CN112397874A

CN112397874A - Radio frequency identification RFID anti-metal microstrip tag antenna

Info

Publication number: CN112397874A
Application number: CN202011195591.4A
Authority: CN
Inventors: 邓欣; 袁红刚; 娄宁; 何华武; 闫善勇
Original assignee: Southwest Electronic Technology Institute No 10 Institute of Cetc
Current assignee: Southwest Electronic Technology Institute No 10 Institute of Cetc
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2021-02-23
Anticipated expiration: 2040-10-30
Also published as: CN112397874B

Abstract

The radio frequency identification RFID anti-metal microstrip tag antenna disclosed by the invention has the advantages of high gain, low cost and long reading distance. The invention is realized by the following technical scheme: the radiation patch, the medium substrate and the metal floor form a resonant cavity, and the radiation patch covers the rectangular groove and the strip-shaped mounting seam which is fixed with the RFID tag chip electrically connected with the radiation patch; a first strip-shaped gap is formed above the U-shaped groove, and a second strip-shaped gap and a third strip-shaped gap are formed on the left side and the right side of the U-shaped groove; the bottom system of rectangular channel has a arch, the one end of bar installation seam run through the arch and with the rectangular channel intercommunication, the other end runs through the bottom of radiation paster, the fringe field of the gap formation at U-shaped groove both ends produces the radiation, and metal floor, radiation paster, feeder and earth connection constitute RFID anti-metal microstrip label antenna. Based on the structure and the slotted design of the antenna, the invention ensures the performance of the tag under the condition of reducing the thickness of the tag.

Description

Radio frequency identification RFID anti-metal microstrip tag antenna

Technical Field

The invention relates to an ultrahigh Frequency Radio Frequency Identification tag antenna applicable to a metal environment, in particular to a Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna.

Background

Radio frequency identification RFID systems have been widely used in the fields of public transportation, personal identification, vehicle management, automatic toll collection, access control, and the like. Radio Frequency identification (rfid) technology, also known as electronic tag or rfid, is a communication technology that can identify a specific target and read and write related data through radio signals without establishing mechanical or optical contact between an identification system and the specific target. The RFID technology is a short-range communication technology that performs contactless two-way communication using a radio frequency. The system collects and identifies the related information of the target object through the radio frequency signal, is widely applied with the advantages of non-contact identification, high identification speed and the like, and is also the most main member in the sensing layer of the Internet of things. The basic principle is that the automatic identification technology for automatically identifying objects and exchanging data is realized by utilizing the energy transmission characteristic of radio frequency signal or electromagnetic field coupling. The RFID technology has the characteristics of strong anti-interference capability, large information storage amount, non-contact, long service life, capability of identifying multiple labels, high response speed and the like. The metal-resistant label is widely applied to occasions needing to identify various metal objects, and overcomes the defects that the reading and writing distance is shortened rapidly, the working reliability is greatly reduced, and even normal reading and writing cannot be realized when a common label is placed on the surface of a metal object. In practical applications of RFID, there are some applications that inevitably involve the metal body. Generally, when electromagnetic waves touch a metal body, the return signals of the electronic tag adhered to the surface of the metal body to a reader/writer are destroyed due to the strong reflection effect, so that the electronic tag is difficult to apply to the surface of the metal body. Passive RFID systems are generally classified into Low Frequency (LF), High Frequency (HF), and Ultra High Frequency (UHF) systems, and are composed of three basic elements, a reader, a tag, and an antenna. The metal and other environment media have an attenuation effect on electromagnetic waves, and the metal surface has a reflection effect on the electromagnetic waves, so that the full performance of the UHF passive RFID system is seriously influenced. The read-write performance of the passive UHF electronic tag antenna can be influenced under different environments, and particularly when a traditional tag (a common ultrahigh frequency electronic tag generally adopts a printed dipole antenna) is attached to a metal surface, the tag is hardly read.

