L-band wave-absorbing material and preparation method thereof

Abstract

The application provides an L-band wave-absorbing material and a preparation method thereof. The wave-absorbing material comprises a Fe-Si-Al composite material, and the composite material is a Fe-Si-Al soft magnetic particle with an oxide layer formed on the surface. The content of each element in the Fe-Si-Al soft magnetic particle raw material is as follows: Fe 84.5-85.5 wt%, Si 9.5-10 wt%, and Al 5-5.5 wt%. The diameter-thickness ratio of the Fe-Si-Al soft magnetic particle raw material is 50-100, and the average diameter is 20-40 mu m. The thickness of the oxide layer is 5-12 nm. The wave-absorbing material has excellent low-frequency wave-absorbing performance, and has the characteristics of thinness, lightness, widebandness and strongness. The impedance matching Z is greater than or equal to 4, the minimum reflectivity of a 5 mm thick product is less than -10 dB within 1-2 GHz, and the product can be used under multiple wavelengths of the L band, thereby meeting the use requirements of the wave-absorbing material.

Description

Technical Field

[0001] This invention belongs to the field of microwave absorbing materials technology, and in particular relates to an L-band microwave absorbing material and its preparation method. Background Technology

[0002] The L-band (1-2 GHz), as a key low-frequency band in the electromagnetic spectrum, holds an irreplaceable position in both civilian and military fields. In the field of modern stealth technology, the L-band serves as the core operating frequency band for early warning radar and low-altitude detection radar, highlighting the increasing demand for electromagnetic scattering suppression. According to classical absorption theory, to achieve efficient low-frequency absorption, materials typically need to possess considerable magnetic loss capacity and matching dielectric properties. This often results in excessive thickness and weight of the absorber. Traditional absorbing materials (such as ferrite and carbonyl iron) have excessively high densities, making it difficult to meet the stringent requirements of modern equipment for thin-layer, lightweight, and broadband absorbing materials. Lightweight polymer composite materials often require increased thickness or sacrificed bandwidth. Achieving effective absorption in the L-band, especially in the 1-1.5 GHz range, presents a severe challenge to material thickness, making it difficult to meet the requirements of thinness and lightweight integration in modern equipment.

[0003] Methods to improve low-frequency microwave absorption performance, such as altering the gold content of iron-silicon-aluminum alloys by adding other elements during metal smelting or reducing the dielectric constant of soft magnetic powders through acid etching, are difficult to industrialize due to demanding experimental conditions, complex procedures, and high costs. Therefore, how to significantly improve the electromagnetic loss and impedance matching characteristics of materials in the L-band with limited thickness through simple and rapid material design and microstructure control has become a focal point and challenge in the current research field of microwave absorbing materials. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an L-band absorbing material and its preparation method, which solves the problems of high density, excessive thickness, inability to maintain excellent absorbing performance in a wide band, and complex, costly, and difficult-to-industrialize preparation methods of existing absorbing materials.

[0005] To achieve the above and other related objectives, the present invention provides an L-band absorbing material and a method for preparing the same.

[0006] The first aspect of this invention provides an iron-silicon-aluminum composite material, wherein the composite material is iron-silicon-aluminum soft magnetic particles with an oxide layer formed on the surface; wherein the content of each element in the raw material of the iron-silicon-aluminum soft magnetic particles is 84.5~85.5wt%, Si 9.5~10wt%, and Al 5~5.5wt%; the aspect ratio of the raw material of the iron-silicon-aluminum soft magnetic particles is 50~100, and the average diameter is 20~40μm; the thickness of the oxide layer is 5~12nm.

[0007] This invention selects sheet-shaped iron-silicon-aluminum soft magnetic particles with a diameter-to-thickness ratio of 50 to 100. Compared with traditional spherical particles, sheet-shaped particles can improve magnetic permeability and have lower density, resulting in superior performance.

[0008] Preferably, the aspect ratio of the iron-silicon-aluminum soft magnetic particles can be 50, 60, 70, 80, 90, or 100.

[0009] Preferably, the average diameter of the iron-silicon-aluminum soft magnetic particles is 30~40μm; including but not limited to 30μm, 32μm, 35μm, 37μm, 38μm and 40μm.

[0010] This invention oxidizes iron-silicon-aluminum soft magnetic particles to obtain an iron-silicon-aluminum composite material with an oxide layer thickness of 5~12nm. The presence of the oxide layer can regulate the dielectric of the material surface, increase the impedance matching Z value, reduce the reflectivity, and give the material excellent wave absorption performance.

[0011] Preferably, the thickness of the oxide layer can be 5nm, 6nm, 7nm, 7.5nm, 8nm, 9nm, 10nm, 11nm, or 12nm.

