Dual-band radio frequency identification tag antenna for metal object

Abstract

A dual band radio frequency identification (RFID) tag antenna for mounting on a metal object includes a dielectric substrate having a first surface and a second surface opposite the first surface; the conductive layer is arranged on the first surface of the dielectric substrate and is used for being attached to the surface of the metal object; an integrated circuit mounted on the second surface of the dielectric substrate; an antenna structure formed on the second surface of the dielectric substrate, the antenna structure being configured to have a first resonance in a first frequency band and a second resonance in a second frequency band; a feed loop structure formed on the second surface of the dielectric substrate, the feed loop structure configured to electromagnetically connect the antenna structure to the integrated circuit; a first via pin penetrating the dielectric substrate, the first via pin electrically connecting a first point on the antenna structure with a corresponding first point on the conductive layer; and a second via pin passing through the dielectric substrate, the second via pin electrically connecting a second point on the antenna structure with a corresponding second point on the conductive layer.

Description

Technical Field

[0001] The present disclosure relates to radio frequency identification (RFID) tags, and more particularly to RFID tag antennas for mounting on metal objects. Background Art

[0002] Nowadays, the rapid development of radio frequency identification (RFID) technology has attracted widespread attention. Due to its long-distance recognition capability in the ultra-high frequency (UHF) band, RFID tags are widely used in supply chain management, inventory inspection, asset tracking, access control automation and other purposes.

[0003] However, many applications require RFID tags to be mounted on conductive metal objects such as motor vehicles, cylinders, containers, weapons, and equipment. When ordinary UHF tags are placed on metal surfaces, their reading distance will be severely reduced due to impedance mismatch, reduced radiation efficiency, and poor directivity. Therefore, so-called anti-metal tags must be specially designed to overcome such problems.

[0004] In the prior art, for the UHF RFID band, tags based on microstrip patch antennas with built-in ground planes have been proposed. However, this will make the antenna extremely large, with a resonant length close to one-quarter of the wavelength, making it difficult to install on small metal objects. In order to achieve miniaturization, although a variety of dipole-like folding tags have been designed, the size of the tag antenna is still large, and because such antennas are composed of multiple layers, the structure is weak. In certain special compact metal platforms such as metal cylinders and bearings, conformal tag antennas are required. Since the above-mentioned designs are large in size and unstable in structure, conformal design is difficult to achieve. In addition, in the past few decades, few dual-band UHF RFID anti-metal tag antennas have been reported. Summary of the invention

[0005] According to one aspect of the present disclosure, a dual-band RFID tag antenna for mounting on a metal object is provided. The dual-band RFID tag antenna includes: a dielectric substrate having a first surface and a second surface opposite to the first surface; a conductive layer provided on the first surface of the dielectric substrate, the conductive layer being used to be attached to the surface of the metal object; an integrated circuit mounted on the second surface of the dielectric substrate; an antenna structure formed on the second surface of the dielectric substrate, the antenna structure being configured to have a first resonance in a first frequency band and a second resonance in a second frequency band; a feed loop structure formed on the second surface of the dielectric substrate, the feed loop structure being configured to electromagnetically connect the antenna structure to the integrated circuit; a first via pin penetrating the dielectric substrate, the first via pin electrically connecting a first point on the antenna structure to a corresponding first point on the conductive layer; and a second via pin penetrating the dielectric substrate, the second via pin electrically connecting a second point on the antenna structure to a corresponding second point on the conductive layer.

[0006] The first resonance and the second resonance enable the dual-band RFID tag antenna to be used in different UHF band applications, such as being used in the 902-928 MHz US band and the 865-868 MHz EU band at the same time. In addition, by providing the conductive layer on the first surface of the dielectric substrate, the dual-band RFID tag antenna can be mounted on a metal object.

[0007] In one embodiment, the dielectric substrate is made of a flexible material, so that the dual-band RFID tag antenna can be installed on both planar metal objects and curved metal objects such as cylindrical bearings.

[0008] In one implementation, the first resonance is an omnidirectional resonance, and the second resonance is a directional resonance.

[0009] In one embodiment, the antenna structure comprises two antenna parts arranged in a dipole structure.

[0010] In one embodiment, each antenna portion includes a first arm portion and a second arm portion. The resonant length of each antenna portion may correspond to a length from an end of the first arm portion to an end of the second arm portion.

