Radar-sound compatible absorption superstructure and preparation method thereof

Abstract

The invention discloses a radar-sound compatible absorption superstructure and a preparation method thereof, and belongs to the technical field of sound absorption and wave-absorbing materials, the superstructure is formed by a wave-absorbing material through fused deposition 3D printing, and has three-dimensional gradient components and a hierarchical pore structure, the hierarchical pore structure comprises a microscopic pore structure and a macroscopic pore structure, the macroscopic hole structure is a space folding inclined hole; microscopic holes and macroscopic holes are formed in the superstructure at the same time, resonance absorption peaks are formed at different frequencies through the composite effect of the micro / macroscopic holes, the problem that a traditional radar-sound wave compatible absorption material is too large in thickness / size is solved, it can be guaranteed that incident electromagnetic waves in different directions can make full contact with an absorber, all-directional multi-stage reflection is achieved, and the absorption efficiency is improved. Moreover, the folded multi-stage inclined holes can prolong the propagation path of sound waves and radar waves under the condition that the thickness of the structural member is not increased, multiple reflections are formed in the folded channel, and therefore rapid wave dissipation is caused in the channel.

Description

Technical Field

[0001] The invention belongs to the technical field of sound-absorbing and wave-absorbing materials, and in particular relates to a radar-acoustic compatible absorption superstructure and a preparation method thereof. Background Art

[0002] Electromagnetic radiation and noise pollution are two of the four major sources of environmental pollution listed by the World Health Organization. Both are invisible pollution that seriously endangers human health. In addition, with the advancement of electronic technology and the enhancement of military strength, various military reconnaissance technologies have emerged in an endless stream. In some special occasions where naval vessels, ship-borne weapons and amphibious equipment are used, radar detection and sonar detection are the most effective and commonly used detection technologies. Therefore, the development of new materials with sound absorption and microwave absorption capabilities is of great significance in the civilian field and the field of national defense and security.

[0003] Since the energy consumption mechanism of materials for microwaves and sound waves is very different, few materials have the ability to absorb both microwaves and sound waves. It is a huge challenge to design and manufacture multifunctional materials with both sound absorption and wave absorption functions. If the traditional method is used to form a double-layer structure of radar wave and sound wave absorption layers to obtain radar-acoustic compatible absorption performance, the large thickness and volume of the material will greatly limit its practical application.

[0004] In the past few years, the rapid emergence of artificial structured metamaterials (MMs) has made it possible to design material parameters, allowing precise control of waves over a wide range of physical ranges at deep subwavelength scales, while opening the door to physical manipulation, by combining sound-absorbing metastructures with absorbing materials to achieve radar-acoustic compatible absorption at limited thickness. Therefore, combining spatially folded multi-level slanted hole structures with absorbing materials can achieve radar-acoustic compatible absorption performance at thin thickness. Summary of the invention

[0005] The present invention provides a radar-acoustic compatible absorption superstructure and a preparation method thereof, which can prepare a supermaterial with excellent sound absorption and wave absorption performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions:

[0007] A radar-acoustic compatible absorbing superstructure, wherein the superstructure is formed by molten deposition 3D printing of absorbing materials, and has a three-dimensional gradient component and a multi-level pore structure, wherein the three-dimensional gradient component is that the distribution of Fe3O4 and CNTs in the PLA matrix of the Fe3O4-CNTs / PLA composite material is carried out according to a certain gradient law, and the content of Fe3O4 gradually increases from one end to the other end of the material, while the content of CNTs gradually decreases;

[0008] The multi-level pores include microscopic pores and macroscopic pore structures, the microscopic pores are evenly distributed inside the entire macroscopic sample, and the pore size is 30-60 μm, and the macroscopic pore structure is a spatially folded oblique pore;

[0009] The thickness of the superstructure is 20-40 mm; the aperture of the space folded oblique hole is 1.4-1.8 mm, the folding angle is 40°-60°, the length of each level of the hole is equal, and the folding angle is also equal, which can ensure that the sound wave / radar wave is always transmitted in a mutually perpendicular direction, increase the number of reflections of the radar wave-sound wave inside the cavity, effectively increase the attenuation distance of the radar wave-sound wave in the air, thereby improving the absorption performance; the inner wall of the folded oblique hole is a rough structure;

[0010] The superstructure material has a sound absorption frequency band of 500-6000 Hz and a wave absorption frequency band of 8.2-12.4 GHz.

