An ultra-high frequency flexible anti-metal interference electronic tag

Abstract

The present application relates to an ultra-high frequency flexible anti-metal interference electronic tag, which belongs to the field of electronic tag technology, and includes a flexible substrate, a main antenna, a matching circuit, an RFID chip, a parasitic antenna, a variable capacitance diode, a coupling strength detection circuit, and a capacitance control circuit. The main antenna is arranged on a flexible substrate; the matching circuit is connected between the main antenna and the RFID chip; the two parasitic antennas are respectively located on both sides of the main antenna, and the closed ends of the parasitic antennas are connected through variable capacitance diodes; the coupling strength detection circuit is used to detect the coupling strength between the main antenna and the parasitic antenna, and output a control signal; the capacitance control circuit adjusts the capacitance of the variable capacitance diode according to the control signal. The present application improves the anti-interference performance of the electronic tag in a metal environment.

Description

Technical Field

[0001] The present application relates to the field of electronic tags, and in particular to an ultra-high frequency flexible anti-metal interference electronic tag. Background Art

[0002] With the continuous development of radio frequency identification (RFID) technology, ultra-high frequency RFID electronic tags have been widely used in warehousing logistics, asset management, vehicle management and other fields due to their advantages of long-distance identification, batch identification, and fast reading. However, in actual application environments, ultra-high frequency RFID electronic tags often need to be attached to the surfaces of various objects to be identified that contain metal materials.

[0003] Common UHF RFID electronic tags usually use electrode antennas made of rigid PCB materials, such as dipole antennas or microstrip patch antennas. These antennas have a certain radiation pattern and inherent impedance in free space.

[0004] When an electronic tag is attached to the surface of an object containing metal materials, electromagnetic coupling will occur between the antenna electrode and the metal surface, changing the current distribution of the antenna, causing the input impedance of the antenna to change, which will change the inherent radiation pattern of the antenna to a certain extent, causing the energy absorption and signal reflection characteristics of the tag to deteriorate, and significantly increase the reading blind area in certain directions. Utility Model Content

[0005] The present application provides an ultra-high frequency flexible anti-metal interference electronic tag for improving the anti-interference performance in a metal environment.

[0006] In the first aspect, the present application provides an ultra-high frequency flexible anti-metal interference electronic tag, comprising a flexible substrate; a main antenna arranged on the flexible substrate, the main antenna is a folded microstrip antenna structure, the operating frequency is an ultra-high frequency RFID frequency band of 860MHz~960MHz, and has a feeding point; at least two parasitic antennas arranged on both sides of the main antenna, the parasitic antenna is arranged in parallel with the main antenna and maintains a certain distance from the main antenna; at least two variable capacitance diodes connected to the parasitic antenna, each parasitic antenna is connected to one of the variable capacitance diodes, and the other end of the variable capacitance diode is connected to the ground plane on the flexible substrate; a coupling strength detection circuit arranged near the feeding point of the main antenna, used to detect the coupling strength between the main antenna and the surrounding environment. a capacitance control circuit arranged on the flexible substrate, the capacitance control circuit being connected to the coupling strength detection circuit and the variable capacitance diode respectively, and being used to adjust the capacitance value of the variable capacitance diode based on the electromagnetic coupling strength signal output by the coupling strength detection circuit; an RFID chip arranged at the feeding point of the main antenna; a matching circuit arranged between the RFID chip and the main antenna, and being used to optimize the impedance matching between the RFID chip and the main antenna; the RFID chip is electrically connected to the matching circuit through an assembly process, and the matching circuit and the main antenna are integrated on the flexible substrate; the parasitic antenna is not electrically connected to the main antenna, but is connected to the main antenna through electromagnetic coupling, and is used to adjust the radiation pattern of the main antenna.

