CN115018031B - Passive chipless RFID humidity detection tag and preparation method thereof - Google Patents

Abstract

The present invention discloses a passive chipless RFID humidity detection tag and a preparation method thereof. The passive chipless RFID humidity detection tag comprises a tag patch unit, a metal floor and a dielectric substrate; the metal floor is arranged on the lower side of the dielectric substrate, and a silver particle conductive layer is sprayed on the dielectric substrate; the tag patch unit is an RFID tag antenna, which is located on the upper surface of the dielectric substrate, and a humidity sensitive material is filled in the metal gaps of two symmetrically arranged tag patch units to form a humidity sensitive material coating area; the RFID humidity detection tag and the preparation method thereof can quickly realize the humidity detection of agricultural products such as fruits and vegetables when in use through the arrangement of the tag patch unit and the dielectric substrate, and have the characteristics of low cost, low power consumption, strong anti-interference ability, easy monitoring, and certain encoding ability compared with the same type of chipless humidity sensors.

Description

A passive chipless RFID humidity detection tag and preparation method thereof

Technical Field

The invention relates to RFID (Radio Frequency Identification), the technical field of radio frequency identification, and in particular to a passive chipless RFID humidity detection tag and a preparation method thereof.

Background technique

Electronic tags, also known as Radio Frequency Identification (RFID), are a contactless automatic identification technology. Radio waves emitted by a card reader system within a range of a few centimeters to a few meters can read the information stored in the electronic tag, thereby obtaining the required information of the item.

In cold chain logistics, agricultural products such as fruits and vegetables have high requirements for humidity and need to be stored and transported at a certain humidity. Too high or too low humidity will affect product quality and may cause spoilage. There are some uncontrollable factors in the process of goods leaving the warehouse and transportation, so it is very meaningful to be able to detect the humidity changes of goods conveniently and quickly. However, there are still the following problems in the detection of humidity during the transportation and storage of agricultural products such as fruits and vegetables:

In the process of cold chain transportation and humidity control: (1) The commonly used solution at present is the cold chain transport vehicle, but the cold chain transport vehicle only controls the temperature changes in the compartment. The humidity control ability is poor because the goods are sometimes too dense. (2) At the same time, during the loading and unloading process of goods, they will be exposed to the natural environment and the humidity will also change. (3) At the same time, in humidity monitoring, the traditional chip tag contains integrated circuit (IC) chips in its structure, which will increase the manufacturing cost accordingly and cannot meet the requirements of large-scale promotion and application in agricultural product storage.

During the storage of agricultural products such as fruits and vegetables: (4) In the past, people stored agricultural products such as fruits and vegetables in a natural indoor environment. The humidity changes with the environment. Too high or too low humidity will affect the quality and the storage time is short; (5) Some fresh agricultural products have strict requirements on the humidity environment, and the existing technology cannot achieve non-contact real-time monitoring to control the humidity within a certain range, so that the agricultural products will rot and deteriorate. At the same time, it is impossible to detect the rot of agricultural products in time and deal with it in time, resulting in moldy fruits affecting the quality of other fruits and vegetables; (6) Common humidity detection sensors require hardware and chips as support, which are costly and have a cumbersome testing process. They are not suitable for the storage of agricultural products;

Therefore, based on the above problems, it is urgent to design a passive chipless RFID humidity detection tag to solve the problems existing in the above-mentioned prior art.

Summary of the invention

In view of the above-mentioned problems, the present invention aims to provide a passive chipless RFID humidity detection tag and a preparation method thereof. The RFID humidity detection tag and the preparation method thereof can quickly realize the humidity detection of agricultural products such as fruits and vegetables when used through the arrangement of a label patch unit and a dielectric substrate, and have the characteristics of low cost, low power consumption, strong anti-interference ability and easy monitoring, and have certain encoding capabilities compared with the same type of chipless humidity sensors.

In order to achieve the above object, the technical solution adopted by the present invention is as follows:

A method for preparing a passive chipless RFID humidity detection tag, comprising the steps of:

S1. Design and prepare RFID tag antennas, and perform simulation tests on RFID tag antennas;

S2. Selecting a paper substrate as a flexible substrate to prepare a dielectric substrate;

S3. Testing the resonant frequency of the RFID tag antenna;

S4. Preparation of SnO ₂ /G humidity sensitive material;

S5. Detect the humidity sensing characteristics of SnO ₂ /G humidity sensitive material;

S6. Design an RFID humidity detection tag based on the RFID tag antenna and SnO ₂ /G humidity sensitive material;

S7. Calibrate the humidity of the RFID humidity detection tag;

S8. Repeat step S7, perform multiple calibrations, and complete the production of the RFID humidity detection label.

