CN108808247B - Near field radio frequency identification antenna with electrically large size identification area - Google Patents
Near field radio frequency identification antenna with electrically large size identification area Download PDFInfo
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- CN108808247B CN108808247B CN201810617989.9A CN201810617989A CN108808247B CN 108808247 B CN108808247 B CN 108808247B CN 201810617989 A CN201810617989 A CN 201810617989A CN 108808247 B CN108808247 B CN 108808247B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/12—Supports; Mounting means
- H01Q1/22—Supports; Mounting means by structural association with other equipment or articles
- H01Q1/2208—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems
- H01Q1/2216—Supports; Mounting means by structural association with other equipment or articles associated with components used in interrogation type services, i.e. in systems for information exchange between an interrogator/reader and a tag/transponder, e.g. in Radio Frequency Identification [RFID] systems used in interrogator/reader equipment
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/36—Structural form of radiating elements, e.g. cone, spiral, umbrella; Particular materials used therewith
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/50—Structural association of antennas with earthing switches, lead-in devices or lightning protectors
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Abstract
The invention discloses a near-field radio frequency identification antenna with an electrically large-size identification area, wherein an antenna structure comprises a first loop antenna arranged on the periphery and a coupling loop antenna arranged in the first loop antenna, the first loop antenna and the coupling loop antenna comprise a plurality of interdigital structures, and the interdigital structures are connected through a transmission line; the middle part of the bottom end of the first loop antenna is bent towards the coupling loop antenna, and a feed port is arranged at the bottom end of the first loop antenna. On one hand, the electric large-size identification area is ensured, the identification distance is increased, on the other hand, under the condition of ensuring the magnetic field intensity and the uniformity of the near field, the magnetic field outside the identification area is reduced, and the misreading of the label is avoided.
Description
Technical Field
The invention relates to the technical field of ultrahigh frequency near-field radio frequency identification antennas, in particular to a near-field radio frequency identification antenna with an electrically large-size identification area.
Background
Radio Frequency Identification (RFID) is a non-contact automatic Identification technology, and is mainly composed of a reader, a tag, and a reader antenna. The reader sends out radio frequency signals, the current generated by the induction of the tag can excite the chip in the tag to work in a space coupling mode, and finally the reader can identify the tag and send out the radio frequency signals, so that the reading and writing of information in the tag are realized. In a near field RFID system, the coupling mode between the reader antenna and the tag may be divided into magnetic field coupling and electric field coupling. If the electric field coupling mode is adopted, the induced energy is transferred in the electric field mode, and the distribution of the electric field is influenced by objects with larger dielectric constants and larger losses around the antenna. In the magnetic field coupling mode, the induced energy is transferred in the form of a magnetic field, which is only affected by objects with a high magnetic permeability. However, in nature, objects with higher dielectric constants are very common, but there are very few objects with higher magnetic permeability, and most experts and scholars study near-field RFID reader antennas based on magnetic field coupling technology in order to make the antennas work reliably in complex environments. For a traditional LF/HF RFID reader antenna, a coil antenna with a small size (the circumference of the coil is smaller than, λ is the wavelength in the free space at the corresponding frequency) is generally used, the direction of the current on the coil can be kept in the same direction, so that a strong and uniform magnetic field can be generated at the center of the coil, however, a new technical problem exists for designing an ultra-high frequency near field RFID reader antenna, that is, the wavelength of electromagnetic waves in an ultra-high frequency band is short, and when designing a near field radio frequency identification reader antenna with an electric large size (the circumference of the coil is larger than, λ is the wavelength in the free space at the corresponding frequency), the current attenuates to zero and changes direction at a quarter wavelength position, which phenomenon weakens the magnetic field strength generated in the antenna area, so that the tag reading capability is reduced. Therefore, how to overcome the current reversal problem so that the antenna generates a strong and uniform magnetic field in an electrically large-sized area is a key to the design of the near-field UHF-RFID antenna.