[0007] By adopting the above technical scheme, on the one hand, by setting a flexible substrate and a folded microstrip antenna, the electronic tag has good flexibility and can be attached to an irregular surface; on the other hand, by setting a parasitic antenna and a variable capacitance diode, the capacitance value of the parasitic antenna can be dynamically adjusted according to the electromagnetic coupling strength of the environment in which the electronic tag is located, and then the radiation pattern of the main antenna is adjusted to reduce the reading blind area in certain directions. At the same time, by setting a coupling strength detection circuit near the main antenna feeding point, the electromagnetic coupling strength between the main antenna and the surrounding environment is detected in real time, and the detection result is fed back to the capacitance control circuit to achieve adaptive adjustment of the capacitance value of the parasitic antenna. In addition, by setting a matching circuit between the RFID chip and the main antenna, the impedance matching between the chip and the antenna can be optimized, and the energy absorption efficiency of the electronic tag can be improved. In summary, the ultra-high frequency flexible anti-metal interference electronic tag provided by the present application can automatically adapt to complex and changeable metal environments, overcome problems such as antenna impedance mismatch and increased radiation blind areas, and improve the anti-interference performance in metal environments.

[0008] In combination with some embodiments of the first aspect, in some embodiments, the coupling strength detection circuit specifically includes: an operational amplifier, whose inverting input terminal is connected to the feeding point of the main antenna through a first voltage-dividing resistor, and whose non-inverting input terminal is connected to the ground through a second voltage-dividing resistor; two Schottky diodes, whose anodes are respectively connected to the feeding point of the main antenna and the inverting input terminal of the operational amplifier, and whose cathodes are connected to each other and grounded; the output terminal of the operational amplifier is connected to the capacitance control circuit, which is used to convert the voltage change of the feeding point of the main antenna into a control signal.

[0009] By adopting the above technical solution, the coupling strength detection circuit uses an operational amplifier and a voltage divider resistor to convert the voltage change of the main antenna feeding point into a control signal related to the electromagnetic coupling strength. Among them, the inverting input terminal and the non-inverting input terminal are respectively connected to the feeding point and the ground through the voltage divider resistor, so that the operational amplifier works in the voltage follower mode, and the output voltage is equal to the feeding point voltage. At the same time, two Schottky diodes are respectively connected to the feeding point and the inverting terminal of the operational amplifier and grounded, which plays a limiting protection role to prevent excessive input voltage from damaging the operational amplifier. The output end of the operational amplifier is connected to the capacitance control circuit, and the detected coupling strength signal is transmitted to the control circuit to realize the dynamic adjustment of the capacitance value of the parasitic antenna. Through the above circuit structure, the coupling strength detection circuit can detect the change of the electromagnetic coupling strength between the main antenna and the surrounding environment in real time and accurately, and provide a reliable control signal for the adaptive tuning of the parasitic antenna, thereby optimizing the radiation performance of the main antenna and improving the reading stability of the electronic tag in a complex metal environment.

[0010] In combination with some embodiments of the first aspect, in some embodiments, the resistance ratio of the first voltage-dividing resistor to the second voltage-dividing resistor is 1:1.

[0011] By adopting the above technical solution, the resistance ratio of the first voltage-dividing resistor and the second voltage-dividing resistor is set to 1:1, which can ensure that the DC potentials of the in-phase input terminal and the inverting input terminal of the operational amplifier are equal, so that the operational amplifier works in the optimal linear range. In this way, the common-mode rejection ratio and voltage following accuracy of the operational amplifier can be improved, so that it can accurately convert the voltage change of the main antenna feeding point into a control signal related to the electromagnetic coupling strength, and reduce the detection error.

[0012] In combination with some embodiments of the first aspect, in some embodiments, the capacitance control circuit specifically includes: a limiting diode, whose anode is connected to the output end of the coupling strength detection circuit and whose cathode is connected to a control voltage output end; a voltage dividing resistor, one end of which is connected to the cathode of the limiting diode and the other end is grounded, and is used to convert the output voltage of the coupling strength detection circuit into a control voltage; the control voltage output ends are respectively connected to the control ends of the variable capacitance diode.

