KR100968711B1 - Rfid tag antenna - Google Patents

Abstract

The present invention relates to a non-contact tag antenna that transmits and receives to and from an RFID reader / writer used in the UHF band. More specifically, the tag IC and the conjugate are matched using an electromagnetic coupling generated between the short-circuit stub and the dipole portion. The present invention relates to an RFID tag antenna having a structure capable of easily generating an inductive reactance value.

According to the present invention, by adjusting the reactance value and the resistance value through the change in the length and width of the shorting stub of the tag antenna, it is very easy to adjust the impedance value required for conjugate matching between the tag antenna and the tag IC. It is possible to miniaturize through the load portion connected to the dipole portion, and there is an excellent effect of reducing the manufacturing cost.

Description

RFID tag antenna {RFID TAG ANTENNA}

The present invention relates to a non-contact tag antenna that transmits and receives to and from an RFID reader / writer used in the UHF band. More specifically, the tag IC and the conjugate are matched using an electromagnetic coupling generated between the short-circuit stub and the dipole portion. The present invention relates to an RFID tag antenna having a structure capable of easily generating an inductive reactance value.

 The RFID system transmits a signal of about 1 W from the reader / writer using a radio signal in the UHF band (860 to 960 MHz), receives the signal at the tag side, and returns a response signal back to the reader / writer side to transmit information in the tag. A system that can be read by a reader / writer. The communication distance is affected by the gain of the tag antenna and the operating voltage of the chip or the surrounding environment, and is about 3 m. The tag consists of an LSI chip connected to the antenna and the antenna feed point.

Recently, RFID (radio frequency identification) systems are rapidly growing in the ultra high frequency (UHF) band where the recognition distance has a tension point. To reduce production costs in RFID systems, tag antennas must be impedance matched directly with tag ICs. In this case, the tag IC has a charge capacitor, which has a large value of conductive reactance. When the impedance of the tag antenna matches the impedance of the tag IC, the amount of power transferred from the antenna to the tag IC is maximized.

However, in the case of folded dipole antenna, slot antenna, and meander antenna, which are mainly used as RFID tag antennas in the UHF band, the large inductive reactance required to match the conjugate impedance with a tag IC having a large conductive reactance value is large. It has no (inductive reactance) value.

For example, Korean Patent Application No. 2005-134628 discloses a tag antenna including a dipole antenna and a feeder on which a chip is mounted, the dipole portion having a length shorter than half the antenna resonance wavelength, and the dipole portion. A tag antenna that can be miniaturized is characterized by having a feeder provided in the center and an end portion provided with an area wider than a line width of the dipole portion at both ends of the dipole portion, but the above patent also has the same problem.

Therefore, it is necessary to design a new type of RFID tag antenna structure with a large value of inductive reactance.

As a result of many years of research efforts to solve the above problems, the inventors have developed an antenna structure capable of generating the inductive reactance values necessary for matching the tag IC with the conjugate impedance using a short stub to complete the present invention. It became.

Accordingly, an object of the present invention is to provide an RFID tag antenna having a structure that can be easily adjusted to generate an inductive reactance value necessary for matching a tag IC with a conjugate impedance.

Another object of the present invention is to provide an RFID tag antenna having a structure capable of easily adjusting the resistance value of a tag antenna.

In addition, another object of the present invention is to provide an RFID tag antenna having a structure in which an impedance value can be adjusted very easily in matching a conjugate between a dipole antenna and a tag IC by adjusting a reactance value and a resistance value of a tag antenna.

In addition, another object of the present invention is to provide an RFID tag antenna that can be miniaturized and can also be manufactured in a paper material using a printing method can also reduce the manufacturing cost.

In order to achieve the above object, the present invention provides an RFID tag antenna including a dipole antenna and a tag IC, wherein the dipole antenna includes: a dipole unit in which the tag IC is installed; And a short stub installed to surround the dipole part.

And a load part surrounding both ends of the dipole part based on the tag IC.

One side of the portion of the dipole portion in which the tag IC is installed is not surrounded by the shorting stub, and is spaced a predetermined distance from the portion where the tag IC is installed so that a starting point of the shorting stub connected to the dipole portion and the shorting stub is connected. It is characterized in that the location.

Adjusting the length between the tag IC and the start point of the short stub to have a reactance value that can achieve a conjugate impedance match with the tag IC.

