An RFID tag device for soil temperature monitoring and a method of manufacturing the same

Abstract

The embodiment of the application discloses a RFID tag device for soil temperature monitoring and a preparation method thereof, relates to the field of graphene RFID sensing technology, and combines an artificial magnetic conductor (AMC), significantly improves antenna gain and reading distance, and realizes long-distance passive soil temperature sensing. The device integrates a temperature sensor and an RFID tag chip, can accurately detect soil temperature and transmit data. In the preparation process, an electromagnetic simulation software is used to design an antenna structure, and a laser engraving technology is used to accurately process the graphene antenna and the AMC, so that the high performance and stability of the device are ensured. The problems of the traditional soil temperature sensor, such as dependence on manual operation, high cost, corrosion and limited transmission distance, are solved, and an efficient, environmentally-friendly and accurate soil temperature monitoring solution is provided for modern agriculture.

Description

Technical Field

[0001] This invention relates to the field of graphene RFID sensing technology, and in particular to an RFID tag device for soil temperature monitoring and its preparation method. Background Technology

[0002] With the rapid development of modern agriculture, soil temperature monitoring has become an increasingly important part of crop growth management.

[0003] Fluctuations in soil temperature directly affect the growth cycle, yield, and quality of crops. Therefore, it is crucial to achieve continuous and accurate monitoring of soil temperature.

[0004] However, traditional soil temperature sensing methods have many limitations: short-range thermometers rely on manual operation, cannot work automatically, are inefficient, and are difficult to transmit data over long distances; while existing wireless sensing devices mostly adopt active designs, which are expensive and not suitable for large-scale deployment. At the same time, most of these devices are made of metal materials, which are susceptible to corrosion when buried in the soil for a long time, leading to performance degradation and potential pollution of the soil environment.

[0005] Furthermore, corrosion of metallic materials limits the lifespan of sensors and increases maintenance costs. Therefore, traditional soil temperature sensing technology falls short in meeting the demands of modern agriculture for precise, automated, and environmentally friendly monitoring.

[0006] Therefore, there is an urgent need for an RFID tag device that can achieve long-distance passive sensing, is corrosion-resistant, and environmentally friendly. Summary of the Invention

[0007] This invention provides an RFID tag device and its manufacturing method for soil temperature monitoring, addressing the problems of existing technologies where short-range thermometers rely on manual operation and cannot transmit data remotely; and wireless devices are costly and, being based on metal, are prone to corrosion and soil contamination. The technical solution is as follows:

[0008] According to one aspect of the present invention, an RFID tag device for soil temperature monitoring and a method for manufacturing the same, the RFID tag device comprising an RFID tag and an AMC module, the RFID tag comprising:

[0009] The dielectric substrate, made of polyethylene terephthalate (PET), is used to support the antenna structure.

[0010] The antenna is a graphene antenna disposed on the upper surface of the dielectric substrate; the antenna includes: an antenna radiator made of high-conductivity graphene material, used for receiving and transmitting radio frequency signals;

[0011] The RFID tag chip is connected to the antenna;

[0012] A temperature sensor, built into the RFID tag chip, is used to detect soil temperature and generate a temperature signal;

[0013] The AMC module includes multiple AMC units, and each AMC unit includes:

[0014] The AMC dielectric substrate uses an FR-4 substrate to provide structural support;

[0015] The surface structure is a graphene film processed by a laser engraving machine, located on the upper surface of the AMC dielectric substrate;

[0016] The underlying structure is fully covered by a graphene film, located on the lower surface of the AMC dielectric substrate;

[0017] An adhesive is used to bond the surface structure and the underlying layer to both sides of the AMC dielectric substrate;

[0018] The RFID tag device is made of multiple AMC units arranged side by side on the lower surface of the RFID tag, so that the AMC module can cover the RFID tag, and the AMC units and the RFID tag are separated by foam.

[0019] In one embodiment, the RFID tag further includes a fine-tuning antenna impedance section, which is symmetrically arranged on the upper and lower sides of the RFID tag chip.

