values. A different standard value is set for each grade. When all measured values ​​exceed the standard value, it can be evaluated that the conditions of the corresponding grade are met. We investigated the grades that can meet the conditions when one book 30 is stacked flat above the RFID tag 1-1 to be inspected, as in this Example 1.

[0116] <Comparative Example 1> Fig. 11 is a plan view showing the conductor pattern of the RFID tag 101 used in Comparative Example 1. Fig. 13 corresponds to Fig. 2 and, like Fig. 2, illustrates only the elements related to the inlay of the RFID tag 101. In Comparative Example 1, measurements were made under the same conditions as in Example 1, except that RFID tags 101 having the existing conductor pattern shown in Fig. 13 were used as the two tags to be attached and placed on the book 30.

[0117] 11 , the RFID tag 101 according to the first comparative example has an inlay that includes an IC chip 121, a loop-shaped conductor 122, and an antenna section 123. The inlay has the loop-shaped conductor 122 and the antenna section 123 formed by dry-laminating an aluminum sheet on a substrate such as a synthetic resin film of polyethylene terephthalate, polypropylene, or the like, and the IC chip 121 mounted at a specified position.

[0118] 1, 2, etc., the IC chip 121 is similar to the IC chip 21 of the embodiment shown in Figures 1 and 2, and therefore a description thereof will be omitted. The shape and function of the loop-shaped conductor 122 are also similar to the loop-shaped conductor 22 of the embodiment, and it has a pair of short side portions 1221A, 1221B extending in the short direction of the RFID tag 101 and a pair of long side portions 1222A, 1222B extending in the longitudinal direction. The loop-shaped conductor 122 is electrically connected to the IC chip 121 and the antenna portion 123.

[0119] The antenna unit 123 has a structure that achieves impedance conjugate matching with the IC chip 121 for radio waves with a frequency of, for example, around 920 MHz (e.g., 860 MHz to 960 MHz, more preferably 915 MHz to 935 MHz). The antenna unit 123 includes two conductors (conductors 123A and 123B) that achieve impedance conjugate matching with the IC chip 121. The conductors 123A and 123B are conductive wiring patterns that are connected to the loop conductor 122 and extend in directions away from the loop conductor 122 (to the positive and negative directions of the X-axis in the example of FIG. 13). The conductive wiring patterns can be formed by existing methods such as pressing or etching copper foil or aluminum foil, plating, silkscreen printing of metal paste, or metal wire; however, in this example, the conductive wiring patterns were formed by aluminum etching.

[0120] The conductor portion 123A and the conductor portion 123B are formed symmetrically with respect to an imaginary line (corresponding to the first imaginary line VL in FIG. 2 ) that passes through approximately the center of the IC chip 121. The imaginary line is a line that is parallel to the XY plane and extends in the Y direction. The imaginary line also divides the RFID tag 101 into approximately two equal regions in the X direction.

[0121] As shown in FIG. 11 , the RFID tag 101 of the comparative example 1 differs from the RFID tag 1 of the above embodiment in that a pair of conductor portions 123A, 123B of the antenna portion 123 are both connected to one of the long side portions 1222B on the Y-positive side of the loop-shaped conductor 122, that the shape of the conductor portions 123A, 123B is not simply rectangular like the rectangular conductor 23 of the above embodiment, but has a more complex shape, for example, including wiring extending in a zigzag pattern, and that the conductor pattern is not formed line-symmetrically with respect to a second imaginary line VS (see FIG. 2 ) that passes through approximately the center of the RFID tag 101 in the short direction (Y direction) and extends in the long direction (X direction) in a planar view.

[0122] In the RFID tag 101 used in the comparative example, the size of the inlay is the same as that of the RFID tag 1 of the above embodiment. That is, the longitudinal dimension (X direction) of the inlay 2 shown in Fig. 11 is 70 mm, and the lateral dimension (Y direction) of the inlay 2 is 14 mm.

[0123] Whether or not the grade conditions set in TIPP were met was determined using each measurement value obtained by performing the same measurements as in Example 1. In Comparative Example 1, the test environment was such that one book 30 was stacked flat above the RFID tag 101 to be inspected, as in Example 1, and therefore the grade that could meet the conditions when one book 30 was stacked flat was investigated, as in Example 1.

[0124] <Results of First Test> As a result of the above-described first test, it was confirmed that Example 1 satisfied the conditions for grades M25C and M30E set by TIPP.

[0125] On the other hand, Comparative Example 1 was unable to satisfy the conditions for grades M25C and M30E.