It is characterized in that for generating a reactance value that can achieve a conjugate impedance match with the tag IC through the electromagnetic coupling generated between the dipole portion or the load portion and the short stub.

The reactance value is proportional to the interval between the dipole portion and the load portion and the short stub and the length of the short stub.

The interval between the dipole portion, the load portion, and the short stub is determined by focusing on the change characteristic of the reactance value of the antenna, rather than the change characteristic of the antenna resistance value.

The resistance value of the tag antenna may be adjusted while varying the width of the shorting stub surrounding the load unit.

The shape of the load portion is characterized in that the circular or polygonal shape.

The short stub is characterized in that the width of the portion surrounding both ends of the dipole portion is wider than the width of the portion parallel to the dipole portion.

The tag antenna is characterized in that printed on the paper by a printing method to be manufactured.

The RFID tag antenna of the present invention has the following excellent effects.

First, according to the RFID tag antenna of the present invention, it is possible to easily adjust the generation of reactance values necessary for matching the tag IC with the conjugate impedance.

In addition, according to the RFID tag antenna of the present invention, it is possible to easily adjust the resistance value of the tag antenna.

In addition, according to the RFID tag antenna of the present invention, by adjusting the reactance value and the resistance value by changing the length and width of the shorting stub of the tag antenna, it is very easy to adjust the impedance value required for conjugate matching between the tag antenna and the tag IC. Can be.

In addition, according to the RFID tag antenna of the present invention, not only miniaturization is possible, but also an antenna can be manufactured on a paper material using a printing technique, and thus, a manufacturing cost thereof can be reduced.

Hereinafter, with reference to the drawings and preferred embodiments of the present invention will be described in detail the technical configuration of the present invention.

FIG. 1A is a picture of a tag antenna actually manufactured according to an embodiment of the present invention, FIG. 1B is a structure diagram of a tag antenna according to another embodiment of the present invention, and FIG. 2 is a structure diagram according to an actual standard of the tag antenna of FIG. to be.

As shown in FIG. 1A, the tag antenna 1 according to the present invention includes a dipole antenna 100 and a tag IC 200. The dipole antenna 100 includes a dipole part 110 and a load part 120. ) And a short-stub 130. Meanwhile, although FIG. 1 illustrates that the dipole antenna 100 includes a dipole part 110, a load part 120, and a short stub 130, in some cases, as shown in FIG. You may comprise 100 only with the dipole part 110 and the shorting stub 130. As shown in FIG.

At this time, when the dipole antenna 100 is composed of only the dipole portion 110 and the shorting stub 130 as shown in Figure 1b, the dipole portion 110, the load portion 120 and the shorting stub 130 as shown in Figure 1a In order to obtain the required reactance value, the length of the dipole portion 110 should be configured longer than that of the case of FIG. Therefore, the configuration as shown in FIG. 1A may be more suitable for downsizing the tag antenna.

Hereinafter, the present invention will be described based on the dipole antenna 100 including the dipole part 110, the load part 120, and the shorting stub 130 as shown in FIG. 1A.

First, when the tag IC 200 is installed in the dipole antenna 100 as shown in the drawing, the dipole unit 110 is preferably a straight dipole which is symmetrical with respect to the tag IC.

The load unit 120 is installed to surround both ends of the dipole unit 110 in a symmetrical manner with respect to the tag IC 200. As shown, the shape of the load unit 120 may be circular, but is not limited to the shape and may be polygonal.

The short stub 130 is installed to surround the dipole part 110 and the load part 120 while being spaced apart from the dipole part 110 and the load part 120, and the tag IC 200 of the dipole part 110 is disposed. One side of the installed portion is not wrapped by the shorting stub 130, and the dipole portion 110 and the shorting stub 130 is connected to be separated by a predetermined distance with respect to the portion where the tag IC 200 is installed. The starting point of the short stub 130 is located.

The short stub 130 is formed to surround the dipole portion 110 and the load portion 120 to increase the reactance value of the antenna, the electromagnetic coupling generated between the dipole portion 110 and the load portion 120 Electromagnetic coupling allows the antenna to have the necessary inductive reactance values. As a result, when the load portion 120 is formed at both ends of the dipole portion 110 as shown in FIG. 1a, the length of the dipole portion 110 may be shorter than that of FIG. 1b.

