CN103020557B - A kind of centreless RFID tag and recognition methods thereof - Google Patents

Abstract

The invention relates to the design of radio frequency identification tags, in particular to a coreless radio frequency identification tag based on space angle information coding. The tags consist of radiating elements with spatial angular properties, such as strip or V-shaped structures. The identification of tag angle information is realized by measuring the back-scattered electric field in the horizontal and vertical polarization directions. In the process of tag identification, the complex scattering field is also used to remove the interference of environmental noise, which can improve the tag identification effect. The structure of the tag is simple, and the manufacturing cost is low; when the tag is working, it occupies a narrow frequency band, which greatly improves the utilization rate of the spectrum, thereby reducing the cost of the entire radio frequency identification system.

Description

A coreless radio frequency identification tag and its identification method

technical field

The invention relates to the technical field of radio frequency identification, in particular to a coreless radio frequency identification tag based on spatial angle information coding and an identification method thereof.

Background technique

Radio Frequency Identification Technology RFID (Radio Frequency Identification) is a technology that uses radio frequency waves for wireless data acquisition. It is one of the most popular intelligent identification technologies and one of the core technologies of the Internet of Things that has attracted great attention from the whole society. Logistics, retail and other fields will have broad application prospects. But the high price of RFID tags limits its application. The high cost of the label is mainly caused by the cost of the chip and packaging. The emerging coreless RFID tags in passive tags provide a solution for reducing the cost of electronic tags. For this reason, the coreless radio frequency identification tag has become a hotspot of current research.

Scholars at home and abroad have done a lot of research work on coreless electronic tags. The current coreless RFID tags can be divided into three categories: time-domain reflection-based, spectrum-based and amplitude/phase-based backscattering . At present, the main problems of coreless RFID tags are: the number of codeable bits of coreless RFID tags based on time domain reflection is limited and the reader is required to have a high-speed RF front end. In addition, the increase in delay will make the receiving time The amplitude of the domain signal becomes smaller, which brings difficulties to the detection; the coreless RFID tag based on the frequency domain signal is essentially a scalar measurement method, which is sensitive to multipath propagation and interference, and it is difficult to achieve large-capacity coding, and most of them use Ultra-wideband systems have low spectrum utilization and high reader system costs; coreless RFID tags based on amplitude/phase backscatter modulation are sensitive to the polarization direction of the reader antenna or the placement angle of the tag. When the direction changes, bit errors will occur, or even no recognition at all.

Contents of the invention

The object of the present invention is to design a coreless radio frequency identification tag which saves frequency spectrum resources and is low cost.

The object of the present invention is achieved through the following measures:

A coreless radio frequency identification tag is composed of a medium and a radiation unit. The radiation unit is a strip patch, which forms an angle α with the polarization direction of the excitation wave, and 0°≤α<180°. The resonant frequency of the tag is determined by the length of the strip patch.

An identification method for a coreless radio frequency identification tag:

1. In the case of no label, the S ₂₁ in the horizontal and vertical directions of the measurement environment is denoted as S _21-XB and S _21-YB respectively;

2. Place the identified label, measure the S ₂₁ of the identified label in the horizontal and vertical directions, denoted as S _21-XT and S _21-YT respectively;

3. The S ₂₁ of the identified tag in the horizontal and vertical directions and the S ₂₁ of the environment in the horizontal and vertical directions are respectively carried out vector subtraction according to formula (1) (2) to remove the interference of environmental noise;

S _21-X =S _21-XT -S _21-XB (1)

S _21-Y =S _21-YT -S _21-YB (2)

4. Judging whether α is an acute angle or an obtuse angle according to the phase relationship between S _21-X and S _21-Y : both are in phase, α is an acute angle, and both are in opposite phase, α is an obtuse angle;

5. Obtain the angle α according to the formula (3) or (4) at the resonant frequency, so as to identify the label,

α=180°×arctg(|S _21-Y |/|S _21-X |)/π(α<90°)(3)

α=180°–180°×arctg(|S _21-Y |/|S _21-X |)/π(α>90°) (4).

A coreless radio frequency identification tag, which is composed of a medium and a radiation unit. The radiation unit itself has obvious spatial angle characteristics and is a V-shaped patch composed of two arms of the same size, one of which is a fixed arm. Consistent with the polarization direction of the excitation wave, the other arm is a rotating arm, forming an angle α with the fixed arm, 0°<α≤180°, preferably 60°≤α≤180°. The resonant frequency of the tag is determined by the arm length of the V-shaped patch.

