Electromagnetic shielding composite material with active and passive infrared stealth function and preparation method thereof

Abstract

The application relates to the technical field of electromagnetic shielding materials, and particularly discloses an electromagnetic shielding composite material with active and passive infrared stealth functions and a preparation method thereof. The composite material comprises an electromagnetic wave reflection layer and a multilayer electromagnetic wave absorption layer. The electromagnetic wave reflection layer is silver-plated bacterial cellulose, and high-efficiency electromagnetic wave reflection is realized by utilizing the high conductivity of the silver-plated bacterial cellulose. The electromagnetic wave absorption layer is composed of bacterial cellulose, multi-walled carbon nanotubes and core-shell magnetic nanoparticles, and from the side close to the electromagnetic wave reflection layer to the outside, the content of the multi-walled carbon nanotubes decreases, and the content of the core-shell magnetic nanoparticles increases, so that a gradient structure is formed; the gradient design can improve the surface impedance matching, promote the electromagnetic wave to enter the material interior, and enhance the electromagnetic loss through the interlayer multiple reflection-absorption process. The material has the functions of high-efficiency electromagnetic shielding and active and passive infrared stealth.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic shielding materials technology, and in particular to an electromagnetic shielding composite material with active and passive infrared stealth functions and its preparation method. Background Technology

[0002] With the continuous development of technologies such as digital communication and intelligent interconnection, electromagnetic interference (EMI) problems are becoming increasingly serious. High-intensity electromagnetic waves not only interfere with the normal operation of precision electronic equipment, leading to data errors or signal loss, but may also pose potential hazards to human health. Therefore, the development of high-performance electromagnetic shielding materials has become a key requirement for ensuring the reliable operation of the electronic information society.

[0003] Meanwhile, the application scenarios of electromagnetic shielding materials are constantly expanding, extending from ambient indoor environments to extreme climatic conditions such as high temperature, high humidity, and severe cold. This requires the materials themselves to possess excellent environmental stability and durability. Especially in fields such as military protection and special equipment, materials also need to integrate special functions such as infrared camouflage: on the one hand, they need to block the thermal radiation of the target object to reduce the temperature difference between it and the environment, thereby achieving passive infrared camouflage; on the other hand, they need to generate interference signals at different temperatures through electrothermal effects, thereby achieving active infrared camouflage.

[0004] However, the design of most current electromagnetic shielding materials is still limited to high shielding effectiveness (SE). To achieve the above-mentioned multi-functional integration, it is often necessary to introduce multiple fillers or complex structures, which often leads to increased material weight, decreased flexibility, complex processes, and high costs. How to develop advanced materials that integrate high-efficiency electromagnetic shielding, wide-temperature stability, and intelligent infrared camouflage without sacrificing practical properties such as lightweight, flexibility, and mechanical strength remains a technical bottleneck that urgently needs to be overcome in this field. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide an electromagnetic shielding composite material with active and passive infrared stealth functions and its preparation method. The electromagnetic shielding composite material of this invention has excellent electromagnetic shielding effect and also has active and passive infrared stealth functions, and can be widely used in precision electronics, aerospace and military equipment and other fields.

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

[0007] This invention provides an electromagnetic shielding composite material with active and passive infrared stealth functions. The electromagnetic shielding composite material includes an electromagnetic wave reflecting layer and multiple electromagnetic wave absorbing layers. The electromagnetic wave reflecting layer is made of silver-plated bacterial cellulose. Each electromagnetic wave absorbing layer is composed of bacterial cellulose, multi-walled carbon nanotubes, and core-shell magnetic nanoparticles. From the direction closer to the electromagnetic wave reflecting layer to the direction farther away from the electromagnetic wave reflecting layer, the content of multi-walled carbon nanotubes in the multiple electromagnetic wave absorbing layers gradually decreases, while the content of core-shell magnetic nanoparticles increases sequentially.

[0008] As a further improvement to the above-described solution of the present invention, the bacterial cellulose content is the same in the multiple electromagnetic wave absorbing layers. This ensures material consistency and avoids instability in mechanical properties caused by natural shrinkage.