[0020] In one embodiment, the AMC module further includes a first frequency modulation section, a second frequency modulation section, and a third frequency modulation section, wherein the first frequency modulation section is used to coarsely adjust the operating frequency of the AMC module, and the second and third frequency modulation sections are used to finely adjust the operating frequency of the AMC module.

[0021] In one embodiment, the RFID tag device for soil temperature monitoring further includes an antenna that is corrosion-resistant and non-metallic.

[0022] In one embodiment, the relative permittivity of the dielectric substrate is between 3 and 4, and the loss tangent of the dielectric substrate is less than 0.05%.

[0023] In one embodiment, the antenna operates in the frequency range of 860MHz to 960MHz, and the dielectric substrate is flat.

[0024] According to one aspect of the present invention, a method for preparing an RFID tag device for soil temperature monitoring is characterized by the following steps: designing an antenna structure that is conjugate-matched to the complex impedance of the chip using electromagnetic simulation software; processing the antenna structure into a graphene antenna by laser cutting on a graphene film; binding the graphene antenna to the RFID tag chip; coating the graphene antenna with high-temperature resistant adhesive; flip-packing and bonding the RFID tag chip to the graphene antenna; and then curing it by high-temperature hot pressing.

[0025] In one embodiment, the method further includes the following steps: using a laser engraving machine to process the surface structure of the artificial magnetic conductor (AMC) unit according to the structure, preparing the bottom layer structure using a single piece of graphene film, and attaching the surface structure and the bottom layer structure to an FR-4 substrate using an adhesive to obtain the artificial magnetic conductor (AMC) unit; repeatedly arranging and combining the artificial magnetic conductor (AMC) units in parallel according to the rules of the set RFID tag device to obtain an AMC module, such that the AMC module can cover the RFID tag, and then attaching the AMC module to the lower surface of the RFID tag.

[0026] In one embodiment, the chip is coated with a high-temperature resistant adhesive and then cured by hot pressing at 170-180°C for 12 seconds.

[0027] The beneficial effects of the technical solution provided by this invention are:

[0028] In the above technical solution, this invention proposes an RFID tag device based on graphene material and its fabrication method to address the needs of soil temperature monitoring. This device significantly improves antenna gain and read distance by using high-conductivity graphene material to fabricate the antenna radiator and combining it with an artificial magnetic conductor (AMC), achieving long-distance passive soil temperature sensing. The device integrates a temperature sensor and an RFID tag chip, enabling accurate detection of soil temperature and data transmission. During fabrication, the antenna structure is designed using electromagnetic simulation software, and the graphene antenna and AMC are precisely processed using laser engraving technology, ensuring the high performance and stability of the device. This effectively solves the problems of traditional soil temperature sensors, such as reliance on manual operation, high cost, susceptibility to corrosion, and limited transmission distance, providing a highly efficient, environmentally friendly, and accurate soil temperature monitoring solution for modern agriculture. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the structure of an RFID tag device according to an exemplary embodiment;

[0031] Figure 2 This is a top view of an AMC unit according to an exemplary embodiment;

[0032] Figure 3 yes Figure 2 A side view of the AMC unit shown in the corresponding embodiment;

[0033] Figure 4 yes Figure 2 A schematic diagram of the arrangement of the AMC module in the RFID tag device in the corresponding embodiment;

[0034] Figure 5 This is a comparative diagram of antenna gain with and without an AMC module in an application scenario;

[0035] Figure 6 yes Figure 5 A comparative diagram showing the antenna readout range with and without an AMC module in the corresponding application scenarios;

[0036] Figure 7 This is a test diagram illustrating whether RFID tag devices equipped with AMC modules have tag reading capabilities under different environments;

[0037] Figure 8 This is a schematic diagram showing a comparative test of an RFID tag device in a salt spray environment and a copper foil salt spray environment in an application scenario. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0040] This application provides an RFID tag device for soil temperature monitoring and its manufacturing method. The device includes an RFID tag and an AMC module. The RFID tag includes: a dielectric substrate made of polyethylene terephthalate (PET) to support the antenna structure; an antenna, which is a graphene antenna disposed on the upper surface of the dielectric substrate; the antenna includes: an antenna radiator made of high-conductivity graphene material to receive and transmit radio frequency signals; an RFID tag chip connected to the antenna; and a temperature sensor built into the RFID tag chip to detect soil temperature and generate a temperature signal.

