KR20090041891A - Rfid tag antenna and rfid tag - Google Patents

Abstract

An antenna for an RFID tag and the RFID tag are provided to control impedance by controlling a current induced to a radiator dipole. An antenna for an RFID tag includes a substrate, a radiator dipole(20), and a T type matching unit(10). The radiator dipole with a meander shape is printed on the substrate. The T type matching unit is formed between the symmetric radiator dipoles. The T type matching unit is integrated with one end of each radiator dipole. The T type matching unit matches the impedance between the radiator dipole and the RFID tag chip. A connection unit(21) of the radiator dipole and the T type matching unit has a branch structure.

Description

RFID tag antenna and RFID tag {RFFID antenna and RDF tag}

The present invention relates to a radio frequency identification (RFID) tag antenna and an RFID tag, and in particular, by forming a connecting portion in which the radiator dipole and the T-type matching part are connected in a branched structure, the T-type matching part in the branching structure. The present invention relates to an RFID tag antenna and an RFID tag for enabling an electric current to be induced in a radiator dipole, and for controlling an impedance of an RFID tag antenna in detail by controlling an amount of current induced in the radiator dipole.

The definition of RFID (Radio Frequency Identification) consists of RFID TAG, various types of antennas, performance readers, local hosts supporting readers, various cabling and network connections, and production, distribution, It is a chip that contains information about the whole process of storage and consumption, has its own antenna, and enables readers to read this information and integrate it with information systems in connection with satellites or mobile communication networks.

In terms of industrial applications, RFID (Radio Frequency Identification), a new technology that can store information over the air by attaching a tiny chip and antenna to an RFID tag, is independent of where it can be recognized. The advantage is that tags can be automatically recognized over much longer distances than barcodes.

In particular, the RFID system has been spotlighted as a technology that will bring great innovation to distribution and logistics as it can automatically identify the item specification, price, distribution route, and deadline when moving, without attaching electronic tags to various items and reading them one by one. .

In RFID TAG technology, an antenna supplies power to a tag, and a tag returns data in response, and a method using a magnetic field and a radio wave are mainly used. That is, it is divided into an inductive coupling method and a backscatter coupling method.

The inductive coupling method is a principle in which a magnetic field generated by generating a strong high frequency in an antenna is operated by a current generated by passing through an antenna coil of a tag, and frequencies of 30MHZ or less (125KHz, 134KHz, 13.56MHz), and the magnetic field is absorbed by the metal.

On the other hand, the backscatter coupling (Backscatter Coupling) method is similar to the radar technology, when the radio waves are transmitted from the antenna, the principle that is used as the power received from the tag, and is used in the frequency band of more than 100MHZ (900MHz, 2.45GHz), the metal Reflection and water are absorbed.

In the case of the backscatter coupling method, a signal propagated as an air condition in the air condition of an antenna of a reader is different from an inductive coupling method using an antenna coil at a close distance. A demodulator receives power from an antenna and generates power used by an RFID tag chip as an RF component of the signal, filters high frequencies, and converts a baseband signal of low frequency into 1 bit AD. Perform the (De-modulator) function.

Inductive Coupling, however, is rich in organic power, so there is no problem in generating power. In the case of Backscatter Coupling, there is almost contact between reader and tag. At close ranges, the input signal is sufficient enough to be about 3.5V, but at a distance of about 5 meters, a very small signal input level of 125mV is introduced.

This small signal is multiplied (using a Voltage Multiplier) to produce the desired power, but a high efficiency Schottky diode with low turn-on voltage is used to shunt the input of very small signals. Or a special type of MOS transistor (MOS Tr) to configure the circuit, there is a disadvantage that the circuit is complicated and the cost is increased.

In theory, the RFID tag chip integrated circuit (TAG IC) may receive the maximum efficiency and the maximum power when the impedance of the antenna and the input impedance of the RFID tag chip are the same. However, the input impedance of the RFID tag chip is increased due to the RLC dispersion of the RFID tag chip itself and the parasitic resistance and capacitance component generated when the TAG IC and the antenna are assembled. The impedance of the antenna and the input impedance of the TAG IC are not exactly the same, they are distorted, and in the 900MHz UHF Tag of this component, the frequency characteristic varies greatly even for several ohms, and the input signal level itself becomes smaller. In other words, it reduces the receiving distance of the TAG, resulting in a severe decrease in yield.