[0011] A method for preparing a radar-acoustically compatible absorbing superstructure comprises the following steps:

[0012] (1) First, the structural component model is constructed using the 3D modeling software UG, and the aperture, folding angle, and thickness of the folded oblique holes inside the superstructure are designed;

[0013] (2) Fe3O4-CNTs composite absorber was prepared by co-precipitation method; PLA powder and Fe3O4-CNTs were configured and mixed evenly in a mass ratio of 1:1, and 3D printing filament was prepared by thermoplastic extrusion molding;

[0014] (3) Finally, according to the designed aperture, folding angle and thickness parameters of the folded inclined hole, the FDM 3D printing method was used to prepare radar wave-sound wave compatible absorption structural parts with different folding angles, apertures and thicknesses.

[0015] In the above steps, the specific process of thermoplastic extrusion in step (2) is as follows: 45 parts of Fe3O4-CNTs composite material, 45 parts of polylactic acid, 5 parts of surface modifier and 5 parts of foaming agent are weighed and mixed evenly according to mass fraction, dried at about 40° and then poured into the feed port of the thermoplastic machine, heated to a molten state and then extruded through a twin-screw extruder, and then combined with a winding machine to process a standard 3D printing consumable with a diameter of about 1.75 mm; wherein the heating temperature is 170°C and the speed of the extrusion screw is 45r / min; the mass ratio of the absorbing raw material powder to the toughening agent is 9:1;

[0016] The specific printing parameters in step (3) are set as follows: printing speed 30 mm / s, filling density 100%, printing temperature 220°C, and platform temperature 60°C.

[0017] Beneficial effects: The present invention provides a radar-acoustic compatible absorption superstructure and a preparation method thereof, which has the following advantages over the prior art:

[0018] (1) A single macroscopic straight / inclined hole structure will cause local material loss, resulting in some incident electromagnetic waves parallel to the hole axis direction to pass directly without interacting with the absorber, which ultimately weakens the wave absorption performance; the superstructure of the present invention simultaneously constructs microscopic holes and macroscopic holes, and the multi-level holes work together to ensure that electromagnetic waves incident from different directions can fully contact the absorber, achieve all-round multi-level reflection, and ensure the wave absorption efficiency at different incident angles; and the folded multi-level inclined holes can extend the propagation path of sound waves and radar waves without increasing the thickness of the structural parts, forming multiple reflections in the folded channel, thereby causing rapid wave dissipation in the channel; at the same time, the spatially folded multi-level inclined hole structure can also achieve broadband absorption performance; and the superstructure of the present invention can extend the hole channel under limited thickness and use the composite effect of microscopic and macroscopic holes to form resonant absorption peaks at different frequencies, solving the problem of excessive thickness / volume of traditional radar-sound wave compatible absorption materials;

[0019] (2) The superstructure of the present invention has a three-dimensional gradient composition. The three components of Fe3O4, CNTs and PLA work synergistically with each other under the condition of three-dimensional gradient distribution. PLA, as a matrix material, provides a support and dispersion environment for Fe3O4 and CNTs; Fe3O4 gives the material magnetism; CNTs can improve the conductivity and mechanical properties of the material; for the Fe3O4-CNTs / PLA composite material, the distribution of Fe3O4 and CNTs in the PLA matrix follows a certain gradient law. From one end of the material to the other end, the content of Fe3O4 gradually increases, and the content of CNTs gradually decreases. This gradient change can make the material have different physical, chemical and mechanical properties at different positions, for example, the material has higher conductivity on one side (due to the higher content of CNTs) and higher magnetism on the other side (due to the higher content of Fe3O4);

[0020] (3) The present invention uses FDM 3D printing technology to process a superstructure with internal multi-level folded oblique holes. By adjusting the aperture, folding angle and thickness of the folded oblique holes, the intensity of the absorption peak and the covered frequency range can be flexibly manipulated, thereby obtaining excellent broadband absorption performance;

[0021] (4) The present invention utilizes 3D printing technology to effectively control the roughness and density of the internal folded channels in the structural member, thereby improving the absorption performance;