[0012] The second aspect of the present invention provides a method for preparing the above-mentioned iron-silicon-aluminum composite material, the method comprising: oxidizing iron-silicon-aluminum soft magnetic particle raw material at 400~500℃ for 2~3h.

[0013] When the oxidation temperature is too low, the oxidation capacity is too weak, resulting in a thin oxide layer; when the oxidation temperature is too high, the oxidation capacity is too strong, resulting in a thick oxide layer.

[0014] When the oxidation time is too short, the oxidation capacity is too weak, resulting in a thin oxide layer; when the oxidation time is too long, the oxidation capacity is too strong, resulting in a thick oxide layer.

[0015] The ultimate goal of oxidation is to achieve an oxide layer of suitable thickness. In actual operation, the oxidation temperature and time can be adjusted as needed. These are merely exemplary conditions and should not be construed as limitations of the present invention.

[0016] Preferably, the method further includes heating to the oxidation temperature, wherein the heating rate is 2~5℃ / min; including but not limited to 2℃ / min, 3℃ / min, 4℃ / min, and 5℃ / min.

[0017] When the heating rate is too fast, such as 10℃ / min, the composition and structure of the oxide layer will become out of control, forming unstable oxides and causing a decline in the material's performance.

[0018] A third aspect of the present invention provides a slurry composition comprising: 200-240 parts of an iron-silicon-aluminum composite material, 200-300 parts of a polyurethane resin, 1-5 parts of a wetting and dispersing agent, 8-15 parts of a coupling agent, 20-30 parts of a vulcanizing agent, and a solvent, wherein the solvent is used to adjust the viscosity of the slurry at 25°C to 20,000-40,000 mPa·s.

[0019] The viscosity of the slurry of the present invention is controlled within the range of 20,000~40,000 mPa·s at 25°C. If the viscosity is too low, the slurry has good fluidity, which is not conducive to fixing and forming on the film. If the viscosity is too high, the solid content in the slurry is high, the fluidity is poor, it is difficult to form a film during the coating process, and the roughness is too large.

[0020] Preferably, the iron-silicon-aluminum composite material is 200-230 parts; including but not limited to 200 parts, 210 parts, 220 parts and 230 parts.

[0021] Preferably, the polyurethane resin can be 200 parts, 210 parts, 220 parts, 230 parts, 240 parts, 244 parts, 250 parts, 260 parts, 270 parts, 280 parts, 290 parts, and 300 parts.

[0022] Adding an appropriate amount of polyurethane resin to the slurry composition can reduce the density of the material, giving it the characteristics of being thin and lightweight.

[0023] Preferably, the wetting and dispersing agent is 1 to 3 parts; including but not limited to 1 part, 1.5 parts, 2 parts, 2.5 parts and 3 parts.

[0024] More preferably, the wetting and dispersing agent is 1 to 1.5 parts.

[0025] Wetting and dispersing agents can make the composition uniformly dispersed in the solvent and prevent agglomeration.

[0026] Preferably, the coupling agent is 8 to 12 parts; including but not limited to 8 parts, 8.5 parts, 9 parts, 9.5 parts, 10 parts, 10.5 parts, 11 parts, 11.5 parts and 12 parts.

[0027] More preferably, the coupling agent is 8 to 10 parts.

[0028] Preferably, the vulcanizing agent can be 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, or 30 parts.

[0029] The coupling agent and the vulcanizing agent work together to combine and cross-link the magnetic powder and resin to form a network structure, thereby improving the mechanical properties of the material.

[0030] Preferably, the polyurethane resin is selected from any one or more of polyether, polyester, polyimide, and polyurea types;

[0031] Preferably, the softening point of the polyurethane resin is 60~80℃; for example, it can be 60℃, 65℃, 70℃, 75℃ or 80℃; the test standard is ASTM D3104.

[0032] Preferably, the hardness of the polyurethane resin is 65~80A; for example, it can be 65A, 70A, 75A or 80A; the test standard is ASTM D2240.

[0033] Preferably, the crystallization time of the polyurethane resin is 10-20 min; for example, it can be 10 min, 13 min, 15 min, 18 min or 20 min; the test standard is ASTM D2471.

[0034] Preferably, the wetting and dispersing agent is selected from any one or two of organosilicon and inorganic silicon.

[0035] More preferably, the wetting and dispersing agent includes any one or more of DC65 waterborne silicone varnish defoamer (Dow Corning), BYK-3565, BYK-3560, BYK-DISPERBYK-2013, and TWIN-4100 (Digo).

[0036] Preferably, the coupling agent is any one or both selected from silane coupling agents and titanate coupling agents.

