Metamaterial RFID anti-interference antenna structure facing severe environment and manufacturing method thereof

Abstract

The invention discloses a metamaterial RFID (Radio Frequency Identification) anti-interference antenna structure for a severe environment and a manufacturing method of the metamaterial RFID anti-interference antenna structure. The middle layer of a substrate of the antenna structure is made of corrosion-resistant polyether-ether-ketone resin doped carbon nanotubes; the upper-layer metal patch of the electromagnetic band gap unit array and the lower-layer metal layer of the annular gap are respectively attached to the upper surface and the lower surface of the middle layer of the substrate; and a self-adaptive impedance matching module is arranged at the joint of the equipment antenna and the feeder line. And each unit in the electromagnetic band gap unit array vertically penetrates through the substrate through a metalized via hole and is connected with the upper-layer metal patch and the lower-layer metal grounding layer of the substrate to form an LC resonance unit. The skin effect of eddy current on the metal surface can be counteracted through the reverse induction current, the loss of energy on the metal surface is greatly reduced, and the radiation efficiency of the metal surface is remarkably improved. In a complex electromagnetic environment, signals can be radiated and received more efficiently, the communication stability and reliability of an RFID system are effectively enhanced, and the probability of signal loss and error codes is reduced.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency identification technology, and relates to a metamaterial RFID anti-interference antenna structure for harsh environments and its manufacturing method. Background Technology

[0002] With the rapid development of IoT technology, antennas, as a core component of wireless communication systems, face severe challenges in special scenarios such as embedded installation on metal surfaces and liquid environment monitoring. Existing antenna technologies suffer from three major bottlenecks in practical applications, severely restricting their widespread adoption in fields such as industrial IoT, smart pipeline monitoring, and underwater communication.

[0003] First, there's the issue of radiation efficiency attenuation in metallic environments. When traditional dipole antennas operate on metal surfaces, the eddy currents induced in the metal medium lead to significant electromagnetic energy loss. According to research data from IEEE Antennas and Wireless Propagation Letters in 2021, the radiation efficiency of conventional antennas on metal surfaces is less than 35%. Existing anti-metal solutions mainly achieve magnetic shielding by stacking ferrite or ceramic substrates, but a thickness of 6mm or more is required to achieve a suppression effect. This approach is unsuitable for thickness-sensitive embedded scenarios such as pipeline monitoring, and the high dielectric constant substrate leads to increased antenna size and narrowed bandwidth (typically <100MHz), making it difficult to meet the requirements of miniaturized devices.

[0004] Secondly, it lacks adaptability to liquid and high-humidity environments. Traditional FR4 substrate antennas exhibit significant dielectric constant drift (up to 15%, according to IEEE Standard 1309-2017 test specifications) in environments with humidity >85%, resulting in a resonant frequency shift exceeding 5%. In underwater scenarios, UHF band antennas experience a sharp decrease in communication distance to less than 0.2m due to the strong absorption of electromagnetic waves by water (ISO / IEC 18000-63 standard test data). Although existing waterproof encapsulation technologies use epoxy resin potting, its high dielectric loss (tanδ>0.02) exacerbates signal attenuation, and static encapsulation methods cannot dynamically adapt to the impedance mismatch between water and air media.

[0005] Third, the limitations of manufacturing processes for complex structures. Metamaterial antennas require multi-layer structures to achieve electromagnetic bandgap modulation, but traditional photolithography processes require multiple alignments of conductive lines between layers, resulting in a yield rate of less than 70%. While multi-layer PCB vacuum lamination processes (equipment cost > $100,000) can achieve partial three-dimensional interconnection, they are difficult to meet the integrated molding requirements of curved / irregular structure antennas.

[0006] In summary, existing technologies either struggle to balance anti-metal performance with device thickness, suffer from dielectric mismatch in environmental adaptability, or face dual constraints of cost and precision in the manufacture of complex structures. Therefore, there is an urgent need for a novel antenna technology that combines anti-metal interference capabilities, environmental adaptability, and low-cost manufacturing processes to overcome the technological barriers in existing application scenarios. Summary of the Invention

[0007] The purpose of this invention is to solve the problems in the prior art, such as the difficulty in balancing anti-metal performance and equipment thickness, the existence of medium mismatch defects in environmental adaptability, or the dual constraints of cost and precision in the manufacturing of complex structures, and to provide a metamaterial RFID anti-interference antenna structure for harsh environments and its manufacturing method.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A metamaterial RFID anti-interference antenna structure for harsh environments, comprising: An electromagnetic bandgap element array is provided, which consists of electromagnetic bandgap elements periodically arranged on the upper metal surface of an antenna substrate. Each electromagnetic bandgap element penetrates the substrate vertically through a metallized via, connecting the upper metal patch to the lower metal ground layer of the substrate to form an LC resonant unit. The electromagnetic bandgap element array counteracts the skin effect of eddy currents on the metal surface through reverse induced current, thereby improving the radiation efficiency of the metal surface. An annular slit radiator is embedded in the lower metal layer of the substrate, and the plane where the annular slit radiator is located is separated from the plane where the electromagnetic bandgap unit array is located by the substrate dielectric layer. The substrate and encapsulation structure are as follows: the substrate has a multilayer structure, the middle layer is made of corrosion-resistant polyether ether ketone resin doped with carbon nanotubes, and the tensile strength is >130MPa; the upper metal patch of the electromagnetic bandgap unit array and the lower metal layer of the annular gap are respectively attached to the upper and lower surfaces of the middle layer of the substrate; the outer layer of the substrate is coated with fluorinated ethylene propylene copolymer as a dielectric encapsulation layer, and the encapsulation layer completely covers the exposed surfaces of the electromagnetic bandgap unit array and the annular gap. An adaptive impedance matching module is installed at the connection between the device antenna and the feeder, which includes an underwater mode low-frequency switching unit, a T-type matching network unit, and an integrated time-domain reflectometer and microcontroller unit for coordinated control. This module is used to adjust the device's operating parameters according to the actual scenario in underwater and harsh liquid environments, and to optimize signal transmission between the antenna and the feeder.

[0009] The electromagnetic bandgap unit has a mushroom-shaped structure with an upper metal patch: the metal patch has a size of 3.2mm × 3.2mm; when electromagnetic waves irradiate the metal patch, an induced current is generated on the patch surface, triggering electromagnetic resonance; the unit period is set to 5mm, which is 1 / 12 of the wavelength of the 915MHz band.

[0010] The metallized via has a diameter of 0.3 mm, penetrates vertically through the substrate, and connects the upper metal patch to the lower metal ground layer of the substrate; the via and the upper and lower metal layers together form a structure with inductive and capacitive characteristics, forming an LC resonant unit.

[0011] Each of the electromagnetic bandgap units is connected to the upper metal patch and the lower metal ground layer of the substrate through a metallized via to form an LC resonant unit. When an electromagnetic wave irradiates the electromagnetic bandgap unit array, an induced current is generated on the upper metal patch. The induced current flows to the lower metal ground layer through the metallized via. During this process, the capacitance characteristics of the metal patch and the inductance characteristics of the via interact to form an LC resonance.

[0012] The annular slot radiator has a slot radius of 26.3 mm and a slot width of 0.5 mm. The annular slot radiator is embedded in the lower metal layer of the substrate, and the substrate provides physical support and electrical isolation. The plane where the annular slot radiator is located is separated from the plane where the electromagnetic bandgap unit array is located by the substrate dielectric layer. The substrate dielectric layer plays a dual role of isolation and coupling, preventing direct electrical short circuit between the two different functional planes, while allowing electromagnetic waves to couple and transmit between the two planes under certain conditions.

[0013] The annular slit radiator and the electromagnetic bandgap unit array are electromagnetically coupled through the substrate dielectric layer. The electromagnetic bandgap unit array has specific frequency response characteristics and suppresses the electromagnetic waves radiated by the annular slit radiator in the 2.4-5.8 GHz frequency band, forming a wide stopband. The size, shape, relative position and spacing parameters of the annular slit radiator and the electromagnetic bandgap unit array are optimized and adjusted through electromagnetic simulation to achieve the best wide stopband characteristics.

[0014] The optimization and adjustment of the annular slit radiator through electromagnetic simulation is specifically as follows: In HFSS software, a three-dimensional model is constructed based on the actual design parameters of the annular slot radiator. The circular shape of the annular slot is defined, and the radius and width are accurately set. At the same time, a substrate model including the lower metal layer and the substrate dielectric layer is constructed, and their size and relative positional relationship are determined. The annular slot radiator is embedded in the lower metal layer of the substrate and is correctly spaced from the plane of the electromagnetic bandgap unit array that will work in cooperation with it through the substrate dielectric layer. Appropriate material properties are defined for each part in the model. The conductivity parameters are set for the metal layer on which the annular slot is based, and the dielectric constant and loss tangent parameters are defined for the substrate dielectric layer. Based on the simulation requirements, radiation boundary conditions are set for the model to simulate open space; based on the structural characteristics of the annular slit and the simulation purpose, lumped port excitation is selected and set at the corresponding position of the annular slit to simulate the excitation of the annular slit radiator. The initial simulation was run. The HFSS software performed electromagnetic field numerical calculations on the model based on Maxwell's equations to solve for the electromagnetic radiation characteristics of the annular slit radiator under the initial settings, including the radiation pattern and frequency response. The frequency response curve of the annular slit radiator was plotted using the post-processing function of HFSS software. Its radiation intensity and transmission characteristics at different frequencies were observed. The radiation pattern of the annular slit radiator at different frequencies and the spatial distribution of radiated energy were analyzed to check whether the radiation pattern met the design expectations. Based on the initial simulation results, the parameters that need to be optimized are determined, including the radius and width of the annular gap, as well as its relative position to the electromagnetic bandgap element array and the parameters of the electromagnetic bandgap element array itself. The optimization goal is to achieve wide stopband characteristics in the 2.4 - 5.8 GHz frequency band, while ensuring that electromagnetic waves can be radiated normally in other frequency bands to meet the system's communication or other electromagnetic function requirements; After the optimization process is completed, the model is reconstructed using the optimized parameters and simulation calculations are performed. The results are then compared with the initial simulation results to verify whether the optimization has achieved the expected goals. If the optimization results meet all design requirements, the optimized parameters will be determined as the final design scheme for subsequent manufacturing, testing and practical application; if problems still exist during the verification process, return to the parameter optimization stage, adjust the optimization parameters or optimization objectives, and repeat the above process until the final scheme is obtained.

[0015] The dielectric encapsulation layer is an outer coating of a 0.2 mm thick fluorinated ethylene propylene copolymer film. The film has a dielectric constant ε_r of 2.1, a temperature coefficient of less than 20 ppm / ℃, and meets the dielectric stability requirements in an environment of -40℃ to 150℃.

[0016] The underwater mode low-frequency switching unit has a built-in environmental sensing sensor for real-time monitoring of the environment in which the device is located. When the device enters the underwater environment, the sensor transmits the environmental information to the control circuit. After the control circuit analyzes and confirms that it is in an underwater application scenario, it automatically switches the device's operating frequency from the current frequency to the 13.56MHz low-frequency band through the internal frequency synthesizer and related control circuits to adapt to the complex underwater environment and improve the device's communication reliability. The T-type matching network unit includes an adjustable inductor L and a capacitor C in a 0402 package. When the device starts up or enters a new working environment, the adjustable inductor L and capacitor C are set to initial values ​​according to preset initial parameters. During device operation, when the integrated time domain reflectometer and the microcontroller work together to control the control unit to provide feedback on the impedance change information between the antenna and the feed line, the parameters of the adjustable inductor L and capacitor C are adjusted through the internal inductor and capacitor adjustment circuit to make the voltage standing wave ratio between the antenna and the feed line less than 1.5. In the integrated time-domain reflectometer and microcontroller co-control unit, the integrated time-domain reflectometer module periodically transmits high-frequency pulse signals to the feeder, receives the reflected waves, and analyzes the time and amplitude information of the reflected waves. Combined with known parameters such as the feeder propagation speed, it calculates the impedance value of the feeder at different locations and obtains the real-time changes in the feeder impedance. The microcontroller receives the feeder impedance measurement data from the integrated time-domain reflectometer module, analyzes and processes it according to a preset algorithm, and when it determines that the measured impedance change exceeds a preset threshold range and the matching network parameters need to be adjusted, it issues a corresponding control signal. The control signal is transmitted to the microelectromechanical system switch through a specific interface. The microelectromechanical system switch switches the inductance and capacitance parameters in the T-type matching network unit according to the control signal to realize the dynamic adjustment of the impedance between the antenna and the feeder.

[0017] A method for manufacturing a metamaterial RFID anti-interference antenna for harsh environments includes the following steps: Matrix material preparation: Select corrosion-resistant polyether ether ketone resin as the matrix material base, and weigh carbon nanotubes at a ratio of 25wt%; put the PEEK resin and carbon nanotubes into a high-speed mixer with a rotation speed of 1000-1500r / min and mix for 30-60 minutes to form a composite material. Preparation of conductive layer material: Prepare silver-graphene composite ink with a solid content of 65wt% and a sheet resistance of <0.5Ω / sq. Place the composite ink in a storage container and stir it thoroughly before use. Layered printing substrate: Selective laser sintering equipment is used. After turning on the equipment, the laser system is adjusted and the laser power is set to 80W. The scanning system is adjusted to make the scanning speed 1000mm / s. The powder spreading system is checked and adjusted and the layer thickness is set to 50μm. Printing process: Polyetheretherketone-carbon nanotube composite powder is evenly spread on the powder bed of the printing platform. According to the three-dimensional model, the laser is controlled to selectively sinter the powder along the set path to form a solid structure. After one layer is printed, the printing platform descends by one layer thickness, the powder spreading system spreads new powder, the laser continues to sinter, and the layers are stacked one by one until the entire substrate is printed. Conductive layer deposition: A piezoelectric printhead with a resolution of 1200 dpi is selected. The printhead is cleaned and calibrated before spraying. Silver-graphene composite ink is loaded into the printhead cartridge. According to the conductive layer pattern, the printhead is controlled to spray conductive ink layer by layer on the pre-printed substrate. Low-temperature curing: The printed part with the conductive layer deposited is placed in a vacuum oven and cured in a vacuum environment. After curing, the printed part is taken out after cooling to room temperature and the adhesion of the conductive layer is tested to ensure that it reaches the 4B level.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The metamaterial RFID anti-interference antenna structure for harsh environments in this invention comprises an electromagnetic bandgap element array consisting of periodically arranged electromagnetic bandgap elements on the upper metal surface of an antenna substrate. Each element penetrates the substrate vertically through a metallized via, connecting the upper metal patch to the lower metal ground layer, forming an LC resonant element. The skin effect of eddy currents on the metal surface can be counteracted by reverse induced current, significantly reducing energy loss on the metal surface and resulting in a significant improvement in the radiation efficiency of the metal surface. In complex electromagnetic environments, it can radiate and receive signals more efficiently, effectively enhancing the communication stability and reliability of the RFID system and reducing the probability of signal loss and bit errors.

[0019] The annular slot radiator is embedded in the lower metal layer of the substrate, and its plane is separated from the plane of the electromagnetic bandgap element array by the substrate dielectric layer. This gives the antenna a specific radiation pattern and impedance characteristics, which can better match the transmission and reception requirements of RFID readers, optimize the signal transmission path, further improve signal transmission efficiency and quality, and ensure accurate and stable data communication even in harsh environments.

[0020] The multi-layered structure of the substrate and the tight bonding between the layers give the antenna high structural strength and stability. When subjected to mechanical vibration, impact, or external pressure, the layers can support and buffer each other, effectively dispersing stress and preventing deformation or damage to the antenna structure. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a three-dimensional exploded view of the metamaterial annular slot antenna of the present invention; Figure 2This is a flowchart of the 3D printing process of the present invention; Figure 3 This is a schematic diagram of the liquid environment impedance matching circuit of the present invention. Detailed Implementation

[0023] 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. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0026] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 The three-dimensional exploded view of the metamaterial annular slot antenna of the present invention includes the spatial arrangement of the EBG array, the annular slot radiator, the PEEK substrate, and the feed line.

[0027] The present invention discloses a metamaterial RFID anti-interference antenna structure for harsh environments, characterized in that it comprises: An electromagnetic bandgap element array is provided, comprising periodically arranged electromagnetic bandgap elements on the upper metal surface of an antenna substrate. Each electromagnetic bandgap element penetrates the substrate vertically through a metallized via, connecting the upper metal patch to the lower metal ground layer, forming an LC resonant unit. The electromagnetic bandgap element array counteracts the skin effect of eddy currents on the metal surface through reverse induced current, thereby improving the radiation efficiency of the metal surface. The electromagnetic bandgap element has a mushroom-shaped structure. The upper metal patch has a size of 3.2mm × 3.2mm. When electromagnetic waves irradiate the metal patch, an induced current is generated on the patch surface, triggering electromagnetic resonance. The element period is set to 5mm, which is 1 / 12 of the wavelength of the 915MHz band. The metallized via has a diameter of 0.3mm, penetrates the substrate vertically, and connects the upper metal patch to the lower metal ground layer. The via, together with the upper and lower metal layers, constitutes a structure with inductive and capacitive characteristics, forming an LC resonant unit.

[0028] Each of the electromagnetic bandgap units is connected to the upper metal patch and the lower metal ground layer of the substrate via metallized vias to form an LC resonant unit. When an electromagnetic wave irradiates the electromagnetic bandgap unit array, an induced current is generated on the upper metal patch. This induced current flows to the lower metal ground layer through the metallized vias. During this process, the capacitive characteristics of the metal patch and the inductive characteristics of the vias interact to form an LC resonance. The resonant frequency of the LC resonant unit is determined by its equivalent inductance L and equivalent capacitance C. When the frequency of the electromagnetic wave is equal to the resonant frequency of the LC resonant unit, a strong resonance phenomenon occurs, and the response of the electromagnetic bandgap unit to the electromagnetic wave is most significant at this time. Due to the periodic arrangement of the electromagnetic bandgap element array, when each element resonates at LC, an electromagnetic bandgap is formed in a specific frequency band. Within this frequency band, the propagation of electromagnetic waves is suppressed, exhibiting high impedance characteristics. In other frequency bands, electromagnetic waves can propagate relatively freely. For RFID antennas in the 915MHz frequency band, by designing the parameters of the electromagnetic bandgap element to form an electromagnetic bandgap in the 915MHz frequency band, interference signals near this frequency band can be effectively suppressed, improving the antenna's anti-interference capability.

[0029] In traditional metal structures, when alternating current passes through, the current concentrates on the metal surface, reducing the effective conduction area, increasing the metal's resistance, generating more energy loss, and decreasing the antenna's radiation efficiency. In electromagnetic bandgap element arrays (EBG), when electromagnetic waves irradiate the metal surface, the EBG structure induces a reverse current. Due to the special structure and LC resonance characteristics of the EBG, the distribution of the induced current on the metal surface differs from that in traditional metal structures; the direction of the reverse induced current is opposite to that of the original eddy current. This reverse induced current can counteract the skin effect of the original eddy current, allowing the current to flow more evenly within the metal rather than just concentrating on the surface. This increases the effective conduction area, reduces the metal's resistance, and decreases energy loss. Actual measurements show that this design increases the metal surface radiation efficiency from 32% to 78% in traditional antennas, while simultaneously increasing the equivalent isotropic radiated power by 12 dB, significantly improving antenna performance and anti-interference capabilities. The antenna structure in this invention can counteract the skin effect of eddy currents on the metal surface through reverse induced current, greatly reducing energy loss on the metal surface and significantly improving its radiation efficiency. In complex electromagnetic environments, this antenna structure can radiate and receive signals more efficiently, effectively enhancing the communication stability and reliability of RFID systems and reducing the probability of signal loss and bit errors.

[0030] An annular slot radiator is embedded in the lower metal layer of a substrate. The plane containing the annular slot radiator is separated from the plane containing the electromagnetic bandgap unit array by a substrate dielectric layer. The slot radius of the annular slot radiator is set to 26.3 mm, and the slot width is 0.5 mm. The annular slot radiator is embedded in the lower metal layer of the substrate, which provides physical support and electrical isolation. The plane containing the annular slot radiator and the plane containing the electromagnetic bandgap unit array are separated by the substrate dielectric layer, which serves a dual function of isolation and coupling, preventing direct electrical short circuits between the two different functional planes while allowing electromagnetic waves to couple and propagate between the two planes under certain conditions. The annular slit radiator and the electromagnetic bandgap unit array are electromagnetically coupled through the substrate dielectric layer. The electromagnetic bandgap unit array has specific frequency response characteristics and suppresses the electromagnetic waves radiated by the annular slit radiator in the 2.4-5.8 GHz frequency band, forming a wide stopband. The size, shape, relative position and spacing parameters of the annular slit radiator and the electromagnetic bandgap unit array are optimized and adjusted through electromagnetic simulation to achieve the best wide stopband characteristics.

[0031] The optimization and adjustment of the annular slit radiator through electromagnetic simulation is specifically as follows: In HFSS software, a three-dimensional model is constructed based on the actual design parameters of the annular slot radiator. The circular shape of the annular slot is defined, and the radius and width are accurately set. At the same time, a substrate model including the lower metal layer and the substrate dielectric layer is constructed, and their size and relative positional relationship are determined. The annular slot radiator is embedded in the lower metal layer of the substrate and is correctly spaced from the plane of the electromagnetic bandgap unit array that will work in cooperation with it through the substrate dielectric layer. Appropriate material properties are defined for each part in the model. The conductivity parameters are set for the metal layer on which the annular slot is based, and the dielectric constant and loss tangent parameters are defined for the substrate dielectric layer. Based on the simulation requirements, radiation boundary conditions are set for the model to simulate open space; based on the structural characteristics of the annular slit and the simulation purpose, lumped port excitation is selected and set at the corresponding position of the annular slit to simulate the excitation of the annular slit radiator. The initial simulation was run. The HFSS software performed electromagnetic field numerical calculations on the model based on Maxwell's equations to solve for the electromagnetic radiation characteristics of the annular slit radiator under the initial settings, including the radiation pattern and frequency response. The frequency response curve of the annular slit radiator was plotted using the post-processing function of HFSS software. Its radiation intensity and transmission characteristics at different frequencies were observed. The radiation pattern of the annular slit radiator at different frequencies and the spatial distribution of radiated energy were analyzed to check whether the radiation pattern met the design expectations. Based on the initial simulation results, the parameters that need to be optimized are determined, including the radius and width of the annular gap, as well as its relative position to the electromagnetic bandgap element array and the parameters of the electromagnetic bandgap element array itself. The optimization goal is to achieve wide stopband characteristics in the 2.4 - 5.8 GHz frequency band, while ensuring that electromagnetic waves can be radiated normally in other frequency bands to meet the system's communication or other electromagnetic function requirements; After the optimization process is completed, the model is reconstructed using the optimized parameters and simulation calculations are performed. The results are then compared with the initial simulation results to verify whether the optimization has achieved the expected goals. If the optimization results meet all design requirements, the optimized parameters will be determined as the final design scheme for subsequent manufacturing, testing and practical application. If problems still exist during the verification process, return to the parameter optimization stage, adjust the optimization parameters or optimization objectives, and repeat the above process until the final scheme is obtained.

[0032] The substrate and encapsulation structure are as follows: the substrate has a multilayer structure, the middle layer is made of corrosion-resistant polyether ether ketone resin doped with carbon nanotubes, and the tensile strength is >130MPa; the upper metal patch of the electromagnetic bandgap unit array and the lower metal layer of the annular gap are respectively attached to the upper and lower surfaces of the middle layer of the substrate; the outer layer of the substrate is coated with fluorinated ethylene propylene copolymer as a dielectric encapsulation layer, and the encapsulation layer completely covers the exposed surfaces of the electromagnetic bandgap unit array and the annular gap.

[0033] The dielectric encapsulation layer is an outer coating of a 0.2 mm thick fluorinated ethylene propylene copolymer film. The film has a dielectric constant ε_r of 2.1, a temperature coefficient of less than 20 ppm / ℃, and meets the dielectric stability requirements in an environment of -40℃ to 150℃.

[0034] An adaptive impedance matching module is installed at the connection between the device antenna and the feeder, which includes an underwater mode low-frequency switching unit, a T-type matching network unit, and an integrated time-domain reflectometer and microcontroller unit for coordinated control. This module is used to adjust the device's operating parameters according to the actual scenario in underwater and harsh liquid environments, and to optimize signal transmission between the antenna and the feeder.

[0035] The underwater mode low-frequency switching unit has a built-in environmental sensing sensor for real-time monitoring of the environment in which the device is located. When the device enters the underwater environment, the sensor transmits the environmental information to the control circuit. After the control circuit analyzes and confirms that it is in an underwater application scenario, it automatically switches the device's operating frequency from the current frequency to the 13.56MHz low-frequency band through the internal frequency synthesizer and related control circuits to adapt to the complex underwater environment and improve the device's communication reliability. The T-type matching network unit includes an adjustable inductor L and a capacitor C in a 0402 package. When the device starts up or enters a new working environment, the adjustable inductor L and capacitor C are set to initial values ​​according to preset initial parameters. During device operation, when the integrated time domain reflectometer and the microcontroller work together to control the control unit to provide feedback on the impedance change information between the antenna and the feed line, the parameters of the adjustable inductor L and capacitor C are adjusted through the internal inductor and capacitor adjustment circuit to make the voltage standing wave ratio between the antenna and the feed line less than 1.5. In the integrated time-domain reflectometer and microcontroller co-control unit, the integrated time-domain reflectometer module periodically transmits high-frequency pulse signals to the feeder, receives the reflected waves, and analyzes the time and amplitude information of the reflected waves. Combined with known parameters such as the feeder propagation speed, it calculates the impedance value of the feeder at different locations and obtains the real-time changes in the feeder impedance. The microcontroller receives the feeder impedance measurement data from the integrated time-domain reflectometer module, analyzes and processes it according to a preset algorithm, and when it determines that the measured impedance change exceeds a preset threshold range and the matching network parameters need to be adjusted, it issues a corresponding control signal. The control signal is transmitted to the microelectromechanical system switch through a specific interface. The microelectromechanical system switch switches the inductance and capacitance parameters in the T-type matching network unit according to the control signal to realize the dynamic adjustment of the impedance between the antenna and the feeder.

[0036] The present invention discloses a method for manufacturing a metamaterial RFID anti-interference antenna for harsh environments, comprising the following steps: Matrix material preparation: Corrosion-resistant polyether ether ketone resin is selected as the matrix material base, and carbon nanotubes are weighed at a ratio of 25wt%. The PEEK resin and carbon nanotubes are placed in a high-speed mixer with a rotation speed of 1000-1500r / min and mixed for 30-60 minutes to ensure that the carbon nanotubes are uniformly dispersed in the PEEK resin, forming a composite material with good electrical conductivity and mechanical strength (tensile strength >130MPa) and a volume resistivity reduced to 10²Ω・cm.

[0037] Preparation of conductive layer material: Prepare silver-graphene composite ink with a solid content of 65wt% and a sheet resistance of <0.5Ω / sq. Place the composite ink in a storage container and stir it thoroughly before use. Layered printing substrate: Selective laser sintering equipment is used. After turning on the equipment, the laser system is adjusted and the laser power is set to 80W. The scanning system is adjusted to make the scanning speed 1000mm / s. The powder spreading system is checked and adjusted and the layer thickness is set to 50μm. Printing process: Polyetheretherketone-carbon nanotube composite powder is evenly spread on the powder bed of the printing platform. According to the three-dimensional model, the laser is controlled to selectively sinter the powder along the set path to form a solid structure. After one layer is printed, the printing platform descends by one layer thickness, the powder spreading system spreads new powder, the laser continues to sinter, and the layers are stacked one by one until the entire substrate is printed. Conductive layer deposition: A piezoelectric printhead with a resolution of 1200 dpi is selected. The printhead is cleaned and calibrated before spraying. Silver-graphene composite ink is loaded into the printhead cartridge. According to the conductive layer pattern, the printhead is controlled to spray conductive ink layer by layer on the pre-printed substrate. Low-temperature curing: The printed part with the conductive layer deposited is placed in a vacuum oven and cured in a vacuum environment. After curing, the printed part is taken out after cooling to room temperature and the adhesion of the conductive layer is tested to ensure that it reaches the 4B level.

[0038] The manufacturing process of integrated printing molding is completed to obtain an integrated molded product with good electrical conductivity and mechanical properties.

[0039] By selecting corrosion-resistant polyetheretherketone resin and adding carbon nanotubes in a certain proportion to create a composite material as the matrix material, the antenna possesses good conductivity and mechanical strength (tensile strength > 130 MPa) and a volume resistivity reduced to 10² Ω·cm, enabling it to withstand harsh environments. A silver-graphene composite ink with a solid content of 65 wt% and a sheet resistance < 0.5 Ω / sq is used as the conductive layer material to ensure conductivity. Selective laser sintering equipment is used to print the substrate layer by layer. By precisely setting parameters such as laser power, scanning speed, and layer thickness, and by layer-by-layer powder spreading and sintering, the solid structure of the substrate can be accurately constructed. A piezoelectric printhead with a resolution of 1200 dpi is used to spray conductive ink layer by layer to achieve conductive layer deposition, ensuring pattern accuracy. Low-temperature curing is carried out in a vacuum environment. Post-curing testing ensures that the conductive layer adhesion reaches a 4B level. Finally, the integrated printing process is completed, resulting in an integrated molded product with good conductivity and mechanical properties, effectively improving the antenna's anti-interference capability and reliability in harsh environments.

[0040] Example 1 Underwater Pipeline RFID Monitoring System Deployment scheme: The antenna is encapsulated in an IP68-rated titanium alloy shell, with the inner wall of the shell coated with an FEP insulating layer, and the overall thickness is 3.5mm; the reader uses Impinj Speedway Revolution R420, with a transmit power of 30dBm and equipped with a watertight RF connector; Operating mode: When water is detected (triggered by humidity sensor), it automatically switches to 13.56MHz low frequency mode.

[0041] Test data Communication performance: The surface reading distance of the metal pipe (5mm wall thickness, 304 stainless steel) is 2.1m (UHF band), which is 7 times higher than that of traditional antennas; in a water depth of 1.5m, the signal strength attenuation is 2.8dB and the bit error rate is stable at 5×10^-7 (compared to the bit error rate of 1×10^-3 of the unencapsulated antenna).

[0042] Environmental tolerance: After 1000 hours of salt spray test (ISO 9227 standard, 5% NaCl solution, 35℃), the change rate of conductive layer resistance is <3%; after temperature cycling test (-40℃~200℃, 100 cycles), the resonant frequency shifts by 0.3% (compared to 8% for conventional FR4 substrate).

[0043] Example 2 The antenna was deployed on the outer wall of a chemical reactor (95% humidity, containing Cl⁻ corrosive gas) using a 3D-printed curved bonding structure (radius of curvature R=50mm). Actual measurement data shows that after 6 months of continuous operation, the radiation efficiency decreased by <5%, meeting the ISA 106 industrial environmental standard.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A metamaterial RFID anti-interference antenna structure for harsh environments, characterized in that, include: An electromagnetic bandgap element array is provided, which consists of electromagnetic bandgap elements periodically arranged on the upper metal surface of an antenna substrate. Each electromagnetic bandgap element penetrates the substrate vertically through a metallized via, connecting the upper metal patch to the lower metal ground layer of the substrate to form an LC resonant unit. The electromagnetic bandgap element array counteracts the skin effect of eddy currents on the metal surface through reverse induced current, thereby improving the radiation efficiency of the metal surface. An annular slit radiator is embedded in the lower metal layer of the substrate, and the plane where the annular slit radiator is located is separated from the plane where the electromagnetic bandgap unit array is located by the substrate dielectric layer. The substrate and encapsulation structure are as follows: the substrate has a multilayer structure, the middle layer is made of corrosion-resistant polyether ether ketone resin doped with carbon nanotubes, and the tensile strength is >130MPa; the upper metal patch of the electromagnetic bandgap unit array and the lower metal layer of the annular gap are respectively attached to the upper and lower surfaces of the middle layer of the substrate; the outer layer of the substrate is coated with fluorinated ethylene propylene copolymer as a dielectric encapsulation layer, and the encapsulation layer completely covers the exposed surfaces of the electromagnetic bandgap unit array and the annular gap. An adaptive impedance matching module is installed at the connection between the device antenna and the feeder, which includes an underwater mode low-frequency switching unit, a T-type matching network unit, and an integrated time-domain reflectometer and microcontroller unit for coordinated control. This module is used to adjust the device's operating parameters according to the actual scenario in underwater and harsh liquid environments, and to optimize signal transmission between the antenna and the feeder.

2. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, The electromagnetic bandgap unit has a mushroom-shaped structure with an upper metal patch: the metal patch has a size of 3.2mm × 3.2mm; when electromagnetic waves irradiate the metal patch, an induced current is generated on the patch surface, triggering electromagnetic resonance; the unit period is set to 5mm, which is 1 / 12 of the wavelength of the 915MHz band.

3. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, The metallized via has a diameter of 0.3 mm, penetrates vertically through the substrate, and connects the upper metal patch to the lower metal ground layer of the substrate; the via and the upper and lower metal layers together form a structure with inductive and capacitive characteristics, forming an LC resonant unit.

4. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, Each of the electromagnetic bandgap units is connected to the upper metal patch and the lower metal ground layer of the substrate through a metallized via to form an LC resonant unit. When electromagnetic waves irradiate the electromagnetic bandgap element array, an induced current is generated on the upper metal patch. The induced current flows to the lower metal ground layer through the metallized via. During this process, the capacitive characteristics of the metal patch and the inductive characteristics of the via interact to form an LC resonance.

5. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, The annular slot radiator has a slot radius of 26.3 mm and a slot width of 0.5 mm. The annular slot radiator is embedded in the lower metal layer of the substrate, and the substrate provides physical support and electrical isolation. The plane where the annular slot radiator is located is separated from the plane where the electromagnetic bandgap unit array is located by the substrate dielectric layer. The substrate dielectric layer plays a dual role of isolation and coupling, preventing direct electrical short circuit between the two different functional planes, while allowing electromagnetic waves to couple and transmit between the two planes under certain conditions.

6. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, The annular slot radiator and the electromagnetic bandgap unit array are electromagnetically coupled through the substrate dielectric layer. The electromagnetic bandgap unit array has specific frequency response characteristics and suppresses the electromagnetic waves radiated by the annular slot radiator in the 2.4-5.8 GHz frequency band, forming a wide stopband. The size, shape, and relative position and spacing parameters of the annular slit radiator with the electromagnetic bandgap element array were optimized and adjusted through electromagnetic simulation to achieve optimal wide stopband characteristics.

7. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 6, characterized in that, The optimization and adjustment of the annular slit radiator through electromagnetic simulation is specifically as follows: In HFSS software, a three-dimensional model is constructed based on the actual design parameters of the annular slot radiator. The circular shape of the annular slot is defined, and the radius and width are accurately set. At the same time, a substrate model including the lower metal layer and the substrate dielectric layer is constructed, and their size and relative positional relationship are determined. The annular slot radiator is embedded in the lower metal layer of the substrate and is correctly spaced from the plane of the electromagnetic bandgap unit array that will work in cooperation with it through the substrate dielectric layer. Appropriate material properties are defined for each part in the model. The conductivity parameters are set for the metal layer on which the annular slot is based, and the dielectric constant and loss tangent parameters are defined for the substrate dielectric layer. Based on the simulation requirements, radiation boundary conditions are set for the model to simulate open space; based on the structural characteristics of the annular slit and the simulation purpose, lumped port excitation is selected and set at the corresponding position of the annular slit to simulate the excitation of the annular slit radiator. The initial simulation was run. The HFSS software performed electromagnetic field numerical calculations on the model based on Maxwell's equations to solve for the electromagnetic radiation characteristics of the annular slit radiator under the initial settings, including the radiation pattern and frequency response. The frequency response curve of the annular slit radiator was plotted using the post-processing function of HFSS software. Its radiation intensity and transmission characteristics at different frequencies were observed. The radiation pattern of the annular slit radiator at different frequencies and the spatial distribution of radiated energy were analyzed to check whether the radiation pattern met the design expectations. Based on the initial simulation results, the parameters that need to be optimized are determined, including the radius and width of the annular gap, as well as its relative position to the electromagnetic bandgap element array and the parameters of the electromagnetic bandgap element array itself. The optimization goal is to achieve wide stopband characteristics in the 2.4 - 5.8 GHz frequency band, while ensuring that electromagnetic waves can be radiated normally in other frequency bands to meet the system's communication or other electromagnetic function requirements; After the optimization process is completed, the model is reconstructed using the optimized parameters and simulation calculations are performed. The results are then compared with the initial simulation results to verify whether the optimization has achieved the expected goals. If the optimization results meet all design requirements, the optimized parameters will be determined as the final design scheme for subsequent manufacturing, testing and practical application. If problems still exist during the verification process, return to the parameter optimization stage, adjust the optimization parameters or optimization objectives, and repeat the above process until the final solution is obtained.

8. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, The dielectric encapsulation layer is an outer coating of a 0.2 mm thick fluorinated ethylene propylene copolymer film. The film has a dielectric constant ε_r of 2.1, a temperature coefficient of less than 20 ppm / ℃, and meets the dielectric stability requirements in an environment of -40℃ to 150℃.

9. The metamaterial RFID anti-interference antenna structure for harsh environments as described in claim 1, characterized in that, The underwater mode low-frequency switching unit has a built-in environmental sensing sensor for real-time monitoring of the environment in which the device is located. When the device enters the underwater environment, the sensor transmits the environmental information to the control circuit. After the control circuit analyzes and confirms that it is in an underwater application scenario, it automatically switches the device's operating frequency from the current frequency to the 13.56MHz low-frequency band through the internal frequency synthesizer and related control circuits to adapt to the complex underwater environment and improve the device's communication reliability. The T-type matching network unit includes an adjustable inductor L and a capacitor C in a 0402 package. When the device starts up or enters a new working environment, the adjustable inductor L and capacitor C are set to initial values ​​according to preset initial parameters. During device operation, when the integrated time domain reflectometer and the microcontroller work together to control the control unit to provide feedback on the impedance change information between the antenna and the feed line, the parameters of the adjustable inductor L and capacitor C are adjusted through the internal inductor and capacitor adjustment circuit to make the voltage standing wave ratio between the antenna and the feed line less than 1.

5. In the integrated time-domain reflectometer and microcontroller co-control unit, the integrated time-domain reflectometer module periodically transmits high-frequency pulse signals to the feeder, receives the reflected waves, and analyzes the time and amplitude information of the reflected waves. Combined with known parameters such as the feeder propagation speed, it calculates the impedance value of the feeder at different locations and obtains the real-time changes in the feeder impedance. The microcontroller receives the feeder impedance measurement data from the integrated time-domain reflectometer module, analyzes and processes it according to a preset algorithm, and when it determines that the measured impedance change exceeds a preset threshold range and the matching network parameters need to be adjusted, it issues a corresponding control signal. The control signal is transmitted to the microelectromechanical system switch through a specific interface. The microelectromechanical system switch switches the inductance and capacitance parameters in the T-type matching network unit according to the control signal to realize the dynamic adjustment of the impedance between the antenna and the feeder.

10. A method for manufacturing a metamaterial RFID anti-interference antenna for harsh environments, characterized in that, Includes the following steps: Matrix material preparation: Corrosion-resistant polyether ether ketone resin is selected as the matrix material base, and carbon nanotubes are weighed at a ratio of 25wt%. The PEEK resin and carbon nanotubes are placed in a high-speed mixer with a rotation speed of 1000-1500r / min and mixed for 30-60 minutes to form a composite material. Preparation of conductive layer material: Prepare silver-graphene composite ink with a solid content of 65wt% and a sheet resistance of <0.5Ω / sq. Place the composite ink in a storage container and stir it thoroughly before use. Layered printing substrate: Selective laser sintering equipment is used. After turning on the equipment, the laser system is adjusted and the laser power is set to 80W. The scanning system is adjusted to make the scanning speed 1000mm / s. The powder spreading system is checked and adjusted and the layer thickness is set to 50μm. Printing process: Polyetheretherketone-carbon nanotube composite powder is evenly spread on the powder bed of the printing platform. According to the three-dimensional model, the laser is controlled to selectively sinter the powder along the set path to form a solid structure. After one layer is printed, the printing platform descends by one layer thickness, the powder spreading system spreads new powder, the laser continues to sinter, and the layers are stacked one by one until the entire substrate is printed. Conductive layer deposition: A piezoelectric printhead with a resolution of 1200 dpi is selected. The printhead is cleaned and calibrated before spraying. Silver-graphene composite ink is loaded into the printhead cartridge. According to the conductive layer pattern, the printhead is controlled to spray conductive ink layer by layer on the pre-printed substrate. Low-temperature curing: The printed part with the conductive layer deposited is placed in a vacuum oven and cured in a vacuum environment. After curing, the printed part is taken out after cooling to room temperature and the adhesion of the conductive layer is tested to ensure that it reaches the 4B level.

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