Liquid metal-carbon nanotube doped photosensitive resin, preparation method and application thereof

Abstract

The application discloses a liquid metal-carbon nanotube doped photosensitive resin and a preparation method and application thereof, and belongs to the technical field of absorption-transmission integrated superstructure materials. The multi-walled carbon nanotubes are functionally treated by adopting a chemical modification method, and the electromagnetic parameters of the multi-walled carbon nanotubes are regulated by introducing a liquid metal dielectric functional group. The liquid metal-loaded carbon nanotubes are doped in the modified photopolymerization resin to obtain the liquid metal-carbon nanotube doped photosensitive resin. The multi-walled carbon nanotubes are functionally treated by adopting a chemical modification method, and the electromagnetic parameters, i.e. the real part and the imaginary part of the dielectric constant, are regulated by introducing a liquid metal eutectic gallium-indium alloy dielectric functional group. The functionalized carbon nanotubes, i.e. the liquid metal-loaded carbon nanotubes, are doped in a polyether acrylate photocuring matrix, i.e. the modified photopolymerization resin, to realize accurate regulation of the electromagnetic performance of the material.

Description

Technical Field

[0001] This invention relates to the field of integrated superstructure materials technology, specifically to a liquid metal-carbon nanotube doped photosensitive resin, its preparation method, and its application. Background Technology

[0002] With the rapid development of modern military technology, the application of electronic information technology in weaponry is becoming increasingly widespread, especially with the large-scale deployment of advanced detection radars and precision-guided weapons, making the battlefield environment increasingly complex. Therefore, stealth technology has become a key means to improve the survivability and penetration effectiveness of weaponry. As one of the primary points of contact between weaponry and electromagnetic waves, radar radomes need to absorb enemy detection electromagnetic waves while allowing friendly communication electromagnetic waves to pass through. Traditional radar radomes can meet the requirement of high transmittance (≥70%) in specific operating frequency bands, such as the X-band and Ku-band, but it is difficult to achieve stealth functionality using traditional absorbing coatings. Therefore, developing a new type of radome that combines absorption and transmission functions is a key point in solving the technical challenge of full stealth for weapon radar equipment, and it is also a current research hotspot and difficulty in the field of international stealth materials.

[0003] Currently, traditional absorbing materials suffer from drawbacks such as narrow bandwidth, large thickness, and heavy weight. Furthermore, they are generally only optimized for specific frequency bands and have limited loss characteristics, making it difficult to meet the stealth requirements of modern equipment requiring broadband absorbing capabilities. In addition, when using traditional absorbing materials to prepare absorbing coatings, the absorption performance of the operating frequency band is often optimized only, failing to allow electromagnetic waves to penetrate well in other frequency bands, thus making it difficult to meet the requirement of novel radomes that combine both absorbing and transmitting functions.

[0004] To achieve both wave transmission and absorption performance, traditional penetrating-penetrating integrated materials commonly employ frequency selective surfaces (FSS). FSSs, with their unique spatial filtering characteristics, are widely used in antenna systems, electromagnetic stealth, and wireless communication systems. Traditional bandpass FSS radomes can achieve lossless transmission of electromagnetic waves within a specific frequency range while reflecting electromagnetic waves of other frequency bands in different directions, thereby enhancing the stealth effect of monostatic radar. However, frequency selective surfaces have significant drawbacks. For example, they can only reflect out-of-band electromagnetic waves, achieving stealth against monostatic radar; furthermore, their operating bandwidth is narrow, typically less than 1 GHz, and their manufacturing process is complex, making large-scale production difficult. In bistatic or multistatic radar detection environments, penetrating-penetrating integrated frequency selective surfaces (FSRs) offer advantages over FSSs. They not only achieve wave transmission in specific frequency bands but also possess a certain degree of wave absorption, effectively improving the target's all-around stealth capabilities while ensuring normal antenna operation.

[0005] However, the above-mentioned integrated absorber-scan material prepared by FSS or FSR has the following problems: it has a single electromagnetic wave dissipation mechanism, can only achieve single-station radar stealth through reflection, has a narrow working bandwidth, poor room temperature conductivity, and complex preparation process, making it impossible to mass-produce. Summary of the Invention

[0006] This invention provides a liquid metal-carbon nanotube doped photosensitive resin, its preparation method, and its application. It effectively solves the technical problems of electromagnetic wave dissipation mechanism, narrow working bandwidth, and poor room temperature conductivity of the integrated absorption and permeation materials prepared by FSS or FSR. At the same time, it provides a photocurable resin composite material that combines high-frequency absorption and low-frequency transmission, and synergistic optimization of mechanical and electromagnetic properties.

[0007] The first objective of this invention is to provide a method for preparing a liquid metal-carbon nanotube-doped photosensitive resin, characterized by comprising the following steps: A modified photopolymer resin was obtained by modifying a photopolymer resin with polyethylene glycol diacrylate as a modifier.

[0008] At 0℃~4℃, liquid metal is dispersed and loaded onto the multi-walled carbon nanotubes using cyclohexane as a solvent to obtain liquid metal-loaded carbon nanotubes; the liquid metal is a eutectic gallium-indium alloy.

[0009] The liquid metal-loaded carbon nanotubes are doped into the modified photopolymer resin to obtain a liquid metal-carbon nanotube-doped photosensitive resin.

[0010] In a preferred embodiment, the mass ratio of polyethylene glycol diacrylate to photopolymer resin is 1:7 to 9.5.

[0011] In a preferred embodiment, the mass ratio of polyethylene glycol diacrylate, multi-walled carbon nanotubes, and liquid metal is 10:1:1 to 10. When the mass ratio of liquid metal exceeds the specified value of 10, such as 15, photocuring cannot be performed.

[0012] In a preferred embodiment, the doping specifically involves adding the liquid metal-loaded carbon nanotubes to the modified photopolymer resin and mechanically stirring to obtain a liquid metal-carbon nanotube-doped photosensitive resin.

[0013] As a preferred embodiment, the preparation method of the polyethylene glycol diacrylate is as follows: at 0℃~4℃, polyethylene glycol is dissolved in anhydrous dichloromethane, an anhydrous dichloromethane solution of acryloyl chloride is added, and then triethylamine is added. The reaction is carried out at 0℃~4℃ under a protective atmosphere, and then at room temperature to generate triethylamine hydrochloride. The by-products in the reaction are removed to obtain polyethylene glycol diacrylate.

[0014] In a preferred embodiment, after reacting at room temperature, the reaction further includes filtration, washing the filtrate with a saturated sodium bicarbonate aqueous solution, removing the solvent by rotary evaporation, precipitating with diethyl ether, washing with diethyl ether, and vacuum drying to obtain polyethylene glycol diacrylate.

[0015] A second objective of this invention is to provide a liquid metal-carbon nanotube-doped photosensitive resin, prepared using any of the preparation methods described above.

[0016] The third objective of this invention is to provide an application of the above-mentioned liquid metal-carbon nanotube-doped photosensitive resin in the preparation of a bilayer absorbent integrated superstructure material for use in radar radomes.

[0017] As a preferred embodiment, the preparation method of the dual-layer permeation integrated superstructure material is as follows: the photoinitiator TPO is added to liquid metal-carbon nanotube doped photosensitive resin, and stirred at room temperature in the dark until the photoinitiator TPO is completely dissolved to obtain a light yellow transparent viscous printing raw material. In an open environment at room temperature, 3D printing is performed on the FSS frequency selective surface to obtain the printed part. The part is then cured under ultraviolet light to obtain the absorption layer, thus obtaining the dual-layer permeation integrated superstructure material.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for preparing a liquid metal-carbon nanotube-doped photosensitive resin. Polyethylene glycol diacrylate is used as a modifier to modify the photopolymer resin, thereby introducing more photocurable reactive groups and improving the photocuring efficiency of the photopolymer resin, resulting in a modified photopolymer resin. This invention employs a chemical modification method to functionalize multi-walled carbon nanotubes by introducing a liquid metal eutectic gallium-indium alloy as a dielectric functional group to adjust the electromagnetic parameters, specifically the real and imaginary parts of the dielectric constant. The functionalized carbon nanotubes, i.e., liquid metal-loaded carbon nanotubes, are then doped into a polyether acrylate photocurable matrix to achieve precise control of the material's electromagnetic properties. This invention uses the prepared liquid metal-carbon nanotube-doped photosensitive resin to prepare a bilayer absorber-permeable integrated superstructure material. The bilayer absorber-permeable integrated superstructure material prepared by this invention has a wide operating bandwidth, with a transmission frequency of 3.5 GHz to 7 GHz and an absorption frequency of 12 GHz to 18 GHz. It also exhibits relatively low conductivity, with an optimal room temperature conductivity of 3.25 × 10⁻⁶. -5 Because the double-layer permeable integrated superstructure material prepared in this invention has many pores inside, electromagnetic waves undergo multiple reflections inside, resulting in loss. Secondly, there will be a certain amount of conduction loss. The most important losses occur inside the carbon nanotubes and at the interface polarization loss between the multi-walled carbon nanotubes and the liquid gallium indium alloy. Therefore, there are many electromagnetic wave dissipation mechanisms. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the preparation process of the double-layer absorbent-permeable integrated superstructure material of the present invention. The upper metamaterial is an absorption layer prepared by liquid metal-carbon nanotube doped photosensitive resin, and the lower FSS layer is an FSS frequency selective surface.

[0020] Figure 2 Figure 1 shows the synthesis and characterization of the polyethylene glycol diacrylate prepared in this invention. Figure 2a is the synthesis route of polyethylene glycol diacrylate, Figure 3b is the proton NMR spectrum of polyethylene glycol diacrylate, Figure 4c is the carbon NMR spectrum of polyethylene glycol diacrylate, and Figure 5d is the infrared spectrum of polyethylene glycol diacrylate.

[0021] Figure 3 The present invention uses photopolymerization resin FLGPC04 and photopolymerization reaction exothermic heat flow curves with different amounts of liquid metal and 1wt% CNTs. FPR is photopolymerization resin FLGPC04.

[0022] Figure 4 Photocuring rheological tests were conducted on the modified photopolymer resin of this invention.

[0023] Figure 5 The figures show a comparison of the morphology and properties of the modified photopolymer resin prepared in Comparative Example 1 of this invention, namely the modified resin, and the liquid metal-carbon nanotube-doped photosensitive resin prepared in Examples 1 to 3 and Comparative Example 3. In the figures, a is the exothermic heat flow curve of the photopolymerization reaction, b is the SEM image of the liquid metal-loaded carbon nanotubes, c is the photocuring rheology diagram of the liquid metal-carbon nanotube-doped photosensitive resin prepared in Example 3, d is the cross-sectional elemental analysis diagram of the 3D printed part, e is the micro-CT image of the 3D printed part, and f is the diameter distribution diagram of the liquid metal particles inside the 3D printed part.

[0024] Figure 6 The diagram shows the complex dielectric constants of the liquid metal-doped photosensitive resins prepared in Comparative Examples 4 to 6 of this invention.

[0025] Figure 7 The figures show two-dimensional and three-dimensional reflection loss diagrams of the liquid metal-carbon nanotube-doped photosensitive resins prepared in Examples 1 to 3 of this invention. Figure a is the three-dimensional reflection loss diagram of Example 1, Figure b is the three-dimensional reflection loss diagram of Example 2, Figure c is the three-dimensional reflection loss diagram of Example 3, Figure d is the two-dimensional reflection loss diagram of Example 1, Figure e is the two-dimensional reflection loss diagram of Example 2, and Figure f is the two-dimensional reflection loss diagram of Example 3.

[0026] Figure 8The figures shown are Cole-Cole diagrams of the liquid metal-carbon nanotube-doped photosensitive resin prepared in Examples 1 to 3 of this invention and the carbon nanotube-doped photosensitive resin prepared in Comparative Example 2, wherein figure a is Comparative Example 2, figure b is Example 1, figure c is Example 2, and figure d is Example 3.

[0027] Figure 9 The simulation results of the electromagnetic field distribution in the double-layer permeable integrated superstructure material prepared in this invention are shown in Figure a, where: Figure a is the electric field intensity at 4.00 GHz; Figure b is the electric field intensity at 9.00 GHz; Figure c is the magnetic field intensity at 4.00 GHz; Figure d is the magnetic field intensity at 9.00 GHz; Figure e is the energy loss at 4.00 GHz; Figure f is the energy loss at 9.00 GHz; Figure g is the electric field intensity at 13.00 GHz; Figure h is the magnetic field intensity at 13.00 GHz; and Figure i is the energy loss at 13.00 GHz.

[0028] Figure 10 The figures are Smith charts of the liquid metal-carbon nanotube-doped photosensitive resin prepared in Examples 1 to 3 of the present invention and the carbon nanotube-doped photosensitive resin prepared in Comparative Example 2, wherein (a) is Comparative Example 2, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

[0029] Figure 11 The images show the physical specimen and measured S-parameters of the double-layer permeable integrated superstructure material prepared according to this invention. Figure a shows a 16cm × 16cm × 0.6cm printed copy of the double-layer permeable integrated superstructure material; Figure b shows a structural unit of the double-layer permeable integrated superstructure material; Figure c shows a magnified SEM image of the top detail; Figure d shows a side view of the double-layer permeable integrated superstructure material unit, with the bottom being an FSS structure and the upper layer being a Schwarz P structure absorbing layer; Figure e shows a physical image of the bottom FSS structure; Figure f shows a dimensional schematic of the FSS structure; and Figure g shows the simulated and measured S-parameters. Detailed Implementation

[0030] To enable those skilled in the art to better understand and implement the technical solutions of this invention, the invention is further described below with reference to specific embodiments. However, the embodiments are not intended to limit the invention. Unless otherwise specified, the following test methods and detection methods are conventional methods; unless otherwise specified, the reagents and raw materials are commercially available.

[0031] As mentioned in the background section of this invention, current integrated absorber-permeable materials suffer from several drawbacks: a single electromagnetic wave dissipation mechanism, achieving single-station radar stealth only through reflection, narrow operating bandwidth, poor room-temperature conductivity, complex fabrication processes, and inability to achieve large-scale production. To address these technical problems, this invention provides a liquid metal-carbon nanotube-doped photosensitive resin, its preparation method, and its applications.

[0032] The technical solution of the present invention will be analyzed and described in detail below.

[0033] This invention first provides a method for preparing liquid metal-carbon nanotube-doped photosensitive resin, comprising the following steps: Polyethylene glycol diacrylate was used as a modifier to modify the photopolymer resin, thereby improving the photocuring efficiency of the photopolymer resin and obtaining a modified photopolymer resin.

[0034] At 0℃~4℃, using cyclohexane as a solvent, liquid metal is dispersed and loaded onto the multi-walled carbon nanotubes to obtain liquid metal-loaded carbon nanotubes, denoted as EGaIn@CNTs; the liquid metal is a eutectic gallium-indium alloy, denoted as EGaIn.

[0035] The liquid metal-loaded carbon nanotubes were mechanically stirred and incorporated into the modified photopolymer resin to obtain a liquid metal-carbon nanotube-doped photosensitive resin.

[0036] In the above technical solution, the photopolymerizing resin used is specifically FLGPCL04, purchased from Shenzhen Formlabs Technology Co., Ltd. The liquid metal eutectic gallium-indium alloy used is purchased from Shanghai McLean Biochemical Technology Co., Ltd., with a gallium to indium mass ratio of 40:60.

[0037] This invention employs a chemical modification method to functionalize multi-walled carbon nanotubes and adjusts the electromagnetic parameters, specifically the real and imaginary parts of the dielectric constant, by introducing a liquid metal eutectic gallium-indium alloy as a dielectric functional group. The functionalized carbon nanotubes, i.e., liquid metal-loaded carbon nanotubes, are then doped into a polyether acrylate photocurable matrix, achieving precise control over the electromagnetic properties of the liquid metal-carbon nanotube-doped photosensitive resin.

[0038] To improve the photocuring efficiency of the photopolymer resin, the mass ratio of polyethylene glycol diacrylate to the photopolymer resin is 1:7 to 9.5. For the above ratio, when the mass ratio of the photopolymer resin is less than 7 (i.e., the proportion of polyethylene glycol diacrylate is higher), the printed structure is softer, has poorer mechanical properties, and the fine, thin structures in the printed structure cannot maintain a good morphology. When the mass ratio of the photopolymer resin is greater than 9.5, because the proportion of polyethylene glycol diacrylate is lower, most of the material uses small molecules from commercial resins as photocurable groups, resulting in an overly rigid material. This leads to weak bending resistance and reduces the doping amount of EGaIn and CNTs.

[0039] To ensure sufficient curing of the liquid metal-carbon nanotube-doped photosensitive resin during subsequent 3D printing and ultraviolet irradiation, the mass ratio of polyethylene glycol diacrylate, multi-walled carbon nanotubes, and liquid metal is 10:1:1 to 10. When the mass ratio of liquid metal exceeds the specified 10, such as 15, photocuring cannot be performed.

[0040] It should be noted that the preparation method of polyethylene glycol diacrylate used in this invention is as follows: at 0℃~4℃, polyethylene glycol is dissolved in anhydrous dichloromethane, an anhydrous dichloromethane solution of acryloyl chloride is added, and then triethylamine is added. The reaction is carried out at 0℃~4℃ under a protective atmosphere, and then at room temperature to generate triethylamine hydrochloride. Byproducts in the reaction are removed. After the room temperature reaction is completed, a mixture is obtained, filtered, and the filtrate is washed with a saturated sodium bicarbonate aqueous solution. The solvent is removed by rotary evaporation, precipitated with diethyl ether, washed with diethyl ether, and dried under vacuum to obtain polyethylene glycol diacrylate.

[0041] This invention also provides a liquid metal-carbon nanotube-doped photosensitive resin, prepared using the above-described method, and applied to the preparation of a bilayer permeable integrated superstructure material. Specifically, 3 wt% of photoinitiator TPO is added to the liquid metal-carbon nanotube-doped photosensitive resin, and stirred at room temperature in the dark until the photoinitiator TPO is completely dissolved, resulting in a light yellow, transparent, viscous printing material. 3D printing is performed in an open environment at room temperature to obtain the printed part, which is then cured under ultraviolet light to obtain a bilayer permeable integrated superstructure material. The light intensity during the 3D printing process is 30 mW / cm². 2 The illumination time was 20 seconds, and the ultraviolet light intensity was 200 mW / cm². 2 The curing time is 30 minutes.

[0042] The 3D model was designed and drawn using Materialize Magics V21 computer-aided design (CAD) software developed by Materialize, a Belgian company. The upper superstructure is a Schwarz P-type structure, and the lower layer is an FSS (Frequency Selective Surface) structure. The aforementioned Schwarz P-structure was printed using the liquid metal-carbon nanotube-doped photosensitive resin of this invention as the raw material. The designed 3D model was imported into slicing software, exported as a .tdp format printer-specific file, and uploaded to the printer.

[0043] 3D printing was performed in an open environment at room temperature using an AUTOCERA-M DLP 3D printer and its accompanying 10dim slicing software manufactured by Beijing Ten Dimensions Technology Co., Ltd.

[0044] The printer's main specifications are as follows: printing area of ​​96mm×54mm×200mm, and exposure resolution of 1920×1080 pixels. After printing, the printed parts are rinsed with ethanol to remove residual material, and then cleaned with isopropanol to remove residual ethanol. The printed parts are then placed in a UV curing chamber for curing to obtain a double-layer, integrated superstructure material.

[0045] In preparing a bilayer permeable integrated superstructure material, this invention involves adding a photoinitiator TPO to a liquid metal-carbon nanotube-doped photosensitive resin. The mixture is stirred at room temperature in the dark until the TPO is completely dissolved, yielding a light yellow, transparent, viscous printing material. This material is then 3D printed on a frequency-selective surface (FSS) under open-air conditions at room temperature to obtain a printed part. The part is then cured under ultraviolet light to obtain an absorption layer plus an FSS, thus producing the bilayer permeable integrated superstructure material. Under the action of the photoinitiator TPO, polyethylene glycol diacrylate undergoes a free radical polymerization reaction, resulting in a photocurable matrix material with tunable mechanical properties.

[0046] The bilayer absorber-permeable integrated superstructure material prepared in this invention has an absorber layer, i.e., the top layer, with periodic gradient pores designed. The typical pore size of the surface layer is r≈0.8mm, and the surface impedance Z is optimized. sThis approach brings the impedance close to free space, i.e., Z0 = 377Ω, minimizing the reflection of the incident wave. When the incident wave enters the absorbing layer material, the three-dimensional conductive network formed by EGaIn@CNTs enhances conductivity loss. Secondly, the interface polarization and dipole polarization induced at the interfaces between EGaIn@CNTs and the resin matrix, and between CNTs and EGaIn, increase with increasing content, contributing more to polarization loss. Finally, the bottom FSS frequency selective surface reflects incompletely absorbed electromagnetic waves back to the absorbing layer for secondary absorption, especially at high frequencies. The bottom FSS frequency selective surface transmits signals within the low-frequency band while simultaneously reflecting out-of-band waves back to the absorbing layer for re-absorption, thereby improving overall absorption efficiency. When the incident electric field is perpendicular to the metal slit array, this structure exhibits strong frequency selectivity. At low frequencies, the slowly changing electric field prolongs the interaction time of the narrow metal strips, promoting charge separation and migration towards the edges. At the edges, the charge remains localized and moves minimally, resulting in limited charge accumulation, weak current, and minimal radiation loss, thus ensuring efficient transmission. At high frequencies, rapidly changing electric fields induce strong electron oscillations, leading to significant absorption and back radiation, thereby hindering transmission. Therefore, the dual-layer integrated absorber-transmitter superstructure material provided by this invention combines the frequency selectivity of the FSS with the absorption capability of the absorbing layer, achieving high-frequency absorption and low-frequency transmission. This functional coupling design achieves effective wave absorption-transmission integration, demonstrating great potential for applications in low-observable radar systems.

[0047] The technical effects of the present invention will be described below through specific embodiments and comparative examples.

[0048] Example 1 A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol (PEG) in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and added dropwise slowly to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate (PEGDA), was completely dried under vacuum.

[0049] S2, Preparation of liquid metal-loaded carbon nanotubes: 1g of liquid metal EGaIn and 1g of multi-walled carbon nanotubes were placed in a cell disruptor and 50mL of cyclohexane was added. The mixture was placed in a cell disruptor and sonicated in an ice-water bath for 3 hours to disperse the liquid metal and load it onto the multi-walled carbon nanotubes. Finally, the cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from breaking, and liquid metal-loaded carbon nanotubes were obtained, denoted as EGaIn@CNTs.

[0050] S3, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04, and the mixture is thoroughly stirred to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, EGaIn@CNTs are incorporated into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-carbon nanotube-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 1wt% EGaIn and 1wt% CNTs, denoted as photosensitive resin-01 with 1wt% EGaIn and 1wt% CNTs doping.

[0051] Example 2 A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol and the mixture was placed in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The precipitate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0052] S2, Preparation of liquid metal-loaded carbon nanotubes: 5g of liquid metal EGaIn and 1g of multi-walled carbon nanotubes were placed in a cell disruptor and 50mL of cyclohexane was added. The mixture was placed in a cell disruptor and sonicated in an ice-water bath for 3 hours to disperse the liquid metal and load it onto the multi-walled carbon nanotubes. Finally, the cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from breaking, and liquid metal-loaded carbon nanotubes were obtained, denoted as EGaIn@CNTs.

[0053] S3, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04, and the mixture is thoroughly stirred to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, EGaIn@CNTs are incorporated into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-carbon nanotube-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 5wt% EGaIn and 1wt% CNTs, denoted as photosensitive resin-05 with 5wt% EGaIn and 1wt% CNTs doping.

[0054] Example 3 A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol (PEG) and the mixture was placed in an ice bath. 12.9 g of acryloyl chloride was dissolved in 500 mL of anhydrous dichloromethane in a 500 mL three-necked flask, and then slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0055] S2, Preparation of liquid metal-loaded carbon nanotubes: 10g of liquid metal EGaIn and 1g of multi-walled carbon nanotubes were placed in a cell disruptor and 50mL of cyclohexane was added. The mixture was placed in a cell disruptor and sonicated in an ice-water bath for 3 hours to disperse the liquid metal and load it onto the multi-walled carbon nanotubes. Finally, the cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from breaking, and liquid metal-loaded carbon nanotubes were obtained, denoted as EGaIn@CNTs.

[0056] S3, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04, and the mixture is thoroughly stirred to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, EGaIn@CNTs are incorporated into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-carbon nanotube-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 10wt% EGaIn and 1wt% CNTs, denoted as photosensitive resin-10 with 10wt% EGaIn and 1wt% CNTs doping.

[0057] Example 4 A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol (PEG) in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and added dropwise slowly to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate (PEGDA), was completely dried under vacuum.

[0058] S2, Preparation of liquid metal-loaded carbon nanotubes: 1g of liquid metal EGaIn and 1g of multi-walled carbon nanotubes were placed in a cell disruptor and 50mL of cyclohexane was added. The mixture was placed in a cell disruptor and sonicated in an ice-water bath for 3 hours to disperse the liquid metal and load it onto the multi-walled carbon nanotubes. Finally, the cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from breaking, and liquid metal-loaded carbon nanotubes were obtained, denoted as EGaIn@CNTs.

[0059] S3, 10g of the polyethylene glycol acrylate is added to 70g of photopolymer resin FLGPC04 and mixed thoroughly by stirring to obtain modified photopolymer resin, denoted as PGD-FLGPC04. Then, EGaIn@CNTs are incorporated into PGD-FLGPC04 by mechanical stirring to obtain liquid metal-carbon nanotube doped photosensitive resin.

[0060] Example 5 A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol (PEG) in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and added dropwise slowly to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate (PEGDA), was completely dried under vacuum.

[0061] S2, Preparation of liquid metal-loaded carbon nanotubes: 1g of liquid metal EGaIn and 1g of multi-walled carbon nanotubes were placed in a cell disruptor and 50mL of cyclohexane was added. The mixture was placed in a cell disruptor and sonicated in an ice-water bath for 3 hours to disperse the liquid metal and load it onto the multi-walled carbon nanotubes. Finally, the cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from breaking, and liquid metal-loaded carbon nanotubes were obtained, denoted as EGaIn@CNTs.

[0062] S3, 10g of the polyethylene glycol acrylate is added to 95g of photopolymer resin FLGPC04 and thoroughly mixed by stirring to obtain modified photopolymer resin, denoted as PGD-FLGPC04. Then, EGaIn@CNTs are incorporated into PGD-FLGPC04 by mechanical stirring to obtain liquid metal-carbon nanotube doped photosensitive resin.

[0063] To further demonstrate the technical effects of the present invention, a comparative example is also provided, as follows: Comparative Example 1 The difference from Example 1 is that only photopolymer resin, i.e. modified resin, is prepared without doping with liquid metal-supported carbon nanotubes.

[0064] A method for preparing a modified photopolymer resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol and the mixture was kept in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0065] S2, 10g of the polyethylene glycol acrylate is added to 90g of photopolymer resin FLGPC04, and the mixture is thoroughly stirred to obtain the modified photopolymer resin, denoted as PGD-FLGPC04.

[0066] Comparative Example 2 The difference from Example 1 is that no liquid metal is added.

[0067] A method for preparing a carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol and the mixture was kept in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0068] S2, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04 and thoroughly mixed by stirring to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, 1g of multi-walled carbon nanotubes are incorporated into PGD-FLGPC04 by mechanical stirring to obtain carbon nanotube-doped photosensitive resin. The above carbon nanotube-doped photosensitive resin contains 1wt% multi-walled carbon nanotubes, denoted as 1wt% CNTs-doped photosensitive resin.

[0069] Comparative Example 3 The difference compared to Example 1 is that the amount of liquid metal added is adjusted to 15g.

[0070] A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol and the mixture was kept in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0071] S2, Preparation of liquid metal-loaded carbon nanotubes: 15g of liquid metal EGaIn and 1g of multi-walled carbon nanotubes were placed in a cell disruptor and 50mL of cyclohexane was added. The mixture was placed in a cell disruptor and sonicated in an ice-water bath for 3 hours to disperse the liquid metal and load it onto the multi-walled carbon nanotubes. Finally, the cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from breaking, and liquid metal-loaded carbon nanotubes were obtained, denoted as EGaIn@CNTs.

[0072] S3, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04, and the mixture is thoroughly stirred to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, EGaIn@CNTs are incorporated into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-carbon nanotube-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 15wt% EGaIn and 1wt% CNTs, denoted as 15wt%EGaIn and 1wt%CNTs-doped photosensitive resin-15.

[0073] Comparative Example 4 The difference from Example 1 is that multi-walled carbon nanotubes are not added.

[0074] A method for preparing a liquid metal-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol (PEG) in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and added dropwise slowly to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The filtrate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate (PEGDA), was completely dried under vacuum.

[0075] S2, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04 and thoroughly mixed by stirring to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, 1g of liquid metal eutectic gallium indium alloy is doped into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 1wt% liquid metal eutectic gallium indium alloy EGaIn, denoted as 1wt% EGaIn-doped photosensitive resin.

[0076] Comparative Example 5 The difference from Example 2 is that multi-walled carbon nanotubes are not added.

[0077] A method for preparing a liquid metal-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol and the mixture was placed in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The precipitate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0078] S2, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04 and thoroughly mixed by stirring to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, 5g of liquid metal eutectic gallium indium alloy is doped into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 5wt% liquid metal eutectic gallium indium alloy EGaIn, denoted as 5wt% EGaIn-doped photosensitive resin.

[0079] Comparative Example 6 The difference from Example 3 is that multi-walled carbon nanotubes are not added.

[0080] A method for preparing a liquid metal-doped photosensitive resin includes the following steps: S1, Synthesis of polyethylene glycol diacrylate: 15.9 g of triethylamine was added to 50 g of polyethylene glycol and the mixture was placed in an ice bath. In a 500 mL three-necked flask, 12.9 g of acryloyl chloride was dissolved in 20 mL of anhydrous dichloromethane and slowly added dropwise to the flask. The reaction was carried out under nitrogen protection in an ice bath for 2 h, followed by reaction at room temperature for 24 h. The mixture was filtered to remove the solids. The filtrate was washed three times with saturated sodium bicarbonate aqueous solution, and the solvent was removed by rotary evaporation. The precipitate was fully precipitated with diethyl ether and washed four times with diethyl ether. Finally, the product, polyethylene glycol diacrylate, denoted as PEGDA, was completely dried under vacuum.

[0081] S2, 10g of the polyethylene glycol acrylate is added to 90g of photopolymerizable resin FLGPC04 and thoroughly mixed by stirring to obtain a modified photopolymerizable resin, denoted as PGD-FLGPC04. Then, 10g of liquid metal eutectic gallium indium alloy is doped into PGD-FLGPC04 by mechanical stirring to obtain a liquid metal-doped photosensitive resin. The above liquid metal-carbon nanotube-doped photosensitive resin contains 10wt% liquid metal eutectic gallium indium alloy EGaIn, denoted as 10wt% EGaIn-doped photosensitive resin.

[0082] The properties of the resins prepared in Examples 1 to 5 and Comparative Examples 1 to 6 of the present invention were tested, and the test results are as follows.

[0083] according to Figure 2 As shown in Figure a, this invention successfully synthesized polyethylene glycol diacrylate. The structure of polyethylene glycol diacrylate was confirmed by ¹H / ¹³C nuclear magnetic resonance, as shown in Figure a. Figure 2 As shown in Figures b and c, characteristic peaks were found: 5.9 ppm, 5.7 ppm, and 5.4 ppm, which are acrylate olefin protons; and 3.8 ppm and 3.1 ppm, which are methylene protons, -O-CH2-CH2-O-. Figure 2 The d-plot shows the corresponding infrared spectrum, where the characteristic absorption bands of the relevant functional groups are clearly marked. Importantly, modification of the photopolymer resin with polyethylene glycol diacrylate significantly improves the photocuring efficiency.

[0084] To achieve the 3D printing of complex, minimally curved electromagnetic absorbers, a commercially available photocurable acrylic polymer, Formlabs photocurable resin or photopolymerizable resin FLGPCL04 (hereinafter referred to as FLGPCL04, or FPR), was selected as the matrix. Electromagnetic absorption and transmission performance critically depends on the parameters of the composite material. Given that FLGP itself is transparent to electromagnetic microwaves, achieving ideal integration of absorption and transmission requires fine-tuning of the electromagnetic parameters, necessitating the addition of conductive EGaIn and CNTs as active ingredients. However, these conductive fillers significantly reduce light transmittance; even adding only 1 wt% EGaIn and 1 wt% CNTs severely reduces photocuring efficiency. Figure 3 As shown. To overcome this limitation, polyethylene glycol diacrylate was synthesized and introduced into the FPR matrix to improve photoreactivity and crosslinking degree. After only 0.4 seconds of UV irradiation, the modified matrix, i.e., the modified photopolymer resin, rapidly transformed from a viscoelastic liquid into an elastic solid. This transformation process was confirmed by photocuring rheological monitoring, as shown. Figure 4 As shown. This high curing reactivity allows the matrix to be incorporated with up to 10 wt% EGaIn, along with 1 wt% carbon nanotubes, such as... Figure 5 As shown in Figure a, increasing the EGaIn loading improves microwave conductivity. However, the composite material containing only EGaIn is not effective; the imaginary part of the dielectric constant ε'' hardly changes, indicating that microwave dielectric loss is negligible. Figure 6 As shown. This inefficiency stems from the lack of a conductive network and interfacial polarization between isolated EGaIn microspheres, highlighting the importance and necessity of carbon nanotubes. Therefore, EGaIn and carbon nanotubes are thoroughly premixed by ultrasonication before incorporation into the matrix. The carbon nanotubes entangle the EGaIn microspheres together, as shown... Figure 5 Figure b shows the effective establishment of the continuous conductive network necessary for electromagnetic wave absorption. Furthermore, even with this loading level of 10wt% EGaIn + 1wt% carbon nanotubes, UV irradiation can induce curing within 5 seconds, as shown in Figure b. Figure 5 The c-shaped diagram eventually forms a homogeneous mixture, as shown in Figure c. Figure 5 The d-figure shows that post-curing analysis performed by microcomputed tomography confirmed that EGaIn microspheres are uniformly distributed and confined throughout the matrix, with microspheres less than 10 µm in diameter accounting for 92%. Figure 5 Figures e and f are shown. To avoid aggregation caused by carbon nanotubes, the CNT content was fixed at 1 wt% in subsequent studies. For simplicity, although all samples contained 1 wt% CNTs, they were labeled only by the EGaIn content.

[0085] Figure 7 These are two-dimensional and three-dimensional reflection loss diagrams of the liquid metal-carbon nanotube-doped photosensitive resins prepared in Examples 1 to 3 of this invention. Figure a shows the three-dimensional reflection loss diagram of Example 1, Figure b shows the three-dimensional reflection loss diagram of Example 2, Figure c shows the three-dimensional reflection loss diagram of Example 3, Figure d shows the two-dimensional reflection loss diagram of Example 1, Figure e shows the two-dimensional reflection loss diagram of Example 2, and Figure f shows the two-dimensional reflection loss diagram of Example 3. Figure a shows the 3D RL mapping of the 1wt% EGaIn composite material, where RL... min =-52.3dB; Figure b shows the 3D RL mapping of the 5wt%EGaIn composite material, RL min =-49.7dB; Figure c shows the 3D RL mapping of the 10wt%EGaIn composite material, RL min =-39.2dB; d graph shows the 2D RL curve of 1wt%EGaIn composite material. At a thickness of 1.9mm, EAB max =4.09GHz; Figure e shows the 2D RL curve of the 5wt%EGaIn composite material. At a thickness of 1.8mm, EAB max=4.80GHz; Figure f shows the 2D RL curve of 10wt% EGaIn composite material. At a thickness of 2.3mm, EAB max =5.98 GHz. While keeping the carbon nanotube content constant, this invention systematically studied the effect of variations in the loading of liquid metal EGaIn on the dielectric constant and electromagnetic properties. For example... Figure 7 As shown, the effective absorption bandwidth, or EAB, increases significantly with increasing EGaIn content. At an EGaIn doping level of 1 wt%, a sample with a thickness of 1.9 mm achieved a maximum absorption bandwidth of 4.08 GHz. When the EGaIn content was further increased to 5 wt%, the EAB extended to 4.80 GHz, even with a slight decrease in thickness to 1.8 mm. When the EGaIn content was further increased to 10 wt%, the EAB extended to 5.98 GHz, but the thickness increased slightly to 2.3 mm.

[0086] Figure 8 The figures show the Cole-Cole plots of composite materials with different EGaIn contents, specifically the Cole-Cole plots of the liquid metal-carbon nanotube-doped photosensitive resin prepared in Examples 1 to 3 of this invention and the carbon nanotube-doped photosensitive resin prepared in Comparative Example 2. Figure a represents Comparative Example 2, Figure b represents Example 1, Figure c represents Example 2, and Figure d represents Example 3. Figure a shows the Cole-Cole plot of the 0wt% EGaIn composite material, which contains only 1wt% carbon nanotubes. It exhibits numerous semicircular arcs and a small number of linear segments, indicating that polarization loss is the main mechanism at this doping level. Figure b shows the Cole-Cole plot of the 1wt% EGaIn composite material, which begins to show a small number of linear segments, indicating that conductivity loss begins to appear. Figure c shows the Cole-Cole plot of the 5wt% EGaIn composite material, which shows a more obvious linear trend, reflecting the increased contribution of conductivity loss in the composite material. Figure d shows the Cole-Cole plot of the 10wt% EGaIn composite material, which exhibits the most significant linear characteristics, indicating that its conductivity loss capability is higher than that of the composite material with lower EGaIn content.

[0087] Figure 9This diagram shows the simulated electromagnetic field distribution in the double-layer permeable integrated superstructure material of this invention. Figure a shows the electric field intensity at 4.00 GHz, figure b shows the electric field intensity at 9.00 GHz, figure c shows the magnetic field intensity at 4.00 GHz, figure d shows the magnetic field intensity at 9.00 GHz, figure e shows the energy loss at 4.00 GHz, figure f shows the energy loss at 9.00 GHz, figure g shows the electric field intensity at 13.00 GHz, figure h shows the magnetic field intensity at 13.00 GHz, and figure i shows the energy loss at 13.00 GHz. To elucidate the working mechanism, this invention constructs a double-layer permeable integrated superstructure material with half the thickness of the upper supermaterial. The surface energy flux density and electromagnetic field are analyzed at representative frequencies: low frequency 4 GHz, mid frequency 9 GHz, and high frequency 13 GHz. Figure 9 As shown. Considering that this double-layer structure is axisymmetric, to simplify the simulation calculation, this invention sets the incident electromagnetic wave as a polarized wave, denoted as TE wave. According to the pseudo-color image of the electric and magnetic field intensity distribution, at low frequencies, such as 4.00 GHz, the electric and magnetic fields inside the material are relatively small, appearing only near the frequency-selective surface of the FSS. This is because the alternating electric field of the incident electromagnetic wave drives the conduction current on the FSS, which excites the induced electric and magnetic fields, dissipating some of the electromagnetic wave energy. However, a strong electric and magnetic field still exists in the space outside the lower surface of the metamaterial. This verifies that most electromagnetic waves penetrate the material, i.e., low-frequency transmission performance, such as... Figure 9 As shown in Figures a, c, and e, at high frequencies, such as 13 GHz, the electric field is mainly distributed on the upper surface of the double-layer permeable monolithic metastructure and near the FSS frequency-selective surface. The intensity decreases sharply near the bottom of the material, and the electric field is extremely weak in the space outside the lower surface. This indicates that high-frequency electromagnetic waves are largely consumed in the upper part of the material. This is because: firstly, the electromagnetic waves reflected by the FSS interfere destructively with the incident wave; and secondly, the metamaterial dissipates the electromagnetic waves through conductivity loss and polarization loss, such as... Figure 9 The g, h, and i plots are shown. From the perspective of magnetic field components, at high frequencies, the magnetic field components of electromagnetic waves are significantly attenuated after passing through the double-layer integrated superstructure material. A strong magnetic field distribution exists near the FSS inside the material, while the magnetic field strength outside the FSS is extremely weak. This indicates that the surface magnetic field strength of the FSS frequency selection is mainly caused by electromagnetic wave reflection. At the same time, the conduction current generates a secondary magnetic field with a direction opposite to the incident wave magnetic field component, which partially cancels out the electromagnetic wave according to Lenz's law. In summary, the power loss of low-frequency electromagnetic waves inside the double-layer integrated superstructure material is extremely low, while the power loss gradually increases with increasing frequency, which is consistent with the technical expectations of this invention for low-frequency wave transmission and high-frequency wave absorption.

[0088] Figure 10The images show Smith charts of the liquid metal-carbon nanotube-doped photosensitive resins prepared in Examples 1-3 of this invention and the carbon nanotube-doped photosensitive resin prepared in Comparative Example 2, where (a) is Comparative Example 2, (b) is Example 1, (c) is Example 2, and (d) is Example 3. Light gray circles represent the areas within the RL... min The frequency ranges corresponding to the real and imaginary parts of the dielectric constant calculated under the condition ≤-10dB indicate that the composite material meets the impedance matching requirements. For example... Figure 10 As shown, with increasing EGaIn content, the curve gradually enters the light gray circle, mainly at higher frequencies. This observation indicates that the microwave absorption performance of the material is enhanced with increasing doping level, especially at 18 GHz.

[0089] Figure 11 The images show the physical specimen and measured S-parameters of the dual-layer permeation-absorbing integrated metastructure material of this invention. Figure a shows a 16cm × 16cm × 0.6cm printed dual-layer metastructure, with the upper layer being a Schwarz P structure (absorber layer) and the lower layer being an FSS (frequency selective surface layer). Figure b shows a single dual-layer metastructure unit, with a base side length of 21.2mm and a pore spacing of 2mm. Figure c is a SEM image of the top surface of the Schwarz P structure, showing a pore diameter of 1.6mm. Figure d is a side view of the dual-layer permeation-absorbing integrated metastructure material unit, with an FSS structure at the bottom (0.8mm thick) and a Schwarz P structure at the top. The P-structure absorption layer, as shown in Figure e, is a physical image of the bottom FSS structure, and Figure f is a dimensional schematic of the FSS structure, with a 1.0 mm gap between adjacent patterns. The longer rectangular element is 12.6 mm long and 0.95 mm wide, while the shorter one is 9.5 mm long and 3.8 mm wide. Figure g shows the simulated and measured S-parameters. The simulated S21 exceeds -3 dB in the 4 GHz to 6 GHz range, while the measured S21 remains above -3 dB in the 3.5 GHz to 7 GHz range. In the 3.8 GHz to 5.8 GHz and 12 GHz to 18 GHz bands, the simulated S11 value is below -10 dB, while the measured S11 values ​​show similar performance in the 3.5 GHz to 7 GHz and 12 GHz to 18 GHz ranges. The simulated and measured curves show a consistent trend in both the absorption and transmission frequency bands. The measured data confirms that the transmission speed in the 3.5GHz to 7GHz range and the absorption speed in the 12GHz to 18GHz range are below -10dB, and the absorption bandwidth in the 9.0GHz to 18GHz range is below -5dB.

[0090] Based on the simulation results, the Schwarz P-type metamaterial with a side length of 15 mm and a height of 12 mm shows considerable potential in low-frequency transmission and high-frequency absorption. However, its absorption bandwidth is only limited to 2.3 GHz, which is still unsatisfactory. Notably, in the transition frequency band of 4 GHz to 12.2 GHz, where S11 < -10 dB and -10 dB < S21 < -3 dB, it is between the transmission requirement and the absorption requirement, and both absorption and transmission efficiency are relatively low. This observation indicates that adding a reflective surface at the bottom, such as an FSS, helps redirect the transmitted waves that do not meet the transmission standard back to the metamaterial for secondary absorption, while still ensuring sufficient transmission. If the reflection frequency band of the FSS matches the absorption frequency band of the metamaterial, it may be possible to improve the low-frequency transmission performance by reducing the thickness of the metamaterial. The secondary absorption mediated by the FSS can then compensate to ensure sufficient overall absorption. To achieve this objective, the present invention conducts systematic simulations to determine the parameters of the frequency selective surface corresponding to the reflection and transmission bands of the metamaterial. Finally, the thickness of the upper-layer metamaterial is reduced to half of its original thickness, that is 6 mm, thereby constructing an optimized double-layer integrated absorbing and transmitting metastructure material.

[0091] The integration of absorption and transmission was experimentally verified by the free-space method. The macroscopic upper metamaterial has a dimension of 160 mm×160 mm×6 mm with a 1.3 mm circular opening on the top, and was successfully fabricated by assembling four DLP-3D printed metamaterials with a printing accuracy of about 25 µm, as shown in Figure 11 panel a. The bottom frequency selective surface, namely the FSS, is designed based on the simulation optimization parameters and fabricated through a one-step 3D printing process, which includes a reserved groove structure, followed by vacuum silver plating in the groove, as shown in Figure 8 panel b.

[0092] The measured and simulated S-parameters of the double-layer integrated absorbing and transmitting metastructure material show that in the low-frequency range, namely 3.5 GHz to 7.0 GHz, S21 ≥ -3 dB and S11 ≤ -10 dB, which meets the standard for effective wave transmission, with a bandwidth of 3.5 GHz. In the entire Ku-band, that is 12.0 GHz to 18.0 GHz, both S11 and S21 remain ≤ -10 dB, showing effective absorption with a bandwidth of 6 GHz. In practical applications, values of S11 ≤ -5 dB and S21 ≤ -5 dB are sufficient, providing a wider absorption bandwidth from 9 GHz to 18 GHz, reaching 9 GHz, as shown in Figure 11 panel g.

[0093] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. A method for preparing a liquid metal-carbon nanotube-doped photosensitive resin, characterized in that, Includes the following steps: A modified photopolymer resin was obtained by modifying a photopolymer resin with polyethylene glycol diacrylate as a modifier; wherein the photopolymer resin is a polyether acrylate photocurable matrix. At 0℃~4℃, liquid metal was dispersed and loaded onto the multi-walled carbon nanotubes using cyclohexane as a solvent. Cyclohexane was removed by freeze-drying to prevent the liquid metal microspheres from rupturing, resulting in liquid metal-loaded carbon nanotubes. The liquid metal was a eutectic gallium-indium alloy. The liquid metal-loaded carbon nanotubes were doped into the modified photopolymer resin to obtain a liquid metal-carbon nanotube-doped photosensitive resin. The mass ratio of polyethylene glycol diacrylate to photopolymer resin is 1:7 to 9.5; The mass ratio of polyethylene glycol diacrylate, multi-walled carbon nanotubes, and liquid metal is 10:1:1 to 10.

2. The method for preparing liquid metal-carbon nanotube-doped photosensitive resin according to claim 1, characterized in that, The doping process specifically involves adding the liquid metal-loaded carbon nanotubes to the modified photopolymer resin and mechanically stirring to obtain a liquid metal-carbon nanotube-doped photosensitive resin.

3. The method for preparing liquid metal-carbon nanotube-doped photosensitive resin according to claim 1, characterized in that, The preparation method of the polyethylene glycol diacrylate is as follows: triethylamine is added to polyethylene glycol, dissolved in anhydrous dichloromethane at 0℃~4℃, then an anhydrous dichloromethane solution of acryloyl chloride is added, and the reaction is carried out at 0℃~4℃ under a protective atmosphere, and then the reaction is carried out at room temperature to obtain polyethylene glycol diacrylate.

4. The method for preparing liquid metal-carbon nanotube-doped photosensitive resin according to claim 3, characterized in that, After reacting at room temperature, the process includes filtration. The filtrate is washed with a saturated sodium bicarbonate aqueous solution, the solvent is removed by rotary evaporation, the precipitate is precipitated with diethyl ether, washed with diethyl ether, and dried under vacuum to obtain polyethylene glycol diacrylate.

5. A liquid metal-carbon nanotube-doped photosensitive resin, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the liquid metal-carbon nanotube doped photosensitive resin of claim 5 in the preparation of a bilayer absorbent integrated superstructure material for use in radar radomes.

7. The application according to claim 6, characterized in that, The preparation method of the dual-layer permeable integrated superstructure material is as follows: TPO photoinitiator is added to liquid metal-carbon nanotube doped photosensitive resin to obtain printing raw material. 3D printing is performed on the FSS frequency selective surface using the printing raw material in an open environment at room temperature, and then cured under ultraviolet light to obtain the dual-layer permeable integrated superstructure material.

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