[0009] As a further improvement to the above-described solution of the present invention, the electromagnetic wave absorbing layer has at least three layers, and the thickness of the electromagnetic shielding composite material is 0.24-0.40 mm. The more layers there are, the more pronounced the interlayer reflection-absorption-reflection process becomes, resulting in superior electromagnetic shielding performance.

[0010] As a further improvement to the above-mentioned solution of the present invention, the core-shell magnetic nanoparticles are carbon-coated iron nanoparticles (Fe@C), carbon-coated nickel nanoparticles (Ni@C), or carbon-coated cobalt nanoparticles (Co@C). The outer carbon layer of the core-shell magnetic nanoparticles is chemically inert, protecting the metal core and ensuring the stability of its function, while also achieving a certain degree of lightweighting. The core-shell magnetic nanoparticles of the present invention are prepared by arc discharge. Magnetic particles (iron, nickel, or cobalt) and graphite carbon powder are uniformly mixed to prepare a composite anode. The mass ratio of magnetic particles to graphite carbon powder is 1-10:1-10. A graphite electrode serves as the cathode. After evacuating the discharge device, helium gas at a pressure of 100 torr is introduced to carry out the discharge reaction. After the reaction, the powder collected around the cavity is the carbon-coated magnetic nanoparticle, with an average particle size of 30-90 nm.

[0011] And / or, the multi-walled carbon nanotubes are hydroxylated multi-walled carbon nanotubes with a diameter of 5-15 nm and a length of 15-30 μm. The carboxyl groups on the surface of the carboxylated multi-walled carbon nanotubes and the hydroxyl groups on the surface of bacterial cellulose form hydrogen bonds, which enhances the interaction within and between the absorbent layers and can improve the mechanical properties of the composite material.

[0012] This invention also provides a method for preparing an electromagnetic shielding composite material with active and passive infrared stealth functions as described above, which includes the following steps:

[0013] Multiple dispersions containing bacterial cellulose, multi-walled carbon nanotubes, and core-shell magnetic nanoparticles were prepared, wherein the mass ratio of the multi-walled carbon nanotubes to the core-shell magnetic nanoparticles was different in the multiple dispersions.

[0014] Multiple portions of the dispersion were sequentially filtered onto silver-plated bacterial cellulose in descending order of multi-walled carbon nanotube content, dried, and hot-pressed to obtain an electromagnetic shielding composite material with active and passive infrared stealth functions.

[0015] By sequentially filtering a gradient dispersion onto silver-plated bacterial cellulose, a multi-layered structure can be precisely constructed. This method is simple, low-cost, and easy to control the proportions of each layer's components. It avoids the use of complex equipment, is suitable for large-scale production, and ensures tight interlayer bonding, which is beneficial for the integration of mechanics and function.

[0016] As a further improvement to the above-mentioned solution of the present invention, the method for preparing the silver-plated bacterial cellulose is as follows: concentrated hydrochloric acid is added dropwise to a stannous chloride solution to obtain a stannous chloride solution acidified with concentrated hydrochloric acid; bacterial cellulose is activated by adding it to the stannous chloride solution acidified with concentrated hydrochloric acid; the solution is filtered and washed until neutral; silver nitrate solution is added for chemical silver plating; the solution is filtered and washed until neutral; the obtained product is added to a glucose aqueous solution, and silver ammonia solution is added dropwise under a water bath; the solution is filtered and washed until neutral to obtain silver-plated bacterial cellulose. Chemical silver plating has the advantages of being environmentally friendly, easy to operate, and requiring low equipment. The silver-plated bacterial cellulose, as a reflective layer, has sufficient conductivity and provides high electromagnetic shielding performance.

[0017] As a further improvement to the above-mentioned scheme of the present invention, the concentration of the stannous chloride solution is 10-20 g / L; the concentration of the concentrated hydrochloric acid is 36%-38%, and the volume ratio of the concentrated hydrochloric acid to the stannous chloride solution is 5-10 mL:1 L; the activation time is 15-30 min; the concentration of the silver nitrate solution is 0.1 mol / L; and the reaction time after adding the silver nitrate solution is 15-30 min.

[0018] As a further improvement to the above-mentioned scheme of the present invention, the glucose content in the glucose aqueous solution is 0.5wt%-1.5wt%; the water bath temperature is 35-45℃; the concentration of the silver ammonia solution is 0.8-1.5mol / L, and the reaction continues for 30min after the silver ammonia solution is added.