[0013] By adopting the above technical solution, the capacitance control circuit uses a limiting diode and a voltage divider resistor to convert the voltage signal output by the coupling strength detection circuit into a tuning voltage suitable for the control end of the variable capacitance diode. Among them, the anode of the limiting diode is connected to the output end of the detection circuit, and the cathode is connected to the control voltage output end and the voltage divider resistor, which plays an overvoltage protection role to prevent excessive detection voltage from damaging the variable capacitance diode. One end of the voltage divider resistor is connected to the cathode of the limiting diode, and the other end is grounded, which is used to convert the detection voltage into the control voltage range required by the variable capacitance diode. The control voltage output end is respectively connected to the control end of each variable capacitance diode, and the capacitance value of the parasitic antenna is dynamically adjusted according to the detected coupling strength signal, thereby optimizing the radiation pattern of the main antenna. Through the above circuit structure, the capacitance control circuit can adaptively adjust the capacitance value of the parasitic antenna according to the electromagnetic coupling strength detected in real time, so that the radiation performance of the main antenna is dynamically optimized, the reading blind area is reduced, and the applicability and reliability of the electronic tag in a complex metal environment are improved.

[0014] In combination with some embodiments of the first aspect, in some embodiments, the breakdown voltage of the limiting diode is not greater than the maximum control voltage of the variable capacitance diode; and the resistance of the voltage divider resistor is greater than 100 times the internal resistance of the variable capacitance diode.

[0015] By adopting the above technical solution, the breakdown voltage of the limiting diode is set to be no greater than the maximum control voltage of the variable capacitance diode, which can ensure that the control voltage output by the capacitance control circuit is always within the safe working range of the variable capacitance diode, preventing the device from being damaged by excessive voltage. At the same time, the resistance of the voltage divider resistor is set to be greater than 100 times the internal resistance of the variable capacitance diode, which can ensure that most of the detection voltage drops on the voltage divider resistor rather than inside the variable capacitance diode, reducing the voltage change at both ends of the variable capacitance diode and improving the accuracy and stability of capacitance control. In addition, the high-resistance voltage divider resistor also plays a current limiting role, preventing excessive current from damaging the variable capacitance diode.

[0016] In combination with some embodiments of the first aspect, in some embodiments, the folded microstrip antenna structure of the main antenna specifically includes: a rectangular radiating plate, whose length is approximately 1 / 4 of the working wavelength; a feeding line connecting one end of the radiating plate with the feeding point of the main antenna; two symmetrical folding arms, respectively connecting two corner points of the radiating plate and folding in the direction of the feeding line.

[0017] By adopting the above technical solution, the main antenna adopts a rectangular radiator with a length of about 1 / 4 of the working wavelength, which can obtain good radiation efficiency and gain in a relatively compact size. The feed line connects one end of the radiator to the feeding point to provide an excitation signal for the antenna. Two symmetrical folding arms connect the two corner points of the radiator respectively and fold toward the feed line to form a closed current loop. On the one hand, this folded microstrip antenna structure can extend the current path of the antenna, reduce the resonant frequency, and reduce the size of the antenna; on the other hand, the introduction of the folding arm increases the electrical length of the antenna, and improves the bandwidth and gain of the antenna. In addition, the symmetrical arrangement of the folding arms helps to improve the polarization characteristics and symmetry of the radiation pattern of the antenna, and reduce side lobes and cross-polarization radiation.

[0018] In combination with some embodiments of the first aspect, in some embodiments, the sum of the lengths of the two folded arms is approximately equal to half the length of the radiation plate, and the two folded arms are symmetrical about the feed line.

[0019] By adopting the above technical solution, the sum of the lengths of the two folded arms is set to half the length of the radiation sheet, which can increase the electrical length of the antenna while avoiding problems such as impedance discontinuity and high-order mode excitation caused by the folded arms being too long. At the same time, the two folded arms are arranged symmetrically about the feeder line, which helps to maintain the symmetry of the antenna radiation pattern, reduce cross-polarization radiation, and improve the polarization purity of the antenna. In addition, the connection position of the folded arm with the radiation sheet and the feeder line has also been optimized to avoid the problems of impedance mismatch and uneven current distribution, ensuring that the antenna has stable input impedance and radiation characteristics throughout the entire operating frequency band.