[0022] (5) Compared with the traditional resonant absorption structure, the superstructure of the present invention does not need to set an air layer at the back, but is a self-contained system with a simple processing method and a short production cycle, which is convenient for large-scale application in actual scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A partial cross-sectional view of a space-folded inclined hole in an embodiment of the present invention;

[0024] Figure 2 Schematic diagram of micro-macro pores in an embodiment of the present invention;

[0025] Figure 3 It is an overall schematic diagram of a simulation model in an embodiment of the present invention;

[0026] Figure 4 Schematic diagram of finite element mesh division in an embodiment of the present invention;

[0027] Figure 5 is a curve showing the relationship between the sound absorption performance of the superstructure in Example 1 at 500-6000 Hz and the aperture of the spatially folded oblique hole;

[0028] Figure 6 is a curve showing the relationship between the sound absorption performance of the superstructure in Example 2 at 500-6000 Hz and the folding angle of the space-folded oblique hole;

[0029] Figure 7 is a curve showing the relationship between the sound absorption performance of the superstructure at 500-6000 Hz and the overall thickness of the structure in Example 3;

[0030] Figure 8 is a wave absorption performance curve of the superstructure in Example 4 at 2-18 GHz as the content of doped carbon nanotubes changes;

[0031] Fig. 9 is a curve of the microwave absorption performance of the superstructure in Example 5 at 2-18 GHz as a function of the calcination temperature;

[0032] Fig.10 is a curve showing the relationship between the microwave absorption performance of the superstructure in Example 6 at 8.2-12.4 GHz and the change in the angle of the space-folded oblique hole;

[0033] Fig.11 is a curve showing the variation of the microwave absorption performance of the superstructure in Example 7 at 8.2-12.4 GHz as the aperture of the spatially folded oblique hole changes;

[0034] Fig.12 The sound absorption performance of the sound absorption structure with the optimal geometric parameters printed by the 3% CNTs-600° C. absorbing wire material with the best absorption performance in Example 8. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0036] like Figure 1 and Figure 2 As shown, a radar-acoustic compatible absorbing superstructure is formed by molten deposition 3D printing of absorbing materials, and has a three-dimensional gradient component and a multi-level pore structure.

[0037] The three-dimensional gradient components are Fe3O4, CNTs, and PLA. These three components work synergistically with each other under the condition of three-dimensional gradient distribution. PLA, as a matrix material, provides a support and dispersion environment for Fe3O4 and CNTs; Fe3O4 gives the material magnetism; CNTs can improve the conductivity and mechanical properties of the material; for Fe3O4-CNTs / PLA composite materials, the distribution of Fe3O4 and CNTs in the PLA matrix follows a certain gradient law. From one end to the other end of the material, the content of Fe3O4 gradually increases, and the content of CNTs gradually decreases.

[0038] like Figure 2 As shown, the multi-level pores include microscopic pores and macroscopic pore structures, the microscopic pores are evenly distributed inside the entire macroscopic sample, and the pore size is 30-60 μm, and the macroscopic pore structure is a multi-level folded oblique pore;

[0039] The thickness of the superstructure is 20-40 mm; the aperture of the multi-level folded oblique hole is 1.4-1.8 mm, the folding angle is 40°-60°, the length of each level of the hole is equal, and the folding angle is also equal, which can ensure that the sound wave / radar wave is always transmitted in a direction perpendicular to each other, increase the number of reflections of the radar wave-sound wave inside the cavity, and effectively increase the attenuation distance of the radar wave-sound wave in the air, thereby improving the absorption performance; the inner wall of the folded oblique hole is a rough structure.

[0040] The method for preparing the above-mentioned radar-acoustic compatible absorbing superstructure material comprises the following steps:

[0041] (1) First, the structural component model is constructed using the 3D modeling software UG, and the aperture, folding angle, and thickness of the folded oblique holes inside the superstructure are designed. The specific process is as follows:

[0042] Since the solid material used in the structure designed by the present invention is a hard material, its density is much greater than the density of air, that is, the acoustic impedance of the solid material is much greater than the acoustic impedance of air, the contact surface between the structure and the air can be set as an acoustic hard boundary condition to avoid the coupling of multiple physical fields, thereby simplifying the calculation process and saving calculation time; the physical fields, materials, region division, solver configuration, etc. used in the simulation are set as follows:

[0043] (a) Model area settings

[0044] A three-dimensional model was established in the model wizard, and the pressure acoustics interface was selected. The sound-absorbing structure established in UG was imported into the COMSOL software, and a duct area identical to the structural area was constructed as the sound wave incident area. Through Boolean operations, all geometric elements were processed as a union, the structural solid domain was deleted, and only the air domain was retained. A virtual domain was added on top of the incident sound field, and this area was set as a perfect matching layer (PML) to isolate the free domain of sound wave propagation to simulate an infinite area, and absorb reflected waves to avoid the influence of secondary reflected waves on the calculation of the structural sound absorption coefficient ( Figure 3 );

[0045] (b) Material Definition

[0046] The solid material of the acoustic superstructure with multi-level inclined hole space folding structure is defined as PLA, and the fluid inside the multi-level inclined hole folding cavity inside the structure is defined as air. The specific structural parameters of the materials are shown in Table 1;

[0047] Table 1 Material parameters of acoustic superstructure

[0048]

[0049] (c) Pressure acoustic setup

[0050] Define the physical field conditions of all domains as pressure acoustics, and define the external boundary conditions of the structure and sound radiation domain as acoustic hard boundaries; set the incident condition in the sound radiation area as background pressure field, the type as plane wave radiation, define the sound pressure amplitude p0 of the incident pressure field as 1Pa, and the sound propagation direction as perpendicular to the structure surface; set the multi-level inclined hole folded cavity part of the structure as narrow area acoustics;

[0051] (d) Grid division

[0052] When dividing the grid, the size and type of the grid determine the quality of the grid, and the quality of the grid division directly determines the time cost of the operation and the accuracy of the calculation results. The smaller the grid division, the more grids there are, and the calculation cost and time will rise linearly. The general principle of dividing the grid is to use as large a grid as possible to reduce the calculation time cost while ensuring the accuracy of the calculation results. However, in acoustic finite element simulation, at least six second-order units should be used to resolve the wavelength. Therefore, when dividing the grid, it is necessary to ensure that the size of the largest grid is at least less than 1 / 6 of the smallest wavelength, that is, the following formula must be satisfied to fully resolve the sound waves of all wavelengths in the frequency domain.

[0053]

[0054] Where C0 represents the speed of sound, that is, the speed at which sound waves propagate in the medium; f max Represents the maximum frequency, which is the highest frequency at which sound waves can propagate in a medium;

[0055] The structural area is divided into tetrahedral grids, and the maximum size of the grid is limited to meet the above conditions. The plane wave incident area and the virtual domain PML layer are meshed by sweeping. In order to ensure that the reflected sound waves are fully absorbed by the PML layer, the number of axial sweeping units of the PML layer grid is defined. Figure 4 The figure shows the schematic diagram of finite element mesh division. After the mesh division is completed, it contains 83658 domain elements, 15730 boundary elements and 4801 edge elements.

[0056] Define the ambient medium air contact surface on the structure surface, set the non-local coupling condition, and define the variable incident sound pressure p inc and p scat , the reflection coefficient is R = p scat / p inc , according to the sound absorption coefficient calculation formula, the sound absorption coefficient expression is defined as α = 1-abs(R)^2;

[0057] (e) Simulation model solver configuration

[0058] Among the direct solvers of COMSOL, the two solvers MUMPS and PARDISO have relatively high computational efficiency. The main difference between different solvers is their relative speed. MUMPS and PARDISO can store solutions outside the core, and the MUMPS solver also supports cluster computing. Through comparative verification, there is no difference in the results obtained by using the two solvers for calculation, but in terms of computational efficiency, the PARDISO solver is significantly higher than the MUMPS solver. Therefore, in order to improve the calculation speed, the PARDISO solver is selected for the finite element solution of the sound-absorbing structure;

[0059] (2) Fe3O4-CNTs composite absorbing material was prepared by co-precipitation method; PLA powder and Fe3O4-CNTs were configured and mixed in a mass ratio of 1:1, and 3D printing filaments were prepared by thermoplastic extrusion molding. Superstructures with different folding angles, apertures and thicknesses were prepared by FDM3D printing processing method for testing the absorbing performance. The appropriate aperture, folding angle and thickness parameters of the folded inclined hole were selected to design radar wave and sound wave compatible absorbing structural parts.