As such, a reactance value that can achieve conjugate impedance matching with the tag IC 200 is provided through the electromagnetic coupling generated between the dipole part 110 and the load part 120 and the shorting stub 130.

Referring to FIG. 2, which is a structural diagram according to the actual standard of the tag antenna illustrated in FIG. 1A, the parameters affecting the characteristics of the tag antenna will be described as follows.

W1: width of the shorting stub 130 surrounding the circular load portion 120

W2: width of the dipole portion 110

W3: width of the shorting stub 130 parallel to the dipole portion 110

L1: length of the dipole portion 110

L2: Distance from tag IC to start point of short stub 130

(Antenna parameter that controls the overall length of the short stub)

R1: radius of the circular load portion 120 connected to the dipole portion 110

S1: spacing between the dipole portion 110 and the load portion 120 and the shorting stub 130

First, the interval S1 between the dipole part 110 and the load part 120 and the short stub 130 and the length of the short stub 130 affect the inductive reactance value of the tag antenna 1. As shown in the experimental results described below, they have a proportionally increasing relationship with each other.

In addition, the distance L2 from the tag IC 200 to the start point of the shorting stub is a characteristic parameter that can be adjusted by changing the reactance value of the tag antenna 1, and the width of the shorting stub 130 surrounding the load unit 120. (W1) is a characteristic parameter that can be adjusted while changing the resistance value of the tag antenna 1.

In addition, the shorting stub 130 may have the same width W3 of the portion parallel to the dipole portion 110 and the width W1 of the portion surrounding the load portion 120, but in a state where the shorting stub 130 is installed. 8A to 8D, when the overall shape is similar to a dumbbell, the resistance value required for the tag antenna 1 can be easily adjusted. Therefore, it is preferable that W3 is wider than W1.

_r=3.4)과 손실(tanδ=0.02 )을 가지는 얇고 유연성이 강한 폴리이미드(polyimide) 기판 위에 도2의 규격에 따라 제작되었는데, 다이폴부(110), 부하부(120) 및 단락스터브(130)는 방사체(radiator)로서 두께 0.47 mil.(=0.012 mm)의 구리(copper)로 제작 되었다. 태그 IC(200)는 912MHz에서 43-j800 옴의 임피던스를 가지는 Philips U-CODE Gen 2 RFID 칩을 사용하였다. 이 때 경우에 따라서는 상기 태그 안테나(1)를 인쇄기법에 의해 종이에 인쇄하여 제조할 수 있다. The tag antenna 1 in the photograph shown in FIG. 1A has a dielectric constant of 1 mil. (= 0.0254 mm) thick.

_r = 3.4) and loss (tanδ = 0.02) on a thin flexible polyimide substrate (polyimide) substrate was manufactured according to the specification of Figure 2, the dipole portion 110, the load portion 120 and the short stub 130 Is a radiator made of copper with a thickness of 0.47 mil. (= 0.012 mm). The tag IC 200 used a Philips U-CODE Gen 2 RFID chip with an impedance of 43-j800 ohms at 912 MHz. In this case, in some cases, the tag antenna 1 may be manufactured by printing on paper by a printing technique.

In more detail, for example, in the dipole portion 110, the length L1 is 23mm, the width W2 is 2mm. The load unit 120 is configured as a load having a circular shape having a radius R1 formed at both ends of the dipole part 110, and the form thereof is not limited to the circle as described above.

On the other hand, if the dipole antenna is composed of the dipole portion 110 and the load portion 120 of the standard, it can be seen that the impedance value of 6.88-j413.17 ohms at 912MHZ, -413.17 at 912MHZ An additional 1213.17 ohm reactance is needed for a dipole antenna with an ohmic reactance to match the conjugate impedance with a tag IC with an impedance of 43-j800 ohms at 912 MHz.

Therefore, in order to increase the reactance value of the tag antenna 1, the dipole antenna 100 may be configured of the dipole portion 110 and the shorting stub 130 as shown in FIG. 1B or the dipole portion 110 as shown in FIG. 1A. ), The load section 120 and the short-circuit stub 130.

