CN113705755B

CN113705755B - Reconfigurable chipless RFID tag design method based on port isolation technology

Info

Publication number: CN113705755B
Application number: CN202110995577.0A
Authority: CN
Inventors: 张黎; 童美松; 邱兰兰; 陆霄洁
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2021-08-27
Filing date: 2021-08-27
Publication date: 2023-08-04
Anticipated expiration: 2041-08-27
Also published as: CN113705755A

Abstract

The invention provides a reconfigurable chipless RFID tag design method based on a port isolation technology, which comprises the following steps: step 1, designing an RFID tag body; step 2, designing a four-port transmission network; step 3, designing a unit encoder; and 4, reading the coded information. Through the design method provided by the invention, the designed single chipless RFID tag can realize various codes, so that the manufacturing cost of the chipless RFID tag is greatly reduced, in addition, the four-port network has a good isolation effect, and the anti-interference capability of the electronic tag is enhanced.

Description

Reconfigurable chipless RFID tag design method based on port isolation technology

Technical Field

The invention belongs to the technical field of microwaves, and relates to a chipless Radio Frequency Identification (RFID) design method.

Background

Radio Frequency Identification (RFID) technology is an automatic identification technology that is currently used in a large number of commercial applications. The technical system mainly comprises an electronic tag for digital coding and a reader for extracting coded data, when the electronic tag enters an effective working area, an antenna in the electronic tag is activated by energy or other excitation emitted by the reader, and a reflected signal of the electronic tag is sent to the reader and then sent to a computer to complete information processing, so that the object target is identified. For different applications, a specific system of radio frequency devices is required. The RFID has longer reading distance, does not need manual intervention, and has stronger penetrability and anti-interference capability. The RFID technology is widely used in the fields of military, logistics, traffic, asset management and the like at present, the volume of the electronic tag is more and more miniaturized, and the data exchange speed is faster and faster. However, the silicon chip used in the chip RFID tag makes the production and application costs high, which is not beneficial to the wide implementation. The chipless RFID is suitable for mass production due to low manufacturing cost, so that research on the chipless RFID becomes a current research hot spot.

The chipless RFID is an RFID technology with wide prospect at present, the chipless RFID label is a radio frequency identification label without a silicon chip, and can be directly printed on an object substrate generally based on a common printed circuit technology, so that the RFID label is convenient and quick to manufacture and simple and understandable in structure. The production cost is greatly reduced due to the chipless RFID technology, and the limitations and shortages of the traditional RFID technology are continuously filled, so that the improvement of the Internet of things technology is promoted.

Disclosure of Invention

The invention aims to provide a reconfigurable chipless RFID label design method based on a port isolation technology, which utilizes the port isolation characteristic of a four-port network to divide the working frequency into N coding bandwidths, and can obtain different coding results by detecting the working frequencies of different ports so as to achieve the purpose of realizing multiple codes by a single chipless RFID label.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

a reconfigurable chipless RFID label design method based on a port isolation technology comprises the following steps:

step 1 designing RFID tag body

An RFID tag body is constructed by adopting a metal grounding plate, a single-layer medium substrate, an open-ended microstrip line and a microstrip transmission line, and the metal grounding plate is arranged below the single-layer medium substrate to form a metal shielding layer; placing the microstrip transmission line and the open-ended microstrip line above a single-layer dielectric substrate, wherein the microstrip transmission line and the open-ended microstrip line form an antenna of the electronic tag;

step 2, designing a four-port transmission network

The microstrip transmission lines form a four-port transmission network, four strip-shaped independent transmission lines and a square shared transmission line are adopted, adjacent independent transmission lines are mutually perpendicular, each port of the four-port transmission network occupies an independent transmission line respectively, and a port microstrip structure is correspondingly formed; the transmission performance of any two ports is not affected by the microstrip structures of other ports, so that port isolation is formed;

step 3, designing a unit encoder

Step 3.1 working Bandwidth splitting

Dividing a working frequency band into N coding bandwidths, wherein each bandwidth internal coding information can be coded into 1 or 0 according to the existence of a unit coder;

the resonance point of the unit encoder corresponds to the center frequency of the encoding bandwidth; the discrete coding of 0 or 1 is realized by setting the existence of a unit coder in the corresponding coding bandwidth;

step 3.2 designing a terminal open microstrip line

Each terminal open-circuit microstrip line corresponds to a unit encoder, and a plurality of terminal open-circuit microstrip lines jointly form a coding structure of the chipless RFID tag; the coding structure may be equivalently a multiband band-reject filter, wherein the capacitance and inductance of each cell may be determined from a filter parameter table known in the art, so that the size of the open-ended microstrip line is calculated from the filter parameters for quantization;

changing the electrical length of the open-ended microstrip line by changing the length of the open-ended microstrip line, thereby quantifying the length of the open-ended microstrip line to change the resonance point of the unit encoder;

the number of the open-ended microstrip lines of each port can be 0 or more;

the impedance matching degree of the tag can be improved by controlling the distance between every two unit encoders, so that the performance of the tag is improved;

step 4, reading the coded information

The coded information is read by adopting the following steps: the detection signals enter from one port of the four-port network, the other port outputs, the unit encoders distributed on the two ports can attenuate signals with specific frequencies, the unit encoders distributed on the other two ports cannot be affected by the detection signals, so that the whole transmission network forms port isolation, and different encoding results can be obtained through different port combinations, thereby realizing the reconstruction of tag encoding.