[0037] More preferably, the coupling agent includes any one or more of KH550, KH560, and vinyltriethoxysilane.

[0038] Preferably, the vulcanizing agent includes any one or more of sulfur, 4,4'-diamino-3,3'-dichlorodiphenylmethane, dicumyl peroxide, di-tert-butyl peroxide, and di(tert-butylperoxide isopropyl)benzene.

[0039] More preferably, the vulcanizing agent is a compound of sulfur and any one or more selected from dicumyl peroxide, di-tert-butyl peroxide, and di(tert-butyl peroxide isopropyl)benzene, wherein the amount of sulfur used is 40-60% of the amount of the vulcanizing agent.

[0040] Preferably, the solvent includes any one or more of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, toluene, xylene, tetrahydrofuran, isopropanol, and n-butanol.

[0041] The solvents described above in this invention can be used alone or in combination. In addition to the solvents mentioned above, low-boiling-point solvents such as tetrahydrofuran and methyl ethyl ketone can be mixed with other high-boiling-point solvents (such as isoflurane, diethylene glycol dimethyl ether, etc.) to adjust the boiling point of the mixed solvent to a suitable range.

[0042] A fourth aspect of the present invention provides a method for preparing the above-mentioned composition slurry, the method comprising mixing the components and stirring at a stirring rate of 1500~3000 r / min for 2~3 h to obtain the slurry.

[0043] Preferably, the stirring rate is 2000~3000 r / min; for example, it can be 2000 r / min, 2500 r / min or 3000 r / min.

[0044] The fifth aspect of the present invention provides the use of the above-mentioned iron-silicon-aluminum composite material and the above-mentioned composition slurry in the preparation of L-band absorbing materials.

[0045] The sixth aspect of the present invention provides a method for preparing the above-mentioned L-band absorbing material, the method comprising: coating the above-mentioned composition slurry onto the surface of a base film, drying it to form an absorbing unit film; stacking multiple absorbing unit films layer by layer and then subjecting them to high-temperature hot pressing treatment to obtain the absorbing material.

[0046] Preferably, for the microwave absorbing unit film, the coating thickness of the composition slurry is 50~500μm.

[0047] More preferably, for the absorbing unit film, the coating thickness of the composition slurry is 50~400μm; for example, it can be 50μm, 100μm, 150μm, 200μm, 250μm, 300μm, 350μm or 400μm.

[0048] If the coating thickness is too small, the material will have poor absorption of electromagnetic waves and high reflectivity; if the thickness is too large, the absorption peak of the material will shift and the absorption capacity in the L-band will be insufficient.

[0049] Preferably, the base film can be a variety of films such as PET (polyethylene terephthalate) film, PI (polyimide) film, LCP (liquid crystal polymer) film, and PEEK (polyether ether ketone) film.

[0050] Preferably, the coating process includes, but is not limited to, blade coating, casting, transfer coating, etc.

[0051] Preferably, the drying process is gradient drying.

[0052] More preferably, the gradient drying includes a first drying stage, a second drying stage, a third drying stage, and a fourth drying stage; wherein the temperature of the first drying stage is 75~85℃, the temperature of the second drying stage is 95~105℃, the temperature of the third drying stage is 110~125℃, and the temperature of the fourth drying stage is 130~160℃.

[0053] More preferably, the drying time for the first drying stage is 2-4 minutes, the drying time for the second drying stage is 2-4 minutes, the drying time for the third drying stage is 5-8 minutes, and the drying time for the fourth drying stage is 2-4 minutes.

[0054] Preferably, the hot pressing temperature is 140~170℃; for example, it can be 140℃, 150℃, 160℃ or 170℃.

[0055] Preferably, the pressure of the hot pressing is 8~15 MPa; for example, it can be 8 MPa, 10 MPa, 12 MPa, 14 MPa or 15 MPa.

[0056] Preferably, the hot pressing time is 3 to 8 minutes.

[0057] More preferably, the hot pressing time is 4 to 6 minutes.

[0058] If the hot pressing temperature or pressure is too low, or the time is too short, the product will not be vulcanized and will have no performance; if the hot pressing temperature or pressure is too high, or the time is too long, the material will age, the surface will blister, and it will not be usable.

[0059] The seventh aspect of the present invention provides an L-band absorbing material obtained by the above preparation method, wherein the thickness of the absorbing material is 4-5 mm; the impedance matching Z of the absorbing material is ≥0.4; and the minimum reflectivity of the L-band absorbing material is <-10 dB.

[0060] The minimum reflectivity of the L-band absorbing materials in this invention is all <-10dB, proving that the material can be used as an absorbing material at least at one wavelength in the L-band.

[0061] Preferably, the impedance matching Z of the L-band absorbing material is 0.4~1.