[0011] The end of the first arm of the first antenna portion may correspond to the first point on the antenna structure, and the end of the first arm of the second antenna portion may correspond to the second point on the antenna structure.

[0012] The second arm portion of each antenna portion may include a curved structure toward the non-peripheral portion of the second surface of the dielectric substrate, so that the overall size of the dual-band RFID tag antenna is not increased while the length of the second arm portion is increased.

[0013] In one embodiment, the dielectric substrate is rectangular. The first point on the antenna structure and the second point on the antenna structure may correspond to diagonally opposite corners of the dielectric substrate.

[0014] In one embodiment, the antenna structure includes a connecting portion disposed adjacent to the feed loop structure. The connecting portion may have a straight edge on a side facing the feed loop structure, and / or a stepped edge on a side facing away from the feed loop structure. The straight edge and the stepped edge are used for impedance matching. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Hereinafter, various embodiments of the present invention will be described by way of non-limiting examples with reference to the accompanying drawings. In the drawings:

[0016] Figure 1A is a cross-sectional view of a dual-band RFID tag antenna according to an embodiment of the present invention;

[0017] Figure 1B A three-dimensional diagram of a dual-band RFID tag antenna according to an embodiment of the present invention;

[0018] Figure 1C A top view of a dual-band RFID tag antenna according to an embodiment of the present invention;

[0019] Figure 2 Shown is the simulated power reflection coefficient of the dual-band RFID tag antenna according to an embodiment of the present invention;

[0020] Figure 3A and Figure 3B The simulated radiation patterns of the dual-band RFID tag antenna according to the embodiment of the present invention at 866 MHz and 920 MHz respectively;

[0021] Figure 4A and Figure 4B Shown are the simulated reading distances of the dual-band RFID tag antenna according to an embodiment of the present invention at 866 MHz and 920 MHz respectively;

[0022] Figure 5 The figure shows the resonant length of the dual-band RFID tag antenna according to the embodiment of the present invention;

[0023] Fig. 6A and Figure 6BThe figure shows the current distribution of the dual-band RFID tag antenna at 866 MHz and 920 MHz respectively according to the embodiment of the present invention;

[0024] Figure 7 Shown is the feed loop matching network;

[0025] Figure 8 Shown are the tag antenna impedance and the tag chip impedance;

[0026] Fig. 9 The present invention is a flowchart of a method for determining design parameters of an RFID tag antenna according to an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present disclosure provides an RFID tag antenna that can be used for two UHF band applications. For example, the present disclosure embodiment can operate in the following two bands: 865-868 MHz EU band; and 902-928 MHz US band. In such applications, the dual-band RFID tag antenna can be installed on metal platforms of different shapes and sizes, such as metal plates, metal cylinders, containers, bearings, and the like.

[0028] Figures 1A to 1C Shown is a dual-band RFID tag antenna according to an embodiment of the present invention. Figure 1A is a cross-sectional view, Figure 1B For a stereogram, Figure 1C This is a top view.

[0029] like Figure 1A As shown, the dual-band RFID tag antenna 100 includes a dielectric substrate 102. In order to enable the dual-band RFID tag antenna 100 to be used for both a flat metal platform and a curved metal platform, the dielectric substrate 102 is made of a flexible material. For example, the AD430 material of Arlon can be selected. In addition, any plastic material can be used for the dielectric substrate 102. In an exemplary embodiment, the size of the dielectric substrate 102 is 20 mm×30 mm×1.5 mm.

[0030] The dual-band RFID tag antenna 100 is manufactured by printed circuit board (PCB) technology. A lower surface conductive coating 104 is provided on the lower surface of the dielectric substrate 102. The lower surface conductive coating 104 covers the lower surface of the dielectric substrate 102. An upper surface conductive coating 106 is provided on the upper surface of the dielectric substrate 102, and the upper surface conductive coating forms an antenna and a feed loop structure described in further detail below. A via pin 108 passes through the dielectric substrate 102 to form a conductive connection between the lower surface conductive coating 104 and the upper surface conductive coating 106. An integrated circuit chip 110 is mounted on the upper surface of the dielectric substrate 102, and the chip is connected to a portion of the upper surface conductive coating 106. The integrated circuit 110 is an RFID tag integrated circuit, such as the Higgs 9 (AH-9) tag chip of Alien.