Therefore, the conventional antenna for the UHF band RFID tag has a structure for impedance conjugate matching with the RFID tag chip. For example, as shown in FIG. 1, a T-type matching portion adopting various T-type matching loop structures for impedance matching is provided.

The T-type matching unit has a structure for achieving a conjugate matching with a high Q impedance while forming a voltage difference between the RF terminal and the ground terminal of the RFID tag chip. The T-type matching loop structure is mostly implemented using a loop line between the RF terminal and the ground terminal of the RFID tag chip.

However, the T-type matching unit can adjust the impedance only by changing the size of the loop line or the connection point of the radiator. In addition, in this method, the impedance matching of the RFID tag chip is difficult because the changing characteristics of the real part and the imaginary part of the impedance vary with frequency.

2A and 3A, since the loop line of the T-type matching portion 10 and the radiator dipole 20 are directly connected, the connection portion 21 and the T-type matching portion 10 are separated. The change in impedance and resonant frequency is large according to the radius of the loop line, which causes a lot of difficulties to achieve accurate impedance conjugate matching. Therefore, in order to maximize the performance of the RFID tag, it is necessary to improve the above disadvantages.

As shown in FIG. 2A, in the conventional RFID tag antenna, the position of the connection part 21, which is a point connecting the T-type matching part 10 and the radiator dipole 20, may be changed. And the resonance frequency change is as shown in FIG. 2B. As shown in Figure 2b, when changing the position of the connecting portion 21 from 1mm to 3mm, it can be seen that the change in impedance and resonant frequency is large. This proves that the impedance adjustment is not easy by changing the position of the connection portion 21.

As shown in FIG. 3A, the loop size of the T-type matching unit 10 may be changed in the conventional RFID tag antenna, and the impedance and the resonance frequency change are as shown in FIG. 3B. As shown in FIG. 3B, when the loop size of the T-type matching unit 10 is changed from 1 mm to 3 mm, it can be seen that the change in impedance and resonance frequency is large. This proves that impedance adjustment is not easy by changing the loop size of the T-type matching section 10.

As described above, when the loop size of the T-type matching unit 10 is changed or the position of the connection unit 21 is changed, the change range of the impedance and the resonance frequency is large. As a result, impedance conjugate matching between the RFID tag antenna and the RFID tag chip is not easy.

The present invention has been made to solve the above problems of the prior art, by forming a connecting portion connecting the radiator dipole and the T-type matching portion in a branched structure, the current in the T-type matching portion and the radiator dipole in the branch structure It is an object of the present invention to provide an RFID tag antenna and an RFID tag that can be induced, and in which the impedance of the RFID tag antenna can be adjusted in detail by controlling the amount of current induced in the radiator dipole.

In order to solve the problems of the present invention as described above, the constituent means constituting the antenna for RFID tag according to the present invention, in the RFID tag antenna, is a substrate, a meander (meander) type printed to be symmetrical to the substrate Is formed between the emitter dipole, the symmetrical radiator dipole, integrally formed with one end of each of the symmetrical radiator dipole, and comprises a T-type matching portion for matching the impedance between the radiator dipole and the RFID tag chip, The connecting portion to which the symmetrical radiator dipole and the T-type matching portion are connected is characterized in that the branch structure.

In addition, the connection unit is characterized in that a plurality of branch structures are connected in series or in parallel. That is, the connection part may be formed in a structure in which a plurality of branch structures are connected in series.

In addition, the branch structure is characterized in that any one of a circular structure, a semi-circular structure and a polygonal structure. That is, if the connection portion can be formed in a branched structure, the shape can be variously changed.

In addition, the terminating end area of the radiator dipole is larger than the other parts, and the terminating end of the radiator dipole is preferably a "c" shape.

Meanwhile, another constituent element of the RFID tag of the present invention may be formed between a substrate, a meander-shaped radiator dipole that is symmetrically printed on the substrate, and the symmetrical radiator dipole. A T-type matching unit integrally formed with one end of each of the symmetrical radiator dipoles and matching an impedance between the radiator dipole and an RFID tag chip, and an RFID tag chip for performing data processing on a transmission / reception signal of the radiator dipole; It is configured to include, characterized in that the connecting portion connecting the symmetrical radiator dipole and the T-type matching portion is a branched structure.