When the ordinary UHF radio frequency identification RFID tag is applied to a metal surface, due to the boundary condition of metal, the reading distance of the tag can be shortened rapidly, even the tag can not be read, the radiation efficiency, the input impedance, the gain, the directional diagram and the like of the tag antenna can be greatly influenced, and the overall performance of the tag is reduced. Particularly, when the tag antenna is close to the metal surface, the radiation efficiency of the antenna is reduced sharply due to the mirror effect of the horizontally polarized wave, so that the passive tag with the working frequency cannot work normally on an object with the metal surface (such as a steel shelf, a container and the like).

In an Ultra High Frequency (UHF) rfid tag system, identification of a tag attached to a metal object carrier is particularly difficult because metal obstacles reflect and interfere with electromagnetic waves. The mode that can solve effectively at metal surface attached RFID label at present mainly has three kinds of modes: firstly, absorbing redundant electromagnetic waves by adopting a wave-absorbing material; secondly, raising the label; and thirdly, a grounded antenna design. For a common passive ultrahigh frequency tag, when the tag is attached to a metal surface, the reading distance of the tag is rapidly reduced and even the tag is difficult to read due to the changes of impedance matching, radiation efficiency and directivity of a tag antenna. It is therefore required to be specially treated or to employ special labels to suit the use on metal surfaces. Meanwhile, the label of the UHF frequency band is generally large in size and cannot be used on an object with a small size, so that the application range of the UHF frequency band RFID system is greatly limited. The suitability, durability and identification accuracy of RFID tags in the face of more complex operating environments and more challenging materials (e.g., metal goods, liquid filled containers) is a serious challenge. In order to solve the problem that the tag antenna cannot be applied in a metal environment, the background environment of the RFID system must be considered when designing the RFID system.

The anti-metal label is a special electronic label, and technically solves the problem that the electronic label cannot be attached to the metal surface for use. The metal-resistant electronic tag can be attached to metal to obtain good reading performance even if the reading distance is longer than that of the metal-resistant electronic tag in the air. By adopting special antenna and circuit design, the electronic tag can effectively prevent metal from interfering radio frequency signals, and the real anti-metal electronic tag has the following outstanding performances: the reading distance of the metal paste is farther than that of the metal paste, which is a good result of the overall design. At present, foreign RFID anti-metal tags have the defects of large volume, high cost, unstable performance, complex design process and the like, and are difficult to meet the application requirements of the actual industry of China.

The distance between the conventional tag antenna and the metal surface is kept to be more than 1cm, so that the volume and the cost of the whole tag are increased although the reading distance of the tag is increased, the bandwidth of the antenna is reduced, the influence of surface metal on the tag antenna is not well solved, and the performance of the tag antenna is far less than that of the tag antenna which is used for a non-metal surface; the micro-strip antenna based on the ceramic medium can also be used on the surface of metal, the volume of the antenna can be very small by utilizing the high dielectric constant of the ceramic medium, the performance of the antenna is very stable by utilizing the surface of the metal as a larger reflecting surface, but the ceramic antenna is not suitable for low-cost batch production of electronic tags because the manufacturing cost of the ceramic antenna is too high; another tag antenna scheme suitable for metal surface is to add a layer of AMC (artificial magnetic conductor) structure between the antenna radiation surface and the metal surface. The magnetic current direction generated between the electronic tag and the AMC is the same as the magnetic current direction between the metal surface and the AMC through the high impedance characteristic of the AMC, so that the gain and the reading distance of the electronic tag are improved, but the difficulty and the cost of the current research of the technology are high, and the technology is still in a laboratory stage. In tests, it is found that when the area of the metal surface is increased to a certain size, the radiation direction of the antenna is distorted, so that the radiation field perpendicular to the radiation surface is weakened, and the gain of the antenna is reduced. The bandwidth of the tag antenna is also an important index for measuring the performance of the antenna, and the wider the frequency band is, the higher the efficiency of the antenna is. The bandwidth of the antenna can be effectively improved by adjusting the height of the dielectric layer, when the height of the dielectric layer is increased, the bandwidth of the antenna is widened, the efficiency of the antenna is improved, but the volume of the antenna is increased by increasing the height of the antenna, and the low-profile characteristic of the antenna is damaged.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides the RFID metal-resistant microstrip tag antenna with low profile, high gain, low cost, longer reading distance, smaller product size and higher cost performance, and can not reduce or reduce less antenna bandwidth and ensure the performance of the tag on the basis of the structure and the slotting design of the antenna under the condition of reducing the thickness of the tag.

