CN109409156B - Antenna impedance adjusting method for UHF RFID tag - Google Patents

Antenna impedance adjusting method for UHF RFID tag Download PDF

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CN109409156B
CN109409156B CN201811283605.0A CN201811283605A CN109409156B CN 109409156 B CN109409156 B CN 109409156B CN 201811283605 A CN201811283605 A CN 201811283605A CN 109409156 B CN109409156 B CN 109409156B
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tag
antenna
chip
impedance
sensitivity
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CN109409156A (en
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沈红伟
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Sichuan Huada Hengxin Technology Co., Ltd.
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Huada Hengxin Technology Co ltd
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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/077—Constructional details, e.g. mounting of circuits in the carrier
    • G06K19/07749—Constructional details, e.g. mounting of circuits in the carrier the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/077—Constructional details, e.g. mounting of circuits in the carrier
    • G06K19/07745—Mounting details of integrated circuit chips
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
    • G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
    • G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
    • G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
    • G06K7/10316—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers
    • G06K7/10346—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves using at least one antenna particularly designed for interrogating the wireless record carriers the antenna being of the far field type, e.g. HF types or dipoles

Abstract

The invention discloses a tag antenna impedance adjusting method, which comprises the following steps: determining tag antenna impedance value ZtagDeviation of (2) to tag sensitivity StagThe influence of (a); forming a contour line of the sensitivity of the label; and according to the impedance value Z of the tag antennatagThe influence of the deviation on the tag sensitivity Stag and the contour line of the tag sensitivity determine the range of the impedance value of the tag antenna.

Description

Antenna impedance adjusting method for UHF RFID tag
Technical Field
The invention relates to the field of UHF RFID tag design, in particular to an antenna impedance adjusting method capable of improving the stability of mass production of UHF RFID tags.
Background
The RFID is a non-contact automatic identification technology, which automatically identifies a target object and obtains related data through a radio frequency signal, does not need manual intervention in identification work, and can work in various severe environments. The RFID technology can identify high-speed moving objects and can identify a plurality of electronic tags simultaneously, and the operation is quick and convenient. The UHF RFID technology is a non-contact automatic identification technology. UHF RFID technology is widely used in logistics, manufacturing, medical care, transportation, retail, defense, and the like. UHF RFID is divided into tags and readers. The label is composed of a label antenna and a label chip.
In the mass production process of UHF RFID tags, due to the deviation of the production process, the sensitivity of the tags has deviation, the stability is reduced, and the yield is reduced.
Therefore, how to improve the stability of mass production of UHF RFID tags is a difficult problem to be solved in the field.
Disclosure of Invention
The invention provides a method for enhancing the reflected power of an ultrahigh frequency RFID (radio frequency identification) tag, which comprises the following steps:
determining tag antenna impedance value ZtagDeviation of (2) to tag sensitivity StagThe influence of (a);
forming a contour line of the sensitivity of the label; and
according to the impedance value Z of the tag antennatagDeviation of (2) to tag sensitivity StagThe effect of (c) and the contour of the tag sensitivity determine the range of tag antenna impedance values.
In one embodiment of the invention, a tag antenna impedance value Z is determinedtagDeviation of (2) to tag sensitivity StagThe effects of (a) include:
sensitivity by tag StagSeparately evaluating the real part R and imaginary part X of the antenna impedance to form a vector gradient D, i.e.
Figure GDA0003247357960000011
The gradient D is a vector, and the place where the absolute value of the gradient D is large indicates the impedance value Z of the tag antennatagTo StagThe influence is large; the place with small absolute value of gradient D indicates the impedance value Z of the tag antennatagTo StagThe influence is small.
In one embodiment of the invention, the sensitivity S of the tagtagThe calculation formula of (a) is as follows:
Figure GDA0003247357960000021
wherein SchipIs chip sensitivity, GtagIs the tag antenna gain, ZtagIs the impedance value of the tag antenna, ZchipIs the impedance value of the tag chip, Zchip *Is ZchipConjugation of (1).
In one embodiment of the invention, determining the range of tag antenna impedance values includes making the real part of the antenna impedance value greater than the real part of the chip impedance conjugate.
In one embodiment of the invention, determining the range of tag antenna impedance values includes equating an imaginary part of the antenna impedance values to a conjugate imaginary part of the chip impedance values.