An identification method for a coreless radio frequency identification tag:

1. In the case of no label, the S ₂₁ in the horizontal and vertical directions of the measurement environment is denoted as S _21-XB and S _21-YB respectively;

2. Place the identified label, measure the S ₂₁ of the identified label in the horizontal and vertical directions, denoted as S _21-XT and S _21-YT respectively;

3. Carry out vector subtraction between the S ₂₁ of the identified tag in the horizontal and vertical directions and the S ₂₁ of the environment in the horizontal and vertical directions according to formula (1) (2) to remove the interference of environmental noise;

4. Select the tag with a 90° angle between the fixed arm and the rotating arm as the reference tag, measure the S ₂₁ of the reference tag in the horizontal direction, expressed as S _21-XR , and perform environmental noise removal processing, as shown in formula (5);

S _21-XR '＝S _21-XR -S _21-XB (5)

5. Judging whether α is an acute angle or an obtuse angle according to the size comparison of the S ₂₁ of the identified label and the reference label in the horizontal direction: if |S _21-X |<|S _21-XR ′|, then α<90°; if |S _21-X |>|S _21-XR ′|, then α>90°;

6. According to the result of 5, choose formula (6) or ( ₇ ), the magnitude |S _{21 - X} | _XR ′| is subtracted to remove the effect of the fixed arm;

|S _21-X ′|=|S _21-XR ′|-|S _21-X |(α<90°)(6)

|S _21-X ′|=|S _21-X |-|S _21-XR ′|(α>90°)(7)

7. Obtain the angle α according to the formula (8) or (9) on the resonant frequency, so as to identify the label,

α=180°×arctg(|S _21-Y |/|S _21-X ′|)/π(α<90°)(8)

α=180°-180°×arctg(|S _21-Y |/|S _21-X ′|)/π(α>90°) (9).

The coreless radio frequency identification tag based on spatial angle information coding according to the present invention adopts a radiation unit with angle characteristics, and utilizes backscattering electric fields in two polarization directions, horizontal and vertical, to identify angles. The tag is not only easy to manufacture and low in cost, but also because tags of the same length occupy the same frequency band under different encoding states, the frequency band occupied by the tag is very narrow, which improves the spectrum utilization and reduces the frequency of the entire RFID system. Cost; the tag also uses a complex scattering field to remove the interference of environmental noise and improve the identification effect of the tag, so the practicability of the tag is extremely high.

Description of drawings

Fig. 1 is the structural representation of bar label of the present invention;

Fig. 2 is the structural representation of V-shaped label of the present invention;

Fig. 3 is a schematic diagram of measuring environment S ₂₁ in the horizontal direction;

Fig. 4 is a schematic diagram of measuring environment S ₂₁ in the vertical direction;

Fig. 5 is a schematic diagram of measuring reference label S ₂₁ in the horizontal direction;

Fig. 6 is a schematic diagram of measuring the S ₂₁ of the identified tag in the horizontal direction;

Fig. ₇ is a schematic diagram of measuring the S21 of the identified tag in the vertical direction.

Detailed ways

The present invention is described in more detail below in conjunction with accompanying drawing example:

Fig. 1 is a specific embodiment of the present invention - a structural schematic diagram of a bar label. The label has a single-layer structure, and its radiation unit is a 60×2mm ² strip patch. The medium is Rogers 4350 (dielectric constant 3.43~3.53, average 3.48), and the medium thickness is 0.8mm. The resonant frequency of the tag is determined by the length of the strip patch. The angle between the strip patch and the polarization direction of the excitation wave is α, and the angle information α is used as the coded information of the label.

A linearly polarized plane wave in the horizontal direction is vertically incident on the label, and the component Exs in the horizontal direction and the component Ey _s in the vertical direction of the backscattered electric field are respectively shown in the formula (10) (11), where k is the proportionality coefficient, and E _i is the incident field strength.

Ex _s =k×E _i ×cosα×cosα(10)

Ey _s =k×E _i ×cosα×sinα(11)

It can be seen that the horizontal component Ex _s and the vertical component Ey _s of the backscattering electric field are respectively proportional to cosα cosα and cosα sinα, then the ratio Ey _s /Ex _s of these two components of the backscattering field is equal to tgα, as shown in the formula ( 12) as shown.