[0062] More preferably, the impedance matching Z of the L-band absorbing material is 0.4~0.7; for example, it can be 0.4, 0.5, 0.6 or 0.7.

[0063] Preferably, the minimum reflectivity of the L-band absorbing material is -11 to -15 dB; for example, it can be -11, -12, -13, -14 or -15.

[0064] Preferably, when the thickness of the L-band absorbing material is 5 mm, the reflectivity of the absorbing material is <-10 dB within the range of 1~1.6 GHz.

[0065] As described above, the L-band absorbing material and its preparation method of the present invention have the following beneficial effects:

[0066] 1. The present invention prepares an iron-silicon-aluminum composite material by selecting soft magnetic powder and using oxidation technology. This material can be used in the preparation of subsequent microwave absorbing materials, and its microwave absorbing performance is significantly better than that of iron-silicon-aluminum soft magnetic powder in the prior art.

[0067] 2. The absorbing material of this invention has excellent low-frequency absorbing performance and features "thin", "light", "wide", and "strong" characteristics; its impedance matching Z≥4, and within the 1~2GHz range, the minimum reflectivity of the 5mm thick product is <-10dB, which can be used in multiple wavelengths in the L-band and meets the requirements for the use of absorbing materials.

[0068] 3. This invention can obtain products with excellent microwave absorption performance by controlling the magnetic powder diameter-to-thickness ratio, surface oxidation technology and hot pressing technology. It has the advantages of simple preparation method and low cost, and is suitable for large-scale industrial production. Attached Figure Description

[0069] Figure 1 The diagram shows the reflectivity of three products with thicknesses of 4 mm, 4.5 mm, and 5 mm prepared in Embodiment 1 of the present invention in the L-band.

[0070] Figure 2 This diagram illustrates the three-dimensional relationship between the thickness of the product in Example 1 of this invention and the frequency and impedance matching Z within the 1-4 GHz frequency range.

[0071] Figure 3 The image shown is a photograph of the 5mm product prepared in Example 1 of this invention.

[0072] Figure 4 The image shown is a photograph of the 5mm product prepared in Comparative Example 15 of this invention. Detailed Implementation

[0073] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0074] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the presence of other method steps before or after the combined steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or defining the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0075] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention; in the specification and claims of the present invention, unless otherwise expressly stated in the text, the singular forms "a", "an" and "this" include the plural forms.

[0076] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0077] To address the problems of existing L-band absorbing materials being heavy, having poor low-frequency absorption performance, and being highly complex in terms of manufacturing processes, this application proposes a novel L-band absorbing material and its preparation method. This application utilizes a composite material prepared by controlling the aspect ratio and iron-silicon-aluminum soft magnetic particles, combined with oxidation treatment. This composite material exhibits significantly superior performance compared to conventional iron-silicon-aluminum magnetic powder and can be used to prepare high-performance L-band absorbing materials. Furthermore, by optimizing the proportions of each component in the slurry formulation, the material achieves both low density and high absorption performance. During the preparation process, by controlling the process parameters of drying and hot pressing, the material achieves a smooth and flat surface. The magnetic powder and resin can cross-link during hot pressing to form a network structure, increasing the material's mechanical properties. The final absorbing material possesses excellent electromagnetic wave absorption performance.

[0078] Example 1

[0079] This embodiment 1 provides a specific L-band absorbing material, the preparation method of which includes the following steps:

[0080] S1. Selection and oxidation treatment of iron-silicon-aluminum magnetic powder.

[0081] Iron-silicon-aluminum magnetic powder was selected, containing 85wt% Fe, 9.6wt% Si, and 5.4wt% Al, with an average diameter of 37μm and an aspect ratio of 70. The magnetic powder was then subjected to an oxidation treatment at 450℃ for 2.5 hours, with a heating rate of 2℃ / min. The initial temperature was room temperature, and the oxide layer thickness was controlled at 7.5nm, resulting in iron-silicon-aluminum magnetic powder with an oxide layer.

[0082] S2, Slurry Preparation

[0083] Take 200 parts of the iron-silicon-aluminum magnetic powder with oxide layer prepared in step S1 above, 244 parts of polyester polyurethane resin in colloidal form (purchased from Dongguan Ruihuan New Material Technology Co., Ltd., softening point 110℃-120℃, hardness 70A, crystallization time 15min), 1 part of wetting and dispersing agent (BYK DISPERBYK®-2150), 10 parts of silane coupling agent KH560, and 12 parts each of sulfur and DTBP. Put all the components together into a stirring and dispersing instrument, add tetrahydrofuran according to the viscosity of the slurry, control the viscosity of the slurry at 25000-30000mPa·s, stir and disperse for 3h, and the stirring rate is 2500r / min.