[0041] The AMC module comprises multiple AMC units. Each AMC unit includes: an AMC dielectric substrate, using an FR-4 substrate, for providing structural support; a surface structure, processed by a laser engraving machine, located on the upper surface of the AMC dielectric substrate; a bottom structure, a graphene film, located on the lower surface of the AMC dielectric substrate; and an adhesive for bonding the surface structure and the bottom structure to both sides of the AMC dielectric substrate.

[0042] The RFID tag device consists of multiple AMC units arranged side-by-side on the lower surface of the RFID tag, allowing the AMC module to cover the RFID tag. A foam separator separates the AMC units from the RFID tag. The connection between the AMC units, the RFID tag, and the foam is not restricted; it can be adhesive or naturally placed, as long as there is physical contact on the surface. The thickness of the foam separator is generally determined through full-wave electromagnetic simulation. In this embodiment, the thickness is 2cm; in another embodiment, it is 0.5cm, and in yet another, it is 4cm. Ideally, the thickness should be between 0.5cm and 4cm, but other thicknesses are also possible.

[0043] The RFID tag also includes a fine-tuning antenna impedance section, which is symmetrically arranged on the top and bottom sides of the RFID tag chip. The AMC module also includes a first frequency modulation section, a second frequency modulation section, and a third frequency modulation section. The first frequency modulation section is used for coarse adjustment of the AMC module's operating frequency, while the second and third frequency modulation sections are used for fine adjustment of the AMC module's operating frequency.

[0044] The antenna is made of corrosion-resistant non-metallic material, the dielectric substrate has a relative permittivity between 3 and 4, and the loss tangent of the dielectric substrate is less than 0.05%. The antenna operates in the frequency range of 860MHz to 960MHz, and the dielectric substrate is flat.

[0045] The AMC module is used to improve antenna gain and enhance signal transmission distance and stability. The AMC module consists of a surface structure, an intermediate dielectric layer (FR-4 substrate), a bottom layer structure (graphene film), and an adhesive. The surface structure is laser-engraved with a specific pattern, and the adhesive firmly attaches the surface and bottom layers to both sides of the intermediate dielectric layer, forming a complete AMC module that effectively reflects incident waves and improves antenna gain.

[0046] The method for manufacturing this RFID tag device includes:

[0047] An antenna structure with complex impedance conjugate matching to the chip was designed using electromagnetic simulation software. Based on the antenna structure, a graphene antenna was fabricated by cutting a graphene film with a laser. The graphene antenna was then bonded to the RFID tag chip. After coating the graphene antenna with high-temperature resistant adhesive, the RFID tag chip was flip-packaged and bonded to the graphene antenna, and then cured by high-temperature hot pressing.

[0048] Furthermore, the surface structure of the artificial magnetic conductor (AMC) unit is processed according to the antenna structure using a laser engraving machine. The bottom layer structure is prepared using a single piece of graphene film. The surface and bottom layers are then attached to the FR-4 substrate using an adhesive to obtain the artificial magnetic conductor (AMC) unit. The artificial magnetic conductor (AMC) units are repeatedly arranged in parallel according to the rules of the set RFID tag device to obtain the AMC module, so that the AMC module can cover the RFID tag. The AMC module is then attached to the lower surface of the RFID tag, with a 2cm foam barrier between the tag and the AMC module. After coating the chip with high-temperature resistant adhesive, it is hot-pressed at 170-180℃ for 12 seconds and then cured.

[0049] Specifically, an antenna structure matching the complex impedance of the chip was designed using electromagnetic simulation software. Based on the designed antenna structure, a graphene antenna was fabricated by cutting a graphene film using a laser. This ensured the antenna's shape and dimensions were precise, meeting specific operating frequency requirements. The antenna possesses high conductivity and excellent radiation performance, enabling effective reception and transmission of radio frequency signals.