That is, as described above, the electromagnetic coupling generated between the dipole portion 110 and / or the load portion 120 and the shorting stub 130 causes the antenna to have an inductive reactance value that can be conjugated with the tag IC. In this case, the inductive reactance value has a characteristic of increasing in proportion to the length of the shorting stub 130 and the interval S1 between the dipole part 110 and / or the load part 120 and the shorting stub 130. Able to know.

Figure 3 is a graph of the change in the reactance of the antenna according to the change of S1, Figure 4 is a graph of the change in the antenna reactance according to the change of R1, Figure 5 is a graph of the change in the resistance value of the antenna according to the change of W1, Fig. 6 is a graph showing the change in reactance value of the antenna according to the change of W1, and Fig. 7 is the antenna current density at 912 MHz, and Figs.

3 to 7 determine the value of the parameter affecting the characteristics of the tag antenna.

First, in order to simplify the parameters constituting the antenna, the width W3 of the shorting stub 130 parallel to the dipole portion 110 was determined to be 1 mm.

As shown in FIG. 3, in order to have a reactance value of 800 ohms at 912 MHz, S1 was determined to be 0.5 mm.

The radius R1 of the circular load was determined to be 4 mm as shown in Figure 4 to have a reactance value of about 800 ohms at 912 MHz.

The resistance value of the tag antenna required for matching the tag IC and the conjugate impedance can be obtained by changing the width W1 of the shorting stub surrounding the circular load as shown in FIG.

At this time, the change in the reactance value according to the change in the width W1 of the shorting stub surrounding the circular load is almost unchanged as shown in FIG.

When the width (W1) of the shorting stub surrounding the circular load changes, the reason why the resistance value of the antenna shows a constant change while the reactance value shows little change can be confirmed by the current density shown in FIG. .

In other words, if the current density flowing through the antenna is checked, the current density is weak at the outer portion of the shorting stub that surrounds the circular load having the width of W1. In addition, the electromagnetic coupling occurring in the gap between the dipole portion 110 and the load portion 120 and the shorting stub 130 affects the change in the reactance value, and the electromagnetic coupling changes in relation to the current density.

Under this premise, the weak current density at the outer part of the shorting stub surrounding a circular load with a width of W1 has little effect on the electromagnetic coupling and consequently on the change in the reactance value of the antenna. It can be seen that.

Therefore, the resistance value required for the tag antenna 1 can be obtained by changing W1. The reactance value required for the tag antenna 1 can be obtained by changing the antenna parameter L2 of FIG. 2 from the change characteristic of the reactance value which increases in proportion to the length of the short stub 130.

Since the total size of the tag antenna of the present invention having the above parameters is 64.1 m * 17.8 mm in width, it is very small, and thus has an antenna structure that is sufficiently small and easily adjusts the reactance value.

On the other hand, the antenna according to the present invention is not limited in its overall shape but preferably forms a dumbbell. At this time, even if the overall shape is a dumbbell shape, since the shape forming both ends of the dumbbell shape is not limited, as shown in Figures 8a to 8d showing the shape of the load portion 120 and the short stub 130, antennas of various structures Can be designed as

Experimental Example 1

The resistance value of the antenna having the above-described parameters is measured and shown in FIG. Referring to FIG. 9, it can be seen that the resistance value of the tag antenna is about 43 ohms at 912 MHz. This resistance value is the same as the resistance value required for tag IC and conjugate matching.

Experimental Example 2

The reactance value of the antenna having the above-described parameters is measured and shown in FIG. Referring to FIG. 10, it can be seen that the reactance value of the tag antenna is about 800 ohms at 912 MHz. This reactance value cancels out from the reactance value of the tag IC to achieve a conjugate impedance match between the tag antenna and the tag IC.

Experimental Example 3

-10 dB of antenna with the above-mentioned parameters (S ₁₁ ) The impedance bandwidth was measured and shown in FIG. 11, it can be seen that the -10dB (S ₁₁ ) impedance bandwidth has a 10MHz (907 ~ 917MHz) satisfying the Korea UHF RFID band (908 ~ 914MHz).

Experimental Example 4

The radiation pattern of the antenna with the above-described parameters is measured and shown in FIG. Referring to Fig. 12, it is similar to the radiation pattern of a typical dipole antenna, and it can be seen that the maximum gain has 2.6 dBi, and null points occurring in the (xy) plane and the (yz) plane are relatively weak. There is this.