In order to solve the above problems, many researchers have proposed several near-field UHF-RFID antennas based on magnetic field coupling technology in recent years. Document [2 ]]（Qing X, Goh C K, and Chen Z N. A Broadband Near-field UHFRFID antenna[J]IEEE Transactions on Antennas and Propagation 2010, 58(12):3829-2(0.47 λ x 0.47 λ, λ being the wavelength in free space at a frequency of 915 MHz), the maximum distance for 100% tag identification can be up to 24 mm. Document [4 ]]（Shi J, Qing X, andChen Z N. Electrically Large Zero-Phase-shift Line Grid-Array UHF near-fieldRFID Reader Antenna[J]IEEE Transactions on Antennas and Propagation 2014,62(4):2201-2(0.94. lamda. times.0.46. lamda.), and the maximum distance of 100% tag identification is 13.5 mm. Document [6]（Shen L W, Zhuang W, Tang WC, and Ma J. Achieving Uniform Perpendicular Magnetic Field Distribution forNear-field UHF RFID[J]IET microwave Antennas and Propagation, 2016, 10(2):215-Direct Currents) using two "interdigital" opposite-phase current units and a feed network with a phase difference of 900, realizes identification area (460 × 160 mm) with large electric size2) The inner magnetic field is uniformly distributed. Document [7 ]]（Pakkathillam J K, Kanagasabai M, Varadhan C,et al. A Novel Fractal Antenna for UHF Near-Field RFID Readers[J]IEEEAntennas and Wireless Propagation reader, 2013, 12(5): 1141-. In summary, none of the above documents mention the problem of tag misreading outside the identification area, which is also a non-negligible problem in near field UHF-RFID antenna design.
It can be seen that the existing near field antenna UHF-RFID antenna based on the magnetic field coupling technology can realize an electrically large-sized identification area, but the problem of tag misreading outside the identification area exists.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to: the near field radio frequency identification antenna with the electrically large identification area is provided, on one hand, the electrically large identification area is ensured, the identification distance is increased, on the other hand, under the condition that the magnetic field intensity and the uniformity of the near field are ensured, the magnetic field outside the identification area is reduced, and the misreading of a label is avoided.
The technical scheme of the invention is as follows:
a near field radio frequency identification antenna with an electrically large-size identification area is disclosed, wherein an antenna structure comprises a first loop antenna arranged on the periphery and a coupling loop antenna arranged in the first loop antenna, the first loop antenna and the coupling loop antenna comprise a plurality of interdigital structures, and the interdigital structures are connected through a transmission line; the middle part of the bottom end of the first loop antenna is bent towards the coupling loop antenna, and a feed port is arranged at the bottom end of the first loop antenna.
In a preferred technical scheme, the interdigital structure comprises an upper block and a lower block matched with the upper block, at least one convex part is arranged on the upper block downwards, the convex part extends into a concave part of the lower block, and a gap is reserved between the convex part and the concave part.
In a preferred embodiment, the capacitance formed by the interdigital structure resonates with the inductance of the connected transmission line at the center frequency.
In a preferred technical scheme, 4 interdigital structures are arranged on each side of the coupling loop antenna.
In an optimal technical scheme, the upper end of the first loop antenna is provided with 7 interdigital structures, the bottom end of the first loop antenna is provided with 10 interdigital structures, and two side ends of the first loop antenna are respectively provided with 8 interdigital structures.
In an optimal technical solution, the length of the bending part at the bottom end of the first loop antenna is close to the length of the bottom end of the coupling loop antenna.
In a preferred technical solution, each edge of the bending portion of the bottom end of the first loop antenna is disposed on 2 interdigital structures.
Compared with the prior art, the invention has the advantages that:
on one hand, the electric large-size identification area is ensured, the identification distance is increased, on the other hand, under the condition of ensuring the magnetic field intensity and the uniformity of the near field, the magnetic field outside the identification area is reduced, and the misreading of the label is avoided.
Drawings
The invention is further described with reference to the following figures and examples:
FIG. 1 is a schematic diagram of an antenna structure according to the present invention;
FIG. 2 is a schematic view of an interdigitated structure according to the present invention;
FIG. 3 is a schematic diagram of the surface current distribution of the antenna of the present invention;
FIG. 4 is a schematic diagram of the simulated and measured return loss of the antenna of the present invention;
FIG. 5 is a schematic diagram of the distribution of the simulated magnetic field of the antenna at different observation heights;
fig. 6 is a graph of antenna tag identification rate versus observation height.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
Example (b):
as shown in fig. 1, a near field rfid antenna having an electrically large size identification area employs FR4 sheet material having a dielectric constant of 4.4, a loss tangent of 0.02, and a thickness of 0.8 mm. The whole antenna is composed of two ring structures: an outer ring structure and an inner parasitic coupling ring structure. Both ring structures are composed of transmission lines and a plurality of 'interdigital structures'. The bottom end of the outer ring is a feeding part and is bent towards the central area. Adopts a double-sided zigzag microstrip line feed structure. Through simulation optimization, the specific structure and size of the antenna are shown in FIG. 1. The outer ring structure is that the loop antenna 10 is arranged at the periphery, the coupling ring structure is that the coupling loop antenna 20 is arranged in the outer ring antenna, the loop antenna 10 and the coupling loop antenna 20 comprise a plurality of interdigital structures 30, and the interdigital structures 30 are connected through a transmission line 13; the middle part of the bottom end of the loop antenna 10 is bent towards the coupling loop antenna 20, and the bottom end of the loop antenna 10 is provided with a feeding port 40.
