TWI437819B - Radio frequency identification tag - Google Patents

Description

Radio frequency identification tag

The invention relates to an RFID tag, in particular to an indirectly coupled RFID tag.

The RFID (Radio Frequency Identification) tag antenna is composed of an RFID chip and a tag antenna, and receives the radio communication signal of an RFID reader through the tag antenna, and transmits or updates the data recorded in the RFID chip or Identification code, RFID tag antenna has the advantages of fast reading speed, long reading distance, no need to read under visual conditions, multiple readings at the same time and not affected by dirt, so in logistics management, access control, and process tracking. .. and so on, you can see the application of RFID technology.

In the application of RFID technology, the design technology of the tag antenna is the key to the success of the application. The reasons include: the design of the antenna determines the cost, the size of the operable bandwidth, the performance of the device, the applicable object, etc. Therefore, there have been quite a few journals on RFID tag antenna design issues published in recent years, and the number of patent applications filed is also considerable.

In the design of the RFID tag antenna, since the characteristic impedance of the RFID chip is not purely resistive, but has multiple resistive and capacitive impedance characteristics, it is different in design from the traditional 50 ohm antenna design. In order to optimize the energy transfer between the RFID chip and the antenna, how to effectively design a conjugate matching with the characteristic impedance of the chip has become an endeavor for the design of the RFID tag antenna.

In addition, the legal operating frequency bands specified by countries all over the world are not the same, such as 902~928MHz in the US, 922~928MHz in Taiwan, 950~956MHz in Japan, and 866~869MHz in Europe. So how to design a broadband tag antenna (860~960MHz) In order to be compatible with UHF RFID systems in other countries, it is also the direction of RFID tag antenna design.

As shown in FIG. 1 , it is an RFID tag antenna of US 2006/0158380, which is an inductive coupling method for implementing conjugate impedance matching and broadband characteristics, and is matched with the equivalent circuit shown in FIG. 2 . The characteristics of the tag antenna are described, characterized in that the imaginary impedance can be completely determined by the coupled signal source of a loop unit 11, and the operating center frequency is completely determined by a radiating structure 12, and then The coupling pitch is used to achieve the requirements of broadband.

However, when designing a tag antenna with a high imaginary impedance (>j200 ohms), a larger size loop structure 11 is required to obtain the desired high imaginary impedance characteristics, but when the loop current path length is greater than ten At one wavelength, the radiation characteristic of the loop structure 11 itself is highlighted. Therefore, the equivalent circuit of the RFID tag antenna (shown in FIG. 2) is no longer applicable, and inductive coupling is used. In the degree of freedom of impedance bandwidth adjustment, it is not easy to achieve a larger bandwidth design, and the regulation of its operating frequency band is completely dependent on the resonant frequency of the radiation structure, and the design flexibility is low.

Accordingly, it is an object of the present invention to provide an RFID tag that increases bandwidth and optimizes energy transfer.

Thus, the RFID tag of the present invention comprises a substrate, a feed unit, and a wafer.

The feed unit is disposed on the substrate and has a loop conductor pattern and a load conductor pattern in parallel with the loop conductor pattern.

The wafer is disposed on the loop conductor pattern of the feed unit and electrically connected to the loop conductor pattern.

The invention has the advantages that the circuit of the loop conductor pattern and the load conductor pattern of the feeding unit respectively generates an equivalent inductive and capacitive circuit, and the control of the resonant frequency of the self is easily realized, so that the permeable The effect of the conjugate matching of the size of the loop conductor pattern and the load conductor pattern is adjusted, so that the form of impedance adjustment is more diverse, and the elasticity of the design is higher, so that the reduced design can be easily realized.

The foregoing and other technical aspects, features and advantages of the present invention will be apparent from the Detailed Description of the <RTIgt;

Before the present invention is described in detail, it is noted that in the following description, similar elements are denoted by the same reference numerals.

As shown in FIG. 3 and FIG. 4, a first preferred embodiment of the radio frequency identification tag of the present invention is a small-sized near field RFID tag antenna, and the radio frequency identification tag includes a substrate 2, a feeding unit 3, and A wafer 4.

The feeding unit 3 is disposed on the substrate 2 and has a loop conductor pattern 31 and a load conductor pattern 32 connected in parallel with the loop conductor pattern 31, wherein the feed conductor of the feed unit 3 The pattern 31 has a square shape and has a first side portion 311 and a second side portion 312 opposite to the first side portion 311, and the wafer 4 is disposed on the second side portion 312. The sheet 2 may be a flexible material of PET resin or ABS resin. In the embodiment, the load conductor pattern 32 is a finger capacitor and has a second side portion 312 which is spaced apart from each other and connected to the loop conductor pattern 31. The extension portion 321 is in the shape of a finger (FIG. 3 is a single set of interdigitated capacitors, and FIG. 4 is a set of interdigitated capacitors).