[0020] In combination with some embodiments of the first aspect, in some embodiments, the two parasitic antennas are respectively located on both sides of the main antenna, and their lengths are equal to that of the main antenna; and the distance between the parasitic antenna and the main antenna is no more than 5 mm.

[0021] By adopting the above technical solution, placing two parasitic antennas on both sides of the main antenna and keeping them at the same length as the main antenna, a current distribution similar to that of the main antenna can be induced in the parasitic antenna through the electromagnetic coupling effect, thereby forming a radiation contribution similar to that of the main antenna. At the same time, limiting the distance between the parasitic antenna and the main antenna to no more than 5 mm can ensure a sufficiently strong coupling effect, making the parasitic antenna more effective in regulating the radiation pattern of the main antenna. In practical applications, by changing the capacitance value of the parasitic antenna, the current phase relationship between the parasitic antenna and the main antenna can be dynamically adjusted, thereby changing the directivity of the main antenna radiation pattern in the horizontal plane and reducing the radiation blind area in certain directions. In addition, the introduction of the parasitic antenna also plays a role in balancing the current distribution of the main antenna, which helps to suppress the excitation of high-order modes and improve the polarization purity and pattern symmetry of the antenna.

[0022] In combination with some embodiments of the first aspect, in some embodiments, the matching circuit includes: a series inductor connected between the RFID chip and the feeding point of the main antenna; and a parallel capacitor connected in parallel at both ends of the RFID chip.

[0023] By adopting the above technical solution, the matching circuit adopts the structure of series inductance and parallel capacitor, which can achieve conjugate impedance matching between the RFID chip and the main antenna in a wider frequency band. Among them, the series inductance is connected between the chip and the main antenna feeding point to compensate for the capacitive impedance of the chip and reduce the resonant frequency; the parallel capacitor is connected in parallel at both ends of the chip to adjust the real part of the chip impedance and improve the impedance matching accuracy. Good impedance matching also helps to suppress reflection at the antenna port, reduce signal loss, and improve the radiation efficiency and communication distance of the electronic tag.

[0024] In combination with some embodiments of the first aspect, in some embodiments, the flexible substrate is made of PET material, whose relative dielectric constant is not greater than 3.5 and whose thickness is less than 0.1 mm; the coupling strength detection circuit, capacitance control circuit, RFID chip and matching circuit are integrated in the surrounding area of ​​the main antenna feeding point, and its area is not greater than 5 mm×5 mm.

[0025] By adopting the above technical solution and selecting PET material to make a flexible substrate, excellent mechanical and electrical properties can be obtained. PET material has good flexibility and bending resistance, and can withstand multiple bending deformations without permanent damage, so that the electronic tag can be reliably attached to various curved surfaces. At the same time, controlling the thickness of the PET substrate below 0.1mm can further improve the flexibility and attachment adaptability of the tag. In addition, PET material also has excellent electrical insulation properties and a low dielectric constant, and its relative dielectric constant is below 3.5. The lower dielectric constant helps to reduce the attenuation and phase shift of the antenna substrate to electromagnetic waves, improve the antenna radiation efficiency, and reduce dielectric loss. The coupling strength detection circuit, capacitance control circuit, RFID chip and matching circuit are highly integrated in the 5mm×5mm area around the main antenna feeding point, which can minimize parasitic effects and interconnection losses, simplify the tag structure, and improve assembly efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural diagram of an electronic tag in an embodiment of the present application.