As shown in fig. 2, the interdigital structure 30 comprises an upper block 31 and a lower block 32 matched with the upper block 31, wherein the upper block 31 is provided with at least one protrusion 311 downwards, the protrusion 311 extends into a recess 321 of the lower block 32, and a certain gap is formed between the protrusion 311 and the recess 321.
The capacitance formed by the interdigital structure 30 resonates with the inductance of the connected transmission line 13 at the center frequency.
The coupling loop antenna 20 has 4 interdigital structures 30 disposed on each side.
The upper end of the loop antenna 10 is provided with 7 interdigital structures 30, the bottom end of the loop antenna 10 is provided with 10 interdigital structures, and two side ends of the loop antenna 10 are respectively provided with 8 interdigital structures.
The length of the bent portion 11 at the bottom end of the loop antenna 10 is close to the length of the bottom end of the coupled loop antenna 20. Each side of the bending portion 11 is disposed on 2 interdigital structures 30.
The working principle of the antenna is as follows: in order to realize the antenna in an electrically large area (320 x 320 mm)20.98 x) and the magnetic field outside the region quickly attenuates to the label identification threshold value. Firstly, a plurality of interdigital structures are adopted on the outer ring and the inner ring, which is equivalent to capacitor loading, and the number and the spacing of the interdigital structures are adjusted to obtain a capacitance value with a proper size, so that each section of transmission line and a capacitor connected with the transmission line resonate at a central frequency, and the capacitance can be offset with inductance on the transmission line. The lagging phase generated by the original current on each transmission line is compensated by resonance, so that the current on the outer ring and the current on the inner ring flow in opposite directions. According to the right-hand spiral rule, magnetic fields between the outer ring and the inner ring are mutually superposed, and magnetic fields in areas outside the outer ring and inside the inner ring are mutually offset; on the other hand, after the capacitor adopting the interdigital structure is loaded, the length of the current on the ring which keeps flowing in the same direction is increased, so that the identification area is enlarged. Then, the feed part is bent towards the central area (y direction) and is close to the inner ring, so that the coupling strength with the inner ring is increased, the magnetic field generated by the inner ring is stronger, the antenna achieves the purpose of uniformly distributing the magnetic field in the whole electric large area, and the magnetic field outside the area is attenuated to the identification threshold.
Fig. 3 is a schematic diagram of the surface current distribution of the antenna at the frequency of 915MHz, and it can be seen that the currents on the two loop structures of the antenna are distributed in the same direction.
Fig. 4 is a schematic diagram of simulated and measured return loss of the antenna of the present invention, and it can be seen from the diagram that the-10 dB impedance bandwidth is 255MHz, from 720MHz to 975MGHz, and includes the whole UHF band. In addition, for the tag using the Gen2 chip, when the magnetic field in the antenna identification area reaches-20 dBA/m, the chip can be ensured to obtain enough driving energy, and the system can work effectively, so that the identification area and the identification distance of the antenna can be judged by observing the distribution situation of the magnetic field above the antenna.
Fig. 5 is a simulated magnetic field distribution diagram of the antenna at different observation height planes. The heights of the observation from left to right are 0.5mm, 20mm and 40mm respectively. From the schematic view of the magnetic field amplitude distribution at viewing heights of 0.5mm and 20mm, it can be seen that at 320X 320mm2The magnetic field intensity in the area is larger than the identification threshold, and the magnetic field distribution is uniform, so that the magnetic field requirement of the near field UHF-RFID system is met. The observation height is a schematic diagram of the magnetic field amplitude distribution at 40mm, and it can be seen from the figure that the antenna has a recognition blind zone at this height. Finally, to verify the performance of the antenna, the area 400 × 400mm is identified directly above the antenna2Divided into 20X 20 squares and tested every 20mm height using the Thin-tag1700 series of labels, and every 5mm height between 20 and 40 mm.
FIG. 6 is a graph showing the result of tag identification rate test, showing that the antenna is realized at 320 × 320mm2In the electrically large-size area, the maximum distance of the tag with the 100% identification rate is 35mm, the maximum identifiable distance is 180mm, the tag outside the identification area cannot be misread, and the tag has good near field characteristics, so that the design purpose is achieved.