[0031] like Figure 1B As shown, the integrated circuit chip 110 is connected to a feed loop 140 disposed at the center of the upper surface of the dielectric substrate 102. The dual-band RFID tag antenna 100 is rectangular, and the via pins 108 are located at the diagonally opposite corners of the dual-band RFID tag antenna 100 (at Figure 1B The via pins 108 connect the upper surface conductive coating 106 to the lower surface conductive coating 104.

[0032] The upper surface conductive coating 106 forms a first antenna portion (or first antenna part) 120A, a second antenna portion (or second antenna part) 120B and a feed loop 140. Figure 1B As shown, the first antenna portion 120A has a first arm 122A and a second arm 124A, and the second arm 124A forms an overlapping section 123 extending along the inner path of the second antenna portion 120B. This overlapping structure increases the effective length of the first antenna portion 120A without increasing the overall size of the dual-band RFID tag antenna 100.

[0033] In order to reduce the size of the dual-band RFID tag antenna 100, two via pins 180 are used to connect the top and bottom conductive surfaces at the edge of the dielectric substrate, thereby changing the radiation form of the tag antenna from a dipole-like structure to a planar inverted F antenna (PIFA).

[0034] Figure 1C1 is a top view of the dual-band RFID tag antenna 100, which shows the layout of the upper surface conductive coating 106. The upper surface conductive coating 106 forms a dipole-like structure that is rotationally symmetrical around the feed loop 140 located at the center of the upper surface. The layout of the surface conductive coating 106 consists of the following three parts: a first antenna part 120A; a second antenna part 120B; and a feed loop 140. As described above, the first antenna part 120A and the second antenna part 120B are rotationally symmetrical 180 degrees around the feed loop 140 located at the center of the upper surface.

[0035] The first antenna portion 120A includes a first arm portion 122A, such as Figure 1C As shown, the arm extends over the entire width of the upper surface from the upper left corner of the upper surface connected to one of the via pins 108A to the lower left corner of the upper surface. The second arm 124A of the first antenna portion 120A is close to the right edge of the upper surface and is separated from the right edge of the upper surface by the second antenna portion 120B. The first arm 122A and the second arm 124A of the first antenna portion 120A are connected by the middle portion 126A of the first antenna portion 120A extending along the bottom edge of the upper surface. The connecting portion 130A of the first antenna portion 120A extends upward from the middle portion 126A of the first antenna portion 120A.

[0036] The connecting portion 130A extends along the adjacent feeding loop 140. The connecting portion 130A has a stepped edge 132A away from the feeding loop 140 and a straight edge 134A toward the feeding loop 140. The stepped edge 132A and the straight edge 134A are used for impedance matching.

[0037] Similarly, the second antenna portion 120B includes a first arm 122B extending from the lower right corner of the upper surface connected to another via pin 108A. The first arm 122B of the second antenna portion 120B extends from the lower right corner of the upper surface to the upper right corner. The second arm 124B of the second antenna portion 120B is close to the left edge of the upper surface and is separated from the left edge of the upper surface by the first arm 122A of the first antenna portion 120A. The first arm 122B and the second arm 124B of the second antenna portion 120B are connected by the middle portion 126B of the second antenna portion 120B extending along the top edge of the upper surface. The connecting portion 130B of the second antenna portion 120B extends downward from the middle portion 126B of the second antenna portion 120B. The connecting portion 130B extends along the adjacent feeding loop 140. The connecting portion 130B has a stepped edge 132B away from the feeding loop 140 and a straight edge 134B toward the feeding loop 140. The stepped edge 132B and the straight edge 134B are used for impedance matching.

[0038] By adjusting the shape of the opening formed between the connecting portions 130A and 130B and the second arm portions 124A and 124B, the input impedance of the tag antenna can be optimized. In this way, the impedance adjustment parameter can be increased to achieve good impedance matching.

[0039] The integrated circuit 110 is connected to the feeding loop 140 .

[0040] Figure 2 FIG. 2 shows the simulated power reflection coefficient of the dual-band RFID tag antenna according to an embodiment of the present invention. Figure 2 As shown, the antenna can generate two resonant frequencies of 866MHz and 920MHz. The tag antenna of this design has two bandwidths of power reflection coefficient (PRC) <-3.0dB at 911.2~915.8MHz and 918.5~921.5MHz.