The purpose of the invention is realized by the following technical scheme: a radio frequency identification, RFID, metal resistant microstrip tag antenna comprising: set up in the positive radiation paster of medium base plate and set up in the metal floor at the medium base plate back, the radiation paster constitutes a resonant cavity, its characterized in that with medium base plate and metal floor ground plane: the radiation patch is provided with a rectangular groove with a downward opening, a U-shaped groove covering the rectangular groove and a strip-shaped mounting seam fixed with an RFID tag chip electrically connected with the radiation patch; a first strip-shaped gap is formed above the U-shaped groove, and a second strip-shaped gap and a third strip-shaped gap are formed on the left side and the right side of the U-shaped groove; the bottom system of rectangular channel has a arch, the one end of bar installation seam run through the arch and with the rectangular channel intercommunication, the other end runs through the bottom of radiation paster, the fringe field of the gap formation at U-shaped groove both ends produces the radiation, and metal floor, radiation paster, feeder and earth connection constitute RFID anti-metal microstrip label antenna.

Compared with the prior art, the invention has the following beneficial effects:

low profile, high gain. The invention adopts the radiation patch arranged on the front surface of the medium substrate and the metal floor arranged on the back surface of the medium substrate, the radiation patch, the medium substrate and the ground plane of the metal floor form a resonant cavity, and the performance of the label is ensured under the condition of reducing the thickness of the label based on the structure and the slotting design of the antenna. When the radiation patch is attached to the surfaces of metal objects with different areas, the radiation patch has good impedance stability, and meanwhile, the gain can be further increased. The size of the tag antenna is further reduced by utilizing the rectangular slot to carry out miniaturization design, so that the resonant wavelength of the antenna is shortened to 1/4 wavelength from the traditional half wavelength, the size of the tag antenna is greatly reduced, and the requirement of small-size metal environment is met. The size of the whole tag antenna is about 90mm multiplied by 25mm multiplied by 4mm, and compared with a tag which is reduced in size by using a high dielectric constant material, the tag antenna is more cost-effective, lower in cost and longer in reading and writing distance. The radiation patch is provided with the rectangular groove with the downward opening, the U-shaped groove covering the rectangular groove and the strip-shaped mounting seam fixed with the RFID tag chip electrically connected with the radiation patch are equivalent to the introduction of the cascade inductor in an equivalent circuit. The slot is arranged on the microstrip radiating patch, so that the microstrip radiating patch has good impedance matching characteristic, and the original surface current path is cut off, so that the current flows in a zigzag way around the slot edge, and the path is lengthened. As the slot length increases, the resonant frequency of the antenna also decreases. The rectangular slot can not only reduce the resonant frequency of the antenna, but also ensure certain gain and bandwidth, has little influence on the performance of the antenna, and is easy to realize circular polarization and dual-frequency dual-polarization characteristics. The antenna has the advantages of high gain, long reading distance, good directivity and impedance matching characteristics, and the bandwidth can cover the RFID frequency range with the central frequency of 915 MHz. The practical test result shows that: the actual measurement is consistent with the simulation result, the reading distance can reach 8m, and the requirement of practical application can be met. The printing structure adopted by the antenna simplifies the production process and has low production cost. The antenna is proved to have the characteristics of high gain, long distance and the like through a large amount of simulation and actual measurement on the antenna.