[0084] S3. Coat the base film with the slurry and dry to form a dry film.

[0085] A PET film with a thickness of 50 μm was selected as the base film. The slurry prepared in step S2 was coated onto the PET film by transfer coating. The film was then heated in an oven at five temperatures: 80 / 100 / 120 / 120 / 130℃, with each temperature held for 3 minutes. After drying for 15 minutes, a dry film with a thickness of 0.4 mm was formed.

[0086] S4. Multiple dry films are hot-pressed to prepare the final product.

[0087] The dry film prepared in step S3 above is subjected to layer-by-layer hot pressing. The pressure during the high-temperature hot pressing stage is 10 MPa, the temperature is 160°C, and the hot pressing time is 5 min, to prepare three products with thicknesses of 4 mm, 4.5 mm, and 5 mm.

[0088] Example 2

[0089] The difference between Example 2 and Example 1 is that the aspect ratio of the iron-silicon-aluminum magnetic powder is 50, while the other conditions and steps are the same as in Example 1.

[0090] Example 3

[0091] The difference between Example 3 and Example 1 is that the aspect ratio of the iron-silicon-aluminum magnetic powder is 100, while the other conditions and steps are the same as in Example 1.

[0092] Example 4

[0093] The difference between Example 4 and Example 1 is that the oxidation time of the iron-silicon-aluminum magnetic powder is replaced with 2 hours, resulting in an oxide layer thickness of 5 nm. All other conditions and steps are the same as in Example 1.

[0094] Example 5

[0095] The difference between Example 5 and Example 1 is that the oxidation time of the iron-silicon-aluminum magnetic powder is replaced with 3 hours, resulting in an oxide layer thickness of 11 nm. All other conditions and steps are the same as in Example 1.

[0096] Example 6

[0097] The difference between Example 6 and Example 1 is that the oxidation temperature of the iron-silicon-aluminum magnetic powder is replaced with 400℃, resulting in an oxide layer thickness of 7nm. All other conditions and steps are the same as in Example 1.

[0098] Example 7

[0099] The difference between Example 7 and Example 1 is that the oxidation temperature of the iron-silicon-aluminum magnetic powder is replaced with 500℃, resulting in an oxide layer thickness of 12nm. All other conditions and steps are the same as in Example 1.

[0100] Example 8

[0101] The difference between Example 8 and Example 1 is that the heating rate during the oxidation of iron-silicon-aluminum magnetic powder is replaced with 5℃ / min, while the other conditions and steps are the same as in Example 1.

[0102] Example 9

[0103] The difference between Example 9 and Example 1 is that the amount of each component added is different during the preparation of the slurry. Specifically, the amount of magnetic powder is 200 parts, the amount of polyester polyurethane resin is 300 parts, the amount of wetting and dispersing agent is 1.5 parts, the amount of silane coupling agent KH560 is 8 parts, and the amount of sulfur and DTBP is 15 parts each. The other conditions and steps are the same as in Example 1.

[0104] Example 10

[0105] The difference between Example 10 and Example 1 is that the amount of each component added is different during the preparation of the slurry. Specifically, the amount of magnetic powder is 200 parts, the amount of polyester polyurethane resin is 200 parts, the amount of wetting and dispersing agent is 1 part, the amount of KH560 coupling agent is 8 parts, and the amount of sulfur and DTBP is 10 parts each. The other conditions and steps are the same as in Example 1.

[0106] Example 11

[0107] The difference between Example 11 and Example 1 is that in the hot pressing stage, the hot pressing pressure is replaced with 8 MPa, while the other conditions and steps are the same as in Example 1.

[0108] Example 12

[0109] The difference between Example 12 and Example 1 is that in the hot pressing stage, the hot pressing pressure is replaced with 15 MPa, while the other conditions and steps are the same as in Example 1.

[0110] Example 13

[0111] The difference between Example 13 and Example 1 is that the hot pressing temperature is replaced with 140°C during the hot pressing stage, while the other conditions and steps are the same as in Example 1.

[0112] Example 14

[0113] The difference between Example 14 and Example 1 is that the hot pressing temperature is replaced with 170°C during the hot pressing stage, while the other conditions and steps are the same as in Example 1.

[0114] Example 15

[0115] The difference between Example 15 and Example 1 is that the iron-silicon-aluminum ratio in the magnetic powder is changed to Fe 84.5wt%, Si 10wt%, and Al 5.5wt%, while the other conditions and steps are the same as in Example 1.

[0116] Example 16

[0117] The difference between Example 16 and Example 1 is that the iron-silicon-aluminum ratio in the magnetic powder is changed to Fe 85wt%, Si 9.5wt%, and Al 5.5wt%, while the other conditions and steps are the same as in Example 1.