[0027] Explanation of reference numerals: 100, flexible substrate; 101, main antenna; 102, matching circuit; 103, RFID chip; 104, parasitic antenna; 105, variable capacitance diode; 106, coupling strength detection circuit; 107, capacitance control circuit. DETAILED DESCRIPTION

[0028] Example 1

[0029] The present application embodiment discloses an ultra-high frequency flexible anti-metal interference electronic tag. Figure 1 The electronic tag comprises: a flexible substrate 100; a main antenna 101 arranged on the flexible substrate 100, the main antenna 101 is a folded microstrip antenna structure, the working frequency is an ultra-high frequency RFID band of 860MHz~960MHz, and has a feeding point; two parasitic antennas 104 arranged on both sides of the main antenna 101, the parasitic antenna 104 is arranged in parallel with the main antenna 101, and keeps a certain distance from the main antenna 101; two variable capacitance diodes 105 connected to the parasitic antenna 104, each parasitic antenna 104 is connected to a variable capacitance diode 105, and the other end of the variable capacitance diode 105 is connected to the ground plane on the flexible substrate 100; a coupling strength detection circuit 106 arranged near the feeding point of the main antenna 101, used to detect the electromagnetic coupling strength between the main antenna 101 and the surrounding environment; a coupling strength detection circuit 106 arranged on the flexible substrate A capacitance control circuit 107 on the base 100, the capacitance control circuit 107 is respectively connected to the coupling strength detection circuit 106 and the variable capacitance diode 105, and is used to adjust the capacitance value of the variable capacitance diode 105 based on the electromagnetic coupling strength signal output by the coupling strength detection circuit 106; an RFID chip 103 is arranged at the feeding point of the main antenna 101; a matching circuit 102 is arranged between the RFID chip 103 and the main antenna 101, and is used to optimize the impedance matching between the RFID chip 103 and the main antenna 101; the RFID chip 103 is electrically connected to the matching circuit 102 through an assembly process, and the matching circuit 102 and the main antenna 101 are integrated on the flexible base 100; the parasitic antenna 104 is not electrically connected to the main antenna 101, and is connected to the main antenna 101 through electromagnetic coupling, and is used to adjust the radiation pattern of the main antenna 101.

[0030] The implementation principle of an ultra-high frequency flexible anti-metal interference electronic tag in the embodiment of the present application is:

[0031] When the electronic tag is in a metal environment, the metal surface will reflect the electromagnetic waves radiated by the main antenna 101, generating an image field opposite to the radiation field of the main antenna 101, resulting in a decrease in the radiation performance of the main antenna 101. At this time, the coupling strength detection circuit 106 disposed near the feeding point of the main antenna 101 will detect a stronger electromagnetic coupling signal, because the reflected electromagnetic waves will generate a stronger coupling with the radiation field of the main antenna 101 at the feeding point.

[0032] The coupling strength detection circuit 106 transmits the detected electromagnetic coupling strength signal to the capacitance control circuit 107. According to the signal, the capacitance control circuit 107 increases the capacitance value of the variable capacitance diode 105 connected between the parasitic antenna 104 and the ground plane. The increase in the capacitance value of the variable capacitance diode 105 means that its impedance decreases, and the coupling between the parasitic antenna 104 and the ground plane is enhanced.

[0033] The parasitic antenna 104 is coupled to the main antenna 101 through an electromagnetic field. When the coupling between the parasitic antenna 104 and the ground plane is enhanced, more high-frequency current is coupled from the main antenna 101 to the parasitic antenna 104, so that the electromagnetic coupling between the parasitic antenna 104 and the main antenna 101 is also enhanced accordingly.

[0034] At this time, the parasitic antenna 104 is equivalent to a "copy" of the main antenna 101, and it forms a similar radiation field with the main antenna 101. Since the parasitic antenna 104 and the main antenna 101 are staggered in space, the radiation fields generated by them also have a phase difference in space. When the radiation fields of the two antennas are superimposed, constructive interference will occur in some directions, enhancing the radiation; while destructive interference will occur in other directions, weakening the radiation.

[0035] By properly designing the position and size of the parasitic antenna 104, its radiation field can be maximized in the direction canceling the metal reflection field, while being relatively small in other directions. In this way, the radiation field of the parasitic antenna 104 can offset the interference of the metal reflection field on the main antenna 101 to a certain extent, thereby improving the radiation performance of the main antenna 101.