Ey _s /Ex _s =tgα(12)

According to the above theoretical analysis, according to the vertical and horizontal components of the backscattered electric field of the tag, the angle α between the strip patch on the tag and the polarization direction of the excitation wave can be obtained, that is, the tag can be identified. Table 1 shows the simulation results of the above bar labels using CST2011.

Table 1 Simulation results of strip patch labels

The angle α between the strip patch and the horizontal direction 0° 15° 30° 45° 60° 75° 105° 120° 135° 150° 165° Resonant frequency/GHz 1.95 1.95 1.95 1.95 1.95 1.95 1.95 1.95 1.95 1.95 1.95 Recognition angle α'/° 0.000015 15.12 30.12 44.97 59.67 73.03 106.97 120.33 135.03 149.88 164.88 Error/° 0.000015 0.12 0.12 0.03 0.33 1.97 1.97 0.33 0.03 0.12 0.12

Fig. 2 is another specific embodiment of the present invention—a schematic structural view of a V-shaped label. The tag is a single-layer structure, and its radiating unit adopts a V-shaped patch with obvious angle characteristics. One arm is fixed and parallel to the polarization direction of the excitation wave. In the x direction, the other arm rotates, and the distance between the fixed arm and the The included angle is α, and the size of the two arms is the same, both are 30×2mm ² . The angle α between the rotating arm and the fixed arm is used as the coded information of the tag. The resonant frequency of the tag is determined by the length of the two arms. The backscatter electric field generated by the fixed arm is mainly in the horizontal direction, while the rotating arm will generate scattered fields in both horizontal and vertical directions. The scattered fields in these two directions are proportional to cosα and sinα respectively. If the electric field generated by the fixed arm can be removed For the scattered field, the angle α can be obtained by the ratio of the scattered field in two directions generated by the rotating arm.

When actually identifying tags, we choose the V-shaped tag with α of 90° as the reference tag to remove the scattered field generated by the fixed arm. The polarization directions are perpendicular to each other, so the part of the horizontal component of the scattered field produced by the rotating arm is very small. If it is ignored, it can be considered that the horizontal component of the label's scattered field is all produced by the fixed arm. In addition, by analyzing the current direction when the V-shaped patch resonates, it can also be found that when α is less than 90°, the direction of the horizontal component of the scattering field of the fixed arm and the rotating arm is opposite, and the scattering field of the rotating arm and the fixed arm cancels out Part; when α is greater than 90°, the two directions are the same, and the scattering fields of the rotating arm and the fixed arm will be superimposed. Therefore, for V-shaped tags, the formula for identifying the angle α of the V-shaped patch needs to be modified according to whether α is acute or obtuse, as

Ey _s-tag /(Ex _s-tag90° -Ex _s-tag )=tgα(α<90°)(13)

Ey _s-tag /(Ex _s-tag -Ex _s-tag90° )=tg(180°-α)(α>90°)(14)

Where Ex _s-tag and Ey _s-tag are the horizontal and vertical components of the backscattered electric field of the V-shaped tag, respectively, and Ex _s-tag90° is the horizontal component of the backscattered electric field of the 90° reference tag. Table 2 shows the simulation results of the above-mentioned V-shaped tags using CST2011.

Table 2 Simulation results of V-shaped patch labels

label name label 1 label 2 label 3 label 4 label 5 label 6 label 7 label 8 label 9 V-shape angle α 60° 75° 90° 105° 120° 135° 150° 165° 180° Resonant frequency/GHz 2.66 2.41 2.31 2.31 2.31 2.31 2.31 2.31 2.31 Recognition degree α'/° 64.21 76.33 88.75 108.41 122.52 136.45 151.06 165.65 180.00 Error/° 4.21 1.33 1.25 3.41 2.52 1.45 1.06 0.65 0

3-7 are block diagrams of a system for measuring V-shaped tags, the second embodiment of the present invention. In order to verify the practicability of the label, the measurement was not carried out in a dark room, but in a natural environment. Since the tag identification designed by the present invention utilizes the backscattered electric fields in the horizontal and vertical directions to obtain the angle, the vector network analyzer can be used as the reader, and the S ₂₁ measured in the horizontal and vertical directions can be utilized. to get angle information. The horn antenna 1 connected to the port 1 of the vector network analyzer is used as the transmitting antenna of the reader to transmit horizontally polarized plane waves, and the horn antenna 2 connected to the port 2 is used as the receiving antenna of the reader to receive the reverse complex scattering field of the tag Signal. Both speakers are exactly the same. The identification steps of the V-shaped label are as follows:

1. Set the vector network analyzer accordingly: set the transmit power to -10dBm, set the frequency sweep range to 1-3GHz, set the frequency sweep points to 201 points, and set the frequency interval to 10MHz;

2. Measure the S ₂₁ of the environment: place the speaker 1 vertically without placing the label, and place the speaker 2 vertically, as shown in Figure 3, and measure the S ₂₁ measured at this time as the horizontal component S of the S ₂₁ of the environment _21-XB ; then the speaker 1 is placed vertically, and the speaker 2 is placed horizontally, as shown in Figure 4, for measurement, and the S ₂₁ measured at this time is taken as the vertical component S _21-YB ;

3. Measure the horizontal component of the S ₂₁ of the reference label: place the 90° reference label between the two speakers and 1m away from the speakers, place the speaker 1 vertically, and place the speaker 2 vertically, as shown in Figure 5, for measurement , the measured S ₂₁ at this time is used as the horizontal component S _21-XR of the S ₂₁ of the reference label;

4. Measure the S ₂₁ of the identified tag: place the identified tag between the two speakers at a distance of 1m from the speakers, place the speaker 1 vertically, and place the speaker 2 vertically, as shown in Figure 6, to measure, at this time The measured S ₂₁ is taken as the horizontal component S _21-XT of the S ₂₁ of the identified tag; then the horn 1 is placed vertically and the horn 2 is placed horizontally, as shown in Figure 7, for measurement, and the measured S ₂₁ at this time is used as the Identify the vertical component S _21-YT of S ₂₁ of the tag;

5. Remove the interference of environmental noise: carry out vector subtraction between the S ₂₁ of the identified label in the horizontal and vertical directions and the S ₂₁ of the background environment in the horizontal and vertical directions according to formula (1) (2), including the level of the reference label The components also need to be treated in the same way, as in formula (5):

S _21-X =S _21-XT -S _21-XB (1)

S _21-Y =S _21-YT -S _21-YB (2)

S _21-XR '＝S _21-XR -S _21-XB (5)

6. Determine whether the included angle α of the V-shaped patch on the identified label is acute or obtuse: judge whether α is an acute angle or an obtuse angle according to the size comparison of S ₂₁ between the identified label and the reference label in the horizontal direction, if |S _{21- X} |<|S _21-XR ′|, then α<90°; if |S _21-X |>|S _21-XR ′|, then α>90°;

7. Remove the influence of the fixed arm: According to the result of step 6, select the amplitude |S21 _-X | of the horizontal component of S21 of the identified label by formula (6) or ( _{7 )} The amplitude |S _21-XR ′| is subtracted;

|S _21-X ′|=|S _21-XR ′|-|S _21-X |(α<90°)(6)

|S _21-X ′|=|S _21-X |-|S _21-XR ′|(α>90°)(7)

8. Derivation of the angle α value: judge the resonance point according to the maximum value of S ₂₁ , and obtain the angle α according to the formula (8) or (9) at the resonance point, so as to identify the label,

α=180°×arctg(|S _21-Y |/|S _21-X ′|)/π(α<90°)(8)

α=180°-180°×arctg(|S _21-Y |/|S _21-X ′|)/π(α>90°) (9).

Table 3 shows the measurement results of the V-shaped label, the second embodiment of the present invention, according to the above steps. It can be seen from the table that tags at different angles can be identified by using the backscattered electric fields in the horizontal and vertical polarization directions, and the identification error is less than 5°.

Table 3 Reading Results

label 1 label 2 label 3 label 4 label 5 label 6 label 7 label 8 label 9 V-shape angle α 60° 75° 90° 105° 120° 135° 150° 165° 180° Resonant frequency/GHz 2.06 2 2.01 1.95 1.92 1.91 1.83 1.82 1.81 Recognition angle α'/° 63.97 75.06 88.22 105.01 122.04 136.27 153.66 167.86 176.81 Error/° 3.97 0.06 1.78 0.01 2.04 1.27 3.66 2.86 3.19

The tag designed by the invention uses the same frequency spectrum under different encoding states, so that the RFID system can work in a narrower frequency band, which greatly improves the frequency utilization rate and reduces the system cost. In addition, the tag uses a complex scattering field to remove the interference of environmental noise during the identification process, which improves the identification effect and the identification error is less than 5°.