[0019] As a further improvement to the above-described scheme of the present invention, in each of the dispersions, the sum of the masses of the multi-walled carbon nanotubes and the core-shell magnetic nanoparticles is equal to the mass of the bacterial cellulose; the content of bacterial cellulose in each of the dispersions is the same as the content of bacterial cellulose in the electromagnetic wave reflecting layer. By adjusting the mass ratio of multi-walled carbon nanotubes to core-shell magnetic nanoparticles and maintaining a consistent bacterial cellulose content, a gradient design of the electromagnetic wave absorption layer can be achieved, optimizing the electromagnetic parameters of each layer, improving impedance matching, thereby enhancing broadband absorption efficiency and infrared modulation flexibility.

[0020] As a further improvement to the above-mentioned solution of the present invention, the drying is carried out at 60-80℃ for 30-45 minutes; the hot pressing is carried out in a hot press at a temperature of 40-60℃ and a pressure of 20-40 MPa for 4-7 hours. Drying at 60-80℃ can effectively remove solvent without damaging the cellulose network; the subsequent hot pressing at 40-60℃ and 20-40 MPa for 4-7 hours can further enhance the interlayer bonding force, ensure that the filler is tightly bonded to the cellulose matrix, ensure the realization of its electromagnetic shielding function, and at the same time improve the material's density, mechanical strength and environmental stability.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention uses silver-plated bacterial cellulose as an electromagnetic wave reflective layer. Its high conductivity ensures maximum shielding effect for electromagnetic waves, guaranteeing that most incident electromagnetic waves are reflected into the material and absorbed. A multilayer electromagnetic wave absorbing layer is prepared by combining bacterial cellulose, multi-walled carbon nanotubes, and core-shell magnetic nanoparticles. Bacterial cellulose biomass material can be sustainably produced through environmentally friendly bioprocesses, is easily controlled, and possesses excellent mechanical properties, making it an excellent choice for a polymer matrix. Carbon nanotubes, due to their high conductivity, high aspect ratio, and ease of forming conductive networks and inducing conductivity losses, can provide good electromagnetic absorption. Magnetic nanoparticles with a core-shell structure can also utilize their magnetic resonance, eddy current loss, and interfacial polarization to dissipate electromagnetic waves. The presence of various fillers enriches the electromagnetic shielding mechanism and improves electromagnetic shielding effectiveness.

[0023] The electromagnetic wave absorbing layer adopts a gradient design: from the direction closer to the electromagnetic wave reflecting layer to the direction farther away from the electromagnetic wave reflecting layer, the content of multi-walled carbon nanotubes decreases while the content of core-shell magnetic nanoparticles increases, thus forming a decrease in conductivity from bottom to top and an increase in magnetism from bottom to top, forming a multi-layered asymmetric electromagnetic double-gradient electromagnetic wave absorbing layer. This design can effectively improve the impedance matching of the material surface, allowing electromagnetic waves to penetrate into the electromagnetic shielding composite material to the maximum extent, and enhancing the absorption and loss of electromagnetic waves by undergoing multiple reflection-absorption-reflection processes between layers.

[0024] In terms of infrared functionality, the highly conductive surface exhibits low infrared reflectivity, and the presence of different fillers also extends the internal heat transfer path, enabling the electromagnetic shielding composite material to have passive infrared stealth capabilities. At the same time, the design of the silver plating layer in the reflective layer gives it excellent electrothermal conversion performance, enabling it to have active infrared camouflage capabilities.

[0025] The preparation method of this invention is simple and effective, with low processing cost, strong operational controllability, and large-scale manufacturing capability. The resulting material exhibits excellent mechanical properties, superior electromagnetic shielding performance, and both active and passive infrared stealth capabilities, making it widely applicable in aerospace, artificial intelligence, electronic communications, and wearable electronic devices. The preparation method of this invention combines vacuum filtration and hot pressing, resulting in a tightly constructed conductive network and a tight interfacial bond in the composite material, ensuring good thermal stability and a long service life. Attached Figure Description

[0026] Figure 1 This is a SEM image of the silver-plated bacterial cellulose in Example 2 of the present invention;

[0027] Figure 2 This is a cross-sectional SEM image of the electromagnetic shielding composite material with active and passive infrared stealth function prepared in Example 2 of the present invention.