In one embodiment of the invention, the real part of the antenna impedance is the real part of the chip impedance conjugate plus Δ R, Δ R being in the range of 10 to 30, and the imaginary part of the antenna impedance is the imaginary part of the chip impedance conjugate plus or minus Δ X, Δ X being in the range of 0 to 10.
Drawings
To further clarify the above and other advantages and features of embodiments of the present invention, a more particular description of embodiments of the invention will be rendered by reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. In the drawings, the same or corresponding parts will be denoted by the same or similar reference numerals for clarity.
FIG. 1 shows a tag sensitivity gradient map.
Fig. 2 shows contour lines of the sensitivity of the tag.
FIG. 3 is an iso-gradient and contour plot of the sensitivity of the tag.
Fig. 4 is a flowchart illustrating an antenna impedance adjusting method for improving the stability of mass production of UHF RFID tags according to an embodiment of the present invention.
Fig. 5 shows a schematic diagram of the real part of the antenna impedance and the real part of the chip impedance.
FIG. 6 is a diagram illustrating the effect of the present invention.
Detailed Description
In the following description, the invention is described with reference to various embodiments. One skilled in the relevant art will recognize, however, that the embodiments may be practiced without one or more of the specific details, or with other alternative and/or additional methods, materials, or components. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of embodiments of the invention. Similarly, for purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the embodiments of the invention. However, the invention may be practiced without specific details. Further, it should be understood that the embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.
Reference in the specification to "one embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.
During the operation of the tag, the sensitivity of the tag is an important parameter for measuring the performance of the tag. In the mass production process, the tag sensitivity changes due to the deviation of the impedance value of the tag chip. The invention provides an antenna impedance adjusting method capable of improving the mass production stability of UHF RFID tags, and the method can enable the influence of the fluctuation of the antenna impedance on the sensitivity of the tags to be small and improve the mass production stability.
Firstly, the working principle of the antenna impedance adjusting method for improving the mass production stability of the UHF RFID label is introduced. The frequency band has an influence on chip impedance, antenna impedance, sensitivity gradient maps, sensitivity contour lines, and the like. For RFID chips and antennas, essentially all electrical parameters are a function of frequency. However, the RFID chip and antenna typically operate in one frequency band, and the following calculations assume that the tag is in the operating frequency band, and therefore ignore this parameter of operating frequency.
The main performance index of a tag is the sensitivity S of the tagtagSensitivity of the tag StagThe calculation formula of (a) is as follows:
Stag＝Schip-Gtag+Mloss [1]
wherein SchipIs chip sensitivity, GtagIs the tag antenna gain, MlossIs the match penalty.
Match loss MlossThe calculation formula of (a) is as follows:
Mloss＝-10ln(1-|Γ|2) [2]
wherein the reflection coefficient is:
Figure GDA0003247357960000031
wherein ZtagIs the impedance value of the tag antenna, ZchipIs the impedance value of the tag chip, Zchip *Is ZchipConjugation of (1).
The above equations [1] to [3] are combined as follows:
Figure GDA0003247357960000032
in mass production of labelsThe main deviation is determined by the impedance value Z of the tag antennatagIs caused by the deviation of (a). Therefore, the impedance value Z of the tag antenna needs to be studiedtagSensitivity of deviation of (2) to the label StagThe influence of (c).
Impedance value Z of tag antennatagIs a complex number having real and imaginary parts, i.e.
Ztag＝R+jX
Wherein R is the tag antenna impedance value ZtagX is the tag antenna impedance value ZtagThe imaginary part of (c).
So that the impedance value Z of the tag antennatagThe deviation of (b) includes the deviation of the real part R and the imaginary part X.
Impedance value Z of tag antennatagDeviation pair S oftagThe effect of (c) can be studied with a gradient D. By definition, the gradient D is determined by the tag sensitivity StagSeparately evaluating the real part R and imaginary part X of the antenna impedance to form a vector gradient D, i.e.
Figure GDA0003247357960000041
The gradient D is a vector, and the place where the absolute value of the gradient D is large indicates the impedance value Z of the tag antennatagTo StagThe influence is large, the mass production has large deviation, and the stability is low; the place with small absolute value of gradient D indicates the impedance value Z of the tag antennatagTo StagThe influence is little, and the deviation that the volume production appears is little, and stability is high.