[0041] Figure 3A and Figure 3B The figure shows the simulated radiation patterns of the dual-band RFID tag antenna of the embodiment of the present invention at 866MHz and 920MHz respectively. At 866MHz, the maximum gain in the visual axis direction is -2.73dBi, indicating that the tag antenna has directional radiation at this frequency. At 920MHz, although the maximum gain direction deviates 45° from the normal direction and the maximum gain is -6.8dBi, the tag antenna radiates omnidirectionally at this frequency.

[0042] Figure 4A and Figure 4B The figure shows the simulated reading distance of the dual-band RFID tag antenna of the embodiment of the present invention at 866MHz and 920MHz respectively. The tag antenna is placed on a 15cm×15cm flat ground, and the maximum reading distance at 866MHz is about 7.5m, and the maximum reading distance at 920MHz is about 6.0m.

[0043] Figure 5 FIG. 2 shows the resonant length of the dual-band RFID tag antenna according to an embodiment of the present invention. Figure 5 As shown, the resonant length is the length of the second antenna portion 120B (equal to the length of the first antenna portion 120A), which is the length from the end of the first arm portion 122B corresponding to one of the via pins 108 to the end of the second arm portion 124B.

[0044] Generally speaking, the resonant length of the antenna is about half the wavelength. "Short pin loading" means that by adding via pins 108 to the PIFA antenna structure, the effective length of the antenna can be effectively reduced. By reducing the resonant length to about a quarter of the wavelength, the resonant frequency of the antenna can reach the UHF frequency. This approach helps to maintain a suitable resonant frequency while reducing the overall size of the tag antenna. Accordingly, Figure 5 The resonant length 500 shown corresponds to one quarter of the resonant wavelength. Note that the overlapping segments of the second arm 124B can further miniaturize the dual-band RFID tag antenna.

[0045] Fig. 6A and Figure 6B Shown are the current distributions of the dual-band RFID tag antenna according to an embodiment of the present invention at 866 MHz and 920 MHz respectively.

[0046] like Fig. 6A As shown in the figure, when operating at 866MHz, the antenna has directional radiation. The basic principle of directional radiation tag antenna is to generate a current spatial distribution along the antenna element through a dipole current. By setting a reflector that works according to the principle of reflecting and focusing electromagnetic waves in a specific direction, the directivity and gain of the tag antenna can be improved. Among them, the reflector is used as a passive device to redirect and concentrate the radiated energy in the desired direction, thereby enhancing the antenna performance.

[0047] like Figure 6B As shown, the antenna is omnidirectional when operating at 920MHz. The basic principle of an omnidirectional tag antenna is to radiate in all directions by generating a balanced current distribution along the loop structure through the loop surface current. The loop antenna should be designed to resonate at the desired operating frequency. Specifically, resonance occurs when the electrical length of the loop corresponds to half the wavelength of the operating frequency or a multiple of half the wavelength. The loop tag antenna should exhibit a balanced surface current distribution along its circumference. This means that the amplitude and phase of the current flowing through different parts of the loop should be relatively consistent.

[0048] Figure 7 The feeding loop matching network is shown in Figure . Figure 7 As shown, the RFID tag antenna can be considered to be obtained by connecting the integrated circuit 110 chip to the radiating structure.

[0049] The loop matching is an impedance matching network that includes a feeding loop structure connected to the feeding line of the tag antenna. The values ​​of each component can be determined by the following equation:

[0050]

[0051]

[0052] Where L is the value of the inductor, C is the value of the capacitor, Cin and Cout are the input and output capacitances of the tag antenna, Zin is the required input impedance of the tag antenna, and f is the operating frequency. The actual values ​​of each component may need to be further adjusted or fine-tuned through simulation or experimental iteration.

[0053] Figure 8 The following table shows the tag antenna impedance and tag chip impedance. Figure 8 As shown, the tag antenna impedance Z a for:

[0054] Z a =R a +jX a

[0055] Tag chip impedance Z c for:

[0056] Z c =R c +jX c

[0057] To achieve maximum power transfer, the complex conjugates of these two impedances should be matched:

[0058] Z a =Z c *

[0059] Fig. 9 The present invention is a flowchart of a method for determining design parameters of an RFID tag antenna according to an embodiment of the present invention.

[0060] First, in step 1202, a tag chip is selected and the input impedance of the tag chip is obtained. In step 1204, an antenna type and a substrate material are selected.