[0028] Figure 3 This is a stress-strain curve of the electromagnetic shielding composite material with active and passive infrared stealth function prepared in Example 2 of the present invention.

[0029] Figure 4 This is an electromagnetic shielding diagram of the electromagnetic shielding composite material with active and passive infrared stealth function obtained in Embodiment 2 of the present invention.

[0030] Figure 5 This is an infrared image of the electromagnetic shielding composite material with active and passive infrared stealth function obtained in Embodiment 2 of the present invention.

[0031] Figure 6 The image shows the electrothermal conversion curve of the electromagnetic shielding composite material with active and passive infrared stealth function prepared in Example 2 of this invention. Detailed Implementation

[0032] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0034] Example 1

[0035] This embodiment proposes an electromagnetic shielding composite material with active and passive infrared stealth capabilities, which includes the following steps:

[0036] S1. Add 1.5g of stannous chloride to 100mL of deionized water, and add 0.5mL of 36% concentrated hydrochloric acid dropwise to prevent hydrolysis, thus preparing an activation solution. Add 20mg of bacterial cellulose BC to the activation solution and stir to sensitize for 30min. Filter the sensitized bacterial cellulose BC and wash with deionized water until the supernatant of the filtrate is neutral. Add the filtered bacterial cellulose BC to 0.1mol / L silver nitrate solution and react for 15min, then filter and wash with deionized water until the supernatant of the filtrate is neutral. The filtered product was added to a 0.9 wt% glucose aqueous solution, and silver ammonia solution was slowly added dropwise in a 40℃ water bath (the preparation process of silver ammonia solution is as follows: first prepare a 0.075 mol / L silver nitrate solution and then add a 2% ammonia aqueous solution dropwise until the precipitate disappears, thus obtaining silver ammonia solution). After the addition is complete, the reaction was continued for 30 min. The obtained product was poured onto a 0.22 μm organic filter membrane to assist filtration and obtain silver-plated bacterial cellulose BC@Ag, which serves as an electromagnetic wave reflective layer.

[0037] S2. Using deionized water as a dispersant, three dispersions were prepared using BC, carboxylated multi-walled carbon nanotubes (MCNT-COOH), and carbon-coated iron nanoparticles (Fe@C): the first dispersion (denoted as dispersion 1) had a mass ratio of BC, MCNT-COOH, and Fe@C of 5:4:1; the second dispersion (denoted as dispersion 2) had a mass ratio of BC, MCNT-COOH, and Fe@C of 5:2:3; and the third dispersion (denoted as dispersion 3) had a mass ratio of BC and Fe@C of 1:1. No MCNT-COOH was added to dispersion 3. The amount of bacterial cellulose added to each dispersion was 20 mg. In this embodiment, carbon-coated iron nanoparticles (Fe@C) are prepared by arc discharge: iron powder and graphite carbon powder are uniformly mixed to prepare a composite anode with a mass ratio of 5:1. A graphite electrode is used as the cathode. After the discharge device is evacuated, helium gas at a pressure of 100 torr is introduced to carry out the discharge reaction. After the discharge reaction is completed, the powder around the cavity is collected, which is the carbon-coated iron nanoparticles (Fe@C).

[0038] S3. Sequentially filter dispersion 1, dispersion 2, and dispersion 3 onto the electromagnetic wave reflective layer obtained in step S1; place the obtained composite film in an oven at 60°C and dry for 30 min; then place it in a hot press and hot press at 40°C and 30 MPa for 4 h to obtain a BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth functions.

[0039] The BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film prepared in this embodiment has a thickness of approximately 0.23 mm, an electromagnetic shielding effectiveness of 51.2 dB, a tensile strength of 49.7 MPa, and a surface temperature of 101.3 °C at a voltage of 1.2 V.