FIG. 1 shows a tag sensitivity gradient map. The x-axis of FIG. 1 is the antenna impedance ZtagReal part, y-axis being the antenna impedance ZtagAn imaginary part. The gradient D is indicated by arrow a2, the arrow direction representing the direction of the gradient D and the arrow length representing the magnitude of the gradient D. The five-pointed star a1 represents the chip impedance conjugate Zchip *When the antenna impedance equals the chip impedance conjugate, there is a reflection coefficient of 0, thus MlossAt 0, the label sensitivity reaches the highest.
By connecting the points of equal tag sensitivity, a contour b2 of tag sensitivity can be drawn, as shown in fig. 2.
As can be seen from fig. 1 and 2:
a) at the point where the tag sensitivity is highest, the antenna impedance should be equal to the chip impedance conjugate.
b) The real part of the antenna impedance value is larger than the conjugate real part of the chip impedance, namely, an arrow representing the gradient value is smaller on the right side of the five-pointed star, and contour lines are sparse. Indicating if the antenna impedance falls in this region. The influence of the fluctuation of the antenna impedance on the sensitivity of the tag is small, and the stability of mass production is high.
c) The real part of the antenna impedance value is smaller than the conjugate real part of the chip impedance value, namely, the left side of the five-pointed star, the arrow representing the gradient value is large, and the contour lines are dense. Indicating if the antenna impedance falls in this region. The influence of the fluctuation of the antenna impedance on the sensitivity of the tag is large, and the stability of mass production is low.
d) The imaginary part of the antenna impedance value is larger than or smaller than the conjugate imaginary part of the chip impedance value, namely, arrows and contour lines representing gradient values are vertically symmetrical above and below the five-pointed star. It is stated that the imaginary part of the antenna impedance should be equal to the conjugate imaginary part of the chip impedance value.
As a result of mass production of the tags, the fluctuation of the real part and the imaginary part of the antenna inevitably occurs. The antenna impedance will consequently be distributed over an area, rather than a point. Therefore, if the center value of the antenna impedance is designed to be equal to the conjugate of the chip impedance, i.e., the antenna impedance appears at the position of the five-pointed star, it will inevitably occur that some antenna impedance appears in the unstable region on the left of the five-pointed star.
Therefore, to avoid this problem, the method of the present invention is implemented as follows:
the real part of the antenna impedance should be slightly larger than the chip impedance conjugate;
the imaginary part of the antenna impedance should be equal to the chip impedance conjugate;
i.e. the antenna impedance position, should be designed to a point to the right of the five-pointed star position. I.e., the dashed circle c4 in fig. 3. The dashed circle c4 is the stable region. For example, the real part of the antenna impedance is the real part of the chip impedance conjugate plus Δ R, which is in the range of 10 to 30, and the imaginary part of the antenna impedance is the imaginary part of the chip impedance conjugate plus or minus Δ X, which is in the range of 0 to 10.
Accordingly, the result of the present invention will be a deviation of the sensitivity of the tag from the maximum sensitivity, with some loss of sensitivity. However, it can be seen that the sensitivity changes slowly because the contour lines on the right side of the pentagram are sparse, and the loss of sensitivity is not significant.
Fig. 4 is a flowchart illustrating an antenna impedance adjusting method for improving the stability of mass production of UHF RFID tags according to an embodiment of the present invention.
First, in step 401, a tag antenna impedance value Z is determinedtagDeviation of (2) to tag sensitivity StagThe influence of (c). In particular, the sensitivity S of the tagtagThe calculation formula of (a) is as follows:
Figure GDA0003247357960000051
wherein ZtagIs the impedance value of the tag antenna, ZchipIs the impedance value of the tag chip, Zchip *Is ZchipConjugation of (1).
Impedance value Z of tag antennatagIs a complex number having real and imaginary parts, i.e.
Ztag＝R+jX
Wherein R is the tag antenna impedance value ZtagX is the tag antenna impedance value ZtagThe imaginary part of (c).
Sensitivity by tag StagSeparately evaluating the real part R and imaginary part X of the antenna impedance to form a vector gradient D, i.e.
Figure GDA0003247357960000052
Then, the points with the same label sensitivity are connected to form a contour line of the label sensitivity.
