JP2007096655A - Antenna for rfid tag and rfid tag - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an antenna for a radio wave type practical RFID tag obtained by shortening, specially, the length of a basic type of a dipole antenna, and the RFID tag. <P>SOLUTION: The antenna for the RFID tag has a dipole of a length 2d which has a slit of a length 2s. In this case, the dipole has one or more branches or inflection points at a position where a creepage distance from the center of the dipole is longer than (s) and shorter than (d), so that the antenna can be shortened in the direction of the dipole. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an antenna for an RFID tag and an RFID tag for writing and reading information by a radio wave system.

  RDID (Radio Frequency Identification) is known in which predetermined information is communicated in a contactless manner using a wireless tag equipped with an IC chip and a predetermined reader / writer device. There are three known RFID methods: an electromagnetic induction method, an electrostatic coupling method, and a radio wave method. Among these methods, the electromagnetic induction method and the electrostatic coupling method have application limitations due to the relatively short communication distance. is there. On the other hand, the radio wave method greatly exceeds the other two methods in communication distance.

  However, in the radio wave system, the size of the antenna, that is, the size of the wireless tag itself is larger than those of the other two systems, and there is an application limit due to another size in which the object to be tagged must be large.

  As one method for solving this problem, Patent Document 1 discloses that the length of the antenna portion is shortened by using an inductive pattern portion.

JP-A-2005-92699

  However, the method of shortening the length direction by changing the shape of the end portion of the dipole from the linear type is not sufficient as a reduction in size of the tag in the sense that the application limit due to the size is greatly relaxed.

  An object of the present invention is to provide a practical RFID tag antenna and an RFID tag of a radio wave system in which the length direction is shortened from the basic type of a dipole antenna.

  The RFID tag antenna according to the present invention is a radio frequency RFID tag antenna including a 2d-long dipole having a slit of 2s in length, and a creepage distance from the center position of the dipole is larger than s and smaller than d The position is characterized in that the dipole has one or more branch points.

  The RFID tag antenna according to the present invention is a radio frequency RFID tag antenna including a 2d-long dipole having a slit of 2s in length, and a creepage distance from the center position of the dipole is larger than s and smaller than d The position is characterized in that the dipole has one or more inflection points.

Moreover, it is more preferable that the branch point or the bending point of the dipole is on both sides with respect to the center position of the dipole. It is more preferable in terms of balance to be on both sides than on one side.
Also, the creepage distance from the center position of the dipole to the nearest branch point or bending point is d1, the creepage distance to the second nearest branch point or bending point is d2, and d1 ≧ s and d1 ≧ d-d2 More preferably, it is characterized.
More preferably, the dipole having a branch point has a bending point at a position where the creepage distance from the center position of the dipole is larger than the branch point.
Moreover, it is preferable that the left and right sides are line-symmetric or point-symmetric with respect to the center position of the dipole.
More preferably, the dipole has one branch point on each side with respect to the center position of the dipole, and the branch angle of each branch branch is approximately 90 degrees and approximately 270 degrees.

Each diverging point with a creepage distance d1 from the center position of the dipole is d1 on both sides with respect to the center position of the dipole, and the branch angle of each branch branch is approximately 90 degrees and approximately 270 degrees. Each branch branch has one bending point whose creepage distance from the center position of the dipole is d2, each bending angle is approximately 90 degrees and approximately 270 degrees, and d1 ≧ s and d1 ≧ d More preferably, -d2.
The above series of features are all inflection points and branch points while maintaining impedance matching conditions, so that the size of the length in the length direction can be reduced without reducing the communication performance ratio of the basic type of the dipole antenna as much as possible. Shortening is possible.
The RFID tag according to the present invention is an RFID tag using the RFID tag antenna as described above.