[0040] Example 2

[0041] This embodiment proposes an electromagnetic shielding composite material with active and passive infrared stealth capabilities, which includes the following steps:

[0042] S1. Add 1.5g of stannous chloride to 100mL of deionized water, and add 0.5mL of 36% concentrated hydrochloric acid dropwise to prevent hydrolysis, thus preparing an activation solution. Add 20mg of bacterial cellulose BC to the activation solution and stir to sensitize for 30min. Filter the sensitized bacterial cellulose BC and wash with deionized water until the supernatant of the filtrate is neutral. Add the filtered bacterial cellulose BC to 0.1mol / L silver nitrate solution and react for 15min. Filter and wash with deionized water until the supernatant of the filtrate is neutral. The filtered product was added to a 0.9 wt% glucose aqueous solution, and silver ammonia solution was slowly added dropwise in a 40℃ water bath (the preparation process of silver ammonia solution is as follows: first prepare a 0.1 mol / L silver nitrate solution and then add a 2% ammonia aqueous solution dropwise until the precipitate disappears, thus obtaining a silver ammonia solution). After the addition is complete, the reaction was continued for 30 min. The obtained product was poured onto a 0.22 μm organic filter membrane to assist filtration and obtain silver-plated bacterial cellulose BC@Ag, which serves as an electromagnetic wave reflective layer.

[0043] S2. Using deionized water as a dispersant, four dispersions were prepared using BC, carboxylated multi-walled carbon nanotubes (MCNT-COOH), and carbon-coated iron nanoparticles (Fe@C): The first dispersion (Dispersion 1) had a mass ratio of BC, MCNT-COOH, and Fe@C of 5:3:2; the second dispersion (Dispersion 2) had a mass ratio of BC, MCNT-COOH, and Fe@C of 5:2:3; the third dispersion (Dispersion 3) had a mass ratio of BC, MCNT-COOH, and Fe@C of 5:1:4; and the fourth dispersion (Dispersion 4) had a mass ratio of BC and Fe@C of 1:1. No MCNT-COOH was added to Dispersion 4. The amount of bacterial cellulose added to each dispersion was 20 mg. In this embodiment, carbon-coated iron nanoparticles (Fe@C) are prepared by arc discharge: iron powder and graphite carbon powder are uniformly mixed to prepare a composite anode with a mass ratio of 5:1. A graphite electrode is used as the cathode. After the discharge device is evacuated, helium gas at a pressure of 100 torr is introduced to carry out the discharge reaction. After the discharge reaction is completed, the powder around the cavity is collected, which is the carbon-coated iron nanoparticles (Fe@C).

[0044] S3. Sequentially filter dispersions 1, 2, 3, and 4 onto the electromagnetic wave reflective layer obtained in step S1; place the resulting composite film in an oven at 60°C and dry for 30 minutes; then place it in a hot press and hot press at 40°C and 30 MPa for 4 hours to obtain a BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth functions.

[0045] Figure 1 Here is a SEM image of the silver-plated bacterial cellulose obtained in this embodiment. Figure 1 As can be seen, this embodiment successfully plated silver on the surface of bacterial cellulose.

[0046] Figure 2 The image shows a SEM image of the BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth functions obtained in this embodiment. The thickness of the electromagnetic shielding composite film obtained in this embodiment is approximately 0.28 mm, as measured by the scale bar.

[0047] Figure 3 This is a stress-strain curve of the BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth functions obtained in this embodiment. Figure 3 The tensile strength can be seen to be 62.1 MPa.

[0048] Figure 4This is an electromagnetic shielding diagram of the BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth functions obtained in this embodiment. Figure 4 As can be seen, its electromagnetic shielding effectiveness is 64.3 dB.

[0049] The BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth functions obtained in this embodiment was placed on different objects: glass (5.2℃), ceramic (38.5℃), plastic (69℃), and metal (150℃). Infrared detection was performed using an infrared imager. Figure 5 You can see (in) Figure 5 In this diagram, T1 is the surface temperature of the thin film, T2 is the actual temperature of the object, and T3 is the temperature of the surrounding environment. On the surfaces of common objects such as glass, ceramics, plastics, and metals, this composite thin film can interfere with the detection of the true temperature of the object it protects, thus exhibiting passive infrared stealth capabilities.

[0050] Figure 6 The graph shows the electrothermal conversion curve of the BC@Ag / MCNT-COOH / Fe@C electromagnetic shielding composite film with active and passive infrared stealth function obtained in this embodiment. It can be seen that the surface temperature of the film can reach 130.4℃ at a voltage of 1.2V.