[0060] Example 1

[0061] (1) Four cylinders with a diameter of 29 mm and a height of 40 mm were constructed using the 3D modeling software UG. Then, spatially folded multi-level inclined holes and microscopic holes were designed inside the cylinders. The apertures of the inclined holes were set to 1.4 mm, 1.6 mm, and 1.8 mm, respectively.

[0062] (2) A polylactic acid (PLA) 3D printing filament with a diameter of 1.75 mm was produced by a thermoplastic extruder; 45 parts of Fe3O4-CNTs composite material, 45 parts of polylactic acid, 5 parts of surface modifier, and 5 parts of foaming agent were weighed and mixed evenly according to the mass fraction; the mixed raw materials were dried at 40° for 3 hours, poured into the feed port of the extruder, the raw materials were heated to a molten state, and the filaments were extruded through a twin-screw extruder, and then the filaments were prepared into a 3D printing filament with a diameter of 1.75 mm and uniform distribution using a winding machine. The heating temperature was 170°C and the screw rotation speed was 45 r / min.

[0063] (3) Using 3D printing to process and shape, the 3D printing parameters are set: printing speed is 30 mm / s, filling density is 100%, printing temperature is 190°C, and platform temperature is 60°C, and finally a broadband sound-absorbing structural part is processed.

[0064] The sound absorption frequency band of the superstructure prepared in this embodiment is 500-6000 Hz, and the sound absorption coefficient is tested using an AWA6290T transfer function sound absorption coefficient measurement system.

[0065] like Figure 5 The figure shows a comparison of the sound absorption coefficients of the superstructure in this embodiment at different apertures d. Compared with the structure with an aperture size of 1.6-1.8 mm, the structure with an aperture of 1.4 mm has a wider effective sound absorption range and exhibits more resonance absorption peaks, especially at 1100 Hz, 3300 Hz, and 5600 Hz. It shows that the selection of a suitable aperture size plays a key role in the sound absorption performance. A too small aperture will increase the acoustic resistance and affect the absorption of medium and low frequency sound waves. In addition, a too small aperture will reduce the air permeability, increase the reflection of sound waves on the surface, reduce the contact opportunity between the sound absorbing structure and the sound waves, and thus reduce the sound absorption effect. A too large aperture will cause the resonance frequency to continuously move toward high frequency, and the effective resonance absorption peak will decrease, shortening the effective sound absorption range of the sound absorbing structure. This is mainly because the increase in aperture will cause the decrease in sound quality and acoustic resistance, resulting in an increase in the resonance frequency. At the same time, the absorption monomer undergoes a process from impedance mismatch with air to impedance matching, and then to impedance mismatch.

[0066] Example 2

[0067] (1) Four cylinders with a diameter of 29 mm and a height of 40 mm were constructed using the 3D modeling software UG. Then, multi-level inclined holes with spatial folding were designed inside the cylinders, where the folding angles of the inclined holes were set to 40°, 50°, and 60°, respectively.

[0068] (2) A polylactic acid (PLA) 3D printing filament with a diameter of 1.75 mm was produced by a thermoplastic extruder, and the specific preparation process was the same as that in Example 1;

[0069] (3) Using 3D printing to process and shape, the 3D printing parameters are set: printing speed is 30 mm / s, filling density is 100%, printing temperature is 200°C, platform temperature is 60°C, and finally a broadband sound absorbing structural part is processed.

[0070] The sound absorption frequency band of the superstructure prepared in this embodiment is 500-6000 Hz, and the sound absorption coefficient is tested using an AWA6290T transfer function sound absorption coefficient measurement system.

[0071] like Figure 6 As shown in the figure, as the spatial folding angle decreases, the peak value of the superstructure's sound absorption coefficient gradually moves to low frequencies, and the effective sound absorption range in the range of 500-6000Hz is wider, especially in the 3000-6000Hz frequency band, the sound absorption coefficient reaches above 0.8, and the sound absorption performance has been greatly improved. When the folding angle is small, the number of reflections of the sound wave inside the structure increases, increasing the chance of contact between the sound wave and the structure, thereby improving the sound absorption coefficient. However, when the folding angle exceeds a certain critical value, the propagation path of the sound wave inside the structure will become shorter, resulting in a decrease in the sound absorption coefficient.

