A double-layer wave-absorbing structure and a preparation method thereof

Abstract

The application provides a double-layer wave-absorbing structure and a preparation method thereof, and comprises a lossy dielectric layer A and a lossy dielectric layer B; the lossy dielectric layer A is used as a surface layer, the base material is polylactic acid, and the filler is spherical carbonyl iron; the lossy dielectric layer B is used as a bottom layer, the base material is polylactic acid, and the filler is nano carbon particles. The lossy dielectric layer A and the lossy dielectric layer B are solidified through a fused deposition modeling 3D printing process to obtain the double-layer wave-absorbing structure. The lossy dielectric layer A is used as a surface layer, the surface wave impedance is greater than the interface wave impedance, the impedance matching degree is good, the surface input impedance and the wave impedance of free space are matched, the front reflection of electromagnetic waves at the interface between air and the absorber is reduced, most of the electromagnetic waves enter the material interior, and then the energy of the electromagnetic waves is absorbed by the high-dielectric-loss and magnetic-loss materials.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, and specifically relates to a double-layer microwave absorbing structure and its preparation method. Background Technology

[0002] Microwave-absorbing materials are an important means of achieving stealth technology. Existing microwave-absorbing coatings have a narrow applicable frequency band, mainly covering the 8-12 GHz band, and the interfacial strength of the coating materials is relatively low. Single-component microwave-absorbing coatings are difficult to achieve broadband stealth requirements. Therefore, a layered design of multiple microwave-absorbing materials is needed to achieve a gradual change in electromagnetic wave impedance within the material, i.e., the wave impedance decreases sequentially from the surface material to the reflective backing. By utilizing the matching of surface input impedance and free-space wave impedance, the frontal reflection of electromagnetic waves at the air-material interface is reduced, allowing most of the electromagnetic waves to enter the material's interior, where the energy is absorbed by the high dielectric loss and magnetic loss materials. Summary of the Invention

[0003] In order to overcome the shortcomings of the existing technology, the inventors have conducted intensive research and provided a double-layer absorbing structure and its preparation method. The electromagnetic wave impedance of the surface and interface of the structure is appropriately gradually changed to improve the electromagnetic loss performance and achieve high-performance stealth of the aircraft.

[0004] The technical solution provided by this invention is as follows:

[0005] Firstly, a double-layer absorbing structure includes a lossy dielectric layer A and a lossy dielectric layer B;

[0006] The loss medium layer A serves as the surface layer, with polylactic acid as the matrix material and spherical carbonyl iron as the filler.

[0007] The loss medium layer B serves as the bottom layer, with polylactic acid as the matrix material and carbon nanoparticles as the filler.

[0008] In conjunction with the first aspect, the mass fraction of carbonyl iron in the loss medium layer A is 40%~70%, and the mass fraction of polylactic acid is 30%~60%.

[0009] In conjunction with the first aspect, the mass fraction of nano-carbon particles in the loss medium layer B is 10%~30%, and the mass fraction of polylactic acid is 70%~90%.

[0010] In conjunction with the first aspect, the thickness of the double-layer absorbing structure is 3~5mm, the thickness of the loss dielectric layer A is 1~4mm, the thickness of the loss dielectric layer B is 1~4mm, and preferably the thickness of the loss dielectric layer A is less than the thickness of the loss dielectric layer B.

[0011] Secondly, a method for fabricating a double-layer absorbing structure includes the following steps:

[0012] Carbonyl iron and polylactic acid composite wires were prepared using carbonyl iron and polylactic acid;

[0013] Nano-carbon particles and polylactic acid composite wires were prepared using nano-carbon particles and polylactic acid.

[0014] A double-layer microwave absorbing structure is obtained by using nano-carbon particle polylactic acid composite wire and forming a loss dielectric layer B through a fused deposition modeling process; on the loss dielectric layer B, carbonyl iron polylactic acid composite wire is used to form a loss dielectric layer A through a fused deposition modeling process.