Next, at step 402, a range of antenna impedance values is determined based on the vector gradient D and the contour of the tag sensitivity. In particular, the tag sensitivity is highest when the antenna impedance should be equal to the chip impedance conjugate. When the real part of the antenna impedance value is larger than the conjugate real part of the chip impedance, namely on the right of the five-pointed star, an arrow representing the gradient value is small, and contour lines are sparse. Indicating if the antenna impedance falls in this region. The influence of the fluctuation of the antenna impedance on the sensitivity of the tag is small, and the stability of mass production is high. When the real part of the impedance value of the antenna is smaller than the conjugate real part of the impedance value of the chip, namely on the left side of the five-pointed star, the arrow representing the gradient value is large, and the contour lines are dense. Indicating if the antenna impedance falls in this region. The influence of the fluctuation of the antenna impedance on the sensitivity of the tag is large, and the stability of mass production is low. When the imaginary part of the antenna impedance value is greater than or less than the conjugate imaginary part of the chip impedance value, i.e., above and below the five-pointed star, the arrows and contours representing the gradient values are vertically symmetric. It is stated that the imaginary part of the antenna impedance should be equal to the conjugate imaginary part of the chip impedance value. For example, the real part of the antenna impedance is the real part of the chip impedance conjugate plus Δ R, which is in the range of 10 to 30, and the imaginary part of the antenna impedance is the imaginary part of the chip impedance conjugate plus or minus Δ X, which is in the range of 0 to 10.
In the embodiment of the invention, because the tag operates in a frequency band, the antenna impedance value should fall to the right of the conjugate of the chip impedance value in the operating frequency band. Fig. 5 is a schematic diagram showing the real part of the antenna impedance and the real part of the chip impedance, wherein the x-axis is frequency and the y-axis is the real part of the impedance. Curve d1 being ZchipCurve d2 is the real part of the designed antenna, 4000ohm |0.61 pF. As shown in FIG. 4, in the 860MHz-960MHz band, the real part of the antenna impedance value is larger than the real part of the chip impedance value.
The technical effect of the implementation of the invention is as shown in fig. 6, and in the working frequency band, the sensitivity test values of a large number of labels are basically overlapped, the fluctuation is small, and the stability is high. In the non-working frequency band, the sensitivity test values of a large number of labels cannot be superposed, the fluctuation is large, and the stability is low.
According to the method, the design target area of the antenna impedance is set, so that the stability of mass production of the tag is improved, and the method has certain advancement.
An embodiment of the invention is described in more detail below with reference to the accompanying drawings of the invention in conjunction with specific embodiments.
The chip impedance value is Zchip4000ohm |0.61 pF. At frequency point 920MHz, there is Zchip20-j282 ohm. Chip sensitivity SchipAntenna gain G of-16 dBmtagThe dipole antenna gain is taken to be 2.1dBi.
The real part value range of the antenna impedance value is from 0-140ohm, the imaginary part value range is from 200-340ohm, and the imaginary part value range and the real part value range are the same, so that the antenna impedance is traversed.
In fig. 1, the antenna impedance is traversed with the x-axis being the real part of the antenna impedance and the y-axis being the imaginary part of the antenna impedance. The five-pointed star a1 is the chip conjugate impedance position, Z chip *20+ j282 ohm. Arrow a2 is the gradient D, the size and direction of the arrow, i.e. the size and direction of the gradient D.
In fig. 2, the antenna impedance is traversed with the x-axis being the real part of the antenna impedance and the y-axis being the imaginary part of the antenna impedance. The five-pointed star b1 is the chip conjugate impedance position, Z chip *20+ j282 ohm. b2 is a contour of the sensitivity of the tag.
As can be seen from fig. 1 and 2, when the antenna impedance is less than 20ohm, the gradient increases, the contour lines are dense, and the range is unstable. And if the real part of the antenna impedance is more than 20ohm, the gradient is reduced, the contour lines are sparse, and the antenna is in a stable position.
In fig. 3, the antenna impedance is traversed with the x-axis being the real part of the antenna impedance and the y-axis being the imaginary part of the antenna impedance. The five-pointed star c1 is the chip conjugate impedance position, Z chip *20+ j282 ohm. c2 is a contour line, an arrow c3 is a gradient D, and a dashed circle c4 is a suggested range of antenna impedance, which is a stable region.
In designing the antenna, the antenna impedance value should be designed to be located at the position of the dashed line circle c4 in the stable range, the real part of the antenna impedance is the real part of the chip impedance conjugate plus Δ R, Δ R is in the range of 10 to 30, the imaginary part of the antenna impedance is the imaginary part of the chip impedance conjugate plus or minus Δ X, and Δ X is in the range of 0 to 10. Rather than the five star c1 position.
In fig. 5, the x-axis is frequency and the y-axis is the real part of impedance. Curve d1 being Zchip＝4000ohm|0.61pThe real part of F, curve d2 is the real part of the designed antenna.