As described above, the antenna parameter value that is most suitable for implementing the present invention may be determined by measuring the change of the antenna characteristic according to the change of the antenna parameter value. Hereinafter, specific experimental results of the antenna parameter for determining the antenna characteristic will be exemplified. Let's examine in more detail.

 Experimental Example 5

In order to examine the characteristics of the antenna reactance value and the resistance value according to the change of S1, the experiment was performed while changing S1 and the results are shown in FIGS. 13A and 13B.

Referring to FIG. 13A, in the UHF RFID band (860 to 960 MHz), the interval S1 has an inductive reactance value only when 0.5 mm (blue), 1 mm (red), and 1.5 mm (green). If it has a value, it has a capacitive reactance value. Therefore, in order to match the tag IC having the capacitive reactance value and the impedance conjugate, it is understood that the value of the interval S1 should be 1.5 mm or less, so that the value is 1.5 mm. Values may be specified among the following values according to the characteristics of the designed antenna. As a result, in an embodiment of the present invention it was determined as 0.5mm as shown in FIG.

Referring to FIG. 13B, since the characteristic change of the resistance value of the antenna according to the change of the interval S1 value is the same as that of FIG. 13, the S1 value preferentially focuses on the characteristic of the change of the reactance value of the antenna rather than the characteristic of the antenna. It can be seen that it must be decided. The reason is that if the value of S1 determined to satisfy the resistance value has the capacitive reactance value of the designed antenna, the tag IC and the conjugate match cannot be made.

 Experimental Example 6

In order to examine the characteristics of the antenna reactance value and the resistance value according to the change of W1 and R1, the experiments were performed while changing W1 and R1 and the results are shown in Tables 1 and 2. At this time, f = 910 MHz.

From Table 1, if (R1 / W1) = 1 [that is, R1 = W1], the resistance value is increased by about 3 times / 1mm, and the reactance value is increased by about 140 Ohm / 1mm. Able to know.

It can be seen from Table 2 that when the width W1 of the shorting stub surrounding the circular load increases, the resistance value increases in proportion to the increase in width, but the reactance value is almost unchanged. This means that the resistance value can be used as a parameter parameter of the antenna that can be easily adjusted.

Experimental Example 7

In order to examine the characteristics of the antenna reactance value and the resistance value according to the length change of the antenna parameter L2, the experiment was performed while changing L2 and the results are shown in Table 3. At this time, f = 910 MHz.

Increasing the length of the antenna parameter L2, which adjusts the overall length of the short stub, means that the connection point of the short stub is gradually moved away from the tag IC. In this case, the antennas have a left-right symmetry structure starting from the tag IC. This means that the starting point of the shorting stub is gradually getting farther away.

As a result, referring to Table 3, the length of the entire short stub decreases as the start point of the short stub decreases, and as a result, the resistance value and the reactance value of the antenna decrease together. At this time, the decrease in reactance is about 12 times faster than the decrease in resistance. Therefore, since the reactance value is more sensitive to the change in the reactance value than the change in the resistance value of the antenna, it can be seen that it can be used as a change control parameter of the reactance value of the antenna designing the parameter L2.

Experimental Example 8

In order to examine the characteristics of the antenna reactance value and the resistance value according to the length change of the antenna parameters W2 and W3, the experiments were performed while changing W2 and W3 and the results are shown in Table 4. At this time, f = 910 MHz.

Referring to Table 4, as the value of the width W2 of the dipole increases, the reactance value and the resistance value of the antenna increase in proportion to the increasing width, which increases as the width W3 of the shorting stub parallel to the dipole increases. It can be seen that the reactance value and the resistance value decrease in proportion to the width.

Therefore, the reactance value and the resistance value of the desired antenna can be approximated by increasing the width W2 of the dipole, and then the error of the approximation can be reduced while adjusting the width W3 of the short stub parallel to the dipole. However, the change characteristics of the resistance and the change characteristics of the reactance are the same, so they must be considered together.

That is, in the case of W2: W3 = 2: 1 ratio, as W2 increases, the impedance of W3 increases by [reactance change / resistance change] = 10, and when W2: W3 = 1: 1, W2 As is increased, the resistance value of W3 is about ½ of the resistance value when W2: W3 = 2: 1, and the reactance value of W3 is about 200, 300, 400, more than the reactance value of W2: W3 = 2: 1 day. 500... It can be seen that the ohms have a feature of decreasing in units of 100 ohms.