[0051] Example 3

[0052] This embodiment proposes an electromagnetic shielding composite material with active and passive infrared stealth capabilities, which includes the following steps:

[0053] S1. Add 1.5g of stannous chloride to 100mL of deionized water, and add 0.5mL of 36% concentrated hydrochloric acid dropwise to prevent hydrolysis, thus preparing an activation solution. Add 20mg of bacterial cellulose BC to the activation solution and stir to sensitize for 30min. Filter the sensitized bacterial cellulose BC and wash with deionized water until the supernatant of the filtrate is neutral. Add the filtered bacterial cellulose BC to 0.1mol / L silver nitrate solution and react for 15min. Filter and wash with deionized water until the supernatant of the filtrate is neutral. The filtered product was added to a 0.9 wt% glucose aqueous solution, and silver ammonia solution was slowly added dropwise in a 40℃ water bath (the preparation process of silver ammonia solution is as follows: first prepare a 0.1 mol / L silver nitrate solution and then add a 2% ammonia aqueous solution dropwise until the precipitate disappears, thus obtaining a silver ammonia solution). After the addition is complete, the reaction continues for 30 min. The obtained product is poured onto a 0.22 μm organic filter membrane to assist filtration and obtain silver-plated bacterial cellulose BC@Ag, which serves as an electromagnetic wave reflective layer.

[0054] S2. Using deionized water as a dispersant, six dispersions were prepared using BC, carboxylated multi-walled carbon nanotubes MCNT-COOH, and carbon-coated nickel nanoparticles Ni@C: the first dispersion (denoted as dispersion 1) had a mass ratio of BC to MCNT-COOH of 1:1, and no Ni@C was added to dispersion 1; the second dispersion (denoted as dispersion 2) had a mass ratio of BC to MCNT-COOH to Ni@C of 5:4:1; the third dispersion (denoted as dispersion 3) had a mass ratio of BC to MCNT-COOH to Ni@C of 5:3:2; the fourth dispersion (denoted as dispersion 4) had a mass ratio of BC to MCNT-COOH to Ni@C of 5:2:3; the fifth dispersion (denoted as dispersion 5) had a mass ratio of BC to MCNT-COOH to Ni@C of 5:1:4; and the sixth dispersion (denoted as dispersion 6) had a mass ratio of BC to Ni@C of 1:1, and no MCNT-COOH was added to dispersion 6. The amount of bacterial cellulose added in each dispersion was 20 mg. In this embodiment, the carbon-coated nickel nanoparticles (Ni@C) were prepared by arc discharge: nickel powder and graphite carbon powder were uniformly mixed to prepare a composite anode, with a mass ratio of nickel powder to graphite carbon powder of 5:1. A graphite electrode served as the cathode. After evacuating the discharge device, helium gas at a pressure of 100 torr was introduced to carry out the discharge reaction. After the reaction was completed, the powder around the cavity was collected, which was the carbon-coated nickel nanoparticles (Ni@C).

[0055] S3. Dispersions 1, 2, 3, 4, 5, and 6 are sequentially filtered onto the electromagnetic wave reflective layer obtained in step S1; the resulting composite film is placed in an oven at 60°C and dried for 30 minutes; then placed in a hot press and hot-pressed at 40°C and 30 MPa for 4 hours to obtain a BC@Ag / MCNT-COOH / Ni@C electromagnetic shielding composite film with active and passive infrared stealth functions.

[0056] The BC@Ag / MCNT-COOH / Ni@C electromagnetic shielding composite film prepared in this embodiment has a thickness of approximately 0.38 mm, an electromagnetic shielding effectiveness of 78.3 dB, a tensile strength of 68.7 MPa, and a surface temperature of 140.6 °C at 1.2 V.