[0015] The double-layer absorbing structure and its preparation method provided by the present invention have the following beneficial effects:

[0016] (1) The present invention provides a double-layer absorbing structure and its preparation method. The loss dielectric layer A of the double-layer absorbing structure is used as the top layer, the matrix material is polylactic acid, and the filler is spherical carbonyl iron; the loss dielectric layer B is used as the bottom layer, the matrix material is polylactic acid, and the filler is nano carbon particles. The loss dielectric layer A is used as the top layer. The surface wave impedance is greater than the interface wave impedance, and the impedance matching is better. By using the surface input impedance and the wave impedance matching of free space, the front reflection of electromagnetic waves at the air-absorber interface is reduced, so that most of the electromagnetic waves enter the interior of the material, and then the energy of the electromagnetic waves is absorbed by the high dielectric loss and magnetic loss materials.

[0017] (2) The present invention provides a double-layer absorbing structure and its preparation method. The composite wire used in the fused deposition molding process is prepared by a two-step melt blending process, which significantly improves the mass ratio and dispersibility of the absorbent and realizes the preparation of a high electromagnetic loss performance absorbing composite wire. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a double-layer absorbing structure;

[0019] Figure 2 Analysis of the microwave absorption performance of the double-layer structure with a 1mm top layer (CI-60 / PLA) and a 4mm bottom layer (NPC-20 / PLA) in Example 1;

[0020] Figure 3 For comparative example 1, the microwave absorption performance of a double-layer structure with a 1mm top layer (NPC-20 / PLA) and a 4mm bottom layer (CI-60 / PLA) is analyzed.

[0021] Figure 4 Analysis of the microwave absorption performance of the double-layer structure with a 2mm top layer (CI-60 / PLA) and a 3mm bottom layer (NPC-20 / PLA) in Example 2;

[0022] Figure 5For the comparative example 2, the microwave absorption performance of the double-layer structure with a 2mm top layer (NPC-20 / PLA) and a 3mm bottom layer (CI-60 / PLA) is analyzed.

[0023] Figure 6 Analysis of the microwave absorption performance of the double-layer structure with a 3mm top layer (CI-60 / PLA) and a 2mm bottom layer (NPC-20 / PLA) in Example 3;

[0024] Figure 7 For the comparative example 3, the microwave absorption performance of the double-layer structure with a 3mm top layer (NPC-20 / PLA) and a 2mm bottom layer (CI-60 / PLA) is analyzed;

[0025] Figure 8 Analysis of the microwave absorption performance of the double-layer structure with a 4mm top layer (CI-60 / PLA) and a 1mm bottom layer (NPC-20 / PLA) in Example 4;

[0026] Figure 9 For comparative example 4, the microwave absorption performance of a double-layer structure with a 4mm top layer (NPC-20 / PLA) and a 1mm bottom layer (CI-60 / PLA) is analyzed.

[0027] Figure 10 This is a summary analysis of the microwave absorption performance of the double-layer structures in Examples 1-4. Detailed Implementation

[0028] The features and advantages of the present invention will become clearer and more explicit from the following detailed description.

[0029] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0030] This invention provides a double-layer absorbing structure, such as Figure 1 As shown, it includes loss dielectric layer A and loss dielectric layer B;

[0031] The loss medium layer A serves as the surface layer, with polylactic acid (PLA) as the matrix material and spherical carbonyl iron (CI) as the filler.

[0032] The loss medium layer B serves as the bottom layer, with polylactic acid as the matrix material and carbon nanoparticles (NPC) as the filler.

[0033] Loss dielectric layer A and loss dielectric layer B are solidified and bonded together through a fused deposition modeling process to obtain a double-layer microwave absorbing structure.

[0034] The loss medium layer A contains 40% to 70% carbonyl iron and 30% to 60% polylactic acid by mass. Preferably, the loss medium layer A contains 40% to 60% carbonyl iron and 40% to 60% polylactic acid by mass. More preferably, the loss medium layer A contains 55% to 60% carbonyl iron and 40% to 45% polylactic acid by mass.