And (3) carrying out modeling simulation by using HFSS (high frequency Structure simulator), and after the simulation result reaches the standard, leading out the simulation model of the antenna and processing and manufacturing the antenna by using a printed circuit board process, wherein the plate is selected from FR4, the dielectric constant is 4.4, the loss tangent is 0.02 and the thickness is 0.8 mm. The used FR-4 dielectric plate has the advantages of low cost, simple structure and easy processing. On the premise of meeting the bandwidth requirement (covering the use range of China UHF-RFID frequency band), the antenna provided by the invention pays more attention to the strength and uniformity of magnetic field distribution in the antenna identification area, so that the reliable reading of the near field label is ensured, the magnetic field strength outside the identification area is smaller than an identification threshold value, and the label cannot be misread outside the identification area.
It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.
Claims (7)
1. A near-field radio frequency identification antenna with an electrically large-size identification area is characterized in that an antenna structure comprises a first loop antenna arranged on the periphery and a coupling loop antenna arranged in the first loop antenna, wherein the first loop antenna and the coupling loop antenna comprise a plurality of interdigital structures which are connected through a transmission line; the middle part of the bottom end of the first loop antenna is bent towards the coupling loop antenna, and a feed port is arranged at the bottom end of the first loop antenna.
2. A near field rfid antenna having an electrically large identification area as claimed in claim 1, wherein the interdigital structure comprises an upper block and a lower block coupled thereto, the upper block having at least one protrusion disposed downwardly, the protrusion extending into a recess of the lower block, the protrusion and recess having a gap.
3. A near field radio frequency identification antenna having an electrically large identification area according to claim 2, wherein the capacitance formed by the interdigital structure resonates with the inductance of the connected transmission line at a center frequency.
4. A near field radio frequency identification antenna having an electrically large identification area according to claim 2 or 3, wherein 4 interdigital structures are provided on each side of the coupled loop antenna.
5. A near field rfid antenna having an electrically large size identification area as claimed in claim 2 or 3, wherein the first loop antenna has 7 interdigital structures at the upper end, 10 interdigital structures at the bottom end, and 8 interdigital structures at the two side ends.
6. A near field rfid antenna having an electrically large identification area as claimed in claim 1 wherein the length of the bend at the bottom end of the first loop antenna is close to the length of the bottom end of the coupled loop antenna.
7. A near field RFID antenna having an electrically large identification area as claimed in claim 6 wherein 2 interdigital structures are provided on each side of the bend at the bottom end of the first loop antenna.
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| CN201810617989.9A CN108808247B (en) | 2018-06-15 | 2018-06-15 | Near field radio frequency identification antenna with electrically large size identification area |
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| CN201810617989.9A CN108808247B (en) | 2018-06-15 | 2018-06-15 | Near field radio frequency identification antenna with electrically large size identification area |
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| CN108808247B true CN108808247B (en) | 2020-03-20 |
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| CN110429386A (en) * | 2019-08-30 | 2019-11-08 | 安徽华米信息科技有限公司 | Smart machine |
| CN113408686B (en) * | 2021-07-20 | 2024-03-15 | 北京计算机技术及应用研究所 | Near field antenna board based on RFID (radio frequency identification) technology |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103151616A (en) * | 2013-01-23 | 2013-06-12 | 浙江大学 | Coupled feeding horizontal omni-directional annular radio frequency identification (RFID) label antenna |
| CN203134983U (en) * | 2013-01-23 | 2013-08-14 | 浙江大学 | A coupled feeding horizontal omnidirectional annular RFID label antenna |
| KR101703065B1 (en) * | 2015-10-27 | 2017-02-06 | 국방과학연구소 | An Isotropic Folded Split Ring Resonator Antenna for Radio Frequency Energy Harvesting |
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| KR20120099861A (en) * | 2011-03-02 | 2012-09-12 | 한국전자통신연구원 | Microstrip patch antenna using planar metamaterial and method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103151616A (en) * | 2013-01-23 | 2013-06-12 | 浙江大学 | Coupled feeding horizontal omni-directional annular radio frequency identification (RFID) label antenna |
| CN203134983U (en) * | 2013-01-23 | 2013-08-14 | 浙江大学 | A coupled feeding horizontal omnidirectional annular RFID label antenna |
| KR101703065B1 (en) * | 2015-10-27 | 2017-02-06 | 국방과학연구소 | An Isotropic Folded Split Ring Resonator Antenna for Radio Frequency Energy Harvesting |
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