Preferably, the preparation process of the RFID tag antenna described in step S1 includes:

S101. The RFID tag antenna is prepared by single-point inkjet printing technology, and the printing is repeated 15 times to form a 50μm resonator conductive layer;

S102. Then use electromagnetic simulation software HFSS for simulation testing. In HFSS software, modeling is done to draw a model diagram of the RFID tag antenna, and simulation testing is performed to verify whether it is feasible;

S103. According to the detection result, the RFID tag antenna is optimized and designed by repeating steps S101 and S102 to obtain an RFID tag antenna with a frequency band of 3.8 GHz.

Preferably, the process of preparing the dielectric substrate in step S2 includes:

S201. Select a paper substrate as a flexible substrate, use silver particle ink as a conductive layer, and use a single-point inkjet inkjet printer to spray ink on the paper substrate to depict the shape of the desired patch unit;

Wherein, the paper substrate is double-sided coated paper;

S202. Place the obtained dielectric substrate in a drying oven and dry it at 120° C. for 30 minutes to sinter it, thereby obtaining a dielectric substrate.

Preferably, the resonant frequency test process of the RFID tag antenna described in step S3 includes:

S301. Use a vector network analyzer to test the resonant frequency of the RFID tag antenna prepared above, and then compare it with the simulation results;

S302. According to the comparison result of S301, if the measured result is greater than 3.8 GHz, consider increasing the number of printing times; if the measured result is less than 3.8 GHz, consider reducing the number of inkjet printing times.

Preferably, the preparation process of the SnO ₂ /G humidity sensitive material in step S4 includes:

S401. Prepare stannous chloride dihydrate, sodium hydroxide and zinc acetate adjustment solution before preparation;

S402. Weigh 0.45 g of stannous chloride dihydrate, 0.6 g of sodium hydroxide and 0.05 g of zinc acetate, and add 15 mL of anhydrous ethanol to 15 mL of deionized water to prepare a mixed solution;

S403. The weighed drug is added to the prepared solution while stirring, and then the beaker containing the solution is placed in an ultrasonic cleaning machine for 5 minutes, and finally the solution is stirred using a magnetic stirrer. After 10 minutes of magnetic stirring, the solution is observed to be milky white, and the reaction solution is prepared;

S404. The solution obtained in step S403 is transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180° C. for 24 hours;

S405. Close the drying oven, remove the reactor and place it in a ventilated place to accelerate its cooling. When cooled to room temperature, the reaction product is removed and the generated white precipitate is washed three times in turn with anhydrous ethanol and deionized water;

S406. The cleaned product is kept at 60°C for 12 hours to prepare the desired SnO ₂ white powder;

S407. Doping the prepared SnO ₂ white powder with graphene (G) to obtain SnO ₂ /G humidity sensitive material.

Preferably, the process of detecting the humidity sensing property of the SnO ₂ /G humidity sensitive material in step S5 includes:

S501. Characterize the moisture-sensitive materials by SEM, TEM, XRD and XPS;

S502. Prepare an interdigital capacitive humidity sensor using humidity-sensitive materials, and test its sensitivity, response characteristics, hysteresis and repeatability.

Preferably, the RFID humidity detection tag integrated design process described in step S6 includes:

S601. Based on the prepared RFID tag antenna and SnO ₂ /G humidity sensitive material, a proper amount of alcohol solution of the humidity sensitive material is sucked by a micron-level micro-syringe, and the alcohol solution of the humidity sensitive material is evenly applied to the humidity sensing area of the RFID tag antenna with a drop amount of 2 μL each time, and then heated at 60° C. for one minute, and repeated 10 times to obtain a detection tag;

S602. Then the detection label obtained in step S601 is dried at 60° C. for 20 minutes to obtain the desired detection label.

Preferably, the process of calibrating the humidity of the RFID humidity detection tag in step S7 includes:

The resonant frequencies at different humidity levels were measured using a vector network analyzer and humidity calibration was performed using a radiosonde.