[0061] Then, in step 1206, the parameters are optimized through research. This step may include: adjusting the length of the feed loop structure to adjust the input impedance of the antenna to match the impedance of the integrated circuit chip. In order to achieve maximum energy transmission between the tag and the chip, conjugate matching is used. Accordingly, when replacing the chip, the input impedance of the antenna needs to be adjusted at the same time. Fig. 9 As shown, in step 1208, it is checked whether the optimized parameters meet the impedance matching requirements. If the requirements are met, the design is completed in step 1210. If the requirements are not met, the method returns to step 1206 for further optimization.

[0062] As described above, the present disclosure provides a highly miniaturized dual-band UHF RFID tag antenna for mounting on small metal objects. In an exemplary embodiment, its total volume is only 20mm×30mm×1.5mm. The tag antenna can be used on both planar platforms and platforms that require conformal properties, such as metal cylinders and bearings.

[0063] The present disclosure also provides an extremely simple and compact folded dipole structure, which is designed for metal-resistant UHF tag antennas. The tag antenna of the present invention can achieve long-distance reading greater than 4 meters. The thickness of the tag antenna of the present invention is extremely thin, and it can be easily configured in a flexible and conformal manner on a partial curved surface.

[0064] Although exemplary embodiments have been described above, it will be appreciated by those skilled in the art that various modifications may be made to these embodiments within the scope and spirit of the present invention.

Claims

1. A dual-band radio frequency identification tag antenna for mounting on a metal object, characterized in that: The dual-band radio frequency identification tag antenna comprises: a dielectric substrate having a first surface and a second surface opposite the first surface; a conductive layer disposed on the first surface of the dielectric substrate, wherein the conductive layer is used to be attached to the surface of the metal object; an integrated circuit mounted on the second surface of the dielectric substrate; an antenna structure formed on the second surface of the dielectric substrate, wherein the antenna structure is configured to have a first resonance in a first frequency band and a second resonance in a second frequency band; a feed loop structure formed on the second surface of the dielectric substrate, wherein the feed loop structure is configured to electromagnetically couple the antenna structure to the integrated circuit; a first via pin extending through the dielectric substrate, wherein the first via pin electrically connects a first point on the antenna structure to a corresponding first point on the conductive layer; and A second via pin extends through the dielectric substrate, wherein the second via pin electrically connects a second point on the antenna structure to a corresponding second point on the conductive layer.

2. The dual-band RFID tag antenna according to claim 1, characterized in that: The dielectric substrate is formed of a flexible material.

3. The dual-band RFID tag antenna according to any one of the preceding claims, characterized in that: The first resonance is an omnidirectional resonance, and the second resonance is a directional resonance.

4. The dual-band RFID tag antenna according to any one of the preceding claims, characterized in that: The antenna structure comprises two antenna parts arranged in a dipole structure.

5. The dual-band RFID tag antenna according to claim 4, characterized in that: Each antenna portion includes a first arm portion and a second arm portion.

6. The dual-band RFID tag antenna according to claim 5, characterized in that: The resonant length of each antenna portion corresponds to the length from the end of the first arm portion to the end of the second arm portion.

7. The dual-band RFID tag antenna according to claim 6, characterized in that: The end of the first arm of the first antenna portion corresponds to the first point on the antenna structure, and the end of the first arm of the second antenna portion corresponds to the second point on the antenna structure.

8. The dual-band RFID tag antenna according to any one of claims 5 to 7, characterized in that: The second arm portion of each antenna portion includes a bent structure toward a non-peripheral portion of the second surface of the dielectric substrate.

9. The dual-band RFID tag antenna according to any one of the preceding claims, characterized in that: The dielectric substrate is rectangular.

10. The dual-band RFID tag antenna according to claim 9, characterized in that: The first point on the antenna structure and the second point on the antenna structure correspond to diagonally opposite corners of the dielectric substrate.

11. The dual-band RFID tag antenna according to any one of the preceding claims, characterized in that: The antenna structure includes a connecting portion disposed adjacent to the feed loop structure.

12. The dual-band RFID tag antenna according to claim 11, characterized in that: The connecting portion has a straight edge on a side facing the feeding loop structure.

13. The dual-band radio frequency identification tag antenna according to claim 11 or 12, characterized in that: The connecting portion has a stepped edge on a side facing away from the feeding loop structure.

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