[0036] In summary, the coupling strength detection circuit 106, the capacitance control circuit 107, the variable capacitance diode 105 and the parasitic antenna 104 work together to form an adaptive anti-metal interference feedback system. When the main antenna 101 is interfered by metal, the system can automatically adjust the electromagnetic coupling strength of the parasitic antenna 104, dynamically generate an "anti-interference" radiation field, offset the influence of the metal reflection field, maintain the radiation performance of the main antenna 101, and ensure the stable operation of the electronic tag in a metal environment.

[0037] Preferably, the coupling strength detection circuit 106 may specifically include: an operational amplifier, whose inverting input terminal is connected to the feeding point of the main antenna 101 through a first voltage-dividing resistor, and whose non-inverting input terminal is connected to the ground through a second voltage-dividing resistor; two Schottky diodes, whose anodes are respectively connected to the feeding point of the main antenna 101 and the inverting input terminal of the operational amplifier, and whose cathodes are connected to each other and grounded; the output terminal of the operational amplifier is connected to the capacitance control circuit 107, which is used to convert the voltage change of the feeding point of the main antenna 101 into a control signal.

[0038] For example, the operational amplifier can use the LM358 chip, which has the characteristics of low power consumption, high gain, rail-to-rail output, etc., and is suitable for use in low-power RFID circuits. The first and second voltage-dividing resistors can use 10kΩ chip resistors, and divide the voltage in a 1:1 ratio, which can linearly convert the voltage change at the feed point to the operational amplifier input. Two Schottky diodes can be connected in parallel using the HSMS-2820 model, which has the characteristics of low conduction voltage and fast switching speed, and can effectively detect the feed point signal.

[0039] Preferably, the resistance ratio of the first voltage-dividing resistor to the second voltage-dividing resistor is 1:1, which can make the voltage at the input terminal of the operational amplifier equal to half of the voltage at the feeding point, thereby not bringing excessive voltage to the chip and ensuring good detection sensitivity.

[0040] The capacitance control circuit 107 may specifically include: a limiting diode, whose anode is connected to the output end of the coupling strength detection circuit 106 and whose cathode is connected to a control voltage output end; a voltage dividing resistor, one end of which is connected to the cathode of the limiting diode and the other end is grounded, and is used to convert the output voltage of the coupling strength detection circuit 106 into a control voltage; and the control voltage output ends are respectively connected to the control ends of the variable capacitance diode 105.

[0041] For example, the limiting diode can be BAS16, whose breakdown voltage is 3.0V, matching the maximum control voltage of the subsequent variable capacitance diode. The voltage divider resistor can be 1MΩ chip resistor, whose resistance is much larger than the forward resistance of the diode, ensuring the linear adjustment range of the control voltage. The variable capacitance diode can be BB833, whose capacitance value is continuously adjustable between 0.5pF and 6.5pF, and whose quality factor is as high as 3000, which is particularly suitable for high-frequency antenna tuning applications.

[0042] Preferably, the breakdown voltage of the limiting diode is not greater than the maximum control voltage of the variable capacitance diode 105; the resistance of the voltage divider resistor is greater than 100 times the internal resistance of the variable capacitance diode 105, which can ensure the stability and adjustment accuracy of the control voltage.

[0043] The main antenna 101 adopts a folded microstrip antenna structure, specifically including: a rectangular radiation plate, whose length is about 1 / 4 of the working wavelength; a feed line connecting one end of the radiation plate and the feeding point of the main antenna 101; two symmetrical folding arms, respectively connecting the two corner points of the radiation plate and folding in the direction of the feed line.

[0044] For example, if the operating frequency is 920MHz, the corresponding free space wavelength is about 326mm. The length of the radiator can be 81mm and the width can be 3mm. The length of the two folded arms is 20mm and the width is the same as the radiator. They are symmetrical about the center of the feed line and folded inward by 15mm. The width of the feed line can be designed to be 1mm and lead out from the bottom of the radiator. The above dimensions can make the input impedance of the antenna in the air close to 50Ω and maintain good impedance matching characteristics in a wider frequency band.