A method for preparing a passive chipless RFID humidity detection tag, wherein the passive chipless RFID humidity detection tag comprises a tag patch unit, a metal floor and a dielectric substrate;

The metal floor is arranged on the lower side of the dielectric substrate, and a silver particle conductive layer is sprayed on the dielectric substrate;

The label patch unit is an RFID label antenna, which is located on the upper surface of the dielectric substrate, and the metal gaps between two symmetrically arranged label patch units are filled with humidity sensitive material to form a humidity sensitive material coating area.

Preferably, the silver particle conductive layer is arranged on the upper surface of the dielectric substrate, including a rectangular narrow band, four U-shaped grooves and two L-shaped strips, wherein RFID tag antennas are symmetrically arranged on both sides of the two large U-shaped grooves, and a humidity sensitive material coating area is provided between the two RFID tag antennas, the rectangular narrow band is arranged at the exact center of the dielectric substrate, the length of which is equal to the longest side of the dielectric substrate, and patch units with the same structure are symmetrically arranged on both sides of the rectangular narrow band.

The beneficial effects of the present invention are as follows: the present invention discloses a passive chipless RFID humidity detection tag and a preparation method thereof. Compared with the prior art, the improvements of the present invention are as follows:

(1) The present invention designs a passive chipless RFID humidity detection tag, comprising a tag patch unit, a metal floor and a dielectric substrate, wherein the metal floor is arranged on the lower side of the dielectric substrate, the tag patch unit is arranged on the dielectric substrate, and a humidity sensitive material coating area is arranged on the silver particle conductive layer. When in use, the humidity of agricultural products such as fruits and vegetables can be quickly detected, and the tag has the advantages of low cost, low power consumption, strong anti-interference ability, easy monitoring, and certain encoding ability compared with the same type of chipless humidity sensors.

(2) The tag patch unit described in the present invention is a chipless RFID tag that works in the ultra-wideband (UWB) frequency band (3.1GHz-10.6GHz) and can be used for humidity sensing; the chipless RFID tag is a carrier-free communication technology suitable for short-range wireless communication, and has the advantages of large system capacity, high transmission rate, and low power consumption; when in use, when the reader transmits a linearly polarized wave to the RFID tag as an inquiry signal, tag patch units of different sizes can resonate at different frequency points, and the radar cross-section (Radar Cross-Section) at the corresponding frequency point in the cross-polarization direction generates a resonance peak;

(3) At the same time, the tag patch unit adopts a microstrip coupled antenna structure, and the humidity sensitive material layer is filled in the grooves and gaps on both sides of the microstrip line. When the tag is placed in different humidity environments, the tag patch unit covered with the humidity sensitive material layer will produce a corresponding frequency offset, and the corresponding humidity value is indirectly obtained according to the amount of offset under different humidity environments;

(4) The tag provided by the present invention implements variable polarization technology. If a vertical linear polarization wave is incident on the tag surface, a specific code can be identified by detecting the horizontal component. This not only simplifies the calibration process during detection, but also increases the isolation between the reader's transmitting and receiving antennas, thereby improving the anti-interference capability.

(5) The present invention prepares SnO2/G humidity sensitive materials and determines the optimal ratio of the humidity sensitive material graphene-tin oxide mixture, so that the two humidity sensitive materials exhibit higher humidity sensing performance, thereby improving the sensitivity of the humidity sensor; at the same time, the humidity sensitive material is coated on the paper substrate, and since the paper substrate also has a certain moisture absorption capacity, it is combined with the humidity sensitive material to exhibit better humidity sensing performance;

(6) When in use, the passive chipless RFID humidity detection tag of the present invention can be directly placed in the packaging box of agricultural products such as fruits and vegetables, and can perform non-contact and rapid humidity monitoring. Warehouse workers can use this RFID humidity detection tag to promptly discover whether the goods exceed the standard or whether the stored goods are corrupt. It has the advantages of being fast, convenient, low-cost, and efficient, and is of great significance to the development of modern smart agriculture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a method for preparing a passive chipless RFID humidity detection tag according to the present invention.

FIG. 2 is a simulation result diagram of S ₂₁ and frequency variation of the RFID tag antenna of the present invention.

FIG. 3 is a diagram showing the magnetic field and electric field distribution of the RFID tag antenna of the present invention.

FIG. 4 is a three-dimensional radiation pattern of the RFID tag antenna of the present invention.

