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

Abstract

The application provides a three-layer wave-absorbing structure and a preparation method thereof, which comprises a lossy dielectric layer A, a lossy dielectric layer B and a lossy dielectric layer C; 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 an intermediate layer, the base material is polylactic acid, and the filler is nano graphite; and the lossy dielectric layer C is used as a bottom layer, the base material is polylactic acid, and the filler is nano carbon particles. The three-layer wave-absorbing structure has gradually decreasing wave impedance from the surface of the lossy dielectric layer A to the interface between the lossy dielectric layers, and the wave impedance of the structure surface is close to the wave impedance of free space, so that most of the electromagnetic waves enter the material interior; the increased intermediate dielectric loss layer plays a transition role of wave impedance, so that the wave impedance is reasonably changed, and the effective wave-absorbing bandwidth is widened; the reflection loss value in the medium frequency band is better than that of the double-layer wave-absorbing material, and the design of the three-layer structure can improve the electromagnetic loss performance in the medium frequency band.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing structure technology, and specifically relates to a three-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 relatively narrow applicable frequency band for stealth. While the effective absorption frequency band can be extended through layered design of microwave-absorbing materials, poor impedance matching at the material interface in the mid-frequency band (4-8 GHz) results in absorption performance that fails to meet expectations. In the design of multilayer microwave-absorbing materials, the materials are arranged as close to their intrinsic impedance as possible to decrease. Therefore, based on the electromagnetic characteristics of different microwave-absorbing materials, a transition layer with a changing impedance gradient is placed between the surface and bottom layers. Through the combined design of multiple layers, the impedance matching of the materials is further improved, achieving a better broadband absorption effect. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, the inventors have conducted intensive research and provided a three-layer absorbing structure and its preparation method. Based on the design of a double-layer absorbing material, an intermediate layer is added as a transition layer for wave impedance to form a three-layer absorbing structure, which makes the wave impedance change reasonably and gradually, further broadens the effective absorption bandwidth, and improves the electromagnetic loss performance in the mid-frequency band.

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

[0005] In the first aspect, a three-layer absorbing structure includes a lossy dielectric layer A, a lossy dielectric layer B, and a lossy dielectric layer C;

[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 an intermediate layer, with polylactic acid as the matrix material and nano-graphite as the filler.

[0008] The loss medium layer C serves as the bottom layer, with polylactic acid as the matrix material and carbon nanoparticles as the filler.

[0009] 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%.

[0010] In conjunction with the first aspect, the mass fraction of nano-graphite in the loss medium layer B is 10%~30%, and the mass fraction of polylactic acid is 70%~90%.

[0011] In conjunction with the first aspect, the mass fraction of carbon nanoparticles in the loss medium layer C is 10%~30%, and the mass fraction of polylactic acid is 70%~90%.

[0012] In conjunction with the first aspect, the thickness of the three-layer absorbing structure is 3~5mm, the thickness of the loss dielectric layer A is 1~3mm, the thickness of the loss dielectric layer B is 1~3mm, and the thickness of the loss dielectric layer C is 1~3mm.

[0013] Secondly, a method for fabricating a three-layer absorbing structure includes the following steps:

[0014] Carbonyl iron and polylactic acid composite wires were prepared using carbonyl iron and polylactic acid;

[0015] Nano-graphite and polylactic acid composite wires were prepared using nano-graphite and polylactic acid.

[0016] Nano-carbon particles and polylactic acid composite wires were prepared using nano-carbon particles and polylactic acid.

[0017] A three-layer microwave absorbing structure is obtained by using nano-carbon particle polylactic acid composite wires and forming a loss dielectric layer C through a fused deposition modeling process; on the loss dielectric layer C, a nano-graphite polylactic acid composite wire is formed by forming a loss dielectric layer B through a fused deposition modeling process; on the loss dielectric layer B, a carbonyl iron polylactic acid composite wire is formed by forming a loss dielectric layer A through a fused deposition modeling process.

[0018] The three-layer absorbing structure and its preparation method provided by the present invention have the following beneficial effects:

[0019] (1) The present invention provides a three-layer absorbing structure and its preparation method, wherein a lossy dielectric layer A is used as the top layer, the matrix material is polylactic acid, and the filler is spherical carbonyl iron; a lossy dielectric layer B is used as the middle layer, the matrix material is polylactic acid, and the filler is nano-graphite; and a lossy dielectric layer C is used as the bottom layer, the matrix material is polylactic acid, and the filler is nano-carbon particles. In the three-layer absorbing structure of the present invention, the wave impedance decreases sequentially from the surface of the lossy dielectric layer A to the interface between the lossy dielectric layers, and the wave impedance of the structure surface is close to the free space wave impedance, so that most of the electromagnetic waves enter the interior of the material; the added intermediate dielectric loss layer plays a transition role in the wave impedance, so that the wave impedance changes reasonably and gradually, and the effective absorption bandwidth is broadened; the reflection loss value in the mid-frequency band is better than that of the double-layer absorbing material, and the design of the three-layer structure can improve the electromagnetic loss performance in the mid-frequency band.