The wafer 4 has an integrated circuit inside, and the wafer 4 is disposed on the loop conductor pattern 31 of the feed unit 3, and is electrically connected to the loop conductor pattern 31.

The loop conductor pattern 31 of the feed unit 3 can generate an inductive equivalent circuit, and the load conductor pattern 32 can generate a capacitive equivalent circuit, and the resonant frequency of the RFID tag is determined by the inductance and the capacitance According to the equivalent circuit of the present invention, the RFID tag of the present invention can not only reduce the size of the RFID tag, but also adjust the relative position of the loop conductor pattern 31 and the load conductor pattern 32 to adjust the resonant frequency to achieve conjugate matching. The effect makes the form of impedance adjustment more diverse, which in turn makes the design more flexible.

As shown in FIG. 5 and FIG. 6 , the second preferred embodiment of the radio frequency identification tag of the present invention is substantially the same as the first preferred embodiment, except that the load conductor pattern 32 is a microstrip line capacitor. And having an extension portion 321 which is spaced apart from each other and connected to the second side portion 312 of the loop conductor pattern 31, as shown in FIG. 5, is a vertical microstrip line capacitance, and the extension portions 321 are from the second side portion 312. The external extension is straight, as shown in FIG. 6 is a horizontal microstrip line capacitance. The extensions 321 are bent outwardly from the second side portion 312. In this embodiment, the microstrip line capacitance can be finely adjusted. The effect of the capacitance value.

As shown in FIG. 7, the third preferred embodiment of the radio frequency identification tag of the present invention is substantially the same as the first preferred embodiment, except that the load conductor pattern 32 is in a square shape and connected to the same. The second side portion 312 of the loop conductor pattern 31 is located in the loop conductor pattern 31. The load conductor pattern 32 has an SMD capacitor, and the SMD capacitor has a better operational effect, but the cost is high.

As shown in FIGS. 8 and 9, the fourth preferred embodiment of the radio frequency identification tag of the present invention is substantially the same as the first preferred embodiment, except that the load conductor pattern 32 is a metal piece and is disposed on the same. On the surface of the substrate 2, the three-turn conductor pattern 31 of the feed unit is disposed on the substrate 2 opposite to the load conductor pattern 32, and the load conductor pattern 32 can also be designed as shown in FIG. In the ㄇ font type, the metal chip capacitor of the embodiment can achieve better operation effect, but the manufacturing process is complicated and the cost is high.

As shown in FIG. 11 , the fifth preferred embodiment of the radio frequency identification tag of the present invention is substantially the same as the first preferred embodiment, except that the radio frequency identification tag further includes a substrate 2 disposed on the substrate 2 . The upper radiation unit 5 has an antenna conductor pattern 51 spaced apart from the first side portion 311 of the loop conductor pattern 31.

In this embodiment, the load conductor pattern 32 of the feed unit 3 is a double-finger capacitor. Of course, it can be replaced with an SMD capacitor, a microstrip line capacitor or a metal piece according to the use requirement of the RFID tag. In addition, the antenna conductor pattern 51 can also take a variety of forms. As shown in FIG. 12, the antenna conductor pattern 51 is a folded dipole antenna. As shown in FIG. 13, the antenna conductor pattern 51 is The structure of the aforementioned antenna is well known to those skilled in the art, and is not a feature of the present invention and will not be described again.

With the above design, the feed unit 3 is used as a coupling signal source, and then the signal energy is indirectly coupled to the radiation unit 5 to form an RFID tag antenna design. As shown in FIG. 14, the coupled signal source is visible. It is a small-sized coupling antenna, so it can be represented by the equivalent circuit Z ₁ , and the radiation unit 5 can be equivalent to Z ₂ , wherein the coupling effect between Z ₁ and Z ₂ can be obtained by the transformer principle. The effect is the mutual inductance Lx shown in Figure 14. This equivalent circuit provides a reference for the adjustment strategy of the designer to quickly analyze the antenna characteristics and the design of the tag antenna.

The feeding unit 3 is formed by combining the inductive loop conductor pattern 31 and the capacitive load conductor pattern 32. Therefore, the resonant frequency of the feeding unit 3 can be expressed as Where L _s and C _s are the equivalent inductance and equivalent capacitance of the coupled signal source in the equivalent circuit, respectively, so that the loop size (ie, L _s value) of the loop conductor pattern 31 can be adjusted, and the load conductor It refers to the length of the pattern 32 (i.e., the value C _s) of the fork structure, coupled to the control signal from the source oscillation frequency value f _s, and thus form so that impedance adjustment can be more diverse.

In addition, the radiation unit 5 can adopt a general antenna structure, for example, a half-wavelength dipole antenna, a folded dipole antenna, and a curved dipole antenna, and the determined resonance frequency can be expressed as f _r , which can be The antenna structure and style of unit 5 are determined.