FIG. 5 is a comparison diagram of the measured and simulated results of the present invention.

FIG. 6 is a SEM image of the SnO ₂ /G mixture of the present invention at a low magnification.

FIG. 7 is a SEM image of G of the present invention at a high magnification.

FIG. 8 is a SEM image of SnO ₂ at a magnification of 35,000 times according to the present invention.

FIG. 9 is a SEM image of SnO ₂ at a magnification of 40,000 times according to the present invention.

FIG. 10 is a TEM image of the entire SnO ₂ /G mixture of the present invention at a magnification of 20,000.

FIG. 11 is a TEM image of the SnO ₂ /G mixture of the present invention at a magnification of 70,000 times.

FIG. 12 is a partial volume TEM image of the SnO ₂ /G mixture of the present invention at a magnification of 30,000.

FIG. 13 is a partial volume TEM image of the SnO ₂ /G mixture of the present invention at a magnification of 80,000.

FIG. 14 is an XRD test diagram of the SnO2/G humidity sensitive material of the present invention.

FIG. 15 is an XPS spectrum of the full spectrum measurement of the SnO ₂ /G nanometer humidity sensitive material of the present invention.

FIG. 16 is an XPS spectrum of the Sn 3d peak of the present invention.

FIG. 17 is an XPS spectrum of O1s of the present invention.

FIG. 18 is a sensitivity test curve diagram of the SnO ₂ /G humidity sensor of the present invention at different relative humidities.

FIG. 19 is a curve diagram of the response time and recovery time of the SnO ₂ /G humidity sensor of the present invention.

FIG. 20 is a hysteresis test curve diagram of the SnO ₂ /G humidity sensor of the present invention.

FIG. 21 is a repeatability test curve diagram of the SnO ₂ /G humidity sensor of the present invention at 57% humidity.

FIG. 22 is a repeatability test curve diagram of the SnO ₂ /G humidity sensor of the present invention at 75% humidity.

FIG. 23 is a humidity sensitivity characteristic curve diagram of the RFID humidity detection tag of the present invention.

FIG. 24 is a top view of the passive chipless RFID humidity detection tag of the present invention.

FIG. 25 is a front view of the passive chipless RFID humidity detection tag of the present invention.

Wherein: in FIG3 , FIG3 (a) is an electric field distribution diagram, and FIG3 (b) is a magnetic field distribution diagram;

In Figures 24 and 25: 1. dielectric substrate, 2. label patch unit, 3. moisture sensitive material coating area, 4. rectangular narrow strip, 5. metal floor.

Detailed ways

In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

Example 1: Referring to a passive chipless RFID humidity detection tag and a preparation method thereof as shown in Figures 1-25, wherein the preparation method of the passive chipless RFID humidity detection tag comprises the steps of:

Part 1: Preparation of tag antenna

S1. Preparation of RFID tag antenna

S101. Read the literature and related electromagnetic knowledge, use single-point inkjet printing technology to prepare RFID tag antennas, and print repeatedly 15 times to form a 50μm resonator conductive layer;

Conductive silver ink is used as the conductive material of the conductive layer and is sprayed onto the paper substrate using an inkjet printer. The specific process is as follows: a BMP file image of the resonator shape to be sprayed in a one-to-one original ratio is imported into the software controlling the inkjet printer, and a resonator shape of the same size is printed out;

S102. Then, the electromagnetic simulation software HFSS is used for simulation test. In the HFSS software, modeling is performed, and a model diagram of the RFID tag antenna is drawn, and simulation test is performed to verify whether it is feasible. The results obtained by simulation are shown in Figures 2-4 below. According to Figures 2-4, it can be seen that: Figure 2 shows the results of insertion loss (S ₂₁ ) and frequency change. It can be seen that when the excitation is injected from one end of the microstrip line, the microstrip coupled line resonator will absorb most of the energy of the incident wave at certain specific frequencies, resulting in three resonance states; among them, the largest resonance amplitude is caused by the resonator in the humidity sensing area, where the frequency is 3.8 GHz; in Figure 3, Figure 3a shows the electric field distribution diagram, and Figure 3b shows the magnetic field distribution diagram; observing its electric field distribution diagram, it can be seen that the electric field radiation intensity is relatively large in the middle position of the microstrip line; observing the magnetic field distribution diagram, the energy is mainly concentrated on the resonator that provides inductance; Figure 4 is the 3D directional diagram of the antenna, the directional diagram is relatively full in shape, and forms a closed sphere, so it can be inferred that the antenna radiation pattern has a certain degree of closure, which ensures the intensity of radiation;