  According to the present invention, it is possible to provide a practical small-sized tag of a radio wave type whose length direction is particularly shortened from the basic type of a dipole antenna.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view of a basic type of a dipole antenna.
As a basic type of the dipole antenna, generally, the case where the length 2d of the dipole 101 is 1/2 of the wavelength used is most preferable for obtaining a resonance state, but the length of the dipole is 1/4 of the wavelength used. Even in this case, the second resonance state can be obtained.
In the present invention, a dipole having a half of the wavelength used is adopted as the basic type of the dipole antenna. Since the operating frequency is 953 MHz, the wavelength is about 31.5 cm, and the dipole length is 15.7 cm, which is half that length. From this numerical value, it can be easily estimated that the operation target is limited if the basic type is used. In practice, however, a value that is about 5% smaller than the exact ½ value is usually adopted. This degree depends on the dielectric constant of the antenna material and is 14.8 cm in the present invention. However, as a tag antenna mounting the IC chip 103, not only the resonance condition but also the condition for obtaining the most efficient supply power for driving the IC chip cannot be satisfied to satisfy the effective communication state. . The conditions for obtaining the supplied power most efficiently can be obtained by selecting the optimum value of resistance (hereinafter referred to as impedance) in a broad sense of a tag composed of an IC chip and an antenna. The slit 102 has the function of adjusting the impedance, and it is necessary to adjust the impedance of the IC chip and the antenna by adjusting the slit length 2s as well as the resonance condition depending on the length of the dipole. It is. Therefore, the length of the slit is not determined by the wavelength used as in the case of the length of the dipole, but depends on the resistance value and capacitance of the IC chip itself, and is specific to the IC chip to be used.
FIG. 2 is a diagram showing the relationship between the slit distance and the communication distance reflecting the adjustment of the impedance. The notation of communication distance is a relative value when the communicable distance of the basic type of the dipole antenna at the reader / writer output of 100 mW is 100%. In the embodiments described later, the communication distance is the same definition. The IC chip used was a UHF band IC chip manufactured by Matrics, USA, and with Auto ID Center Class 0 specification. The reader / writer was RDR-JAP-001 manufactured by the same company, and the filter function of the US specification (915MHz) was changed and modified to comply with the domestic radio wave law (953MHz). The test of each example described later was also performed using a similar IC chip or the like.

  The antenna pattern including the slit can be formed by screen-printing a conductive paste on a base film or by etching. In the following examples, an antenna pattern prepared by aluminum etching was used.

FIGS. 3 and 4 show examples of antenna deformation patterns having inflection points. Specifically, it has one bending point each having a creepage distance k from the center position of the dipole to the bending point at symmetrical positions on both sides with respect to the center position of the dipole, and the bending angles are 90 degrees and 270 respectively. It is what you did.
As a common notation in the following description, the bending angle and the branching angle are expressed as 0 degrees when not bent or branched, and the clockwise plus angle θ degrees with the outer direction to which the dipole is directed as a reference line. The “outward direction of the dipole” means the end direction of the dipole immediately before bending or branching. The distance from the center position of the dipole to the bending point or the branch point is a centerline creepage distance considering the width (thickness) of the dipole. The direction of the slit (the horizontal direction on the paper surface) is referred to as the length direction, and the direction perpendicular to the slit (the vertical direction on the paper surface) is referred to as the width direction. The examples shown in FIGS. 3 and 4 and the following FIGS. 5, 6, 7, and 8 are examples in which bending points and branch points are provided on both sides with respect to the center position of the dipole. Depending on the tag shape, etc., it may be provided only on one side.

The example shown in FIG. 3 is a case where d>d1> s and d1 is close to d, that is, a case where there is a bending point outside the slit and far from the center of the dipole. The example shown in FIG. It shows a case where>d1> s and d1 is close to s, that is, a case where the bending point is located outside the slit and close to the dipole center.
As for the position of the inflection point, that is, the value of d1, the larger the value of d1, the smaller the rate of performance degradation with respect to the communication performance when the basic type of the dipole antenna is used as a reference. The shortening effect is small. As for the bending angle, the larger the absolute value of (θ-180), the better. Further, when the absolute value of (θ−180) is smaller than 90, there is no shortening effect in the length direction, and only the communication performance is lowered. With respect to symmetry, it is more preferable that the shape of the antenna maintain line symmetry or point symmetry with respect to the center position of the dipole even from the point of resonance that is the original function of the dipole. The shape of the antenna refers to the shape of a dipole or a slit.

  The example shown in FIGS. 4A and 4B is a pattern example for verifying the function of the slit, that is, the importance of impedance matching. FIG. 4A shows a pattern in which only the shortening in the length direction is obtained without satisfying the condition of d1> s and maintaining the slit length satisfying the impedance matching in the state of s> d1. FIG. 4 (b) shows a pattern in which s> d1 is the same as in FIG. 4 (a), but the slit itself is bent and the slit length is the same as that satisfying impedance matching. . As a result, in both examples shown in FIGS. 4A and 4B, communication cannot be performed unless the reader / writer and the tag are brought into close contact with each other, and the verification is confirmed as an example of failure of the impedance condition.