[0057] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0058] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An electromagnetic shielding composite material with active and passive infrared stealth capabilities, characterized in that, The electromagnetic shielding composite material includes an electromagnetic wave reflecting layer and multiple electromagnetic wave absorbing layers. The electromagnetic wave reflecting layer is made of silver-plated bacterial cellulose. Each electromagnetic wave absorbing layer is composed of bacterial cellulose, multi-walled carbon nanotubes, and core-shell magnetic nanoparticles. From the direction closer to the electromagnetic wave reflecting layer to the direction farther away from the electromagnetic wave reflecting layer, the content of multi-walled carbon nanotubes gradually decreases, while the content of core-shell magnetic nanoparticles increases sequentially. The electromagnetic wave absorbing layer has at least three layers. The core-shell magnetic nanoparticles are carbon-coated iron nanoparticles, carbon-coated nickel nanoparticles, or carbon-coated cobalt nanoparticles. The content of bacterial cellulose is the same in each of the multiple electromagnetic wave absorbing layers. The sum of the masses of the multi-walled carbon nanotubes and the core-shell magnetic nanoparticles in each electromagnetic wave absorbing layer is equal to the mass of the bacterial cellulose. The content of bacterial cellulose in each electromagnetic wave absorbing layer is the same as the content of bacterial cellulose in the electromagnetic wave reflecting layer.

2. The electromagnetic shielding composite material with active and passive infrared stealth function according to claim 1, characterized in that, The thickness of the electromagnetic shielding composite material is 0.24-0.40 mm.

3. The electromagnetic shielding composite material with active and passive infrared stealth function according to claim 1, characterized in that, The core-shell magnetic nanoparticles were prepared by arc discharge method; And / or, the multi-walled carbon nanotubes are carboxylated multi-walled carbon nanotubes with a diameter of 5-15 nm and a length of 15-30 μm.

4. A method for preparing an electromagnetic shielding composite material with active and passive infrared stealth function as described in any one of claims 1-3, characterized in that, It includes the following steps: Multiple dispersions containing bacterial cellulose, multi-walled carbon nanotubes, and core-shell magnetic nanoparticles were prepared, wherein the mass ratio of the multi-walled carbon nanotubes to the core-shell magnetic nanoparticles was different in the multiple dispersions. Multiple portions of the dispersion were sequentially filtered onto silver-plated bacterial cellulose in descending order of multi-walled carbon nanotube content, dried, and hot-pressed to obtain an electromagnetic shielding composite material with active and passive infrared stealth functions.

5. The method for preparing the electromagnetic shielding composite material with active and passive infrared stealth function according to claim 4, characterized in that, The method for preparing the silver-plated bacterial cellulose is as follows: concentrated hydrochloric acid is added dropwise to a stannous chloride solution to obtain a stannous chloride solution acidified with concentrated hydrochloric acid. Bacterial cellulose was activated by adding it to a stannous chloride solution acidified with concentrated hydrochloric acid; Filter and wash until the filtrate is neutral. Add silver nitrate solution to react, filter, and wash until the filtrate is neutral. Add the obtained product to a glucose aqueous solution, add silver ammonia solution dropwise under a water bath, filter, and wash until neutral to obtain silver-plated bacterial cellulose.

6. The method for preparing the electromagnetic shielding composite material with active and passive infrared stealth function according to claim 5, characterized in that, The concentration of the stannous chloride solution is 10-20 g / L; the concentration of the concentrated hydrochloric acid is 36%-38%, and the volume ratio of the concentrated hydrochloric acid to the stannous chloride solution is 5-10 mL:1 L; the activation time is 15-30 min; the concentration of the silver nitrate solution is 0.1 mol / L; and the reaction time after adding the silver nitrate solution is 15-30 min.

7. The method for preparing the electromagnetic shielding composite material with active and passive infrared stealth function according to claim 5, characterized in that, The glucose content in the glucose aqueous solution is 0.5wt%-1.5wt%; the water bath temperature is 35-45℃; the concentration of the silver ammonia solution is 0.8-1.5mol / L, and the reaction continues for 30min after the silver ammonia solution is added.

8. The method for preparing the electromagnetic shielding composite material with active and passive infrared stealth function according to claim 4, characterized in that, In each of the dispersions, the sum of the masses of the multi-walled carbon nanotubes and the core-shell magnetic nanoparticles is equal to the mass of the bacterial cellulose; the content of bacterial cellulose in each of the dispersions is the same as the content of bacterial cellulose in the electromagnetic wave reflecting layer.

9. The method for preparing the electromagnetic shielding composite material with active and passive infrared stealth function according to claim 4, characterized in that, The drying process involves drying at 60-80℃ for 30-45 minutes; the hot pressing process involves hot pressing in a hot press at a temperature of 40-60℃ and a pressure of 20-40MPa for 4-7 hours.

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