S103. According to the test results, repeat steps S101 and S102 to optimize the design of the RFID tag antenna to obtain a RFID tag antenna with a frequency band of 3.8 GHz;

S2. Preparation of dielectric substrate

S201. Select a paper substrate as a flexible substrate, use silver particle ink as a conductive layer, and use a single-point inkjet inkjet printer to spray ink on the paper substrate to depict the shape of the desired patch unit;

Wherein, the paper substrate is double-sided coated paper;

S202. The obtained dielectric substrate is placed in a drying oven at 120° C. and dried for 30 min to sinter it to obtain a dielectric substrate;

S3. Test the resonant frequency of the RFID tag antenna

S301. Use a vector network analyzer to test the resonant frequency of the RFID tag antenna prepared above, and then compare it with the simulation results;

The vector network analyzer is used to transmit and receive signals. The signals are transmitted to the RFID tag antenna and then reflected by the vector network analyzer, and the resonant frequency results are displayed. The measured-simulated comparison results are shown in Figure 5. It can be seen from Figure 5 that: Figure 5 shows the comparison diagram of the measured and simulated humidity detection tags. It can be seen that the measured curve is offset to the left relative to the simulated curve. This is because it is carried out under non-ideal conditions, and the accuracy of the manufacturing process will also affect the resonant frequency.

S302. Optimize the RFID tag antenna based on the comparison results of S301

Specifically, the RFID tag antenna is optimized by increasing the number of inkjet printing times. If the measured result is greater than 3.8 GHz, consider increasing the number of printing times; if the measured result is less than 3.8 GHz, consider reducing the number of inkjet printing times;

Part II: Preparation of SnO ₂ /G (tin oxide/graphene) humidity-sensitive materials

S4. Preparation of SnO ₂ /G humidity sensitive material

S401. Prepare drugs. Before preparation, prepare stannous chloride dihydrate (SnCl ₂ ·2H ₂ O) and sodium hydroxide (NaOH). Since the presence of potassium hydroxide will make the prepared precursor solution alkaline, zinc acetate needs to be added to adjust the pH value of the solution, and it also has the function of modifying the morphology of SnO ₂ ;

S402. Prepare a reaction solution, weigh 0.45 g of stannous chloride dihydrate, 0.6 g of sodium hydroxide and 0.05 g of zinc acetate, and at the same time, add 15 mL of anhydrous ethanol to 15 mL of deionized water to prepare a mixed solution;

S403. The weighed drug is added to the prepared solution while stirring, and then the beaker containing the solution is placed in an ultrasonic cleaning machine for 5 minutes to accelerate the dissolution of the drug, and finally the solution is stirred using a magnetic stirrer. After 10 minutes of magnetic stirring, the solution is observed to be milky white, and the reaction solution is prepared;

S404. The solution obtained above was transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180° C. for 24 hours;

S405. Close the drying oven, remove the reactor and place it in a ventilated place to accelerate its cooling. When cooled to room temperature, the reaction product is removed and the generated white precipitate is washed three times in turn with anhydrous ethanol and deionized water;

S406. The cleaned product is kept at 60°C for 12 hours to prepare the desired SnO ₂ white powder;

S407. Doping the prepared SnO ₂ white powder with graphene (G) to obtain SnO ₂ /G humidity sensitive material.

S5. Detection of the humidity sensing properties of SnO ₂ /G humidity sensitive materials

S501. Characterize the moisture-sensitive materials by SEM, TEM, XRD and XPS;

The SEM detection images are shown in Figure 6-9. It can be seen from Figure 6-9 that: Figure 6-9 is the SEM images at different magnifications. It can be seen that _SnO2 is approximately spherical and has a small diameter; while graphene (G) is a flake material. After the two materials are doped, they show a larger surface area and have better moisture absorption performance;