[0050] Furthermore, the surface structure of the AMC unit is fabricated using a laser engraving machine according to the designed antenna structure. The bottom layer structure is prepared using a single piece of graphene film. An adhesive is then used to attach the surface and bottom layers to the FR-4 substrate, resulting in a complete AMC unit. Combining AMC units to form an AMC module improves antenna gain and enhances signal transmission capability. The AMC module significantly improves antenna gain, allowing electromagnetic wave signals to penetrate the soil more effectively, enabling long-distance sensing.

[0051] Furthermore, the chip's built-in temperature sensor detects soil temperature and generates a temperature signal. The RFID tag chip acquires this temperature signal through the sensor and transmits it via an antenna, enabling real-time monitoring and data transmission of soil temperature. The temperature sensor accurately detects soil temperature, and the RFID tag chip sends the temperature data and tag ID to an external reader for remote monitoring.

[0052] Furthermore, the graphene antenna is bonded to the chip. After coating the antenna with high-temperature resistant adhesive, the chip is flip-packaged and bonded to the antenna, and then cured using a high-temperature hot-pressing method at 170-180℃. According to the established RFID tag device rules, the AMC unit is repeatedly combined and bonded to the lower surface of the RFID tag, ensuring that the AMC module completely covers the RFID tag. The overall assembly of the device is completed, ensuring that all components are firmly connected. The device has a compact structure, and all components work together to achieve stable monitoring of soil temperature and data transmission.

[0053] like Figure 1 The diagram shows a top view of the RFID tag device, which is mainly used in the field of soil temperature monitoring. Its overall structure consists of several key parts.

[0054] Specifically, the white area represents the dielectric substrate, the dark gray area represents the graphene antenna on top of the dielectric substrate, the gap g indicates the chip bonding location, the symmetrical gray columnar blocks are used for fine-tuning the antenna impedance, and the area formed by l1, l2, l3, w1, w2, and w3 is used for coarse-tuning the antenna impedance. Geometric parameters: l1=37 mm, w1=30 mm, l2=20 mm, w2=20 mm, l3=8.5 mm, w3=8.9 mm, a=1 mm, b1=5.5 mm, b2=4 mm, b3=3 mm, g=1.25 mm, s=0.3 mm. The chip location represents the area where the temperature sensing chip and antenna are bonded.

[0055] The antenna portion of the tag is fabricated using a laser engraving machine. The antenna radiator has a specific shape, and its dimensions are precisely designed to ensure good radio frequency performance. The desired shape is cut into the graphene film using a laser, and excess material is removed to obtain the antenna. This method is precise and fast, and can be mass-produced industrially. Next, anisotropic conductive adhesive is used to electrically connect the chip pins to the antenna port, resulting in a complete graphene RFID tag.

[0056] Specifically, the dielectric substrate, serving as the basic support structure of the device, is flat. Its physical properties have a significant impact on the device's performance. The relative permittivity is strictly controlled within a specific range (between 3 and 4), and the loss tangent is less than 0.05%. This design ensures low loss during signal transmission, guaranteeing stable operation of the device.

[0057] The graphene antenna is the core component for the device to achieve wireless communication. The antenna radiator is made of high-conductivity graphene material, and its precise shape is cut into the graphene film using laser engraving technology and then mounted on one side of the dielectric substrate. Its dimensional parameters, such as length 'a', are carefully designed to meet specific operating frequency requirements (operating frequency range of 860MHz to 960MHz), enabling it to efficiently receive and transmit radio frequency signals.

[0058] The Artificial Magnetic Conductor (AMC) module is located on the lower surface of the RFID tag. It consists of a surface structure, an intermediate dielectric layer, a bottom layer, and an adhesive. The surface structure is patterned using a laser engraving machine. The intermediate dielectric layer uses an FR-4 substrate, providing support and insulation. The bottom layer is a graphene film. The adhesive firmly attaches the surface and bottom layers to both sides of the intermediate dielectric layer. The introduction of the AMC module significantly enhances the antenna gain and increases the signal transmission distance.