[0126] As described above, the results of the first experiment showed that even when the RFID tag to be inspected is attached to a book 30 and another RFID tag is stacked above the book 30, the conductor pattern of the RFID tag 1 of this embodiment is less susceptible to the effects of moisture contained in the pages of the book 30 to which it is attached, compared to the existing conductor pattern of the RFID tag 101 of the comparative example shown in Figure 11.Furthermore, even when other tags that hinder the reading of information by each of the antennas 51 to 54 are present, it is less susceptible to the effects of these obstructions on communication, and a decrease in communication performance can be suppressed.

[0127] <Settings for Second Test> Example 2 and Comparative Example 2 were set as follows, and a second test was conducted to verify the influence of the conductor pattern of the inlay 2 on the communication performance of the RFID tag.

[0128] 9, a test was conducted to read information from an RFID tag 1-1 using only the first antenna 51, which was arranged horizontally among the four RFID antennas. The long side of the RFID tag 1-1 placed on the mounting base 55 was oriented in the 0 degree direction as described above, and the long side of the RFID tag 1-1 was directly facing the first antenna 51.

[0129] Under these conditions, the frequency characteristics of the RFID tag 1-1 were measured. The measurement frequency band of the radio wave for wireless communication during measurement was 800 to 1000 MHz, and the EIRP (Equivalent Isotropically Radiated Power) was 3.28 W. The frequency measurement was performed in a test environment in which only the RFID tag 1-1 to be inspected was placed alone at a predetermined point on the mounting table 55, that is, the book 30 and other RFID tags 1-2 were removed from the state shown in FIG. 9 . Furthermore, in Example 2, unlike Example 1, the distance of the first antenna 51 from the position where the RFID tag 1-1 was placed on the mounting table 55 was made variable.

[0130] <Comparative Example 2> In Comparative Example 2, measurements were performed under the same conditions as in Example 2, except that the tag to be inspected, which was placed at a predetermined point on the mounting table 55, was an RFID tag 101 having an existing conductor pattern shown in Figure 11.

[0131] <Results of Second Test> Fig. 12 is a diagram showing the frequency characteristics of Example 2 and Comparative Example 2 measured in the second test. Fig. 12(A) shows the frequency characteristics of Example 2, and Fig. 12(B) shows the frequency characteristics of Comparative Example 2. In each of Figs. (A) and (B), the horizontal axis represents the frequency (MHz) of the radio wave for wireless communication, and the vertical axis represents the communicable distance (m) from each RFID tag 1-1, 101 to the first antenna 51. In Fig. 12, the upper and lower limits of the frequency at which the communicable distance is approximately 13 m or more for each frequency characteristic are indicated by thick dotted lines, and the frequency range between these upper and lower limits is indicated by thick dotted arrows A and B. The ranges of these arrows A and B are the "peak frequencies" of each frequency characteristic.

[0132] 12(B), it was confirmed that in Comparative Example 2, the peak frequency range B shifts to the lower frequency side due to the miniaturization of the tag size, for example, due to the reduction in the area of ​​the gap portion of the loop-shaped conductor 122. In contrast to this, in Example 2, the range of frequencies applicable to the carrier wave can be increased by providing the first strip portions 232A, 232C and the second strip portions 232B, 232B in the antenna portion of the tag, and therefore, it was confirmed that the peak frequency range A can be maintained on the higher frequency side than in Comparative Example 2, and that the peak frequency can be maintained in a wider frequency band than in Comparative Example 2, as shown by arrow A in FIG.

[0133] <Settings for the Third Test> Examples 3 to 8 and Comparative Example 3 were set as follows, and a third test was conducted to verify the influence of the conductor pattern of the inlay 2 on the communication performance of the RFID tag.

[0134] Example 3 In a simulation environment, a model of the RFID tag 1 having the conductive pattern of the inlay 2 shown in Figures 1 and 2 was created using the dimensions of each part shown in Figure 3. That is, the outer dimensions of the inlay 2 were set to 70 x 14 mm, and the dimension LA of the first strip portions 232A, 232C and the second strip portions 232B, 232D in the tag longitudinal direction (X direction) was set to 14.6 mm (see Figure 3). Furthermore, the width dimension LB of each of the strip portions 232A to 232D in the tag transverse direction (Y direction) was set to 0.5 mm, and the gap dimension LC between each of the strip portions 232A to 232D and the rectangular conductors 23A, 23B in the tag transverse direction was set to 1.0 mm.

[0135] Using the created model, a wireless communication operation simulation was performed. The measurement frequency band for wireless communication radio waves was 800 to 1000 MHz, and the VSWR (Voltage Standing Wave Ratio) characteristics were measured under the simulation environment. In addition, the voltage value around the IC chip 21 in the inlay 2 was measured at the operating frequency where the VSMR characteristics take the minimum value, i.e., the value when the RFID tag 1 is in the most sensitive state.