[0045] Preferably, the sum of the lengths of the two folded arms is approximately equal to half the length of the radiation sheet, and the two folded arms are symmetrical about the feed line, which helps to improve the radiation efficiency of the antenna and increase the bandwidth. The two parasitic antennas 104 are respectively located on both sides of the main antenna 101, and their lengths are equal to the length of the main antenna 101; the distance between the parasitic antenna 104 and the main antenna 101 is not greater than 5 mm.

[0046] For example, the parasitic antenna 104 can adopt the same folded microstrip structure as the main antenna 101, and its size parameters are exactly the same as those of the main antenna. The two parasitic antennas are placed on both sides of the main antenna, and the spacing can be set to 2mm, which can produce appropriate coupling strength without taking up too much space. The open end of the parasitic antenna faces the feeding end of the main antenna, and the closed end is connected to the variable capacitor, which can form a good current distribution.

[0047] Preferably, the matching circuit 102 includes: a series inductor connected between the RFID chip 103 and the feeding point of the main antenna 101; and a parallel capacitor connected in parallel across the RFID chip 103.

[0048] For example, the RFID chip can use the MonzaR6 chip, which has an input impedance of about 13-j122Ω at 920MHz. To achieve conjugate matching, a 1.2nH 0402 high-frequency chip inductor can be used as a series inductor, and a 0.6pF 0201 high-frequency chip capacitor can be used as a parallel capacitor. Under such matching conditions, the electronic tag can obtain a reflection coefficient below -15dB, a receiving sensitivity of up to -20dBm, and a reading distance of more than 10m.

[0049] Preferably, the flexible substrate 100 is made of PET material, whose relative dielectric constant is not greater than 3.5 and whose thickness is less than 0.1 mm; the coupling strength detection circuit 106, the capacitance control circuit 107, the RFID chip 103 and the matching circuit 102 are integrated in the surrounding area of ​​the feeding point of the main antenna 101, and the area thereof is not greater than 5 mm×5 mm.

[0050] For example, the flexible substrate 100 can be made of Melinex ST506 PET film, which has a relative dielectric constant of 3.0, a dielectric loss tangent of 0.002, and a thickness of only 50 μm, and can be used to make high-performance flexible antennas and circuits. The LGA packaged integrated circuit chip can highly integrate the coupling strength detection circuit 106, the capacitance control circuit 107, and the RFID chip 103 in a 3mm×3mm package, and then use the pads in the package to connect the matching circuit 102 to the antenna feeding point. This highly integrated design can control the overall size of the electronic tag within 40mm×10mm×0.1mm.

[0051] The coupling strength detection circuit 106 uses a voltage-dividing resistor and an operational amplifier to convert the change in the voltage at the feeding point of the main antenna 101 into a control signal output. When there is metal interference, the voltage at the feeding point will increase, and the coupling strength detection circuit 106 outputs a higher control signal. The capacitance control circuit 107 converts the control signal into a control voltage of 0~3V through a limiting diode and a voltage-dividing resistor, and applies it to the variable capacitance diode 105. The higher the control voltage, the greater the capacitance value of the variable capacitance diode 105, the stronger the coupling between the parasitic antenna 104 and the ground, and the stronger the electromagnetic coupling between the parasitic antenna 104 and the main antenna 101. The enhanced parasitic antenna 104 is equivalent to a "copy" of the main antenna 101, and its radiation field can offset part of the metal reflection interference, thereby improving the radiation performance of the main antenna 101. When there is no metal interference, the voltage at the feeding point is low, the capacitance value of the variable capacitance diode 105 is small, and the parasitic antenna 104 has less influence on the main antenna 101. Therefore, this embodiment can effectively suppress the influence of the metal environment on the performance of the electronic tag by detecting the interference degree of the main antenna 101 and adaptively adjusting the electromagnetic coupling strength of the parasitic antenna 104.