  If the impedance matching is not satisfied, it can be judged from the result shown in FIG. 2 that the communication function is greatly deteriorated. From the verification results of the examples shown in FIGS. 4 (a) and 4 (b), I understand that. The length of the slit for impedance adjustment is the distance between the short-circuit points of the dipole at the symmetrical position across the IC chip, and the slit length must be a length in a linear configuration. Furthermore, providing a bending point in the state of s> d1 is because the slit length condition or slit linearity condition or symmetry condition must be broken, and impedance matching by the slit cannot be satisfied. , Which means that the shortening limit in the length direction is 2s.

  5 and 6 show examples of deformation patterns having branch points. Specifically, it has one branch point each with a distance d1 from the center position of the dipole to the branch point at symmetrical positions on both sides with respect to the center position of the dipole, and the branch angles are 90 degrees and 270 degrees, respectively. It is a thing.

The example shown in FIG. 5 is a case where d>d1> s and d1 is close to d, that is, a case where there is a branch point outside the slit and far from the center of the dipole, and FIG. And d1 is close to s, that is, the case where the branch point is located outside the slit and near the dipole center.
The position of the branch point, that is, the value of d1, unlike the case of the bending point, has two branch branches at the branch point, so that the dependence of the communication performance on the position is small. Therefore, when aiming at shortening in the length direction, it is more preferable to provide a branch point than a bending point. As with the bending angle, the branching angle is preferably around 90 degrees and 270 degrees in terms of the shortening effect in the length direction, and the symmetry is the same as in the bending case.

  7 and 8 show examples of deformation patterns having a branch point and a bending point. Specifically, it has one branch point each with a distance d1 from the center position of the dipole to the branch point at symmetrical positions on both sides with respect to the center position of the dipole, and the branch angles are 90 degrees and 270 degrees, respectively. In this case, each of the four branch branches has a bending point at a creepage distance d2 from the dipole center, and d> d2> d1> s.

  The example shown in FIG. 7 is a case where d> d2> d1> s and d2 is close to d, and the example shown in FIG. 8 is a case where d> d2> d1> s and d2 is close to d1. The distance b from the center position of the dipole to the branch point is the same as in the examples shown in FIGS. 7 and 8, and the length direction is the same. In the example shown in FIG. 7 and FIG. 8, the length in the width direction is different as a result, but the communication performance is better as the width direction is larger. Accordingly, when only the shortening in the length direction is sufficient, it is preferable to select a pattern close to the pattern shown in FIG. 7, and in the case where both the length direction and the width direction need to be shortened, in consideration of the communication performance, FIG. A pattern close to the pattern shown in the above is selected. Although it is a balance with communication performance, the communication distance when using the basic type of the dipole antenna shown in FIG. 1 is less than 10 m in UHF band communication, the communication performance is reduced by about 50%. Since there is a communication distance of several meters, the pattern in FIG. 8 is effective when the size of the tag is more important than the communication distance due to the size of the object to which the tag is attached. The branching angle, bending angle, and symmetry characteristics are basically the same as those in FIGS.

[Example]
[Example 1]
In the first embodiment, the value of d1 is set to 52 mm in the example shown in FIG. As a result, the length direction was 110 mm, the width direction was 23.5 mm, and the communication distance was 82% of the basic pattern of the dipole antenna. Since the dimensions take into account the dipole width and the minimum necessary line spacing, it is inevitable that the dimensions will be slightly larger than the simple calculation values. The same applies to the following examples, but the dipole width was 4.7 mm and the thickness was 30 μm.

[Example 2]
In the second embodiment, the value of d1 is set to 32 mm in the example shown in FIG. As a result, the length direction was 70 mm, the width direction was 43 mm, and the communication distance was 50% of the basic pattern of the dipole antenna. In this example, the length direction is shortened as much as possible, but the decrease in communication distance is only 50%.

[Example 3]
In the third embodiment, the value of d1 is set to 52 mm in the example shown in FIG. As a result, the length direction was 110mm, the width direction was 43mm, and the communication distance was 90% of the basic pattern of the dipole antenna. Although the width direction is larger than that of the first embodiment, the communication distance is 90% of the basic type of the dipole antenna.