[0020] (2) The present invention provides a three-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

[0021] Figure 1 This is a schematic diagram of a three-layer absorbing structure;

[0022] Figure 2 Analysis of the microwave absorption performance of a three-layer structure consisting of a 1mm top layer (CI-60 / PLA), a 1mm middle layer (NGP-10 / PLA), and a 3mm bottom layer (NPC-20 / PLA) in Example 1;

[0023] Figure 3 Analysis of the microwave absorption performance of the three-layer structure of Example 2, consisting of a 1mm top layer (CI-60 / PLA), a 2mm middle layer (NGP-10 / PLA), and a 2mm bottom layer (NPC-20 / PLA);

[0024] Figure 4 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 Comparative Example 1 was analyzed. Detailed Implementation

[0025] The features and advantages of the present invention will become clearer and more apparent from the following detailed description.

[0026] 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.

[0027] This invention provides a three-layer absorbing structure, such as Figure 1 As shown, it includes loss dielectric layer A, loss dielectric layer B and loss dielectric layer C;

[0028] 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.

[0029] The loss medium layer B serves as an intermediate layer, with polylactic acid as the matrix material and nano-graphite (NGP) as the filler.

[0030] The loss dielectric layer C is used as the bottom layer, the matrix material is polylactic acid, and the filler is carbon nanoparticles (NPC).

[0031] Loss dielectric layer A, loss dielectric layer B, and loss dielectric layer C are solidified and bonded together through a fused deposition modeling process to obtain a three-layer microwave absorbing structure.

[0032] 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.

[0033] The loss medium layer B contains 10% to 30% graphite nanoparticles and 70% to 90% polylactic acid. Preferably, the loss medium layer B contains 10% to 20% graphite nanoparticles and 80% to 90% polylactic acid. More preferably, the loss medium layer B contains 10% to 15% graphite nanoparticles and 85% to 90% polylactic acid.

[0034] The loss medium layer C contains 10% to 30% carbon nanoparticles and 70% to 90% polylactic acid. Preferably, the loss medium layer C contains 10% to 20% carbon nanoparticles and 80% to 90% polylactic acid. More preferably, the loss medium layer C contains 15% to 20% carbon nanoparticles and 85% to 90% polylactic acid.

[0035] The thickness of the three-layer absorbing structure is 3-5 mm, the thickness of lossy dielectric layer A is 1-3 mm, the thickness of lossy dielectric layer B is 1-3 mm, and the thickness of lossy dielectric layer C is 1-3 mm; preferably, the thickness of lossy dielectric layer A is 1-2 mm, the thickness of lossy dielectric layer B is 1-2 mm, and the thickness of lossy dielectric layer C is 2-4 mm. More preferably, the thickness of lossy dielectric layer A is less than the thickness of lossy dielectric layer C.

[0036] A three-layer absorbing structure consisting of lossy dielectric layer A, lossy dielectric layer B, and lossy dielectric layer C can extend the effective absorption frequency band through the stacked design of the absorbing materials. However, due to the suboptimal impedance matching at the material interfaces, the absorption performance in the mid-frequency band cannot reach the expected effect. The electromagnetic loss performance of the three-layer absorbing material of this invention is superior to that of a two-layer absorbing material. The added intermediate dielectric loss layer acts as a transition layer for the wave impedance, resulting in a reasonable gradual change in wave impedance and broadening the effective absorption bandwidth. The reflection loss value in the mid-frequency band is better than that of a two-layer absorbing material, and the three-layer structure design can improve the electromagnetic loss performance in the mid-frequency band.

[0037] The working principle of the three-layer structure of this invention is as follows: from the surface of the lossy dielectric layer A to the interface between the lossy dielectric layers, the wave impedance decreases sequentially, and the wave impedance at the surface of the structure is close to the free-space wave impedance, allowing most of the electromagnetic waves to enter the interior of the material. The added intermediate dielectric lossy layer acts as a transition layer for the wave impedance, resulting in a reasonable gradual change in wave impedance and broadening the effective absorption bandwidth. The reflection loss value in the mid-frequency band is superior to that of a double-layer absorbing material, and the three-layer structure design can improve the electromagnetic loss performance in the mid-frequency band.