[0059] The temperature sensor is responsible for detecting soil temperature in real time and generating a temperature signal. After the RFID tag chip obtains the temperature signal through the temperature sensor, it sends the temperature data and tag ID to an external reader through the antenna.

[0060] like Figure 2 and Figure 3 As shown, the top layer of the AMC is a graphene surface structure, the middle layer is an FR-4 dielectric substrate (relative permittivity 4.3, loss tangent 0.025), and the bottom layer is a monolithic graphene structure. Geometric parameters: x1=46mm, x2=44.9 mm, sl1=36.9mm, sw1=0.8mm, sl2=20mm, sw2=2mm, sl3=6mm, sw3=2mm, g1=1mm. Where x1 is the substrate side length; x2 is the AMC unit side length; sl1 and sw1 are the length and width of the first frequency modulation section, used for coarse adjustment of the AMC operating frequency; sl2 and sw2 are the length and width of the second frequency modulation section, used for fine adjustment of the AMC operating frequency; sl3 and sw3 are the long and short sides of the third frequency modulation section, used for fine adjustment of the AMC operating frequency.

[0061] Specifically, the surface structure of the AMC is similar to that of a graphene antenna, processed using a laser engraving machine. The bottom layer structure is a single piece of graphene film. The surface and bottom layers are attached to the FR-4 substrate using adhesive, together forming a complete AMC unit. In actual use, to fully cover the tag, the AMC module uses a combination of multiple units.

[0062] As shown in the top view Figure 2As shown, the overall layout of the device is compact and reasonable. The surface structure of the AMC unit has unique patterns, which are precisely processed by a laser engraving machine. These patterns work together with the intermediate dielectric layer and the underlying structure to optimize the antenna performance.

[0063] As shown in the side view Figure 3 As shown, the hierarchical structure of the unit is clearly visible. The AMC dielectric substrate, with a thickness of h=3mm, serves as the support. The surface structure AMC is located on one side, and the bottom structure Ground is on the other. The device's dimensional parameters can be optimized according to actual application scenarios and performance requirements to ensure the stability and reliability of the device when buried in soil. Simultaneously, the bottom of the device contacts the ground, while other structures or protective layers can be installed on top to adapt to different soil environments.

[0064] like Figure 4 As shown, in the underground temperature sensing RFID tag device of this invention, the AMC module adopts a three-unit arrangement. The three units are tightly attached to the substrate with adhesive to form a whole. Experiments show that this arrangement can increase the maximum reading distance of the tag from 10.1m to 16.8m (gain increased to 5.9dBi). Especially when the tag is buried in deep soil, the combined module can effectively enhance the electromagnetic wave penetration capability and ensure stable data transmission.

[0065] like Figure 5 The figure shows a comparison of antenna gain with and without an AMC module. The solid line represents the antenna gain with an AMC module, and the dashed line represents the antenna gain without an AMC module. It is clear from the figure that the gain increase is significant in certain key directions. This means that the AMC module can effectively enhance the antenna's signal transmission and reception capabilities in specific directions, expand signal coverage, and improve communication quality.

[0066] like Figure 6 As shown, the antenna read distance is compared with and without an AMC module. The antenna read distance with an AMC module (solid line) is significantly greater than that without an AMC module (dashed line) across most frequency ranges. At a specific frequency point, the read distance reaches its peak. This indicates that the AMC module increases the antenna's reading distance, enabling RFID tag devices to communicate effectively with external readers at greater distances.

[0067] Through the above process, it can be seen that the AMC module can reflect the incident wave without changing its phase, thereby enabling the superposition of electromagnetic waves of the same phase to increase the gain and thus improve the reading distance of the RFID tag. Without the AMC module, the maximum gain is 1.6 dBi, and the maximum reading distance of the tag is 10.1 m. With the AMC module, the maximum gain is 5.9 dBi, and the maximum reading distance can be increased to 16.8 m. The AMC module increases the tag reading distance by 1.6 times, effectively enhancing the antenna's radiation capability.