Drawings

FIG. 1 is a schematic structural diagram of an RFID anti-metal microstrip tag antenna of the present invention. In the figure, 1-a dielectric substrate, 2-a radiating patch, 3-a rectangular groove, 4-a first strip-shaped gap, 5-a second strip-shaped gap, 6-a third strip-shaped gap, 7-an RFID tag chip and 8-a bump.

FIG. 2 is a dimension labeling diagram of the RFID anti-metal microstrip tag antenna of the present invention.

Fig. 3 is a diagram illustrating the effect of different patch lengths on the antenna impedance for a patch width of 25 mm. Where 3a is a curve of the influence of the patch length L on the resistance, and 3b is a curve of the influence of the patch length L on the reactance.

Fig. 4 is a graph illustrating the effect of different patch widths on the antenna impedance for a patch length of 93 mm. Where 4a is a curve of the influence of the patch width W on the resistance, and 4b is a curve of the influence of the patch width W on the reactance.

Fig. 5 is a graph of simulation results of an influence curve of a chip position on the impedance of the tag antenna, wherein 5a is an influence curve of the chip position on the resistance, and 5b is an influence curve of the chip position on the reactance.

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.

Detailed Description

See fig. 1. In a preferred embodiment described below, a radio frequency identification, RFID, metal resistant microstrip tag antenna, comprises: set up in positive radiation paster (2) of medium base plate (1) and set up in the metal floor at medium base plate (1) back, radiation paster (2) and medium base plate (1) and metal floor ground plane constitute a resonant cavity, its characterized in that: the radiation patch (2) is provided with a rectangular groove (3) with a downward opening, a U-shaped groove covering the rectangular groove (3) and a strip-shaped mounting seam fixed with an RFID tag chip (7) electrically connected with the radiation patch (2); a first strip-shaped gap (4) is formed above the U-shaped groove, and a second strip-shaped gap (5) and a third strip-shaped gap (6) are formed on the left side and the right side of the U-shaped groove; the bottom system of rectangular channel (3) has one arch (8), and the one end of bar installation seam runs through arch (8) and with rectangular channel (3) intercommunication, the other end runs through the bottom of radiation paster (2), the fringing field of the gap formation at U-shaped groove both ends produce the radiation, and metal floor, radiation paster (2), feeder and earth connection constitute the anti metal microstrip label antenna of RFID.

Aiming at the application requirements of the ultrahigh frequency RFID electronic tag for the metal surface at present, the RFID anti-metal microstrip tag antenna of the embodiment is firstly printed on a piece of PVC film planar material by silver paste or copper, aluminum and the like, and after the tag chip is installed, the planar PVC film tag is pasted on a square dielectric material along a folding line. In the embodiment, the length and width dimensions of the radiation patch (2) are smaller than those of the dielectric substrate (1). The length and width of the metal floor are the same as those of the dielectric substrate (1). The rectangular groove (3) and the U-shaped groove are located in the left half area of the radiation patch. The leftmost end of the first strip-shaped gap (4) is communicated with the second strip-shaped gap (5), and the rightmost end of the first strip-shaped gap (4) is communicated with the third strip-shaped gap (6). The second strip-shaped gap (5) and the third strip-shaped gap (6) are perpendicular to the first strip-shaped gap (4).

Specifically, in the embodiment, the dielectric material is a polytetrafluoroethylene glass cloth double-sided copper-clad plate with a thickness, and has the advantages of thin thickness and low cost, wherein the thickness of 0.5mm is one of the thinnest tags seen in the current anti-metal tag antenna research, and the thinnest of the current anti-metal tag product is 0.8 mm; and etching the front surface of the polytetrafluoroethylene glass cloth double-sided copper-clad plate to form the radiation patch structure required by the application.