[0038] This invention also provides a method for fabricating a three-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-graphite polylactic acid composite material using nano-graphite and polylactic acid includes the following steps:

[0045] S1, dry nano-graphite and polylactic acid powder in an oven at 80°C for at least 12 h;

[0046] S2, disperse the mixture of nano-graphite 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 1.75 mm. 0.05 mm composite wire.

[0049] (3) The preparation of nano-carbon particle polylactic acid composite material using nano-carbon particles and polylactic acid includes the following steps:

[0050] S1, dry the carbon nanoparticles and polylactic acid powder in an oven at 80~100℃ for at least 12 h;

[0051] 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;

[0052] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0053] 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.

[0054] (4) A loss medium layer C is formed using nano-carbon particle polylactic acid composite wire through fused deposition modeling (FDM). On top of loss medium layer C, a loss medium layer B is formed using nano-graphite polylactic acid composite wire through FDM. On top of loss medium layer B, a loss medium layer A is formed using carbonyl iron polylactic acid composite wire through FDM, resulting in a three-layer microwave absorbing structure. The optimal printing temperature for the composite wire is 200~230℃, and the printing speed is 30~40 mm / s.

[0055] 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.

[0056] Table 1. Comparison of the performance of the microwave absorbing composite wires reported in the literature with those prepared in this invention.

[0057]

[0058] Note: CI-60 / PLA means that the carbonyl iron content is 60% and the remainder is PLA matrix material; NGP-10 / PLA means that the nano-graphite content is 10% and the remainder is PLA matrix material; NPC-20 / PLA means that the nano-carbon particle content is 20% and the remainder is PLA matrix material.

[0059] [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.

[0060] [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.

[0061] [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.

[0062] [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.

[0063] Example

[0064] Example 1

[0065] Example 1 provides a method for fabricating a three-layer absorbing structure, which includes the following steps:

[0066] (1) The preparation of carbonyl iron polylactic acid composite material using carbonyl iron and polylactic acid includes the following steps:

[0067] S1, carbonyl iron and polylactic acid powder are dried in an oven at 80°C for 12 h;

[0068] 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;

[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 CI-60 / PLA.

[0071] (2) The preparation of nano-carbon particle polylactic acid composite material using nano-carbon particles and polylactic acid includes the following steps:

[0072] S1, the nano-carbon particles and polylactic acid powder were dried in an oven at 80°C for 12 h;

[0073] S2, a mixture of nano-graphite particles and polylactic acid in a mass ratio of 1:9 was dispersed in a planetary mixer at a speed of 60 r / min for 8 h;

[0074] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0075] 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 NGP-10 / PLA.

[0076] (3) The preparation of nano-carbon particle polylactic acid composite material using nano-carbon particles and polylactic acid includes the following steps:

[0077] S1, the nano-carbon particles and polylactic acid powder were dried in an oven at 80°C for 12 h;

[0078] S2, a mixture of carbon nanoparticles 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;

[0079] S3 involves melting and mixing the mixture, then extruding it through a granulator to produce composite material particles.

[0080] 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.

[0081] (4) A loss medium layer C is formed using nano-carbon particle polylactic acid (PLA) absorbing composite wire through fused deposition modeling (FDM). On top of loss medium layer C, a loss medium layer B is formed using nano-graphite PLA composite wire through FDM. On top of loss medium layer B, a loss medium layer A is formed using carbonyl iron PLA composite wire through FDM, resulting in a three-layer absorbing structure: CI-60-1mm / NGP-10-1mm / NPC-20-3mm. The optimal printing temperature for the composite wire is 230℃, and the printing speed is 40 mm / s.

[0082] The three-layer absorbing structure CI-60-1mm / NGP-10-1mm / NPC-20-3mm uses lossy dielectric layer A (CI-60 / PLA) as the top layer with a thickness of 1mm; lossy dielectric layer B (NGP-10 / PLA) as the middle layer with a thickness of 1mm; and lossy dielectric layer C (NPC-20 / PLA) as the bottom layer with a thickness of 3mm, for a total thickness of 5mm.

[0083] For the three-layer material design, CI-60 / PLA is used as the top layer (1 mm thick), NGP-10 / PLA as the middle layer (1 mm thick), and NPC-20 / PLA as the bottom layer (3 mm thick). The mode variation curves of the surface reflection loss and interface wave impedance of the three-layer structure with frequency are shown below. Figure 2 As shown, two absorption peaks appear within the frequency range, corresponding to reflection loss values ​​of -16.7 dB (5.6 GHz) and -32.3 dB (16.7 GHz), respectively, with effective absorption frequency bands of 4.7–7.2 GHz and 14.3–18 GHz, respectively. The reflection loss values ​​in the 7.2–14.3 GHz band are all less than -6.6 dB, indicating a certain electromagnetic loss capability, and the distribution is relatively uniform. Figure 2 In this context, surfacelayer is the surface layer, interface layer 01 is the interface layer between the surface layer and the intermediate layer, and interface layer 02 is the interface layer between the intermediate layer and the bottom layer.