[0136] <Example 4> In the model of RFID tag 1, measurements were performed under the same conditions as in Example 3, except that the dimension LA of the first strip portions 232A, 232C and the second strip portions 232B, 232D in the tag longitudinal direction was shortened by 5 mm to 9.6 mm.

[0137] <Example 5> In the model of RFID tag 1, measurements were performed under the same conditions as in Example 3, except that the dimension LA of the first strip portions 232A, 232C and the second strip portions 232B, 232D in the tag longitudinal direction was shortened by 10 mm to 4.6 mm.

[0138] <Example 6> In the model of RFID tag 1, measurements were performed under the same conditions as in Example 3, except that the dimension LA of the first strip portions 232A, 232C and the second strip portions 232B, 232D in the tag longitudinal direction was increased by 5 mm to 19.6 mm.

[0139] Example 7 Measurements were made under the same conditions as in Example 3 for the model of the RFID tag 1, except that the width dimension LB of each of the strip portions 232A to 232D in the short side direction of the tag was increased by 1 mm to 1.5 mm.

[0140] <Example 8> In the model of RFID tag 1, measurements were performed under the same conditions as in Example 3, except that the gap dimension LC in the short side direction of the tag between each strip portion 232A to 232D and the rectangular conductors 23A and 23B was increased by 1 mm to 2.0 mm.

[0141] Comparative Example 3 Measurements were performed under the same conditions as in Example 3, except that the first strip portions 232A, 232C and the second strip portions 232B, 232D were all removed from the model of the RFID tag 1.

[0142] <Results of Third Test> The results of the third test are shown in Table 1 below. The VSMR values ​​shown in Table 1 indicate the minimum values ​​in the VSMR characteristics, i.e., the values ​​when the RFID tag has the best sensitivity. The frequencies at which the minimum values ​​were obtained were within the range of 923 to 925 (MHz) for all of Examples 3 to 8 and Comparative Example 3.

[0143]

[0144] As shown in Examples 3 to 6 in Table 1, it was shown that as the dimension LA of the strip portions 232A to 232D was increased from 4.6 mm to 14.6 mm, the VSWR decreased, and the sensitivity of the RFID tag 1 improved. On the other hand, when the dimension LA was further increased to 19.6 mm, the VSMR increased slightly compared to when the dimension LA was 14.6 mm, and the sensitivity decreased slightly. Similarly, as shown in Examples 3 to 6, it was shown that as the dimension LA of the strip portions 232A to 232D was increased from 4.6 mm to 14.6 mm, the voltage value of the inlay 2 around the IC chip 21 increased, and the sensitivity of the RFID tag 1 improved. On the other hand, when the dimension LA was further increased to 19.6 mm, the voltage value decreased slightly compared to when the dimension LA was 14.6 mm, and the sensitivity decreased slightly.

[0145] On the other hand, as shown in Comparative Example 3 in Table 1, when the strip portions 232A to 232D were not present, the VSMR increased significantly compared to the examples, and the voltage value of the inlay 2 around the IC chip 21 decreased significantly, resulting in a deterioration in the sensitivity of the RFID tag.

[0146] From the above, it has been shown that in the RFID tag 1, when the external dimensions of the inlay 2 are 70 x 14 mm, it is preferable that the dimension LA of each strip portion 232A to 232D is in the range of 4.6 mm to 19.6 mm, more preferably 9.4 mm to 19.6 mm, even more preferably 14.6 mm to 19.6 mm, and most preferably 14.6 mm.

[0147] Furthermore, as shown in Example 7 of Table 1, when the width dimension LB of each strip portion 232A-232D in the tag short-side direction was increased by 1 mm to 1.5 mm compared to Example 3, the VSMR increased. In other words, the VSMR increased as the width dimension LB of the strip portions 232A-232D was increased. However, when the width dimension LB was 1.5 mm, the VSMR was similar to that of Example 5, and was significantly lower than that of Comparative Example 3. The voltage value around the IC chip 21 was also significantly higher, so the sensitivity of the RFID tag 1 can be said to be within the acceptable range. This indicates that, in the RFID tag 1, when the external dimensions of the inlay 2 are 70 x 14 mm, the width dimension LB of each strip portion 232A-232D in the tag short-side direction is preferably 0.5 mm to 1.5 mm, and 0.5 mm is more preferable.