See fig. 2. Let the size of the tag chip be W₀×L₀＝3×1mm²The distance from the center of the label chip to the left radiation edge is d; the size of the substrate is 98 x 28mm²The size of the metal floor on the back surface is the same as that of the substrate, and the size of the radiation patch is W multiplied by L which is smaller than that of the substrate. On the radiation patch, a dimension W is provided₁×L₁The rectangular groove and the U-shaped groove can enable two ends of two pins of the tag chip to form differential current through the rectangular groove structure, so that the work of the tag chip is met, and meanwhile, the rectangular groove can also adjust the impedance of an antenna; the U-shaped groove structure can enable the microstrip antenna to form a meander structure, so that the size of the antenna is reduced, the patch can form a coupling structure through a U-shaped groove gap, a large inductance value can be generated, and impedance matching of the tag antenna is achieved.

See fig. 3. For a microstrip antenna, its patch length directly affects the resonant frequency of the tag antenna. The impedance values of the tag antenna of the radiating patch of the tag under different lengths L and widths W are firstly studied, and the curves in the figure represent L as 90mm, 91mm, 92mm, 93mm, 94mm and 95mm from right to left respectively. It can be seen that the longer the antenna radiating patch, the lower the frequency at which the tag antenna is best matched to the tag chip.

See fig. 4. The curves from right to left in the figure show that W is 23mm, 24mm, 25mm, 26mm, 27mm respectively, and it can be seen that the wider the patch width, the lower the frequency at which the tag antenna is best matched with the tag chip, with a fixed patch length.

See fig. 5. Under the condition that the length of the fixed tag antenna patch is 92mm and the width of the fixed tag antenna patch is 25mm, d represents the distance between the central position of the tag chip and the left edge of the radiation patch, and the distance is also the central positions of the similar rectangular groove and the U-shaped groove formed in the radiation patch. The curves in the figure represent d from right to left as 34.5mm, 35.5mm, 36.5mm, 37.5mm and 38.5mm, respectively. It can be seen that the center of the chip has a large influence on the impedance of the tag antenna, and when the chip is closer to the center of the radiation patch, i.e. d is larger, the optimal matching frequency of the tag antenna and the tag chip is lower, whereas when the chip is closer to the edge of the radiation patch, the optimal matching frequency is higher.

The size of the radiating patch of the tag antenna and the position of the chip have a large influence on the impedance of the tag antenna, and have similar influence results on the resistance and the reactance. Similarly, in the radiating patch, the rectangular slot and the U-shaped slot have a large influence on the impedance of the tag antenna. Length L of rectangular groove₁And width W₁Length L of U-shaped groove₂(length of first bar slit) and arm length W₂(the length of the second strip gap and the third strip gap), and the width gap of the U-shaped groove₁(width of first stripe slit) and gap₂(the width of the second and third strip slots) has an effect on the tag antenna impedance. The length L1 of the rectangular slot has a great influence on the impedance of the tag antenna, and L is determined by the impedance of the tag chip₁The longer the tag antenna is, the lower the frequency of best matching with the tag chip is. Width W of rectangular groove₁The wider the best match frequency. Length L of U-shaped groove₂For tag skyThe line impedance effect is also significant, but its arm length W₂The impedance is less affected. The width of the U-shaped slot at different portions also has a large effect on the impedance of the tag antenna. The tag antenna also satisfies the wavelength λ/4 resonance condition, with the resonance frequency fr primarily related to the length L and width W of the patch. The relationship between them can be approximated as: fr ═ c/[4(L + W)]Where c represents the speed of light. W is known by parameter scanning analysis of antenna impedance characteristics₁The change of (2) has a large influence on the impedance of the antenna when the slot length W is set₁<When the antenna is 34mm, the impedance change is relatively smooth, and the whole antenna is inductive; as the slot length continues to increase, the real part impedance of the antenna increases dramatically and the antenna appears capacitive. At the length W of the slot₁When the impedance is 31mm, the impedance is 11+ j194 Ω, and the impedance of the tag chip is conjugate-matched. The bandwidth of the antenna can be effectively improved by adjusting the height h of the dielectric layer, when the height of the dielectric layer is increased, the bandwidth of the antenna is widened, the efficiency of the antenna is improved, but the volume of the antenna is increased by increasing the height of the antenna, and the low-profile characteristic of the antenna is damaged. In summary, in this embodiment, h is 5.1mm to 6mm in the design. According to simulation analysis, when the height h of the medium is 5mm, the bandwidth of the antenna with the reflection coefficient below-10 dB is 30MHz (the antenna frequency is 910-940 MHz), and the antenna has good frequency band characteristics.