[Example 4]
In the fourth embodiment, the value of d1 is set to 32 mm in the example shown in FIG. As a result, the length direction was 70mm, the width direction was 83mm, and the communication distance was 89% of the basic type of the dipole antenna. Compared with the third embodiment, the width direction is larger, but the communication performance is not deteriorated even if the length direction is shortened.

[Example 5]
In the fifth embodiment, the value of d1 is set to 32 mm and the value of d2 is set to 52 mm in the example shown in FIG. As a result, the length direction was 70mm, the width direction was 46mm, and the communication distance was 88% of the basic type of the dipole antenna. Compared with the fourth embodiment, the width direction is further shortened so that the communication performance does not deteriorate.

[Example 6]
In the sixth embodiment, the value of d1 is set to 32 mm and the value of d2 is set to 42 mm in the example shown in FIG. As a result, the length direction was 70 mm, the width direction was 25 mm, and the communication distance was 50% of the basic pattern of the dipole antenna. Although the communication distance is halved, it is a minimum pattern in both the length direction and the width direction, which is an extremely effective example in an operation in which the tag size is more important than the communication distance.
Table 1 shows a list of measurement results according to the above examples.

  By providing a bending point and a branch point under a certain condition with respect to the basic type of the dipole antenna, it is possible to reduce the size of the radio frequency type electronic tag and greatly reduce the restriction of the operation target.

The top view of the basic type of a dipole type antenna. The figure which shows the relationship of the communication distance which reflected adjustment of the length and impedance of a slit. The top view of an example (Example 1) which has the bending point of the antenna of this invention. The top view of an example (Example 2) of the deformation pattern which has the bending point of the antenna of this invention, (a) is a top view of the example of the failure of the impedance condition (slit length failure), which is an example of the deformation pattern having the bending point (B) is also a plan view of another failure example (slit shape failure) of the impedance condition. The top view of an example (Example 3) of the deformation pattern which has a branch point of the antenna of this invention. The top view of an example (Example 4) of the deformation pattern which has a branch point of the antenna of this invention. The top view of an example (Example 5) of the deformation pattern which has the bending point and branching point of the antenna of this invention. The top view of an example (Example 6) of the deformation pattern which has the bending point and branching point of the antenna of this invention.

Explanation of symbols

101 Dipole
102 slit
103 IC chip
d 1/2 the length of the dipole (creepage length)
s 1/2 the slit length (creepage length)
d1 Creepage distance from the center of the dipole to the nearest bend or branch point
d2 Creepage distance from the center point of the dipole to the bending or branching point closest to the second position

Claims (9)

  In a radio frequency RFID tag antenna having a 2d long dipole with a 2s long slit, one or more dipoles branch at a position where the creepage distance from the center of the dipole is larger than s and smaller than d An RFID tag antenna having a point.   In a radio frequency RFID tag antenna having a 2d long dipole with a 2s long slit, the dipole has one or more bends at a position where the creepage distance from the center of the dipole is larger than s and smaller than d An RFID tag antenna having a point.   3. The RFID tag antenna according to claim 1, wherein a branch point or a bending point of the dipole is on both sides with respect to a center position of the dipole. The creepage distance from the center position of the dipole to the nearest branching or bending point is d1, and the creeping distance to the second nearest branching or bending point is d2, and d1 ≧ s and d1 ≧ d-d2 The RFID tag antenna according to claim 3, wherein the antenna is an RFID tag antenna.   5. The RFID tag antenna according to claim 4, wherein the dipole having a branch point has a bending point at a position where a creeping distance from a center position of the dipole is larger than the branch point.   6. The RFID tag antenna according to claim 1, wherein the shape of the antenna is line-symmetrical or point-symmetrical with respect to the center position of the dipole.   7. The dipole has one branch point on each side with respect to the center position of the dipole, and the branch angle of each branch branch is approximately 90 degrees and approximately 270 degrees. The antenna for RFID tags as described in 2.   The diverging point with a creepage distance d1 from the center position of the dipole has one each on both sides with respect to the center position of the dipole, and the branch angles of the respective branch branches are approximately 90 degrees and approximately 270 degrees, Each branch branch has one bending point whose creeping distance from the center position of the dipole is d2, each bending angle is approximately 90 degrees and approximately 270 degrees, and d1 ≧ s and d1 ≧ d-d2 The RFID tag antenna according to any one of 1 to 7, wherein the antenna is for RFID tags. The RFID tag using the antenna for RFID tags as described in any one of Claim 1 to 8.

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