[0072] Example 3

[0073] (1) Using the 3D modeling software UG, three spatial folded multi-level inclined hole sound absorbing parts with different heights were constructed. The diameter of the fixed structure was 29 mm, the hole diameter was 1.4 mm, and the folding angle was 40°. Then, the heights of the structure were set to 20 mm, 30 mm, and 40 mm respectively.

[0074] (2) Use a thermoplastic extruder to produce polylactic acid (PLA) 3D printing filaments with a diameter of 1.75 mm; weigh 45 parts of Fe3O4-CNTs composite material, 45 parts of polylactic acid, 5 parts of surface modifier, and 5 parts of foaming agent according to mass fraction and mix them evenly; after drying the above mixed raw materials at 40° for 3 hours, pour them into the feed port of the extruder, heat the raw materials to a molten state, extrude the filaments through a twin-screw extruder, and then use a winding machine to prepare the filaments into 3D printing filaments with a diameter of 1.75 mm and uniform distribution. The heating temperature is 170°C and the screw rotation speed is 45r / min;

[0075] (3) Using 3D printing to process and shape, the 3D printing parameters are set: printing speed is 30 mm / s, filling density is 100%, printing temperature is 210°C, platform temperature is 60°C, and finally a broadband sound-absorbing structural part is processed.

[0076] like Figure 7As shown, when the thickness of the sound absorbing member is 40 mm, the effective sound absorption range is the widest. In the frequency band of 2400-6000 Hz, the sound absorption coefficient is above 0.6, achieving a nearly perfect sound absorption effect. In the frequency band of 3200-5400 Hz, the sound absorption coefficient is above 0.9, achieving a perfect sound absorption effect. Properly increasing the thickness can broaden the resonance frequency range and improve the mid- and low-frequency sound absorption performance, but too high a thickness will lead to a decrease in high-frequency sound absorption performance and violate the lightweight design principle. Therefore, the design thickness of the present invention is 10-40 mm.

[0077] Example 4

[0078] (1) The Fe3O4-CNTs composite material was prepared by co-precipitation method. First, different masses of CNTs powder were mixed with Fe3O4 powder to form mixed powders with mass fractions of 0%, 1%, 3%, 5%, 7%, and 9%, respectively.

[0079] (2) The composite powder was dissolved in 100 mL of ethanol, sealed and stirred for 30 min.

[0080] (3) Dry the precipitate in an oven at 80°C and take it out.

[0081] (4) After grinding, 1 g of the composite powder was mixed with paraffin wax in a mass ratio of 1:1, and then stirred under constant temperature heating and pressed into a coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm.

[0082] The electromagnetic parameters of the coaxial ring are tested by a vector network analyzer, such as Figure 8 As shown, when the doping ratio of CNTs is 3%, the material has the best wave absorption performance. At a thickness of 2.55 mm, the effective absorption bandwidth is 4.1 GHz and the strongest absorption peak can reach -59 dB.

[0083] Example 5

[0084] (1) In order to further improve the microwave absorption performance of the material, the composite material with a mass fraction of 3% was calcined at 400°C, 600°C, and 800°C respectively;

[0085] (2) After grinding, 1 g of the composite powder was mixed with paraffin wax in a mass ratio of 1:1, and then stirred under constant temperature heating and pressed into a coaxial ring with an inner diameter of 3.04 mm and an outer diameter of 7 mm;

[0086] The electromagnetic parameters of the coaxial ring are tested by a vector network analyzer, such as Fig. 9 As shown, when the calcination temperature is 600°C, the material has the best wave absorption performance. At a thickness of 1.65 mm, the effective absorption bandwidth is 4.6 GHz, which further reduces the optimal matching thickness of the material.

[0087] Example 6

[0088] (1) Using the 3D modeling software UG, three cuboids with a length and width of 22.86 × 10.16 mm and a height of 5 mm were constructed, and then spatial folding structures with folding angles of 40°, 50°, and 60° were set on the three cuboids respectively;

[0089] (2) A Fe3O4 / CNTs-600℃ / PLA composite 3D printing filament with a diameter of 1.75 mm was manufactured by a thermoplastic extruder; 45 parts of Fe3O4-CNTs composite material, 45 parts of polylactic acid, 5 parts of surface modifier, and 5 parts of foaming agent were weighed and mixed evenly according to the mass fraction; the mixed raw materials were dried at 50° for 3 hours, poured into the feed port of the extruder, the raw materials were heated to a molten state, and the filaments were extruded through a twin-screw extruder, and then the filaments were prepared into a 3D printing filament with a diameter of 1.75 mm and uniform distribution by a winding machine, wherein the heating temperature was 190°C and the rotation speed of the screw was 45r / min;

[0090] (3) Using 3D printing to process and shape, the 3D printing parameters are set: printing speed is 30 mm / s, filling density is 100%, printing temperature is 200°C, platform temperature is 60°C, and finally a broadband absorbing structural part is processed.