Through simulation analysis and impedance debugging of the tag, the optimal parameter combination can be finally determined as shown in the following table:

parameter(s)

L

W

d

L1

W1

L2

W2

gap₁

gap₂

Size of

93mm

25mm

36.5mm

19mm

7mm

24mm

7mm

0.5mm

1mm

It can be seen that, under the condition of reducing the thickness of the tag, based on the antenna structure and the slotting design of the present application, good impedance matching can be realized through the adjustment of the slotting size and the antenna size, so that the maximum reading distance of the tag antenna is increased, and the performance of the tag is effectively ensured.

The foregoing is a preferred embodiment of the present invention, it is to be understood that the invention is not limited to the form disclosed herein, but is not to be construed as excluding other embodiments, and is capable of other combinations, modifications, and environments and is capable of changes within the scope of the inventive concept as expressed herein, commensurate with the above teachings, or the skill or knowledge of the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A radio frequency identification, RFID, metal resistant microstrip tag antenna comprising: set up in positive radiation paster (2) of medium base plate (1) and set up in the metal floor at medium base plate (1) back, radiation paster (2) and medium base plate (1) and metal floor ground plane constitute a resonant cavity, its characterized in that: the radiation patch (2) is provided with a rectangular groove (3) with a downward opening, a U-shaped groove covering the rectangular groove (3) and a strip-shaped mounting seam fixed with an RFID tag chip (7) electrically connected with the radiation patch (2); a first strip-shaped gap (4) is formed above the U-shaped groove, and a second strip-shaped gap (5) and a third strip-shaped gap (6) are formed on the left side and the right side of the U-shaped groove; the bottom system of rectangular channel (3) has one arch (8), and the one end of bar installation seam runs through arch (8) and with rectangular channel (3) intercommunication, the other end runs through the bottom of radiation paster (2), the fringing field of the gap formation at U-shaped groove both ends produce the radiation, and metal floor, radiation paster (2), feeder and earth connection constitute the anti metal microstrip label antenna of RFID.

2. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the RFID metal-resistant microstrip tag antenna is printed on a PVC (polyvinyl chloride) film plane material by silver paste or copper and aluminum, and after a tag chip is installed, a PVC film tag is pasted on a square dielectric material along a fold line.

3. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the length and width of the radiation patch (2) are smaller than those of the dielectric substrate (1).

4. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the length and width of the metal floor are the same as those of the dielectric substrate (1).

5. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the rectangular groove (3) and the U-shaped groove are located in the left half area of the radiation patch.

6. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the leftmost end of the first strip-shaped gap (4) is communicated with the second strip-shaped gap (5), and the rightmost end of the first strip-shaped gap (4) is communicated with the third strip-shaped gap (6).

7. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the second strip-shaped gap (5) and the third strip-shaped gap (6) are perpendicular to the first strip-shaped gap (4).

8. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: on the radiation patch with length L and width W, a dimension W is arranged₁×L₁The rectangular groove and the U-shaped groove are in a rectangular groove structure, so that differential current is formed at two ends of two pins of the tag chip, and meanwhile, the rectangular groove can also adjust the impedance of the antenna.

9. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the microstrip antenna with the U-shaped groove structure forms a meander structure, and the patch forms a coupling structure to generate inductance value through the gap of the U-shaped groove, so that impedance matching of the tag antenna is realized.

10. The Radio Frequency Identification (RFID) metal-resistant microstrip tag antenna of claim 1 wherein: the tag antenna satisfies the wavelength λ/4 resonance condition, and the relationship between the resonance frequency fr and the length L and width W of the patch can be approximately expressed as: fr ═ c/[4(L + W) ], where c denotes the speed of light.