TEM detection images are shown in Figures 10-13. Figures 10-13 are TEM images at different magnifications. It can also be seen that SnO ₂ is approximately spherical, while graphene (G) is flaky, which verifies the material morphology represented by the SEM image; the XRD detection image is shown in Figure 14. It can be seen from Figure 14 that: Figure 14 shows the lattice structure of the humidity-sensitive material. XRD shows that the SnO ₂ /G sample was successfully synthesized, and no crystalline phase of other impurities was observed except for the main sample; the XPS detection images are shown in Figures 15-18. It can be seen from Figures 15-18 that: Figure 15 is the full spectrum of the humidity-sensitive material. It can be seen that it only contains three elements, Sn, O, and C, proving that it does not contain other impurities. Figures 16-18 are single-element high-definition spectra of the three elements Sn, O, and C, respectively. Their valence states can be seen, which once again proves that the SnO ₂ /G humidity-sensitive material has been synthesized;

That is, it can be obtained that the SEM, TEM, XRD, and XPS characterizations of the humidity-sensitive material prepared in this embodiment meet the requirements;

S502. Prepare an interdigital capacitive humidity sensor using a humidity-sensitive material, and test its sensitivity, response characteristics, hysteresis and repeatability to verify the humidity-sensing properties of the humidity-sensitive material;

The test results are shown in Figures 19-23. It can be seen from Figures 19-23 that: Figure 19 is the sensitivity curve under different humidity conditions. It can be seen that with the increase of humidity, the capacitance value gradually decreases, and a few seconds after the humidity environment is converted, it maintains dynamic equilibrium; Figure 20 is the response time and recovery time curve. It can be seen that the response time is 13s, the recovery time is 11.5s, and the dynamic equilibrium state is reached quickly, indicating fast response and short recovery time; Figure 21 is the hysteresis test curve, it can be seen that the SnO ₂ The capacitance of the electrode of the SnO2/G humidity sensor changes regularly during the process of upward adsorption of water vapor and downward desorption of water vapor, and is positively correlated with humidity. The two curves have a high degree of overlap. Under the relative humidity of 11%, there is a maximum difference, and the maximum hysteresis value is 5.37%, indicating that the humidity hysteresis is small and the sensor performance is good; Figures 22-23 are repeatability tests under 57% and 75% relative humidity conditions, respectively. It can be seen that under the same humidity conditions, except for the difference in similarity when the relative humidity is 0%RH, the output values remain highly similar in the 57%RH and 75%RH humidity environments. By analyzing the experimental results, we can conclude that the _SnO2 /G humidity sensor has a certain good repeatability after multiple tests;

Part 3: Integrated design of passive chipless RFID humidity detection tag

S6. RFID humidity detection tag integrated design

S601. Based on the prepared RFID tag antenna and SnO ₂ /G humidity sensitive material, firstly, a micron-level microsyringe draws an appropriate amount of alcohol solution of the humidity sensitive material, and the alcohol solution of the humidity sensitive material is evenly applied to the humidity sensing area of the RFID tag antenna with a drop amount of 2 μL each time, and then heated at 60° C. for one minute, and repeated 10 times to obtain a detection tag;

S602. Then the detection label obtained in step S601 is dried at 60°C for 20 minutes to obtain the desired detection label;

S7. Calibrate humidity on RFID humidity detection tag

A vector network analyzer is used to measure the resonant frequency under different humidity conditions, and a sounding instrument is used to calibrate the humidity. The use of a sounding instrument can more accurately measure the relative humidity value, thereby calibrating the prepared RFID humidity detection tag, that is, different humidity environments correspond to different resonant frequencies.

S8. Repeat step S7 and perform multiple calibrations to obtain the humidity sensitivity characteristic curve of the RFID humidity detection tag as shown in Figures 24 and 25, obtain a more accurate measurement result, and complete the production of the RFID humidity detection tag.

Preferably, the passive chipless RFID humidity detection tag obtained by the above preparation method comprises a tag patch unit 2, a metal floor 5 and a dielectric substrate 1.

The metal floor 5 is arranged on the lower side of the dielectric substrate 1, and a silver particle conductive layer is sprayed on the dielectric substrate 1;

The label patch unit 2 is an RFID tag antenna, which is located on the upper surface of the dielectric substrate 1, and the humidity sensitive material is filled in the metal gap between two symmetrically arranged label patch units to form a humidity sensitive material coating area 3.

Preferably, the silver particle conductive layer is arranged on the upper surface of the dielectric substrate, including a rectangular narrow band, four U-shaped grooves and two L-shaped strips, wherein RFID tag antennas are symmetrically arranged on both sides of the two large U-shaped grooves, and a humidity sensitive material coating area is provided between the two RFID tag antennas, the rectangular narrow band 4 is arranged at the exact center of the dielectric substrate, the length of which is equal to the longest side of the dielectric substrate, and patch units with the same structure are symmetrically arranged on both sides of the rectangular narrow band.