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1 is that the iron-silicon-aluminum ratio in the magnetic powder is changed to Fe 84wt%, Si 11wt%, and Al 5wt%, while the other conditions and steps are the same as in Example 1.

[0120] Comparative Example 2

[0121] The difference between Comparative Example 2 and Example 1 is that the iron-silicon-aluminum ratio in the magnetic powder is changed to Fe 86wt%, Si 10wt%, and Al 4wt%, while the other conditions and steps are the same as in Example 1.

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 1 is that the aspect ratio of the iron-silicon-aluminum magnetic powder is 40, while the other conditions and steps are the same as in Example 1.

[0124] Comparative Example 4

[0125] The difference between Comparative Example 4 and Example 1 is that the aspect ratio of the iron-silicon-aluminum magnetic powder is 100, while the other conditions and steps are the same as in Example 1.

[0126] Comparative Example 5

[0127] The difference between Comparative Example 5 and Example 1 is that the oxidation time of the iron-silicon-aluminum magnetic powder is replaced with 1 hour, resulting in an oxide layer thickness of 3 nm. All other conditions and steps are the same as in Example 1.

[0128] Comparative Example 6

[0129] The difference between Comparative Example 6 and Example 1 is that the oxidation time of the iron-silicon-aluminum magnetic powder was replaced with 5 hours, resulting in an oxide layer thickness of 15 nm. All other conditions and steps were the same as in Example 1.

[0130] Comparative Example 7

[0131] The difference between Comparative Example 7 and Example 1 is that the oxidation temperature of the iron-silicon-aluminum magnetic powder is replaced with 350°C, resulting in an oxide layer thickness of 4nm. All other conditions and steps are the same as in Example 1.

[0132] Comparative Example 8

[0133] The difference between Comparative Example 8 and Example 1 is that the oxidation temperature of the iron-silicon-aluminum magnetic powder is replaced with 550°C, resulting in an oxide layer thickness of 20 nm. All other conditions and steps are the same as in Example 1.

[0134] Comparative Example 9

[0135] The difference between Comparative Example 9 and Example 1 is that the heating rate during the oxidation of iron-silicon-aluminum magnetic powder is replaced with 10℃ / min, while the other conditions and steps are the same as in Example 1.

[0136] Comparative Example 10

[0137] The difference between Comparative Example 10 and Example 1 is that the amount of each component added is different during the preparation of the slurry. Specifically, the amount of magnetic powder is 200 parts, polyester polyurethane resin is 370 parts, wetting and dispersing agent is 1.8 parts, KH560 coupling agent is 8 parts, and sulfur and DTBP are 17 parts each.

[0138] Comparative Example 11

[0139] The difference between Comparative Example 11 and Example 1 is that the amount of each component added is different during the preparation of the slurry. Specifically, the amount of magnetic powder is 200 parts, polyester polyurethane resin is 134 parts, wetting and dispersing agent is 0.7 parts, KH560 coupling agent is 8 parts, and sulfur and DTBP are 7 parts each.

[0140] Comparative Example 12

[0141] The difference between Comparative Example 12 and Example 1 is that the hot pressing pressure is replaced with 7 MPa during the hot pressing stage, while the other conditions and steps are the same as in Example 1.

[0142] Comparative Example 13

[0143] The difference between Comparative Example 13 and Example 1 is that the hot pressing pressure is replaced with 20 MPa in the hot pressing stage, while the other conditions and steps are the same as in Example 1.

[0144] Comparative Example 14

[0145] The difference between Comparative Example 14 and Example 1 is that the hot pressing temperature is replaced with 100°C during the hot pressing stage, while the other conditions and steps are the same as in Example 1.

[0146] Comparative Example 15

[0147] The difference between Comparative Example 15 and Example 1 is that the hot pressing temperature is replaced with 200°C during the hot pressing stage, while the other conditions and steps are the same as in Example 1.

[0148] Comparative Example 16

[0149] The difference between Comparative Example 16 and Example 1 is that the iron-silicon-aluminum magnetic powder was not oxidized, while the other conditions and steps were the same as in Example 1.

[0150] Test section

[0151] The density, appearance, impedance matching Z, and reflectivity in the L-band of the 5mm product prepared in Example 1 were tested, and the reflectivity in the L-band of the 4mm and 4.5mm products was also tested. The appearance, impedance matching Z, and reflectivity in the L-band of the 5mm products prepared in Examples 2-16 and Comparative Examples 2-16 were also tested. Specific test results are shown in Table 1, and the specific test or calculation methods are as follows:

[0152] 1) Density test: The density of the material was tested using the water displacement method. The density of the product in Example 1 was 1.586 g / cm³. 3 .