According to the RFID tag antenna and the RFID tag of the present invention having the above-described problems and constituent means, since the connecting portion connecting the radiator dipole and the T-type matching part is formed in a branched structure, the T-type matching in the branch structure. It is possible to induce a current in the negative and the radiator dipole, and the impedance of the RFID tag antenna can be adjusted in detail by controlling the amount of current induced in the radiator dipole, so that the impedance matching between the RFID antenna and the RFID chip is easy. There is one advantage.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the antenna for RFID ID tag and the RFID tag of the present invention having the above-described problems, constituent means and effects.

4A to 4C are various plan views of the antenna for RFID tag according to the present invention.

As shown in FIGS. 4A to 4C, the antenna for RFID ID tag according to the present invention includes a substrate (not shown), a radiator dipole 20 having a meander shape that is symmetrically printed on the substrate, and the symmetrical radiator dipole. It comprises a T-type matching portion 10 formed between the (20).

The substrate (not shown) is a substrate on which the radiator dipole 20 and the T-type matching portion 10 are formed, and may be formed of various non-conductors. For example, the substrate may use printed paper such as wood, teflon and plastic.

The radiator dipole 20 printed on the substrate is formed to be symmetrical to both sides of the T-type matching portion 10, as shown in FIGS. 4A to 4C. And the radiator dipole 20 has a meander shape meander (meander).

The radiator dipole 20 mediates RF signal power between an RFID reader and an RFID tag chip, and is preferably manufactured by printing with a conductive ink made of a metal coating such as gold, silver, copper, and bronze on the substrate. . The size is designed so that the resonance occurs at the frequency of use, so that the electromagnetic field is well radiated to the space.

The T-type matching portion 10 formed between the symmetrical radiator dipoles 20 is integrally formed with one end of each of the radiator dipoles 20, as shown in FIGS. 4A to 4C. The T-type matching unit 10 matches the impedance between the RFID tag antenna and the RFID tag chip including the radiator dipole 20.

In the present invention, a structural change was made to easily match the impedance between the RFID tag antenna and the RFID tag chip including the radiator dipole 20. That is, the connecting part 21 connecting the symmetrical radiator dipole 20 and the T-type matching part 10 is changed into a branching structure.

The connecting portion 21 having the branching structure has a branching structure divided into two branches, unlike the conventional one made of a single line. The connecting portion 21 having such a branching structure serves to induce a current in the T-type matching portion 10 and the radiator dipole 20, and by controlling the amount of current induced in the radiator dipole 20. The impedance of the RFID tag antenna can be finely adjusted.

As shown in FIGS. 4A and 4B, the connection part 21 may be formed in one branch structure, and in some cases, as shown in FIG. 4C, a plurality of branch structures may be connected in series. It may be formed in parallel. That is, the connection part 21 may be formed by connecting a plurality of branch structures in series or in parallel.

The branch structure constituting the connecting portion 21 may be formed in various shapes. That is, as shown in Figure 4a, it may be formed in a semi-circular structure, as shown in Figure 4b, may be formed in a circular structure, or may be formed in a polygonal structure such as triangle or square.

On the other hand, the area of the end portion 23 of the radiator dipole 20 is preferably formed larger than the other portions of the radiator dipole 20, as shown in Figure 4a and 4b. In addition, the shape of the terminal 23 of the radiator dipole 20 is preferably a "c" shape.

The end 23 of the radiator dipole 20 is a point where the maximum or minimum of the electric field changes with time, and is the point where the radiation resistance is the greatest in the electric dipole antenna.

As in the present invention, increasing the area of the end 23 of the radiator dipole 20 increases the radiation efficiency of the antenna, but the tag should be implemented within a limited size and exhibit the maximum performance. Therefore, the emitter structure was implemented in a "c" shape to have the maximum performance compared to the size. As shown in FIG. 5, the current has a uniform current distribution among the magnetic field walls.

The terminal 23 structure of the radiator dipole 20 according to the present invention, when considering the phase and magnitude of the current, it can be seen that the magnetic field wall, which is one of the boundary conditions at the center of the letter "c" is formed. . It is also conceivable that structures having the same current and phase are open to each other because they are formed at adjacent distances from each other.