[0035] The loss medium layer B contains 10% to 30% carbon nanoparticles and 70% to 90% polylactic acid. Preferably, the loss medium layer B contains 10% to 20% carbon nanoparticles and 80% to 90% polylactic acid. More preferably, the loss medium layer B contains 15% to 20% carbon nanoparticles and 85% to 90% polylactic acid.

[0036] The thickness of the double-layer absorbing structure is 3-5 mm, the thickness of the loss dielectric layer A is 1-4 mm, and the thickness of the loss dielectric layer B is 1-4 mm; preferably, the thickness of the loss dielectric layer A is 1-2 mm, and the thickness of the loss dielectric layer B is 2-4 mm. More preferably, the thickness of the loss dielectric layer A is less than the thickness of the loss dielectric layer B.

[0037] The working principle of the double-layer absorbing structure: From the surface of the loss dielectric layer A to the interface between loss dielectric layers A and B, the wave impedance decreases sequentially. By utilizing the matching of surface input impedance and free space wave impedance, the frontal reflection of electromagnetic waves at the air-absorber interface is reduced, allowing most of the electromagnetic waves to enter the interior of the material, where the energy of the electromagnetic waves is absorbed by the high dielectric loss material (loss dielectric layer B) and the magnetic loss material (loss dielectric layer A).

[0038] This invention also provides a method for fabricating a double-layer absorbing structure, comprising the following steps:

[0039] (1) The preparation of carbonyl iron polylactic acid composite material using carbonyl iron and polylactic acid includes the following steps:

[0040] S1, dry carbonyl iron and polylactic acid powder in an oven at 80~100℃ for at least 12 h;

[0041] S2, disperse the mixture of carbonyl iron and polylactic acid in a planetary mixer at a speed of 60~100 r / min for at least 8 h;

[0042] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0043] S4. The dried composite material particles are poured into a single-screw extruder. The composite particles are further mixed in the screw under the action of heating and melting, screw friction, and shearing. The molten mixture is extruded from the die and, through the combined action of water cooling and traction sizing, yields composite wire with a diameter of approximately 1.75 mm. 0.05 mm composite wire.

[0044] (2) The preparation of nano-carbon particle polylactic acid composite material using nano-carbon particles and polylactic acid includes the following steps:

[0045] S1, dry the carbon nanoparticles and polylactic acid powder in an oven at 80~100℃ for at least 12 h;

[0046] S2, disperse the mixture of nano-carbon particles and polylactic acid in a planetary mixer at a speed of 60~100 r / min for at least 8 h;

[0047] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0048] S4. The dried composite material particles are poured into a single-screw extruder. The composite particles are further mixed in the screw under the action of heating and melting, screw friction, and shearing. The molten mixture is extruded from the die and, through the combined action of water cooling and traction sizing, yields composite wire with a diameter of approximately 1.75 mm. 0.05 mm composite wire.

[0049] (3) A loss medium layer B is formed by using nano-carbon particle polylactic acid composite wire and fused deposition modeling process; on the loss medium layer B, a carbonyl iron polylactic acid composite wire is formed by fused deposition modeling process to obtain a double-layer microwave absorbing structure. The optimal printing temperature of the composite wire is 200~230℃ and the printing speed is 30~40 mm / s.

[0050] The effective absorption bandwidth (reflection loss less than -10 dB) of the loss dielectric layer A and loss dielectric layer B prepared by this invention at a matching thickness of 3 mm is significantly better than that of the absorbing composite wires in the literature, exhibiting stronger electromagnetic loss performance. This is due to the two-step melt blending preparation process, which significantly improves the mass ratio and dispersibility of the absorber, enabling the preparation of absorbing composite wires with high electromagnetic loss performance.

[0051] Table 1. Comparison of the performance of the microwave absorbing composite wires reported in the literature with those prepared in this invention.

[0052]

[0053] Note: CI-60 / PLA means that the carbonyl iron content is 60% and the remainder is PLA matrix material; NPC-20 / PLA means that the nano carbon particles content is 20% and the remainder is PLA matrix material.