[0091] The electromagnetic parameters of the absorbing structure are tested by vector network analyzer, such as Fig.10 As shown in the figure, when the folding angle is 50°, the structural component has the best absorbing performance, the effective absorption bandwidth is 3.22 GHz, almost covering the entire X-band, and the strongest absorption peak can reach -43 dB.

[0092] Example 7

[0093] (1) The 3D modeling software UG was used to construct three rectangular blocks with a length and width of 22.86 × 10.16 mm and a height of 5 mm. Then, spatial folding structures with aperture sizes of 1.4 mm, 1.6 mm, and 1.8 mm were set on the three rectangular blocks respectively.

[0094] (2) A Fe3O4-CNTs / PLA composite 3D printing filament with a diameter of 1.75 mm was produced by a thermoplastic extruder. The specific preparation process was the same as that in Example 6.

[0095] (3) Using 3D printing to process and shape, the 3D printing parameters are set: printing speed is 30 mm / s, filling density is 100%, printing temperature is 210°C, and platform temperature is 60°C, and finally a broadband absorbing structural part is processed.

[0096] The electromagnetic parameters of the absorbing structure are tested by vector network analyzer, see Fig.11When the aperture of the inclined hole is 1.4 mm, the wave absorption performance of the structural component is the best, the effective absorption bandwidth is 3.05 GHz, and the strongest absorption peak can reach -23 dB.

[0097] Example 8

[0098] (1) Based on the above test results, a spatial folding structure sound-absorbing structural component with a height of 40 mm, a folding angle of 40°, and an aperture of 1.4 mm was constructed using the 3D modeling software UG;

[0099] (2) Then, a Fe3O4-CNTs-600℃ / PLA composite 3D printing filament with a diameter of 1.75mm is manufactured through a thermoplastic extruder; 45 parts of Fe3O4-CNTs composite material, 45 parts of polylactic acid, 5 parts of surface modifier, and 5 parts of foaming agent are weighed and mixed evenly according to the mass fraction; the above mixed raw materials are dried at 40° for 3 hours, poured into the feed port of the extruder, and the raw materials are heated to a molten state and extruded through a twin-screw filament, and then a winding machine is used to prepare the filament into a 3D printing filament with a diameter of 1.75mm and uniform distribution. The heating temperature is 190℃, and the rotation speed of the screw is 45r / min;

[0100] (3) Using 3D printing to process and shape, the 3D printing parameters are set: printing speed is 30 mm / s, filling density is 100%, printing temperature is 220°C, platform temperature is 60°C, and finally a broadband sound-absorbing structural part is processed.

[0101] like Fig.12 As shown, the sound absorbing structural member prepared in this embodiment has excellent sound absorbing performance at low, medium and high frequencies.

[0102] The above are only preferred embodiments of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A radar-acoustically compatible absorbing superstructure, characterized in that: The superstructure is formed by absorbing material through molten deposition 3D printing, and has a three-dimensional gradient component and a multi-level pore structure. The multi-level pores include microscopic pores and macroscopic pore structures. The microscopic pores are evenly distributed inside the entire superstructure, and the macroscopic pore structure is a folded oblique hole arranged in the superstructure.

2. The radar-acoustically compatible absorbent superstructure according to claim 1, characterized in that: The aperture of the microscopic hole is 30-60 μm; the aperture of the folded oblique hole is 1.4-1.8 mm, and the folding angle is 40°-60°.

3. The radar-acoustically compatible absorbent superstructure according to claim 1 or 2, characterized in that: The length of each level of the folded inclined hole is equal and the folding angle is equal.