[0148] Furthermore, as shown in Example 8 of Table 1, when the gap dimension LC in the short-side direction of the tag between each of the strip portions 232A to 232D and the rectangular conductors 23A, 23B was increased by 1 mm to 2.0 mm compared to Example 3, the VSMR increased, that is, the VSMR increased the further the strip portions 232A to 232D were separated from the rectangular conductors 23A, 23B. However, even when the gap dimension LC was 2.0 mm, the VSMR was similar to that of Example 5, and was significantly lower than that of Comparative Example 3, and the voltage value around the IC chip 21 was also significantly higher, so it can be said that the sensitivity of the RFID tag 1 was within the acceptable range. This shows that in the RFID tag 1, when the external dimensions of the inlay 2 are 70 x 14 mm, the gap dimension LC in the short direction of the tag between each strip portion 232A to 232D and the rectangular conductors 23A, 23B is preferably 1.0 mm to 2.0 mm, and 1.0 mm is more preferable.

[0149] The present embodiment has been described above with reference to specific examples. However, the present disclosure is not limited to these specific examples. Design modifications to these specific examples made by a person skilled in the art as appropriate are also included within the scope of the present disclosure as long as they comprise the features of the present disclosure. The elements of the above-described specific examples, as well as their arrangement, conditions, shape, etc., are not limited to those exemplified and can be modified as appropriate. The elements of the above-described specific examples can be combined in various ways as appropriate, as long as no technical contradictions arise.

[0150] In the above embodiment, the shape of the inlay 2 of the RFID tag 1, 1A, particularly the shape of the antenna pattern including the loop conductor 22 and the pair of rectangular conductors 23A, 23B, is illustrated as a horizontally long rectangular shape in a plan view seen from the Z direction, with the X direction as the longitudinal direction (first direction) and the Y direction as the lateral direction (second direction), as shown in Figures 2 and 7. However, the shape of the inlay 2 may be other than rectangular. For example, it may be a substantially square shape in which the dimensions in the first direction and the second direction are equal, or a vertically long rectangular shape in which the dimensions in the first direction are shorter than the dimensions in the second direction, i.e., the longitudinal direction and the lateral direction are reversed in the examples of Figures 2 and 7.

[0151] In the above-described embodiments, the RFID tags 1 and 1A are shaped like a rectangle in a plan view from the Z direction, with the X direction as the longitudinal direction (first direction) and the Y direction as the lateral direction (second direction), as shown in Figures 2 and 7. However, the tag shape may be other than rectangular. For example, the RFID tag may be oval, trapezoidal, rhombic, circular, square, or other shapes. Even if the RFID tag is shaped like a shape other than a rectangle, the shape of the inlay 2 does not necessarily have to be the same as the tag shape, and may be the rectangular shape described above.

[0152] This international application claims priority based on Japanese Patent Application No. 2023-215948 filed on December 21, 2023, the entire contents of which are incorporated herein by reference.

[0153] 1, 1A RFID tag 21 IC chip 22 Loop-shaped conductor 23A, 23B Pair of rectangular conductors 231A, 231C First protrusion 231B, 231D Second protrusion 232A, 232C First strip portion 232B, 232D Second strip portion L1 First distance L2 Second distance L3 Third distance X Longitudinal direction (first direction) Y Shortitudinal direction (second direction)

Claims

1. An RFID tag comprising: an IC chip on which identification information is recorded; a loop-shaped conductor formed in a ring and connected to the IC chip; a pair of rectangular conductors extending from the loop-shaped conductor on both sides in a first direction and formed in a rectangular shape; a pair of first protrusions in each of the pair of rectangular conductors protruding from the rectangular conductor to the outside in the second direction from one side in a second direction perpendicular to the first direction; a pair of second protrusions in each of the pair of rectangular conductors protruding from the rectangular conductor to the outside in the second direction from the other side in the second direction; a pair of first strip parts each protruding from the pair of first protrusions along the first direction toward a center side in the first direction from the pair of first protrusions; and a pair of second strip parts each protruding from the pair of second protrusions along the first direction toward a center side in the first direction from the pair of second protrusions and formed in a strip; an RFID tag, wherein a second distance to a tip of a first strip portion and a third distance from the IC chip to the tips of the pair of second strip portions are formed to be different lengths, at least one of the first distance, the second distance, and the third distance is set to be an electrical length that is a multiple of 1 / 4 of the wavelength of the operating frequency of the RFID tag, and the remaining of the first distance, the second distance, and the third distance is set to be an electrical length different from the electrical length that is a multiple of 1 / 4 of the wavelength of the operating frequency of the RFID tag.

2. The RFID tag according to claim 1, wherein the IC chip is positioned at the center in the first direction and shifted to one side from the center in the second direction, and the pair of first rectangular portions and the pair of second rectangular portions have the same length in the first direction.

3. The RFID tag according to claim 1, wherein the IC chip is positioned at the center in the first direction and the second direction, and the pair of first rectangular portions and the pair of second rectangular portions are formed so as to have different lengths in the first direction.

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