[0068] To verify the reading capability of the RFID tag device in different soil environments, tests were conducted in three different soil environment scenarios.

[0069] like Figure 7 As shown, the test was set up with three different soil environment scenarios. Figure (a) shows shallow soil without an AMC module, where the temperature can be read; Figure (b) shows deep soil without an AMC module, where the temperature cannot be read; Figure (c) shows deep soil with an AMC module, where the temperature can be read.

[0070] As can be seen, when the device adopts the AMC module, the external reader can successfully read the tag information in the same deep soil environment, and the data transmission is stable. This fully demonstrates that the AMC module can effectively enhance signal penetration capability, enabling the RFID tag device to work normally in complex environments such as deep soil, thus expanding the application range and reliability of the device.

[0071] Due to the increased gain, the electromagnetic waves radiated by the tag antenna can penetrate the dielectric layer better, making it more suitable for high-loss environments like soil. Experiments were conducted on the tags in three scenarios. When a single tag is buried in shallow soil, it can be read; however, when buried in deep soil, it cannot be read due to the significant electromagnetic wave attenuation caused by the soil. Conversely, when the tag is combined with an AMC module, the increased gain and read distance allow it to be read even when buried in deep soil. The AMC module expands the tag's application scenarios, enabling it to collect data from deeper soil layers while also improving stability when operating in shallow soil.

[0072] Reading distance test: The reading distance of the RFID tag device was tested in different soil environments, including shallow soil, deep soil, and deep soil environment with AMC module. The effect of AMC module on improving antenna gain and reading distance was verified. Results show that the device with AMC module can still be stably read in deep soil, with a significantly improved reading distance, proving that AMC module effectively enhances antenna radiation capability and signal transmission stability.

[0073] like Figure 8 As shown, the RFID tag device was tested and verified:

[0074] Salt spray corrosion test: Graphene film and copper foil were treated in a salt spray environment of 35℃, 80% relative humidity, and 5% sodium chloride solution for 72 hours, and their corrosion was observed. Figure (a) shows a schematic diagram of the graphene film before the experiment, Figure (b) shows a schematic diagram of the graphene film after the experiment, Figure (c) shows a schematic diagram of the copper foil before the experiment, and Figure (d) shows a schematic diagram of the copper foil after the experiment. This verified the corrosion resistance of the graphene film in humid and complex environments such as soil. The results show that the graphene film showed no signs of corrosion after treatment and remained intact; while the copper foil showed large areas of copper rust after treatment, proving that the graphene film has excellent corrosion resistance.

[0075] Through the above process, the structure of this embodiment of the invention comprises a dielectric substrate, a graphene antenna, and an AMC module. Each component is ingeniously designed with optimized parameters, ensuring stable operation of the device in soil temperature monitoring. Regarding application performance, a comparison with and without an AMC module shows that the AMC module significantly improves antenna gain and read distance, enhancing signal coverage and operational stability. Testing indicates that the device performs well in shallow soil, while in deep soil, the device with the AMC module can communicate stably, while the device without the AMC module cannot read data. In conclusion, this RFID tag device, with its unique structure and the advantages of the AMC module, demonstrates excellent applicability and reliability in the field of soil temperature monitoring, providing an effective solution for related applications.

[0076] Compared with related technologies, the beneficial effects of the present invention are:

[0077] 1. This invention enables long-distance passive soil temperature sensing, and the sensor is corrosion-resistant and environmentally friendly. By using corrosion-resistant, high-conductivity graphene material as the radiator of the RFID tag antenna to replace traditional metal materials, the problem of metal corrosion and pollution in soil is avoided. At the same time, the temperature sensing function is realized by using an RFID chip with an integrated temperature sensor, and the AMC module made of graphene is used to improve the antenna gain, so that the electromagnetic wave signal can better penetrate the soil and realize long-distance sensing.