Preferably, the dielectric substrate 1 is double-sided coated paper.

Preferably, in addition to the humidity sensing area and the long microstrip line on the label, the remaining L-type and U-type resonators are coded as "1" if the resonator exists and coded as "0" if it does not exist; at the same time, the resonator in the humidity sensing area is coded as "1", so there are four coding states of "100", "110", "101" and "111", which makes the detection label have a certain coding capability.

Preferably, the relevant principles and effects of the passive chipless RFID humidity detection tag described in this embodiment are:

(1) Both the paper medium substrate and the SnO2/G humidity sensitive material involved in this embodiment have humidity sensing performance, and the humidity sensing performance will be improved when the two are combined;

(2) According to the differences in the physical and chemical properties of materials, humidity-sensitive materials can be classified as follows: semiconductors, polymer films, graphene and its derivatives, and ceramic materials. However, in laboratory tests and practical applications, it is found that a single humidity-sensitive material exhibits limited humidity sensing performance. After being doped with different materials, the material performance advantages complement each other and exhibit better performance. At the same time, when graphene derivatives and semiconductor materials are doped to prepare the required humidity-sensitive materials, metal oxides such as SnO2, In2O3, ZnO and MoS2 are all wide-bandgap semiconductor materials. When a single semiconductor material is used as a humidity-sensitive material, due to the small number of free electrons and holes and poor mobility, it tends to be in an insulating state and exhibits poor humidity sensing performance.

Therefore, after the above experimental verification, it is found that water in the environment will attach to the molecular gap of the semiconductor material in the form of molecules and hydroxyl groups; due to the existence of chemical bonds and hydroxyl groups, the electron transmission is changed, the conductivity of the N-type semiconductor material is increased, or the conductivity of the P-type semiconductor material is reduced; therefore, this embodiment uses graphene (graphene, G) and tin oxide (SnO ₂ ) to prepare the humidity sensitive material, which not only has some excellent properties of graphene, but also has a wider band gap; and the tin atoms in the material exist in the form of Sn ⁴⁺ , indicating that tin dioxide is in a relatively stable state, therefore, the SnO ₂ /G humidity sensitive material has good humidity sensing performance;

(3) Under different humidity conditions, water molecules are adsorbed onto the surface of the humidity-sensitive material, changing the dielectric constant of the material. In addition, the dielectric constant of the paper substrate will also change to a certain extent. Therefore, the resonant frequency of the RFID tag detection tag will shift to the left under the adsorption of water molecules. The humidity value can be quantified from the offset.

The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims (10)