[0084] As can be seen from the wave impedance moduli, in the 2.6-6.8 GHz and 12.9-18.0 GHz frequency bands, the surface wave impedance is greater than the interface wave impedance, which conforms to the gradual change of wave impedance. Therefore, the effective absorption frequency bands of the two absorption peaks are within these two frequency bands. In the 6.8-12.9 GHz frequency band, the surface wave impedance is less than the interface wave impedance, but the difference is small, which will only cause a small portion of electromagnetic waves to be reflected.

[0085] Example 2

[0086] Example 2 uses the preparation method in Example 1 to form a three-layer absorbing structure CI-60-1mm / NGP-10-2mm / NPC-20-2mm. The lossy dielectric layer A (CI-60 / PLA) is the top layer with a thickness of 1mm; the lossy dielectric layer B (NGP-10 / PLA) is the middle layer with a thickness of 2mm; and the lossy dielectric layer C (NPC-20 / PLA) is the bottom layer with a thickness of 2mm. The total thickness of the three-layer absorbing structure is 5mm.

[0087] The surface reflection loss and interface wave impedance modulus of the three-layer structure as a function of frequency are shown in the following curves: Figure 3 As shown, two absorption peaks appear within the frequency range, corresponding to reflection loss values ​​of -10.7 dB (6.1 GHz) and -24.1 dB (17.2 GHz), respectively, with effective absorption frequency bands of 5.7-6.6 GHz and 15.3-18 GHz, respectively. The reflection loss value in the 7.2-14.3 GHz frequency band is less than -5.7 dB, indicating a certain electromagnetic loss capability. Figure 3In this context, surface layer is the top layer, interfacelayer 01 is the interface layer between the top layer and the middle layer, and interface layer 02 is the interface layer between the middle layer and the bottom layer.

[0088] As can be seen from the wave impedance moduli, in the 2.6-6.3 GHz and 16.2-18.0 GHz frequency bands, the surface wave impedance is greater than the interface wave impedance, which conforms to the gradual change of wave impedance. Therefore, the effective absorption frequency bands of the two absorption peaks are within these two frequency bands. In the 6.3-16.2 GHz frequency band, the surface wave impedance is less than the interface wave impedance, and the difference is small, which will only cause a small portion of electromagnetic waves to be reflected.

[0089] Comparative Example 1

[0090] Comparative Example 1 is the same as Example 1, except that a double-layer absorbing structure CI-60-1mm / NPC-20-4mm is prepared, with 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.

[0091] Comparative 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 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 -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.

[0092] Comparing the electromagnetic loss performance of Example 1 and Comparative Example 1, the effective absorption bandwidth of Example 1 is superior to that of Comparative Example 1. The three-layer absorbing material design with an added intermediate layer allows for a reasonable gradual change in wave impedance. The intermediate layer acts as a transition layer for wave impedance, improving the electromagnetic loss performance in the mid-frequency band, with reflection losses all less than -6.6 dB. The present invention has been described in detail above with specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the 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 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 three-layer absorbing structure, characterized in that, It includes loss dielectric layer A, loss dielectric layer B and loss dielectric layer C; 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 an intermediate layer, with polylactic acid as the matrix material and nano-graphite as the filler. The loss medium layer C serves as the bottom layer, with polylactic acid as the matrix material and carbon nanoparticles as the filler.

2. The three-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 three-layer absorbing structure according to claim 1, characterized in that, The loss medium layer B contains 10% to 30% graphite nanoparticles and 70% to 90% polylactic acid.

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

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

6. A method for preparing a three-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-graphite and polylactic acid composite wires were prepared using nano-graphite and polylactic acid. Nano-carbon particles and polylactic acid composite wires were prepared using nano-carbon particles and polylactic acid. The loss dielectric layer C is formed by using nano-carbon particle polylactic acid composite wire and a melt deposition molding process. On the loss dielectric layer C, a nano-graphite polylactic acid composite wire is used to form the loss dielectric layer B through a fused deposition modeling process; on the loss dielectric layer B, a carbonyl iron polylactic acid composite wire is used to form the loss dielectric layer A through a fused deposition modeling process, resulting in a three-layer microwave absorbing structure.

7. The method for preparing the three-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 three-layer absorbing structure according to claim 6, characterized in that, The steps for preparing nano-graphite-polylactic acid composite wires using nano-graphite and polylactic acid include: The nano-graphite and polylactic acid powders were dried. The mixture of nano-graphite 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 three-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.

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

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