It can be seen that the operating band is 860MHz-960MHz, and the curve d2 is larger than the curve d1, so that the position of this band on fig. 3 is located to the right of the five-pointed star c1, and substantially falls within the dashed circle c4, which is in accordance with the design expectation.
FIG. 6 is a diagram illustrating the effect of the present invention. In fig. 6, the x-axis is frequency and the y-axis is tag sensitivity test value. The multiple curves in fig. 6 are the tag sensitivity test values. It can be seen that the patent implementation effect is as follows: in the non-working frequency band, the dispersion of a plurality of curves is increased, and the stability is poor. In the working frequency band, a plurality of curves are basically overlapped, and the label shows good stability.
In conclusion, this embodiment proves that the method of the present invention can make mass production labels have good stability.
In some embodiments of the invention, the methods disclosed herein may be implemented by hardware means, software means, or any combination thereof. Examples of hardware devices may include processors, microprocessors, circuits, circuit elements (e.g., transistors, resistors, capacitors, inductors, and so forth), integrated circuits, Application Specific Integrated Circuits (ASIC), Programmable Logic Devices (PLD), Digital Signal Processors (DSP), Field Programmable Gate Array (FPGA), logic gates, registers, semiconductor device, chips, microchips, chip sets, and so forth.
Examples of software may include software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, functions, methods, procedures, software interfaces, Application Program Interfaces (API), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof.
Some embodiments may be implemented, for example, using a machine-readable storage medium or article. A storage medium may store an instruction or a set of instructions that, when executed by a machine, may cause the machine to perform a method and/or operations in accordance with the embodiments. Such a machine may include, for example, any suitable processing platform, computing device, processing device, computing system, processing system, computer, processor, or the like, and may be implemented using any suitable combination of hardware and/or software.
Embodiments may include a storage medium or a machine-readable article. For example, any suitable type of memory unit, memory device, memory article, memory medium, storage device, storage article, storage medium and/or storage unit may be included, such as, for example, memory, removable or non-removable media, erasable or non-erasable media, writeable or re-writeable media, digital or analog media, hard disk, floppy disk, compact disk read Only memory (CD-ROM), compact disk recordable (CD-R), compact disk Rewriteable (CD-RW), optical disk, magnetic media, magneto-optical media, removable memory cards or disks, various types of Digital Versatile Disk (DVD), a tape, a cassette, or the like. The instructions may include any suitable type of code, such as source code, assembly code, interpreted code, executable code, static code, dynamic code, encrypted code, and the like, implemented using any suitable high-level, low-level, object-oriented, visual, compiled and/or interpreted programming language.
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various combinations, modifications, and changes can be made thereto without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention disclosed herein should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims (2)

1. A method for adjusting antenna impedance of a tag includes:
determining tag antenna impedance value Ztag Deviation of (2) to tag sensitivity Stag The influence of (a);
forming a contour line of the sensitivity of the label; and
according to the impedance value Z of the tag antennatag Deviation of (2) to tag sensitivity Stag Shadow ofSounding and a contour line of the sensitivity of the tag, and determining the range of the impedance value of the tag antenna;
the determined tag antenna impedance value ZtagDeviation of (2) to tag sensitivity StagThe effects of (a) include:
sensitivity by tag StagSeparately evaluating the real part R and imaginary part X of the antenna impedance to form a vector gradient D, i.e.
Figure FDA0003247357950000011
Wherein the gradient D is a vector;
the contour line of the label sensitivity is obtained by connecting points with the same label sensitivity; sensitivity S of the labeltagThe calculation formula of (a) is as follows:
Figure FDA0003247357950000012
wherein SchipIs chip sensitivity, GtagIs the tag antenna gain, ZtagIs the impedance value of the tag antenna, ZchipIs the impedance value of the tag chip, Zchip *Is ZchipConjugation of (1);
the range of tag antenna impedance values includes:
the real part of the antenna impedance value is larger than the conjugate real part of the chip impedance; the real part of the antenna impedance is the real part of the chip impedance conjugate plus delta R; said Δ R is in the range of 10 to 30;
the imaginary part of the antenna impedance value is equal to the conjugate imaginary part of the chip impedance value; the imaginary part of the antenna impedance is the conjugate imaginary part of the chip impedance plus or minus delta X; the Δ X is in the range of 0 to 10.
2. A system for adjusting antenna impedance, comprising:
a memory storing machine executable instructions; and
a processor configured to perform the method of claim 1.
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