[0054] [1] Hu Zhenglang, Wu Haihua, Yang Zenghui, et al. Preparation and microwave absorption properties of graphene-iron-nickel alloy-polylactic acid composite materials. Journal of Composite Materials, 2022, 39: 1-14.

[0055] [2] Ye X.Cong, Yang C.C., Ou Yang B., et al. Microwave absorption properties of graphene-reinforced FeSiAl-MoS2 / PLA composites. Journal of Composite Materials, 2023, 40(2): 911-928.

[0056] [3]Duan Y, Liang Q, Yang Z, et al. A wide-angle broadband electromagnetic absorbing metastructure using 3D printing technology. Materials&Design, 2021, 208: 109900.

[0057] [4] Ye Xicong, Ouyang Bin, Yang Chao, et al. Preparation of graphene-carbonyl iron powder wire and analysis of its microwave absorption properties. Journal of Composite Materials, 2021, 39: 1-12.

[0058] Example

[0059] Example 1 and Comparative Example 1

[0060] Example 1 provides a method for fabricating a double-layer absorbing structure, which includes the following steps:

[0061] (1) The preparation of carbonyl iron polylactic acid composite material using carbonyl iron and polylactic acid includes the following steps:

[0062] S1, carbonyl iron and polylactic acid powder are dried in an oven at 80°C for 12 h;

[0063] S2, a mixture of carbonyl iron and polylactic acid in a mass ratio of 6:4 was dispersed in a planetary mixer at a speed of 60 r / min for 8 h;

[0064] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0065] S4, the dried composite material particles are poured into a single-screw extruder. The composite particles are further mixed in the screw under the action of heating and melting, screw friction, and shearing. The molten mixture is extruded from the die and, through the combined action of water cooling and traction sizing, yields a diameter of 1.75 mm. 0.05 mm composite wire CI-60 / PLA.

[0066] (2) The preparation of nano-carbon particle polylactic acid composite material using nano-carbon particles and polylactic acid includes the following steps:

[0067] S1, the nano-carbon particles and polylactic acid powder were dried in an oven at 80°C for 12 h;

[0068] S2, a mixture of nano-carbon particles and polylactic acid in a mass ratio of 2:8 was dispersed in a planetary mixer at a speed of 60 r / min for 8 h;

[0069] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0070] S4, the dried composite material particles are poured into a single-screw extruder. The composite particles are further mixed in the screw under the action of heating and melting, screw friction, and shearing. The molten mixture is extruded from the die and, through the combined action of water cooling and traction sizing, yields a diameter of 1.75 mm. 0.05 mm composite wire NPC-20 / PLA.

[0071] (3) A loss medium layer B is formed by using nano-carbon particle polylactic acid absorbing composite wire and a fused deposition modeling process. On the loss medium layer B, a loss medium layer A is formed by using carbonyl iron polylactic acid absorbing composite wire and a fused deposition modeling process, resulting in a double-layer absorbing structure CI-60-1mm / NPC-20-4mm. The printing temperature of the wire is 230℃ and the printing speed is 40 mm / s.

[0072] The double-layer absorbing structure CI-60-1mm / NPC-20-4mm has a lossy dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 1mm and a lossy dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 4mm; the total thickness of the double-layer absorbing structure is 5mm.

[0073] As a comparative example 1, a double-layer absorbing structure NPC-20-1mm / CI-60-4mm was prepared, with loss dielectric layer B (NPC-20 / PLA) as the top layer with a thickness of 1mm and loss dielectric layer A (CI-60 / PLA) as the bottom layer with a thickness of 4mm, for a total thickness of 5mm.

[0074] Example 1 uses CI-60 / PLA as the top layer (1 mm thick) of the double-layer absorbing material and NPC-20 / PLA as the bottom layer (4 mm thick). The mode variation curves of the surface reflection loss and interface wave impedance of the double-layer structure with frequency are shown below. Figure 2 As shown, two absorption peaks appear within the frequency range, corresponding to reflection losses of -36.9 dB (4.8 GHz) and -23.2 dB (16.7 GHz), respectively, with effective absorption frequency bands of 3.8–6.4 GHz and 14.9–18 GHz. The reflection loss values ​​in the 6.4–14.9 GHz band are all less than -5.8 dB, indicating a certain electromagnetic loss capability, and the distribution is relatively uniform. From the wave impedance modulus, it can be seen that in the 2.6–5.5 GHz and 10.4–18 GHz bands, the surface wave impedance is greater than the interface wave impedance, consistent with the gradual change in wave impedance. Therefore, the effective absorption frequency bands of the two absorption peaks are within these two frequency bands.