Advantageous effects

Through the reconfigurable of label code, single chipless RFID label can realize multiple coding, greatly reduced chipless RFID's cost of manufacture, the label distributes on the microstrip transmission line with clockwise rotation mode, makes compact structure, reaches miniaturized purpose, and four port network has fine isolation effect, has strengthened electronic tags's interference killing feature.

Drawings

FIG. 1 is an overall schematic diagram of a reconfigurable RFID tag encoding device based on port isolation technology

FIG. 2 is a schematic diagram of a combination of coding units according to the present invention

FIG. 3 is a schematic side view of a reconfigurable RFID tag encoding device based on port isolation technology

FIG. 4 is a schematic diagram of a front view of a reconfigurable RFID tag encoding device based on port isolation technology

FIG. 5 is a diagram of S12 parameter simulation results for a reconfigurable RFID tag encoding device

FIG. 6 is a diagram of S13 parameter simulation results for a reconfigurable RFID tag encoding device

FIG. 7 is a diagram of S14 parameter simulation results for a reconfigurable RFID tag encoding device

FIG. 8 is a diagram of S23 parameter simulation results for a reconfigurable RFID tag encoding device

FIG. 9 is a diagram of S24 parameter simulation results of a reconfigurable RFID tag encoding device

FIG. 10 is a diagram of S34 parameter simulation results for a reconfigurable RFID tag encoding device

Numerical marking:

1. metal grounding plate

2. Single-layer dielectric substrate

3-1 to 3-8, open-ended microstrip lines, i.e. coding units

4-0 to 4-4 microstrip transmission line

Detailed Description

Fig. 1 is a schematic diagram of a reconfigurable RFID tag coding device based on port isolation technology, and the configuration structure of the reconfigurable RFID tag coding device is a metal grounding plate (1), a single-layer dielectric substrate (2) and microstrip transmission lines (4-0 to 4-4) of open-ended microstrip lines (3-1 to 3-8). The metal grounding plate is arranged at the lowest layer, a single-layer dielectric substrate (2) is arranged in the middle of the metal grounding plate, and open-ended microstrip lines (3-1 to 3-8) and microstrip transmission lines (4-0 to 4-4) are formed after the dielectric substrate is etched. Excitation is added to 4 ports (port 1 to port 4) of the microstrip transmission line, and coding unit combinations are arranged for open-ended microstrip lines (3-1 to 3-8).

The theory of open-ended microstrip lines (3-1 to 3-8) designed by the present invention is available from the following. The trap circuit of the invention belongs to a first-order prototype circuit, uses a circuit based on a series LC resonance unit, and the circuit element after conversion is shown as a formula (1)

Wherein the subscript c denotes the low-pass cutoff. According to microstrip theory, an open-ended microstrip line having a length of λ/4 at ω0 can be regarded as an RLC resonant circuit [ microwave technology basis ], the circuit element size of which is shown in formula (2).

Wherein Z is _0i Is the characteristic impedance of the open-ended microstrip line, α is the attenuation coefficient, and li is the length of the open-ended microstrip line. Establishing a relationship between the characteristic impedance of the terminating open microstrip line and the characteristic impedance of the transmission line, wherein w is readily available (3) _c ' represents the normalized cut-off frequency of the lowpass prototype filter, with a value of 1, C _c 'R ₀ /R ₀ ' gi/Z0o, Z0o is the characteristic impedance of the transmission line.

The butterworth filter component has the value shown in formula (5), and the circuit n=1 is designed.

The combined type (3), the formula (4) and the formula (5) can obtain models of the microstrip trap circuit of the chipless RFID tag designed in the specification, and the models are as follows

Z _0i ＝F(f _i ,w _si ,ε _r ,t,h)

Z _0o ＝F(f _o ,w _so ,ε _r ,t,h) (6)

Wherein Z is _0i 、f _i 、w _si 、l _i Respectively representing the characteristic impedance, the working frequency, the width and the length of the ith terminal open-circuit microstrip line; z is Z _0o 、w _so Representing the characteristic impedance and width of the microstrip transmission line; f (f) _o Is the center working frequency; Δw represents the relative bandwidth of each tag; epsilon _r And t and h are dielectric constants, copper thickness and dielectric thickness of the dielectric plate, and the function F is used for solving characteristic impedance through materials and physical parameters.

Experiment verification

The coding unit combination according to the invention is described below with reference to fig. 2, the described embodiments being only a part of the embodiments according to the invention, all other embodiments being obtained without inventive effort on the basis of the embodiments according to the invention falling within the scope of protection of the invention. A schematic diagram of the combination of 8 coding units employed in the present invention is shown in fig. 2. The 8 coding units are respectively etched in a cross combination mode according to the electric length and connected to microstrip transmission lines (4-1 to 4-4), (3-1) and (3-5), (3-2) and (3-6), (3-3) and (3-7) and (3-4) and (3-8). The reason for the cross combination is as follows, because the resonance points formed by the adjacent electric length coding units are adjacent, reading errors are easy to cause during identification, and the coding bandwidths can be uniformly distributed by adopting a spacing combination mode, so that the coupling phenomenon between two frequencies with relatively close intervals is reduced, and the false identification rate is reduced.