1. A method for preparing a passive chipless RFID humidity detection tag, characterized in that: comprising the steps of: S1. Design and prepare RFID tag antennas, and perform simulation tests on RFID tag antennas; S2. Selecting a paper substrate as a flexible substrate to prepare a dielectric substrate; S3. Testing the resonant frequency of the RFID tag antenna; S4. Preparation of SnO ₂ /G humidity sensitive material; S5. Detect the humidity sensing characteristics of SnO ₂ /G humidity sensitive material; S6. Design an RFID humidity detection tag based on the RFID tag antenna and SnO ₂ /G humidity sensitive material; S7. Calibrate the humidity of the RFID humidity detection tag; S8. Repeat step S7, perform multiple calibrations, and complete the production of the RFID humidity detection label. 2. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the preparation process of the RFID tag antenna described in step S1 includes: S101. The RFID tag antenna is prepared by single-point inkjet printing technology, and the printing is repeated 15 times to form a 50μm resonator conductive layer; S102. Then use electromagnetic simulation software HFSS for simulation testing. In HFSS software, modeling is done to draw a model diagram of the RFID tag antenna, and simulation testing is performed to verify feasibility; S103. According to the detection result, the RFID tag antenna is optimized and designed by repeating steps S101 and S102 to obtain an RFID tag antenna with a frequency band of 3.8 GHz. 3. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the preparation process of the dielectric substrate described in step S2 includes: S201. Select a paper substrate as a flexible substrate, use silver particle ink as a conductive layer, and use a single-point inkjet inkjet printer to spray ink on the paper substrate to depict the shape of the desired patch unit; Wherein, the paper substrate is double-sided coated paper; S202. The obtained dielectric substrate is placed in a drying oven and dried at 120° C. for 30 minutes to sinter it, thereby obtaining a dielectric substrate. 4. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the resonant frequency test process of the RFID tag antenna in step S3 includes: S301. Use a vector network analyzer to test the resonant frequency of the RFID tag antenna prepared above, and then compare it with the simulation results; S302. According to the comparison result of S301, if the actual measured result is greater than 3.8 GHz, increase the number of printing times; if the actual measured result is less than 3.8 GHz, reduce the number of inkjet printing times. 5. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the preparation process of the SnO ₂ /G humidity sensitive material in step S4 comprises: S401. Prepare stannous chloride dihydrate, sodium hydroxide and zinc acetate adjustment solution before preparation; S402. Weigh 0.45 g of stannous chloride dihydrate, 0.6 g of sodium hydroxide and 0.05 g of zinc acetate, and add 15 mL of anhydrous ethanol to 15 mL of deionized water to prepare a mixed solution; S403. The weighed drug is added to the prepared solution while stirring, and then the beaker containing the solution is placed in an ultrasonic cleaning machine for 5 minutes, and finally the solution is stirred using a magnetic stirrer. After 10 minutes of magnetic stirring, the solution is observed to be milky white, and the reaction solution is prepared; S404. The solution obtained in step S403 is transferred to a 50 mL polytetrafluoroethylene-lined stainless steel autoclave and reacted at 180° C. for 24 hours; S405. Close the drying oven, remove the reactor and place it in a ventilated place to accelerate its cooling. When cooled to room temperature, the reaction product is removed and the generated white precipitate is washed three times in turn with anhydrous ethanol and deionized water; S406. The cleaned product is kept at 60°C for 12 hours to prepare the desired SnO ₂ white powder; S407. Doping the prepared SnO ₂ white powder with graphene (G) to obtain SnO ₂ /G humidity sensitive material. 6. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the detection process of the humidity sensing property of the SnO ₂ /G humidity sensitive material in step S5 comprises: S501. Characterize the moisture-sensitive materials by SEM, TEM, XRD and XPS; S502. Prepare an interdigital capacitive humidity sensor using humidity-sensitive materials, and test its sensitivity, response characteristics, hysteresis and repeatability. 7. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the RFID humidity detection tag integrated design process described in step S6 includes: S601. Based on the prepared RFID tag antenna and SnO ₂ /G humidity sensitive material, a proper amount of alcohol solution of the humidity sensitive material is sucked by a micron-level micro-syringe, and the alcohol solution of the humidity sensitive material is evenly applied to the humidity sensing area of the RFID tag antenna with a drop amount of 2 μL each time, and then heated at 60° C. for one minute, and repeated 10 times to obtain a detection tag; S602. Then the detection label obtained in step S601 is dried at 60° C. for 20 minutes to obtain the desired detection label. 8. The method for preparing a passive chipless RFID humidity detection tag according to claim 1, characterized in that: the process of calibrating the humidity of the RFID humidity detection tag in step S7 comprises: The resonant frequencies at different humidity levels were measured using a vector network analyzer and humidity calibration was performed using a radiosonde. 9. A passive chipless RFID humidity detection tag is prepared by the preparation method according to claim 1, wherein the passive chipless RFID humidity detection tag comprises a tag patch unit, a metal floor and a dielectric substrate; The metal floor is arranged on the lower side of the dielectric substrate, and a silver particle conductive layer is sprayed on the dielectric substrate; The label patch unit is an RFID label antenna, which is located on the upper surface of the dielectric substrate, and the metal gaps between two symmetrically arranged label patch units are filled with humidity sensitive material to form a humidity sensitive material coating area. 10. A passive chipless RFID humidity detection tag according to claim 9, characterized in that: the silver particle conductive layer is arranged on the upper surface of the dielectric substrate, including a rectangular narrow band, four U-shaped grooves and two L-shaped strips, wherein the two large U-shaped grooves are symmetrically provided with RFID tag antennas on both sides, and the humidity sensitive material coating area is between the two RFID tag antennas, the rectangular narrow band is arranged at the center of the dielectric substrate, the length is equal to the longest side of the dielectric substrate, and patch units with the same structure are symmetrically provided on both sides of the rectangular narrow band.