[0075] Comparative Example 1 uses NPC-20 / PLA as the top layer (1 mm thick) of the double-layer absorbing material and CI-60 / PLA as the bottom layer (4 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 3 As shown, the effective reflection loss frequency band is 3.4-5.2 GHz, and the minimum reflection loss is -24.8 dB (4.2 GHz). The electromagnetic loss performance of the structure is not as good as the scheme using CI-60 / PLA as the surface layer. It can be seen from the wave impedance mode that in the 4.5-15.2 GHz frequency band, the surface wave impedance is less than the interface wave impedance. The electromagnetic wave impedance mismatch causes the electromagnetic waves to be reflected.

[0076] Example 2 and Comparative Example 2

[0077] Example 2 uses the preparation method in Example 1 to form a double-layer absorbing structure CI-60-2mm / NPC-20-3mm. The double-layer absorbing structure CI-60-2mm / NPC-20-3mm has a loss dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 2mm and a loss dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 3mm, for a total thickness of 5mm.

[0078] Comparative Example 2 uses the preparation method in Example 1 to form a double-layer absorbing structure NPC-20-2mm / CI-60-3mm. The double-layer absorbing structure NPC-20-2mm / CI-60-3mm has a lossy dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 2mm and a lossy dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 3mm, for a total thickness of 5mm.

[0079] Example 2 uses CI-60 / PLA as the top layer (2 mm thick) of the double-layer absorbing material and NPC-20 / PLA as the bottom layer (3 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 4 As shown, two absorption peaks appear within the frequency range, corresponding to reflection losses of -13.8 dB (5.7 GHz) and -16.3 dB (15.8 GHz), respectively, with effective absorption frequency bands of 4.8–7.2 GHz and 13.6–18 GHz, respectively. The reflection loss values ​​in the 7.2–13.6 GHz band are all less than -7.1 dB, indicating a certain electromagnetic loss capability, and the distribution is relatively uniform. From the wave impedance modulus, it can be seen that in the 2.6–7.2 GHz and 12.6–18 GHz bands, the surface wave impedance is greater than the interface wave impedance, consistent with the gradual change in wave impedance. Therefore, the effective absorption frequency bands of the two absorption peaks are within these two frequency bands.

[0080] Comparative Example 2 uses NPC-20 / PLA as the top layer (2 mm thick) of the double-layer absorbing material and CI-60 / PLA as the bottom layer (3 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 5 As shown, the effective reflection loss frequency band is 3.0-4.7 GHz, and the minimum reflection loss is -20.0 dB (3.8 GHz). The electromagnetic loss performance of the structure is not as good as the scheme using CI-60 / PLA as the surface layer. It can be seen from the wave impedance mode that in the 4.6-15.9 GHz frequency band, the surface wave impedance is less than the interface wave impedance. The electromagnetic wave impedance mismatch causes the electromagnetic waves to be reflected.

[0081] Example 3 and Comparative Example 3

[0082] Example 3 uses the preparation method in Example 1 to form a double-layer absorbing structure CI-60-3mm / NPC-20-2mm. The double-layer absorbing structure CI-60-3mm / NPC-20-2mm has a loss dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 3mm and a loss dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 2mm, for a total thickness of 5mm.

[0083] Comparative Example 3 uses the preparation method in Example 1 to form a double-layer absorbing structure NPC-20-3mm / CI-60-2mm. The double-layer absorbing structure NPC-20-3mm / CI-60-2mm has a lossy dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 3mm and a lossy dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 2mm, for a total thickness of 5mm.