By adjusting the relative positions of the two resonance frequencies f _s , f _r and the coupling pitch of the feeding unit 3 and the radiation unit 5, that is, the half power bandwidth characteristic diagram shown in FIG. 15, the broadband characteristic can be designed. The tag antenna, along with the impedance characteristic diagram shown in Figure 16, increases the freedom of impedance design, making it easy to conjugate with the RFID chip.

Therefore, the radiation unit 5 is provided by the radiation unit 5 of the single-group interdigitated structure, and the loop conductor pattern 31 of the folded dipole antenna is used as the radiation structure of the tag antenna, so that the operation bandwidth is 160 MHz (830~) 990MHz), twice the bandwidth of the conventional (80MHz), does cover the operating band of UHF RFID systems worldwide.

In summary, the loop conductor pattern 31 of the feed unit 3 is used to generate an inductive equivalent circuit, which generates a capacitive equivalent circuit, making it easy to achieve its own resonant frequency. The regulation can be achieved by adjusting the size of the loop conductor pattern and the load conductor pattern to achieve a conjugate matching effect, thereby achieving a downsizing design, so that the form of the impedance adjustment is more diverse, so the object of the present invention can be achieved. .

However, the above is only the four preferred embodiments of the present invention, and the scope of the present invention is not limited thereto, that is, the simple equivalent changes made by the scope of the present invention and the description of the invention are Modifications are still within the scope of the invention.

2. . . Substrate

3. . . Feeding unit

31. . . Loop conductor pattern

311. . . First side

312. . . Second side

32. . . Load conductor pattern

321. . . Extension

4. . . Wafer

5. . . Radiation unit

51. . . Antenna conductor pattern

Figure 1 is a top plan view of an RFID tag antenna of the prior art US2006/0158380;

Figure 2 is a circuit diagram illustrating the equivalent circuit of Figure 1;

Figure 3 is a partial plan view showing a first preferred embodiment of the radio frequency identification tag of the present invention;

Figure 4 is a partial plan view showing another aspect of the first preferred embodiment;

Figure 5 is a partial plan view showing a second preferred embodiment of the radio frequency identification tag of the present invention;

Figure 6 is a partial plan view showing another aspect of the second preferred embodiment;

Figure 7 is a partial plan view showing a third preferred embodiment of the radio frequency identification tag of the present invention;

Figure 8 is a partial plan view showing a fourth preferred embodiment of the radio frequency identification tag of the present invention;

Figure 9 is a partial cross-sectional view, to help explain Figure 8;

Figure 10 is a partial plan view showing another aspect of the fourth preferred embodiment;

Figure 11 is a plan view showing a fifth preferred embodiment of the radio frequency identification tag of the present invention;

Figure 12 is a top plan view showing another aspect of the radiation unit of the fifth preferred embodiment;

Figure 13 is a top plan view showing another aspect of the radiation unit of the fifth preferred embodiment;

Figure 14 is a circuit diagram showing the equivalent circuit of the fifth preferred embodiment;

Figure 15 is a characteristic diagram showing the characteristics of the half power bandwidth of the fifth preferred embodiment; and

Figure 16 is a characteristic diagram showing the impedance characteristics of the fifth preferred embodiment.

2. . . Substrate

3. . . Feeding unit

31. . . Loop conductor pattern

311. . . First side

312. . . Second side

32. . . Load conductor pattern

321. . . Extension

4. . . Wafer

Claims (7)

An RFID tag comprises: a substrate; a feed unit disposed on the substrate and having a loop conductor pattern, and a load conductor pattern in parallel with the loop conductor pattern, the loop conductor pattern and The load conductor patterns respectively generate an equivalent circuit having inductivity and capacitance, and a resonant frequency of the feed unit changes with the loop conductor pattern and the load conductor pattern; and a wafer is disposed at the feed The loop conductor pattern of the unit is electrically connected to the loop conductor pattern. The radio frequency identification tag according to the first aspect of the invention, wherein the loop conductor pattern of the feeding unit has a square shape and has a first side portion and a second side opposite to the first side portion At the edge, the wafer is disposed on the second side. The radio frequency identification tag according to claim 2, further comprising a radiation unit disposed on the substrate, the radiation unit having an antenna conductor pattern spaced from a first side of the loop conductor pattern . The radio frequency identification tag according to claim 3, wherein the antenna conductor pattern is selected from the group consisting of a half-wavelength dipole antenna, a curved dipole antenna, a folded dipole antenna or a bow-tie antenna. The radio frequency identification tag according to claim 2, wherein the load conductor pattern is a finger capacitor and has an extension extending in two phases and connecting the second side of the loop conductor pattern. The extension is in the shape of a finger. The radio frequency identification tag of claim 2, wherein the load conductor pattern is a microstrip line capacitor and has an extension extending in two phases and connecting the second side of the loop conductor pattern. The radio frequency identification tag according to claim 2, wherein the load conductor pattern is a metal piece and is disposed on the surface of the substrate, and the loop conductor pattern of the feeding unit is opposite to the load conductor pattern. Placed on the substrate.