Experimental Example 9

In order to examine the characteristics of the antenna reactance value and the resistance value according to the length change of the antenna parameter L1, the experiment was performed while changing L1 and the results are shown in Table 5. At this time, f = 910 MHz.

Referring to Table 5, as the length of the dipole increases, the length of the shorting stub parallel to the dipole increases together. As the physical length of the antenna increases, the resistance value of the antenna increases proportionally with it. In addition, since the electromagnetic coupling length generated between the dipole portion and the shorting stub also increases, the reactance value of the antenna increases proportionally. That is, when the length L1 of the dipole is reduced, the reactance value and the resistance value of the antenna decrease in proportion. In particular, when the length of L1 is 20 mm or more, it can be seen that the change range of the reactance and the resistance value is large.

On the other hand, the present invention has been described with reference to the embodiments, which are merely exemplary, those of ordinary skill in the art will understand that various modifications and equivalent embodiments are possible therefrom. The true scope of technical protection should be defined by the appended claims.

Figure 1a is a tag antenna picture actually produced according to an embodiment of the present invention

1B is a structural diagram of a tag antenna according to another embodiment of the present invention.

2 is a structural diagram according to the actual standard of the tag antenna of FIG.

Figure 3 is a graph of the change in reactance value of the antenna according to the change of S1

4 is a graph showing the change in the antenna reactance value according to the change in R1;

5 is a graph of the change in the resistance value of the antenna according to the change of W1;

6 is a graph of change in reactance value of an antenna according to a change in W1;

Figure 7 shows antenna current density at 912 MHz

8A to 8D are structural diagrams of various design examples of the antenna according to the shape of the load portion and the short stub;

9 is a characteristic change of a resistance value of an antenna according to an embodiment of the present invention;

10 is a characteristic change in reactance values of an antenna according to an embodiment of the present invention.

FIG. 11 is a calculated characteristic of S ₁₁ of an antenna according to an embodiment of the present invention. FIG.

12 is a radiation pattern at 912MHz of the antenna according to an embodiment of the present invention

13A and 13B are graphs showing the results of experiments while varying S1 to examine the characteristics of the antenna reactance value and the resistance value according to the change of S1.

<Description of main parts of drawing>

1: tag antenna 100: dipole antenna

110: dipole portion 120: load portion

130: short circuit stub 200: tag IC

Claims (11)

An RFID tag antenna comprising a dipole antenna and a tag IC, The dipole antenna, A dipole unit in which the tag IC is installed; And RFID tag antenna, characterized in that it comprises a short stub (short-stub) installed to surround the dipole portion. The RFID tag antenna of claim 1, further comprising a load unit installed to surround both ends of the dipole unit based on the tag IC. The method of claim 1, wherein one side of the portion of the dipole portion in which the tag IC is installed is not surrounded by the shorting stub, and is spaced a predetermined distance from the portion in which the tag IC is installed so that the dipole portion is connected to the shorting stub. RFID tag antenna, characterized in that the starting point of the short circuit stub is located. 4. The RFID tag antenna of claim 3, wherein the tag IC and the dipole antenna are adjusted to have a reactance value to achieve conjugate impedance matching by adjusting a length between the tag IC and a start point of the short stub. . 3. The method of claim 2, wherein the tag IC and the dipole antenna generate reactance values through which electromagnetic coupling between the dipole portion or the load portion and the shorting stub can achieve conjugate impedance matching. RFID tag antenna. The RFID tag antenna of claim 5, wherein the reactance value is proportional to a distance between the dipole portion, the load portion, and the short stub and the length of the short stub. The RFID tag of claim 6, wherein the interval between the dipole portion, the load portion, and the short stub is determined by focusing on a change characteristic of a reactance value of the dipole antenna, rather than a change characteristic of a resistance value of the dipole antenna. antenna. The RFID tag antenna of claim 2, wherein the resistance value of the dipole antenna can be adjusted while changing a width of a shorting stub surrounding the load unit. The RFID tag antenna of claim 2, wherein the load portion has a circular or polygonal shape. The RFID tag antenna of claim 1, wherein the shorting stub has a width wider than a width of a portion parallel to the dipole portion. delete

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