4. The radar-acoustically compatible absorbent superstructure of claim 1, wherein: The three-dimensional gradient component is that the distribution of Fe3O4 and CNTs in the PLA matrix of the Fe3O4-CNTs / PLA superstructure composite material follows a certain gradient law. From one end to the other end of the material, the content of Fe3O4 gradually increases, while the content of CNTs gradually decreases.

5. The radar-acoustically compatible absorbent superstructure of claim 1, wherein: The thickness of the superstructure is 20-40 mm.

6. The radar-acoustically compatible absorbent superstructure of claim 2, wherein: The inner wall of the folding inclined hole is a rough structure.

7. The method for preparing a radar-acoustically compatible absorbing superstructure according to any one of claims 1 to 6, characterized in that: The following steps are involved: (1) The superstructure model was constructed using the 3D modeling software UG, and the diameter, folding angle, and thickness of the folded oblique holes inside the superstructure were designed; (2) preparing Fe3O4-CNTs composite absorber by coprecipitation method; mixing Fe3O4-CNTs composite material, polylactic acid, surface modifier and foaming agent uniformly, and preparing 3D printing filament by thermoplastic extrusion molding; (3) Finally, according to the designed aperture, folding angle and thickness parameters of the folded inclined hole, the FDM 3D printing method was used to prepare the radar wave and sound wave compatible absorption superstructure.

8. The method for preparing a radar-acoustically compatible absorbing superstructure according to claim 7, characterized in that: The process of the thermoplastic extrusion is as follows: 45 parts of Fe3O4-CNTs composite material, 45 parts of polylactic acid, 5 parts of surface modifier and 5 parts of foaming agent are weighed and mixed evenly according to mass fraction, and then poured into the feed port of the thermoplastic machine after drying at 40°C, and then heated to a molten state and extruded through a twin-screw extruder, and then combined with a winding machine to process a standard 3D printing consumable with a diameter of about 1.75 mm; wherein the heating temperature is 170°C, and the speed of the extrusion screw is 45r / min; the mass ratio of the absorbing raw material powder to the toughening agent is 9:

1.

9. The method for preparing a radar-acoustically compatible absorbing superstructure according to claim 7, characterized in that: The parameters of 3D printing were set as follows: printing speed 30 mm / s, filling density 100%, printing temperature 220 °C, and platform temperature 60 °C.

10. The method for preparing a radar-acoustically compatible absorbing superstructure according to claim 7, characterized in that: Step (1) specifically includes the following steps: A three-dimensional model was established in the model wizard, and the pressure acoustics interface was selected. The sound-absorbing structure established in UG was imported into the COMSOL software, and a duct area identical to the structural area was constructed as the sound wave incident area. Through Boolean operations, all geometric elements were processed as a union, the structural solid domain was deleted, and only the air domain was retained. A virtual domain was added on top of the incident sound field, and this area was set as a perfect matching layer to isolate the free domain of sound wave propagation to simulate an infinite area, and absorb reflected waves to avoid the influence of secondary reflected waves on the calculation of the structural sound absorption coefficient. The solid material of the acoustic superstructure of the multi-level inclined hole space folding structure is defined as PLA, the fluid inside the multi-level inclined hole folding cavity inside the structure is defined as air, the physical field conditions of all domains are defined as pressure acoustics, and the external boundary conditions of the structure and sound radiation domain are defined as acoustic hard boundaries; the incident condition in the sound radiation area is set as the background pressure field, the type is plane wave radiation, the sound pressure amplitude p0 of the incident pressure field is defined as 1Pa, and the sound propagation direction is perpendicular to the structure surface; the multi-level inclined hole folding cavity part of the structure is set as narrow area acoustics; The structure area is divided into tetrahedral grids to ensure that the size of the largest grid is at least less than 1 / 6 of the smallest wavelength. That is, the following formula is satisfied to fully analyze the sound waves of all wavelengths in the frequency domain. Where C0 represents the speed of sound, that is, the speed at which sound waves propagate in the medium; f max Represents the maximum frequency, which is the highest frequency at which sound waves can propagate in a medium; Define the ambient medium air contact surface on the structure surface, set the non-local coupling condition, and define the variable incident sound pressure p inc and p scat , the reflection coefficient is R = p scat / p inc , according to the sound absorption coefficient calculation formula, the sound absorption coefficient expression is defined as α = 1-abs(R)^2; The PARDISO solver is used to perform finite element solution of the sound absorbing structure.

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