Certainly, the present invention can also have other multiple embodiments, without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding deformations according to the present invention, but these corresponding changes and deformations All should belong to the protection scope of the claims of the present invention.

Claims (3)

1. a recognition methods for centreless RFID tag, is characterized in that, step is:

1), without under label condition, the S on the horizontal and vertical direction of measurement environment ₂₁, be expressed as S _21-XBwith S _21-YB;

2), place be identified label, measure be identified label S in the horizontal and vertical directions ₂₁, be expressed as S _21-XTwith S _21-YT;

3), label S in the horizontal and vertical directions will be identified ₂₁with environment S in the horizontal and vertical directions ₂₁the interference that subtraction of vector removes neighbourhood noise is carried out respectively by formula (1) (2);

S _21-X＝S _21-XT-S _21-XB(1)

S _21-Y＝S _21-YT-S _21-YB(2)

4), according to S _21-Xwith S _21-Yphase relation judge that α is acute angle or obtuse angle: both homophases, α is acute angle, and both are anti-phase, and α is obtuse angle;

5), in resonance frequency angle [alpha] is obtained by formula (3) or (4), thus identification label; If α is <90 °, select formula (3), if α is >90 °, select formula (4),

α＝180°×arctg(|S _21-Y|/|S _21-X|)/π (3)

α＝180°–180°×arctg(|S _21-Y|/|S _21-X|)/π (4)；

Described centreless RFID tag, is made up of medium and radiating element, and described radiating element is bar shaped paster, and it becomes α angle with the polarised direction of field wave, 0 °≤α < 180 °.

2. a recognition methods for centreless RFID tag, is characterized in that, step is:

1), without under label condition, the S on the horizontal and vertical direction of measurement environment ₂₁, be expressed as S _21-XBwith S _21-YB;

2), place be identified label, measure be identified label S in the horizontal and vertical directions ₂₁, be expressed as S _21-XTwith S _21-YT;

3), label S in the horizontal and vertical directions will be identified ₂₁with environment S in the horizontal and vertical directions ₂₁the interference that subtraction of vector removes neighbourhood noise is carried out by formula (1) (2);

S _21-X＝S _21-XT-S _21-XB(1)

S _21-Y＝S _21-YT-S _21-YB(2)

4), the label of selecting fixed arm and pivot arm in 90 ° as reference label, witness mark label S in the horizontal direction ₂₁, be expressed as S _21-XR, and do decyclization border noise processed, as shown in formula (5);

S _21-XR′＝S _21-XR-S _21-XB(5)

5), according to being identified label and reference label S in the horizontal direction ₂₁size relatively judge that α is acute angle or obtuse angle: if | S _21-X| <|S _21-XR' |, then α <90 °; If | S _21-X| >|S _21-XR' |, then α >90 °;

6), according to 5) result, label S will be identified ₂₁the amplitude of horizontal component | S _21-X| with the S of reference label ₂₁the amplitude of horizontal component | S _21-XR' | subtract each other, to remove the impact of fixed arm, if α is <90 °, select formula (6), if α is >90 °, select formula (7);

|S _21-X′|＝|S _21-XR′|-|S _21-X| (6)

|S _21-X′|＝|S _21-X|-|S _21-XR′| (7)

7), in resonance frequency angle [alpha] is obtained by formula (8) or (9), thus identification label, if α is <90 °, select formula (8), if α is >90 °, select formula (9)

α＝180°×arctg(|S _21-Y|/|S _21-X′|)/π (8)

α＝180°-180°×arctg(|S _21-Y|/|S _21-X′|)/π (9)；

Described centreless RFID tag, be made up of medium and radiating element, described radiating element is the V-arrangement paster be made up of the two arms of same size, wherein one arm is fixed arm, consistent with the polarised direction of field wave, another arm is pivot arm, becomes α angle with fixed arm, 0 ° of < α≤180 °.

3. the recognition methods of a kind of centreless RFID tag according to claim 2, is characterized in that, described α angle is 60 °≤α≤180 °.