[0052] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. An ultra-high frequency flexible anti-metal interference electronic tag, characterized in that: include a flexible substrate; A main antenna disposed on the flexible substrate, the main antenna being a folded microstrip antenna structure, operating at an ultra-high frequency RFID band of 860 MHz to 960 MHz, and having a feeding point; At least two parasitic antennas are arranged on both sides of the main antenna, wherein the parasitic antennas are arranged in parallel with the main antenna and keep a certain distance from the main antenna; at least two variable capacitance diodes connected to the parasitic antennas, each parasitic antenna being connected to one variable capacitance diode, and the other end of the variable capacitance diode being connected to a ground plane on the flexible substrate; A coupling strength detection circuit arranged near the feeding point of the main antenna, used for detecting the electromagnetic coupling strength between the main antenna and the surrounding environment; a capacitance control circuit disposed on the flexible substrate, the capacitance control circuit being connected to the coupling strength detection circuit and the variable capacitance diode, respectively, and being used to adjust the capacitance value of the variable capacitance diode based on the electromagnetic coupling strength signal output by the coupling strength detection circuit; an RFID chip disposed at a feed point of the main antenna; a matching circuit disposed between the RFID chip and the main antenna, for optimizing impedance matching between the RFID chip and the main antenna; The RFID chip is electrically connected to the matching circuit through an assembly process, and the matching circuit and the main antenna are integrated on the flexible substrate; The parasitic antenna is not electrically connected to the main antenna, but is connected to the main antenna by electromagnetic coupling, and is used to adjust the radiation pattern of the main antenna.

2. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 1 is characterized in that: The coupling strength detection circuit specifically comprises: an operational amplifier, whose inverting input terminal is connected to the feeding point of the main antenna through a first voltage-dividing resistor, and whose non-inverting input terminal is connected to the ground through a second voltage-dividing resistor; Two Schottky diodes, whose anodes are connected to the feeding point of the main antenna and the inverting input terminal of the operational amplifier respectively, and whose cathodes are connected to each other and grounded; The output end of the operational amplifier is connected to the capacitance control circuit, and is used to convert the voltage change of the main antenna feeding point into a control signal.

3. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 2 is characterized in that: The resistance ratio of the first voltage-dividing resistor to the second voltage-dividing resistor is 1:

1.

4. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 1 is characterized in that: The capacitance control circuit specifically comprises: a limiting diode, an anode of which is connected to the output end of the coupling strength detection circuit, and a cathode of which is connected to a control voltage output end; a voltage-dividing resistor, one end of which is connected to the cathode of the limiting diode and the other end is grounded, and is used to convert the output voltage of the coupling strength detection circuit into a control voltage; The control voltage output terminals are respectively connected to the control terminals of the variable capacitance diodes.

5. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 4 is characterized in that: The breakdown voltage of the limiting diode is not greater than the maximum control voltage of the variable capacitance diode; and the resistance value of the voltage dividing resistor is greater than 100 times the internal resistance of the variable capacitance diode.

6. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 1 is characterized in that: The folded microstrip antenna structure of the main antenna specifically includes: A rectangular radiator whose length is about 1 / 4 of the operating wavelength; a feed line connecting one end of the radiation sheet and a feed point of the main antenna; Two symmetrical folding arms are respectively connected to two corner points of the radiation sheet and are folded toward the direction of the feed line.

7. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 6 is characterized in that: The sum of the lengths of the two folded arms is approximately equal to half the length of the radiation sheet, and the two folded arms are symmetrical about the feeding line.

8. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 1 is characterized in that: The two parasitic antennas are respectively located on both sides of the main antenna, and their lengths are equal to that of the main antenna; and the distance between the parasitic antenna and the main antenna is no greater than 5 mm.

9. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 1, characterized in that: The matching circuit comprises: a series inductor connected between the RFID chip and a feed point of the main antenna; A parallel capacitor is connected in parallel at both ends of the RFID chip.

10. The ultra-high frequency flexible anti-metal interference electronic tag according to claim 9, characterized in that: The flexible substrate is made of PET material, with a relative dielectric constant of no more than 3.5 and a thickness of less than 0.1 mm; the coupling strength detection circuit, capacitance control circuit, RFID chip and matching circuit are integrated in the surrounding area of ​​the main antenna feeding point, with an area of ​​no more than 5 mm×5 mm.

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