As an example, the single-layer dielectric plate (2) has a dielectric substrate material RT5870, a relative dielectric constant of 2.33, a thickness of 0.785 mm, and a loss tangent ratio of 0.0012.

Fig. 4 is a schematic front view of a reconfigurable RFID tag encoding device based on port isolation technology. In this embodiment, the cross-combined pairs of code elements are etched vertically on the microstrip transmission line in a clockwise manner to form 4 pairs of code element groups, each code element group having a spacing distance of 10.50 mm, a transmission line width of 4 mm, and each code element group having a width of 1 mm. In the invention, more coding capacity can be obtained by changing the electrical length (l 1-l 8) of the open-ended microstrip line, and coding of 0 or 1 is realized by setting whether the coding unit corresponding to the resonance position is etched, in the embodiment, the resonance point code at the etched coding unit is 1, and the resonance point code at the non-etched coding unit is 0.

Table I shows the physical parameters of the structure shown in FIG. 4

Parameters (parameters)	l ₁	l ₂	l ₃	l ₄	l ₅	l ₆	l ₇	l ₈	d	w	g
												Value (mm)	13.1	14.3	15.8	16.9	19.4	21.8	24.7	28	10.50	4.00	1.00

Fig. 5 is a diagram of S12 parameter simulation results of the reconfigurable RFID tag encoding apparatus. The results of the parameters of this example S12 obtained by connecting port 1 and port 2 are shown. After the port 1 and the port 2 are connected, current is fed into the two ports, so that the current is mainly concentrated on the microstrip transmission lines (4-1, 4-0 and 4-2) and acts on the coding units (3-1, 3-5, 3-6 and 3-2), and the port isolation technology can prevent other coding units from being affected. It should be noted that, when the frequency band division is performed in this embodiment, if the given frequency band is too narrow, the frequency band coupling between the tags is easy to be serious, the error code occurs in the detection information, so that the reliability of the system is reduced, if the divided frequency band is too wide, the frequency band resource is wasted, therefore, the working bandwidth of the predefined chipless RFID is 1.8GHz-3.9GHz, after the working frequency band is evenly divided, 8-bit codes can be obtained, and the corresponding frequency points are 1.8GHz, 2.1GHz, 2.4GHz, 2.7GHz, 3GHz, 3.3GHz, 3.6GHz and 3.9GHz, respectively. The coding units generating resonance points shown in fig. 5 are (3-1, 3-5, 3-6, 3-2), and the corresponding resonance frequencies are 2.39GHz,2.72GHz,3.70GHz, and 4.06GHz, respectively, and the coding is set to 00110011.

Similarly, fig. 6 is a diagram of simulation results of S13 parameters of the reconfigurable RFID tag encoding apparatus obtained by connecting ports 1 and 3, and the encoding is set to 0100110.

Fig. 7 is a diagram showing simulation results of S14 parameters of the reconfigurable RFID tag encoding apparatus obtained by connecting ports 1, 4, and the encoding set is 10101010.

Fig. 8 is a diagram of the simulation result of S23 parameters of the reconfigurable RFID tag encoding apparatus obtained by connecting ports 2, 3, the encoding set to 01010101.

Fig. 9 is a diagram showing simulation results of S24 parameters of the reconfigurable RFID tag encoding apparatus obtained by connecting ports 2 and 4, and the encoding set is 10011001.

Fig. 10 is a diagram showing simulation results of S34 parameters of the reconfigurable RFID tag encoding apparatus obtained by connecting ports 3, 4, the encoding set to 11001100.

The above S parameters are all transmission coefficients.

Once the traditional coding device is manufactured, the structure is fixed, the coding mode can not be changed any more, and one RFID corresponds to one coding mode. In order to obtain an 8-bit code combination, 2 is required ⁸ And (3) electronic tags. In this embodiment, 6 coding combinations (corresponding to fig. 5-10: S12, S13, S14, S23, S24, S34 in this embodiment) can be obtained for one electronic tag, so only design 2 is needed ⁸ And/6 electronic tags can obtain 8-bit code combination. The method greatly increases the coding density, reduces the manufacturing cost of the chipless RFID, has good isolation effect, and greatly enhances the anti-interference capability of the electronic tag.

The embodiments described above are only some of the embodiments of the invention, on the basis of which all other embodiments obtained without making inventive efforts fall within the scope of protection of the invention. The invention can be extended to obtain more coding capacity by changing the electrical length (l 1-l 8) of the open-ended microstrip line, and coding of '0' or '1' is realized by setting whether the coding unit corresponding to the resonance position is etched or not.

Claims

1. A reconfigurable chipless RFID label design method based on a port isolation technology comprises the following steps: