A filling type stepped structure wave absorber based on additive manufacturing technology and a preparation method and application thereof

Abstract

The application belongs to the technical field of wave-absorbing devices, and discloses a filling type stepped structure wave-absorber based on additive manufacturing technology, which comprises a PLA stepped cavity structure formed based on FDM technology, a composite wave-absorbing agent and a grounded metal bottom layer, the wave-absorbing body is arranged in a five-layer stepped unit period, and from top to bottom, the wave-absorbing body comprises a wave-transparent layer, a matching layer, a wave-absorbing layer, a re-wave-absorbing layer and a metal reflecting layer; the composite wave-absorbing agent is formed by mixing and filling rGO-Fe3O4 / Ec composite microsphere material and paraffin at a fixed ratio, and the content of graphene in the rGO-Fe3O4 / Ec composite microsphere material is different between different layers; and the grounded metal bottom layer is a high-conductivity metal sheet. The bandwidth of the wave-absorbing body can be adjusted within a certain range by the content of graphene in the rGO-Fe3O4 / Ec microsphere composite and the thickness of the stepped layer, and the effective absorption of the wave-absorbing body can reach the full frequency range of 2-18 GHz (-10 dB).

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing device technology, specifically relating to a filled stepped structure microwave absorber based on additive manufacturing technology. Background Technology

[0002] With the rapid development of modern communication and radar technologies, electromagnetic interference is becoming increasingly serious. Therefore, the development of novel broadband absorbing materials and their fabrication techniques has become a current research hotspot. As a key component in the fields of electromagnetic compatibility (EMC) and stealth technology, the main function of absorbing electromagnetic waves is to reduce electromagnetic radiation and scattering by converting them into other forms of energy, thereby reducing electromagnetic interference. Currently, commercially available absorbing materials mainly include coated absorbing materials and multilayer absorbing materials.

[0003] Traditional coating-type microwave absorbing materials typically use magnetic materials such as graphite and ferrite as base materials, and achieve the microwave absorption effect by coating a thin layer of resistive polymer on the surface of the substrate. For example, Feng et al. prepared barium ferrite-doped EPDM rubber radar absorbing materials and found that the complex permittivity and complex permeability both increased with the increase of the barium ferrite attack fraction (Feng Yongbao, Qiu Tai. Complex Permeability and Permittivity and Microwave Absorption Property of Barium Ferrite / EPDM Rubber RadarAbsorbing Materials in 2-18GHz[C] / / Asia-Pacific Conference Proceedings.IEEE, 2005.); Song Yuhua et al. used self-made fiber I and fiber II mixed with short-cut carbon fiber to fill rigid polyurethane foam plastic and found that the absorption frequency of the foam plastic filled with carbon fiber was narrower; fiber I and fiber II mixed with carbon fiber can broaden the frequency band and the absorption performance is enhanced with the increase of the thickness of the plastic sample (Song Yuhua, Yu Mingxun, Zhu Hongli, et al. Research on radar wave absorbing polyurethane foam plastic[, Engineering Plastics Application, 2007, 34(12)13-16.). However, this type of coating-type absorbing material has some drawbacks, such as high manufacturing cost, poor mechanical strength, poor durability, etc., which limits its application in the wide frequency band.

[0004] Multilayer gradient structures offer limitless possibilities for achieving broadband absorption performance. For example, Chinese patent CN108770327B discloses a gradient layered foamed microwave absorbing material and its preparation method. This method utilizes an absorbing agent and a soluble polymer matrix to foam and prepare multilayered foamed absorbing layers. The gradient distribution of these layers reduces electromagnetic wave reflection within the material and increases its absorption. However, traditional gradient composite material microwave absorbing structures are often manufactured using conventional methods such as carving, molding, and impregnation, which are unsuitable for complex structures. With the gradual maturation of additive manufacturing technology, its advantages of low cost, high efficiency, and high precision have led to its widespread application in the manufacturing of complex microwave absorbing structures. Therefore, combining additive manufacturing technology offers higher manufacturing efficiency, higher precision, and lower costs, enabling the creation of more complex absorber structures and providing a more convenient shell manufacturing technology for achieving broadband absorption performance.

[0005] Therefore, it is necessary to design a novel filler-type stepped structure micro-absorbing body based on additive manufacturing technology to solve the above problems. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a filled stepped structure microwave absorber based on additive manufacturing technology, which has a longer lifespan and wider bandwidth.

[0007] To achieve the above objectives, the present invention provides a filled stepped structure microwave absorber based on additive manufacturing technology, comprising a cavity shell, a layered composite microwave absorber, and a metal base plate.

[0008] Preferably, the cavity shell is composed of gradient layered units arranged periodically in the x and y directions, each unit being a square, with the side length of the square decreasing by 1-3 mm from bottom to top.

[0009] Preferably, the cavity shell is prepared by FDM-3D printing technology using any one of PLA, thermoplastic resin, polycarbonate, and ABS.

[0010] Preferably, the composite microwave absorber is composed of a homogeneous mixture of rGO-Fe3O4 / EC composite microspheres and paraffin wax, with a mass ratio of rGO-Fe3O4 / EC composite microspheres to paraffin wax of 1:3-3:1.

[0011] Preferably, the layered composite absorbing agent consists of, from top to bottom, a wave-transmitting layer, a matching layer, a wave-absorbing layer, and a re-absorbing layer.

[0012] More preferably, the thickness of the wave-transparent layer is 2-5 mm, wherein the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 2wt%-10wt%; the thickness of the matching layer is 4-10 mm, wherein the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 2wt%-9wt%; the thickness of the wave-absorbing layer is 2-8 mm, wherein the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 5wt%-15wt%; and the thickness of the re-absorbing layer is 4-10 mm, wherein the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 5wt%-16wt%.

[0013] Preferably, the metal base layer is an alloy of one or more of copper, aluminum, gold, and silver, with a thickness of 0.02mm-2mm.

[0014] This invention also provides a method for preparing a filled stepped structure microwave absorber based on additive manufacturing technology, comprising the following steps:

[0015] (1) Preparation of aqueous phase: Add industrial gelatin and sodium dodecyl sulfonate to deionized water and mix evenly to obtain aqueous phase;

[0016] (2) Preparation of oil phase: Add epoxy resin and ethyl cellulose to dichloromethane and mix evenly to obtain oil phase;

[0017] (3) Preparation of dichloromethane-rGO: Reduced graphene oxide was ultrasonically dispersed in dichloromethane to obtain dichloromethane-rGO;

[0018] (4) Add Fe3O4 powder and dichloromethane-rGO to the oil phase prepared in step (2), disperse by ultrasonication, and stir at 30°C for 30 min at a speed of 600 r / min to make it homogeneous and obtain a dispersion.

[0019] (5) Preparation of rGO-Fe3O4 / EC composite microspheres: The ultrasonic dispersion was slowly added to the aqueous phase prepared in step (1), and stirred at a constant temperature of 35°C. The stirring speed was increased from 150 r / min to 1200 r / min, and stirring was continued for 3 hours to obtain the formed microspheres. Then the temperature was raised to 45°C and stirred for 2 hours to solidify. After washing with deionized water 2-3 times, the microspheres were dried at 60°C to obtain rGO-Fe3O4 / EC composite microspheres.

[0020] (6) Preparation of composite microwave absorbing agent: The rGO-Fe3O4 / EC composite microspheres prepared in step (5) are homogeneously mixed with melted paraffin to obtain composite microwave absorbing agent;

[0021] (7) The cavity shell was prepared using FDM-3D printing technology;

[0022] (8) After the composite microwave absorbing agent solidifies, it is pressed into a tablet with a density of 1.-1.5 kg / m³ using a tablet press at 5-6 MPa. 3 The cubes are filled into the cavity shell, and a metal base plate is placed on top to prepare a filled stepped structure microwave absorber.

[0023] Preferably, the industrial gelatin in step (1) has a mass fraction of 2-3 wt% in the aqueous phase, and the sodium dodecyl sulfonate has a mass fraction of 0.1-1 wt% in the aqueous phase;

[0024] In step (2), the epoxy resin in the oil phase has a mass fraction of 1.5-2 wt%, and the ethyl cellulose in the oil phase has a mass fraction of 1.5-2 wt%.

[0025] The reduced graphene oxide in step (3) has a mass fraction of 0.24-1 wt% in dichloromethane-rGO.

[0026] The Fe3O4 powder in step (4) has a mass fraction of 1-2 wt% in the oil phase.

[0027] More preferably, the mass fraction of industrial gelatin in the aqueous phase is 2.4 wt%, and the mass fraction of sodium dodecyl sulfonate in the aqueous phase is about 0.4 wt%.

[0028] The epoxy resin in step (2) has a mass fraction of 3.8 wt% in the oil phase, and the ethyl cellulose has a mass fraction of 3.8 wt% in the oil phase.

[0029] The mass fraction of the redox graphene in the dichloromethane ultrasonic dispersion in step (3) is 0.24-0.64 wt%, and the particle size of the redox graphene is 300-800 mesh.

[0030] This invention also provides an application of a filler-type stepped structure absorber based on additive manufacturing technology in the fields of communication and radar.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. rGO-Fe3O4 / Ec composite microspheres were prepared using rGO and Fe3O4. By adjusting the amount of rGO, various rGO-Fe3O4 / Ec composite microspheres with different rGO mass fractions can be obtained. These composite microspheres can achieve efficient and broadband absorption of microwaves.

[0033] 2. Composite microwave absorbers were prepared by combining composite microspheres with different rGO mass fractions with paraffin wax. The composite microwave absorbers were then pressed into different sizes to prepare composite microwave absorbers. These were filled into a stepped cavity shell and finally covered with a metal base plate to prepare a filled stepped structure microwave absorber. This absorber is polarization insensitive and its bandwidth can be adjusted within a certain range by the graphene content in the rGO-Fe3O4 / Ec microsphere composite and the thickness of the stepped layer. It can achieve effective absorption (-10 dB) across the entire frequency band in the range of 2-18 GHz. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the absorption periodic unit of the absorber in this invention. In the figure, 1 is the wave-transmitting layer, 2 is the matching layer, 3 is the wave-absorbing layer, 4 is the re-absorbing layer, 5 is the metal base plate layer, and 6 is the cavity shell.

[0035] Figure 2 This is a schematic diagram of the overall structure of the absorber in this invention.

[0036] Figure 3 The reflection loss curve of rGO-Fe3O4 / EC composite microspheres with an rGO mass fraction of 6.6 wt% prepared in Example 1.

[0037] Figure 4 The reflection loss curves are from experimental tests and simulations of the absorber prepared in Example 1.

[0038] Figure 5 This is a schematic diagram of the preparation process of the hollow shell and the filling process of the composite absorbing agent in this invention. Detailed Implementation

[0039] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0040] In the following examples, the Fe3O4 powder had a particle size of 1-2 μm and was purchased from Nanjing Xindun Alloy Co., Ltd.; the rGO (graphene oxide) had a particle size of 300-800 mesh and was purchased from Yichang Xincheng Graphite Co., Ltd.

[0041] Example 1

[0042] Preparation such as Figure 1-2The absorber shown contains 36 absorbing periodic units, each without gaps. The specific fabrication process is as follows:

[0043] (1) Take 200 mL of deionized water, add 5 g of industrial gelatin (DEL) and 1 g of sodium dodecyl sulfate (SDBS) as emulsifiers, mix well to obtain the aqueous phase;

[0044] (2) Take 125 mL of dichloromethane, add 2.5 g of epoxy resin (EP) and 2.5 g of ethyl cellulose (Ec), mix well to obtain the oil phase;

[0045] (3) Take 0.3g of graphene oxide (rGO) and place it in 125mL of dichloromethane, and disperse it by ultrasonication to obtain dichloromethane-rGO ultrasonic dispersion;

[0046] (4) Add 2g of Fe3O4 powder and 0.3g of dichloromethane-rGO ultrasonic dispersion to the oil phase prepared in step (2) and stir continuously at a constant temperature of 30℃ for 30 minutes at a speed of 600r / min until the mixture is uniform and a dispersion is obtained.

[0047] (5) Slowly add the dispersion to the aqueous phase obtained in step (1), continue stirring at a constant temperature, and increase the speed from 150 r / min to 1200 r / min, then continue stirring at a constant temperature of 35°C for 3 hours; after the microspheres are formed, increase the temperature to 45°C and continue stirring at a constant temperature for 2 hours to solidify the microspheres, then wash with deionized water 2-3 times, and dry at 60°C to obtain rGO-Fe3O4 / EC composite microspheres with an rGO mass fraction of 4.1 wt%;

[0048] (6) Repeat the above operation to change the amount of rGO added to obtain rGO-Fe3O4 / EC composite microspheres with different rGO mass fractions. When 0.5g of graphene is added, 6.6wt% rGO-Fe3O4 / EC composite microspheres are prepared. When 0.8g of graphene is added, 10.2wt% rGO-Fe3O4 / EC composite microspheres are prepared.

[0049] (7) Using FDM-3D printing technology, a cavity shell was prepared using PLA (polylactic acid). (6) The process parameters of the printer were as follows: the temperature of the heated bed and the nozzle were 50℃ and 200℃, respectively; the printing speed was 30mm / s; the printing layer thickness was 0.1mm; the deposition angle was 45°; the filling density was 100%; the thickness of the cavity shell was 2mm; each cycle unit had four layers; the thickness of each layer from top to bottom was 3.5mm, 5mm, 3.5mm, 5mm; and the side length of each layer from top to bottom was 24mm, 26mm, 28mm, 30mm.

[0050] (8) Melt paraffin and homogenize it with rGO-Fe3O4 / EC at a ratio of 1:1. After solidification, press the 6.6wt% rGO-Fe3O4 / EC microsphere paraffin mixture into a tablet with a density of 1.15 kg / m³ by applying a pressure of 5-6 MPa using a tablet press. 3 Thirty-six uniform 3.5mm*24mm*24mm cubes were used as wave-transmitting layers (1); thirty-six uniform 5mm*26mm*26mm cubes of a microsphere paraffin mixture containing 4.1wt% rGO-Fe3O4 / EC microspheres were molded into matching layers (2); thirty-six uniform 5mm*28mm*28mm cubes of a microsphere paraffin mixture containing 6.6wt% rGO-Fe3O4 / EC microspheres were molded into absorbing layers (3); thirty-six uniform 5mm*30mm*30mm cubes of a microsphere paraffin mixture containing 10.2wt% rGO-Fe3O4 / EC microspheres were molded into reabsorbing layers (4).

[0051] (9) Fill the gradient periodic absorber shell with the above blocks in order of their size, and finally cover it with a block with a thickness of 0.02 mm, a side length of 195 mm, and an electrical conductivity of 5.8 × 10⁻⁶. 7 A square copper plate of S / m is used as the metal base layer (5) to complete the preparation of the absorber.

[0052] The relative complex permittivity and relative complex permeability of rGO-Fe3O4 / EC composite microspheres with a rGO mass fraction of 6.6 wt% were measured using an R&SZNA (Rohde & Schwarz) vector network analyzer in the frequency range of 2-18 GHz. The test results characterize the reflection loss as follows: Figure 3 As shown, 6.6 wt% rGO-Fe3O4 / EC composite microspheres with a thickness of 2 mm achieved the minimum reflection loss (-27.1 dB) at 12.9 GHz.

[0053] The reflectivity of this absorber in the 2-18 GHz range was tested in a microwave anechoic chamber using the bow-shaped method, and the results are as follows: Figure 3 As shown, the absorber can effectively absorb (-10 dB) across the entire frequency range of 2-18 GHz.

[0054] Comparative Example 1

[0055] The method and steps are the same as in Example 1, except that the mass fraction of rGO is changed to 4.1wt%. According to the simulation results obtained by CST STRUDIO SUITE software, it is not possible to achieve full-band absorption in the 2GHz-18GHz frequency band. Effective absorption (-10dB) is achieved only in the 6.2GHz-18GHz frequency band within this bandwidth, and the minimum reflection loss (-30.2dB) is achieved at 7.4GHz.

[0056] Comparative Example 2

[0057] The method and steps are the same as in Example 1, except that the mass fraction of rGO in both the transparent layer and the matching layer is changed to 10.2 wt%, and the mass fraction of rGO in the absorbing layer and the second absorbing layer is changed to 6.6 wt% to prepare the absorber. Simulation results using CST STRUDIO SUITE software show that it cannot achieve full-band absorption in the 2GHz-18GHz frequency band, only achieving effective absorption (-10dB) in the 2.1GHz-2.5GHz, 4.5GHz-5.7GHz, and 8.2GHz-18GHz frequency bands, and reaching minimum reflection damage (-26.5dB) at 5.12GHz.

[0058] Comparative Example 3

[0059] The method and steps are the same as in Example 1, except that the dimensions of the wave-transmitting layer, matching layer, absorbing layer, and re-absorbing layer are all changed to 5mm*28mm*28mm to prepare the absorber. Simulation results using CST STRUDIO SUITE software show that this absorber structure cannot achieve effective absorption across the entire frequency band from 2GHz to 18GHz, and within this band, it only achieves effective absorption (-10dB) in the 2GHz-3.37GHz range, reaching minimum reflection loss (-17.44dB) at 2GHz.

[0060] Comparative Example 4

[0061] The method and steps are the same as in Example 1, except that the dimensions of the wave-transmitting layer, matching layer, absorbing layer, and re-absorbing layer are all changed to 5mm*28mm*28mm, and the mass fraction of rGO is changed to 4.1wt%. Simulation results using CST STRUDIO SUITE software show that this absorber structure cannot achieve effective absorption across the entire 2GHz-18GHz frequency band, and within this band, it only achieves effective absorption (-10dB) in the 2GHz-3.376GHz range.

[0062] Comparative Example 5

[0063] The method and steps are the same as in Example 1, except that the thickness of each layer is changed: the thickness of the wave-transmitting layer is changed to 5mm, the thickness of the matching layer is changed to 6mm, the thickness of the absorbing layer is changed to 6mm, and the thickness of the re-absorbing layer is changed to 7mm. Simulation results using CST STRUDIO SUITE software show that this structure can achieve effective absorption (-10dB) across the entire frequency band from 2GHz to 18GHz, and achieves minimum reflection loss (-28.8dB) at 3.14GHz.

Claims

1. A filled stepped structure microwave absorber based on additive manufacturing technology, characterized in that: It includes a hollow shell (6), a layered composite microwave absorber and a metal base plate (5); the composite microwave absorber is composed of a homogeneous mixture of rGO-Fe3O4 / EC composite microspheres and paraffin wax, with a mass ratio of rGO-Fe3O4 / EC composite microspheres to paraffin wax of 1:3-3:

1.

2. The filler-type stepped structure microwave absorber based on additive manufacturing technology according to claim 1, characterized in that: The hollow shell (6) is a gradient layered unit arranged periodically in the x, y, z directions. Each unit is a square, and from bottom to top, the side length of the square of each unit decreases by 2 mm.

3. A filled stepped structure microwave absorber based on additive manufacturing technology according to claim 1 or 2, characterized in that: The cavity shell is made of any one of PLA thermoplastic resin, polycarbonate, or ABS using FDM-3D printing technology.

4. The filler-type stepped structure microwave absorber based on additive manufacturing technology according to claim 1, characterized in that: The layered composite absorbing agent consists of, from top to bottom, a wave-transmitting layer (1), a matching layer (2), a wave-absorbing layer (3), and a re-absorbing layer (4).

5. A filled stepped structure microwave absorber based on additive manufacturing technology according to claim 4, characterized in that: The thickness of the wave-transparent layer (1) is 2-5 mm, and the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 2wt%-10wt%. The thickness of the matching layer (2) is 4-10 mm, and the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 2wt%-9wt%. The thickness of the wave-absorbing layer (3) is 2-8 mm, and the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 5wt%-15wt%. The thickness of the re-absorbing layer (4) is 4-10 mm, and the mass fraction of graphene in the rGO-Fe3O4 / EC composite microspheres is 5wt%-16wt%.

6. The filler-type stepped structure microwave absorber based on additive manufacturing technology according to claim 1, characterized in that: The metal base layer is an alloy of one or more of copper, aluminum, gold, and silver, with a thickness of 0.02-2 mm.

7. A method for preparing a filled stepped structure microwave absorber based on additive manufacturing technology as described in any one of claims 1-6, characterized in that: Includes the following steps: (1) Preparation of aqueous phase: Add industrial gelatin and sodium dodecylbenzenesulfonate to deionized water and mix evenly to obtain aqueous phase; (2) Preparation of oil phase: Add epoxy resin and ethyl cellulose to dichloromethane and mix evenly to obtain oil phase; (3) Preparation of dichloromethane-rGO: Reduced graphene oxide was ultrasonically dispersed in dichloromethane to obtain dichloromethane-rGO; (4) Add Fe3O4 powder and dichloromethane-rGO to the oil phase prepared in step (2), disperse by ultrasonication, and stir at a constant temperature of 30°C to obtain a dispersion. (5) Preparation of rGO-Fe3O4 / EC composite microspheres: The ultrasonic dispersion was slowly added to the aqueous phase prepared in step (1), and the microspheres were obtained by stirring at 35°C for 3 hours. Then the microspheres were heated to 45°C and stirred for 2 hours to solidify. After washing with deionized water 2-3 times, the microspheres were dried to obtain rGO-Fe3O4 / EC composite microspheres. (6) Preparation of composite microwave absorbing agent: The rGO-Fe3O4 / EC composite microspheres prepared in step (5) are homogeneously mixed with melted paraffin to obtain composite microwave absorbing agent; (7) The cavity shell was prepared using FDM-3D printing technology; (8) After the composite absorbing agent solidifies, it is pressed into a cube and filled into the cavity shell. The metal base plate is then covered to prepare a filled stepped structure absorbing body.

8. The preparation method according to claim 7, characterized in that: In step (1), the industrial gelatin has a mass fraction of 2-3 wt% in the aqueous phase, and the sodium dodecyl sulfonate has a mass fraction of 0.1-1 wt% in the aqueous phase. In step (2), the epoxy resin in the oil phase has a mass fraction of 1.5-2 wt%, and the ethyl cellulose in the oil phase has a mass fraction of 1.5-2 wt%. The reduced graphene oxide in step (3) has a mass fraction of 0.24-1 wt% in dichloromethane-rGO. The Fe3O4 powder in step (4) has a mass fraction of 1-2 wt% in the oil phase.

9. The application of a filler-type stepped structure absorber based on additive manufacturing technology as described in any one of claims 1-6, or a filler-type stepped structure absorber based on additive manufacturing technology prepared by the preparation method described in any one of claims 1-8, in the fields of communication and radar.

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