If each structure forms a magnetic field wall and has the same phase with a uniform current distribution, the antenna's efficiency is increased because the electrical effective opening cross-sectional area of the antenna appears to be large.

FIG. 6A shows the current density distribution in the case where the connecting portion 21 has a branch structure according to the present invention, FIG. 6B shows the distribution of the surface current, and FIG. 6C shows the circular portion shown in FIG. Show the current direction. That is, the current induced in the radiator dipole can be confirmed through the current density and the current direction in the branched structure of the present invention, and it shows that the radiator induces a current to operate in the dipole.

On the other hand, Figure 7a shows that the inner radius (a) and outer radius (b) of the connecting portion 21 can be changed, Figure 7b shows the change in impedance and frequency when the inner radius of the connecting portion 21 changes 7C is a graph showing a change in impedance and frequency when the outer radius of the connection portion 21 is changed.

7A to 7C, it can be seen that the density of the current between the T-type matching portion and the radiator dipole can be adjusted by modifying the inner radius or the outer radius of the connecting portion having the branched structure, and the radius of the branched structure line. The amount of current is adjusted by adjusting the inner or outer radius. Therefore, by more precisely adjusting the amount of current induced in the radiator dipole in the T-type matching part, the antenna input impedance can be easily and efficiently adjusted.

As shown in FIGS. 7B and 7C, even if the inner radius and the outer radius of the connection part 21 according to the present invention are changed, it can be seen that the impedance and the frequency change are not large. This, in turn, makes it possible to precisely adjust the impedance by changing the inner and outer radii of the connection part 21 of the present invention, and consequently, the impedance matching becomes easy.

On the other hand, the antenna for RFID tag according to the present invention having the structure and characteristics as described above is used for the RFID tag. That is, an RFID tag may be completed by connecting an antenna having the above structure to the RFID tag chip. The RFID tag chip performs data processing on the transmit / receive signal of the radiator dipole. That is, the RFID tag chip senses RF signal power from an antenna and performs data processing, and includes a modulation, a detection circuit, a rectifier circuit, a microprocessor, and the like.

1 is a real picture of a conventional RFID tag antenna.

2A and 2B are diagrams illustrating a change in position of the connection unit and a graph showing a change in impedance and resonance frequency accordingly.

3A and 3B are graphs illustrating variation in loop size of a T-type matching unit and changes in impedance and resonance frequency accordingly.

4A to 4C are various plan views of the antenna for RFID tag according to the present invention.

5 is an exemplary view showing the shape and current distribution of the radiator dipole end portion according to the present invention.

6a to 6c are photographs showing the flow of current density and surface current formed in the RFID tag antenna according to the present invention.

7A to 7C are diagrams illustrating variation of inner and outer radii of a connection part according to the present invention, and graphs showing changes in impedance and frequency accordingly.

Explanation of symbols on the main parts of the drawings

10: T-type matching portion 20: radiator dipole

21 connection part 23 radiator dipole end part

Claims (5)

In the antenna for RFID tag, Board; A meander-shaped radiator dipole which is symmetrically printed on the substrate; Is formed between the symmetrical radiator dipoles, integrally formed with one end of each of the symmetrical radiator dipoles, and comprises a T-type matching unit for matching the impedance between the radiator dipoles and RFID tag chip, And a connecting part connecting the symmetrical radiator dipole and the T-type matching part has a branched structure. The method according to claim 1, The connection part is an RFID tag antenna, characterized in that a plurality of branch structure is connected in series or in parallel. The method according to claim 1 or 2, The branch structure is an RFID tag antenna, characterized in that any one of a circular structure, a semi-circular structure and a polygonal structure. The method according to claim 1, An end portion of the radiator dipole is an "D" shaped antenna for RFID tag. In the RFID tag, Board; A meander-shaped radiator dipole which is symmetrically printed on the substrate; A T-type matching part formed between the symmetrical radiator dipoles and integrally formed with one end of each of the symmetrical radiator dipoles to match an impedance between the radiator dipole and an RFID tag chip; Including an RFID tag chip for performing data processing for the transmission and reception signal of the radiator dipole, The RFID tag of claim 4, wherein the connecting portion to which the symmetrical radiator dipole and the T-type matching portion are connected is a branched structure.

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