[0078] 2. This invention has the advantages of improving antenna radiation capability and signal transmission stability. By using graphene to make the AMC module, the AMC module can reflect the incident wave without changing the phase, so that the electromagnetic waves in the same phase are superimposed to improve the gain, thereby improving the reading distance of RFID tags and enhancing the radiation capability of the antenna in high-loss environments such as soil, thus ensuring the stability of signal transmission.

[0079] It should be understood that although the steps in the flowcharts of the accompanying figures are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the accompanying figures may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the sub-steps or stages of other steps.

[0080] The above description is only a partial embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An RFID tag device for soil temperature monitoring, characterized by, The RFID tag device includes an RFID tag and an artificial magnetic conductor structure (AMC) module. The RFID tag includes: The dielectric substrate, made of polyethylene terephthalate (PET), is used to support the antenna structure; the relative permittivity of the dielectric substrate is between 3 and 4, and the loss tangent of the dielectric substrate is less than 0.05%. The antenna is a graphene antenna disposed on the upper surface of the dielectric substrate; the antenna includes: an antenna radiator made of high-conductivity graphene material, used for receiving and transmitting radio frequency signals; An RFID tag chip is connected to the antenna; the RFID tag also includes a fine-tuning antenna impedance section, which is symmetrically arranged on the upper and lower sides of the RFID tag chip. A temperature sensor, built into the RFID tag chip, is used to detect soil temperature and generate a temperature signal; The AMC module includes: The AMC dielectric substrate uses an FR-4 substrate to provide structural support; The surface structure is a graphene film processed by a laser engraving machine, located on the upper surface of the AMC dielectric substrate; The underlying structure is fully covered by a graphene film, located on the lower surface of the AMC dielectric substrate; An adhesive is used to bond the surface structure and the underlying layer to both sides of the AMC dielectric substrate; The RFID tag device is made of multiple AMC modules arranged side by side on the lower surface of the RFID tag, so that the AMC modules can cover the RFID tag, and the AMC modules and the RFID tag are separated by a 2cm thick foam. The AMC module further includes a first frequency modulation section, a second frequency modulation section, and a third frequency modulation section. The first frequency modulation section is used to coarsely adjust the operating frequency of the AMC module, and the second and third frequency modulation sections are used to finely adjust the operating frequency of the AMC module.

2. The RFID tag device for soil temperature monitoring as described in claim 1, characterized in that, The RFID tag device for soil temperature monitoring also includes an antenna that is corrosion-resistant and non-metallic.

3. The RFID tag device for soil temperature monitoring as described in claim 1, characterized in that, The antenna operates in the frequency range of 860MHz to 960MHz, and the dielectric substrate is flat.

4. A method for preparing an RFID tag device for soil temperature monitoring as described in any one of claims 1 to 3, characterized in that, Includes the following steps: An antenna structure with complex impedance conjugate matching to an RFID tag chip was designed using electromagnetic simulation software. Based on the antenna structure, a graphene antenna was fabricated by cutting a graphene film with a laser. The graphene antenna is bound to the RFID tag chip. After coating the graphene antenna with high-temperature resistant adhesive, the RFID tag chip is flip-packaged and bonded to the graphene antenna, and then cured by high-temperature hot pressing.

5. The method for preparing an RFID tag for soil temperature monitoring as described in claim 4, characterized in that, It also includes the following steps: The surface structure of the artificial magnetic conductor (AMC) module is obtained by processing the antenna structure using a laser engraving machine. The bottom structure is prepared by using a single piece of graphene film. The surface structure and the bottom structure are then attached to the FR-4 substrate using an adhesive to obtain the artificial magnetic conductor (AMC) module. According to the rules of the set RFID tag device, the artificial magnetic conductor (AMC) modules are repeatedly arranged in parallel to obtain the AMC module, so that the AMC module can cover the RFID tag, and then the AMC module is attached to the lower surface of the RFID tag.

6. The method for preparing an RFID tag device for soil temperature monitoring as described in claim 4, characterized in that, After coating the chip with high-temperature resistant adhesive, it is cured by hot pressing at 170-180℃ for 12 seconds.

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