[0084] Example 3 uses CI-60 / PLA as the top layer (3 mm thick) of the double-layer absorbing material and NPC-20 / PLA as the bottom layer (2 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 6 As shown, two absorption peaks appear within the frequency range, corresponding to reflection losses of -7.8 dB (5.8 GHz) and -12.0 dB (16.5 GHz), respectively, with an effective absorption frequency band of 15.3–18.0 GHz. The effective absorption frequency band is relatively reduced because the frequency band near the first absorption peak does not reach effective absorption. From the wave impedance modulus, it can be seen that in the 2.6–9.3 GHz and 16.8–18.0 GHz frequency bands, the surface wave impedance is greater than the interface wave impedance, indicating good impedance matching and the appearance of two absorption peaks. The higher reflection loss value corresponding to the first absorption peak is related to the attenuation characteristics of the constituent materials.

[0085] Comparative Example 3 uses NPC-20 / PLA as the top layer (3 mm thick) of the double-layer absorbing material and CI-60 / PLA as the bottom layer (2 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 7 As shown, the effective reflection loss frequency bands are 3.0-4.5 GHz and 16.2-18 GHz, with a minimum reflection loss of -15.2 dB (3.6 GHz). The electromagnetic loss performance of this structure is inferior to the scheme using CI-60 / PLA as the surface layer. The wave impedance modes show that in the 5.4-18.0 GHz frequency band, the surface wave impedance is less than the interface wave impedance, and this electromagnetic wave impedance mismatch leads to a large amount of electromagnetic wave reflection.

[0086] Example 4 and Comparative Example 4

[0087] Example 4 uses the preparation method in Example 1 to form a double-layer absorbing structure CI-60-4mm / NPC-20-1mm. The double-layer absorbing structure CI-60-4mm / NPC-20-1mm has a loss dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 4mm and a loss dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 1mm, for a total thickness of 5mm.

[0088] Comparative Example 4 uses the preparation method in Example 1 to form a double-layer absorbing structure NPC-20-4mm / CI-60-1mm. The double-layer absorbing structure NPC-20-4mm / CI-60-1mm has a loss dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 4mm and a loss dielectric layer B (NPC-20 / PLA) as the bottom layer with a thickness of 1mm, for a total thickness of 5mm.

[0089] Example 4 uses CI-60 / PLA as the top layer (4 mm thick) of the double-layer absorbing material and NPC-20 / PLA as the bottom layer (1 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 8 As shown, two absorption peaks appear within the frequency range, corresponding to reflection losses of -7.5 dB (5.6 GHz) and -17.7 dB (17.5 GHz), respectively, with an effective absorption frequency band of 15.9–18.0 GHz. The effective absorption frequency band is relatively reduced because the frequency band near the first absorption peak does not reach effective absorption. From the wave impedance modulus, it can be seen that in the 2.6–12.4 GHz and 14.4–18.0 GHz frequency bands, the surface wave impedance is greater than the interface wave impedance, indicating good impedance matching and the appearance of two absorption peaks. The higher reflection loss value corresponding to the first absorption peak is related to the attenuation characteristics of the constituent materials.

[0090] Comparative Example 4 uses NPC-20 / PLA as the top layer (4 mm thick) of the double-layer absorbing material and CI-60 / PLA as the bottom layer (1 mm thick). The surface reflection loss and interface wave impedance mode variation curves of the double-layer structure with frequency are shown below. Figure 9 As shown, the effective reflection loss frequency band is 3.1-4.5 GHz, and the minimum reflection loss is -14.7 dB (3.6 GHz). The electromagnetic loss performance of the structure is not as good as the scheme using CI-60 / PLA as the surface layer. As can be seen from the wave impedance mode, in the 7.3-18.0 GHz frequency band, the surface wave impedance is less than the interface wave impedance. The electromagnetic wave impedance mismatch leads to a large amount of electromagnetic wave reflection.