[0153] 2) Appearance test: Under natural light or 60W~100W fluorescent lighting conditions, the distance between the naked eye and the test object is within 30cm~45cm. The sample is rotated vertically and horizontally; the entire test surface is scanned for 5~10 seconds. If the surface of the absorbing material is smooth and flat without particles, bubbles, holes, cracks, etc., it is considered "normal".

[0154] 3) Impedance matching Z: The calculation formula is as follows:

[0155]

[0156] Z in Z0 and Z0 represent the input impedance and free-space impedance of the absorber, respectively; μ r Represents relative complex permeability;

[0157] ε r t represents the relative complex permittivity; t represents the thickness of the wave body; c represents the speed of light; f represents the frequency; and j is the imaginary unit.

[0158] Relative complex permeability (μ) r ) and relative complex permittivity (ε r The testing method is as follows: the sample is made into a 3mm*7mm coaxial ring and tested using an Agilent E8363B vector network analyzer.

[0159] 4) Reflectivity: Calculated using the following formula:

[0160]

[0161] Where Z is the impedance matching value, which is calculated from the above formula.

[0162] The reflectivity of the three products with thicknesses of 4 mm, 4.5 mm, and 5 mm prepared in Example 1 in the L-band is as follows: Figure 1 As shown, the 5mm thick product exhibits the best absorption performance in the L-band, with a reflectivity (RL) of less than -10dB within the 1~1.6GHz range and a minimum reflectivity of -13.7dB, demonstrating its ability to maintain good absorption performance over a wide range of 1~1.6GHz. Furthermore, as the material thickness decreases, the peak of the minimum reflectivity shifts to the right. In practical applications, the material thickness can be adjusted to meet the requirements of different wavelengths within the L-band.

[0163] Figure 2 The three-dimensional relationship between the thickness of the product in Example 1 and the frequency and impedance matching Z is shown in the 1~4GHz frequency range. It can be seen that when the product thickness is 4~5mm in the 1~2GHz frequency range, the impedance matching Z of the material is ≥0.4.

[0164] Figure 3 The image shown is a photograph of the 5mm product prepared in Example 1, which has a smooth and flat surface.

[0165] Figure 4 The image shown is a photograph of the 5mm product prepared in Comparative Example 15. Due to excessively high hot pressing temperature, the surface of the material blistered, making it unsuitable for normal testing and use.

[0166] Table 1 Performance test results of the 5mm products prepared in Examples 1-16 and Comparative Examples 1-16

[0167] Experimental Example Minimum reflectance (dB) 1 ~ 2 GHz Impedance matching Z Appearance Example 1 -13.45 0.63 Normal Example 2 -13 0.61 Normal Example 3 -13 0.61 Normal Example 4 -13.5 0.62 Normal Example 5 -13.7 0.62 Normal Example 6 -13 0.61 Normal Example 7 -14 0.63 Normal Example 8 -13 0.61 Normal Example 9 -11.3 0.49 Normal Example 10 -10.8 0.45 Normal Example 11 -12 0.55 Normal Example 12 -13 0.61 Normal Example 13 -13.5 0.62 Normal Example 14 -14 0.63 Normal Example 15 -11 0.43 Normal Example 16 -13 0.61 Normal Comparative Example 1 -9 0.35 Normal Comparative Example 2 -9.7 0.38 Normal Comparative Example 3 -8 0.31 Normal Comparative Example 4 -7.2 0.26 Surface rough Comparative Example 5 -6 0.22 Normal Comparative Example 6 -8 0.31 Normal, surface slightly yellow Comparative Example 7 -7 0.25 Normal Comparative Example 8 -8 0.31 Normal, surface slightly yellow Comparative Example 9 -6.5 0.23 Normal Comparative Example 10 -3.5 0.28 Normal Comparative Example 11 -9.2 0.36 Normal Comparative Example 12 / / / Comparative Example 13 -13 0.61 Surface severely cracked Comparative Example 14 / / / Comparative Example 15 / / / Comparative Example 16 No absorption 0.43 Normal

[0168] As shown in Table 1, the 5mm products prepared in Examples 1-16 have normal appearance, without particles, bubbles, holes, cracks, etc.; the minimum reflectivity in the 1-2GHz range is all <-10dB, proving that they can be used normally in the L-band. However, the 5mm products in Comparative Examples 1-16 have a minimum reflectivity in the 1-2GHz range that is all >-10dB, and cannot be used as absorbing materials in the L-band. In Comparative Example 4, the excessively large aspect ratio of the magnetic powder resulted in poor slurry flowability, difficulty in viscosity control, and a rough material surface. In Comparative Examples 6 and 8, the slight yellowing of the product surface was due to an excessively thick oxide layer on the magnetic powder. In Comparative Example 12, insufficient pressure during the hot-pressing stage prevented vulcanization, resulting in no microwave absorption performance. In Comparative Example 13, excessive hot-pressing pressure caused severe surface cracking; furthermore, excessive pressure also caused serious damage to the machine. In Comparative Example 14, the excessively low temperature during the hot-pressing stage prevented vulcanization, resulting in no microwave absorption performance. In Comparative Example 15, excessively high temperature during the hot-pressing stage caused blistering on the product surface, making performance testing impossible. In Comparative Example 16, using unoxidized magnetic powder, the prepared product showed no reflectance absorption peak in the 1-2G range. Its absorption peak was specifically at 0.6 GHz, with a minimum reflectance of -8.75 dB.

[0169] In summary, this invention optimizes the mass ratio of iron, silicon, and aluminum in the magnetic powder, the aspect ratio of the magnetic powder, and oxidizes the magnetic powder; it also controls the proportion of magnetic powder in the slurry, as well as the process parameters during film drying and hot pressing, ultimately preparing a microwave absorbing material for the L-band. Compared with traditional magnetic materials, this material exhibits superior electromagnetic wave absorption performance in the L-band, possessing the characteristics of being "thin," "light," "wide," and "strong." Moreover, the preparation method is simple, low-cost, and highly industrially scalable.

[0170] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An L-band absorbing material, characterized in that, The thickness of the L-band absorbing material is 4~5mm; the impedance matching Z of the absorbing material is ≥0.4; the absorbing material is prepared by the following method: coating the composition slurry onto the surface of the base film and drying it to form an absorbing unit film; The microwave absorbing material is obtained by stacking multiple microwave absorbing unit films layer by layer and then subjecting them to high-temperature hot pressing. The composition slurry includes: 200-240 parts of iron-silicon-aluminum composite material, 200-300 parts of polyurethane resin, 1-5 parts of wetting and dispersing agent, 8-15 parts of coupling agent, 20-30 parts of vulcanizing agent, and solvent. The solvent is used to adjust the viscosity of the slurry at 25°C to 20000-40000 mPa·s. The iron-silicon-aluminum composite material is iron-silicon-aluminum soft magnetic particles with an oxide layer formed on the surface. The content of each element in the iron-silicon-aluminum soft magnetic particle raw material is Fe 84.5-85.5 wt%, Si 9.5-10 wt%, and Al 5-5.5 wt%. The aspect ratio of the iron-silicon-aluminum soft magnetic particle raw material is 50-100, and the average diameter is 20-40 μm. The thickness of the oxide layer is 5-12 nm.

2. The L-band absorbing material according to claim 1, characterized in that, The preparation method of the iron-silicon-aluminum composite material includes: oxidizing the iron-silicon-aluminum soft magnetic particle raw material at 400~500℃ for 2~3h.

3. The L-band absorbing material according to claim 2, characterized in that, The preparation method further includes heating to the oxidation temperature, wherein the heating rate is 2~5℃ / min.

4. The L-band absorbing material according to claim 1, characterized in that, The polyurethane resin is selected from any one or more of polyether, polyester, polyimide, and polyurea types; And / or, the wetting and dispersing agent is any one or two selected from organosilicon and inorganic silicon; And / or, the coupling agent is any one or both selected from silane coupling agents and titanate coupling agents; And / or, the vulcanizing agent includes any one or more of sulfur, 4,4'-diamino-3,3'-dichlorodiphenylmethane, dicumyl peroxide, di-tert-butyl peroxide, and di(tert-butylperoxide isopropyl)benzene; And / or, the solvent includes any one or more of methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate, toluene, xylene, tetrahydrofuran, isopropanol, and n-butanol.

5. The L-band absorbing material according to claim 1, characterized in that, The method for preparing the composition slurry includes mixing the components and stirring for 2-3 hours at a stirring rate of 1500-3000 r / min.

6. A method for preparing an L-band absorbing material as described in any one of claims 1 to 5, characterized in that, The method includes: coating a composition slurry onto the surface of a base film and drying it to form a microwave absorbing unit film; stacking multiple microwave absorbing unit films layer by layer and then subjecting them to high-temperature hot pressing to obtain the microwave absorbing material.

7. The preparation method according to claim 6, characterized in that, For the microwave absorbing unit film, the coating thickness of the composition slurry on the base film is 50~500μm; And / or, the drying is gradient drying; And / or, the hot pressing temperature is 140~170℃; And / or, the hot pressing pressure is 8~15 MPa; And / or, the hot pressing time is 3~8 minutes.

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