[0091] In summary, CI-60 / PLA and NPC-20 / PLA composite materials were selected to design a double-layer structure, with a total thickness constraint of 5 mm. CI-60 / PLA was used as the top layer of the double-layer absorbing material (thickness ranging from 1 to 4 mm), and NPC-20 / PLA was used as the bottom layer (thickness ranging from 4 to 1 mm). The surface reflection loss of the four designed double-layer structures as a function of frequency is shown in the figure below. Figure 10 As shown, it can be seen that as the surface layer thickness decreases, the positions of the two absorption peak frequencies shift to both sides, and the effective absorption bandwidth expands. Among them, the double-layer structure with a 1 mm surface layer of CI-60 / PLA and a 4 mm bottom layer of NPC-20 / PLA exhibits the best electromagnetic loss capability, with effective absorption frequency bands of 3.8~6.4 GHz and 14.9~18 GHz. The reflection loss values ​​in the 6.4~14.9 GHz frequency band are all less than -5.8 dB, indicating a certain electromagnetic loss capability, and the distribution is relatively uniform.

[0092] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0093] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A double-layer absorbing structure, characterized in that, Includes loss dielectric layer A and loss dielectric layer B; The loss medium layer A serves as the surface layer, with polylactic acid as the matrix material and spherical carbonyl iron as the filler. The loss medium layer B serves as the bottom layer, with polylactic acid as the matrix material and carbon nanoparticles as the filler.

2. The double-layer absorbing structure according to claim 1, characterized in that, The carbonyl iron content in the loss medium layer A is 40%~70%, and the polylactic acid content is 30%~60%.

3. The double-layer absorbing structure according to claim 1, characterized in that, The mass fraction of carbon nanoparticles in the loss medium layer B is 10%~30%, and the mass fraction of polylactic acid is 70%~90%.

4. The double-layer absorbing structure according to claim 1, characterized in that, The thickness of the double-layer absorbing structure is 3~5mm, the thickness of the loss dielectric layer A is 1~4mm, and the thickness of the loss dielectric layer B is 1~4mm.

5. The double-layer absorbing structure according to claim 1, characterized in that, The thickness of the loss dielectric layer A is less than the thickness of the loss dielectric layer B.

6. A method for preparing a double-layer absorbing structure according to any one of claims 1 to 5, characterized in that, Includes the following steps: Carbonyl iron and polylactic acid composite wires were prepared using carbonyl iron and polylactic acid; Nano-carbon particles and polylactic acid composite wires were prepared using nano-carbon particles and polylactic acid. A loss dielectric layer B is prepared by using nano-carbon particle polylactic acid composite wire and a fused deposition modeling process; on the loss dielectric layer B, a carbonyl iron polylactic acid composite wire is prepared by a fused deposition modeling process to obtain a double-layer microwave absorbing structure.

7. The method for preparing the double-layer absorbing structure according to claim 6, characterized in that, The step of preparing carbonyl iron and polylactic acid composite wire using carbonyl iron and polylactic acid includes: Carbonyl iron and polylactic acid powder are dried; The carbonyl iron and polylactic acid mixture is thoroughly dispersed in a planetary mixer; The mixture is melted, combined, and extruded through a granulator to produce composite material particles; The dried composite material particles are poured into a screw extruder, and the molten mixture is extruded from the die. The composite wire is obtained through the combined action of cooling and traction sizing.

8. The method for preparing the double-layer absorbing structure according to claim 6, characterized in that, The step of preparing nano-carbon particle polylactic acid composite wire using nano-carbon particles and polylactic acid includes: The carbon nanoparticles and polylactic acid powder were dried. The mixture of carbon nanoparticles and polylactic acid in a certain proportion is thoroughly dispersed in a planetary mixer; The mixture is melted, combined, and extruded through a granulator to produce composite material particles; The dried composite material particles are poured into a screw extruder, and the molten mixture is extruded from the die. The composite wire is obtained through the combined action of cooling and traction sizing.

9. The method for preparing the double-layer absorbing structure according to claim 6, characterized in that, When using fused deposition modeling (FDM) to form lossy dielectric layer A and lossy dielectric layer B, the printing temperature of the composite wire is 200~230℃ and the printing speed is 30~40 mm / s.

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